Papers for Tuesday, Aug 22 2023

Examining the properties of subhalos with strong gravitational lensing images can shed light on the nature of dark matter. From upcoming large-scale surveys, we expect to discover orders of magnitude more strong lens systems that can be used for subhalo studies. To optimally extract information from a large number of strong lensing images, machine learning provides promising avenues for efficient analysis that is unachievable with traditional analysis methods, but application of machine learning techniques to real observations is still limited. We build upon previous work, which uses a neural likelihood-ratio estimator, to constrain the effective density slopes of subhalos and demonstrate the feasibility of this method on real strong lensing observations. To do this, we implement significant improvements to the forward simulation pipeline and undertake careful model evaluation using simulated images. Ultimately, we use our trained model to predict the effective subhalo density slope from combining a set of strong lensing images taken by the \textit{Hubble Space Telescope}. We found the subhalo slope measurement of this set of observations to be steeper than the slope predictions of cold dark matter subhalos. Our result adds to several previous works that also measured high subhalo slopes in observations. Although a possible explanation for this is that subhalos with steeper slopes are easier to detect due to selection effects and thus contribute to statistical bias, our result nevertheless points to the need for careful analysis of more strong lensing observations from future surveys.

Upcoming experiments will map the spatial distribution of the 21-cm signal over three-dimensional volumes of space during the Epoch of Reionization (EoR). Several methods have been proposed to mitigate the issue of astrophysical foreground contamination in tomographic images of the 21-cm signal, one of which involves the excision of a wedge-shaped region in cylindrical Fourier space. While this removes the $k$-modes most readily contaminated by foregrounds, the concurrent removal of cosmological information located within the wedge considerably distorts the structure of 21-cm images. In this study, we build upon a U-Net based deep learning algorithm to reconstruct foreground wedge-removed maps of the 21-cm signal, newly incorporating light-cone effects. Adopting the Square Kilometre Array (SKA) as our fiducial instrument, we highlight that our U-Net recovery framework is robust to instrumental limitations and noise. We subsequently evaluate the efficacy of recovered maps in guiding high-redshift galaxy searches and providing context to existing galaxy catalogues. This will allow for studies of how the high-redshift galaxy luminosity function varies across environments, and ultimately refine our understanding of the connection between the ionization state of the intergalactic medium (IGM) and galaxies during the EoR.

We explore the kinematic gas properties of six $5.5<z<7.4$ galaxies in the JWST Advanced Deep Extragalactic Survey (JADES), using high-resolution JWST/NIRSpec multi-object spectroscopy of the rest-frame optical emission lines [OIII] and H$\alpha$. The objects are small and of low stellar mass ($\sim 1\,$kpc; $M_*\sim10^{7-9}\,{\rm M_\odot}$), less massive than any galaxy studied kinematically at $z>1$ thus far. The cold gas masses implied by the observed star formation rates are $\sim 10\times$ larger than the stellar masses. We find that their ionised gas is spatially resolved by JWST, with evidence for broadened lines and spatial velocity gradients. Using a simple thin-disc model, we fit these data with a novel forward modelling software that accounts for the complex geometry, point spread function, and pixellation of the NIRSpec instrument. We find the sample to include both rotation- and dispersion-dominated structures, as we detect velocity gradients of $v(r_{\rm e})\approx100-150\,{\rm km\,s^{-1}}$, and find velocity dispersions of $\sigma_0\approx 30-70\,{\rm km\,s^{-1}}$ that are comparable to those at cosmic noon. The dynamical masses implied by these models ($M_{\rm dyn}\sim10^{9-10}\,{\rm M_\odot}$) are larger than the stellar masses by up to a factor 40, and larger than the total baryonic mass (gas + stars) by a factor of $\sim 3$. Qualitatively, this result is robust even if the observed velocity gradients reflect ongoing mergers rather than rotating discs. Unless the observed emission line kinematics is dominated by outflows, this implies that the centres of these galaxies are dark-matter dominated or that star formation is $3\times$ less efficient, leading to higher inferred gas masses.

Spatial variations in the Lyman-$\alpha$ forest opacity at $z<6$ seem to require a late end to cosmic reionization. In this picture, the universe contains neutral hydrogen 'islands' of up to 100 cMpc$/h$ in extent down to redshifts as low as $z\sim 5.3$. This delayed end to reionization also seems to be corroborated by various other observables. An implication of this scenario is that the power spectrum of the cosmological 21-cm signal at $z<6$ is enhanced relative to conventional reionization models by orders of magnitude. However, these neutral hydrogen islands are also predicted to be at the locations of the deepest voids in the cosmological large-scale structure. As a result, the distribution of the 21-cm signal from them is highly non-Gaussian. We derive the 21-cm bispectrum signal from these regions using high-dynamic-range radiative transfer simulations of reionization. We find that relative to conventional models in which reionization is complete at $z>6$, our model has a significantly larger value of the 21-cm bispectrum. The neutral islands also imprint a feature in the isosceles bispectrum at a characteristic scale of $\sim 1$ cMpc$^{-1}$. We also study the 21-cm bispectrum for general triangle configuration by defining a triangle index. It should be possible to detect the 21-cm bispectrum signal at $\nu\gtrsim 200$ MHz using SKA1-LOW for 1080 hours of observation, assuming optimistic foreground removal.

Sgr A* is the variable electromagnetic source associated with accretion onto the Galactic center supermassive black hole. While the near-infrared (NIR) variability of Sgr A* was shown to be consistent over two decades, unprecedented activity in 2019 challenges existing statistical models. We investigate the origin of this activity by re-calibrating and re-analyzing all of our Keck Observatory Sgr A* imaging observations from 2005-2022. We present light curves from 69 observation epochs using the NIRC2 imager at 2.12 $\mu$m with laser guide star adaptive optics. These observations reveal that the mean luminosity of Sgr A* increased by a factor of $\sim$3 in 2019, and the 2019 light curves had higher variance than in all time periods we examined. We find that the 2020-2022 flux distribution is statistically consistent with the historical sample and model predictions, but with fewer bright measurements above 0.6 mJy at the $\sim$2$\sigma$ level. Since 2019, we have observed a maximum $K_s$ (2.2 $\mu$m) flux of 0.9 mJy, compared to the highest pre-2019 flux of 2.0 mJy and highest 2019 flux of 5.6 mJy. Our results suggest that the 2019 activity was caused by a temporary accretion increase onto Sgr A*, possibly due to delayed accretion of tidally-stripped gas from the gaseous object G2 in 2014. We also examine faint Sgr A* fluxes over a long time baseline to search for a quasi-steady quiescent state. We find that Sgr A* displays flux variations over a factor of $\sim$500, with no evidence for a quiescent state in the NIR.

The Cosmic Evolution Early Release Science (CEERS) program observed the Extended Groth Strip with the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) in 2022. In this paper, we discuss the four MIRI pointings that observed with longer wavelength filters, including F770W, F1000W, F1280W, F1500W, F1800W, and F2100W. We compare the MIRI galaxies with the Spitzer/MIPS 24$\mu$m population in the EGS field. We find that MIRI can observe an order of magnitude deeper than MIPS in significantly shorter integration times, attributable to JWST's much larger aperture and MIRI's improved sensitivity. MIRI is exceptionally good at finding faint ($L_{\rm IR}<10^{10} L_\odot$) galaxies at $z\sim1-2$. We find that a significant portion of MIRI galaxies are "mid-IR weak"--they have strong near-IR emission and relatively weaker mid-IR emission, and most of the star formation is unobscured. We present new IR templates that capture how the mid-IR to near-IR emission changes with increasing infrared luminosity. We present two color-color diagrams to separate mid-IR weak galaxies and active galactic nuclei (AGN) from dusty star-forming galaxies and find that these color diagrams are most effective when used in conjunction with each other. We present the first number counts of 10$\mu$m sources and find that there are $\lesssim10$ IR AGN per MIRI pointing, possibly due to the difficulty of distinguishing AGN from intrinsically mid-IR weak galaxies (due to low metallicities or low dust content). We conclude that MIRI is most effective at observing moderate luminosity ($L_{\rm IR}=10^9-10^{10}L_\odot$) galaxies at $z=1-2$, and that photometry alone is not effective at identifying AGN within this faint population.

The influx of massive amounts of data from current and upcoming cosmological surveys necessitates compression schemes that can efficiently summarize the data with minimal loss of information. We introduce a method that leverages the paradigm of self-supervised machine learning in a novel manner to construct representative summaries of massive datasets using simulation-based augmentations. Deploying the method on hydrodynamical cosmological simulations, we show that it can deliver highly informative summaries, which can be used for a variety of downstream tasks, including precise and accurate parameter inference. We demonstrate how this paradigm can be used to construct summary representations that are insensitive to prescribed systematic effects, such as the influence of baryonic physics. Our results indicate that self-supervised machine learning techniques offer a promising new approach for compression of cosmological data as well its analysis.

The detection of high-energy astrophysical neutrinos by IceCube has opened a new window on our Universe. While IceCube has measured the flux of these neutrinos at energies up to several PeV, much remains to be discovered regarding their origin and nature. Currently, measurements are limited by the small sample size of astrophysical neutrinos and by the difficulty of discriminating between electron and tau neutrinos. TAMBO is a next-generation neutrino observatory specifically designed to detect tau neutrinos in the 1-100 PeV energy range, enabling tests of neutrino physics at high energies and the characterization of astrophysical neutrino sources. The observatory will comprise an array of water Cherenkov and plastic scintillator detectors deployed on the face of the Colca Canyon in the Peruvian Andes. This unique geometry will facilitate a high-purity measurement of astrophysical tau neutrino properties. In this talk, I will present the prospects of TAMBO in the context of next-generation neutrino observatories and provide an overview of its current status.

Weak lensing of the cosmic microwave background is rapidly emerging as a powerful probe of neutrinos, dark energy, and new physics. We present a fast computation of the non-linear CMB lensing power spectrum which combines non-linear perturbation theory at early times with power spectrum emulation using cosmological simulations at late times. Comparing our calculation with lightcones from the FLAMINGO 5.6 Gpc cube dark-matter-only simulation, we confirm its accuracy to 1% (2%) up to multipoles L = 3000 (L = 5000) for a nuLambdaCDM cosmology consistent with current data. Clustering suppression due to small-scale baryonic phenomena such as feedback from active galactic nuclei can reduce the lensing power by of order 10%. To our perturbation theory and emulator-based calculation we add SP(k), a new fitting function for this suppression, and confirm its accuracy compared to the FLAMINGO hydrodynamic simulations to 4% at L = 5000, with similar accuracy for massive neutrino models. We further demonstrate that scale-dependent suppression due to neutrinos and baryons approximately factorize, implying that a careful treatment of baryonic feedback can limit biasing neutrino mass constraints.

Origin of wide varieties of quasi-periodic oscillation (QPO) observed in compact sources is still not well established. Its frequencies range from mHz to kHz spanning all compact objects. Are different QPOs, with different frequencies, originating from different Physics? We propose that the emergence of QPOs is the result of nonlinear resonance of fundamental modes present in accretion disks forced by external modes including that of the spin of the underlying compact object. Depending on the properties of accreting flow, e.g. its velocity and gradient, resonances, and any mode locking, take place at different frequencies, exhibiting low to high frequency QPOs. We explicitly demonstrate the origin of higher frequency QPOs for black holes and neutron stars by a unified model and outline how the same physics could be responsible to produce lower frequency QPOs. The model also predicts the spin of black holes, and constrains the radius of neutron stars and the mass of both.

So far, numerical simulations of ultra-faint dwarf galaxies (UFDs) failed to properly reproduce the observed size-luminosity relation. In particular, no hydro-dynamical-run managed to form UFDs with a half light radius as small as 30 pc as seen in several UFD candidates. We tackle this problem by developing a simple but numerically clean and powerful method in which predictions of the stellar content of UFDs from LCDM cosmological hydro-dynamical-simulations is combined with very high resolution dark matter only runs. This method allows to trace the build-up history of UFDs and determine the impact of the merger of building-block objects on their final size. We found that, while no UFDs more compact than 20 pc can be formed, slightly larger system are reproduced only if all member stars are issued from the same initial mini-halo. However this imposes (i) the total virial mass to be smaller than 3x10^8Msol, (ii) the stellar content prior to the end of the re-ionisation epoch to be very compact (<15 pc) and strongly gravitationally bound, a challenge for current hydro-dynamical numerical simulations. If initial stellar building blocks are larger than 35 pc the size of the UFD will extend to 80 pc. Finally, our study shows that UFDs keep strong imprints of their build-up history in the form of elongated or extended stellar halos. Those features can erroneously be interpreted as tidal signatures.

We study the periodic enhancement of either trailing or leading segments of the resonance elliptical rings in the dynamical model of the Galaxy which reproduces distributions of observed velocities derived from Gaia DR3 (EDR3) data along the Galactocentric distance. The model disc forms a nuclear ring, an inner combined ring and outer resonance rings R1 and R2. The backbone of the inner combined ring is banana-type orbits around the Lagrange equilibrium points L4 and L5. Orbits associated with the unstable equilibrium points L1 and L2 also support the inner ring. We have found the changes of the morphology of the inner ring with a period of P=0.57+/-0.02 Gyr, which is close to the period of revolution along the long-period orbits around the points L4 and L5. A possible explanation of these morphological changes is the formation of an overdensity which then begins circulating along the closed contour. In the region of the Outer Lindblad Resonance (OLR), we have found the changes of the morphology of the outer rings with a period of P=2.0+/-0.1 Gyr. Probably, the morphological changes of the outer rings are due to the orbits trapped by the OLR. These orbits exhibit librations of the direction of orbital elongation with respect to the minor axis of the bar as well as the long-term variations in the stellar angular momentum, energy, average radius of the orbit, and eccentricity. Among many librating orbits, we discovered orbits with the libration period of P=1.91+/-0.01 Gyr, which may cause the morphological changes of the outer rings.

Imaging Atmospheric Cherenkov Telescopes (IACTs) are used to detect bright nanosecond-duration flashes of optical light originating from interactions of cosmic/gamma-rays in the atmosphere. A natural calibration source with similar characteristics does not exist; however, satellite-based laser systems provide a potential alternative. The CALIPSO satellite is one such facility which uses a suite of instruments to gather information about the atmosphere. Of particular interest is the CALIOP instrument, which emits 20-nanosecond laser pulses at 1064 nm and 532 nm at a rate of 20 Hz towards the Earth. The TAIGA-HiSCORE collaboration announced a detection of CALIOP laser pulses at the 37th ICRC in 2021, demonstrating that the laser footprint extends to at least tens of kilometers from the subsatellite point. We have used the VERITAS IACT to observe CALIPSO, and show here the results of using these observations to help to calibrate the array. We also discuss the potential of this technique for cross-calibration between different IACT facilities and for relative calibration between the telescopes of future large arrays.

IceCube-Gen2 is an expansion of the IceCube neutrino observatory at the South Pole that aims to increase the sensitivity to high-energy neutrinos by an order of magnitude. To this end, about 10,000 new optical modules will be installed, instrumenting a fiducial volume of about 8 km^3. Two newly developed optical module types increase current sensitivity per module by a factor of three by integrating 16 and 18 newly developed four-inch PMTs in specially designed 12.5-inch diameter pressure vessels. Both designs use conical silicone gel pads to optically couple the PMTs to the pressure vessel to increase photon collection efficiency. The outside portion of gel pads are pre-cast onto each PMT prior to integration, while the interiors are filled and cast after the PMT assemblies are installed in the pressure vessel via a pushing mechanism. This paper presents both the mechanical design, as well as the performance of prototype modules at high pressure (70 MPa) and low temperature (-40 degree Celsius), characteristic of the environment inside the South Pole ice.

The bright star $\lambda$ Ser hosts a hot Neptune with a minimum mass of 13.6 $M_\oplus$ and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system, and to constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite (TESS), and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and to estimate the wind braking torque. We conclude that the remaining uncertainty on stellar age currently prevents an unambiguous interpretation of the properties of $\lambda$ Ser, and that the rate of angular momentum loss appears to be higher than for other stars with similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.

We investigate the relation between the spatiotemporal evolution of the dimming region and the dominant direction of the filament eruption and CME propagation for the 28 October 2021 X1.0 flare/CME event observed from multiple viewpoints by Solar Orbiter, STEREO-A, SDO, and SOHO. We propose a method to estimate the dominant dimming direction by tracking its area evolution and emphasize its accurate estimation by calculating the surface area of a sphere for each pixel. To determine the early flux rope propagation direction, we perform 3D reconstruction of the CME via graduated cylindrical shell modeling (GCS) and tie-pointing of the filament. The dimming initially expands radially and later shifts southeast. The orthogonal projections of the reconstructed height evolution of the erupting filament onto the solar surface are located in the sector of the dominant dimming growth, while the orthogonal projections of the inner part of GCS reconstruction align with the total dimming area. The filament reaches a maximum speed of $\approx$250 km/s at a height of about $\approx$180 Mm. The direction of its motion is strongly inclined from the radial (64$^\circ$ to the East, 32$^\circ$ to the South). The 50$^\circ$ difference in the 3D direction between the CME and the filament leg closely corresponds to the CME half-width determined from reconstruction, suggesting a potential relation of the reconstructed filament to the associated leg of the CME body. Our findings highlight that the dominant propagation of the dimming growth reflects the direction of the erupting magnetic structure (filament) low in the solar atmosphere, though the filament evolution is not related directly to the direction of the global CME expansion. The overall dimming morphology closely resembles the inner part of the CME reconstruction, validating the use of dimming observations to obtain insight into the CME direction.

AT2022cmc was recently reported as the first on-axis jetted tidal disruption event (TDE) discovered in the last decade, and the fourth on-axis jetted TDE candidate known so far. In this work, we present NuSTAR hard X-ray (3--30 keV) observations of AT2022cmc, as well as soft X-ray (0.3--6 keV) observations obtained by NICER, Swift, and XMM-Newton. Our analysis reveals that the broadband X-ray spectra can be well described by a broken power-law with $f_\nu \propto \nu^{-0.5}$ ($f_\nu \propto \nu^{-1}$) below (above) the rest-frame break energy of $E_{\rm bk}\sim 10$ keV at observer-frame $t_{\rm obs}=7.8$ and 17.6 days since discovery. At $t_{\rm obs} = 36.2$ days, the X-ray spectrum is consistent with either a single power-law of $f_\nu \propto \nu^{-0.8}$ or a broken power-law with spectral slopes similar to the first two epochs. By modeling the spectral energy distribution evolution from radio to hard X-ray across the three NuSTAR observing epochs, we find that the sub-millimeter/radio emission originates from external shocks at large distances $\gtrsim\! 10^{17}$ cm from the black hole, the UV/optical light comes from a thermal envelope with radius $\sim\!10^{15}$ cm, and the X-ray emission is consistent with synchrotron radiation powered by energy dissipation at intermediate radii within the (likely magnetically dominated) jet. Our interpretation differs from the model proposed by Pasham et al. (2023) where both the radio and X-rays come from the same emitting zone in a matter-dominated jet. Our model for the jet X-ray emission has broad implications on the nature and radiation mechanism of relativistic jets in other sources such as gamma-ray bursts.

NGC1277 is a compact but massive lenticular galaxy that shows no signs of the presence of dark matter. We find that this galaxy's behavior is consistent not only with Newtonian dynamics, but also with the predictions of Scalar--Tensor--Vector--Gravity, also known as MOG (MOdified Gravity). The compact size of the galaxy, in combination with its large mass, ensures that there are no observable deviations between the predictions of Newtonian and MOG orbital velocities within the galaxy's visible radius.

We investigate the orbital stability of a tilted circumbinary planetary system with three giant planets. The planets are spaced by a constant number ($\Delta$) of mutual Hill radii in the range $\Delta=3.4-12.0$ such that the period ratio of the inner pair is the same as the outer pair. A tilted circumbinary planetary system can be unstable even if the same system around a coplanar binary is stable. For an equal mass binary, we find that the stability of a three-planet system is qualitatively similar to that of a two-planet system, but the three-planet system is more unstable in mean motion resonance regions. For an unequal mass binary, there is significantly more instability in the three-planet system as the inner planets can undergo von-Zeipel-Kozai-Lidov oscillations. Generally in unstable systems, the inner planets are more likely to be ejected than the outer planets. The most likely unstable outcome for closely spaced systems, with $\Delta \lesssim 8$, is a single remaining stable planet. For more widely separated systems, $\Delta \gtrsim 8$, the most likely unstable outcome is two stable planets, only one being ejected. An observed circumbinary planet with significant eccentricity may suggest that it was formed from an unstable system. Consequently, a binary can host three tilted giant planets if the binary stars are close to equal mass and provided that the planets are well spaced and not close to a mean motion resonance.

Although a variety of phenomena may create a geomagnetic storm on Earth, the most severe geomagnetic storms arise from solar activity, and in particular, coronal mass ejections (CMEs) and solar flares. CMEs and flares originate primarily from sunspots. The "aa index" is a metric which ranks all of the strongest geomagnetic storms between 1868 and 2010 based on a variety of characteristics taken from several sources. This paper examines correlations between the aa index of the most severe geomagnetic storms and the intrinsic characteristics of the sunspots from which they originated. We find a correlation between the total rank of the aa index of the storms and the "total intensity" of the sunspot, where total intensity is defined as the sunspot's mean intensity multiplied by its area. The correlation has an R-Squared = 0.690 and R-Squared = 0.855 when a potentially corrupted data point is removed.

Although stellar radii from asteroseismic scaling relations agree at the percent level with independent estimates for main sequence and most first-ascent red giant branch stars, the scaling relations over-predict radii at the tens of percent level for the most luminous stars ($R \gtrsim 30 R_{\odot}$). These evolved stars have significantly superadiabatic envelopes, and the extent of these regions increase with increasing radius. However, adiabaticity is assumed in the theoretical derivation of the scaling relations as well as in corrections to the large frequency separation. Here, we show that a part of the scaling relation radius inflation may arise from this assumption of adiabaticity. With a new reduction of Kepler asteroseismic data, we find that scaling relation radii and Gaia radii agree to within at least $2\%$ for stars with $R \lesssim 30 R_{\odot}$, when treated under the adiabatic assumption. The accuracy of scaling relation radii for stars with $50 R_{\odot} \lesssim R \lesssim 100 R_{\odot}$, however, is not better than $10\%-15\%$ using adiabatic large frequency separation corrections. We find that up to one third of this disagreement for stars with $R \approx 100 R_{\odot}$ could be caused by the adiabatic assumption, and that this adiabatic error increases with radius to reach $10\%$ at the tip of the red giant branch. We demonstrate that, unlike the solar case, the superadiabatic gradient remains large very deep in luminous stars. A large fraction of the acoustic cavity is also in the optically thin atmosphere. The observed discrepancies may therefore reflect the simplified treatment of convection and atmospheres.

We explore the electromagnetic wave modes that can exactly exist in a cosmological plasma dominated by dark energy due to a cosmological constant. It is found that, in the cold and hot plasma cases, electromagnetic plasma waves can be found in an exact manner. The effect of this cosmology appears as a time-dependent potential in the wave equation for the modes that effectivelly modifies the frequency response of the plasma. This potential depends on the metric of the spacetime and on the thermodynamical properties of the plasma. For both cases, cold and hot, the solutions are found in terms of Airy and Bessel functions, respectively, which satisfy some physical initial conditions. These solutions impose discretization conditions on the wavelengths of the electromagnetic plasma waves. Thus, only some specific wave modes can exist exactly on this dark energy cosmology. Relaxing those conditions, we obtain other solutions that approximate to plane waves only in the very hot plasma limit.

GW190814 was reported during LIGO's and Virgo's third observing run with the most asymmetric component masses (a $\sim 23$ $M_{\odot}$ black hole and a $\sim2.6$ $M_{\odot}$ compact object). Under the assumption that this event is a binary black hole (BBH) merger formed through the isolated binary evolution channel, we reanalyze the publicly released data of GW190814 with the modified astrophysical priors on the effective spin $\chi_{\rm eff}$, and further explore its formation history using detailed binary modeling. We show that GW190814 is likely to have been formed through the classical common envelope channel. Our findings show that the properties inferred using the modified astrophysical priors are consistent with those inferred by the uniform priors. With the newly-inferred properties of GW190814, we perform detailed binary evolution of the immediate progenitor of the BBH (namely a close binary system composed of a BH and a helium star) in a large parameter space, taking into account mass-loss, internal differential rotation, supernova kicks, and tidal interactions between the helium star and the BH companion. Our findings show that GW190814-like events could be formed in limited initial conditions just after the common envelope phase: a $\sim 23$ $M_{\odot}$ BH and a helium star of $M_{\rm ZamsHe}$ $\sim$ 8.5 $M_{\odot}$ at solar metallicity ($\sim$ 7.5 $M_{\odot}$ at 10\% solar metallicity) with an initial orbital period at around 1.0 day. Additionally, the inferred low spin of the secondary indicates that the required metallicity for reproducing GW190814-like events should not be too low (e.g., Z $\gtrsim$ 0.1 $Z_{\odot}$).

In this paper, we consider a comprehensive investigation of the cosmological model described by $f(R,T) = R + 2\lambda T$ (where $\lambda$ represents a free parameter) in light of the most recent observational data. By constraining the model using $Hubble$ and $Pantheon$ datasets, we determine its compatibility with the observed behavior of the Universe. For this purpose, we adopt a parametric form for the effective equation of state (EoS) parameter. This parametric form allows us to describe the evolution of the EoS parameter with respect to redshift and investigate its behavior during different cosmic epochs. The analysis of the deceleration parameter reveals an accelerating Universe with a present value of $q_0=-0.64^{+0.03}_{-0.03}$, indicating the current phase of accelerated expansion. The transition redshift is found to be $z_{tr}=0.53^{+0.04}_{-0.03}$, marking the epoch of transition from deceleration to acceleration. We also analyze the evolution of important cosmological parameters including density parameter, pressure, effective EoS, and stability. These findings collectively demonstrate the viability of the $f(R,T)$ cosmological model as a robust candidate capable of engendering the requisite negative pressure, thereby efficiently propelling cosmic expansion. Moreover, the undertaken stability analysis underscores the model's stability within the broader cosmic landscape. By providing the best-fit values for the coupling parameter $\lambda$, this approach motivates and encourages further explorations into the extensive landscape of this model and its potential applications across diverse realms of cosmology and astronomy.

The rotation of sunspots around their umbral center has long been considered as an important process in leading to solar eruptions, but the underlying mechanism remains unclear. A prevailing physical picture on how sunspot rotation leads to eruption is that, by twisting the coronal magnetic field lines from their footpoints, the rotation can build up a magnetic flux rope and drive it into some kinds of ideal magnetohydrodynamics (MHD) instabilities which initiate eruptions. Here with a data-inspired MHD simulation we studied the rotation of a large sunspot in solar active region NOAA 12158 leading to a major eruption, and found that it is distinct from prevailing theories based on ideal instabilities of twisted flux rope. The simulation suggests that, through successive rotation of the sunspot, the coronal magnetic field is sheared with a central current sheet created progressively within the sheared arcade before the eruption, but without forming a flux rope. Then the eruption is instantly triggered once fast reconnection sets in at the current sheet, while a highly twisted flux rope is created during the eruption. Furthermore, the simulation reveals an intermediate evolution stage between the quasi-static energy-storage phase and the impulsive eruption-acceleration phase. This stage may corresponds to slow-rise phase in observation and it enhances building up of the current sheet.

We discuss the properties of companions to B stars in the Scorpius-Centaurus association (age ~15 Myr, 181 B-stars). We gathered available data combining high contrast imaging samples with evidence of companions from Gaia, from eclipsing binaries, and from spectroscopy. We evaluated the completeness of the binary search and estimated the mass and semi-major axis for all detected companions. These data provide a complete sample of stellar secondaries for separation >3 au, and they are highly informative as to closer companions. We found evidence for 200 companions around 181 stars. The fraction of single star is 15.2\pm 4.1% for stars with M_A>3.5 Msun while it is 31.5\pm 5.9% for lower-mass stars. The median semi-major axis of the orbits of the companions is smaller for B than in A stars, confirming a turn-over previously found for OB stars. The mass distribution of the very wide (a>1000 au) and closer companions is different. Very few companions of massive stars M_A>5.0 Msun have a mass below solar and even fewer are M stars with a semi-major axis <1000 au. The scarcity of low-mass companions extends throughout the whole sample. Most early B stars are in compact systems with massive secondaries, while lower-mass stars are mainly in wider systems with a larger spread in mass ratios. We interpret our results as the formation of secondaries with a semi-major axis <1000 au (about 80% of the total) by fragmentation of the disk of the primary and selective mass accretion on the secondaries. The observed trends with primary mass may be explained by a more prolonged phase of accretion episodes on the disk and by a more effective inward migration. We detected twelve new stellar companions from the BEAST survey and of a new BD companion at 9.6 arcsec from HIP74752 using Gaia data, and we discuss the cases of possible BD and low-mass stellar companions to HIP59173, HIP62058, and HIP64053.

Multi-band (B, V and R) photometric and spectroscopic observations of six poorly studied contact binaries carried out at the Western Sydney University and Las Cumbres Observatory were analysed using a recent version of the Wilson-Devenney code. All six were found to be of extreme low mass ratio ranging from 0.073 to 0.149. All are of F spectral class with the mass of the primary component ranging from 1.05Msun to 1.48Msun. None show light curve features of enhanced choromospheric activity (O'Connell Effect) however five of the six do have significant ultraviolet excess indicating presence of increased magnetic and chromospheric activity. Period analysis based on available survey data suggests two systems have a slowly increasing period suggesting mass transfer from the secondary to the primary, two have a slow declining period with likely mass transfer from primary to the secondary while one shows a steady period and one undergoing transition from a declining to increasing period suggesting possible mass transfer reversal. We also compare light curve solutions against theoretical markers of orbital stability and show that three of six systems have mass ratios within the theoretical instability limit and maybe regarded as potential merger candidates.

We present the orbital period variability and evolutionary status of the W UMa-type binary system V864 Mon from accurately measured fundamental parameters. New $BV$ photometric observations of this system were performed in 2019 January and 2022 January, and the first high-resolution spectroscopic observations were carried out on three nights between 2019 January and March. A total of 29 times of minimum light were collected to examine the behavior of the orbital period. Our analysis of these timings indicates a continuous period increase at a rate of $+$2.62$\times$10$^{-7}$ d yr$^{-1}$ over the past 20 years, which can be interpreted as a mass transfer from the less massive primary to the secondary component with a rate of 1.22$\times$10$^{-7}$ M$_\odot$ yr$^{-1}$. We measured the radial velocities (RVs) for both components, and determined the effective temperature and projected rotational velocity of the more massive secondary star to be $T_{\rm eff,2}$ = 5450 $\pm$ 94 K and $v_2 \sin i$ = 192 $\pm$ 40 km s$^{-1}$, respectively, from the comparison of the observed spectrum at the primary minimum and the theoretical models. The individual masses and radii of both components were determined from a simultaneous analysis of the light and RV curves, which are $M_1$ = 0.34 $\pm$ 0.02 M$_\odot$, $R_1$ = 0.69 $\pm$ 0.01 R$_\odot$, and $M_2$ = 1.06 $\pm$ 0.04 M$_\odot$, $R_2$ = 1.16 $\pm$ 0.02 R$_\odot$, respectively. Our results indicate that V864 Mon is a W-subtype of W UMa stars with time-varying spot activity. The positions in the mass-luminosity and mass-radius diagrams indicate that the secondary star belongs to the main sequence region, while the hotter primary is located beyond the terminal-age main sequence.

The results of photometric and spectral observations of T CrB obtained in a wide range of wavelengths in 2011-2023 are presented. We use the near-IR light curves to determine a new ephemeris $JD_{min} = 2455828.9 + 227.55 \cdot E$ for the times of light minima when the red giant is located between the observer and the hot component. The flux ratio H$\alpha$/H$\beta$ varied from ~3 to ~8 in 2020-2023, which may be due to a change in the flux ratio between the X-ray and optical ranges. It is shown that the value of H$\alpha$/H$\beta$ depends on the rate of accretion onto the hot component of the system. Based on high-speed follow-up observations obtained on June 8, 2023, we detected a variability of the HeII $\lambda 4686$ line with a characteristic time-scale of ~25 min, the amplitude of variability in the $B$ band was ~0.07$^m$. Simulations of the near-IR light curves accounting for the ellipsoidal effect allowed us to obtain the parameters of the binary system: the Roche lobe filling factor of the cool component $\mu=1.0$, the mass ratio $q=M_{cool}/M_{hot}=0.65\pm0.2$, the orbit inclination $i=56^\circ\pm4^\circ$. A comparison of the light curve obtained in 2005-2023 with the 1946 outburst template made it possible to predict the date of the upcoming outburst - January 2024.

After the discovery of rings around the largest known Centaur object, (10199) Chariklo, we carried out observation campaigns of stellar occultations produced by the second-largest known Centaur object, (2060) Chiron, to better characterize its physical properties and presence of material on its surroundings. We predicted and successfully observed two stellar occultations by Chiron. These observations were used to constrain its size and shape by fitting elliptical limbs with equivalent surface radii in agreement with radiometric measurements. Constraints on the (2060) Chiron shape are reported for the first time. Assuming an equivalent radius of R$_{equiv}$ = 105$^{+6}_{-7}$ km, we obtained a semi-major axis of a = 126 $\pm$ 22 km. Considering Chiron's true rotational light curve amplitude and assuming it has a Jacobi equilibrium shape, we were able to derive a 3D shape with a semi-axis of a = 126 $\pm$ 22 km, b = 109 $\pm$ 19 km, and c = 68 $\pm$ 13 km, implying in a volume-equivalent radius of R$_{vol}$ = 98 $\pm$ 17 km, implying a density of 1119 $\pm$ 4 kg m$^{-3}$. We determined the physical properties of the 2011 secondary events around Chiron, which may then be directly compared with those of Chariklo rings, as the same method was used. Data obtained from SAAO in 2018 do not show unambiguous evidence of the proposed rings, mainly due to the large sampling time. Meanwhile, we discarded the possible presence of a permanent ring similar to (10199) Chariklo's C1R in optical depth and extension. Using the first multi-chord stellar occultation by (2060) Chiron and considering it to have a Jacobi equilibrium shape, we derived its 3D shape. New observations of a stellar occultation by (2060) Chiron are needed to further investigate the material's properties around Chiron, such as the occultation predicted for September 10, 2023.

Since the early sixties, our view of radio galaxies and quasars has been drastically shaped by discoveries made thanks to observations of radio sources listed in the Third Cambridge catalog and its revised version (3CR). However, the largest fraction of data collected to date on 3CR sources was performed with relatively old instruments, rarely repeated and/or updated. Importantly, the 3CR contains only objects located in the Northern Hemisphere thus having limited access to new and innovative astronomical facilities. To mitigate these limitations we present a new catalog of powerful radio sources visible from the Southern Hemisphere, extracted from the GLEAM 4-Jy (G4Jy) catalog and based on equivalent selection criteria as the 3CR. This new catalog, named G4Jy- 3CRE, where the E stands for "equivalent", lists a total of 264 sources at declination below -5 degrees and with 9 Jy limiting sensitivity at ~178 MHz. We explored archival radio maps obtained with different surveys and compared then with optical images available in the Pan-STARRS, DES and DSS databases to search for optical counterparts of their radio cores. We compared mid-infrared counterparts, originally associated in the G4Jy, with the optical ones identified here and we present results of a vast literature search carried out to collect redshift estimates for all G4Jy-3CRE sources resulting in a total of 145 reliable z measurements.

Representative samples of F-, G-, K-type stars located out of the Solar Neighbourhood has started to be available in spectroscopic surveys. The fraction of metal-poor ([Fe/H]~$\lesssim -0.8$~dex) giants becomes increasingly relevant to far distances. In metal-poor stars, effective temperatures ($T_{\mathrm{eff}}$) based on LTE spectroscopy and on former colour-$T_{\mathrm{eff}}$ relations of still wide use have been reported to be inaccurate. It is necessary to re-calibrate chemical abundances based on these $T_{\mathrm{eff}}$ scales in the multiple available surveys to bring them to the same standard scale for their simultaneous use. For that, a complete sample of standards is required, which so far, is restricted to a few stars with quasi-direct $T_{\mathrm{eff}}$ measurements. We aim at providing a legacy sample of metal-poor standards with proven accurate atmospheric parameters. We add 47 giants to the sample of metal-poor dwarfs of Giribaldi et al. 2021, thereby constituting the Titans metal-poor reference stars. $T_{\mathrm{eff}}$ was derived by 3D non-LTE H$\alpha$ modelling, whose accuracy was tested against interferometry and InfraRed Flux Method (IRFM). Surface gravity (log $g$) was derived by fitting Mg~I~b triplet lines, whose accuracy was tested against asteroseismology. Metallicity was derived using Fe II lines, which was verified to be identical to the [Fe/H] derived from non-LTE spectral synthesis. $T_{\mathrm{eff}}$ from 3D non-LTE H$\alpha$ is equivalent to interferometric and IRFM temperatures within a $\pm$46~K uncertainty. We achieved precision of $\sim$50~K for 34 stars with spectra with the highest S/N. For log $g$, we achieved a total uncertainty of $\pm$0.15~dex. For [Fe/H], we obtained a total uncertainty of $\pm$0.09~dex. We find that the ionization equilibrium of Fe lines under LTE is not valid in metal-poor giants.

For bright transients such as Gamma-Ray Bursts (GRBs), the Ultra-Violet/Optical Telescope (UVOT) operates under event mode at early phases, which records incident positions and arrival time for each photon. The event file is able to be screened into many exposures to study the early light curve of GRBs with a high time resolution, including in particular the rapid brightening of the UV/Optical emission. Such a goal, however, is hampered for some extremely bright GRBs by the saturation in UVOT event images. For moderately saturated UVOT sources, in this work we develop the method proposed in Jin et al. (2023) to recover their photometries. The basic idea is to assume a stable point spread function (PSF) of UVOT images, for which the counts in the core region (i.e., an aperture of a radius of 5 arcsec) and the wing region (i.e., an annulus ranging from 15 arcsec to 25 arcsec) should be a constant and the intrinsic flux can be reliably inferred with data in the ring. We demonstrate that in a given band, a tight correlation does hold among the background-removed count rates in the core and the wing. With the new method, the bright limit of measuring range for UVOT V and B bands increases ~ 1.7 mag, while only ~ 0.7 mag for U band due to the lack of bright calibration sources. Systematic uncertainties are ~ 0.2 mag for V, B and U bands.

Recently, the Large High Altitude Air Shower Observatory (LHAASO) collaboration presents the first catalog of $\gamma$-ray sources using 508 days LHAASO data from March 2021 to September 2022. This catalog contains five active galactic nuclei (AGNs), of which four are blazars and one is a liner-type AGN. In this work, we establish averaged multi-wavelength SEDs by combining data from $Fermi$-Large Area Telescope, $Swift$, $ZTF$, and $WISE$ with the same period as the LHAASO detection. In general, these five AGNs are found in low states at all wavelengths. To study the multi-wavelength properties of these AGNs, several jet emission models, including the one-zone leptonic model, the one-zone leptonic and hadronuclear ($pp$) model, the one-zone proton-synchrotron model, and the spine-layer model are applied to reproduce their averaged SEDs, respectively. We find that the one-zone leptonic model can reproduce most of the SEDs, except for the high-energy tail of LHAASO spectra. To improve the fitting, emission from $pp$ interactions is favoured in the framework of one-zone model. The spine-layer model, which can be treated as a multi-zone scenario, also can provide good spectra fits. The influence of different extragalactic background light models on fitting LHAASO energy spectrum is also discussed.

Combined tearing-thermal evolution plays an important role in the disruption of current sheets, and formation of cool condensations within the solar atmosphere. However, this has received limited attention to date. We numerically explore a combined tearing and thermal instability that causes the break up of an idealized current sheet in the solar atmosphere. The thermal component leads to the formation of localized, cool condensations within an otherwise 3D reconnecting magnetic topology. We construct a 3D resistive magnetohydrodynamic simulation of a force-free current sheet under solar atmospheric conditions that incorporate the non-adiabatic influence of background heating, optically thin radiative energy loss, and magnetic field aligned thermal conduction with the open source code MPI-AMRVAC. Multiple levels of adaptive mesh refinement reveal the self-consistent development of finer-scale condensation structures within the evolving system. The instability in the current sheet is triggered by magnetic field perturbations concentrated around the current sheet plane, and subsequent tearing modes develop. This in turn drives thermal runaway associated with the thermal instability of the system. We find subsequent, localized cool plasma condensations that form under the prevailing low plasma-$\beta$ conditions, and demonstrate that the density and temperature of these condensed structures are similar to more quiescent coronal condensations. Synthetic counterparts at Extreme-UltraViolet (EUV) and optical wavelengths show the formation of plasmoids (in EUV), and coronal condensations similar to prominences and coronal rain blobs in the vicinity of the reconnecting sheet. Our simulations imply that 3D reconnection in solar current sheets may well present an almost unavoidable multi-thermal aspect, that forms during their coupled tearing-thermal evolution.

The destiny of complex organic molecules (COMs) in star-forming regions is interlinked with various evolutionary phases. Therefore, identifying these species in diversified environments of identical star-forming regions would help to comprehend their physical and chemical heritage. We identified multiple COMs utilizing the Large Program `Astrochemical Surveys At IRAM' (ASAI) data, dedicated to chemical surveys in Sun-like star-forming regions with the IRAM 30 m telescope. It was an unbiased survey in the millimetre regime, covering the prestellar core, protostar, outflow region, and protoplanetary disk phase. Here, we have reported some transitions of seven COMs, namely, methanol (CH3OH), acetaldehyde (CH3CHO), methyl formate (CH3OCHO), ethanol (C2H5OH), propynal (HCCCHO), dimethyl ether (CH3OCH3), and methyl cyanide (CH3CN) in some sources L1544, B1-b, IRAS4A, and SVS13A. We found a trend among these species from the derived abundances using the rotational diagram method and MCMC fit. We have found that the abundances of all of the COMs, except for HCCCHO, increase from the L1544 (prestellar core) and peaks at IRAS16293-2422 (class 0 phase). It is noticed that the abundance of these molecules correlate with the luminosity of the sources. The obtained trend is also visible from the previous interferometric observations and considering the beam dilution effect.

We conducted isothermal MHD simulations with self-gravity to investigate the properties of dense cores in cluster-forming clumps. Two different setups were explored: a single rotating clump and colliding clumps. We focused on determining the extent to which the formed dense cores inherit the rotation and magnetic field of the parental clump. Our statistical analysis revealed that the alignment between the angular momentum of dense cores, $\bf{L}_{\rm core}$, and the rotational axis of the clump is influenced by the strength of turbulence and the simulation setup. In single rotating clumps, we found that $\bf{L}_{\rm core}$ tends to align with the clump's rotational axis if the initial turbulence is weak. However, in colliding clumps, this alignment does not occur, regardless of the initial turbulence strength. This misalignment in colliding clumps is due to the induced turbulence from the collision and the isotropic gas inflow into dense cores. Our analysis of colliding clumps also revealed that the magnetic field globally bends along the shock-compressed layer, and the mean magnetic field of dense cores, $\bf{B}_{\rm core}$, aligns with it. Both in single rotating clumps and colliding clumps, we found that the angle between $\bf{B}_{\rm core}$ and $\bf{L}_{\rm core}$ is generally random, regardless of the clump properties. We also analyzed the dynamical states of the formed cores and found a higher proportion of unbound cores in colliding clumps. In addition, the contribution of rotational energy was only approximately 5% of the gravitational energy, regardless of the model parameters for both single and colliding cases.

The radiation mechanism of fast radio bursts (FRBs) has been extensively studied but still remains elusive. Coherent radiation is identified as a crucial component in the FRB mechanism, with charged bunches also playing a significant role under specific circumstances. In the present research, we propose a phenomenological model that draws upon the coherent curvature radiation framework and the magnetized neutron star, taking into account the kinetic energy losses of outflow particles due to inverse Compton scattering (ICS) induced by soft photons within the magnetosphere. By integrating the ICS deceleration mechanism for particles, we hypothesize a potential compression effect on the particle number density within a magnetic tube/family, which could facilitate achieving the necessary size for coherent radiation in the radial direction. This mechanism might potentially enable the dynamic formation of bunches capable of emitting coherent curvature radiation along the curved magnetic field. Moreover, we examine the formation of bunches from an energy perspective. Our discussion suggests that within the given parameter space the formation of bunches is feasible. Finally, we apply this model to FRB 20190520B, one of the most active repeating FRBs discovered and monitored by FAST. Several observed phenomena are explained, including basic characteristics, frequency downward drifting, and bright spots within certain dynamic spectral ranges.

SPI-ACS/INTEGRAL is one of the most sensitive orbital gamma-ray detectors in energy range above 80 keV. Since 2002 it registered several thousands of gamma-ray bursts, including the bursts associated with LIGO-Virgo gravitational wave events GW 170817 and GW 190425. No dedicated in-flight calibrations were performed for SPI-ACS/INTEGRAL, complicating estimation of spectral and energetic characteristics of an event. Using data of GBM/Fermi we perform cross-calibration of SPI-ACS/INTEGRAL, based on 1032 bright GRBs registered by both experiments. We find the conversion factor between instrumental counts from SPI-ACS and energy units from GBM to be dependent on hardness of GRB spectrum (defined as the characteristic energy value, $E_{p}$) and on location of a source in spacecraft based coordinate system. We determine the corresponding analytical model to calculate the conversion factor and estimate its accuracy empirically. Sensitivity of SPI-ACS/INTEGRAL to detect gamma-ray transients is also investigated. Using the calibration we re-estimate energetics of GRB/GW 190425, detected by SPI-ACS/INTEGRAL alone. We constrain possible range of the characteristic energy $E_{p}$ and isotropic equivalent of total energy, emitted in gamma-rays $E_{iso}$ for GRB 190425, using the $ E_{p,i} $ -- $ E_{iso} $ (Amati) correlation. The calibration model could be applied to any transients with energy spectrum, analogous to gamma-ray bursts.

A unique X-ray occultation event in NGC 6814 during an XMM-Newton observation in 2016 has been reported, providing useful information of the absorber and the corona. We revisit the event with the aid of the hardness ratio (HR) - count rate (CR) plot and comparison with two other absorption-free XMM exposures in 2009 and 2021. NGC 6814 exhibits a clear "softer-when-brighter" variation pattern during the exposures, but the 2016 exposure significantly deviates from the other two in the HR - CR plot. While spectral fitting does yield transient Compton-thin absorption corresponding to the eclipse event in 2016, rather than easing the tension between exposures in the HR - CR plot, correcting the transient Compton-thin absorption results in new and severe deviation within the 2016 exposure. We show that the eclipsing absorber shall be clumpy (instead of a single Compton-thin cloud), with an inner denser region composed of both Compton-thin and Compton-thick clouds responsible for the previously identified occultation event, and an outer sparser region with Compton-thin clouds which eclipses the whole 2016 exposure. With this model, all the tension in the HR - CR plots could be naturally erased, with the observed spectral variability during the 2016 exposure dominated by the variation of absorption. Furthermore, the two warm absorbers (with different ionization and column densities but similar outflowing velocities) detected in the 2016 exposure shall also associate with the transient absorber, likely due to ablated or tidal stretched/disrupted fragments. This work highlights the unique usefulness of the HR - CR plot while analysing rare occultation events.

To explain both the dynamics of a globular cluster and its production of gravitational waves from coalescing binary black holes, it is necessary to understand its population of dynamically-formed binaries. We provide a theoretical understanding of this population, benchmarked by direct $N$-body models. We find that clusters on average have only one dynamically-assembled binary at any given time. This is different from theoretical expectations and models of binary populations, which predict a larger number of binaries ($\sim 5$), especially for low-$N$ clusters ($\sim 100$), or in the case of two-mass models, low number of black holes. We argue that the presence of multiple binaries is suppressed by a high rate of binary-binary interactions, which efficiently ionise one of the binaries involved. These also lead to triple formation and potentially gravitational wave (GW) captures, which may provide an explanation for the recently reported efficiency of binary black hole mergers with non-zero ($\gtrsim 0.01$) eccentricity in low-mass clusters.

Extreme Ultraviolet images of the Sun are becoming an integral part of space weather prediction tasks. However, having different surveys requires the development of instrument-specific prediction algorithms. As an alternative, it is possible to combine multiple surveys to create a homogeneous dataset. In this study, we utilize the temporal overlap of SoHO/EIT and SDO/AIA 171~\AA ~surveys to train an ensemble of deep learning models for creating a single homogeneous survey of EUV images for 2 solar cycles. Prior applications of deep learning have focused on validating the homogeneity of the output while overlooking the systematic estimation of uncertainty. We use an approach called `Approximate Bayesian Ensembling' to generate an ensemble of models whose uncertainty mimics that of a fully Bayesian neural network at a fraction of the cost. We find that ensemble uncertainty goes down as the training set size increases. Additionally, we show that the model ensemble adds immense value to the prediction by showing higher uncertainty in test data that are not well represented in the training data.

A planetary system can undergo multiple episodes of intense dynamical activities throughout its life, resulting in the production of star-grazing planetesimals (or exocomets) and pollution of the host star. Such activity is especially pronounced when giant planets interact with other small bodies during the system's evolution. However, due to the chaotic nature of the dynamics, it is difficult to determine the properties of the perturbing planet(s) from the observed planetesimal-disruption activities. In this study, we examine the outcomes of planetesimal-planet scatterings in a general setting, with the goal of determining the likelihood and timescale of planetesimal disruption by the host star as a function of the planet properties. We obtain a new analytical expression for the minimum distance a scattering body can reach, extending previous results by considering finite planet eccentricity and non-zero planetesimal mass. Through N-body simulations, we derive the distribution of minimum distances and the likelihood and timescales of three possible outcomes of planetesimal-planet scatterings: collision with the planet, ejection, and disruption by the star. We identify four defining dimensionless parameters (the planet eccentricity, planet-to-star mass ratio, planet radius to semi-major axis ratio, and the stellar disruption radius to planet semi-major axis ratio) that enable us to scale the problem and generalize our findings to a wide range of orbital configurations. Using these results, we explore three applications: falling evaporating bodies in the Beta Pictoris system, white dwarf pollution due to planetesimal disruption and planet engulfment by main-sequence stars.

We identify a previously undetected periodicity at a frequency of 49.08$\pm$0.01 d$^{-1}$ (period of 29.34$\pm$0.01 minutes) during a super-outburst of V844 Her observed by TESS. V844 Her is an SU UMa type cataclysmic variable with an orbital period of 78.69 minutes, near the period minimum. The frequency of this new signal is constant in contrast to the superhump oscillations commonly seen in SU UMa outbursts. We searched without success for oscillations during quiescence using MDM, TESS, and XMM-Newton data. The lack of a periodic signal in the XMM light curve and the relatively low X-ray luminosity of V844 Her suggests that it is not a typical IP. We consider the possibility that the 29 min signal is the result of super-Nyquist sampling of a Dwarf Nova Oscillation with a period near the 2-minute cadence of the TESS data. Our analysis of archival AAVSO photometry from a 2006 super-outburst supports the existence of a 29 min oscillation, although a published study of an earlier superoutburst did not detect the signal. We compare the X-ray properties of V844 Her with short orbital period intermediate polars (IP), V1025 Cen and DW Cnc. We conclude that the new signal is a real photometric oscillation coming from the V844 Her system and that it is unlikely to be an aliased high-frequency oscillation. The steady frequency of the new signal suggests that its origin is related to an asynchronously rotating white dwarf in V844 Her, although the precise mechanism producing the flux variations remains unclear.

Close-in lava planets represent an extreme example of terrestrial worlds, but their high temperatures may allow us to probe a diversity of crustal compositions. The brightest and most well-studied of these objects is 55 Cancri e, a nearby super-Earth with a remarkably short 17-hour orbit. However, despite numerous studies, debate remains about the existence and composition of its atmosphere. We present upper limits on the atmospheric pressure of 55 Cnc e derived from high-resolution time-series spectra taken with Gemini-N/MAROON-X. Our results are consistent with current crustal evaporation models for this planet which predict a thin $\sim$ 100 mbar atmosphere. We conclude that, if a mineral atmosphere is present on 55 Cnc e, the atmospheric pressure is below 100 mbar.

Aerocapture is the technique of using planetary atmospheres to decelerate a spacecraft in a single pass to achieve nearly fuel-free orbit insertion. Aerocapture has been extensively studied since the 1980s but has never been flown yet. The entry conditions encountered during aerocapture are strongly destination dependent, and performance benefit offered by aerocapture is also destination dependent. Aerocapture is applicable to all atmosphere-bearing destinations with the exception of Jupiter and Saturn, whose extreme entry conditions make aerocapture infeasible. A recent study by the NASA Science Mission Directorate highlighted the need for baseline design reference missions, as a starting point for system level architecture studies. The present study uses the Aerocapture Mission Analysis Tool (AMAT) to compile a list of design reference missions at Venus, Earth, Mars, Titan, Uranus, and Neptune. These reference missions can provide an initial assessment of the feasibility of aerocapture for a proposed mission, and provide intial baseline values for more detailed system studies. The reference mission set provides a quick estimate of the entry conditions, control requirements, and aero-thermal loads for architectural level studies.

In magnetized, stratified astrophysical environments such as the Sun's corona and solar wind, Alfv\'enic fluctuations ''reflect'' from background gradients, enabling nonlinear interactions and thus dissipation of their energy into heat. This process, termed ''reflection-driven turbulence,'' is thought to play a crucial role in coronal heating and solar-wind acceleration, explaining a range of observational correlations and constraints. Building on previous works focused on the inner heliosphere, here we study the basic physics of reflection-driven turbulence using reduced magnetohydrodynamics in an expanding box -- the simplest model that can capture the local turbulent plasma dynamics in the super-Alfv\'enic solar wind. Although idealized, our high-resolution simulations and simple theory reveal a rich phenomenology that is consistent with a diverse range of observations. Outwards-propagating fluctuations, which initially have high imbalance, decay nonlinearly to heat the plasma, becoming more balanced and magnetically dominated. Despite the high imbalance, the turbulence is strong because Els\"asser collisions are suppressed by reflection, leading to ''anomalous coherence'' between the two Els\"asser fields. This coherence, together with linear effects, causes the turbulence to anomalously grow the ''anastrophy'' (squared magnetic potential) as it decays, forcing the energy to rush to larger scales and forming a ''$1/f$-range'' energy spectrum as it does so. At late times, the expansion overcomes the nonlinear and Alfv\'enic physics, forming isolated, magnetically dominated ''Alfv\'en vortex'' structures that minimize their nonlinear dissipation. These results can plausibly explain the observed radial and wind-speed dependence of turbulence imbalance, residual energy, plasma heating, and fluctuation spectra, as well as making testable predictions for future observations.

An infrared excess over the stellar photospheric emission of main-sequence stars has been found in interferometric surveys, commonly attributed to the presence of hot exozodiacal dust (HEZD). While submicrometer-sized grains in close vicinity to their host star have been inferred to be responsible for the found near-infrared excesses, the presence and amount of larger grains as part of the dust distributions are weakly constrained. We quantify how many larger grains (above-micrometer-sized) could be present in addition to submicrometer-sized grains, while being consistent with observational constraints. This is important in order to distinguish between various scenarios for the origin of HEZD and to better estimate its observational appearance when observed with future instruments. We extended a model suitable to reproduce current observations of HEZD to investigate a bimodal size distribution. By deriving the characteristics of dust distributions whose observables are consistent with observational limits from interferometric measurements in the $K$ and $N$ bands we constrained the radii of sub- and above-micrometer-sized grains as well as their mass, number, and flux density ratios. In the most extreme cases of some of the investigated systems, large grains $\gtrsim 10\,\mu$m might dominate the mass budget of HEZD while contributing up to 25$\,$% of the total flux density originating from the dust at a wavelength of 2.13$\,\mu$m and up to 50$\,$% at a wavelength of 4.1$\,\mu$m; at a wavelength of 11.1$\,\mu$m their emission might clearly dominate over the emission of small grains. While it is not possible to detect such hot-dust distributions using ALMA, the ngVLA might allow us to detect HEZD at millimeter wavelengths. Large dust grains might have a more important impact on the observational appearance of HEZD than previously assumed, especially at longer wavelengths.

Directly imaging Earth-sized exoplanets with a visible-light coronagraph instrument on a space telescope will require a system that can achieve $\sim10^{-10}$ raw contrast and maintain it for the duration of observations (on the order of hours or more). We are designing, manufacturing, and testing Dual Purpose Lyot coronagraph (DPLC) masks that allow for simultaneous wavefront sensing and control using out-of-band light to maintain high contrast in the science focal plane. Our initial design uses a tiered metallic focal plane occulter to suppress starlight in the transmitted coronagraph channel and a dichroic-coated substrate to reflect out-of-band light to a wavefront sensing camera. The occulter design introduces a phase shift such that the reflected channel is a Zernike wavefront sensor. The dichroic coating allows higher-order wavefront errors to be detected which is especially critical for compensating for residual drifts from an actively-controlled segmented primary mirror. A second-generation design concept includes a metasurface to create polarization-dependent phase shifts in the reflected beam, which has several advantages including an extended dynamic range. We will present the focal plane mask designs, characterization, and initial testing at NASA's High Contrast Imaging Testbed (HCIT) facility.

The tera-electronvolt (TeV) light curve of gamma-ray burst (GRB) 221009A shows an unprecedentedly rapid rise at the beginning epoch. This phenomenon could be due to the strong absorption of photons and electrons within the emitting region. As the external shock expands outwards and the radius increases, the volume of matter also increases, leading to a gradual decrease in the optical depth for TeV photons. We explore several possibilities for the physical origin of this peculiar behavior. We calculate the optical depth for TeV photons due to annihilation with lower energy photons in the external shock and scattering by electrons produced via cascading of the TeV emission. Even under aggressive assumptions, we find the optical depths for these processes are orders of magnitude too small to explain the observed light curve. Other sources of absorbers, such as electrons in the ejecta or external shock, also do not yield sufficient optical depths. Therefore, the origin of the early peculiar TeV light curve remains uncertain.

We present the results of an unbiased $^{12}$CO/$^{13}$CO/C$^{18}$O ($J$ = 1-0) survey in a portion of the third Galactic quadrant (TGQ): $l$ = [219.75, 229.75]$^\circ$ and $b$ = [-5.25, 5.25]$^\circ$. The high-resolution and high-sensitivity data sets help to unravel the distributions and physical properties of the molecular clouds (MCs) in the mapped area. In the LSR velocity range from -1 to 85 km/s, the molecular material successfully traces the Local, Perseus, and Outer arms. In the TGQ, the Outer arm appears to be more prominent than that in the second Galactic quadrant (SGQ), but the Perseus arm is not as conspicuous as that in the SGQ. A total of 1,502 $^{12}$CO, 570 $^{13}$CO, and 53 C$^{18}$O molecular structures are identified, spanning over $\sim2$ and $\sim6$ orders of magnitude in size and mass, respectively. Tight mass-radius correlations and virial parameter-mass anticorrelations are observable. Yet, it seems that no clear correlations between velocity dispersion and effective radius can be found over the full dynamic range. The vertical distribution of the MCs renders evident pictures of the Galactic warp and flare.

Solar flares can release coronal magnetic energy explosively and may impact the safety of near-earth space environments. Their structures and properties on macroscale have been interpreted successfully by the generally-accepted two-dimension standard model invoking magnetic reconnection theory as the key energy conversion mechanism. Nevertheless, some momentous dynamical features as discovered by recent high-resolution observations remain elusive. Here, we report a self-consistent high-resolution three-dimension magnetohydrodynamical simulation of turbulent magnetic reconnection within a flare current sheet. It is found that fragmented current patches of different scales are spontaneously generated with a well-developed turbulence spectrum at the current sheet, as well as at the flare loop-top region. The close coupling of tearing-mode and Kelvin-Helmholtz instabilities plays a critical role in developing turbulent reconnection and in forming dynamical structures with synthetic observables in good agreement with realistic observations. The sophisticated modeling makes a paradigm shift from the traditional to three-dimension turbulent reconnection model unifying flare dynamical structures of different scales.

The specific angular momenta ($j_t$) of stars, baryons as a whole and dark matter haloes contain clues of vital importance about how galaxies form and evolve. Using a sample of 70 spiral galaxies, we perform a preliminary analysis of $j_t$, and introduce a new quantity, e.g., areal density of angular momentum (ADAM) ($j_t~M_\star/4R_d^2$) as an indication for the existence of jet in spiral galaxies. The percentage of spiral galaxies having jet(s) shows strong correlation with the ADAM, although the present sample is incomplete.

In our recent catalogue of BY Draconis (BY Dra) variables based on Zwicky Transient Facility data, we found traces of a period gap in the period-colour diagram. We combined our BY Dra database with catalogues from the {\sl Kepler} and K2 surveys, revealing a prominent period gap. Here, we use this combined ZTF-{\sl Kepler}-K2 data set to investigate the origin of the period gap observed for BY Dra stars using chromospheric activity indices. We use low- and medium-resolution spectra from the LAMOST Data Release 7 to derive magnetic activity indices for the Ca {\sc ii} H and K and H$\alpha$ emission lines. We find a strong dependence of chromospheric activity on both stellar mass and rotation period. For partially convective K-M-type stars, the activity decreases steeply up to an age of $\sim$700-1000 Myr, subsequently evolving to the type of low-level saturation associated with spin-down stallation. In contrast, F-G-type stars with thinner convective envelopes exhibit constant activity with increasing age. We suspect that the observed steep decrease for partially convective stars is driven by core-envelope coupling. This mechanism reduces differential rotation at the core-envelope transition, hence leading to decreased magnetic activity. Moreover, we derive activity indices for previously known star clusters and find similar trends as regards their activity levels as a function of age. In particular, very low-level activity is observed around the location of the period gap. Therefore, we conclude that the period gap, defined by the non-detection of variable sources, is driven by a minimum in chromospheric activity.

Mergers of binary neutron stars are multimessenger sources of gravitational waves that have an optical luminous counterpart, commonly referred to as 'kilonova'. Inspired by the detection of GW170817, intensive searches have been conducted during the LIGO/Virgo O3 run. However, despite these efforts, no verified kilonova was detected. In this work, we present a parameter constraint method based on non-detection of optical searching considering both GW skymap, limited sky coverage, cadence, limiting magnitudes and the probability of astrophysical origin. We use our method to place constraints on EoS of neutron star based on follow-up during O3 run and obtain $M_{\rm TOV} = 2.170^{+0.120}_{-0.108}\ M_{\odot}$ at 90\% confidence level with the combination of other observations. And we also take outlook for WFST targeting kilonova throughout the LIGO/Virgo O4 run. With more events handled, we will obtain more stringent constraints on EoS and kilonova populations.

Decayless kink oscillations of plasma loops in the solar corona may contain an answer to the enigmatic problem of solar and stellar coronal heating. The polarisation of the oscillations gives us a unique information about their excitation mechanisms and energy supply. However, unambiguous determination of the polarisation has remained elusive. Here, we show simultaneous detection of a 4-min decayless kink oscillation from two non-parallel lines-of-sights, separated by about 104\textdegree, provided by unique combination of the High Resolution Imager on Solar Orbiter and the Atmospheric Imaging Assembly on Solar Dynamics Observatory. The observations reveal a horizontal or weakly oblique linear polarisation of the oscillation. This conclusion is based on the comparison of observational results with forward modelling of the observational manifestation of various kinds of polarisation of kink oscillations. The revealed polarisation favours the sustainability of these oscillations by quasi-steady flows which may hence supply the energy for coronal heating.

In the third paper of this series aimed at developing the tools for analysing resolved stellar populations using the cameras on board of the James Webb Space Telescope (JWST), we present a detailed multi-band study of the 2 Gyr Galactic open cluster NGC 2506. We employ public calibration data-sets collected in multiple filters to: (i) derive improved effective Point Spread Functions (ePSFs) for ten NIRCam filters; (ii) extract high-precision photometry and astrometry for stars in the cluster, approaching the main-sequence (MS) lower mass of ~0.1 Msun; and (iii) take advantage of the synergy between JWST and Gaia DR3 to perform a comprehensive analysis of the cluster's global and local properties. We derived a MS binary fraction of ~57.5 %, extending the Gaia limit (~0.8 Msun) to lower masses (~0.4 Msun) with JWST. We conducted a study on the mass functions (MFs) of NGC 2506, mapping the mass segregation with Gaia data, and extending MFs to lower masses with the JWST field. We also combined information on the derived MFs to infer an estimate of the cluster present-day total mass. Lastly, we investigated the presence of white dwarfs (WDs) and identified a strong candidate. However, to firmly establish its cluster membership, as well as that of four other WD candidates and of the majority of faint low-mass MS stars, further JWST equally deep observations will be required. We make publicly available catalogues, atlases, and the improved ePSFs.

In several jetted AGNs, structured jets have been observed. In particular spine-sheath configurations where the jet is radially divided into two or more zones of different flow velocities. We present a model based on the particle and radiation transport code CR-ENTREES. Here, interaction rates and secondary particle and photon yields are pre-calculated by Monte Carlo event generators or semi-analytical approximations. These are then used to create transition matrices, that describe how each particle spectrum evolves with time. This code allows for arbitrary injection of primary particles, and the possibility to choose which interaction to include (photo-meson production, Bethe-Heitler pair-production, inverse-Compton scattering, $\gamma$-$\gamma$ pair production, decay of all unstable particles, synchrotron radiation -- from electrons, protons, and all relevant secondaries before their respective decays -- and particle escape). In addition to the particle and radiation interactions taking place in each homogeneous zone, we implement the feedback between the two zones having different bulk velocities. The main mechanism at play when particles cross the boundary between the two zones is shear acceleration. We follow a microscopic description of this acceleration process to create a corresponding transition matrix and include it in our numerical setup. Furthermore, each zone's radiation field can be used as an external target photon field for the other zone's particle interactions. We present here the first results of the effect of a two-zone spine-sheath jet, by applying this model to typical low-luminosity AGNs.

Fundamental to our understanding of planetary bulk compositions is the relationship between their masses and radii, two properties that are often not simultaneously known for most exoplanets. However, while many previous studies have modeled the two-dimensional relationship between planetary mass and radii, this approach largely ignores the dependencies on other properties that may have influenced the formation and evolution of the planets. In this work, we extend the existing nonparametric and probabilistic framework of \texttt{MRExo} to jointly model distributions beyond two dimensions. Our updated framework can now simultaneously model up to four observables, while also incorporating asymmetric measurement uncertainties and upper limits in the data. We showcase the potential of this multi-dimensional approach to three science cases: (i) a 4-dimensional joint fit to planetary mass, radius, insolation, and stellar mass, hinting of changes in planetary bulk density across insolation and stellar mass; (ii) a 3-dimensional fit to the California Kepler Survey sample showing how the planet radius valley evolves across different stellar masses; and (iii) a 2-dimensional fit to a sample of Class-II protoplanetary disks in Lupus while incorporating the upper-limits in dust mass measurements. In addition, we employ bootstrap and Monte-Carlo sampling to quantify the impact of the finite sample size as well as measurement uncertainties on the predicted quantities. We update our existing open-source user-friendly \texttt{MRExo} \texttt{Python} package with these changes, which allows users to apply this highly flexible framework to a variety of datasets beyond what we have shown here.

Context. Metal-poor brown dwarfs are poorly understood because they are extremely faint and rare. Only a few candidates have been identified as T-type subdwarfs in infrared surveys and their optical properties remain unconstrained. Aims. We aim to improve the knowledge of the optical properties of T subdwarf candidates to break the degeneracy between metallicity and temperature and to investigate their atmospheric properties. Methods. Deep $z$-band images of 10 known T subdwarf candidates were collected with the 10.4-m Gran Telescopio Canarias. Low-resolution optical spectra for two of them were obtained with the same telescope. Photometric measurements of the $z$-band flux were performed for all the targets and they were combined with infrared photometry in $J, H, K, W1$ and $W2$-bands from the literature to obtain the colours. The spectra were compared with solar-metallicity T dwarf templates and with laboratory spectra. Results. We found that the targets segregate into three distinct groups in the $W1 - W2$ vs. $z - W1$ colour-colour diagram. Group I objects are mixed with solar-metallicity T dwarfs. Group III objects have $W1 - W2$ colours similar to T dwarfs but very red $z - W1$ colours. Group II objects lie between Group I and III. The two targets for which we obtained spectra are located in Group I and their spectroscopic properties resemble normal T dwarfs but with water features that are deeper and have a shape akin to pure water. Conclusions. We conclude that the $W1 - W2$ vs. $z - W1$ colour-colour diagram is excellent to break the metallicity-temperature degeneracy for objects cooler than L-type. A revision of the spectral classification of T subdwarf might be needed in the future, according to the photometric and spectroscopic properties of WISE1810 and WISE0414 in Group III discussed in this work.

Cloud computing offers an opportunity to run compute-resource intensive climate models at scale by parallelising model runs such that datasets useful to the exoplanet community can be produced efficiently. To better understand the statistical distributions and properties of potentially habitable planetary atmospheres we implemented a parallelised climate modelling tool to scan a range of hypothetical atmospheres.Starting with a modern day Earth atmosphere, we iteratively and incrementally simulated a range of atmospheres to infer the landscape of the multi-parameter space, such as the abundances of biological mediated gases (\ce{O2}, \ce{CO2}, \ce{H2O}, \ce{CH4}, \ce{H2}, and \ce{N2}) that would yield `steady state' planetary atmospheres on Earth-like planets around solar-type stars. Our current datasets comprises of \numatmospheres simulated models of exoplanet atmospheres and is available publicly on the NASA Exoplanet Archive. Our scalable approach of analysing atmospheres could also help interpret future observations of planetary atmospheres by providing estimates of atmospheric gas fluxes and temperatures as a function of altitude. Such data could enable high-throughput first-order assessment of the potential habitability of exoplanetary surfaces and sepcan be a learning dataset for machine learning applications in the atmospheric and exoplanet science domain.

We report on several new results using anisotropies of UHECRs. We improve and extend the work of Ding, Globus and Farrar, who modeled the UHECR dipole assuming sources follow the dark matter distribution, accounting for deflections in the Galactic and extragalactic magnetic fields but using a simplified treatment of interactions during propagation. The work presented here employs an accurate and self-consistent treatment of the evolution of composition during propagation, allows for and explores the impact of "bias" in the relation between UHECR sources and the dark matter distribution, and investigates the possible generation of arrival-direction-dependent composition anisotropies. Limits on the source number density consistent with the observed anisotropies are derived for the case where UHECR sources follow the dark matter distribution, and compared to a homogeneous source distribution case.

In our work, we analyse $5\times10^{4}$ single pulses from the recycled pulsar PSR J2222$-$0137 in one of its scintillation maxima observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). PSR J2222$-$0137 is one of the nearest and best studies of binary pulsars and a unique laboratory for testing gravitational theories. We report single pulses' energy distribution and polarization from the pulsar's main-pulse region. The single pulse energy follows the log-normal distribution. We resolve a steep polarization swing, but at the current time resolution ($64\,\mu{\rm s}$), we find no evidence for the orthogonal jump in the main-pulse region, as has been suspected. We find a potential sub-pulse drifting period of $P_{3} \sim 3.5\,P$. We analyse the jitter noise from different integrated numbers of pulses and find that its $\sigma_{j}$ is $270\pm{9}\,{\rm ns}$ for 1-hr integration at 1.25 GHz. This result is useful for optimizing future timing campaigns with FAST or other radio telescopes.

Double white dwarf (WD) merger process and their post-merger evolution are important in many fields of astronomy, such as supernovae, gamma-ray bursts, gravitational waves, etc. The evolutionary outcomes of double ultra-massive WD merger remnants are still a subject of debate, though the general consensus is that the merger remnant will collapse to form a neutron star. In this work, we investigate the evolution of a 2.20Msun merger remnant stemmed from the coalescence of double 1.10Msun ONe WDs. We find that the remnant ignites off-centre neon burning at the position near the surface of primary WD soon after the merger, resulting in the stable inwardly propagating oxygen/neon (O/Ne) flame. The final outcomes of the merger remnant are sensitive to the effect of convective boundary mixing. If the mixing cannot stall the O/Ne flame, the flame will reach the centre within 20 years, leading to the formation of super Chandrasekhar mass silicon core, and its final fate probably be neutron star (NS) through iron-core-collapse supernova. In contrast, if the convective mixing is effective enough to prevent the O/Ne flame from reaching the centre, the merger remnant will undergo electron capture supernova to form an ONeFe WD. Meanwhile, we find that the wind mass loss process may hardly alter the final fate of the remnant due to its fast evolution. Our results imply that the coalescence of double ONe WDs can form short lived giant like object, but the final outcomes (NS or ONeFe WD) are influenced by the uncertain convective mixing in O/Ne flame.

Spectral energy distributions (SEDs) from X-ray to far-infrared (FIR) wavelengths are presented for a sample of 1246 X-ray luminous active galactic nuclei (AGN; $L_{0.5-10\rm{keV}}>10^{43}$ erg s$^{-1}$), with $z_{\rm{spec}}<1.2$, selected from Stripe 82X, COSMOS, and GOODS-N/S. The rest-frame SEDs show a wide spread ($\sim2.5$ dex) in the relative strengths of broad continuum features at X-ray, ultraviolet (UV), mid-infrared (MIR), and FIR wavelengths. A linear correlation (log-log slope of 0.7$\pm0.04$) is found between $L_{\rm{MIR}}$ and $L_{\rm{X}}$. There is significant scatter in the relation between the $L_{\rm{UV}}$ and $L_{\rm{X}}$ due to heavy obscuration, however the most luminous and unobscured AGN show a linear correlation (log-log slope of 0.8$\pm0.06$) in the relation above this scatter. The relation between $L_{\rm{FIR}}$ and $L_{\rm{X}}$ is predominantly flat, but with decreasing dispersion at $L_{\rm{X}}>10^{44}$ erg s$^{-1}$. The ratio between the "galaxy subtracted" bolometric luminosity and the intrinsic $L_{\rm{X}}$ increases from a factor of $\sim$$10-70$ from log $L_{\rm{bol}}/{\rm(erg\; s}^{-1})=44.5-46.5$. Characteristic SED shapes have been determined by grouping AGN based on relative strengths of the UV and MIR emission. The average $L_{1\mu\rm{m}}$ is constant for the majority of these SED shapes, while AGN with the strongest UV and MIR emission have elevated $L_{1\mu\rm{m}}$, consistent with the AGN emission dominating their SEDs at optical and NIR wavelengths. A strong correlation is found between the SED shape and both the $L_{\rm{X}}$ and $L_{\rm{bol}}$, such that $L_{\rm{bol}}/L_{\rm{X}}=20.4\pm1.8$, independent of the SED shape. This is consistent with an evolutionary scenario of increasing $L_{\rm{bol}}$ with decreasing obscuration as the AGN blows away circumnuclear gas.

India's third Moon mission Chandrayaan 3 will deploy a lander and a rover at a high latitude location of the Moon enabling us to carry out first ever in-situ science investigations of such a pristine location that will potentially improve our understanding on primary crust formation and subsequent modification processes. The primary landing site (PLS), is situated at 69.367621 degS, 32.348126 degE. As a contingency, an alternate landing site (ALS) was also selected at nearly the same latitude but nearly 450 km west to PLS. In this work, a detailed study of the geomorphology, composition, and temperature characteristics of ALS has been carried out using the best-ever high resolution Chandrayaan 2 OHRC DEMs and Ortho images, datasets obtained from Chandrayaan 1 and on-going Lunar Reconnaissance Orbiter. For understanding the thermophysical behaviour, we used a well-established thermophysical model. We found that the Chandrayaan 3 ALS is characterised by a smooth topography with an elevated central part. The ALS is a scientifically interesting site with a high possibility of sampling ejecta materials from Tycho and Moretus. Based on the spectral and elemental analysis of the site, Fe is found to be near approx. 4.8 wt.%, with Mg approx. 5 wt.%, and Ca approx. 11 wt.%. Compositionally, ALS is similar to PLS with a highland soil composition. Spatial and diurnal variability of around 40 K and 175 K has been observed in the surface temperatures at ALS. Although belonging to similar location like PLS, ALS showed reduced daytime temperatures and enhanced night-time temperatures compared to PLS, indicating a terrain of distinctive thermophysical characteristics. Like PLS, ALS is also seems to be an interesting site for science investigations and Chandrayaan 3 is expected to provide new insights into the understanding of lunar science even if it happens to land in the alternate landing site.

We compare the observational properties between $^{12}$CO, $^{13}$CO, and C$^{18}$O and summarize the observational parameters based on 7069 clouds sample from the Milky Way Imaging Scroll Painting (MWISP) CO survey in a section of the third Galactic quadrant. We find that the $^{13}$CO angular area ($A_{\rm ^{13}CO}$) generally increases with that of $^{12}$CO ($A_{\rm ^{12}CO}$), and the ratio of $A_{\rm ^{13}CO}$ to $A_{\rm ^{12}CO}$ is 0.38 by linear fitting. We find that the $^{12}$CO and $^{13}$CO flux are tightly correlated as $F_{\rm ^{13}CO}~=~0.17~ F_{\rm ^{12}CO}$ with both fluxes calculated within the $^{13}$CO-bright region. This indicates that the abundance $X_{\rm ^{13}CO}$ is a constant to be 6.5$^{+0.1}_{-0.5}$ $\times 10^{-7}$ for all samples under assumption of local thermodynamic equilibrium (LTE). Additionally, we observed that the X-factor is approximately constant in large sample molecular clouds. Similarly, we find $F_{\rm C^{18}O}~=~0.11~F_{\rm ^{13}CO}$ with both fluxes calculated within C$^{18}$O-bright region, which indicates that the abundance ratios ${X_{\rm ^{13}CO}/X_{\rm C^{18}O}}$ stays the same value 9.7$^{+0.6}_{-0.8}$ across the molecular clouds under LTE assumption. The linear relationships of $F_{\rm ^{12}CO}$ vs. $F_{\rm ^{13}CO}$ and $F_{\rm ^{13}CO}$ vs. $F_{\rm C^{18}O}$ hold not only for the $^{13}$CO-bright region or C$^{18}$O-bright region, but also for the entire molecular cloud scale with lower flux ratio. The abundance ratio ${X_{\rm ^{13}CO}/X_{\rm C^{18}O}}$ inside clouds shows a strong correlation with column density and temperature. This indicates that the ${X_{\rm ^{13}CO}/X_{\rm C^{18}O}}$ is dominated by a combination of chemical fractionation, selectively dissociation, and self-shielding effect inside clouds.

Atom interferometers offer promising new avenues for detecting ultra-light dark matter (ULDM). The exceptional sensitivity of atom interferometers to fluctuations in the local gravitational potential exposes them to sources of noise from human (anthropogenic) and animal (synanthropic) activity, which may obscure signals from ULDM. We characterise potential anthropogenic and synanthropic noise sources and examine their influence on a year-long measurement campaign by AION-10, an upcoming atom interferometer experiment that will be located at the University of Oxford. We propose a data cleaning framework that identifies and then masks anthropogenic and synanthropic noise. With this framework, we demonstrate that even in noisy conditions, the sensitivity to ULDM can be restored to within between 10% and 40% of an atom shot noise-limited experiment, depending on the specific composition of the anthropogenic and synanthropic noise. This work provides an important step towards creating robust noise reduction analysis strategies in the pursuit of ULDM detection with atom interferometers.

We present results from an optical search for Local Group dwarf galaxy candidates associated with the Ultra-Compact High Velocity Clouds (UCHVCs) discovered by the ALFALFA neutral hydrogen survey. The ALFALFA UCHVCs are isolated, compact HI clouds with projected sizes, velocities, and estimated HI masses that suggest they may be nearby dwarf galaxies, but that have no clear counterpart in existing optical survey data. We observed 26 UCHVCs with the WIYN 3.5-m telescope and One Degree Imager (ODI) in two broadband filters and searched the images for resolved stars with properties that match those of stars in typical dwarf galaxies at distances <2.5 Mpc. We identify one promising dwarf galaxy candidate at a distance of ~570 kpc associated with the UCHVC AGC 268071, and five other candidates that may deserve additional follow-up. We carry out a detailed analysis of ODI imaging of a UCHVC that is close in both projected distance and radial velocity to the outer-halo Milky Way globular cluster Pal 3. We also use our improved detection methods to reanalyze images of five UCHVCs that were found to have possible optical counterparts during the first phase of the project, and confirm the detection of a possible stellar counterpart to the UCHVC AGC 249525 at an estimated distance of ~2 Mpc. We compare the optical and HI properties of the dwarf galaxy candidates to the results from recent theoretical simulations that model satellite galaxy populations in group environments, as well as to the observed properties of galaxies in and around the Local Group.

We test the tenet of statistical isotropy of the standard cosmological model via a homology analysis of the cosmic microwave background temperature maps. Examining small sectors of the normalized maps, we find that the results exhibit a dependence on whether we compute the mean and variance locally from the masked patch, or from the full masked sky. Assigning local mean and variance for normalization, we find the maximum discrepancy between the data and model in the galactic northern hemisphere at more than $3.5$ s.d. for the PR4 dataset at degree-scale. For the PR3 dataset, the C-R and SMICA maps exhibit higher significance than the PR4 dataset at $\sim 4$ and $4.1$ s.d. respectively, however the NILC and SEVEM maps exhibit lower significance at $\sim 3.4$ s.d. The southern hemisphere exhibits high degree of consistency between the data and the model for both the PR4 and PR3 datasets. Assigning the mean and variance of the full masked sky decreases the significance for the northern hemisphere, the tails in particular. However the tails in the southern hemisphere are strongly discrepant at more than $4$ standard deviations at approximately $5$ degrees. The $p$-values obtained from the $\chi^2$-statistic exhibit commensurate significance in both the experiments. Examining the quadrants of the sphere, we find the first quadrant to be the major source of the discrepancy. Prima-facie, the results indicate a breakdown of statistical isotropy in the CMB maps, however more work is needed to ascertain the source of the anomaly. Regardless, these map characteristics may have serious consequences for downstream computations such as parameter estimation, and the related Hubble tension.

U Equ is an unusual maser-hosting IR source discovered in the 1990s. It was tentatively classified as a post-AGB star with a unique optical spectrum displaying rare emission and absorption features from molecular gas. In 2022, we discovered that its optical spectrum has drastically changed. Methods: Optical high-resolution spectra of U Equ from SALT are supplemented by archival data and NIR photometry from NOT. New spectral line observations with the Effelsberg telescope and ALMA are presented. Results: No circumstellar molecular features are present in the contemporary optical spectra of U Equ. Non-photospheric absorption and emission from neutral and ionized species dominate the current spectrum. Some of the observed features indicate an outflow with a terminal velocity of 215 km\s. The H\&K lines of [Ca II] indicate a photosphere of spectral type F. Photometric measurements show that the source has been monotonically increasing its optical and NIR fluxes since the beginning of this century. SEDs at different epochs show dusty circumstellar material arranged in a highly-inclined disk. At a distance of 4 kpc, the source's luminosity is 10$^4$ L$_{\odot}$. Conclusions: The object has changed considerably in the last three decades, either due to geometrical reconfiguration of the circumstellar medium, evolutionary changes in the central star, or owing to an accretion event that has started in the system very recently. Observationally, U Equ appears to resemble the Category 0 of disk-hosting post-AGB stars, especially the post-common envelope binary HD 101584. It is uncertain if the drastic spectral change and the associated optical/MIR rise in brightness are common in post-AGB stars but such a radical change may be related to the real-time onset of the evolution of the system into a planetary nebula. We find that the post-AGB star V576 Car has undergone a similar transformation as U Equ.

We present the updated open-source code Complete History of Interaction-Powered Supernovae (CHIPS) that can be applied to modeling supernovae (SNe) arising from an interaction with massive circumstellar medium (CSM) as well as the formation process of the CSM. Our update mainly concerns with extensions to hydrogen-poor SNe from stripped progenitors, targeting modeling of interaction-powered SNe Ibc such as Type Ibn and Icn SNe. We successfully reproduce the basic properties of the light curves of these types of SNe that occur after partial eruption of the outermost layer with a mass of $0.01$--$0.1\,M_\odot$ at $\lesssim 1$ year before explosion. We also find that the luminosity of the observed precursors can be naturally explained by the outburst that creates the dense CSM, given that the energy of the outburst is efficiently dissipated by collision with an external material, possibly generated by a previous mass eruption. We discuss possible scenarios causing eruptive mass-loss based on our results.

This study investigates low luminosity Fanaroff-Riley Type 0 (FR0) radio galaxies as a potentially significant source of ultra-high energy cosmic rays (UHECRs). Due to their much higher prevalence in the local universe compared to more powerful radio galaxies (about five times more than FR-1s), FR0s may provide a substantial fraction of the total UHECR energy density. To determine the nucleon composition and energy spectrum of UHECRs emitted by FR0 sources, simulation results from CRPropa3 are fit to Pierre Auger Observatory data. The resulting emission spectral indices, rigidity cutoffs, and nucleon fractions are compared to recent Auger results. The FR0 simulations include the approximately isotropic distribution of FR0 galaxies and various intergalactic magnetic field configurations (including random and structured fields) and predict the fluxes of secondary photons and neutrinos produced during UHECR propagation through cosmic photon backgrounds. This comprehensive simulation allows for investigating the properties of the FR0 sources using observational multi-messenger data.

We report on the first comprehensive study of the coronal mass ejections (CMEs) associated with $\sim$25 MeV solar energetic proton (SEP) events in 1980-2013 observed in the low/inner corona by the Mauna Loa Solar Observatory (MLSO) Mk3 and Mk4 coronameters. Where possible, these observations are combined with spacebased observations from the Solar Maximum Mission C/P, P78-1 SOLWIND or SOHO/LASCO coronagraphs. The aim of the study is to understand directly-measured (rather than inferred from proxies) CME motions in the low to middle corona and their association with SEP acceleration, and hence attempt to identify early signatures that are characteristic of SEP acceleration in ground-based CME observations that may be used to warn of impending SEP events. Although we find that SEP events are associated with CMEs that are on average faster and wider than typical CMEs observed by MLSO, a major challenge turns out to be determining reliable estimates of the CME dynamics in the low corona from the 3-minute cadence Mk3/4 observations since different analysis techniques can produce inconsistent results. This complicates the assessment of what early information on a possible SEP event is available from these low coronal observations

We propose a novel means of directly measuring cosmological distances using scintillated microlensing of fast radio bursts (FRBs). In standard strong lensing measurements of cosmic expansion, the main source of systematic uncertainty lies in modeling the mass profile of galactic halos. Using extra-galactic stellar microlensing to measure the Hubble constant avoids this systematic uncertainty as the lens potential of microlenses depends only on a single parameter: the mass of the lens. FRBs, which may achieve nanosecond precision on lensing time delays, are well-suited to precision measurements of stellar microlensing, for which the time delays are on the order of milliseconds. However, typical angular separations between the microlensed images on the order of microarcseconds make the individual images impossible to spatially resolve with ground-based telescopes. We propose leveraging scintillation in the ISM to resolve the microlensed images, effectively turning the ISM into an astrophysical-scale interferometer. Using this technique, we estimate a 6\% uncertainty on $H_0$ from a single observed scintillated microlensing event, with a sub-percent uncertainty on $H_0$ achievable with only 30 such events. With an optical depth for stellar microlensing of $10^{-3}$, this may be achievable in the near future with upcoming FRB telescopes.

The inner structure of core-helium burning (CHeB) stars remains uncertain due to the yet unknown nature of mixing at the boundary of their cores. Large convective cores beyond a bare Schwarzschild model are favoured both from theoretical arguments and from asteroseismological constraints. However, the exact nature of this extra mixing, and in particular the possible presence of semiconvective layers, is still debated. In this work, we approach this problem through a new avenue by performing the first full-sphere 3D hydrodynamics simulations of the interiors of CHeB stars. We use the PPMstar explicit gas dynamics code to simulate the inner 0.45 $M_{\odot}$ of a 3 $M_{\odot}$ CHeB star. Simulations are performed using different Cartesian grid resolutions (768$^3$, 1152$^3$ and 1728$^3$) and heating rates. We use two different initial states, one based on MESA's predictive mixing scheme (which yields a large overshoot region) and one based on the convective premixing approach (which exhibits a semiconvective interface). The general behaviour of the flow in the convective core and in the stable envelope (where internal gravity waves are observed) is consistent with our recent simulations of core convection in massive main-sequence stars, and so are the various scaling relations. The semiconvective layers are dominated by strong internal gravity waves that do not produce measurable species mixing, but overshooting motions from the convective core gradually homogenize the semiconvective interface. This process can possibly completely erase the semiconvective layers, which would imply that CHeB stars do not harbour a semiconvection zone.

We present cosmological constraints derived from peak counts, minimum counts, and the angular power spectrum of the Subaru Hyper Suprime-Cam first-year (HSC Y1) weak lensing shear catalog. Weak lensing peak and minimum counts contain non-Gaussian information and hence are complementary to the conventional two-point statistics in constraining cosmology. In this work, we forward-model the three summary statistics and their dependence on cosmology, using a suite of $N$-body simulations tailored to the HSC Y1 data. We investigate systematic and astrophysical effects including intrinsic alignments, baryon feedback, multiplicative bias, and photometric redshift uncertainties. We mitigate the impact of these systematics by applying cuts on angular scales, smoothing scales, statistic bins, and tomographic redshift bins. By combining peaks, minima, and the power spectrum, assuming a flat-$\Lambda$CDM model, we obtain $S_{8} \equiv \sigma_8\sqrt{\Omega_m/0.3}= 0.810^{+0.022}_{-0.026}$, a 35\% tighter constraint than that obtained from the angular power spectrum alone. Our results are in agreement with other studies using HSC weak lensing shear data, as well as with Planck 2018 cosmology and recent CMB lensing constraints from the Atacama Cosmology Telescope and the South Pole Telescope.

The dominant source of radio continuum emissions at low frequencies is synchrotron radiation, which originates from star-forming regions in disk galaxies and from powerful jets produced by active galactic nuclei (AGN). We studied the Bootes field using the upgraded Giant Meterwave Radio Telescope (uGMRT) at 400 MHz, achieving a central minimum off-source RMS noise of 35$\mu$Jy beam$^{-1}$ and a catalogue of 3782 sources in $\sim6$ sq. degrees of the sky. The resulting catalogue was compared to other radio frequency catalogues, and the corrected normalised differential source counts were derived. We use standard multi-wavelength techniques to classify the sources in star-forming galaxies (SFGs), radio-loud (RL) AGN, and radio-quiet (RQ) AGN that confirm a boost in the SFGs and RQ\,AGN AGN populations at lower flux levels. For the first time, we investigated the properties of the radio--IR relations at 400\,MHz in this field. The $L_{\rm 400 MHz}$--$L_{\rm TIR}$ relations for SFGs were found to show a strong correlation with non-linear slope values of $1.10\pm0.01$, and variation of $q_{\rm TIR}$ with $z$ is given as, $q_{\rm TIR} = (2.19 \pm 0.07)\ (1+z)^{-0.15 \pm 0.08}$. This indicates that the non-linearity of the radio--IR relations can be attributed to the mild variation of $q_{\rm TIR}$ values with $z$. The derived relationships exhibit similar behaviour when applied to LOFAR at 150 MHz and also at 1.4 GHz. This emphasises the fact that other parameters like magnetic field evolution with $z$ or the number densities of cosmic ray electrons can play a vital role in the mild evolution of $q$ values.

We investigate the formation of intermediate mass black holes (IMBHs) through hierarchical mergers of stellar origin black holes (BHs), as well as BH mergers formed dynamically in nuclear star clusters. Using a semi-analytical approach which incorporates probabilistic mass-function-dependent double BH (DBH) pairing, binary-single encounters, and a mass-ratio-dependent prescription for energy dissipation in hardening binaries, we find that IMBHs with masses of $\mathcal{O}(10^2)$~--~$\mathcal{O}(10^4)\,\rm M_\odot$ can be formed solely through hierarchical mergers in timescales of a few $100$\,Myrs to a few\,Gyrs. Clusters with escape velocities $\gtrsim400$\,km\,s$^{-1}$ inevitably form high-mass IMBHs. The spin distribution of IMBHs with masses $\gtrsim 10^3M_\odot$ is strongly clustered at $\chi\sim 0.15$; while for lower masses, it at $\chi\sim 0.7$. Eccentric mergers are more frequent for equal-mass binaries containing first- and/or second-generation BHs. Metal-rich, young, dense clusters can produce up to $20\%$ of their DBH mergers with eccentricity $\geq0.1$ at $10\,\rm Hz$, and $\sim2$~--~$9\%$ of all in-cluster mergers can form at $>10$\,Hz. Nuclear star clusters are therefore promising environments for the formation of highly-eccentric DBH mergers, detectable with current gravitational-wave detectors. Clusters of extreme mass ($\sim10^8$\,M$_\odot$) and density ($\sim10^8$\,M$_\odot$pc$^{-3}$) can have about half of all of their DBH mergers with primary masses $\geq100$\,M$_\odot$. The fraction of in-cluster mergers increases rapidly with increasing cluster escape velocity, being nearly unity for $v_{\rm esc}\gtrsim 200$\,km\,s$^{-1}$. Cosmological merger rate of DBHs from nuclear clusters varies $\approx0.01-1$\,Gpc$^{-3}$yr$^{-1}$.

For a pair of supermassive black holes (SMBHs) in the remnant of a dual galaxy merger, well-known models exist to describe their dynamical evolution until the final coalescence accompanied by the emission of a low-frequency gravitational wave (GW) signal. In this article, we investigate the dynamical evolution of three SMBH triple systems recovered from the ROMULUS25 cosmological simulation to explore common dynamical evolution patterns and assess typical coalescence times. For this purpose, we construct initial conditions from the ROMULUS25 data and perform high-resolution gravitodynamical \N-body simulations. We track the orbital evolution from the galactic inspiral to the formation of hard binaries at sub-parsec separation and use the observed hardening rates to project the time of coalescence. In all cases, the two heaviest black holes form an efficiently hardening binary that merges within fractions of the Hubble time. The lightest SMBH either gets ejected, forms a stable hierarchical triple system with the heavier binary, forms a hardening binary with the previously merged binary's remnant, or remains on a wide galactic orbit. The coalescence times of the lighter black holes are thus significantly longer than for the heavier binary, as they experience lower dynamical friction and stellar hardening rates. We observe the formation of hierarchical triples when the density profile of the galactic nucleus is sufficiently steep.

Cold, substellar objects such as brown dwarfs have long been recognized as contaminants in color-selected samples of active galactic nuclei (AGNs). In particular, their near- to mid-infrared colors (1--5 $\mu$m) can closely resemble the V-shaped ($f_{\lambda}$) spectra of highly-reddened accreting supermassive black holes, the little red dots, especially at $6 < z < 7$. Recently, a NIRCam-selected sample of little red dots over 45 arcmin$^2$ has been followed-up with deep NIRSpec multi-object prism spectroscopy through the UNCOVER program. By investigating the acquired spectra, we identify three out of the 13 followed-up objects as brown dwarfs with temperatures between 650 and 1300 K and distances between 0.8 and 4.8 kpc. We identify the remaining 10 objects as extragalactic sources at $z_{\rm spec} > 3$. Given that three of these sources are the strongly lensed images of the same AGN (Abell2744-QSO1), we derive a brown dwarf contamination fraction of 27\% in this NIRCam-selection of little red dots. We find that in the near-infrared filters, brown dwarfs appear much bluer than the highly-reddened AGN, providing an avenue for distinguishing the two and compiling cleaner samples of photometrically-selected highly-reddened AGN.

We demonstrate that the searches for dark sector particles can provide probes of reheating scenarios, focusing on the cosmic millicharge background produced in the early universe. We discuss two types of millicharge particles (mCPs): either with, or without, an accompanying dark photon. These two types of mCPs have distinct theoretical motivations and cosmological signatures. We discuss constraints from the overproduction and mCP-baryon interactions of the mCP without an accompanying dark photon, with different reheating temperatures. We also consider the $\Delta N_{\rm eff}$ constraints on the mCPs from kinetic mixing, varying the reheating temperature. The regions of interest in which the accelerator and other experiments can probe the reheating scenarios are identified in this paper for both scenarios. These probes can potentially allow us to set an upper bound on the reheating temperature down to $\sim 10$ MeV, much lower than the previously considered upper bound from inflationary cosmology at around $\sim 10^{16}$ GeV. In addition, we find parameter regions in which the two mCP scenarios may be differentiated by cosmological considerations. Finally, we discuss the implications of dedicated mCP searches and future CMB-S4 observations.

High-energy collisions at the High-Luminosity Large Hadron Collider (HL-LHC) will produce an enormous flux of particles along the beam collision axis that is not accessible by existing LHC experiments. Multi-particle production in the far-forward region is of particular interest for astroparticle physics. High-energy cosmic rays produce large particle cascades in the atmosphere, extensive air showers (EAS), which are driven by hadron-ion collisions under low momentum transfer in the non-perturbative regime of QCD. Thus, the understanding of high-energy hadronic interactions in the forward region is crucial for the interpretation of EAS data and for the estimation of backgrounds for searches of astrophysical neutrinos. The Forward Physics Facility (FPF) is a proposal to build a new underground cavern at the HL-LHC which will host a variety of far-forward experiments to detect particles outside the acceptance of the existing LHC experiments. We will present the current status of plans for the FPF and highlight the synergies with astroparticle physics. In particular, we will discuss how measurements at the FPF will improve the modeling of high-energy hadronic interactions in the atmosphere and thereby reduce the associated uncertainties of measurements in the context of multi-messenger astrophysics.

We study the inflationary model constructed from a Spatially Covariant Gravity (SCG). The Lagrangian for the SCG in our consideration is expressed as the polynomial of irreducible SCG monomials where the total number of derivatives of each monomial is two, and the theory propagates two tensorial degrees of freedom of gravity up to the first order in cosmological perturbations. The condition for having two tensorial degrees of freedom studied earlier in literature for such theories is derived in vacuum. We extend the condition for having two tensorial degrees of freedom to the case where a scalar field is included by imposing a gauge-fixing. We apply the resulting SCG to describe inflationary universe. The observational predictions such as the scalar spectral index and tensor-to-scalar ratio from this model are investigated. We find that the tensor-to-scalar ratio in this model can either be in the order of unity or be small depending on the parameter of the model.

False-vacuum eternal inflation can be described as a random walk on the network of vacua of the string landscape. In this paper we show that the problem can be mapped naturally to a problem of directed percolation. The mapping relies on two general and well-justified approximations for transition rates: 1.~the downward approximation, which neglects ``upward" transitions, as these are generally exponentially suppressed; 2. the dominant decay channel approximation, which capitalizes on the fact that tunneling rates are exponentially staggered. Lacking detailed knowledge of the string landscape, we model the network of vacua as random graphs with arbitrary degree distribution, including Erd\"os-R\'enyi and scale-free graphs. As a complementary approach, we also model regions of the landscape as regular lattices, specifically Bethe lattices. We find that the uniform-in-time probabilities proposed in our previous work favor regions of the landscape poised at the directed percolation phase transition. This raises the tantalizing prospect of deriving universal statistical distributions for physical observables, characterized by critical exponents that are insensitive to the details of the underlying landscape. We illustrate this with the cosmological constant, and show that the resulting distribution peaks as a power-law for small positive vacuum energy, with a critical exponent uniquely determined by the random graph universality class.

Charged current neutrino-nucleon reactions, generally called Urca processes, are crucial actors of a neutron star's thermal evolution. The so-called direct processes show a pronounced threshold under which the reaction is kinematically suppressed. This suppression does not apply to "modified" Urca processes which involve interaction with an additional nucleon. Calculations of the modified Urca neutrino rates were established for cold neutron star matter and for dilute hot matter, in both cases under strong assumptions. In this paper, we revise the calculations of the modified Urca neutrino rates for dense and hot matter, and for different compositions. We study the influence of different approximations used in previous computations. We derive expressions for the rates of modified Urca neutrino emissivity within thermal field theory and perform the phase space integration numerically using mainly importance sampling Monte-Carlo techniques. The neutrino emissivity of modified and direct processes are established and compared. We find in particular that the modified Urca process is not necessarily suppressed with respect to the direct process above the threshold of the latter at moderate densities and temperatures, in contrast to what is generally assumed. Numerical results are confirmed by an estimation of the ratio of modified to direct Urca rates with a simple analytic approximation, thereby showing the regimes of suppression for the modified processes depending on temperature and density. These results show that modified Urca rates have to be considered carefully upon evaluating neutrino opacities in dense and warm matter.

These notes are self-contained, with the first six chapters used for a one-semester course with recommended texts by Wald, Misner, Thorne, and Wheeler (MTW), and, particularly for gravitational waves, by Schutz and by Thorne and Blandford. In its treatment of topics covered in these standard texts, the presentation here typically includes steps between equations that are skipped in Wald or MTW. Treatments of gravitational waves, particle orbits in black-hole backgrounds, the Teukolsky equation, and the initial value equations are motivated in part by the dramatic discoveries of gravitational waves from the inspiral and coalescence of binary black holes and neutron stars, advances in numerical relativity, and the expected launch of the LISA space-based observatory. Students are assumed to have encountered special relativity, but these notes give a detailed presentation with a geometrical orientation, starting with with time dilation and length contraction and including relativistic particles, fluids, electromagnetism, and curvilinear coordinates. Chaps. 2-5 cover curvature, the Einstein equation, relativistic stars, and black holes. Chap. 6, on gravitational waves, includes a discussion of detection and of noise in interferometric detectors. Chap. 7, on the initial value problem, has a section on the form of the equations used in numerical relativity. Its notation is that used, for example, in Baumgarte and Shapiro and Shibata; the presentation here is taken in part from the text by Friedman and Stergioulas. The notes also have a chapter on the Newman-Penrose formalism and the Teukolsky equation. Following that is a chapter on black-hole thermodynamics and a final chapter on the gravitational action and on conserved quantities for asymptotically flat spacetimes, using Noether's theorem.

Limits on the "thermal relic" warm dark matter mass are apparently inconsistent with measurements of the warm dark matter temperature-to-mass ratio. We try to understand this problem.

Pulsar Timing Arrays (PTAs) are expected to be able to detect gravitational waves (GWs) from individual supermassive black hole binaries in the near future. In order to identify the host galaxy of a gravitational wave source, the angular resolution of PTAs should be much better than that expected from the conventional methodology of PTAs. We study the potential usefulness of precise pulsar-distance measurements in the determination of the sky location of a single GW source. Precise distance information from external observations such as astrometry by Very Long Baseline Interferometry is incorporated as priors in the PTA analysis and we evaluate the precision of the sky location of a GW source by simulating PTA data of 12 milli-second pulsars with only the GW signal and the Gaussian white noise in the timing residuals. We show that only a few pulsars with a distance precision of 1 pc will improve the precision of the source location by more than 1 order in the presence of white noise of 10 ns.

According to the best-fit parameters of the Standard Model, the Higgs field's potential reaches a maximum at a field value $h \sim 10^{10-11}$ GeV and then turns over to negative values. During reheating after inflation, resonance between the inflaton and the Higgs can cause the Higgs to fluctuate past this maximum and run down the dangerous side of the potential if these fields couple too strongly. In this paper, we place constraints on the inflaton-Higgs couplings such that the probability of the Higgs entering the unstable regime during reheating is small. To do so, the equations of motion are approximately solved semi-analytically, then solved fully numerically. Next the growth in variance is used to determine the parameter space for $\kappa$ and $\alpha$, the coupling coefficients for inflaton-Higgs cubic and quartic interactions, respectively. We find the upper bounds of $\kappa < 1.6 \times 10^{-5} m_\phi \sim 2.2 \times 10^8$ GeV and $\alpha < 10^{-8}$ to allow the Higgs to remain stable in most Hubble patches during reheating, and we also find the full two parameter joint constraints. We find a corresponding bound on the reheat temperature of $T_\text{reh} \lesssim 9.2 \times 10^9$ GeV. Additionally, de Sitter temperature fluctuations during inflation put a lower bound on inflaton-Higgs coupling by providing an effective mass for the Higgs, pushing back its hilltop during inflation. These additional constraints provide a lower bound on $\alpha$, while $\kappa$ must also be non-zero for the inflaton to decay efficiently.

We calculate the friction experienced by ultrarelativistic bubble walls resulting from the $1 \rightarrow 2$ light-to-heavy transition process, with finite-wall-width effects fully taken into account. In this process, the light particle is excited from the order-parameter scalar field, while the two heavy particles are excitations of a dark matter scalar field. Unlike earlier estimates suggesting a friction scaling as $\gamma_w^0$, where $\gamma_w$ represents the Lorentz factor of the wall velocity, our more precise numerical analysis reveals a logarithmic dependence of the friction on $\gamma_w$. We offer a numerical fit to capture this frictional pressure accurately. Our analysis verifies that the friction stemming from the $1 \rightarrow 2$ light-to-heavy transition is typically much smaller than the friction from the $1 \rightarrow 1$ transmission of the dark matter particles.