Papers for Monday, Oct 09 2023

Tidal disruption events (TDEs) occur when a star enters the tidal radius of a supermassive black hole (SMBH). If the star only grazes the tidal radius, a fraction of the stellar mass will be accreted in a partial TDE (pTDE). The remainder can continue orbiting and may re-disrupted at pericenter, causing a repeating pTDE. pTDEs may be as or more common than full TDEs (fTDEs), yet few are known. In this work, we present the discovery of the first repeating pTDE from a systematically-selected sample, AT\,2020vdq. AT\,2020vdq was originally identified as an optically- and radio-flaring TDE. Around $3$ years after its discovery, it rebrightened dramatically and rapidly in the optical. The optical flare was remarkably fast and luminous compared to previous TDEs. It was accompanied by extremely broad (${\sim}0.1c$) optical/UV spectral features and faint X-ray emission ($L_X \sim 3\times10^{41}$\,erg\,s$^{-1}$), but no new radio-emitting component. Based on the transient optical/UV spectral features and the broadband light curve, we show that AT\,2020vdq is a repeating pTDE. We then use it to constrain TDE models; in particular, we favor a star originally in a very tight binary system that is tidally broken apart by the Hills mechanism. We also constrain the repeating pTDE rate to be $10^{-6}$ to $10^{-5}$ yr$^{-1}$ galaxy$^{-1}$, with uncertainties dominated by the unknown distribution of pTDE repeat timescales. In the Hills framework, this means the binary fraction in the galactic nucleus is of the order few percent.

An important characteristic of cosmic reionization is the growth of ionized gas bubbles surrounding early luminous objects. Understanding the connections between the formation and coalescence of these bubbles and their originating astrophysical sources is equally critical. We present results from a study of bubble sizes using the state-of-the-art THESAN radiation-hydrodynamics simulation suite, which self-consistently models radiation transport and realistic galaxy formation. We employ the mean-free path method, and track the evolution of the effective ionized bubble size at each point ($R_{\rm eff}$) throughout the Epoch of Reionization. We show there is a slow growth period for regions ionized early, but a rapid flash ionization process for regions ionized later as they immediately enter a large, pre-existing bubble. We also find that bright sources are preferentially in larger bubbles, and find consistency with recent observational constraints at $z \gtrsim 9$, but tension with idealized Lyman-alpha damping-wing models at $z \approx 7$ when the size distribution is complex. We find that high overdensity regions have larger characteristic bubble sizes, but the correlation decreases as reionization progresses, likely due to the runaway formation of large percolated bubbles. Finally, we compare the redshift at which a region transitions from neutral to ionized ($z_{\rm reion}$) with the time it takes to reach a given bubble size and conclude that $z_{\rm reion}$ is a reasonable local probe of small-scale bubble size statistics ($R_\text{eff} \lesssim 1$ cMpc). However, for larger bubbles, the correspondence between $z_{\rm reion}$ and size statistics weakens due to the time delay between the onset of reionization and the expansion of a large bubble, particularly at high redshifts.

The emergence of massive, optically-faint galaxies in infrared observations has revealed that our view of the high-redshift Universe was previously incomplete. With the advent of JWST, we can for the first time probe the rest-frame optical emission of galaxies at $z>3$ with high sensitivity and spatial resolution, thus moving towards a more complete census of the galaxy population at high redshifts. To this end, we present a sample of 148 massive, dusty galaxies from the JWST/CEERS survey, colour-selected using solely JWST bands. With deep JWST/NIRCam data from 1.15$\mu$m to 4.44$\mu$m and ancillary HST/ACS and WFC3 data, we determine the physical properties of our sample using spectral energy distribution fitting with BAGPIPES. We demonstrate that our selection method efficiently identifies massive ($\mathrm{\langle \log M_\star/M_\odot \rangle \sim 10}$) and dusty ($\mathrm{\langle A_V\rangle \sim 2.7\ mag}$) sources, with a majority at $z>3$ and predominantly lying on the galaxy main-sequence. The main results of this work are the stellar mass functions (SMF) of red, optically-faint galaxies from redshifts between $3<z<8$: these galaxies make up a significant fraction of the pre-JWST total SMF at $3<z<4$, and dominate the high-mass end of the pre-JWST SMF at $4<z<6$ and $6<z<8$, suggesting that our census of the galaxy population needs amendment at these epochs. While larger areas need to be surveyed in the future, our results suggest already that the integrated stellar mass density at $\mathrm{\log M_\star/M_\odot>9.25}$ may have been underestimated by $\sim$20-25% at $z\sim3-6$, and $\sim$110% at $z\sim6-8$.

The origin and formation of globular clusters has remained a mystery. We present a formation scenario for ancient globular cluster-like objects that form in ultra-high resolution simulations (smallest cell size $<0.1\,\mathrm{pc}$, mass resolution $M_\mathrm{cell}=4\,\mathrm{M}_\odot$). The simulations are cosmological zoom-in simulations of dwarf galaxies within the stellar mass range $10^{6-7}\,\mathrm{M}_\odot$ that match Local Group dwarf properties well. Our investigation reveals globular clusters hosting ancient stellar populations, characterized by a lack of dark matter in the present epoch. The clusters exhibit short, episodic star formation histories, occasionally marked by the presence of multiple stellar generations. The metallicity distributions show a widening, encompassing stars in the range of $10^{-4} < Z_\star/\mathrm{Z}_\odot < 1$. The presence of these objects is attributable to star formation occurring within low-mass dark matter halos ($M_\mathrm{halo}\approx10^6\,\mathrm{M}_\odot$) during the early stages of the Universe, preceding Reionization ($z\gtrsim7$). As these clusters are accreted into dwarf galaxies, dark matter is preferentially subjected to tidal stripping, with an average accretion redshift of $\bar{z} \approx 5$.

In this work, we use the Jansky VLA Sky Survey (VLASS) to compile the first sample of six radio-selected tidal disruption events (TDEs) with transient optical counterparts. While we still lack the statistics to do detailed population studies of radio-selected TDEs, we use these events to suggest trends in host galaxy and optical light curve properties that may correlate with the presence of radio emission, and hence can inform optically-selected TDE radio follow-up campaigns. We find that radio-selected TDEs tend to have faint and cool optical flares, as well as host galaxies with low SMBH masses. Our radio-selected TDEs also tend to have more energetic, larger radio emitting regions than radio-detected, optically-selected TDEs. We consider possible explanations for these trends, including by invoking super-Eddington accretion and enhanced circumnuclear media. Finally, we constrain the radio-emitting TDE rate to be $\gtrsim 10$ Gpc$^{-3}$ yr$^{-1}$.

We present the first analysis of JWST near-infrared spectroscopy of stellar flares from TRAPPIST-1 during transits of rocky exoplanets. Four flares were observed from 0.6--2.8 $\mu$m with NIRISS and 0.6--3.5 $\mu$m with NIRSpec during transits of TRAPPIST-1b, f, and g. We discover P$\alpha$ and Br$\beta$ line emission and characterize flare continuum at wavelengths from 1--3.5 $\mu$m for the first time. Observed lines include H$\alpha$, P$\alpha$-P$\epsilon$, Br$\beta$, He I $\lambda$0.7062$\mu$m, two Ca II infrared triplet (IRT) lines, and the He I IRT. We observe a reversed Paschen decrement from P$\alpha$-P$\gamma$ alongside changes in the light curve shapes of these lines. The continuum of all four flares is well-described by blackbody emission with an effective temperature below 5300 K, lower than temperatures typically observed at optical wavelengths. The 0.6--1 $\mu$m spectra were convolved with the TESS response, enabling us to measure the flare rate of TRAPPIST-1 in the TESS bandpass. We find flares of 10$^{30}$ erg large enough to impact transit spectra occur at a rate of 3.6$\substack{+2.1 \\ -1.3}$ flare d$^{-1}$, $\sim$10$\times$ higher than previous predictions from K2. We measure the amount of flare contamination at 2 $\mu$m for the TRAPPIST-1b and f transits to be 500$\pm$450 and 2100$\pm$400 ppm, respectively. We find up to 80% of flare contamination can be removed, with mitigation most effective from 1.0--2.4 $\mu$m. These results suggest transits affected by flares may still be useful for atmospheric characterization efforts.

The physical quantity that directly controls the feedback of active galactic nuclei (AGNs) in galactic nuclei (AGN) in elliptical galaxies remains to be determined. The discovery of molecular gas around the AGNs suggests that the gas is fueling the AGNs. Therefore, we analyze Atacama Large Millimeter/submillimeter Array (ALMA) data on CO line (J=1-0, 2-1, 3-2) emission and estimate the mass of molecular gas within 500pc of the center of 12 normal elliptical galaxies and 10 of the brightest cluster galaxies (BCGs). We find that the mass (M_mol~10^5-10^9 M_sun) has a correlation with the jet power of their AGNs, which is represented by P_cav~6.2x10^42(M_mol/10^7M_sun)^{0.68} erg s^{-1}. We also find that M_mol is correlated with the AGN continuum luminosities at ~1.4GHz (L_{1.4}) and ~100-300GHz (L_con). Since P_cav reflects galactic-scale, long-term AGN activity, while the continuum luminosities reflect local (~<500pc), short-term AGN activity, our results suggest that the AGN activity depends on the amount of the gas, regardless of its time scale. On the other hand, we cannot find a clear correlation between the mass of the black holes in the AGNs (M_BH) and P_cav. While this is probably because the black holes in our sample galaxies have similar masses, it suggests that M_mol, rather than M_BH, is the main factor that controls the AGN activity. We confirm that the origin of the continuum emission from the AGNs at ~1.4-300GHz is mostly synchrotron radiation.

The multiwavelength properties of radio-emitting tidal disruption events (TDEs) are poorly understood. In a previous paper, we presented the first sample of radio-selected, optically-detected TDEs, which included two events (VT J1008 and VT J2012) associated with late-time (${\sim}2$ years post-optical flare) intermediate with emission lines that are largely unprecedented from TDEs. In this paper, we investigate these two events in detail. The multiwavelength properties of these events are otherwise consistent with optically-selected TDEs. They are hosted by green valley, E+A/Balmer dominated galaxies with low star formation rates and black holes masses $M_{\rm BH}\approx 10^{5-6}\,M_\odot$. The optical flare shapes are fully consistent with those of optically-selected TDEs, although they are slightly faint and cool at peak. The radio emission from both events is consistent with wide-angle, non-relativistic outflows with $L_R({\rm GHz}) \sim 10^{38}$ erg s$^{-1}$. Balmer and Helium emission lines are detected from both events with full-width-half-maxima ${\sim}700$ km s$^{-1}$ and asymmetric line profiles. VT J1008 additionally shows coronal line emission with a similar width. The lines from VT J2012 are redshifted by ${\sim}700$ km s$^{-1}$ relative to the host galaxy. We show that these events share many characteristics in common with the ambiguous class of extreme coronal line emitters. We argue that the lines are likely associated with a radiative shock or dense, photoionized clumps of outflowing gas in the circumnuclear medium.

The James Webb Space Telescope (JWST) is capable of probing extremely early eras of our Universe when the supersonic relative motions between dark matter and baryonic overdensities modulate structure formation ($z>\sim 10$). We study low-mass galaxy formation including this "stream velocity" using high resolution AREPO hydrodynamics simulations, and present theoretical predictions of the UV luminosity function (UVLF) and galaxy stellar mass function (GSMF) down to extremely faint and low mass galaxies ($M_{UV}>\sim-15$, $10^4M_\odot<=M_*<=10^8 M_\odot)$. We show that, although the stream velocity suppresses early star formation overall, it induces a short period of rapid star formation in some larger dwarfs, leading to an enhancement in the faint-end of the UVLF at $z=12$. We demonstrate that JWST observations are close to this enhanced regime, and propose that the UVLF may constitute an important probe of the stream velocity at high redshift for JWST and future observatories.

We present the results of observations aimed at discovering and studying pulsars in the core-collapsed globular cluster (GC) NGC 6522 performed by the MeerTIME and TRAPUM Large Survey Project with the MeerKAT telescope. We have discovered two new isolated pulsars bringing the total number of known pulsars in the cluster to six. PSR J1803$-$3002E is a mildly recycled pulsar with spin period of 17.9 ms while pulsar PSR J1803$-$3002F is a slow pulsar with spin period of 148.1 ms. The presence of isolated and slow pulsars is expected in NGC 6522 and confirms the predictions of previous theories for clusters at this stage in evolution. We further present a tentative timing solution for the millisecond pulsar (MSP) PSR J1803$-$3002C combining older observations taken with the Parkes 64m radio telescope, Murriyang. This solution implies a relatively small characteristic age of the pulsar in contrast with the old age of the GC. The presence of a slow pulsar and an apparently young MSP, both rare in GCs, suggests that their formation might be linked to the evolutionary stage of the cluster.

Many stellar-mass Black Holes (sBHs) are expected to orbit supermassive black holes at galactic centers. For galaxies with Active Galactic Nuclei (AGN), it is likely that the sBHs reside in a disk. We study the formation of sBH binaries via gravitational wave emission in such disks. We examine analytically the dynamics of two sBHs orbiting a supermassive black hole, estimate the capture cross-section, and derive the eccentricity distribution of bound binaries at different frequency bands. Thus, we estimate that $\sim 50\%$ of the merging stellar-mass black hole binaries, assembled in this manner, have high eccentricities, $e\gtrsim0.5$, in the LIGO-Virgo-KAGRA band. A considerable fraction of these mergers leads to a direct plunge rather than an eccentric inspiral. More eccentric mergers would be observed for sBHs with higher random velocities, closer to the supermassive black hole, or at lower observing frequency bands, as planned in future gravitational wave detectors such as the Einstein Telescope and LISA.

Transit Timing Variations (TTVs) can be induced by a range of physical phenomena, including planet-planet interactions, planet-moon interactions, and stellar activity. Recent work has shown that roughly half of moons would induce fast TTVs with a short period in the range of two-to-four orbits of its host planet around the star. An investigation of the Kepler TTV data in this period range identified one primary target of interest, Kepler-1513 b. Kepler-1513 b is a $8.05^{+0.58}_{-0.40}$ $R_\oplus$ planet orbiting a late G-type dwarf at $0.53^{+0.04}_{-0.03}$ AU. Using Kepler photometry, this initial analysis showed that Kepler-1513 b's TTVs were consistent with a moon. Here, we report photometric observations of two additional transits nearly a decade after the last Kepler transit using both ground-based observations and space-based photometry with TESS. These new transit observations introduce a previously undetected long period TTV, in addition to the original short period TTV signal. Using the complete transit dataset, we investigate whether a non-transiting planet, a moon, or stellar activity could induce the observed TTVs. We find that only a non-transiting perturbing planet can reproduce the observed TTVs. We additionally perform transit origami on the Kepler photometry, which independently applies pressure against a moon hypothesis. Specifically, we find that Kepler-1513 b's TTVs are consistent with an exterior non-transiting $\sim$Saturn mass planet, Kepler-1513 c, on a wide orbit, $\sim$5$\%$ outside a 5:1 period ratio with Kepler-1513 b. This example introduces a previously unidentified cause for planetary interlopers in the exomoon corridor, namely an insufficient baseline of observations.

Investigating Protostellar Accretion (IPA) is a Cycle 1 JWST program using the NIRSpec+MIRI IFUs to obtain 2.9--28 $\mu$m spectral cubes of five young protostars with luminosities of 0.2 to 10,000 L$_{\odot}$ in their primary accretion phase. This paper introduces the NIRSpec 2.9--5.3 $\mu$m data of the inner 840-9000 au with spatial resolutions from 28-300 au. The spectra show rising continuum emission, deep ice absorption, emission from H$_{2}$, H~I, and [Fe~II], and the CO fundamental series in emission and absorption. Maps of the continuum emission show scattered light cavities for all five protostars. In the cavities, collimated jets are detected in [Fe~II] for the four $< 320$~L$_{\odot}$ protostars, two of which are additionally traced in Br-$\alpha$. Knots of [Fe~II] emission are detected toward the most luminous protostar, and knots of [FeII] emission with dynamical times of $< 30$~yrs are found in the jets of the others. While only one jet is traced in H$_2$, knots of H$_2$ and CO are detected in the jets of four protostars. H$_2$ is seen extending through the cavities showing they are filled by warm molecular gas. Bright H$_2$ emission is seen along the walls of a single cavity, while in three cavities, narrow shells of H$_2$ emission are found, one of which has an [Fe~II] knot at its apex. These data show cavities containing collimated jets traced in atomic/ionic gas surrounded by warm molecular gas in a wide-angle wind and/or gas accelerated by bow shocks in the jets.

$\eta$ Carinae is an extremely luminous and energetic colliding-wind binary. The combination of its orbit and orientation, with respect to our line of sight, enables direct investigation of the conditions and geometry of the colliding winds. We analyse optical He I 5876 and 7065 $\unicode{x212B}$ line profiles from the Global Jet Watch observatories covering the last 1.3 orbital periods. The sustained coverage throughout apastron reveals the distinct dynamics of the emitting versus absorbing components: the emission lines follow orbital velocities whilst one of the absorption lines is detected only around apastron ($0.08 < \phi < 0.95$) and exhibits velocities that deviate substantially from the orbital motion. To interpret these deviations, we conjecture that this He I absorption component is formed in the post-shock primary wind, and is only detected when our line of sight intersects with the shock cone formed by the collision of the two winds. We formulate a geometrical model for the colliding winds in terms of a hyperboloid in which the opening angle and location of its apex are parameterised in terms of the ratio of the wind momentum of the primary star to that of companion. We fit this geometrical model to the absorption velocities, finding results that are concordant with the panchromatic observations and simulations of $\eta$ Carinae. The model presented here is an extremely sensitive probe of the exact geometry of the wind momentum balance of binary stars, and can be extended to probe the latitudinal dependence of mass loss.

Neutrinos in dense environments like core-collapse supernovae (CCSNe) and neutron star mergers (NSMs) can undergo fast flavor conversions (FFCs) once the angular distribution of neutrino lepton number crosses zero along a certain direction. Recent advancements have demonstrated the effectiveness of machine learning (ML) in detecting these crossings. In this study, we enhance prior research in two significant ways. Firstly, we utilize realistic data from CCSN simulations, where neutrino transport is solved using the full Boltzmann equation. We evaluate the ML methods' adaptability in a real-world context, enhancing their robustness. In particular, we demonstrate that when working with artificial data, simpler models outperform their more complex counterparts, a noteworthy illustration of the bias-variance tradeoff in the context of ML. We also explore methods to improve artificial datasets for ML training. In addition, we extend our ML techniques to detect the crossings in the heavy-leptonic channels, accommodating scenarios where $\nu_x$ and $\bar\nu_x$ may differ. Our research highlights the extensive versatility and effectiveness of ML techniques, presenting an unparalleled opportunity to evaluate the occurrence of FFCs in CCSN and NSM simulations.

The accretion disks that fuel active galactic nuclei (AGN) may house numerous stars and compact objects, formed in situ or captured from nearby star clusters. Embedded neutron stars and black holes may form binaries and eventually merge, emitting gravitational waves detectable by LIGO/VIRGO. AGN disks are a particularly promising environment for the production of high-mass gravitational wave events involving black holes in the pair instability mass gap, and may facilitate electromagnetic counterparts to black hole binary mergers. However, many orders of magnitude separate the typical length scales of binary formation and those on which gravitational waves can drive binary inspirals, making binary mergers inside the disk uncertain. Previous hydrodynamical simulations of binaries have either been restricted to two dimensions entirely, or focused on binaries aligned with the midplane of the disk. Herein we present the first three-dimensional, high-resolution, local shearing-box hydrodynamical simulations of disk-embedded binaries over a range of orbital inclinations. We find that retrograde binaries can shrink up to four times as quickly as prograde binaries, and that all binaries not perfectly aligned (or anti-aligned) with the AGN disk are driven into alignment. An important consequence of this is that initially retrograde binaries will traverse the inclinations where von Zeipel-Lidov-Kozai oscillations can drive binary eccentricities to large values, potentially facilitating mergers. We also find that interactions with the AGN disk may excite eccentricities in retrograde binaries and cause the orbits of embedded binaries to precess.

Up to 150000 asteroids will be visible in the images of the ESA Euclid space telescope, and the instruments of Euclid offer multiband visual to near-infrared photometry and slitless spectra of these objects. Most asteroids will appear as streaks in the images. Due to the large number of images and asteroids, automated detection methods are needed. A non-machine-learning approach based on the StreakDet software was previously tested, but the results were not optimal for short and/or faint streaks. We set out to improve the capability to detect asteroid streaks in Euclid images by using deep learning. We built, trained, and tested a three-step machine-learning pipeline with simulated Euclid images. First, a convolutional neural network (CNN) detected streaks and their coordinates in full images, aiming to maximize the completeness (recall) of detections. Then, a recurrent neural network (RNN) merged snippets of long streaks detected in several parts by the CNN. Lastly, gradient-boosted trees (XGBoost) linked detected streaks between different Euclid exposures to reduce the number of false positives and improve the purity (precision) of the sample. The deep-learning pipeline surpasses the completeness and reaches a similar level of purity of a non-machine-learning pipeline based on the StreakDet software. Additionally, the deep-learning pipeline can detect asteroids 0.25-0.5 magnitudes fainter than StreakDet. The deep-learning pipeline could result in a 50% increase in the number of detected asteroids compared to the StreakDet software. There is still scope for further refinement, particularly in improving the accuracy of streak coordinates and enhancing the completeness of the final stage of the pipeline, which involves linking detections across multiple exposures.

While it is now known that double neutron star binary systems (DNSs) are copious producers of heavy elements, there remains much speculation about whether they are the sole or even principal site of rapid neutron-capture (r-process) nucleosynthesis, one of the primary ways in which heavy elements are produced. The occurrence rates, delay times, and galactic environments of DNSs hold sway over estimating their total contribution to the elemental abundances in the Solar system and the Galaxy. Furthermore, the expected elemental yield for DNSs may depend on the merger parameters themselves -- such as their stellar masses and radii -- which is not currently considered in many galactic chemical evolution models. Using the characteristics of the observed sample of DNSs in the Milky Way as a guide, we predict the expected nucleosynthetic yields that a population of DNSs would produce upon merger, and we compare that nucleosynthetic signature to the heavy-element abundance pattern of the Solar system elements. We find that with our current models, the present DNS population favors production of the lighter r-process elements, while underproducing the heaviest elements relative to the Solar system. This inconsistency could imply an additional site for the heaviest elements or a population of DNSs much different from that observed today.

We present deep upper limits from the 2014 Murchison Widefield Array (MWA) Phase I observing season, with a particular emphasis on identifying the spectral fingerprints of extremely faint radio frequency interference (RFI) contamination in the 21~cm power spectra (PS). After meticulous RFI excision involving a combination of the \textsc{SSINS} RFI flagger and a series of PS-based jackknife tests, our lowest upper limit on the Epoch of Reionization (EoR) 21~cm PS signal is $\Delta^2 \leq 1.61\cdot10^4 \text{ mK}^2$ at $k=0.258\text{ h Mpc}^{-1}$ at a redshift of 7.1 using 14.7 hours of data. By leveraging our understanding of how even fainter RFI is likely to contaminate the EoR PS, we are able to identify ultra-faint RFI signals in the cylindrical PS. Surprisingly this signature is most obvious in PS formed with less than an hour of data, but is potentially subdominant to other systematics in multiple-hour integrations. Since the total RFI budget in a PS detection is quite strict, this nontrivial integration behavior suggests a need to more realistically model coherently integrated ultra-faint RFI in PS measurements so that its potential contribution to a future detection can be diagnosed.

The results of a spectral survey of the region of massive star formation DR21OH in the 4-mm wavelength range are presented. Sixty-nine molecules and their isotopologues have been detected, ranging from simple diatomic or triatomic species such as SO, SiO and CCH, to complex organic molecules such as CH$_3$OCHO or CH$_3$OCH$_3$. The obtained results qualitatively repeat the results of the survey of the same source at 3~mm. The inventories of molecules found at 3mm and 4mm overlap to a great extent. However, at 4 mm we found a number of species that have no allowed transitions in the 3-mm wavelength range, e.g. DCN, DNC, or SO$^+$. The bulk of the molecules detected at 4~mm are those that are common for dense cores, e.g., HC$_3$N or CH$_3$CCH, but some of the detected species are typical for hot cores. The latter include complex organic molecules CH$_3$OCHO, CH$_3$CH$_2$OH, CH$_3$OCH$_3$, etc. However, the detected emission of these molecules probably arises in a gas heated to 30 K only. Nine molecules, including complex species CH$_3$C$_3$N, CH$_3$CH$_2$CN, CH$_3$COCH$_3$, were found by spectral line stacking. This demonstrates the prospects of the method in the study of molecular clouds.

We propose a cosmological dark matter production mechanism in the form of a longitudinal massive vector boson. We build upon the work of Graham et.al. including non-minimal couplings of the massive vector with gravity, developing a well motivated set-up from an effective field theory perspective. We carefully track the dynamics of vector field in passing from inflation to radiation dominated universe to show that the late time abundance of longitudinal modes -- excited initially by the quantum fluctuations during inflation -- can provide the observed dark matter abundance for sufficiently weak non-minimal coupling and wide range of vector masses $5 \times 10^{-7} \lesssim m\, [{\rm eV}] \lesssim 5 \times 10^{3}$. The final abundance of dark matter depends on two parameter, the vector mass and its non-minimal coupling with gravity. We discuss experimental venues to probe this framework, including the production of a stochastic gravitational wave background. The latter is especially interesting, as the same mechanism that generates dark matter can potentially lead to the production of gravitational waves in the LISA frequency band, through the second-order effects of large dark matter iso-curvature perturbations at small scales. We take a first step in this direction, identifying the potential information that gravitational wave experiments can provide on the parameter space of dark matter within this scenario.

In this paper, we present a simple, one-step, self-consistent, and fast resonance scattering model rsapec based on the AtomDB database. This model can be used as an alternative to the commonly used APEC model for fitting such X-ray spectra with optically thick lines. The current model is intended, in general, for verifying the presence of the effect and for spectral modeling of galaxy clusters and elliptical galaxies under applicable assumptions. We test rsapec to derive the line suppression in the elliptical galaxy NGC 4636 and the Perseus cluster of galaxies and obtain resonance suppression of ~ 1.24 and ~ 1.30, respectively.

We describe the results of a new reverberation mapping program focused on the nearby Seyfert galaxy NGC 3227. Photometric and spectroscopic monitoring were carried out from 2022 December to 2023 June with the Las Cumbres Observatory network of telescopes. We detected time delays in several optical broad emission lines, with H$\beta$ having the longest delay at $\tau_{\rm cent}=4.0^{+0.9}_{-0.9}$ days and He II having the shortest delay with $\tau_{\rm cent}=0.9^{+1.1}_{-0.8}$ days. We also detect velocity-resolved behavior of the H$\beta$ emission line, with different line-of-sight velocities corresponding to different observed time delays. Combining the integrated H$\beta$ time delay with the width of the variable component of the emission line and a standard scale factor suggests a black hole mass of $M_{\rm BH}=1.1^{+0.2}_{-0.3} \times 10^7 M_{\odot}$. Modeling of the full velocity-resolved response of the H$\beta$ emission line with the phenomenological code CARAMEL finds a similar mass of $M_{\rm BH}=1.2^{+1.5}_{-0.7} \times 10^7 M_{\odot}$, and suggests that the H$\beta$-emitting broad line region (BLR) may be represented by a biconical or flared disk structure that we are viewing at an inclination angle of $\theta_i \approx 33^{\circ}$ and with gas motions that are dominated by rotation. The new photoionization-based BLR modeling tool BELMAC finds general agreement with the observations when assuming the best-fit CARAMEL results, however BELMAC prefers a thick disk geometry and kinematics that are equally comprised of rotation and inflow. Both codes infer a radially extended and flattened BLR that is not outflowing.

The BL Lac 1ES 2344+514 is known for temporary extreme properties (e.g., a shift of the synchrotron SED peak energy $\nu_{synch,p}$ above 1keV). While those extreme states were so far observed only during high flux levels, additional multi-year observing campaigns are required to achieve a coherent picture. Here, we report the longest investigation of the source from radio to VHE performed so far, focusing on a systematic characterisation of the intermittent extreme states. While our results confirm that 1ES 2344+514 typically exhibits $\nu_{synch,p}>$1keV during elevated flux periods, we also find periods where the extreme state coincides with low flux activity. A strong spectral variability thus happens in the quiescent state, and is likely caused by an increase of the electron acceleration efficiency without a change in the electron injection luminosity. We also report a strong X-ray flare (among the brightest for 1ES 2344+514) without a significant shift of $\nu_{synch,p}$. During this particular flare, the X-ray spectrum is among the softest of the campaign. It unveils complexity in the spectral evolution, where the common harder-when-brighter trend observed in BL Lacs is violated. During a low and hard X-ray state, we find an excess of the UV flux with respect to an extrapolation of the X-ray spectrum to lower energies. This UV excess implies that at least two regions contribute significantly to the infrared/optical/ultraviolet/X-ray emission. Using the simultaneous MAGIC, XMM-Newton, NuSTAR, and AstroSat observations, we argue that a region possibly associated with the 10 GHz radio core may explain such an excess. Finally, we investigate a VHE flare, showing an absence of simultaneous variability in the 0.3-2keV band. Using a time-dependent leptonic modelling, we show that this behaviour, in contradiction to single-zone scenarios, can instead be explained by a two-component model.

From the formation mechanisms of stars and compact objects to nuclear physics, modern astronomy frequently leverages surveys to understand populations of objects to answer fundamental questions. The population of dark and isolated compact objects in the Galaxy contains critical information related to many of these topics, but is only practically accessible via gravitational microlensing. However, photometric microlensing observables are degenerate for different types of lenses, and one can seldom classify an event as involving either a compact object or stellar lens on its own. To address this difficulty, we apply a Bayesian framework that treats lens type probabilistically and jointly with a lens population model. This method allows lens population characteristics to be inferred despite intrinsic uncertainty in the lens-class of any single event. We investigate this method's effectiveness on a simulated ground-based photometric survey in the context of characterizing a hypothetical population of primordial black holes (PBHs) with an average mass of $30 M_{\odot}$. On simulated data, our method outperforms current black hole (BH) lens identification pipelines and characterizes different subpopulations of lenses while jointly constraining the PBH contribution to dark matter to ${\approx}25$\%. Key to robust inference, our method can marginalize over population model uncertainty. We find the lower mass cutoff for stellar origin BHs, a key observable in understanding the BH mass gap, particularly difficult to infer in our simulations. This work lays the foundation for cutting-edge PBH abundance constraints to be extracted from current photometric microlensing surveys.

The recent Dark Energy Survey Year 1 (DES-Y1) analysis of galaxy cluster abundances and weak lensing produced $\Omega_{\rm m}$ and $\sigma_8$ constraints in 5.6$\sigma$ tension with Planck. It is suggested in that work that this tension is driven by unmodelled systematics in optical cluster selection. We present a novel simulation-based forward modeling framework that explicitly incorporates cluster selection into its model predictions. Applying this framework to the DES-Y1 data we find consistency with Planck, resolving the tension found in the DES-Y1 analysis. An extension of this approach to the final DES data set will produce robust constraints on $\Lambda$CDM parameters and correspondingly strong tests of cosmological models.

Neptune's Trojan asteroids have been observed to have a variety of optical colors, most notably red (g $-$ r < 0.75) vs. ultra-red (g $-$ r > 0.75), but the underlying cause of these different color classifications is unknown. Near-IR spectroscopy can be used as a probe of the surface composition of these objects, as broad ice bands for a variety of materials are present in the near-IR. Here, we present the first results of a spectroscopic survey of Neptune's Trojan asteroids using the NIRSpec instrument on JWST. We compare the near-IR spectra of eight Neptune Trojans (NTs) based on different optical color classifications and with model spectra of different ices. We find that most of our targets are consistent with a surface covered in a thin layer of H$_2$O and CO$_2$ ices, while the only NT to reliably be classified as ultra-red is covered in ice tholins in addition to CO$_2$. Ice tholins are a known reddening agent when subjected to irradiation, so these results support the hypothesis that differences in optical color are due to differences in irradiation of the surfaces of these bodies. Since NTs have very similar orbits and therefore generally similar levels of irradiation at the current time, our results suggest that these objects have unique origins or there is ongoing processing of the surfaces of these objects through stochastic disturbances such as impacts.

Coagulation in the dense interstellar medium (ISM) is an important process that determines the size of the largest grains. We use submillimetre galaxies (SMGs) as laboratories of grain coagulation, since some of them host the densest ISM on a galactic scale among various populations of galaxies known. We examine how large the grains can be in such dense environments based on the mean ISM density estimated from the observed typical dust mass density in SMGs. We also consider local density enhancement based on a model of supersonic turbulence, which is expected from strong stellar feedback. In the unlimited coagulation model, in which we do not impose any coagulation threshold velocity, grains as large as $\sim 30~\mu$m can form under the observationally estimated mean gas density if the Mach number of turbulence is $\mathcal{M}\gtrsim 3$. We exclude this possibility since the observed emissivity index $\beta\simeq 2$ in the far infrared (FIR) indicates that such large grains cannot actively form in SMGs. This means that coagulation does not proceed in an unlimited way: 30-$\mu$m grains should have velocities larger than the coagulation threshold. If we use a coagulation threshold (upper limit) grain velocity ($\sim 0.08$ km s$^{-1}$) taken from a theoretical study, grains likely grow only up to $\mu$m size, which is small enough not to affect the FIR emissivity index. The above results indicate that SMGs can be used to constrain the physical processes relevant to coagulation.

Coronal Mass Ejections (CMEs) are subject to changes in their direction of propagation, tilt, and other properties. This is because CMEs interact with the ambient solar wind and other large-scale magnetic field structures. In this work, we report on the observations of the 2012 October 5 stealth CME using coronagraphic and heliospheric images. We find clear evidence of a continuous rotation of the CME, i.e., an increase in the tilt angle, estimated using the Graduated Cylindrical Shell (GCS) reconstruction at different heliocentric distances, up to 58 solar radii. We find a further increase in the tilt at L1 estimated from the toroidal and cylindrical flux rope fitting on the in situ observations of IMF and solar wind parameters. This study highlights the importance of observations of Heliospheric Imager (HI), onboard the Solar TErrestrial RElations Observatory (STEREO). In particular, the GCS reconstruction of CMEs in HI field-of-view promises to bridge the gap between the near-Sun and in-situ observations at the L1. The changes in the CME tilt has significant implications for the space weather impact of stealth CMEs.

We present ALMA sub-arcsecond-resolution observations of both continuum and molecular lines at 345 GHz towards the massive star-forming region IRAS 16351-4722 (hereafter I16351). A total of 12 dust cores were detected based on high spatial resolution observations of the continuum. Among them, a high-mass core (11.6 Msun) and a low-mass core (1.7 Msun) show abundant molecular line emissions. 164 molecular transitions from 29 species and 104 molecular transitions from 25 species are identified in the high-mass and low-mass cores, respectively. Complex organic molecules (COMs) such as CH3OH, CH3OCHO, CH3OCH3, C2H5OH, and C2H5CN are detected in the two cores. Under the assumption of local thermodynamic equilibrium (LTE), rotational temperatures and column densities of the COMs are derived with the XCLASS software. The maximum rotation temperature values in the low-mass core and the high-mass core were found to be approximately 130 K and 198 K, respectively. Additionally, the line widths in the high-mass core are larger than those in the low-mass one. Abundant complex organic molecular line transitions, high gas temperatures, and smaller line widths indicate the presence of a low-mass line-rich core in the massive star formation region for the first time, while the high-mass line-rich core shows hot core property. When comparing the molecular abundances of CH3OH, CH3OCHO, CH3OCH3 and C2H5OH of the two cores with other hot cores and hot corinos reported in the literature, we further confirm that both a hot core and a low-mass line-rich core are simultaneously detected in I16351.

We present here the timing and spectral analysis of SGR J1830$-$0645 based on an AstroSat observation carried out on 2020 October 16, about a week after the onset of its first detected X-ray outburst. Using data taken with Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC), we have detected 0.9$-$10 keV coherent pulsations at a period of $\sim$10.4 s. The pulse profiles were single-peaked, asymmetric and consisted of minor peaks attributable to hot spots on the neutron star surface. The pulsed fraction evolved significantly with energy; increasing up to energies around 5 keV and a steep drop thereafter. The 0.9--25 keV SXT--LAXPC energy spectrum is best described with two thermal components having temperatures $\sim$0.46 keV and $\sim$1.1 keV (emission radii of $\sim$2.4 km and $\sim$0.65 km, respectively, assuming a distance of 4 kpc) along with a power-law component having photon index of $\sim$0.39. We report the detection of 67 X-ray bursts having an average duration of $\sim$33 ms. The brightest burst lasted for about 90 ms and had a 3--25 keV fluence of $\sim 5 \times 10^{-9}$ erg cm$^{-2}$.

ESA's Rosetta spacecraft at comet 67P/Churyumov-Gerasimenko (67P) was the first mission that accompanied a comet over a substantial fraction of its orbit. On board was the ROSINA mass spectrometer suite to measure the local densities of the volatile species sublimating from the ices inside the comet's nucleus. Understanding the nature of these ices was a key goal of Rosetta. We analyzed the primary cometary molecules at 67P, namely H$_2$O and CO$_2$, together with a suite of minor species for almost the entire mission. Our investigation reveals that the local abundances of highly volatile species, such as CH$_4$ and CO, are reproduced by a linear combination of both H$_2$O and CO$_2$ densities. These findings bear similarities to laboratory-based temperature programmed desorption experiments of amorphous ices and imply that highly volatile species are trapped in H$_2$O and CO$_2$ ices. Our results do not show the presence of ices dominated by these highly volatile molecules. Most likely, they were lost due to thermal processing of 67P's interior prior to its deflection to the inner solar system. Deviations in the proportions co-released with H$_2$O and CO$_2$ can only be observed before the inbound equinox, when the comet was still far from the sun and the abundance of highly volatile molecules associated with CO$_2$ outgassing were lower. The corresponding CO$_2$ is likely seasonal frost, which sublimated and lost its trapped highly volatile species before re-freezing during the previous apparition. CO, on the other hand, was elevated during the same time and requires further investigation.

We present a new approach to the pointing determination of Imaging Atmospheric Cherenkov Telescopes (IACTs). This method is universal and can be applied to any IACT with minor modifications. It uses the trajectories of the stars in the field of view of the IACT's main camera and requires neither dedicated auxiliary hardware nor a specific data taking mode. The method consists of two parts: firstly, we reconstruct individual star positions as a function of time, taking into account the point spread function of the telescope; secondly, we perform a simultaneous fit of all reconstructed star trajectories using the orthogonal distance regression method. The method does not assume any particular star trajectories, does not require a long integration time, and can be applied to any IACT observation mode. The performance of the method is assessed with commissioning data of the Large-Sized Telescope prototype (LST-1), showing the method's stability and remarkable pointing performance of the LST-1 telescope.

Double white dwarf systems are of great astrophysical importance in the field of gravitational wave and Type Ia supernova. While the binary fraction of CO core white dwarf is about a few percents, the extremely low mass white dwarfs are all thought to be within binary systems. In this work, we report the orbital solution of a double degenerate system: J033847.06+413424.24, an extremely low mass He core white dwarf orbiting a CO core white dwarf. With LAMOST and P200, time domain spectroscopic observations have been made and spectral atmosphere parameters are estimated to be $T_{\rm eff}\sim22500$ K and log $g\sim5.6$ dex. Combining Gaia parallax, 3D extinction, and evolution tracks, we estimate a radius of $\sim0.12$ $R_{\odot}$ and a mass of $\sim0.22$ $M_{\odot}$. With the 37 single exposure spectra, the radial velocities are measured and the orbital parameters are estimated to be $P=0.1253132(1)$ days, $K1=289\pm4$ km/s and $V_{sys}=-41\pm3$ km/s. The radial velocity based system ephemeris is also provided. The light curves from several photometric surveys show no orbital modulation. The orbital solution suggests that the invisible companion has a minimum mass of about 0.60 $M_{\odot}$ and is $\sim0.79$ $M_{\odot}$ for an inclination of $60.0^{\circ}$, indicating most probably a CO core white dwarf. The system is expected to merge in about 1 Gyr. With present period and distance ($\sim596$ pc) it can not irradiate strong enough gravitational wave for LISA. More double degenerate systems are expected to be discovered and parameterized as the LAMOST survey goes on.

We propose a line list that may be useful for the abundance analysis of G-type stars in the wavelength range 4080 -- 6780 A. It is expected that the line list will be useful for surveys/libraries with overlapping spectral regions (e.g. ELODIE/SOPHIE libraries, UVES-580 setting of Gaia-ESO), and in particular for the analysis of F- and G-type stars in general. The atomic data are supplemented by detailed references to the sources. We estimated the Solar abundances using stellar lines and the high-resolution Kitt Peak National Observatory (KPNO) spectra of the Sun to determine the uncertainty in the log gf values. By undertaking a systematic search that makes use of the lower excitation potential and gf-values and using revised multiplet table as an initial guide, we identified 363 lines of 24 species that have accurate gf-values and are free of blends in the spectra of the Sun and a Solar analogue star, HD 218209 (G6V), for which accurate and up-to-date abundances were obtained from both ELODIE and PolarBASE spectra of the star. For the common lines with the Gaia-ESO line list v.6 provided by the Gaia-ESO collaboration, we discovered significant inconsistencies in the gf-values for certain lines of varying species.

Cross-correlation techniques have been used since 1974 and, since 1979, the analysis based on the Fourier Method has been applied. However, we are currently obtaining data with spectral resolution higher than those for which this technique was developed, hence some revision seems timely. The principal aim of this work is to adapt Tonry and Davis' method and implementing it for the treatment of very high spectral resolution data. We have applied this technique to two different sets of spectroscopic data of moderate and high resolutions obtained with the MUSE and MEGARA spectrographs respectively. Using stellar spectra obtained with these two instruments (i) we have optimised the input parameters; (ii) we have analysed the method assumptions; and (iii) we have compared the results for the two sets of data. The optimal method parameters applied to MUSE data are $k_{min}$ $\sim$ 3, $k_{max}$ $\sim$ 60 and 512 bins, which correspond to a uniform velocity shift value of $\Delta $v = 27.1 km/s. For MEGARA data, we propose the values $k_{min}$ $\sim$ 3, $k_{max}$ $\sim$ 350 and 4096 bins finding that the cross-correlation function lost its Gaussian behavior at higher resolutions. Thus, we have developed an equivalent mathematical method that can be used for this kind of data. Additionally, the velocity dispersion error analysis suggests that the greatest error introduced in this method is due to the subtraction or masking of the nebular lines. For the application cross-correlation techniques to high spectral resolution data, we propose to calculate the galaxy-galaxy and star-galaxy correlations, with widths $\mu_{gg}$ and $\mu_{gt}$ respectively. Then, the width of the broadening function can be calculated as $\sigma = \sqrt{\mu_{gg}^2 - \mu_{gt}^2}$.

Gamma-ray bursts (GRBs) are the most electromagnetically luminous cosmic explosions. They are powered by collimated streams of plasma (jets) ejected by a newborn stellar-mass black hole or neutron star at relativistic velocities (near the speed of light). Their short-lived (typically tens of seconds) prompt $\gamma$-ray emission from within the ejecta is followed by long-lived multi-wavelength afterglow emission from the ultra-relativistic forward shock. This shock is driven into the circumburst medium by the GRB ejecta that are in turn decelerated by a mildly-relativistic reverse shock. Forward shock emission was recently detected up to teraelectronvolt-energy $\gamma$-rays, and such very-high-energy emission was also predicted from the reverse shock. Here we report the detection of optical and gigaelectronvolt-energy $\gamma$-ray emission from GRB 180720B during the first few hundred seconds, which is explained by synchrotron and inverse-Compton emission from the reverse shock propagating into the ejecta, implying a low-magnetization ejecta. Our optical measurements show a clear transition from the reverse shock to the forward shock driven into the circumburst medium, accompanied by a 90-degree change in the mean polarization angle and fluctuations in the polarization degree and angle. This indicates turbulence with large-scale toroidal and radially-stretched magnetic field structures in the reverse and forward shocks, respectively, which tightly couple to the physics of relativistic shocks and GRB jets -- launching, composition, dissipation and particle acceleration.

We investigate a mechanism of primordial black hole (PBH) formation that avoids any dependence on specific inflationary features or exotic physics. In this scenario, the required large curvature fluctuations leading to PBH formation are generated after inflation by the quantum fluctuations of a light stochastic spectator field during inflation, when this field transiently dominates the energy density. We calculate the dynamics of such a spectator field during and after inflation, the distribution of induced curvature perturbations and their non-Gaussian tails leading to the copious production of PBHs. For a plateau-like potential, this scenario produces an extended PBH mass distribution with a peak at the solar-mass scale when one takes into account the effects of the thermal history. What is remarkable in this scenario is the absence of parameter fine-tuning. Instead, it invokes an anthropic selection over all the realizations of PBH abundances predicted by the field stochasticity. This scenario offers a novel perspective for the formation of PBHs with minimal ingredients and without the need of fine-tuning. It is amenable to observational tests, notably with the gravitational-wave observations of black hole mergers and of a background at nanoHertz frequency, as recently observed by pulsar timing arrays.

Kinematics of shocks, ejecta knots, and the compact remnant of a supernova remnant gives an insight into the nature of the progenitor and surrounding environment. We report on a proper motion measurement of X-ray knots and rims of the magnetar-hosting supernova remnant RCW 103. Chandra data obtained in three epochs, 1999, 2010, and 2016 are used. We find a global deceleration of 12 knots and rims both in northern and southern regions within the last $\sim 24$ yrs, even though its age is thought to be larger than 2 kyr. Some of them even changed their moving directions from outward ($\sim 1,000$ km s$^{-1}$) to inward ($\sim -2,000$ km s$^{-1}$). Our findings can be explained with a collision with a high-density medium both in the northern and southern edges of the remnant, although the remnant may still be expanding in the wind-blown cavity. The proper motion of the associated magnetar 1E161348$-$5055 is possibly detected with a velocity of $\approx 500$ km s$^{-1}$.

In the framework of the IMEGIN Large Program, we used the NIKA2 camera on the IRAM 30-m telescope to observe the edge-on galaxy NGC 891 at 1.15 mm and 2 mm and at a FWHM of 11.1" and 17.6", respectively. Multiwavelength data enriched with the new NIKA2 observations fitted by the HerBIE SED code (coupled with the THEMIS dust model) were used to constrain the physical properties of the ISM. Emission originating from the diffuse dust disk is detected at all wavelengths from mid-IR to mm, while mid-IR observations reveal warm dust emission from compact HII regions. Indications of mm excess emission have also been found in the outer parts of the galactic disk. Furthermore, our SED fitting analysis constrained the mass fraction of the small (< 15 Angstrom) dust grains. We found that small grains constitute 9.5% of the total dust mass in the galactic plane, but this fraction increases up to ~ 20% at large distances (|z| > 3 kpc) from the galactic plane.

We present a detailed analysis of the spectral and timing characteristics of a 7-Hz type-A quasi-periodic oscillation (QPO) detected in NICER observations of the black hole X-ray binary MAXI J1348-630 during its high-soft state. The QPO is broad and weak, with an integrated fractional rms amplitude of 0.9 per cent in the 0.5-10 keV band. Thanks to the large effective area of NICER, combined with the high flux of the source and a relatively long accumulative exposure time, we construct the first rms and phase-lag spectra for a type-A QPO. Our analysis reveals that the fractional rms amplitude of the QPO increases with energy from below 1 per cent at 1 keV to 3 per cent at 6 keV. The shape of the QPO spectrum is similar to that of the Comptonised component, suggesting that the Comptonised region is driving the variability. The phase lags at the QPO frequency are always soft taking the lowest energy as reference. By jointly fitting the time-averaged spectrum of the source and the rms and phase-lag spectra of the QPO with the time-dependent Comptonisation model vkompthdk, we find that the radiative properties of the type-A QPO can be explained by a vertically extended Comptonised region with a size of 2300 km.

Solar flare electron acceleration is an efficient process, but its properties (mechanism, location) are not well constrained. Via hard X-ray (HXR) emission, we routinely observe energetic electrons at the Sun, and sometimes we detect energetic electrons in interplanetary space. We examine if the plasma properties of an acceleration region (size, temperature, density) can be constrained from in-situ observations, helping to locate the acceleration region in the corona, and infer the relationship between electrons observed in-situ and at the Sun. We model the transport of energetic electrons, accounting for collisional and non-collisional effects, from the corona into the heliosphere (to 1.0 AU). In the corona, electrons are transported through a hot, over-dense region. We test if the properties of this region can be extracted from electron spectra (fluence and peak flux) at different heliospheric locations. We find that cold, dense coronal regions significantly reduce the energy at which we see the peak flux and fluence for distributions measured out to 1.0 AU, the degree of which correlates with the temperature and density of plasma in the region. Where instrument energy resolution is insufficient to differentiate the corresponding peak values, the spectral ratio of [7-10) to [4-7) keV can be more readily identified and demonstrates the same relationship. If flare electrons detected in-situ are produced in, and/or transported through hot, over-dense regions close to HXR-emitting electrons, then this plasma signature should be present in their lower-energy spectra (1-20 keV), observable at varying heliospheric distances with missions such as Solar Orbiter.

We perform two-dimensional particle-in-cell simulations of magnetic reconnection for various strengths of the guide field (perpendicular to the reversing field), in magnetically-dominated electron-positron plasmas. Magnetic reconnection under such conditions could operate in accretion disk coronae around black holes. There, it has been suggested that the trans-relativistic bulk motions of reconnection plasmoids containing inverse-Compton-cooled electrons could Compton-upscatter soft photons to produce the observed non-thermal hard X-rays. Our simulations are performed for magnetizations $3 \leq \sigma \leq 40$ (defined as the ratio of enthalpy density of the reversing field to plasma enthalpy density) and guide field strengths $0 \leq B_{\rm g}/B_0 \leq 1$ (normalized to the reversing field strength $B_0$). We find that the mean bulk energy of the reconnected plasma depends only weakly on the flow magnetization but strongly on the guide field strength -- with $B_{\rm g}/B_0 = 1$ yielding a mean bulk energy twice smaller than $B_{\rm g}/B_0 = 0$. Similarly, the dispersion of bulk motions around the mean -- a signature of stochasticity in the plasmoid chain's motions -- is weakly dependent on magnetization (for $\sigma \gtrsim 10$) but strongly dependent on the guide field strength -- dropping by more than a factor of two from $B_{\rm g}/B_0 = 0$ to $B_{\rm g}/B_0 = 1$. In short, reconnection in strong guide fields ($B_{\rm g}/B_0 \sim 1$) leads to slower and more ordered plasmoid bulk motions than its weak guide field ($B_{\rm g}/B_0 \sim 0$) counterpart.

It is well known among the scientific community that solar flare activity often begins well before the main impulsive energy release. Our aim is to investigate the earliest phase of four distinct flares observed by Solar Orbiter/STIX and determine the relationships of the newly heated plasma to flare structure and dynamics. The analysis focuses on four events that were observed from both Earth and Solar Orbiter, which allows for a comparison of STIX observations with those of GOES/XRS and SDO/AIA. The early phases of the events were studied using STIX and GOES spectroscopic analysis to investigate the evolution of the physical parameters of the plasma, including the isothermal temperature and emission measure. Furthermore, to determine the location of the heated plasma, STIX observations were combined with AIA images. The events with clear emission prior to the impulsive phase show elevated temperatures ($> 10\,\mathrm{MK}$) from the very beginning, which indicates that energy release started before any detection by STIX. Although the temperature shows little variation during the initial phase, the emission measure increases by about two orders of magnitude, implying a series of incrementally greater energy releases. The spectral analysis of STIX and GOES from the very first time bins suggests that the emission has a multi-thermal nature, with a hot component of more than $10\,\mathrm{MK}$. This analysis confirms the existence of "hot onsets," with STIX detecting the hot onset pattern even earlier than GOES. These elevated temperatures imply that energy release actually begins well before any detection by STIX. Therefore, hot onsets may be significant in the initiation, early development, or even prediction of solar flares.

Centaurus A is one of the closest radio-galaxies to Earth. Its proximity allowed us to extensively study its active galactic nucleus but the core emission mechanism remains elusive because of local strong dust and gas obscuration. The capability of polarimetry to shave-off contaminating emission has been exploited without success in the near-infrared by previous studies but the very recent measurement of the 2 - 8 keV polarization by the Imaging X-ray Polarimetry Explorer (IXPE) brought the question back to the fore. To determine what is the prevalent photon generation mechanism to the multi-wavelength emission from the core of Centaurus A, we retrieved from the archives the panchromatic polarization measurements of the central compact component. We built the total and polarized flux spectral energy distributions of the core and demonstrated that synchrotron self-Compton models nicely fit the polarized flux from the radio to the X-ray band. The linear polarization of the synchrotron continuum is perpendicular to the jet radio axis from the optical to the radio band, and parallel to it at higher energies. The observed smooth rotation of the polarization angle in the ultraviolet band is attributed to synchrotron emission from regions that are getting closer to the particle acceleration site, where the orientation of the jet's magnetic fields become perpendicular to the jet axis. This phenomenon support the shock acceleration mechanism for particle acceleration in Centaurus A, in line with IXPE observations of several high-synchrotron peak blazars.

It is a challenge to study the formation process of massive stars: their formation time is short, they are few, often deeply embedded, and at relatively large distances. Our strategy is to study the outcome of the star formation process and to look for signatures remnant of the formation. We have access to a unique sample of (massive) pre-main-sequence (PMS) stars in the giant HII region M17, showing a photosphere and circumstellar disk. The aim is to determine the variability properties of the hot gaseous disks to understand the physical origin of the emission lines and identify dominant physical processes in these disks. We have obtained multiple-epoch (4-5 epochs) VLT/X-shooter spectra of six young stars in M17 covering about a decade. Using stacked spectra we update the spectral classification and identify circumstellar features. With the temporal variance method (TVS) we determine the extent and amplitude of the spectral line variations. The double-peaked emission lines in the PMS stars with gaseous disks are used to determine peak-to-peak velocities, V/R-ratios and the radial velocity of the systems. We identify many disk features, under which a new detection of CO bandhead and CI emission. In three of the stars we detect spectral variability, mainly in lines originating in the circumstellar disk, in a velocity range up to 320 km/s. In two PMS stars the ratio between the blue and red peaks shows a correlation with the peak-to-peak velocity, possibly explained by a spiral-arm structure in the disk. The PMS stars with variability are at similar positions in the HRD but show significant differences in disk lines and variability. The extent and timescale of the variability differs for each star and per line (sets). We find indications for an accretion flow, slow disk winds and/or disk structures in the hot gaseous inner disk as the cause of the variability in these PMS stars.

The vast majority of stars in the nearby stellar neighborhood are M dwarfs. Their low masses and luminosities result in slow rates of nuclear evolution and minimal changes to the star's observable properties, even along astronomical timescales. However, they possess relatively powerful magnetic dynamos and resulting X-ray to UV activity, compared to their bolometric luminosities. This magnetic activity does undergo an observable decline over time, making it an important potential age determinant for M dwarfs. Observing this activity is important for studying the outer atmospheres of these stars, but also for comparing the behaviors of different spectral type subsets of M dwarfs, e.g., those with partially vs. fully convective interiors. Beyond stellar astrophysics, understanding the X-ray to UV activity of M dwarfs over time is also important for studying the atmospheres and habitability of any hosted exoplanets. Earth-sized exoplanets, in particular, are more commonly found orbiting M dwarfs than any other stellar type, and thermal escape (driven by the M dwarf X-ray to UV activity) is believed to be the dominant atmospheric loss mechanism for these planets. Utilizing recently calibrated M dwarf age-rotation relationships, also constructed as part of the $\textit{Living with a Red Dwarf}$ program (Engle & Guinan 2023), we have analyzed the evolution of M dwarf activity over time, in terms of coronal (X-ray), chromospheric (Lyman-$\alpha$, and Ca II), and overall X--UV (5--1700 Angstrom) emissions. The activity-age relationships presented here will be useful for studying exoplanet habitability and atmospheric loss, but also for studying the different dynamo and outer atmospheric heating mechanisms at work in M dwarfs.

This work aims to investigate the polarisation convention of the Giant Metrewave Radio Telescope (GMRT) and understand whether these follow the standard IAU/IEEE convention. The GMRT antennas are prime focus antennas, i.e. the radiation falling on the feed reverses its circular polarisation. If this reflection is not taken into account, it will result in a reversal of circular polarisation. We carried out several tests to understand the GMRT polarisation convention. The observations were carried out on several strong and highly polarised pulsars with known polarisation properties at GMRT wavelengths, mainly covering bands 2, 3 and 4. In addition, we tracked the polarisation from the GMRT feed to the fibre optic system, and fibre optic system to the user end. The study indicates that GMRT channels 1 and 2 are true R and L, however, since GMRT is a prime focus instrument, the reflection due to the dish reverses the sense of polarisation and converts RCP into LCP and vice versa. This has not been taken into account and because of this reason, GMRT Stokes V and U signs need to be reversed to make them consistent with the IAU/IEEE convention. This objective can be achieved by reassigning channel 1 to L and channel 2 to R for all circular feeds, i.e. bands 2, 3, and 4. The study remains inconclusive for band 5, which has linear feeds.

Assuming that the first adiabatic invariant for radiating particles in relativistic jets is conserved, we investigate the change in brightness temperature along the jet axis. We show that in this case the observed break in the dependence of the brightness temperature on the distance to the central engine can be explained.

One key piece of evidence for dark matter is the flat rotation curve problem: the disagreement between measured galactic rotation curves and their luminous mass. A novel solution to this problem is presented here. A model of relativistic frame effects on Doppler shifts due to the slightly curved frames of an emitting galaxy and the Milky Way is derived. This model predicts observed Doppler shifted spectra (in excess of the luminous mass) based only on the observed luminous matter profile and one free model parameter. Fits to the 175 galaxies reported in the SPARC database of galactic rotation profiles and accurate photometry measurements are compared between this novel model and dark matter and MOND (RAR) models. We find on the SPARC sample of 175 galaxies; that MOND-RAR has an average reduced chisquare of $\chi^2_r = 4.22$ for 175 galaxies fitted, the isothermal dark matter model has $\chi^2_r = 1.90$ for 165 galaxies fitted, and the new model we present has $\chi^2_r = 2.39$ for 172 galaxies fitted. Implications of this model are discussed.

The nearby irregular galaxy NGC4449 has a star formation rate of about 0.4 solar masses/yr and should host of order 70 SNRs younger than 20,000 years, a typical age for SNRs expanding into to an ISM with unit density to reach the radiative phase. We have carried out an optical imaging and spectroscopic survey in an attempt to identify these SNRs. This task is challenging because diffuse gas with elevated ratios of [SII]:H-alpha is omnipresent in NGC4449, {causing confusion when using this common diagnostic for SNRs. Using narrow-band interference-filter images, we first identified 49 objects that have elevated [SII]:H-alpha ratios compared to nearby HII regions. Using Gemini-N and GMOS, we then obtained high-resolution spectra of 30 of these SNR candidates, 25 of which have [SII]:H-alpha ratios greater than 0.5. Of these, 15 nebulae are almost certainly SNRs, based on a combination of characteristics: higher [OI]:H-alpha ratios and broader line widths than observed from HII regions. The remainder are good candidates as well, but need additional confirmation. Surprisingly, despite having superior imaging and spectroscopic data sets to examine, we are unable to confirm most of the candidates suggested by Leonidaki (2013). While NGC4449 is likely an extreme case because of the high surface brightness and elevated [SII]:H-alpha ratio of diffuse gas, it highlights the need for sensitive high-resolution optical spectroscopy, or high spatial resolution radio or X-ray observations that can ensure accurate SNR identifications in external galaxies.

The aim of this work is to study the anisotropic weak lensing signal associated with the mass distribution of massive clusters of galaxies using the Cosmic Microwave Background (CMB) data. For this purpose, we stack patches of the Planck Collaboration 2018 CMB lensing convergence map centered on SDSS DR8 redMaPPer clusters within the redshift range [0.4, 0.5]. We obtain mean radial profiles of the convergence parameter k finding strong signals at scales as large as 40 Mpc/h. By orienting the clusters along their major axis defined through the galaxy member distribution, we find a significant difference between the parallel and perpendicular oriented convergence profiles. The amplitude of the profile along the parallel direction is about 50% larger than that along the perpendicular direction, indicating that the clusters are well aligned with the surrounding mass distribution. From a model with an anisotropic surface mass density, we obtain a suitable agreement for both mass and ellipticities of clusters compared to results derived from weak lensing shear estimates, finding strong evidence of the correlation between the galaxy cluster member distribution and the large--scale mass distribution.

The origin of the cold phase in the CGM is a highly debated question. We investigate the contribution of satellite galaxies to the cold gas budget in the circumgalactic medium (CGM)of a Milky Way-like host galaxy. We perform controlled experiments with three different satellite mass distributions and identify several mechanisms by which satellites can add cold gas to the CGM, including ram pressure stripping and induced cooling in the mixing layer of the stripped cold gas. These two mechanisms contribute a comparable amount of cold gas to the host CGM. We find that the less massive satellites ($\leq 10^9 M_\odot$) not only lose all of their cold gas in a short period ($\sim$ 0.5-1 Gyr), but their stripped cold clouds also mix with the hot CGM gas and get heated up quickly. However, stellar feedback from these less massive satellites can hugely alter the fate of their stripped gas. Feedback speeds up the destruction of the stripped cold clouds from these satellites by making them more diffuse with more surface area. On the other hand, the more massive satellites (LMC or SMC-like $\sim 10^{10} M_\odot$) can add cold gas to the total gas budget of the host CGM for several Gyrs.

We present an implementation of a Bayesian mixture model using Hamiltonian Monte Carlo (HMC) techniques to search for spatial separation of Galactic dust components. Utilizing intensity measurements from \Planck High Frequency Instrument (HFI), we apply this model to high-latitude Galactic dust emission. Our analysis reveals a strong preference for a spatially-varying two-population dust model in intensity, with each population being well characterized by a single-component dust spectral-energy distribution (SED). While no spatial information is built into the likelihood, our investigation unveils spatially coherent structures with high significance, pointing to a physical origin for the observed spatial separation. These results are robust to our choice of likelihood and of input data. Furthermore, they are favored over a single-component dust model by Bayesian evidence calculations. Incorporating \IRAS 100\,$\mu m$ to constrain the Wein-side of the blackbody function, we find the dust populations differ at the $2.5\sigma$ level on the spectral index ($\beta_d$) vs. temperature $(T_d)$ plane. The presence of a multi-population dust has implications for component separation techniques frequently employed in the recovery of the Cosmic Microwave Background.

Coherent elastic neutrino-nucleus scattering (CE$\nu$NS) and other rare-event physics searches, like dark matter detection, have been especially furthered by increasing sensitivity to low-energy particle interactions. Experiments using multiple detector technologies have sought CE$\nu$NS at the most intense terrestrial sources of neutrinos: spallation facilities and nuclear reactors. This thesis reports on the feasibility of using cryogenic pure CsI as an improved next-generation CE$\nu$NS target at the up-and-coming European Spallation Source. Calibrations and simulations presented here predict an increase by a factor of at least $\sim33$ in the rate of observable neutrino-induced events per unit mass, compared to past use of room-temperature CsI[Na]. Also reported is the first measurement of CE$\nu$NS from antineutrinos at the Dresden Generating Station, a power nuclear reactor, employing a large-mass semiconducting germanium diode dubbed NCC-1701. In each section on detecting these neutrino couplings, the importance of understanding device response to low-energy nuclear recoils is highlighted. Finally, finding synergy for tools developed to extricate sub-keV CE$\nu$NS signals, a search for the exotic mode of muon decay $\mu^+ \xrightarrow{} e^+X$ was performed. New sensitivity limits in previously untouched parameter space for a massive boson dark matter candidate of cosmological interest are presented.

Axion dark matter (DM) produces echo images of bright radio sources via stimulated decay. These images appear as a faint radio line centered at half the axion mass, with the line width set by the DM velocity dispersion. Due to the kinematics of the decay, the echo can be emitted in the direction nearly opposite to the incoming source of stimulating radiation, meaning that axions effectively behave as imperfect monochromatic mirrors. We present an all-sky analysis of axion DM-induced echo images using extragalactic radio point sources, Galactic supernova remnants (SNRs), and Galactic synchrotron radiation (GSR) as sources of stimulating radiation. The aggregate signal strength is not significantly affected by unknown properties of individual sources of stimulating radiation, which we sample from an empirical distribution to generate an ensemble of realizations for the all-sky signal template. We perform forecasts for CHIME, HERA, CHORD, HIRAX, and BURSTT, finding that they can run as competitive axion experiments simultaneously with other objectives, requiring no new hardware.

The temporal property of the compressible magneto-hydrodynamic (MHD) turbulence remains a fundamental unsolved question. Recent studies based on the spatial-temporal analysis in the global frame of reference suggest that the majority of fluctuation power in turbulence does not follow any of the MHD wave dispersion relations but has very low temporal frequency with finite wavenumbers. Here, we demonstrate that the Lorentzian broadening of the dispersion relations of the three MHD modes where the nonlinear effects act like the damping of a harmonic oscillator can explain many salient features of frequency spectra for all MHD modes. The low frequency fluctuations are dominated by modes with the low parallel wavenumbers that have been broadened by the nonlinear processes. The Lorentzian broadening widths of the three MHD modes exhibit scaling relations to the global frame wavenumbers and are intrinsically related to energy cascade of each mode. Our results provide a new window to investigate the temporal properties of turbulence which offers insights for building a comprehensive understanding of the compressible MHD turbulence.

Combining multiple gravitational-wave observations allows for stringent tests of general relativity, targeting effects that would otherwise be undetectable using single-event analyses. We show that the finite size of the observed catalog induces a significant source of variance. If not appropriately accounted for, general relativity can be excluded with arbitrarily large credibility even if it is the underlying theory of gravity. This effect is generic and entirely analogous to the so-called "cosmic variance" of cosmology: in essence, we only have one catalog that contains all the events. We show that the cosmic variance holds for arbitrarily large catalogs and cannot be suppressed by selecting "golden" observations with large signal-to-noise ratios. We present a mitigation strategy based on bootstrapping (i.e. resampling with repetition) that allows assigning uncertainties to one's credibility on the targeted test. We demonstrate our findings using both toy models and real gravitational-wave data. In particular, we quantify the impact of the cosmic variance on the ringdown properties of black holes using the latest LIGO/Virgo catalog.

Graviton-photon conversions in a given external electric or magnetic field, known as the Gertsenshtein mechanism, are usually treated using the four-potential for photons. In terms of the electric and magnetic (EM) fields, however, proper identification of the fields in curved spacetime is important. By misidentifying the fields in Minkowski form, as is often practiced in the literature, we show that the final equation for photon conversion is correct in transverse-tracefree gauge only for planar gravitational waves in a uniform and constant external field. Even in the former method, to recover the EM fields from the four-potential in curved spacetime, one should properly take into account the metric involved in the relation. By including the metric perturbation in the graviton conversion equation, we show that a magnetic environment can cause exponential instability term in gravitational wave equation.

We consider the symmetric teleparallel $f\left( Q\right) $-gravity in Friedmann--Lema\^{\i}tre--Robertson--Walker cosmology with nonzero spatial curvature. For a nonlinear $f\left( Q\right) $ model there exist always the limit of General\ Relativity with or without the cosmological constant term. The de Sitter solution is always provided by the theory and for the specific models $f_{A}\left( Q\right) \simeq Q^{\frac{\alpha}{\alpha-1}}% ~,~f_{B}\left( Q\right) \simeq Q+f_{1}Q^{\frac{\alpha}{\alpha-1}}$ and $f_{C}\left( Q\right) \simeq Q+f_{1}Q\ln Q$ it was found to be the unique attractor. Consequently small deviations from STGR can solve the flatness problem and lead to a de Sitter expansion without introduce a cosmological constant term. This result is different from that given by the power-law theories for the other two scalar of the trinity of General Relativity. What makes the nonlinear symmetric teleparallel theory to stand out are the new degree of freedom provided by the connection defined in the non-coincidence frame which describes the nonzero spatial curvature.

We investigate false vacuum decay of a relativistic scalar field initialized in the metastable minimum of an asymmetric double-well potential. The transition to the true ground state is a well-defined initial-value problem in real time, which can be formulated in nonequilibrium quantum field theory on a closed time path. We employ the non-perturbative framework of the two-particle irreducible (2PI) quantum effective action at next-to-leading order in a large-N expansion. We also compare to classical-statistical field theory simulations on a lattice in the high-temperature regime. By this, we demonstrate that the real-time decay rates are comparable to those obtained from the conventional Euclidean (bounce) approach. In general, we find that the decay rates are time dependent. For a more comprehensive description of the dynamics, we extract a time-dependent effective potential, which becomes convex during the nonequilibrium transition process. By solving the quantum evolution equations for the one- and two-point correlation functions for vacuum initial conditions, we demonstrate that quantum corrections can lead to transitions that are not captured by classical-statistical approximations.

The Space Time Explorer and QUantum Equivalence principle Space Test (STE-QUEST) recently proposed, aims at performing a precision test of the weak equivalence principle (WEP), a fundamental cornerstone of General Relativity. Taking advantage of the ideal operation conditions for high-precision quantum sensing on board of a satellite, it aims to detect possible violations of WEP down to the $10^{-17}$ level. This level of performance leads to stringent environmental requirements on the control of the spacecraft. We assume an operation of a dual-species atom interferometer of rubidium and potassium isotopes in a double-diffraction configuration and derive the constraints to achieve an E\"otv\"os parameter $\eta=10^{-17}$ in statistical and systematic uncertainties. We show that technical heritage of previous satellite missions, such as MICROSCOPE, satisfies the platform requirements to achieve the proposed objectives underlying the technical readiness of the STE-QUEST mission proposal.

In the present work, we perform a comparative study of different interacting dark energy (DE) models using the Statefinder diagnostics. In particular, 17 different forms of the energy transfer rate $Q$ between DE and dark matter (DM) were focused on, belonging to the following categories: i) linear models in energy densities of DE and DM, ii) non-linear models, iii) models with a change of direction of energy transfer between DE and DM, iv) models involving derivatives of the energy densities, v) parametrized interactions through a function of the coincidence parameter $\tilde{r}$, and finally we also consider vi) two kinds of models with a self-interaction between DM, without DE. These models have been already studied in the literature and constrained with observational data available at that time. In order to discriminate between them at background level, we use the Statefinder diagnostic, based on the computation and study of the so-called Statefinder parameters $r$, $s$ in addition to the deceleration parameter $q$. We plot the evolution trajectories for the several interacting models on the $r-q$, $r-s$ planes, and we find some distinctive features and departures from $\Lambda$CDM and other DE models, as Quintessence, Chaplygin Gas, running vacuum models (RVM) and Galileon.

Computer power is a constantly increasing demand in scientific data analyses, in particular when Markov Chain Monte Carlo (MCMC) methods are involved, for example for estimating integral functions or Bayesian posterior probabilities. In this paper, we describe the benefits of a parallel computation of MCMC using a cloud-based, serverless architecture: first, the computation time can be spread over thousands of processes, hence greatly reducing the time the user should wait to have its computation completed. Second, the overhead time required for running in parallel several processes is minor and grows logarithmically with respect to the number of processes. Third, the serverless approach does not require time-consuming efforts for maintaining and updating the computing infrastructure when/if the number of walkers increases or for adapting the code to optimally use the infrastructure. The benefits are illustrated with the computation of the posterior probability distribution of a real astronomical analysis.