Papers for Thursday, May 12 2022

We present two novel additions to the semi-analytic solution of Lyman $\alpha$ (Ly$\alpha$) radiative transfer in spherical geometry: (1) implementation of the correct boundary condition for a steady source, and (2) solution of the time-dependent problem for an impulsive source. For the steady-state problem, the solution can be represented as a sum of two terms: a previously-known analytic solution of the equation with mean intensity $J=0$ at the surface, and a novel, semi-analytic solution which enforces the correct boundary condition of zero-ingoing intensity at the surface. This solution is compared to that of the Monte Carlo method, which is valid at arbitrary optical depth. It is shown that the size of the correction is of order unity when the spectral peaks approach the Doppler core and decreases slowly with line center optical depth, specifically as $(a \tau_0)^{-1/3}$, which may explain discrepancies seen in previous studies. For the impulsive problem, the time, spatial, and frequency dependence of the solution are expressed using an eigenfunction expansion in order to characterize the escape time distribution and emergent spectra of photons. It is shown that the lowest-order eigenfrequency agrees well with the decay rate found in the Monte Carlo escape time distribution at sufficiently large line-center optical depths. The characterization of the escape-time distribution highlights the potential for a Monte Carlo acceleration method, which would sample photon escape properties from distributions rather than calculating every photon scattering, thereby reducing computational demand.

Recently, based on a novel analysis of the Planck satellite data, a hint of a uniform rotation of the polarization of cosmic microwave background photons, called isotropic cosmic birefringence, has been reported. The suggested rotation angle of polarization of about $0.2-0.4$ degrees strongly suggests that it is determined by the fine structure constant, which can be naturally explained over a very wide parameter range by the domain walls of axion-like particles. Interestingly, the axion-like particle domain walls predict not only isotropic cosmic birefringence but also anisotropic one that reflects the spatial distribution of the axion-like particle field on the last scattering surface. In this Letter, we perform lattice simulations of the formation and evolution of domain walls in the expanding universe and obtain for the first time the two-point correlation function and power spectrum of the scalar field that constitutes the domain walls. We find that while the power spectrum is generally consistent with analytical predictions based on random wall distributions, there is a predominant excess on the scale corresponding to the Hubble radius. Applying our results to the anisotropic cosmic birefringence, we predict the power spectrum of the rotation angles induced by the axion-like particle domain walls and show that it is within the reach of future observations of the cosmic microwave background.

The offset microlensing degeneracy, recently proposed by Zhang et al. (2021), has been shown to generalize the close-wide and inner-outer caustic degeneracies into a unified regime of magnification degeneracy in the interpretation of 2-body planetary microlensing observations. The offset degeneracy states that for two planetary lenses that differ only in the projected star-planet separation ($s_{\rm A}\neq s_{\rm B}$), the source trajectory is required to cross their point of equal magnification on the lens-axis, located at $u=(s_{\rm A}-1/s_{\rm A}+s_{\rm B}-1/s_{\rm B})/2$ from the primary, to give rise to degenerate observations. Crucially, the above formalism applies to all three caustic topologies, and implies that the $s_{\rm A}=1/s_{\rm B}$ solution of the close-wide degeneracy never strictly manifests in microlensing observations unless $u=0$. However, the offset degeneracy was proposed upon numerical calculations, and no theoretical justification was given. Here, we provide a theoretical treatment of the offset degeneracy, which demonstrates its nature as a mathematical degeneracy. From first principles, we show that the offset degeneracy formalism is exact to zeroth-order in the mass ratio ($q$) for two cases: when the source crosses the lens-axis inside of caustics, and for $(s_A-s_B)^6\ll1$ when crossing outside of caustics. The extent to which the offset degeneracy persists in oblique source trajectories is explored numerically. Additionally, it is shown that the superposition principle allows for a straightforward generalization to $N$-body microlenses with $N$-1 planetary lens components ($q\ll1$), which results in a $2^{N-1}$-fold degeneracy. Lastly, we demonstrate that the recently proposed "$s^\dagger$" heuristic results from the $s\rightarrow1$ limit of the offset degeneracy, and thus does not correctly unify the close-wide and inner-outer degeneracies.

Blazars are a peculiar class of active galactic nuclei (AGNs) that enlighten the sky at all wavelengths. The electromagnetic emission of these sources is jet-dominated resulting in a spectral energy distribution (SED) that has a typical double-humped shape. X-ray photons provide a wealth of information on the physics of each source as in the X-ray band we can observe the tail of SED first peak, the rise of the second one or the transition between the two. NuSTAR, thanks to its capability of focusing X-rays up to 79 keV provides broadband data particularly suitable to compute SEDs in a still poorly explored part of the spectrum. In the context of the Open Universe initiative we developed a dedicated pipeline, NuSTAR_Spectra, a shell-script that automatically downloads data from the archive, generates scientific products and carries out a complete spectral analysis. The script homogeneously extracts high level scientific products for both NuSTAR's telescopes and the spectral characterisation is performed testing two phenomenological models. The corresponding X-ray properties are derived from the data best-fit and the SEDs are also computed. The systematic processing of all blazar observations of the NuSTAR public archive allowed us to release the first hard X-ray spectroscopic catalogue of blazars (NuBlazar). The catalogue, updated to September 30th, 2021, includes 253 observations of 126 distinct blazars, 30 of which have been multiply observed.

We use deep spectroscopy from the Hubble Space Telescope (HST) Wide-Field-Camera 3 (WFC3) IR grisms combined with broad-band photometry to study the stellar populations, gas ionization and chemical abundances in star-forming galaxies at $z\sim 1.1-2.3$. The data stem from the CANDELS Lyman-$\alpha$ Emission At Reionization (CLEAR) survey. At these redshifts the grism spectroscopy measure the [OII] 3727, 3729, [OIII] 4959, 5008, H-$\beta$ strong emission features, which constrain the ionization parameter and oxygen abundance of the nebular gas. We compare the line flux measurements to predictions from updated photoionization models (MAPPINGS (Kewley et al. 2019), which include an updated treatment of nebular gas pressure, log P/k = $n_e T_e$. Compared to low-redshift samples ($z\sim 0.2$) at fixed stellar mass, llog M / M$_\odot$ = 9.4-9.8, the CLEAR galaxies at z=1.35 (z=1.90) have lower gas-phase metallicity, $\Delta$(log Z) = 0.25 (0.35) dex, and higher ionization parameters, $\Delta$(log q) = 0.25 (0.35) dex, where U = q/c. We provide updated analytic calibrations between the [OIII], [OII], and H-$\beta$ emission line ratios, metallicity, and ionization parameter. The CLEAR galaxies show that at fixed stellar mass, the gas ionization parameter is correlated with the galaxy specific star-formation rates (sSFRs), where $\Delta$ log q = 0.4 $\Delta$(log sSFR), derived from changes in the strength of galaxy H-$\beta$ equivalent width. We interpret this as a consequence of higher gas densities, lower gas covering fractions, combined with higher escape fraction of H-ionizing photons. We discuss both tests to confirm these assertions and implications this has for future observations of galaxies at higher redshifts.

X-ray binaries provide exceptional laboratories for understanding the physics of matter under the most extreme conditions. Until recently, there were few, if any, observational constraints on the circumbinary environments of X-ray binaries at $\sim$ 100-5000 AU scales; it remains unclear how the accretion onto the compact objects or the explosions giving rise to the compact objects interact with their immediate surroundings. Here, we present the first high-contrast adaptive optics images of X-ray binaries. These observations target all X-ray binaries within $\sim$ 3 kpc accessible with the Keck/NIRC2 vortex coronagraph. This paper focuses on one of the first key results from this campaign: our images reveal the presence of 21 sources potentially associated with the $\gamma$ Cassiopeiae analog high-mass X-ray binary RX J1744.7$-$2713. By conducting different analyses - a preliminary proper motion analysis, a color-magnitude diagram and a probability of chance alignment calculation - we found that three of these 21 sources have a high probability of being bound to the system. If confirmed, they would be in wide orbits ($\sim$ 450 AU to 2500 AU). While follow-up astrometric observations will be needed in $\sim$ 5-10 years to confirm further the bound nature of these detections, these discoveries emphasize that such observations may provide a major breakthrough in the field. In fact, they would be useful not only for our understanding of stellar multiplicity but also for our understanding of how planets, brown dwarfs and stars can form even in the most extreme environments.

AT2019pev is a nuclear transient in a narrow-line Seyfert 1 galaxy at $z=0.096$. The archival ultraviolet, optical and infrared data showed features of both tidal disruption events (TDEs) and active galactic nuclei (AGNs), and its nature is not fully understood. We present detailed X-ray observations of AT2019pev taken with Swift, Chandra and NICER over 173 days of its evolution since the first Swift XRT epoch. The X-ray luminosity increases by a factor of five in five days from the first Swift XRT epoch to the lightcurve peak. The lightcurve decays by a factor of ten over $\sim$75 days and then flattens with a weak re-brightening trend at late times. The X-ray spectra show a "harder-when-brighter" trend before peak and a "harder-when-fainter" trend after peak, which may indicate a transition of accretion states. The archival ground-based optical observations show similar time evolution as the X-ray lightcurves. Beyond the seasonal limit of the ground-based observations, the Gaia lightcurve is rising toward an equally bright or brighter peak 223 days after the optical discovery. Combining our X-ray analysis and archival multi-wavelength data, AT2019pev more closely resembles an AGN transient.

The merger rate density evolution of binary compact objects and the properties of their host galaxies carry crucial information to understand the sources of gravitational waves. Here, we present galaxyRate, a new code that estimates the merger rate density of binary compact objects and the properties of their host galaxies, based on observational scaling relations. We generate our synthetic galaxies according to the galaxy stellar mass function of star forming and passive galaxies. We estimate the metallicity according to both the mass-metallicity relation (MZR) and the fundamental metallicity relation (FMR). Also, we take into account galaxy-galaxy mergers and the evolution of the galaxy properties from the formation to the merger of the binary compact object. We find that the merger rate density evolution with redshift changes dramatically depending on the choice of the star-forming galaxy main sequence, especially in the case of binary black holes (BBHs) and black hole neutron star systems (BHNSs). The slope of the merger rate density evolution of BBHs and BHNSs is steeper if we assume the MZR with respect to the FMR, because the latter predicts a shallower decrease of metallicity with redshift. In contrast, binary neutron stars (BNSs) are only mildly affected by both the galaxy main sequence and metallicity relation. Overall, BBHs and BHNSs tend to form in low-mass metal-poor galaxies and merge in high-mass metal-rich galaxies, while BNSs form and merge in massive galaxies. The metallicity distribution of the host galaxies is significantly affected by the adopted metallicity relation. We predict that passive galaxies host at least ~5-10 %, ~15-25 %, and ~ 15-35 % of all BNS, BHNS and BBH mergers in the local Universe.

We probe the environmental properties of X-ray supernova remnants (SNRs) at various points along their evolutionary journey, especially the S-T phase, and their conformance with theoretically derived models of SNR evolution. The remnant size is used as a proxy for the age of the remnant. Our data set includes 34 Milky Way, 59 Large Magellanic Cloud (LMC), and 5 Small Magellanic Cloud (SMC) SNRs. We select remnants that have been definitively typed as either core-collapse (CC) or Type Ia supernovae, with well-defined size estimates, and a thermal X-ray flux measured over the entire remnant. A catalog of SNR size and X-ray luminosity is presented and plotted, with ambient density and age estimates from the literature. Model remnants with a given density, in the Sedov-Taylor (S-T) phase, are overplotted on the diameter-vs-luminosity plot, allowing the evolutionary state and physical properties of SNRs to be compared to each other, and to theoretical models. We find that small, young remnants are predominantly Type Ia remnants or high luminosity CCs, suggesting that many CC SNRs are not detected until after they have emerged from the progenitor's wind-blown bubble. An examination of the distribution of SNR diameters in the Milky Way and LMC reveals that LMC SNRs must be evolving in an ambient medium which is 30% as dense as that in the Milky Way. This is consistent with ambient density estimates for the Galaxy and LMC.

We present a fast algorithm to produce light curves of distant stars undergoing microlensing near critical curves. The need of these type of algorithms is motivated by recent observations of microlensing events of distant stars at high redshift and at extreme magnification factors. The algorithm relies on a low-resolution computation of the deflection field due to an ensemble of microlenses near critical curves, and takes advantage of the slowly varying nature of the deflection field to infer the magnification of the unresolved images.

The NGC 346 young stellar system and associated N66 giant HII region in the Small Magellanic Cloud are the nearest example of a massive star forming event in a low metallicity ($Z\approx0.2Z_{\odot}$) galaxy. With an age of $\lesssim$3Myr this system provides a unique opportunity to study relationships between massive stars and their associated HII region. Using archival data, we derive a total H$\alpha$ luminosity of L(H$\alpha$)=4.1$\times$10$^{38}$ergs$^{-1}$ corresponding to an H-photoionization rate of 3$\times$10$^{50}$s$^{-1}$. A comparison with a predicted stellar ionization rate derived from the more than 50 known O-stars in NGC 346, including massive stars recently classified from HST FUV spectra, indicates an approximate ionization balance. Spectra obtained with SALT suggest the ionization structure of N66 could be consistent with some leakage of ionizing photons. Due to the low metallicity, the far ultraviolet luminosity from NGC 346 is not confined to the interstellar cloud associated with N66. Ionization extends through much of the spatial extent of the N66 cloud complex, and most of the cloud mass is not ionized. The stellar mass estimated from nebular L(H$\alpha$) appears to be lower than masses derived from the census of resolved stars which may indicate a disconnect between the formation of high and low mass stars in this region. We briefly discuss implications of the properties of N66 for studies of star formation and stellar feedback in low metallicity environments.

Red supergiant (RSGs) are cool massive stars in a late phase of their evolution when the stellar envelope becomes fully convective. They are the brightest stars in the universe at infrared light and can be detected in galaxies far beyond the Local Group, allowing for accurate determination of chemical composition of galaxies. The study of their physical properties is extremely important for various phenomena including the final fate of massive stars as type II supernovae and gravitational wave progenitors. We explore the well-studied nearby young stellar cluster chi Per. Using Gaia EDR3 data, we find the distance of the cluster (d = 2.260+-0.020 kpc). We then investigate the variability of the convection-related surface structure as a source for parallax measurement uncertainty. We use state-of-the-art 3D radiative hydrodynamics simulations with CO5BOLD and the post-processing radiative transfer code OPTIM3D to compute intensity maps in the Gaia G photometric system. We calculate the variabiltiy, as a function of time, of the intensity-weighted mean from the synthetic maps. We then select the RSG stars in the cluster and compare their uncertainty on parallaxes to the predictions of photocentre displacements. The synthetic maps of RSG show extremely irregular and temporal variable surfaces due to convection-related dynamics. Consequentially, the position of the photo-center varies during Gaia measurements between 0.033 and 0.130 AU (up to 5% of the corresponding simulation stellar radius). We argue that the variability of the convection-related surface structures accounts for a substantial part of the Gaia EDR3 parallax error of the RSG sample. We suggest that the variation of the uncertainty on Gaia parallax could be exploited quantitatively using appropriate 3D simulations to extract, in a unique way, important information about the stellar dynamics and parameters of RSG stars.

In a recent paper (V\'an, P.; Abe, S. Physica A 2022, 588, 126505), it has been discovered that a scalar field coupled to a fluid and allowed to be a thermodynamic variable in consistency with the second law of thermodynamics is only gravitational and accordingly emergence of extended Newtonian gravity has been predicted. The resulting field equation for the potential of this emergent force is nonlinear and admits the logarithmic potential as a singular solution, suggesting its relevance to the dark matter conundrum. Here, a general analysis of the nonlinear field equation is performed. It is found that the emergent force field exhibits the unsharp crossover between the 1/r and 1/r^2 forces outside the fluid, depending on a spatial scale characteristic of the present theory to be observationally tested in the context of the dark matter conundrum. Then, the action functional is constructed for the potential of the emergent field and the field energy is shown to be free from an infrared divergence. A comment is also made on the difference of the present theory from MOND (modified Newtonian dynamics).

Observations of the TeV halos associated with nearby pulsars indicate that these objects inject significant fluxes of very high-energy electron-positrons pairs into the interstellar medium (ISM), thereby likely providing the dominant contribution to the cosmic-ray positron flux. In this paper, we use the cosmic-ray positron fraction as measured by the AMS-02 Collaboration to constrain the characteristics of the local pulsar population. For reasonable model parameters, we find that we can obtain good agreement with the measured positron fraction up to energies of $E_e \sim 300 \, {\rm GeV}$. At higher energies, the positron fraction is dominated by a small number of pulsars, making it difficult to reliably predict the shape of the expected positron fraction. The low-energy positron spectrum supports the conclusion that pulsars typically transfer approximately $\eta \sim 5-20\%$ of their total spindown power into the production of very high-energy electron-positron pairs, producing a spectrum of such particles with a hard spectral index, $\alpha \sim 1.5-1.7$. Such pulsars typically spindown on a timescale on the order of $\tau \sim 10^4 \, {\rm years}$. Our best fits were obtained for models in which the radio and gamma-ray beams from pulsars are detectable to 28% and 62% of surrounding observers, respectively.

We present the results of 8 epochs of simultaneous UV and X-ray observations of the highly variable ultraluminous X-ray source (ULX) Holmberg II X-1 with AstroSat -- Indian multiwavelength space satellite. During the entire observation period from late 2016 to early 2020, Holmberg II X-1 showed a moderate X-ray luminosity of $8\times10^{39}$ erg/s and a hard power-law spectrum with $\Gamma \lesssim 1.9$. Due to low variability of the object in X-rays (by a factor 1.5) and insignificant variability in the UV range (upper limit $\approx25$%) we could not find reliable correlation between flux changes in these ranges. Inside each particular observation, the X-ray variability amplitude is higher, it reaches a factor of 2-3 respect to the mean level at the time scales of $\sim10$ ks or even shorter. We discussed our results in terms of three models of a heated donor star, a heated disk and a heated wind, and estimated the lower limit to the variability which would allow to reject at least part of them.

Spacecraft and ground-based observations show that the main rings of Saturn lack particles larger than 10 m. Tidal or collisional destruction of satellites/comets have been proposed as the origin of the main rings; however, Saturn's tide alone cannot grind km-sized fragments into submeter-sized particles because of the high mechanical strength of water ice and rock. The question arises as to why such large particles are not left in the current ring. It is known that thermal stress induced by diurnal and seasonal temperature variations can cause weathering and fragmentation of boulders and contribute to dust and regolith production on the Moon and terrestrial planets, and then such thermal stress can break particles larger than a critical radius while cannot smaller than the critical radius. In this study, we examined the role of thermal stress acting on Saturn's ring particles. We found that thermal stress can grind porous ring particles larger than 10-20 m, which explains the lack of particles larger than 10 m in Saturn's ring. Also, fragmentation by thermal stress can be adoptable for the Epsilon rings of Uranus. Furthermore, thermal stress caused by diurnal or seasonal temperature variation acting on boulders on surfaces of icy satellites and asteroids may play an important role in the evolution of their sizes. Our calculations explain the lack of boulders on icy satellites, except in the geologically active provinces such as the tiger stripes of Enceladus, where boulders are supplied by recent geological activity. We predict that future observations can find numerous boulders around Europa's geologically active cracks.

Furrows are a concentric system of tectonic troughs, and are the oldest recognizable surface feature on Ganymede. We analyzed the distribution of furrows utilizing Voyager and Galileo images and found that furrows over Ganymede's surface are part of a global concentric circular structure. If this multi-ring structure is impact origin, this is the largest impact structure identified so far in the solar system. Deviations of the shapes of the furrows from the concentricity are small everywhere, which implies that the relative location of the blocks of the dark terrains over the entire surface of Ganymede has not changed appreciably even during formation of the bright terrains. The estimate of the impactor size is difficult, but an 150km-radius impactor is consistent with the observed properties of furrows. The furrow-forming impact should have significant effects on the satellite's geological and internal evolution, which are expected to be confirmed by future explorations of Jupiter's icy moons, such as the JUICE (Jupiter Icy moon Explorer) or Europa Clipper mission.

Asteroid 162173 Ryugu is a rubble-pile asteroid, whose top-shape is compatible with models of deformation by spin up. Rims of major craters on Ryugu have an east-west asymmetric profile; their western crater rims are sharp and tall, while their eastern crater rims are rounded and low. Although there are various possible explanations, we theoretically assess the effect of asteroid rotation as the possible reason for this east-west asymmetry. It is known that the trajectories and fates of ejecta are affected by the rotation. The Coriolis force and the inertial speed of the rotating surface are the factors altering the ejecta trajectories. Consequently, we found that the east-west asymmetric crater rims might be formed as a result of rotation, when the inertial speed of the rotating surface is nearly equal to the first cosmic velocity of the body. In other words, it is possible that the observed east-west asymmetric rims of the Urashima, Cendrillon, and Kolobok craters were formed when Ryugu's rotation period was ~3.6 h.

Dozens of families of asteroids in the asteroid belt have similar orbits and compositions because they formed through a collision. However, the icy debris beyond the orbit of Neptune, called the Kuiper Belt, contains only one known family, the Haumea family. So far, no self-consistent explanation for the formation of the Haumea family can match all geophysical and orbital characteristics of the family without invoking extremely improbable events. Here, we show that the family is adequately explained as the product of a merging binary near the end of Neptune's orbital migration. The unique orbital signature of a merging binary, which was not found in extensive searches, is effectively erased during the final stages of migration, providing an explanation for all aspects of the Haumea family. By placing the formation of the Haumea family in the broader context of solar system formation, we demonstrate a proof-of-concept model for the formation of Haumea.

A claimed detection of cosmological tensor perturbations from inflation via B-mode polarization of the cosmic microwave background requires distinguishing other possible B-mode sources. One such potential source of confusion is primordial magnetic fields. For sufficiently low-amplitude B-mode signals, the microwave background temperature and polarization power spectra from power-law tensor perturbations and from a power-law primordial magnetic field are indistinguishable. However, we show that such a magnetic field will induce a small-scale Faraday rotation which is detectable using four-point statistics analogous to gravitational lensing of the microwave background. The Faraday rotation signal will distinguish a magnetic-field induced B-mode polarization signal from tensor perturbations for effective tensor-scalar ratios larger than 0.001, detectable in upcoming polarization experiments.

Jellyfish galaxies are an excellent tool to investigate the short-term effects of ram pressure stripping (RPS) on star formation in cluster environments. It has been thought that the star formation activity of jellyfish galaxies may depend on the host cluster properties, but previous studies have not yet found a clear correlation. In this study, we estimate the \Ha-based star formation rates (SFRs) of five jellyfish galaxies in massive clusters ($\sigma_{v, {\rm cl}}\gtrsim1000~{\rm km~s^{-1}}$) at $z\sim0.3-0.4$ using Gemini GMOS/IFU observations to explore the relationship. Combining our results with those in the literature, we find that the star formation activity of jellyfish galaxies shows a positive correlation with their host cluster velocity dispersion as a proxy of cluster mass and dynamical states. We divide the jellyfish galaxy sample into two groups with strong and weak RPS signatures using a morphological class. In the phase-space diagram, the jellyfish galaxies with strong RPS features show a higher SFR and a stronger central concentration than those with weak RPS features. We estimate their SFR excess relative to the star formation main sequence (starburstiness; $R_{\rm SB}={\rm SFR/SFR_{MS}}(z)$) and the density of the surrounding intracluster medium (ICM) using scaling relations with the cluster velocity dispersion. As a result, the starburstiness of jellyfish galaxies with strong RPS signatures clearly exhibits positive correlations with cluster velocity dispersion, ICM density, and strength of ram pressure. This shows that the relation between RPS and star formation activity of jellyfish galaxies depends on the host cluster properties and strength of ram pressure.

Gravitational lensing of gamma-ray bursts (GRBs) can provide an opportunity to probe the massive compact objects in the universe at different redshifts. We have discovered two consecutive pulses in the light curve of GRB 090717034, with the same temporal profile and different count rate, separated by a time interval, which is identified as gravitationally lensed candidate in Fermi/GBM GRB catalogue \citep{Kalantari}. Here, we use the $\chi^2$ method to investigate the similarity of the temporal profile variability of the two pulses as a gravitationally lensed candidate GRB. We find the magnification factor and the time delay between two pulses to correspond to minimising the $\chi^2$ function. Then, we perform a Monte Carlo simulation on a sample of mock lensed GRBs and compare the $\chi^2$ of the lensed GRB candidate with the simulation, which confirms this candidate with $1\sigma$ confidence level. Assuming that GRB 090717034 is lensed by a point-like object, the redshifted lens mass is about $M_L(1+z)=(4.220\pm 6.615) \times 10^6 M_{\odot}$. The lens of this GRB is a candidate for a super-massive black hole along the line of sight to the GRB.

I analyzed Transiting Exoplanet Survey Satellite (TESS) observations of the 2020 superoutburst of the SU~UMa-type dwarf nova V844 Her. This object showed "textbook" superhump stages A, B and C confirmed by modern satellite observations. The resultant figure can be used for an illustration of the concept of superhump stages under the Creative Commons (CC-BY-NC) licence. During the growing phase of superhumps, the period was initially close to, but slightly longer than the orbital period. Observers should pay attention to the presence of such a phenomenon not to confuse the phenomenon with early superhumps seen in WZ Sge stars. After the superoutburst, superhumps were detected for additional 18 d with the same period and no orbital signal was detected. Small wiggles with a period of ~0.5 d were recorded in the post-superoutburst phase and they may be the same phenomenon recorded in the Kepler data of the SU UMa star V585 Lyr.

As the Universe expands, the redshift of distant sources changes with time. Here we discuss gravitational lensing phenomena that are consequence of the redshift drift between lensed source, gravitational lens, and observer. When the source is located very close to the drifting caustics, a pair of images could occur (or disappear) because of the cosmological expansion. Furthermore, lensing systems act as signal converters of the redshift drift. The angular position, magnification, distortion, and time delay of already existing multiple images change. We estimate the expected frequency of these phenomena and the prospects to observe them in the era of deep and large surveys. The drift detection in image separation could be within reach of next generation surveys with $\mu$arcsec angular resolution.

We present spectroscopic confirmation of candidate strong gravitational lenses using the Keck Observatory and Very Large Telescope as part of our ASTRO 3D Galaxy Evolution with Lenses (AGEL) survey. We confirm that 1) search methods using Convolutional Neural Networks (CNN) with visual inspection successfully identify strong gravitational lenses and 2) the lenses are at higher redshifts relative to existing surveys due to the combination of deeper and higher resolution imaging from DECam and spectroscopy spanning optical to near-infrared wavelengths. We measure 104 redshifts in 77 systems selected from a catalog in the DES and DECaLS imaging fields (r<22 mag). Combining our results with published redshifts, we present redshifts for 68 lenses and establish that CNN-based searches are highly effective for use in future imaging surveys with a success rate of 88% (defined as 68/77). We report 53 strong lenses with spectroscopic redshifts for both the deflector and source (z_src>z_defl), and 15 lenses with a spectroscopic redshift for either the deflector (z_defl>0.21) or source (z_src>1.34). For the 68 lenses, the deflectors and sources have average redshifts and standard deviations of 0.58+/-0.14 and 1.92+/-0.59 respectively, and corresponding redshift ranges of (0.21<z_defl<0.89) and (0.88<z_src<3.55). The AGEL systems include 41 deflectors at zdefl>0.5 that are ideal for follow-up studies to track how mass density profiles evolve with redshift. Our goal with AGEL is to spectroscopically confirm ~100 strong gravitational lenses that can be observed from both hemispheres throughout the year. The AGEL survey is a resource for refining automated all-sky searches and addressing a range of questions in astrophysics and cosmology.

High-frequency wave phenomena present a great deal of interest as one of the possible candidates to contribute to the energy input required to heat the corona as a part of the AC heating theory. However, the resolution of imaging instruments up until the Solar Orbiter have made it impossible to resolve the necessary time and spatial scales. The present paper reports on high-frequency transverse motions in a small loop located in a quiet Sun region of the corona. The oscillations were observed with the HRIEUV telescope (17.4 nm) of the EUI instrument onboard the Solar Orbiter. We detect two transverse oscillations in short loops with lengths of 4.5 Mm and 11 Mm. The shorter loop displays an oscillation with a 14 s period and the longer a 30 s period. Despite the high resolution, no definitive identification as propagating or standing waves is possible. The velocity amplitudes are found to be equal to 72 km/s and 125 km/s, respectively, for the shorter and longer loop. Based on that, we also estimated the values of the energy flux contained in the loops - the energy flux of the 14 s oscillation is 1.9 kW m^-2 and of the 30 s oscillation it is 6.5 kW m^-2 . While these oscillations have been observed in the Quiet Sun, their energy fluxes are of the same order as the energy input required to heat the active solar corona. Numerical simulations were performed in order to reproduce the observed oscillations. The correspondence of the numerical results to the observations provide support to the energy content estimates for the observations. Such high energy densities have not yet been observed in decayless coronal waves, and this is promising for coronal heating models based on wave damping.

The Rotation powered pulsars Crab, Vela and Geminga have double peaked folded light curves (FLC) at $\gamma$-ray energies, that have an approximate reflection symmetry. Here this aspect is studied at soft X-ray energy by analyzing a high resolution FLC of the Crab pulsar obtained at $1 - 10$ keV using the {\it{NICER}} observatory. The rising edge of the first peak of the FLC and the reflected version of the falling edge of the second peak are compared in several ways, and phase ranges are identified where the two curves are statistically similar. The best matching occurs when the two peaks are aligned, but only in a small phase range of $\approx 0.0244$ just below their peaks; their mean difference is $-0.78 \pm 1.8$ photons/sec with a reduced $\chi^2$ of $0.93$. If the first curve is convolved by a Laplace function, the corresponding numbers are phase range of $\approx 0.0274$, mean difference of $-1.23 \pm 1.30$ and $\chi^2$ of $0.76$. These phase ranges are much smaller than those over which the reflection symmetry has been perceived. Therefore the only way the two edges can have a mirror relation over a substantial phase range is if one invokes a broad and faint emission component of amplitude $\approx 100$ photons/sec and width $\approx 0.1$ in phase, centered at phase $\approx 0.1$ beyond the second peak.

Being directly observed in the Doppler shift and imaging data and indirectly as quasi-periodic pulsations in solar and stellar flares, slow magnetoacoustic waves offer an important seismological tool for probing many vital parameters of the coronal plasma. A recently understood active nature of the solar corona for magnetoacoustic waves, manifested through the phenomenon of wave-induced thermal misbalance, led to the identification of new natural mechanisms for the interpretation of observed properties of waves. A frequency-dependent damping of slow waves in various coronal plasma structures remains an open question, as traditional wave damping theories fail to match observations. We demonstrate that accounting for the back-reaction caused by thermal misbalance on the wave dynamics leads to a modification of the relationship between the damping time and oscillation period of standing slow waves, prescribed by the linear theory. The modified relationship is not of a power-law form and has the equilibrium plasma conditions and properties of the coronal heating/cooling processes as free parameters. It is shown to readily explain the observed scaling of the damping time with period of standing slow waves in hot coronal loops. Functional forms of the unknown coronal heating process, consistent with the observed frequency-dependent damping, are seismologically revealed.

Some HII regions that surround young stellar clusters are bordered by molecular shells that appear to expand at a rate inconsistent with our current model simulations. In this study we focus on the dynamics of Sharpless 171 (including NGC 7822), which surrounds the cluster Berkeley 59. We aim to compare the velocity pattern over the molecular shell with the mean radial velocity of the cluster for estimates of the expansion velocities of different shell structures, and to match the observed properties with model simulations. Optical spectra of 27 stars located in Berkeley 59 were collected at the Nordic Optical Telescope, and a number of molecular structures scattered over the entire region were mapped in $^{13}$CO(1-0) at Onsala Space Observatory. We obtained radial velocities and MK classes for the cluster's stars. At least four of the O stars are found to be spectroscopic binaries, in addition to one triplet system. From these data we obtain the mean radial velocity of the cluster. From the $^{13}$CO spectra we identify three shell structures, expanding relative to the cluster at moderate velocity (4 km/s), high velocity (12 km/s), and in between. The high-velocity cloudlets extend over a larger radius and are less massive than the low-velocity cloudlets. We performed a model simulation to understand the evolution of this complex. Our simulation of the Sharpless 171 complex and Berkeley 59 cluster demonstrates that the individual components can be explained as a shell driven by stellar winds from the massive cluster members. However, our relatively simple model produces a single component. Modelling of the propagation of shell fragments through a uniform interstellar medium demonstrates that dense cloudlets detached from the shell are decelerated less efficiently than the shell itself. They can reach greater distances and retain higher velocities than the shell.

Stellar sources of gamma rays are one of the front lines in modern astrophysics whose understanding can benefit from observational tools not originally designed for their study. We take advantage of the high precision photometric capabilities of present-day space facilities to obtain a new perspective on the optical behavior of the X-ray and gamma-ray binary LS I +61 303. Previously unknown phenomena whose effects manifest with amplitudes below 0.01 magnitude can now be clearly observed and studied. Our work is mainly based on the analysis of optical and gamma-ray archival data and uses the tools recommended by the different collaborations that provide these valuable observational resources (in particular, the TESS and Fermi orbiting observatories). In addition, complementary ground-based optical spectroscopy has also been conducted. We report the discovery of small-amplitude optical flares on timescales of a day in the LS I +61 303 light curve. Different alternative scenarios to explain their origin are tentatively proposed.

We present a new upgraded version of the MOCCA code for the study of dynamical evolution of globular clusters and its first application to the study of evolution of multiple stellar populations. We explore a range of initial conditions spanning different structural parameters for the first (FG) and second population (SG) and we analyze their effect on the binary dynamics and survival. The set of simulations shown here represents the first phase of the new MOCCA-SURVEY-2 project which will be further extended. Here, we focus our attention on the number ratio of FG and SG binaries, its variation with the distance from the cluster center, and the way their abundances are affected by various cluster initial properties. We find that SG stars more abundant in clusters that were initially tidally filling. Conversely, FG stars stay more abundant in clusters that were initially tidally underfilling. We also find that the ratio between binary fractions is not affected by the way we calculate these fractions (e.g. with the use of all binaries, only main-sequence binaries or observational binaries, i.e. main-sequence stars > 0.4 MSun, mass ratios > 0.5). We find also that the evolution of mixing between populations presents the same features even if we take into account all single stars too. This implies that the main-sequence stars themselves are a very good proxy for probing entire populations of FG and SG in star clusters. We also discuss how our findings relate to the observations of Milky Way GCs. We show that with MOCCA models we are able to reproduce the observed range of SG fractions for any Milky Way GC for which we know this fraction. We show how the SG fractions depend on the initial conditions. We provide also an explanation what could be the initial conditions of star clusters, which at the Hubble time, have more numerous FG, and which more numerous SG stars.

We perform a full nuclear-network numerical calculation of the $r$-process nuclei in binary neutron-star mergers (NSMs), with the aim of estimating $\gamma$-ray emissions from the remnants of Galactic NSMs up to $10^6$ years old. The nucleosynthesis calculation of 4,070 nuclei is adopted to provide the elemental composition ratios of nuclei with an electron fraction $Y_{\rm e}$ between 0.10 and 0.45 . The decay processes of 3,237 unstable nuclei are simulated to extract the $\gamma$-ray spectra. As a result, the NSMs have different spectral color in $\gamma$-ray band from various other astronomical objects at less than $10^5$ years old. In addition, we propose a new line-diagnostic method for $Y_{\rm e}$ that uses the line ratios of either $^{137{\rm m}}$Ba/$^{85}$K or $^{243}$Am/$^{60{\rm m}}$Co, which become larger than unity for young and old $r$-process sites, respectively, with a low $Y_{\rm e}$ environment. From an estimation of the distance limit for $\gamma$-ray observations as a function of the age, the high sensitivity in the sub-MeV band, at approximately $10^{-9}$ photons s$^{-1}$ cm$^{-2}$ or $10^{-15}$ erg s$^{-1}$ cm$^{-2}$, is required to cover all the NSM remnants in our Galaxy if we assume that the population of NSMs by \citet{2019ApJ...880...23W}. A $\gamma$-ray survey with sensitivities of $10^{-8}$--$10^{-7}$ photons s$^{-1}$ cm$^{-2}$ or $10^{-14}$--$10^{-13}$ erg s$^{-1}$ cm$^{-2}$ in the 70--4000 keV band is expected to find emissions from at least one NSM remnant under the assumption of NSM rate of 30 Myr$^{-1}$. The feasibility of $\gamma$-ray missions to observe Galactic NSMs are also studied.

With the increase in the number of observed gravitational wave (GW) signals, detecting strongly lensed GWs by galaxies has become a real possibility. Lens galaxies also contain microlenses (e.g., stars and black holes), introducing further frequency-dependent modulations in the strongly lensed GW signal within the LIGO frequency range. The multiple lensed signals in a given lens system have different underlying macro-magnifications ($|\mu|$) and are located in varied microlens densities ($\Sigma_\bullet$), leading to different levels of microlensing distortions. This work quantifies the fraction of strong lens systems affected by microlensing using realistic mock observations. We study 50 quadruply imaged systems (quads) by generating 50 realizations for each lensed signal. However, our conclusions are equally valid for lensed signals in doubly imaged systems (doubles). The lensed signals studied here have $|\mu|\sim[0.5, 10]$ and $\Sigma_\bullet\sim[10, 10^3]~{\rm M}_\odot/{\rm pc^2}$. We find that the microlensing effects are more sensitive to the macro-magnification than the underlying microlens density, even if the latter exceeds $10^3~{\rm M}_\odot/{\rm pc^2}$. The mismatch between lensed and unlensed GW signals rarely exceeds $1\%$ for nearly all binary black hole sources in the total mass range [10 M$_\odot$, 200 M$_\odot$]. This implies that microlensing is not expected to affect the detection or the parameter estimation of such signals and does not pose any further challenges in identifying the different lensed counterparts when macro-magnification is ${\leq}10$. Such a magnification cut is expected to be satisfied by ${\sim}50\%$ of the detectable pairs in quads and ${\sim}90\%$ of the doubles in the fourth observing run of the LIGO-Virgo detector network.

The Universe may feature large-scale inhomogeneities beyond the standard paradigm, implying that statistical homogeneity and isotropy may be reached only on much larger scales than the usually assumed $\sim$100 Mpc. This means that we are not necessarily typical observers and that the Copernican principle could be recovered only on super-Hubble scales. Here, we do not assume the validity of the Copernican principle and let Cosmic Microwave Background, Baryon Acoustic Oscillations, type Ia supernovae, local $H_0$, cosmic chronometers, Compton y-distortion and kinetic Sunyaev-Zeldovich observations constrain the geometrical degrees of freedom of the local structure, which we parametrize via the $\Lambda$LTB model -- basically a non-linear radial perturbation of a FLRW metric. In order to quantify if a non-Copernican structure could explain away the Hubble tension, we pay careful attention to computing the Hubble constant in an inhomogeneous universe, and we adopt model selection via both the Bayes factor and the Akaike information criterion. Our results show that, while the $\Lambda$LTB model can successfully explain away the $H_0$ tension, it is favored with respect to the $\Lambda$CDM model only if one solely considers supernovae in the redshift range that is used to fit the Hubble constant, that is, $0.023<z<0.15$. If one considers all the supernova sample, then the $H_0$ tension is not solved and the support for the $\Lambda$LTB model vanishes. Combined with other data sets, this solution to the Hubble tension barely helps. Finally, we have reconstructed our local spacetime. We have found that data are best fit by a shallow void with $\delta_L \approx -0.04$ and $r^{\mathrm{out}}_L \approx 300$ Mpc, which, interestingly, lies on the border of the 95\% credible region relative to the standard model expectation.

We generalise the relativistic accretion thick disc model to the background of a spinning charged accelerating black hole described by the C-metric to study the effects of this background on the disc model. We show the properties of this accretion disc model and its dependence on the initial parameters. This background can be distinguishable from the Kerr space-time by analysing the observing features of accretion discs.

This talk reviews the scientific motivations, the potential difficulty and recent advances in cosmology using cluster number-counts in the X-ray band. Our forward modelling approach shows that many of the practical and conceptual shortcomings can now be overcome. We present recent results from the XMM-XXL survey. The next step is to apply artificial intelligence techniques on simulations. This allows us to bypass the unnecessarily complicated scaling relation formalism. The net gain is to significantly reduce the number of free parameters and to provide direct access both to the cosmological parameters and to truly physical ingredients, such as AGN feedback. In this way, we achieve cluster cosmology without explicit cluster mass calculation.

Using the extended halo-based group finder developed by Yang et al. (2021), which is able to deal with galaxies via spectroscopic and photometric redshifts simultaneously, we construct galaxy group and candidate protocluster catalogs in a wide redshift range ($0 < z < 6$) from the joint CFHT Large Area $U$-band Deep Survey (CLAUDS) and Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) deep data set. Based on a selection of 5,607,052 galaxies with $i$-band magnitude $m_{i} < 26$ and a sky coverage of $34.41\ {\rm deg}^2$, we identify a total of 2,232,134 groups, within which 402,947 groups have at least three member galaxies. We have visually checked and discussed the general properties of those richest groups at redshift $z>2.0$. By checking the galaxy number distributions within a $5-7\ h^{-1}\mathrm{Mpc}$ projected separation and a redshift difference $\Delta z \le 0.1$ around those richest groups at redshift $z>2$, we identified a list of 761, 343 and 43 protocluster candidates in the redshift bins $2\leq z<3$, $3\leq z<4$ and $z \geq 4$, respectively. In general, these catalogs of galaxy groups and protocluster candidates will provide useful environmental information in probing galaxy evolution along the cosmic time.

We study the cosmological constraints on the non-minimal scalar-curvature mixing $\xi R \phi^2$ in inflationary cosmology with a class of scalar field inflaton potentials (i) $V = V_0 \phi^pe^{-\lambda\phi}$, (ii) $V = V_0 (1 - \phi^{p})e^{-\lambda\phi}$ (iii) $V=V_0(1-\lambda\phi)^p$ and (iv) $V=V_0\frac{\alpha\phi^2}{1+\alpha\phi^2}$. We obtain constraints on the non-minimal coupling parameter $\xi$ for $\phi$ values of the potentials $V$ corresponding to potential parameters $\lambda,~p$ and $\alpha$ by comparing these with the Planck+WMAP data on spectral index of curvature perturbations generated during inflation. We find that in the parameters space all the above listed potentials can generate the e-fold number $N=40-60$ necessary for any successful inflation model. The scalar spectral index $n_s$ and the tensor to scalar ratio $r$ are found to lie within $3\sigma$ C.L of Planck 2018 data for the potentials (i) $V\propto \phi^pe^{\lambda\phi}$ with $\lambda=0, p=2$; $\lambda=0.1, p=2,~4$; $ \lambda =0.01, p=2,~4$; (ii) $V\propto (1-\phi^{p})e^{-\lambda\phi}$ for $\lambda =0.01, p=2,4$, (iii) $V\propto (1-\lambda\phi)^p$ for $\lambda=\pm 1,p=\pm 2$. We also find that the potential $V\propto \frac{\alpha\phi^2}{1+\alpha\phi^2}$ with $\alpha=1,2$ can produce the $n_s$ and $r$ values which are consistent with the WMAP3 data.

Linear cosmological observables can be used to probe elastic scattering of dark matter (DM) with baryons. Availability of high-precision data requires a critical reassessment of any assumptions that may impact the accuracy of constraints. All existing cosmological constraints of DM-baryon scattering assume that DM has a Maxwell-Boltzmann (MB) velocity distribution in order to compute heat- and momentum-exchange rates. This assumption is not always justified and does not allow for probing DM self-interactions in addition to its interactions with baryons. Lifting the MB assumption requires solving the full collisional Boltzmann equation (CBE), which is highly non-trivial. Earlier work proposed a more tractable Fokker-Planck (FP) approximation to the CBE, but its accuracy remained unknown. In this work, we numerically solve the exact CBE for the first time, in a homogeneous expanding background. We consider DM-baryon scattering cross-sections that are positive power-laws of relative velocity. We derive analytical expressions for the collision operator in the case of isotropic differential scattering cross-sections. We then solve the background CBE numerically and use our solution for the DM velocity distribution to compute the DM-baryon heat-exchange rate, which we compare against those obtained with the MB assumption and FP approximation. Over a broad range of DM-to-baryon mass ratios, we find that the FP approximation leads to a maximum error of 17%, significantly better than the up to 160% error introduced by the MB assumption. While our results strictly apply only to the background evolution, the accuracy of the FP approximation is likely to carry over to perturbations. This motivates its implementation into cosmological Boltzmann codes, where it can supersede the much less accurate MB assumption, and allow for a more general exploration of DM interactions with baryons and with itself.

By performing a set of numerical relativity simulations for the merger of binary neutron stars with several mass ratios, the properties of ejected matter in dynamical and post-merger phases are investigated for the cases in which the remnant massive neutron star collapses into a black hole in $\lesssim 20$ ms after the onset of merger. The dynamical mass ejection is investigated in three-dimensional general relativistic hydrodynamics simulations with an approximate neutrino-radiation transfer. The resulting post-merger systems are then mapped onto the axisymmetric ones and used as the initial conditions of axisymmetric long-term radiation-hydrodynamics simulations supposing that the effective viscosity should arise as a result of magnetohydrodynamical activity in the post-merger system. We show that the typical electron fraction of the dynamical ejecta is lower for the merger of more asymmetric binaries, and hence, heavier $r$-process nuclei are dominantly synthesized. We also show that the post-merger ejecta has only a mild neutron-richness, which results in the production of lighter $r$-process nuclei, irrespective of the binary mass ratio and that the ejecta mass is larger for the merger of more asymmetric binaries due to the larger disk mass. Thus, for the asymmetric merger case, the underproduction of lighter $r$-process nuclei can be compensated by the post-merger ejecta. As a result, by summing up both ejecta components, the solar residual $r$-process pattern is approximately reproduced irrespective of the binary mass ratio. Implications of our results associated with the mass distribution of compact NS binaries and the magnetar scenario of short gamma-ray bursts are discussed.

The properties that govern the production and escape of hydrogen ionizing photons (Lyman continuum; LyC with energies >13.6 eV) in star-forming galaxies are still poorly understood, but they are key to identifying and characterizing the sources that reionized the Universe. Here we empirically explore the relationship between the hardness of ionizing radiation and the LyC leakage in a large sample of low-$z$ star-forming galaxies from the recent HST Low-$z$ Lyman Continuum Survey. Using SDSS stacks and deep XShooter observations, we investigate the hardness of the ionizing spectra ($Q_{\rm He^+}/Q_{\rm H}$) between 54.4 eV (He$^{+}$) and 13.6 eV (H) from the optical recombination lines HeII 4686A and H$\beta$ 4861A for galaxies with LyC escape fractions spanning a wide range, $f_{\rm esc} \rm (LyC) \simeq 0 - 90\%$. We find that the observed intensity of HeII/H$\beta$ is primarily driven by variations in the metallicity, but is not correlated with LyC leakage. Both very strong ($<f_{\rm esc} \rm (LyC)> \simeq 0.5$) and non-leakers ($ < f_{\rm esc} \rm (LyC) > \simeq 0$) present similar observed intensities of HeII/H$\beta$ at comparable metallicity, between $\simeq 0.01$ and $\simeq 0.02$ for $12 + \log({\rm O/H}) > 8.0$ and $<8.0$, respectively. Our results demonstrate that $Q_{\rm He^+}/Q_{\rm H}$ does not correlate with $f_{\rm esc} \rm (LyC)$, which implies that strong LyC emitters do not show harder ionizing spectra than non-leakers at similar metallicity.

X-ray eclipse mapping is a promising modelling technique, capable of constraining the mass and/or radius of neutron stars (NSs) or black holes (BHs) in eclipsing binaries and probing any structure surrounding the companion star. In eclipsing systems, the binary inclination, $i$, and mass ratio, $q$ relate via the duration of totality, $t_{e}$. The degeneracy between $i$ and $q$ can then be broken through detailed modelling of the eclipse profile. Here we model the eclipses of the NS low-mass X-ray binary Swift J1858.6$-$0814 utilising archival NICER observations taken while the source was in outburst. Analogous to EXO 0748$-$676, we find evidence for irradiation driven ablation of the companion's surface by requiring a layer of stellar material to surround the companion star in our modelling. This material layer extends $\sim 7000 - 14000$ km from the companion's surface and is likely the cause of the extended, energy-dependent and asymmetric ingress and egress that we observe. Our fits return an inclination of $i \sim 81^{\circ}$ and a mass ratio $q \sim 0.14$. Using Kepler's law to relate the mass and radius of the companion star via the orbital period ($\sim$ 21.3 hrs), we subsequently determine the companion to have a low mass in the range $0.183 M_{\odot} \leq M_{cs} \leq 0.372 M_{\odot}$ and a large radius in the range $1.02 R_{\odot} \leq R_{cs} \leq 1.29 R_{\odot}$. Our results, combined with future radial velocity amplitudes measured from stellar absorption/emission lines, can place precise constraints on the component masses in this system.

In this paper we study four concrete models, based on no-scale supergravity with SU(2,1)/SU(2)\-$ \times$ U(1) symmetry. We modify either the K\"ahler potential or the superpotential using extra terms. In this scenario, the induced Gravitational Waves, are calculated to be detectable by the future space-based observations such as LISA, BBO and DECIGO. The models under study are interrelated, as they all yield the Starobinsky effective-like scalar potential in the unmodified case. We evaluate numerically the scalar power spectrum and the stochastic background of the Gravitational Waves, satisfying the observational Planck cosmological constraints for inflation. We find that the fine-tuning of the additional parameters in these models, is smaller if we require exclusively the production of Gravitational Waves, than in the case where in addition we produce Primordial Black Holes enough to account for the Dark Matter of the Universe.

We analyse the kinematical and dynamical state of the galaxy cluster RXCJ1230.7+3439, at z=0.332, using 93 new spectroscopic redshifts of galaxies acquired at the 3.6m TNG telescope and from SDSS DR16 public data. We find that RXCJ1230 appears as a clearly isolated peak in the redshift space, with a global line-of-sight velocity dispersion of $1004_{-122}^{+147}$ km s$^{-1}$, and showing a very complex structure with the presence of three subclusters. Our analyses confirm that the three substructures detected are in a pre-merger phase, where the main interaction takes place with the south-west subclump. We compute a velocity dispersion of $\sigma_\textrm{v} \sim 1000$ and $\sigma_\textrm{v} \sim 800$ km s$^{-1}$ for the main cluster and the south-west substructure, respectively. The central main body and south-west substructure differ by $\sim 870$ km s$^{-1}$ in the LOS velocity. From these data, we estimate a dynamical mass of $M_{200}= 9.0 \pm 1.5 \times 10^{14}$ M$_{\odot}$ and $4.4 \pm 3.3 \times 10^{14}$ M$_{\odot}$ for the RXCJ1230 main body and south-west clump, respectively, which reveals that the cluster will suffer a merging characterized by a 2:1 mass ratio impact. We solve a two-body problem for this interaction and find that the most likely solution suggests that the merging axis lies almost contained in the plane of the sky and the subcluster will fully interact in $\sim0.3$ Gyr. The comparison between the dynamical masses and those derived from X-ray data reveals a good agreement within errors (differences $\sim 15$\%), which suggests that the innermost regions ($<r_{500}$) of the galaxy clumps are almost in hydrostatical equilibrium. To summarize, RXCJ1230 is a young but also massive cluster in a pre-merging phase accreeting other galaxy systems from its environment.

We derive a new upper bound on the tensor-to-scalar ratio parameter $r$ using the frequentist profile likelihood method. We vary all the relevant cosmological parameters of the $\Lambda$CDM model, as well as the nuisance parameters. Unlike the Bayesian analysis using Markov Chain Monte Carlo (MCMC), our analysis is independent of the choice of priors. Using $Planck$ Public Release 4, BICEP/Keck Array 2018, $Planck$ CMB lensing, and BAO data, we find an upper limit of $r<0.037$ at 95% C.L., similar to the Bayesian MCMC result of $r<0.038$ for a flat prior on $r$ and a conditioned $Planck$ lowlEB covariance matrix.

Context. Component separation is the process to extract the sources of emission in astrophysical maps generally by taking into account multi-frequency information. Developing more reliable methods to perform component separation is crucial for future CMB experiments. Aims. We aim to develop a new method based on fully convolutional neural networks called the Cosmic microwave background Extraction Neural Network (CENN) in order to extract the CMB signal in total intensity. The frequencies used are the Planck channels 143, 217 and 353 GHz. We validate the network at all sky, and at three latitude intervals: lat1=0^{\circ}<b<5^{\circ}, lat2=5^{\circ}<b<30^{\circ} and lat3=30^{\circ}<b<90^{\circ}, without using any Galactic or point source masks. Methods. For training, we make realistic simulations in the form of patches of area 256 pixels, which contain the CMB, Dust, CIB and PS emissions, Sunyaev-Zel'dovich effect and the instrumental noise. After validate the network, we compare the power spectrum from input and output maps. We analyse the power spectrum from the residuals at each latitude interval and at all sky and we study the performance of our model dealing with high contamination at small scales. Results. We obtain a power spectrum with an error of 13{\pm}113 {\mu}K^2 for multipoles up to above 4000. For residuals, we obtain 7{\pm}25 {\mu}K^2 for lat1, 2{\pm}10 {\mu}K^2 for lat2 and 2{\pm}3 {\mu}K^2 for lat3. For all sky, we obtain 5{\pm}12 {\mu}K^2. We validate the network in a patch with strong contamination at small scales, obtaining an error of 50{\pm}120 {\mu}K^2 and residuals of 40{\pm}10 {\mu}K^2. Conclusions. Fully convolutional neural networks are promising methods to perform component separation in future CMB experiments. Particularly, CENN is reliable against different levels of contamination from Galactic and point source foregrounds at both large and small scales.

The stability of particles in the cosmic soup is an important property that can affect the cosmic evolution. In this work, we update the constraints on the decaying cold dark matter scenario, when the decay products are effectively massless. We assume, as a base case, that all of dark matter is unstable and it can decay on cosmological time scales. We then extend the analysis to include the scenario where only a fraction of dark matter is unstable, while the remaining part is composed of the standard, stable, dark matter. We consider observations of cosmological probes at linear scales, i.e., Planck 2018 cosmic microwave background temperature, polarization, and lensing measurements, along with geometrical information from baryon acoustic oscillation (BAO) measurements from SDSS DR7, BOSS DR12, eBOSS DR16 and 6dFGS, to derive conservative constraints on the dark matter decay rate. We consider these datasets separately, to assess the relative constraining power of each dataset, as well as together to asses the joint constraints. We find the most stringent upper limit on the decay rate of decaying cold dark matter particles to be $\Gamma_\mathrm{DCDM} < 0.129 \times 10^{-18}\,\mathrm{s}^{-1}$ (or, equivalently, the dark matter lifetime $\tau_\mathrm{DCDM} > 246$ Gyr) at 95\% C.L. for the combination of Planck primary anisotropies, lensing and BAO.

The jets launched by actively accreting black holes are capable of launching several of the massive (million or billion solar mass) molecular outflows observed in galaxies. These outflows could suppress or enhance star formation in galaxies. To investigate the stability of clouds capable to form stars in outflows, we modeled CO and HCO+ ALMA data of the galaxy IC5063, in which black-hole jets impact molecular clouds. Using a radiative transfer code that self-consistently performs astrochemical and thermal balance calculations based on the available gas heating sources, we found that mechanical heating and cosmic ray (CR) heating are fully capable of individually reproducing the data. In our best-fit model, CRs provide about 1/3rd of the dense gas heating at the radio lobes, emphasizing the role of this often neglected mechanism in heating the gas and potentially generating outflows. The gas temperature and density indicate that the jet passage leads to an increase of about 1 order of magnitude in the internal pressure Pi of molecular clouds (with Pi/k from 8*10^5 up to 7*10^6 K cm^-3), irrespective of the excitation mechanism. From the fluxes of [S II] and [N II] lines in VLT MUSE data, the external pressure Pe of molecular clouds increases in several regions enough to exceed Pi. This result leads us to conclude that we are observing the expansion of an ionized overpressurized cocoon that compresses molecular clouds and that could lead to their collapse. Some jet-impacted clouds, nonetheless, near pathways that the jet cleared have increased Pi and decreased Pe. They are likely to undergo evaporation of their outer layers. Part of the evaporated layers could mass load the outflow thanks to ram pressure from co-spatial ionized gas flows. The observed pressure changes thus suggest that both star formation enhancement and suppression could simultaneously occur.

Gravitational wave (GW) backgrounds of cosmological origin are expected to be nearly isotropic, with small anisotropies resembling those of the cosmic microwave background. We analyse the case of a scalar-induced GW background and clarify in the process the relation between two different approaches to calculating GW anisotropies. We focus on GW scenarios sourced by a significantly peaked scalar spectrum, which are frequently considered in the context of primordial black holes production. We show that the resulting GW anisotropies are characterised by a distinct frequency dependence. We explore the observational consequences concentrating on a GW background enhanced in the frequency band of space-based GW detectors. We study the detectability of the signal through both cross-correlations among different space-based GW detectors, and among GW and CMB experiments.

The Closeby Habitable Exoplanet Survey (CHES) mission is proposed to discover habitable-zone Earth-like planets of the nearby solar-type stars (~10pc away from our solar system) via micro-arcsecond relative astrometry. The major scientific goals of this mission are: to search for Earth Twins or the terrestrial planets in habitable zones orbiting 100 FGK nearby stars; further to conduct a comprehensive survey and extensively characterize the nearby planetary systems. CHES will offer the first direct measurements of true masses and inclinations of Earth Twins and super-Earths orbiting our neighbor stars based on micro-arcsecond astrometry from space. This will definitely enhance our understanding of the formation of diverse nearby planetary systems and the emergence of other worlds for solar-type stars, and finally to reflect the evolution of our own solar system. The primary payload is a high-quality mirror with a diameter of 1.2 m, a FOV of 0.44{\deg} x 0.44{\deg}. The coaxial three-reflection TMA system is designed, along with Mosaic CCDs and the laser metrology technique, to archive 1 {\mu}as astrometric precision at 500nm~900nm. CHES satellite operates at the Sun-Earth L2 point and observes the entire target stars for 5 years. CHES will produce fruitful achievements not only in the Earth-like planets but also for cosmology, dark matter and black holes, which helps us better understand the philosophy, life and planet.

We present a new approach to studies of bubble dynamics in fluids. Relying on particle-based simulations, this method is general and suitable for cases where the commonly used perfect fluid description fails. We study expanding true vacuum bubbles surrounded by free or self-interacting particles and quantify how self-interactions affect the terminal bubble wall velocity. We find that, for sufficiently strongly self-interacting fluids, local thermal equilibrium is maintained around the bubble wall and the fluid profile is similar to that obtained with the perfect fluid description.

The scale-dependent bias effect on the galaxy power spectrum is a very promising probe of the local primordial non-Gaussianity (PNG) parameter $f_{\rm NL}$, but the amplitude of the effect is proportional to $f_{\rm NL}b_{\phi}$, where $b_{\phi}$ is the linear PNG galaxy bias parameter. Our knowledge of $b_{\phi}$ is currently very limited, yet nearly all existing $f_{\rm NL}$ constraints and forecasts assume precise knowledge for it. Here, we use the BOSS DR12 galaxy power spectrum to illustrate how our uncertain knowledge of $b_{\phi}$ currently prevents us from constraining $f_{\rm NL}$ with a given statistical precision $\sigma_{f_{\rm NL}}$. Assuming different fixed choices for the relation between $b_{\phi}$ and the linear density bias $b_1$, we find that $\sigma_{f_{\rm NL}}$ can vary by as much as an order of magnitude. Our strongest bound is $f_{\rm NL} = 16 \pm 16\ (1\sigma)$, while the loosest is $f_{\rm NL} = 230 \pm 226\ (1\sigma)$ for the same BOSS data. The impact of $b_{\phi}$ can be especially pronounced because it can be close to zero. We also show how marginalizing over $b_{\phi}$ with wide priors is not conservative, and leads in fact to biased constraints through parameter space projection effects. Independently of galaxy bias assumptions, the scale-dependent bias effect can only be used to detect $f_{\rm NL} \neq 0$ by constraining the product $f_{\rm NL}b_{\phi}$, but the error bar $\sigma_{f_{\rm NL}}$ remains undetermined and the results cannot be compared with the CMB; we find $f_{\rm NL}b_{\phi} \neq 0$ with $1.6\sigma$ significance. We also comment on why these issues are important for analyses with the galaxy bispectrum. Our results strongly motivate simulation-based research programs aimed at robust theoretical priors for the $b_{\phi}$ parameter, without which we may never be able to competitively constrain $f_{\rm NL}$ using galaxy data.

One of the fundamental factors regulating the evolution of galaxies is stellar feedback. However, we still do not have strong observational constraints on the relative importance of the different feedback mechanisms (e.g. radiation, ionised gas pressure, stellar winds) in driving HII region evolution and molecular cloud disruption. In this letter, we constrain the relative importance of the various feedback mechanisms from young massive star populations by resolving HII regions across the disk of the nearby star-forming galaxy NGC 1672. We combine measurements of ionised gas nebular lines obtained by PHANGS-MUSE, with high-resolution imaging from the HST in both the narrow-band H{\alpha} and broad-band filters. We identify a sample of 40 isolated, compact HII regions in the HST H{\alpha} image, for which we measure the sizes that were previously unresolved in seeing-limited ground-based observations. Additionally, we identify the ionisation source(s) for each HII region from catalogues produced as part of the PHANGS-HST survey. We find that the HII regions investigated are mildly dominated by thermal or wind pressure, yet their elevation above the radiation pressure is within the expected uncertainty range. We see that radiation pressure provides a substantially higher contribution to the total pressure than previously found in the literature over similar size scales. In general, we find higher pressures within more compact HII regions, which is driven by the inherent size scaling relations of each pressure term, albeit with significant scatter introduced by the variation in the stellar population properties (e.g. luminosity, mass, age, metallicity). For nearby galaxies, here we provide a promising approach that could yield the statistics required to map out how the importance of different stellar feedback mechanisms evolve over the lifetime of an HII region.

In this paper, we present the first observation of optical emission of a downward-directed terrestrial gamma ray flash (TGF). The optical emission was observed by a high-speed video camera Phantom v2012 in conjunction with the Telescope Array (TA) surface detector, lightning mapping array, interferrometer, fast antenna, and the national lightning detection network. The suite of gamma and lightning instruments, timing resolution, and source proximity offers us an unprecedented look at the TGF phenomena. On September 11 of 2021 we observed a storm above the TA detector. The storm resulted in six extremely energetic TGF events that were produced by flashes with return stroke peak currents up to 223 kA. The observed TGFs were found to correlate directly to the initial burst pulse signal of the lightning flash while producing an intense optical signature. Results from this study allow us to furthers the understanding regarding the initiation mechanism of TGFs.

Dense clouds of neutrinos and antineutrinos can exhibit fast collective flavor oscillations. Previously, in Phys. Rev. Lett. 126 (2021) 061302, we proposed that such flavor oscillations lead to depolarization, i.e., an irreversible mixing of the flavors, whose extent depends on the initial momentum distributions of the different flavors. In this paper, we elaborate and extend this proposal, and compare it with related results in the literature. We present an accurate analytical estimate for the lower resting point of the fast flavor pendulum and underline the relaxation mechanisms, i.e., transverse relaxation, multipole cascade, and mixing of flavor-waves, that cause it to settle down. We estimate the extent of depolarization, its dependence on momentum and net lepton asymmetry, and its generalization to three flavors. Finally, we prescribe approximate analytical recipes for the depolarized distributions and fluxes that can be used in supernova/nucleosynthesis simulations and supernova neutrino phenomenology.

Detecting gravitational waves from coalescing compact binaries allows us to explore the dynamical, nonlinear regime of general relativity and constrain modifications to it. Some of the gravitational-wave events observed by the LIGO-Virgo Collaboration have sufficiently high signal-to-noise ratio in the merger, allowing us to probe the relaxation of the remnant black hole to its final, stationary state - the so-called black-hole ringdown, which is characterized by a set of quasinormal modes. Can we use the ringdown to constrain deviations from general relativity, as predicted by several of its contenders? Here, we address this question by using an inspiral-merger-ringdown waveform model in the effective-one-body formalism, augmented with a parametrization of the ringdown based on an expansion in the final black hole's spin. We give a prescription on how to include in this waveform model, the quasinormal mode frequencies calculated on a theory-by-theory basis. In particular, we focus on theories that modify general relativity by higher-order curvature corrections, namely, Einstein-dilaton-Gauss-Bonnet (EdGB), dynamical Chern-Simons (dCS) theories, and cubic- and quartic-order effective-field-theories (EFT) of general relativity. We use this parametrized waveform model to measure the ringdown properties of the two loudests ringdown signals observed so far, GW150914 and GW200129. We find that while EdGB theory cannot be constrained with these events, we can place upper bounds on the fundamental length-scale of cubic- ($\ell_{\rm cEFT} \leqslant 38.2$ km) and quartic-order ($\ell_{\rm qEFT} \leqslant 51.3$ km) EFTs of general relativity, and of dCS gravity ($\ell_{\rm dCS} \leqslant 38.7$ km). The latter result is a concrete example of a theory presently unconstrained by inspiral-only analyses which, however, can be constrained by merger-ringdown studies with current gravitational-wave data.

If Dark Matter halos possess the gravitational equivalent of an intrinsic magnetic spin, a formal analogy exists between the low redshift behaviour of the Cosmic Web in a flat FLRW background, and a crystal of spins submerged in a thermal reservoir with temperature $T \propto H(t)$. We argue that, within the use of the Bianchi type IX geometry to describe the gravitational collapse of matter inhomogeneities, the spins are nothing but the heritage of its underlying $SU(2)$ symmetry. Therefore, just like electrons in quantum mechanics, these structures may have spin independently from their orbital angular momentum. We explore the phenomenological implications on cosmological scales of a possible late time phase transition of the Cosmic Web towards (the gravitational equivalent of) a ferromagnetic state, described qualitatively using the Ising model in the mean field approximation.

We analytically investigate a new family of horizonless compact objects in vector-tensor theories of gravity, called ultracompact vector stars. They are sourced by a vector condensate, induced by a non-minimal coupling with gravity. They can be as compact as black holes, thanks to their internal anisotropic stress. In the spherically symmetric case their interior resembles an isothermal sphere, with a singularity that can be resolved by tuning the available integration constants. The star interior smoothly matches to an exterior Schwarzschild geometry, with no need of extra energy-momentum tensor at the star surface. We analyse the behaviour of geodesics within the star interior, where stable circular orbits are allowed, as well as trajectories crossing in both ways the star surface. We analytically study stationary deformations of the vector field and of the geometry, which break spherical symmetry, and whose features depend on the vector-tensor theory we consider. We introduce and determine the vector magnetic susceptibility as a probe of the star properties, and we analyze how the rate of rotation of the star is affected by the vector charges.

Because the Klein-Gordon and Proca equations involve $\hbar$, they describe quantum fields. Their solutions, however, may be treated as classical if their typical action obeys $S^{\rm typical}\gg \hbar$. This is possible due to their bosonic nature, allowing states with many particles. We show, by generic arguments, that the typical action for such bosonic stars is ${\mathcal{S}^{\rm typical}}/{\hbar}\gtrsim \left({M^{\rm max}}/{M_{\rm Pl}}\right)^2\sim 10^{76}\left({M^{\rm max}}/{M_\odot}\right)^2$, where $M^{\rm max}$ is the maximal bosonic star mass of the particular model and $M_{\rm Pl}$ is the Planck mass. Thus, for models allowing $M^{\rm max}\gg M_{\rm Pl}$ and for solutions with mass $\sim M^{\rm max}$, the classical treatment is legitimate, which includes masses in the astrophysical interesting range $\gtrsim M_\odot$.

The spectra of the relic gravitons are customarily normalized in the low-frequency domain where the signal of the concordance paradigm is expected to peak and this is why their contribution to the temperature and polarization anisotropies of the microwave background is only described by the tensor to scalar ratio. If the consistency relations are broken, the same strategy is accomplished by introducing the tensor spectral index as a further independent parameter. When the dominant component of the spectral energy density is distributed for frequencies much larger than the aHz, the logic behind this conventional approach is much less compelling. The improved bounds in the audio band and the current data from the pulsar timing arrays in the nHz region motivate a new strategy for the absolute normalization of the cosmic background of relic gravitons. After introducing a general four-dimensional action for the analysis of the relic gravitons the new approach is illustrated in the case of conventional and unconventional inflationary models.

The neutrino interaction length scales with energy, and becomes comparable to Earth's diameter above 10's of TeV energies. Over terrestrial distances, the tau's short lifetime leads to an energetic regenerated tau neutrino flux, tau neutrino to tau to tau neutrino, within the Earth. The next generation of neutrino experiments aim to detect ultra-high energy neutrinos. Many of them rely on detecting either the regenerated tau neutrino, or a tau decay shower. Both of these signatures can be affected by the polarization of the tau through the energy distribution of the secondary particles produced from the tau's decay. While taus produced in weak interactions are nearly 100 percent polarized, it is expected that taus experience some depolarization due to electromagnetic interactions in the Earth. In this paper, for the first time we quantify the depolarization of taus in electromagnetic energy loss. We find that tau depolarization has only small effects on the final energy of tau neutrinos or taus produced by high energy tau neutrinos incident on the Earth. Tau depolarization can be directly implemented in Monte Carlo simulations such as nuPyProp and TauRunner.

Gravitational waves (GW) creates correlations in the arrival times of pulses from different pulsars. The expected correlation $\mu(\gamma)$ as a function of the angle $\gamma$ between the directions to two pulsars was calculated by Hellings and Downs, for an isotropic and unpolarized GW background with no long-range correlations. One may ask: given a set of noise-free observations, are they consistent with that expectation? To answer this, we first calculate the expected variance $\sigma^2(\gamma)$ in the correlation (as pulsar pairs with fixed separation angle $\gamma$ are swept around the sky) for a single unpolarized GW source. We then use this to derive a simple analytic expression for the "cosmic variance" arising from a set of discrete point sources uniformly scattered in space. The overall scale of the fractional fluctuation in the correlation is the ratio of the distance to the closest (typical) source to the distance to the most distant (typical) source, which in our universe is probably around 1%. We then compute the mean and variance of the Hellings and Downs correlation for a general polarized point source. The mean follows the standard Hellings and Downs curve, and the variance is the sum of an unpolarized term, a polarized term, and a cross term, for which we give simple closed analytic forms. As examples, we compute the mean and variance of the correlation for a circular binary inspiral signal, both with and without the "pulsar terms" that are often neglected. The means are identical, but the inclusion of the pulsar terms increases the variance by about a factor of four and changes the relative weights of the three variance terms. This shows that measurements of the cosmic variance might provide further information about the nature of GW sources.