Papers for Monday, Mar 06 2023

Blazars are among the most powerful accelerators and are expected to produce a bright TeV $\gamma$-ray flux. However, TeV $\gamma$-rays are attenuated by interactions with intergalactic radiation before reaching Earth. These interactions produce cascades that transfer the TeV power into the GeV band, powering both extended halos around bright sources and a large contribution to the isotropic $\gamma$-ray background (IGRB). Using state-of-the-art blazar models and recent IGRB measurements, we rule out models where blazars effectively transfer their TeV power into GeV $\gamma$-rays. Three possible solutions include: (1) strong spectral cuts on bright blazars, which are at odds with local blazar observations, (2) collective plasma effects that can prevent the development of blazar cascades, the effectiveness of which is debated, (3) an increase in the effective $\gamma$-ray opacity from axion-like particles.

The problem of missing baryons in the local universe remains an open question. One propose alternative is that at low redshift missing baryons are in the form of the Warm Hot Intergalactic Medium (WHIM). In order to test this idea, we present a detailed analysis of X-ray high-resolution spectra of six extragalactic sources, Mrk 421, 1ES 1028+511, 1ES 1553+113, H2356-309, PKS 0558-504 and PG 1116+215, obtained with the XMM-Newton Reflection Grating Spectrometer to search for signals of WHIM and/or circumgalactic medium (CGM) X-ray absorbing gas. We fit the X-ray absorption with the IONeq model, allowing us to take into account the presence of X-ray spectral features due to the multiphase component of the local ISM. An additional IONeq component is included to model the WHIM absorption, instead of the traditional Gaussian absorption line modeling. We found no statistical improvement in the fits when including such component in any of the sources, concluding that we can safely reject a successful detection of WHIM absorbers towards these lines of sights. Our simulation shows that the presence of the multiphase ISM absorption features prevents detection of low-redshift WHIM absorption features in the 17 A spectral region for moderate exposures using high-resolution spectra.

We build a statistical framework to infer the global properties of the satellite system of the Andromeda galaxy (M31) from the properties of individual dwarf galaxies located in the Pan-Andromeda Archaelogical Survey (PAndAS) and the previously determined completeness of the survey. Using forward modeling, we infer the slope of the luminosity function of the satellite system, the slope of its spatial density distribution, and the size-luminosity relation followed by the dwarf galaxies. We find that the slope of the luminosity function is $\beta=-1.5\pm0.1$. Combined with the spatial density profile, it implies that, when accounting for survey incompleteness, M31 hosts $92_{-26}^{+19}$ dwarf galaxies with $M_\textrm{V}<-5.5$ and a sky-projected distance from M31 between 30 and 300kpc. We conclude that many faint or distant dwarf galaxies remain to be discovered around Andromeda, especially outside the PAndAS footprint. Finally, we use our model to test if the higher number of satellites situated in the hemisphere facing the Milky Way could be explained simply by the detection limits of dwarf galaxy searches. We rule this out at $>99.9\%$ confidence and conclude that this anisotropy is an intrinsic feature of the M31 satellite system. The statistical framework we present here is a powerful tool to robustly constrain the properties of a satellite system and compare those across hosts, especially considering the upcoming start of the Euclid or Rubin large photometric surveys that are expected to uncover a large number of dwarf galaxies in the Local Volume.

We present an update to Via Machinae, an automated stellar stream-finding algorithm based on the deep learning anomaly detector ANODE. Via Machinae identifies stellar streams within Gaia, using only angular positions, proper motions, and photometry, without reference to a model of the Milky Way potential for orbit integration or stellar distances. This new version, Via Machinae 2.0, includes many improvements and refinements to nearly every step of the algorithm, that altogether result in more robust and visually distinct stream candidates than our original formulation. In this work, we also provide a quantitative estimate of the false positive rate of Via Machinae 2.0 by applying it to a simulated Gaia-mock catalog based on Galaxia, a smooth model of the Milky Way that does not contain substructure or stellar streams. Finally, we perform the first full-sky search for stellar streams with Via Machinae 2.0, identifying 102 streams at high significance within the Gaia Data Release 2, of which only 10 have been previously identified. While follow-up observations for further confirmation are required, taking into account the false positive rate presented in this work, we expect approximately 90 of these stream candidates to correspond to real stellar structures.

A new model grid containing 228,016 synthetic red supergiant explosions (Type II supernovae) is introduced. Time evolution of spectral energy distributions from 1 A to 50,000 A (100 frequency bins in a log scale) is computed at each time step up to 500 days after explosion in each model. We provide light curves for the filters of the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST), Zwicky Transient Facility (ZTF), Sloan Digital Sky Servey (SDSS), and the Neil Gehrels Swift Observatory, but light curves for any photometric filters can be constructed by convolving any filter response functions to the synthetic spectral energy distributions. We also provide bolometric light curves and photosphere information such as photospheric velocity evolution. The parameter space covered by the model grid is five progenitor masses (10, 12, 14, 16, and 18 Msun at the zero-age main sequence, solar metallicity), ten explosion energies (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 x 10^51 erg), nine 56Ni masses (0.001, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, and 0.3 Msun), nine mass-loss rates (1e-5.0, 1e-4.5, 1e-4.0, 1e-3.5, 1e-3.0, 1e-2.5, 1e-2.0, 1e-1.5, and 1e-1.0 Msun/yr with a wind velocity of 10 km/s), six circumstellar matter radii (1, 2, 4, 6, 8, and 10 x 10^14 cm), and ten circumstellar structures (beta = 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0). 56Ni is assumed to be uniformly mixed up to the half mass of a hydrogen-rich envelope. This model grid can be a base for rapid characterizations of Type II supernovae with sparse photometric sampling expected in LSST through a Bayesian approach, for example. The model grid is available at https://doi.org/10.5061/dryad.pnvx0k6sj.

We selected 35 low-mass SFGs (7.8<log(M$_*$/M$_{\odot}$)<10.2) from deep spectroscopic surveys based on their CIII]1908 emission. We used follow-up NIR observations to examine their rest-optical emission lines and identify ionized outflow signatures through broad emission wings detected after Gaussian modeling of [OIII]4959,5007 profiles. We characterized the galaxies' gas-phase metallicity and carbon-to-oxygen (C/O) abundance using a Te-based method via the OIII]1666/[OIII]5007 ratio and photoionization models. We find line ratios and rest-frame EWs characteristic of high-ionization conditions powered by massive stars. Our sample displays mean rest-frame EW([OIII]5007)~560\r{A} while 20% of them show EW([OIII]4959,5007)>1000\r{A} and EW(CIII])>5\r{A}, closely resembling those now seen in EoR galaxies with JWST. We find low gas-phase metallicities 12+log(O/H)~7.4-8.5 and C/O abundances from 21%-173% solar, with an apparent increasing trend with metallicity. From our [OIII]4959,5007 profile modeling, we find that 65% of our sample shows an outflow component, which is shifted relative to the ionized gas systemic velocity, with mean $v_{max}$~280 km/s which correlates with the $\Sigma_{SFR}$. We find that the mass-loading factor $\mu$ of our sample is typically lower than in more massive galaxies from literature but higher than in typical local dwarf galaxies. In the stellar mass range covered, we find that $\mu$ increases with $\Sigma_{SFR}$ thus suggesting that for a given stellar mass, denser starbursts in low-mass galaxies produce stronger outflows. Thus, galaxies with higher $\mu$ tend to have lower metallicity, more intense bursts, and higher EW([OIII]5007). Our results complement the picture drawn by similar studies at lower redshift, suggesting that the removal of ionized gas in low-mass SFGs driven by stellar feedback is regulated by their stellar mass and by their $\Sigma_{SFR}$.

We study accretion disk-corona connection in Seyfert 1 galaxies using simultaneous UV/X-ray observations of NGC 4593 (July 14-18, 2016) and NGC 7469 (October 15-19, 2017) performed with AstroSat. We use the X-ray (0.5-7.0 keV) data acquired with the Soft X-ray Telescope (SXT) and the UV (FUV: 130-180 nm, NUV: 200-300 nm) data obtained with the Ultra-Violet Imaging Telescope (UVIT). We also use the contemporaneous Swift observations of NGC 4593 and demonstrate AstroSat's capability for X-ray/UV correlation studies. We performed UV/X-ray cross-correlation analysis using the Interpolated and the Discrete Cross-Correlation Functions and found similar results. In the case of NGC 4593, we found that the variations in the X-rays lead to those in the FUV and NUV bands by ~ 38 ks and ~ 44 ks, respectively. These UV lags favour the disk reprocessing model, they are consistent with the previous results within uncertainties. In contrast, we found an opposite trend in NGC 7469 where the soft X-ray variations lag those in the FUV and NUV bands by ~ 41 ks and ~ 49 ks, respectively. The hard lags in NGC 7469 favour the Thermal Comptonization model. Our results may provide direct observational evidence for the variable intrinsic UV emission from the accretion disk which acts as the seed for thermal Comptonization in a hot corona in a lamp-post like geometry. The non-detection of disk reverberation photons in NGC 7469, using AstroSat data, is most likely due to a high accretion rate resulting in a hot accretion disk and large intrinsic emission.

We present a multi-epoch spectroscopic study of LkCa 4, a heavily spotted non-accreting T Tauri star. Using SpeX at NASA's Infrared Telescope Facility (IRTF), 12 spectra were collected over five consecutive nights, spanning $\approx$ 1.5 stellar rotations. Using the IRTF SpeX Spectral Library, we constructed empirical composite models of spotted stars by combining a warmer (photosphere) standard star spectrum with a cooler (spot) standard weighted by the spot filling factor, $f_{spot}$. The best-fit models spanned two photospheric component temperatures, $T_{phot}$ = 4100 K (K7V) and 4400 K (K5V), and one spot component temperature, $T_{spot}$ = 3060 K (M5V) with an $A_V$ of 0.3. We find values of $f_{spot}$ to vary between 0.77 and 0.94 with an average uncertainty of $\sim$0.04. The variability of $f_{spot}$ is periodic and correlates with its 3.374 day rotational period. Using a mean value for $f^{mean}_{spot}$ to represent the total spot coverage, we calculated spot corrected values for $T_{eff}$ and $L_\star$. Placing these values alongside evolutionary models developed for heavily spotted young stars, we infer mass and age ranges of 0.45-0.6 $M_\odot$ and 0.50-1.25 Myr, respectively. These inferred values represent a twofold increase in the mass and a twofold decrease in the age as compared to standard evolutionary models. Such a result highlights the need for constraining the contributions of cool and warm regions of young stellar atmospheres when estimating $T_{eff}$ and $L_\star$ to infer masses and ages as well as the necessity for models to account for the effects of these regions on the early evolution of low-mass stars.

NGC 6819 is an open cluster of age 2.4 Gyr that was in the NASA Kepler spacecraft field of view from 2009 to 2013. The central part of the cluster was observed in a 200 x 200 pixel `superstamp' during these four years in 30-minute cadence photometry, providing a unique long time-series high-precision data set. The cluster contains 'blue straggler' stars, i.e., stars on the main sequence above the cluster turnoff that should have left the main sequence to become red giants. We present light curves and pulsation frequency analyses derived from custom photometric reductions for five confirmed cluster members--four blue stragglers and one star near the main-sequence turnoff. Two of these stars show a rich spectrum of $\delta$ Scuti pulsation modes, with 236 and 124 significant frequencies identified, respectively, while two stars show mainly low-frequency modes, characteristic of $\gamma$ Doradus variable stars. The fifth star, a known active x-ray binary, shows only several harmonics of two main frequencies. For the two $\delta$ Scuti stars, we use a frequency separation--mean-density relation to estimate mean density, and then use this value along with effective temperature to derive stellar mass and radius. For the two stars showing low frequencies, we searched for period-spacing sequences that may be representative of gravity-mode or Rossby-mode sequences, but found no clear sequences. The common age for the cluster members, considered along with the frequencies, will provide valuable constraints for asteroseismic analyses, and may shed light on the origin of the blue stragglers.

We present the spectral and spatial evolution of H$_2$O masers associated with the water fountain source IRAS 18043$-$2116 found in the observations with the Nobeyama 45 m telescope and the Australia Telescope Compact Array. We have found new highest velocity components of the H$_2$O masers (at the red-shifted side $V_{\rm LSR}\simeq376~\mathrm{km~s}^{-1}$ and at the blue-shifted side $V_{\rm LSR}\simeq$ $-165~\mathrm{km~s}^{-1}$), and the resulting velocity spread of $\simeq 540~\mathrm{km~s}^{-1}$ breaks the speed record of fast jets/outflows in this type of sources. The locations of those components have offsets from the axis joining the two major maser clusters, indicating a large opening angle of the outflow ($\sim60^{\circ}$). The evolution of the maser cluster separation of $\sim$2.9 mas yr$^{-1}$ and the compact ($\sim0.''2$) CO emission source mapped with the Atacama Large Millimeter-submillimeter Array suggest a very short ($\sim$30 yr) timescale of the outflow. We also confirmed the increase in the flux density of the 22 GHz continuum source. The properties of the jet and the continuum sources and their possible evolution in the transition to the planetary nebula phase are further discussed.

We have determined stellar mass functions of 120 Milky Way globular clusters and massive LMC/SMC star clusters based on a comparison of archival Hubble Space Telescope photometry with a large grid of direct N-body simulations. We find a strong correlation of the global mass function slopes of star clusters with both their internal relaxation times as well as their lifetimes. Once dynamical effects are being accounted for, the mass functions of most star clusters are compatible with an initial mass function described by a broken power-law distribution $N(m) \sim m^\alpha$ with break masses at 0.4 M$_\odot$ and 1.0 M$_\odot$ and mass function slopes of $\alpha_{Low}=-0.3$ for stars with masses $m<0.4$ M$_\odot$, $\alpha_{High}=-2.30$ for stars with $m>1.0$ M$_\odot$ and $\alpha_{Med}=-1.65$ for intermediate-mass stars. Alternatively, a log-normal mass function with a characteristic mass $\log M_C = -0.36$ and width $\sigma_C=0.28$ for low-mass stars and a power-law mass function for stars with $m>1$ M$_\odot$ also fits our data. We do not find a significant environmental dependency of the initial mass function with either cluster mass, density, global velocity dispersion or metallicity. Our results lead to a larger fraction of high-mass stars in globular clusters compared to canonical Kroupa/Chabrier mass functions, increasing the efficiency of self-enrichment in clusters and helping to alleviate the mass budget problem of multiple stellar populations in globular clusters. By comparing our results with direct N-body simulations we finally find that only simulations in which most black holes are ejected by natal birth kicks correctly reproduce the observed correlations.

The distribution of stars and stellar remnants (white dwarfs, neutron stars, black holes) within globular clusters holds clues about their formation and long-term evolution, with important implications for their initial mass function (IMF) and the formation of black hole mergers. In this work, we present best-fitting multimass models for 37 Milky Way globular clusters, which were inferred from various datasets, including proper motions from Gaia EDR3 and HST, line-of-sight velocities from ground-based spectroscopy and deep stellar mass functions from HST. We use metallicity dependent stellar evolution recipes to obtain present-day mass functions of stars and remnants from the IMF. By dynamically probing the present-day mass function of all objects in a cluster, including the mass distribution of remnants, these models allow us to explore in detail the stellar (initial) mass functions of a large sample of Milky Way GCs. We show that, while the low-mass mass function slopes are strongly dependent on the dynamical age of the clusters, the high-mass slope ($\alpha_3; m > 1 M_\odot$) is not, indicating that the mass function in this regime has generally been less affected by dynamical mass loss. Examination of this high-mass mass function slope suggests an IMF in this mass regime consistent with a Salpeter IMF is required to reproduce the observations. This high-mass IMF is incompatible with a top-heavy IMF, as has been proposed recently. Finally, no significant correlation is found between the high-mass IMF slope and cluster metallicity.

We present an overview of the ASTRO-H (Hitomi) Soft X-Ray Spectrometer (SXS) and the X-Ray Imaging and Spectrometer Mission (XRISM) {\it Resolve} spectrometer. In each, a 36-pixel X-ray micro-calorimeter array operated at 50 mK covers a $3 \times 3$ arc-minute field of view. The instruments are designed to achieve an energy resolution of better than 7 eV over the 0.3 -- 12 keV energy range and operate for more than 3 years in orbit. Actually, the SXS achieved the energy resolution of $\sim$5 eV in orbit, but it was lost after only a month of operation due to the loss of spacecraft attitude control. For the recovery mission, XRISM will be equipped with the {\it Resolve} spectrometer which has mostly the same design as SXS and is expected to have the same in-flight performance.

We present a statistical study of 180 dust continuum sources identified in 33 massive cluster fields by the ALMA Lensing Cluster Survey (ALCS) over a total of 133 arcmin$^{2}$ area, homogeneously observed at 1.2 mm. ALCS enables us to detect extremely faint mm sources by lensing magnification, including near-infrared (NIR) dark objects showing no counterparts in existing {\it Hubble Space Telescope} and {\it Spitzer} images. The dust continuum sources belong to a blind sample ($N=141$) with S/N $\gtrsim$ 5.0 (a purity of $>$ 0.99) or a secondary sample ($N=39$) with S/N= $4.0-5.0$ screened by priors. With the blind sample, we securely derive 1.2-mm number counts down to $\sim7$ $\mu$Jy, and find that the total integrated 1.2mm flux is 20.7$^{+8.5}_{-6.5}$ Jy deg$^{-2}$, resolving $\simeq$ 80 % of the cosmic infrared background light. The resolved fraction varies by a factor of $0.6-1.1$ due to the completeness correction depending on the spatial size of the mm emission. We also derive infrared (IR) luminosity functions (LFs) at $z=0.6-7.5$ with the $1/V_{\rm max}$ method, finding the redshift evolution of IR LFs characterized by positive luminosity and negative density evolution. The total (=UV+IR) cosmic star-formation rate density (SFRD) at $z>4$ is estimated to be $161^{+25}_{-21}$ % of the established measurements, which were almost exclusively based on optical$-$NIR surveys. Although our general understanding of the cosmic SFRD is unlikely to change beyond a factor of 2, these results add to the weight of evidence for an additional ($\approx 60$ %) SFRD component contributed by the faint-mm population, including NIR dark objects.

The power spectrum of magnetic-field fluctuations in the fast solar wind ($V_{\rm SW}> 500 \mbox{ km} \mbox{ s}^{-1}$) at magnetohydrodynamic (MHD) scales is characterized by two different power laws on either side of a break frequency $f_{\rm b}$. The low-frequency range at frequencies $f$ smaller than $f_{\rm b}$ is often viewed as the energy reservoir that feeds the turbulent cascade at $f>f_{\rm b}$. At heliocentric distances $r$ exceeding $60$ solar radii ($R_{\rm s}$), the power spectrum often has a $1/f$ scaling at $f<f_{\rm b}$; i.e., the spectral index is close to $-1$. In this study, measurements from the encounter $10$ of ${Parker Solar Probe}$ (PSP) with the Sun are used to investigate the evolution of the magnetic-field power spectrum at $f< f_{\rm b}$ at $r<60 R_{\rm s}$ during a fast radial scan of a single fast-solar-wind stream. We find that the spectral index in the low-frequency part of the spectrum decreases from approximately $-0.61$ to $-0.94$ as $r$ increases from $17.4 $ to $45.7$ solar radii. Our results suggest that the $1/f $ spectrum that is often seen at large $r$ in the fast solar wind is not produced at the Sun, but instead develops dynamically as the wind expands outward from the corona into the interplanetary medium.

Some active asteroids have been proposed to be the result of impact events. Because active asteroids are generally discovered serendipitously only after their tail formation, the process of the impact ejecta evolving into a tail has never been directly observed. NASA's Double Asteroid Redirection Test (DART) mission, apart from having successfully changed the orbital period of Dimorphos, demonstrated the activation process of an asteroid from an impact under precisely known impact conditions. Here we report the observations of the DART impact ejecta with the Hubble Space Telescope (HST) from impact time T+15 minutes to T+18.5 days at spatial resolutions of ~2.1 km per pixel. Our observations reveal a complex evolution of ejecta, which is first dominated by the gravitational interaction between the Didymos binary system and the ejected dust and later by solar radiation pressure. The lowest-speed ejecta dispersed via a sustained tail that displayed a consistent morphology with previously observed asteroid tails thought to be produced by impact. The ejecta evolution following DART's controlled impact experiment thus provides a framework for understanding the fundamental mechanisms acting on asteroids disrupted by natural impact.

The possibilities of organizing an observation service for solar activity in order to provide space weather forecasting are considered. The most promising at this stage is the creation of a ground-based observation network. Such a network should include solar magnetographs that provide observation of large-scale magnetic fields of the Sun, and patrol optical telescopes designed to detect coronal mass ejections and solar flares. The data of magnetographic observations provide an assessment of recurrent solar winds. Patrol telescopes operating in continuous mode allow detecting the moments of eruption and determining the parameters of coronal mass ejections at the initial stage of acceleration. The network service can be supplemented with other types of observations in the radio and optical bands. The paper considers the composition of observational tools, as well as methods and models for forecasting.

In response to a recent criticism, appeared in arXiv:2303.00341, we argue that the standard scenario to form primordial black holes in the early universe based on a phase of ultra-slow-roll in single-field inflation is not ruled out.

A star's rotation rate is difficult to estimate without surface inhomogeneities such as dark or bright spots. This paper presents asteroseismic results to determine the rotation rates of $\delta$ Sct-type pulsating primary stars in two eclipsing binary systems, AB Cas and OO Dra. After removing the binarity-induced light variations from the archival TESS data and carefully examining the combination frequencies, we identified 12 independent frequencies for AB Cas and 11 frequencies for OO Dra, with amplitudes higher than $\sim$0.3 mmag, as $\delta$ Sct-type pulsation frequencies excited in each primary star. The theoretical frequencies for seismic analysis were obtained by fully considering the rotation effects. Grid fitting for various stellar properties, such as mass, radius, metallicity, and rotation rate, yielded the best solution for which theoretical frequencies and stellar parameters agreed well with the observations. The rotation rate of the AB Cas primary was tightly constrained to 0.81 $\pm$ 0.01 day$^{-1}$ ($f_{\rm rot} / f_{\rm orb}$ = 1.11$^{+0.01}_{-0.02}$), which is slightly faster than the synchronized rotation. In contrast, the rotation rate of 0.63 $\pm$ 0.01 day$^{-1}$ for the OO Dra primary is lower than the synchronous value of approximately 0.81 day$^{-1}$. Subsynchronous rotation is uncommon in short-period binaries, and its physical mechanism is not yet well understood. Our results show that asteroseismology can be used to precisely measure the rotation rate of fast-rotating $\delta$ Sct stars and thus provide a valuable constraint on rotation-orbit synchronization in close binary systems.

We estimate the fraction of halos that host supermassive black holes (SMBHs) forming through the direct collapse (DC) scenario by using cosmological N -body simulations combined with a semi-analytic model for galaxy evolution. While in most of earlier studies the occurrence of the DC is limited only in chemically pristine halos, we here suppose that the DC can occur also in halos with metallicity below a threshold value $Z_{\rm th} = 0$--$10^{-3}~{\rm Z}_{\bigodot}$, considering the super-competitive accretion pathway for DC black hole (DCBH) formation. In addition, we consider for the first time the effect of Lyman-Werner (LW) radiation from stars within host halos, i.e., internal radiation. We find that, with low threshold metallicities of $Z_{\rm th} \leq 10^{-4}~{\rm Z}_{\bigodot}$, the inclusion of internal radiation rather reduces the number density of DCBHs from $0.2$--$0.3$ to $0.03$--$0.06~{\rm Mpc}^{-3}$. This is because star formation is suppressed due to self-regulation, and the LW flux emitted by neighboring halos is reduced. Only when $Z_{\rm th}$ is as high as $10^{-3}~{\rm Z}_{\bigodot}$, internal radiation enhances the number density of DCBHs from $0.4$ to $1~{\rm Mpc}^{-3}$, thereby decreasing the threshold halo mass above which at least one DCBH forms from $2\times 10^{9}$ to $9\times 10^{8}~{\rm M}_{\bigodot}$. We also find that halos with $M_{\rm halo} \gtrsim 10^{11}$--$10^{12}~{\rm M}_{\bigodot}$ can host more than one DCBH at $z = 0$. This indicates that the DC scenario alone can explain the observed number of SMBH-hosting galaxies.

In April-May 2018, the RATAN-600 radio telescope carried out monitoring observations of 16 solar-like nearby star systems in four frequency bands. Registration was carried out with an increased sampling frequency of $\sim 18$ Hz. An algorithm for data processing in the mode of source passing through the radiation pattern by the method of dispersion analysis with noise filtering is described. The processing took into account the correction of the transit time for the secular shift of the right ascension of the sources due to their relative proximity. There have been several unidentified cases of anomalous excess of the standard deviation of noise from stationary values. For the most sensitive receivers in the 2.68 and 6.38 cm bands, this anomaly detection threshold with a 99% probability was $\sim 100$ mJy.

The radiation from accreting X-ray pulsars was expected to be highly polarized, with some estimates for the polarization degree of up to 80%. However, phase-resolved and energy-resolved polarimetry of X-ray pulsars is required in order to test different models and to shed light on the emission processes and the geometry of the emission region. Here we present the first results of the observations of the accreting X-ray pulsar Vela X-1 performed with the Imaging X-ray Polarimetry Explorer (IXPE). Vela X-1 is considered to be the archetypal example of a wind-accreting high-mass X-ray binary system, consisting of a highly magnetized neutron star accreting matter from its supergiant stellar companion. The spectro-polarimetric analysis of the phase-averaged data for Vela X-1 reveals a polarization degree (PD) of 2.3$\pm$0.4% at the polarization angle (PA) of -47.3$\pm$5.4 deg. A low PD is consistent with the results obtained for other X-ray pulsars and is likely related to the inverse temperature structure of the neutron star atmosphere. The energy-resolved analysis shows the PD above 5 keV reaching 6-10%, and a 90 deg difference in the PA compared to the data in the 2-3 keV range. The phase-resolved spectro-polarimetric analysis finds a PD in the range 0-9% with the PA varying between -80 and 40 deg.

The description of the tempo-spatial evolution of the composition of cosmic gas on galactic scales is called 'modelling galactic chemical evolution'. It aims to use knowledge about sources of nucleosynthesis and how they change the composition of interstellar gas, following the formation of stars and the ejection of products from nuclear fusion during their evolution and terminating explosions. Sources of nucleosynthesis are diverse: Stars with hydrostatic nuclear burning eject some of the products, and core-collapse supernovae add ejecta. Binary interactions lead to sources such as thermonuclear supernovae and kilonovae. Tracing ejecta from sources, with their different frequencies and environments, through the interstellar medium and successive star formation cycles is the goal of model descriptions. A variety of descriptions exists, from analytical through semi-analytical, numerical or stochastic approaches, gradually making descriptions of compositional evolution of cosmic matter more realistic, teaching us about the astrophysical processes involved in this complex aspect of our universe. Radioactive isotopes add important ingredients to such modelling: The intrinsic clock of the radioactive decay process adds a new aspect of the modelling algorithms that leads to different constraints on the important unknowns of star formation activity and interstellar transports. Several prominent examples illustrate how modelling the abundances of radioactive isotopes and their evolution have resulted in new lessons; among these are the galaxy-wide distribution of 26Al and 60Fe, the radioactive components of cosmic rays, the interpretations of terrestrial deposits of 60Fe and 244Pu, and the radioactive-decay daughter isotopes that were found in meteorites and characterise the birth environment of our solar system.

We present a data-driven approach to automatically detect L dwarfs from Sloan Digital Sky Survey(SDSS) images using an improved Faster R-CNN framework based on deep learning. The established L dwarf automatic detection (LDAD) model distinguishes L dwarfs from other celestial objects and backgrounds in SDSS field images by learning the features of 387 SDSS images containing L dwarfs. Applying the LDAD model to the SDSS images containing 93 labeled L dwarfs in the test set, we successfully detected 83 known L dwarfs with a recall rate of 89.25% for known L dwarfs. Several techniques are implemented in the LDAD model to improve its detection performance for L dwarfs,including the deep residual network and the feature pyramid network. As a result, the LDAD model outperforms the model of the original Faster R-CNN, whose recall rate of known L dwarfs is 80.65% for the same test set. The LDAD model was applied to detect L dwarfs from a larger validation set including 843 labeled L dwarfs, resulting in a recall rate of 94.42% for known L dwarfs. The newly identified candidates include L dwarfs, late M and T dwarfs, which were estimated from color (i-z) and spectral type relation. The contamination rates for the test candidates and validation candidates are 8.60% and 9.27%, respectively. The detection results indicate that our model is effective to search for L dwarfs from astronomical images.

Cyanamide (NH2CN) and its isomer, carbodiimide (HNCNH), may form adenine in the interstellar medium (ISM) via a series of reactions. Therefore, they are considered key prebiotic molecules in the study of the origin of life. We used the three-phase NAUTILUS chemical code, which includes the gas, the dust surface, and the icy mantle, to investigate the formation and destruction of cyanamide and carbodiimide. We added over 200 new chemical reactions of the two isomers and related species, and established a relatively complete network. We applied cold core, hot corino/core and shock models to simulate the different physical environments, and found that the two isomers are mainly produced by the free radical reactions on grain surfaces. Our simulated results suggest that cyanamide and carbodiimide molecules come from surface chemistry at early evolutionary stages. Then they are released back to the gas phase, either by thermal process (in hot cores, hot corinos) or shock-induced desorption (in shock regions).We speculate that it is an inefficient route to form a tautomer of adenine by starting from molecules cyanoacetylene (C3NH), cyanamide and carbodiimide in ISM.

Fast X-ray Transients (FXTs) are X-ray flares with a duration ranging from a few hundred seconds to a few hours. Possible origins include the tidal disruption of a white dwarf by an intermediate-mass black hole, a supernova shock breakout, and a binary neutron star merger. We present the X-ray light curve and spectrum, and deep optical imaging of the FXT XRT 210423, which has been suggested to be powered by a magnetar produced in a binary neutron star merger. Our Very Large Telescope and Gran Telescopio Canarias (GTC) observations began on May 6, 2021, thirteen days after the onset of the flare. No transient optical counterpart is found in the 1" (3$\sigma$) X-ray uncertainty region of the source to a depth $g_{s}$=27.0 AB mag. A candidate host lies within the 1" X-ray uncertainty region with a magnitude of 25.9 $\pm$ 0.1 in the GTC/HiPERCAM $g_s$-filter. Due to its faintness, it was not detected in other bands, precluding a photometric redshift determination. We detect two additional candidate host galaxies; one with $z_{\rm spec}=1.5082 \pm 0.0001$ and an offset of 4.2$\pm$1" (37$\pm$9 kpc) from the FXT and another one with $z_{\rm phot}=1.04^{+0.22}_{-0.14}$, at an offset of 3.6$\pm$1" (30$\pm$8 kpc). Based on the properties of all the prospective hosts we favour a binary neutron star merger, as previously suggested in the literature, as explanation for XRT 210423.

We present a nonparametric morphology analysis of the stellar continuum and nebular emission lines for a sample of local galaxies. We explore the dependence of the various morphological parameters on wavelength and morphological type. Our goal is to quantify the difference in morphology between the stellar and nebular components. We derive the nonparametric morphological indicators of 364 galaxies from the CALIFA Survey. To calculate those indicators, we apply the StatMorph package on the high-quality integral field spectroscopic data cubes, as well as to the most prominent nebular emission-line maps, namely [OIII]$\lambda$5007, H$\alpha$, and [NII]$\lambda$6583. We show that the physical size of galaxies, M$_{20}$ index, and concentration have a strong gradient from blue to red optical wavelengths. We find that the light distribution of the nebular emission is less concentrated than the stellar continuum. A comparison between the nonparametric indicators and the galaxy physical properties revealed a very strong correlation of the concentration with the specific star-formation rate and morphological type. Furthermore, we explore how the galaxy inclination affects our results. We find that edge-on galaxies show a more rapid change in physical size and concentration with increasing wavelength due to the increase in optical free path. We conclude that the apparent morphology of galaxies originates from the pure stellar distribution, but the morphology of the ISM presents differences with respect to the morphology of the stellar component. Our analysis also highlights the importance of dust attenuation and galaxy inclination in the measurement of nonparametric morphological indicators, especially in the the wavelength range 4000-5000 \r{A}.

A macroscopic and kinetic relativistic description for a decoupled multi-fluid cosmology endowed with gravitationally induced particle production of all components is proposed. The temperature law for each decoupled particle species is also kinetically derived. The present approach points to the possibility of an exact (semi-classical) quantum-gravitational kinetic treatment by incorporating back reaction effects for an arbitrary set of dominant decoupled components. As an illustration we show that a cosmology driven by creation of cold dark matter and baryons (without dark energy) evolves like $\Lambda$CDM. However, the complete physical emulation is broken when photon creation is added to the mixture thereby pointing to a crucial test in the future. The present analysis also open up a new window to investigate the Supernova-CMB tension on the values of $H_0$, as well as the $S_8$ tension since creation of all components changes slightly the CMB results and the expansion history both at early and late times. Finally, it is also argued that cross-correlations between CMB temperature maps and the Sunyaev-Zeldovich effect may provide a crucial and accurate test confronting extended CCDM and $\Lambda$CDM models.

We present the first release of the Calar Alto CAFOS direct imaging data, a project led by the Spanish Virtual Observatory with the goal of enhancing the use of the Calar Alto archive by the astrophysics community. Data Release 1 contains 23903 reduced and astrometrically calibrated images taken from March 2008 to July 2019 with a median of the mean uncertainties in the astrometric calibration of 0.04 arcsec. The catalogue associated to 6132 images in the Sloan gris filters provides accurate astrometry and PSF calibrated photometry for 139337 point-like detections corresponding to 21985 different sources extracted from a selection of 2338 good-quality images. The mean internal astrometric and photometric accuracies are 0.05 arcsec and 0.04 mag, respectively In this work we describe the approach followed to process and calibrate the images, and the construction of the associated catalogue, together with the validation quality tests carried out. Finally, we present three cases to prove the science capabilities of the catalogue: discovery and identification of asteroids, identification of potential transients, and identification of cool and ultracool dwarfs.

By searching the Open Supernova Catalog, an extra-galactic transient host galaxy database, and literature analyses, I present the largest sample of type Ia supernova (SN Ia) siblings to date. The sample comprises 158 galaxies, consisting of 327 confirmed SNe Ia - over 10 times larger than existing sibling SN Ia samples. SN siblings share host galaxies, and thus share global environmental properties and associated systematic uncertainties. This makes them valuable for both cosmological and astrophysical analyses; for example, sibling SNe Ia allow for comparison of environmental properties within the same galaxy, progenitor comparisons, rates analyses, and multiple calibrations of the Hubble-Lema\^{\i}tre constant. This large sample will provide a variety of new avenues of research, and be of great interest to the wider SN Ia community. To give an example use of this sample, I define a cosmology sub-sample of 50 siblings; and use it to compare light-curve properties between sibling pairs. I find no evidence for correlations in stretch ($x_1$) and colour ($c$) between pairs of siblings. Moreover, by comparing to a simulation of a comparable set of random pairs of SNe Ia, I find that siblings are no more similar in $x_1$ and $c$ than any random pair of SNe Ia. Given that siblings share the same hosts, differences in $x_1$ and $c$ between siblings cannot be due to global galaxy properties. This raises important questions regarding environmental systematics for SN Ia standardisation in cosmology, and motivates future analyses of sibling SNe Ia.

We derive from first principles equations for bosonic, non-relativistic and self-interacting dark matter which can include both a condensed, low momentum ``fuzzy'' component and one with higher momenta that may be approximated as a collection of particles. The resulting coupled equations consist of a modified Gross-Pitaevskii equation describing the condensate and a kinetic equation describing the higher momentum modes, the ``particles'', along with the Poisson equation for the gravitational potential sourced by the density of both components. Our derivation utilizes the Schwinger-Keldysh path integral formalism and applies a semi-classical approximation which can also accommodate collisional terms amongst the particles and between the particles and the condensate to second order in the self-coupling strength. The equations can therefore describe both CDM and Fuzzy Dark Matter in a unified way, allowing for the coexistence of both phases and the inclusion of quartic self-interactions.

We constrain the Chameleon \textit{screening} mechanism in galaxy clusters, essentially obtaining limits on the coupling strength $\beta$ and the asymptotic value of the field $\phi_{\infty}$. For this purpose, we utilized a collection of the 9 relaxed galaxy clusters within the X-COP compilation in the redshift range of $z \le 0.1$. We implement the formalism assuming an NFW mass profile for the dark matter density and study the degeneracy present between the mass $\M$ and the chameleon coupling with a high degree of improvement in the constraints for excluded parameter space. We recast our constrain to an upper limit on the scalaron field in \fofr sub-class of models of $|f_{R0}|\le 9.2\times 10^{-6}$, using all the nine clusters and $|f_{R0}|\le 1.2\times 10^{-5}$ using only 5 clusters with WL priors taken into account, at a $95\%$ confidence level. These bounds are consistent with existing limits in the literature and tighter than the constraints obtained with the same method by previous studies.

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 minutes was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement ($\beta$) was possible. In the years prior to impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be -33.0 +/- 1.0 (3$\sigma$) minutes. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a significant amount of momentum to the asteroid beyond what the DART spacecraft carried.

In analytical models of structure formation, protohalos are routinely assumed to be peaks of the smoothed initial density field, with the smoothing filter being spherically symmetric. This works reasonably well for identifying a protohalo's center of mass, but not its shape. To provide a more realistic description of protohalo boundaries, one must go beyond the spherical picture. We suggest that this can be done by looking for regions of fixed volume, but arbitrary shape, that minimize the enclosed energy. Such regions are surrounded by surfaces over which (a slightly modified version of) the gravitational potential is constant. We show that these equipotential surfaces provide an excellent description of protohalo shapes, orientations and associated torques.

We investigate the properties of mergers that are comparable to the Gaia-Sausage-Enceladus (GSE) using cosmological hydrodynamical simulations of Milky Way-like galaxies. It was previously shown that these mergers occur over a wide range of times ($6-10\,$Gyr ago). We find that the merger progenitors span an order of magnitude in their peak stellar mass ($3\times10^8<M_{\star}/\rm{M}_{\odot}<4\times10^9$) and include both rotation and pressure-supported galaxies ($0.10<D/T<0.77$). In a minority of cases, the GSE-like debris is comprised of stars from more than one merger progenitor. However, there is a close similarity in their chemodynamical property distributions and the triaxial shapes of their debris are comparable around the Solar radius, so it is not always possible to distinguish their debris. The merger progenitors host a variety of luminous satellites ($0-8$ with $M_{*}>10^6\,\rm{M}_{\odot}$), but most of these do not follow the merger to low orbital energies. Between $0-1$ of these satellites may survive to $z=0$, but with no clear signatures of their past association. We show that the fraction of stars originating from GSE-like mergers is reduced for lower metallicities (reaching a minimum around $\text{[Fe/H]} = -2$), and also within $5\,$kpc of the galactic centre. Whilst these central regions are dominated by $\textit{in-situ}$ stars, the $\textit{ex-situ}$ fraction trends towards a 100 per cent asymptote when considering the most metal-poor stars ($\text{[Fe/H]}\ll-2.5$). Considering this, its near proximity, and its small volume on the sky, the Galactic centre lends itself as a prime environment in the search for the stars from the earliest galaxies, whilst avoiding contamination from GSE stars.

The modern study of astrophysical transients has been transformed by an exponentially growing volume of data. Within the last decade, the transient discovery rate has increased by a factor of ~20, with associated survey data, archival data, and metadata also increasing with the number of discoveries. To manage the data at this increased rate, we require new tools. Here we present YSE-PZ, a transient survey management platform that ingests multiple live streams of transient discovery alerts, identifies the host galaxies of those transients, downloads coincident archival data, and retrieves photometry and spectra from ongoing surveys. YSE-PZ also presents a user with a range of tools to make and support timely and informed transient follow-up decisions. Those subsequent observations enhance transient science and can reveal physics only accessible with rapid follow-up observations. Rather than automating out human interaction, YSE-PZ focuses on accelerating and enhancing human decision making, a role we describe as empowering the human-in-the-loop. Finally, YSE-PZ is built to be flexibly used and deployed; YSE-PZ can support multiple, simultaneous, and independent transient collaborations through group-level data permissions, allowing a user to view the data associated with the union of all groups in which they are a member. YSE-PZ can be used as a local instance installed via Docker or deployed as a service hosted in the cloud. We provide YSE-PZ as an open-source tool for the community.

We revisit stellar energy-loss bounds on the Yukawa couplings $g_{\rm B,L}$ of baryophilic and leptophilic scalars $\phi$. The white-dwarf luminosity function yields $g_{\rm B}\lesssim 7 \times 10^{-13}$ and $g_{\rm L}\lesssim 4 \times 10^{-16}$, based on bremsstrahlung from ${}^{12}{\rm C}$ and ${}^{16}{\rm O}$ collisions with electrons. In models with a Higgs portal, this also implies a bound on the scalar-Higgs mixing angle $\sin \theta \lesssim 2 \times 10^{-10}$. Our new bounds apply for $m_\phi\lesssim {\rm 1~keV}$ and are among the most restrictive ones, whereas for $m_\phi\lesssim 0.5\,{\rm eV}$ long-range force measurements dominate. Besides a detailed calculation of the bremsstrahlung rate for degenerate and semi-relativistic electrons, we prove with a simple argument that non-relativistic bremsstrahlung by the heavy partner is suppressed relative to that by the light one by their squared-mass ratio. This large reduction was overlooked in previous much stronger bounds on $g_{\rm B}$. In an Appendix, we provide fitting formulas (few percent precision) for the bremsstrahlung emission of baryophilic and leptophilic scalars as well as axions for white-dwarf conditions, i.e., degenerate, semi-relativistic electrons and ion-ion correlations in the ``liquid'' phase.

In view of the observed flat rotation curves of spiral galaxies and motivated by the simple fact that within newtonian gravity a stationary axisymmetric mass distribution or dark matter vortex of finite extent readily displays a somewhat flattened out velocity rotation curve up to distances comparable to the extent of such a vortex transverse to the galaxy's disk, the possibility that such a flattening out of rotation curves may rather be a manifestation of some stationary axisymmetric space-time curvature of purely gravitational character, without the need of some dark matter particles, is considered in the case of the gravimagnetic dipole carrying opposite NUT charges and in the tensionless limit of its Misner string, as an exact vacuum solution to Einstein's equations. Aiming for a first assessment of the potential of such a suggestion easier than a full fledged study of its geodesics, the situation is analysed within the limits of weak field gravito-electromagnetism and nonrelativistic dynamics. Thereby leading indeed to interesting and encouraging results.

The minimum testable dark matter (DM) mass for almost all DM signatures in celestial bodies is determined by the rate at which DM evaporates. DM evaporation has previously been calculated assuming a competition between the gravitational potential of the object, and thermal kicks from the celestial-body matter. We point out a new effect, where mediators with a range larger than the interparticle spacing induce a force proportional to the density gradient of celestial objects, forming an evaporation barrier for the DM. This effect can be so significant that evaporation does not occur even for sub-MeV DM, in stark contrast to previous calculations. This opens up a wide range of new light DM searches, many orders of magnitude in DM mass below the sensitivity of direct detection.

Superconducting cavities can operate analogously to Weber bar detectors of gravitational waves, converting mechanical to electromagnetic energy. The significantly reduced electromagnetic noise results in increased sensitivity to high-frequency signals well outside the bandwidth of the lowest mechanical resonance. In this work, we revisit such signals of gravitational waves and demonstrate that a setup similar to the existing "MAGO" prototype, operating in a scanning or broadband manner, could have sensitivity to strains of $\sim 10^{-22} - 10^{-18}$ for frequencies of $\sim 10 \ \text{kHz} - 1 \ \text{GHz}$.

The Cosmic Gravitational Wave Background (CGWB) is an irreducible background of gravitational waves generated by particle exchange in the early Universe plasma. Standard Model particles contribute to such a stochastic background with a peak at $f\sim 80$ GHz. Any physics beyond the Standard Model (BSM) may modify the CGWB spectrum, making it a potential testing ground for BSM physics. We consider the impact of general BSM scenarios on the CGWB, including an arbitrary number of hidden sectors. We find that the largest amplitude of the CGWB comes from the sector that dominates the energy density after reheating and confirm the dominance of the SM for standard cosmological histories. For non-standard cosmological histories, such as those with a stiff equation of state $\omega >1/3$, like in kination, BSM physics may dominate and modify the spectrum substantially. We conclude that, if the CGWB is detected at lower frequencies and amplitudes compared to that of the SM, it will hint at extra massive degrees of freedom or hidden sectors. If it is instead measured at higher values, it will imply a period with $\omega >1/3$. We argue that for scenarios with periods of kination in the early Universe, a significant fraction of the parameter space can be ruled out from dark radiation bounds at BBN.

Within the quark nugget model, dark matter particles may be represented by compact composite objects composed of a large number of quarks or antiquarks. Due to strong interaction with visible matter, antiquark nuggets should manifest themselves in the form of rare atmospheric events on the Earth. They may produce ionized trails in the atmosphere similar to the meteor trails. There are, however, several features which should allow one to distinguish antiquark nugget trails from meteor ones. We study the properties of ionized trails from antiquark nuggets in the air and show that they may be registered by standard meteor radar detectors. Non-observation of such trails pushes up the mean baryon charge number in the quark nugget model, $|B|>4\times 10^{27}$.

We describe here how planetary ephemerides are built in the framework of General Relativity and how they can be used to test alternative theories. We focus on the definition of the reference frame (space and time) in which the planetary ephemeris is described, the equations of motion that govern the orbits of solar system bodies and light rays. After a review on the existing planetary and lunar ephemerides, we summarize the results obtained considering full modifications of the ephemeris framework with direct comparisons with the observations of planetary systems, with a specific attention for the PPN formalism. We then discuss other formalisms such as Einstein-dilaton theories, the massless graviton and MOND. The paper finally concludes on some comments and recommendations regarding misinterpreted measurements of the advance of perihelia.

The title reaction is studied using a quasi-classical trajectory method for collision energies between 0.1 meV and 10 eV, considering the vibrational excitation of H$_2^+$ reactant. A new potential energy surface is developed based on a Neural Network many body correction of a triatomics-in-molecules potential, which significantly improves the accuracy of the potential up to energies of 17 eV, higher than in other previous fits.The effect of the fit accuracy and the non-adiabatic transitions on the dynamics are analyzed in detail.The reaction cross section for collision energies above 1 eV increases significantly with the increasing of the vibrational excitation of H$_2^+$($v'$), for values up to $v'$=6. The total reaction cross section (including the double fragmentation channel) obtained for $v'$=6 matches the new experimental results obtained by Savic, Schlemmer and Gerlich [Chem. Phys. Chem. 21 (13), 1429.1435(2020)]. The differences among several experimental setups, for collision energies above 1 eV, showing cross sections scattered/dispersed over a rather wide interval, can be explained by the differences in the vibrational excitations obtained in the formation of H$_2^+$ reactants. On the contrary, for collision energies below 1 eV, the cross section is determined by the long range behavior of the potential and do not depend strongly on the vibrational state of H$_2^+$. In addition in this study, the calculated reaction cross sections are used in a plasma model and compared with previous results. We conclude that the efficiency of the formation of H$_3^+$ in the plasma is affected by the potential energy surface used.

The cross helicity (velocity--magnetic-field correlation) effects in the magnetic-field induction and momentum transport in the magnetohydrodynamic (MHD) turbulence are investigated with the aid of the multiple-scale renormalized perturbation expansion analysis. The outline of the theory is presented with reference to the role of the cross-interaction response functions between the velocity and magnetic field. In this formulation, the expressions of the turbulent fluxes: the turbulent electromotive force (EMF) in the mean induction equation and the Reynolds and turbulent Maxwell stresses in the momentum equation are obtained. Related to the expression of EMF, the physical origin of the cross-helicity effect in dynamos, as well as other dynamo effects, is discussed. In order to understand the actual role of the turbulent cross helicity, its transport equations is considered. Several generation mechanisms of cross helicity are discussed with illustrative examples. On the basis of the cross-helicity production mechanisms, its effect in stellar dynamos is discussed. The role of cross helicity in the momentum transport and global flow generation is also argued. Characteristic features of turbulence effects in fast reconnection are reviewed with special emphasis on the role of cross helicity in localizing the effective resistivity. Finally, a remark is addressed on an approach that elucidates the structure generation and sustainment in extremely strong turbulence. An appropriate formulation for the anti-diffusion effect, which acts against the usual diffusion effect, is needed. Turbulence modeling approach based on such an analytical formulation is also argued in comparison with the conventional heuristic modeling. The importance of the self-consistent framework treating the non-linear interaction between the mean field and turbulence is stressed as well.

Simultaneous measurements of neutron star masses and radii can be used to constrain deviations from general relativity (GR) as was recently demonstrated for the spontaneous scalarization model of Damour and Esposito-Far\`{e}se (DEF). Here, we investigate the general applicability of the same procedure beyond this single example. We first show that a simple variation of the DEF model renders the same mass-radius measurements ineffective for obtaining constraints. On the other hand, a recently popular and distinct model of scalarization that arises in scalar-Gauss-Bonnet theory can be constrained similarly to the original DEF model, albeit due to a slightly different underlying mechanism. These establish that using the mass-radius data can potentially constrain various theories of gravity, but the method also has limitations.

In the context of direct searches of sub-GeV Dark Matter particles with germanium detectors, the EDELWEISS collaboration has tested a new technique to tag ionizing events using NbSi transition edge athermal phonon sensors. The emission of the athermal phonons generated by the Neganov-Trofimov-Luke effect associated with the drift of electrons and holes through the detectors is used to tag ionization events generated in specific parts of the detector localized in front of the NbSi sensor and to reject by more than a factor 5 (at 90% C.L.) the background from heat-only events that dominates the spectrum above 3 keV. This method is able to improve by a factor 2.8 the previous limit on spin-independent interactions of 1 GeV/c2 WIMPs obtained with the same detector and data set but without this tagging technique.

In this study, we review some current studies on Gravitational Lensing for black holes, mainly in the context of general relativity. We mainly focus on the analytical studies related to lensing with references to observational results. We start with reviewing lensing in spherically symmetric Schwarzschild spacetime, showing how to calculate deflection angles before moving to the rotating counterpart, the Kerr metric. Furthermore, we extend our studies for a particular class of newly proposed solutions called black-bounce spacetimes and discuss throughout the review how to explore lensing in these spacetimes and how the various parameters can be constrained using available astrophysical and cosmological data.

Constant-curvature solutions lie at the very core of gravitational physics, with Schwarzschild and (Anti)-de Sitter being two of the most paradigmatic examples. Although such kind of solutions are very well-known in General Relativity, that is not the case for theories of gravity beyond the Einsteinian paradigm. In this article, we provide a systematic overview on $f(R)$ models allowing for constant-curvature solutions, as well as of the constant-curvature solutions themselves. We conclude that the vast majority of these $f(R)$ models suffer, in general, from several shortcomings rendering their viability extremely limited, when not ruled out by physical evidence. Among these deficiencies are instabilities (including previously unforeseen strong-coupling problems) and issues limiting the predictive power of the models. Furthermore, we will also show that most $f(R)$-exclusive constant-curvature solutions also exhibit a variety of unphysical properties.

We investigate whether photon ring observations in black hole imaging are able to distinguish between the Kerr black hole in general relativity and alternative black holes that deviate from Kerr. Certain aspects of photon rings have been argued to be robust observables in Very-Long-Baseline Interferometry (VLBI) black hole observations which carry imprints of the underlying spacetime. The photon ring shape, as well as its Lyapunov exponent (which encodes the narrowing of successive photon subrings), are detailed probes of the underlying geometry; measurements thereof have been argued to provide a strong null test of general relativity and the Kerr metric. However, a more complicated question is whether such observations of the photon ring properties can distinguish between Kerr and alternative black holes. We provide a first answer to this question by calculating photon rings of the Johannsen, Rasheed-Larsen, and Manko-Novikov black holes. We find that large deviations from Kerr and large observer inclinations are needed to obtain measurable differences in the photon ring shape. In other words, the Kerr photon ring shape appears to be the universal shape even for deviating black holes at low inclinations. On the other hand, the Lyapunov exponent shows more marked variations for deviations from the Kerr metric. Our analysis lays out the groundwork to determine deviations from the Kerr spacetime in photon rings that are potentially detectable by future observing missions.

We provide a discussion on a light ray in a charged black hole solution in massive gravity. To serve the purpose, we exploit the optical geometry of the black hole solution and find the Gaussian curvature in weak gravitational lensing. Furthermore, we discuss the deflection angle of the light ray in both plasma and non-plasma mediums using the Gauss-Bonnet theorem on the black hole. We also analyze the Regge--Wheeler equation and derive rigorous bounds on the greybody factors of linearly charged massive BTZ black hole. We also study the shadow or silhouette generated by charged massive BTZ black holes. The effects of charge and cosmological constant on the radius of the shadow are also discussed.