Papers for Monday, Jul 24 2023

It seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star (NS) merger event, GW170817/GRB 170817A/kilonova AT2017gfo, places irreconcilable constraints to models of the prompt emission of this gamma-ray burst (GRB). The observed time delay between the merger of the two NSs and the trigger of the GRB and the thermal tail of the prompt emission can hardly be reproduced by these models simultaneously. We argue that the merger remnant should be an NS (last for, at least, a large fraction of 1s), and that the difficulty can be alleviated by the delayed formation of the accretion disk due to the absorption of high-energy neutrinos emitted by the NS and the delayed emergence of an effective viscous in the disk. Further, we extend the consideration of the effect of the energy deposition of neutrinos emitted from the NS. If the NS is the central object of a GRB with a distance and duration similar to that of GRB 170817A, thermal emission of the thermal bubble inflated by the NS after the termination of accretion may be detectable. If our scenario is verified, it would be of interest to investigate the cooling of nascent NSs.

Telescopes capture images with a particular point spread function (PSF). Inferring what an image would have looked like with a much sharper PSF, a problem known as PSF deconvolution, is ill-posed because PSF convolution is not an invertible transformation. Deep generative models are appealing for PSF deconvolution because they can infer a posterior distribution over candidate images that, if convolved with the PSF, could have generated the observation. However, classical deep generative models such as VAEs and GANs often provide inadequate sample diversity. As an alternative, we propose a classifier-free conditional diffusion model for PSF deconvolution of galaxy images. We demonstrate that this diffusion model captures a greater diversity of possible deconvolutions compared to a conditional VAE.

The implications of perturbative QCD (PQCD) calculations on neutron stars are carefully examined. While PQCD calculations above baryon chemical potential $\mu_B\sim2.4$ GeV demonstrate the potential of ruling out a wide range of neutron star equations of state (EOSs), these types of constraints only affect the most massive neutron stars in the vicinity of the Tolman-Oppenheimer-Volkoff (TOV) limit, resulting in bounds on neutron star EOSs that are orthogonal to those from current or future astrophysical observations, even if observations near the TOV limit are made. Assuming the most constraining scenario, PQCD considerations favor low values of the speed of sound squared $C_s$ at high $\mu_B$ relevant for heavy neutron stars, but leave predictions for the radii and tidal deformabilities almost unchanged for all the masses. Such considerations become irrelevant if the maximum speed of sound squared inside neutron stars does not exceed about $C_{s,\mathrm{max}}\sim0.5$, or if the matching to PQCD is performed above $\mu_B\simeq2.9$ GeV. Furthermore, the large uncertainties associated with the current PQCD predictions make it impossible to place any meaningful bounds on neutron star EOSs as of now. Interestingly, if PQCD predictions for pressure at around $\mu_B\simeq2.4$ GeV is refined and found to be low ($\lesssim 1.5$ GeV/fm$^3$), evidence for a soft neutron star inner core EOS would point to the presence of a strongly interacting phase dominated by non-perturbative physics beyond neutron star densities.

The fast flavor conversions (FFCs) of neutrinos generally exist in core-collapse supernovae and binary neutron-star merger remnants, and can significantly change the flavor composition and affect the dynamics and nucleosynthesis processes. Several analytical prescriptions were proposed recently to approximately explain or predict the asymptotic outcome of FFCs for systems with different initial or boundary conditions, with the aim for providing better understandings of FFCs and for practical implementation of FFCs in hydrodynamic modeling. In this work, we obtain the asymptotic survival probability distributions of FFCs in a survey over thousands of randomly sampled initial angular distributions by means of numerical simulations in one-dimensional boxes with the periodic boundary condition. We also propose improved prescriptions that guarantee the continuity of the angular distributions after FFCs. Detailed comparisons and evaluation of all these prescriptions with our numerical survey results are performed. The survey dataset is made publicly available to inspire the exploration and design for more effective methods applicable to realistic hydrodynamic simulations.

Aims. We aim to understand how Hepsilon is formed in the quiet Sun. In particular, we consider the particular physical mechanism that sets its source function and extinction, how it is formed in different solar structures, and why it is sometimes observed in emission. Methods. We used a 3D radiative magnetohydrodynamic (MHD) simulation that accounts for non-equilibrium hydrogen ionization, run with the Bifrost code. To synthesize Hepsilon and Ca II H spectra, we made use of the RH code, which was modified to take into account the non-equilibrium hydrogen ionization. To determine the dominant terms in the H${\epsilon}$ source function, we adopted a multi-level description of the source function. Using synthetic spectra and simulation, we studied the contribution function to the relative line absorption or emission and compared it with atmospheric quantities at different locations. Results. Our multi-level source function description suggests that the H${\epsilon}$ source function is dominated by interlocking, with the dominant interlocking transition being through the ground level, populating the upper level of H${\epsilon}$ via the Lyman series. This makes the H${\epsilon}$ source function partly sensitive to temperature. The H${\epsilon}$ extinction is set by Lyman-${\alpha}$. In some cases, this temperature dependence gives rise to H${\epsilon}$ emission, indicating heating. High-resolution observations reveal that H${\epsilon}$ is not just a weak absorption line. Regions with H${\epsilon}$ in emission are especially interesting to detect small-scale heating events in the lower solar atmosphere, such as Ellerman bombs. Thus, H${\epsilon}$ can be an important new diagnostic tool for studies of heating in the solar atmosphere, augmenting the diagnostic potential of Ca II H when observed simultaneously

We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope. Another 33 millisecond pulsars (MSPs) discovered in deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems co-located with LAT sources also likely harbor gamma-ray MSPs. This catalog thus reports roughly 340 gamma-ray pulsars and candidates, 10% of all known pulsars, compared to $\leq 11$ known before Fermi. Half of the gamma-ray pulsars are young. Of these, the half that are undetected in radio have a broader Galactic latitude distribution than the young radio-loud pulsars. The others are MSPs, with 6 undetected in radio. Overall, >235 are bright enough above 50 MeV to fit the pulse profile, the energy spectrum, or both. For the common two-peaked profiles, the gamma-ray peak closest to the magnetic pole crossing generally has a softer spectrum. The spectral energy distributions tend to narrow as the spindown power $\dot E$ decreases to its observed minimum near $10^{33}$ erg s$^{-1}$, approaching the shape for synchrotron radiation from monoenergetic electrons. We calculate gamma-ray luminosities when distances are available. Our all-sky gamma-ray sensitivity map is useful for population syntheses. The electronic catalog version provides gamma-ray pulsar ephemerides, properties and fit results to guide and be compared with modeling results.

Sodium iodide (NaI) based cryogenic scintillating calorimeters using quantum sensors for signal read out have shown promising first results towards a model-independent test of the annually modulating signal detected by the DAMA/LIBRA dark matter experiment. The COSINUS collaboration has previously reported on the first above-ground measurements using a dual channel readout of phonons and light based on transition edge sensors (TESs) that allows for particle discrimination on an event-by-event basis. In this letter, we outline the first underground measurement of a NaI cryogenic calorimeter read out via the novel remoTES scheme. A 3.67 g NaI absorber with an improved silicon light detector design was operated at the Laboratori Nazionali del Gran Sasso, Italy. A significant improvement in the discrimination power of $e^-$/$\gamma$-events to nuclear recoils was observed with a five-fold improvement in the nuclear recoil baseline resolution, achieving $\sigma$ = 441 eV. Furthermore, we present a limit on the spin-independent dark-matter nucleon elastic scattering cross-section achieving a sensitivity of $\mathcal{O}$(pb) with an exposure of only 11.6 g d.

We introduce Project GIBLE (Gas Is Better resoLved around galaxiEs), a suite of cosmological zoom-in simulations where gas in the circumgalactic medium (CGM) is preferentially simulated at ultra-high numerical resolution. Our initial sample consists of eight galaxies, all selected as Milky Way-like galaxies at $z=0$ from the TNG50 simulation. Using the same galaxy formation model as IllustrisTNG, and the moving-mesh code AREPO, we re-simulate each of these eight galaxies maintaining a resolution equivalent to TNG50-2 ($m_{\rm{gas}}$ $\sim$ $8 \times 10^5 {\rm M}_{\odot}$). However, we use our super-Lagrangian refinement scheme to more finely resolve gas in the CGM around these galaxies. Our highest resolution runs achieve 512 times better mass resolution ($\sim$ $10^3 {\rm M}_{\odot}$). This corresponds to a median spatial resolution of $\sim$ $75$ pc at $0.15~R_{\rm{200,c}}$, which coarsens with increasing distance to $\sim$ $700$ pc at the virial radius. We make predictions for the covering fractions of several observational tracers of multi-phase CGM gas: HI, MgII, CIV and OVII. We then study the impact of improved resolution on small scale structure. While the abundance of the smallest cold, dense gas clouds continues to increase with improving resolution, the number of massive clouds is well converged. We conclude by quantifying small scale structure with the velocity structure function and the auto-correlation function of the density field, assessing their resolution dependence. The GIBLE cosmological hydrodynamical simulations enable us to improve resolution in a computationally efficient manner, thereby achieving numerical convergence of a subset of key CGM gas properties and observables.

UV and optical continuum reverberation mapping is powerful for probing the accretion disk and inner broad-line region. However, recent reverberation mapping campaigns in the X-ray, UV, and optical have found lags consistently longer than those expected from the standard disk reprocessing picture. The largest discrepancy to-date was recently reported in Mrk 335, where UV/optical lags are up to 12 times longer than expected. Here, we perform a frequency-resolved time lag analysis of Mrk 335, using Gaussian processes to account for irregular sampling. For the first time, we compare the Fourier frequency-resolved lags directly to those computed using the popular Interpolated Cross-Correlation Function (ICCF) method applied to both the original and detrended light curves. We show that the anticipated disk reverberation lags are recovered by the Fourier lags when zeroing in on the short-timescale variability. This suggests that a separate variability component is present on long timescales. If this separate component is modeled as reverberation from another region beyond the accretion disk, we constrain a size-scale of roughly 15 light-days from the central black hole. This is consistent with the size of the broad line region inferred from H$\beta$ reverberation lags. We also find tentative evidence for a soft X-ray lag, which we propose may be due to light travel time delays between the hard X-ray corona and distant photoionized gas that dominates the soft X-ray spectrum below 2 keV.

The identification and characterization of massive ($\gtrsim 0.8~M_\odot$) white dwarfs is challenging in part due to their low luminosity. Here we present two candidate single-lined spectroscopic binaries, Gaia DR3 4014708864481651840 and 5811237403155163520, with K-dwarf primaries and optically dark companions. Both have orbital periods of $P\sim 0.45$ days and show rotational variability, ellipsoidal modulations, and high-amplitude radial velocity variations. Using light curves from the Transiting Exoplanet Survey Satellite (TESS), radial velocities from ground-based spectrographs, and spectral energy distributions, we characterize these binaries to describe the nature of the unseen companion. We find that both systems are consistent with a massive white dwarf companion. Unlike simple ellipsoidal variables, star spots cause the light curve morphology to change between TESS sectors. We attempt to constrain the orbital inclination using PHOEBE binary light curve models, but degeneracies in the light curves of spotted stars prevent a precise determination. Finally, we search for similar objects using Gaia DR3 and TESS, and comment on these systems in the context of recently claimed compact object binaries.

Short-lived radioisotopes, in particular 26-Al and 60-Fe, are thought to contribute to the internal heating of the Earth, but are significantly more abundant in the Solar System compared to the Interstellar Medium. The presence of their decay products in the oldest Solar System objects argues for their inclusion in the Sun's protoplanetary disc almost immediately after the star formation event that formed the Sun. Various scenarios have been proposed for their delivery to the Solar System, usually involving one or more core-collapse supernovae of massive stars. An alternative scenario involves the young Sun encountering an evolved Asymptotic Giant Branch (AGB) star. AGBs were previously discounted as a viable enrichment scenario for the Solar System due to the presumed low probability of an encounter between an old, evolved star and a young pre-main sequence star. We report the discovery in Gaia data of an interloping AGB star in the star-forming region NGC2264, demonstrating that old, evolved stars can encounter young forming planetary systems. We use simulations to calculate the yields of 26-Al and 60-Fe from AGBs and their contribution to the long-term geophysical heating of a planet, and find that these are comfortably within the range previously calculated for the Solar System.

Extreme mass ratio inspirals (EMRIs) take place when a stellar-mass black hole (BH) merges with a supermassive black hole (SMBH). The gravitational wave emission from such an event is expected to be detectable by the future Laser Interferometer Space Antenna (LISA) and other mHz detectors. It was recently suggested that the EMRI rate in SMBH binary systems is orders of magnitude higher than the EMRI rate around a single SMBH with the same total mass. Here we show that this high rate can produce thousands of SMBH-BH sources at a redshift of unity. We predict that LISA may detect a few hundred of these EMRIs with signal-to-noise ratio above SNR>=8 within a four-year mission lifetime. The remaining sub-threshold sources will contribute to a large confusion noise, which is approximately an order of magnitude above LISA's sensitivity level. Finally, we suggest that the individually detectable systems, as well as the background noise from the sub-threshold EMRIs, can be used to constrain the SMBH binary fraction in the low-redshift Universe.

Constraining the strength of gas turbulence in protoplanetary discs is an open problem that has relevant implications for the physics of gas accretion and planet formation. In this work, we gauge the amount of turbulence in 6 of the discs observed in the DSHARP programme by indirectly measuring the vertical distribution of their dust component. We employ the differences in the gap contrasts observed along the major and the minor axes due to projection effects, and build a radiative transfer model to reproduce these features for different values of the dust scale heights. We find that (a) the scale heights that yield a better agreement with data are generally low ($\lesssim 4$ AU at a radial distance of $100$ AU), and in almost all cases we are only able to place upper limits on their exact values; these conclusions imply (assuming an average Stokes number of $\approx10^{-2}$) low turbulence levels of $\alpha_{\rm SS}\lesssim10^{-3}-10^{-4}$; (b) for the 9 other systems we considered out of the DSHARP sample, our method yields no significant constraints on the disc vertical structure; we conclude that this is because these discs have either a low inclination or gaps that are not deep enough. Based on our analysis we provide an empirical criterion to assess whether a given disc is suitable to measure the vertical scale height.

The relative enrichment of s-process to $\alpha$-elements ([s/$\alpha$]) has been linked with age, providing a potentially useful avenue in exploring the Milky Way's chemical evolution. However, the age--[s/$\alpha$] relationship is non-universal, with dependencies on metallicity and current location in the Galaxy. In this work, we examine these chemical clock tracers across birth radii ($\rm \text{R}_\text{birth}$), recovering the inherent trends between the variables. We derive $\rm \text{R}_\text{birth}$ and explore the [s/$\alpha$]--age--$\rm \text{R}_\text{birth}$ relationship for 36,652 APOGEE DR17 red giant and 24,467 GALAH DR3 main sequence turnoff and subgiant branch disk stars using [Ce/Mg], [Ba/Mg], and [Y/Mg]. We discover that the age--[s/Mg] relation is strongly dependent on birth location in the Milky Way, with stars born in the inner disk having the weakest correlation. This is congruent with the Galaxy's initially weak, negative [s/Mg] radial gradient, which becomes positive and steep with time. We show that the non-universal relations of chemical clocks is caused by their fundamental trends with $\rm \text{R}_\text{birth}$ over time, and suggest that the tight age--[s/Mg] relation obtained with solar-like stars is due to similar $\rm \text{R}_\text{birth}$ for a given age. Our results are put into context with a Galactic chemical evolution model, where we demonstrate the need for data-driven nucleosynthetic yields.

The onset of star formation is set by the collapse of filaments in the interstellar medium. From a theoretical point of view, an isolated cylindrical filament forms cores via the edge effect. Due to the self-gravity of a filament, the strong increase in acceleration at both ends leads to a pile-up of matter which collapses into cores. However, this effect is rarely observed. Most theoretical models consider a sharp density cut-off at the edge of the filament, whereas a smoother transition is more realistic and would also decrease the acceleration at the ends of the filament. We show that the edge effect can be significantly slowed down by a density gradient, although not completely avoided. However, this allows perturbations inside the filament to grow faster than the edge. We determine the critical density gradient for which the timescales are equal and find it to be of the order of several times the filament radius. Hence, the density gradient at the ends of a filament is an essential parameter for fragmentation and the low rate of observed cases of the edge effect could be naturally explained by shallow gradients.

Following the assumption that the disc substructures observed in protoplanetary discs originate from the interaction between the disc and the forming planets embedded therein, we aim to test if these putative planets could represent the progenitors of the currently observed giant exoplanets. We performed N-body simulations assuming initially three, four, five or seven planets. Our model includes pebble and gas accretion, migration, damping of eccentricities and inclinations, disc-planet interaction and disc evolution. We locate the planets in the positions where the gaps in protoplanetary discs have been observed and we evolve the systems for 100Myr including a few Myr of gas disc evolution, while also testing three values of $\alpha$ viscosity. For planetary systems with initially three and four planets we find that most of the growing planets lie beyond the RV detection limit of 5AU and only a small fraction of them migrate into the inner region. We also find that these systems have too low final eccentricities to be in agreement with the observed giant planet population. Systems initially consisting of five or seven planets become unstable after $\approx$40Kyr of integration time. This clearly shows that not every gap can host a planet. The general outcome of our simulations - too low eccentricities - is independent of the disc's viscosity and surface density. Further observations could either confirm the existence of an undetected population of wide-orbit giants or exclude the presence of such undetected population to constrain how many planets hide in gaps even further.

There is a growing interest in astrophysics to fill in the observational gamma-ray MeV gap. We, therefore, developed a CsI:Tl calorimeter prototype as a subsystem to a balloon-based Compton and Pair-production telescope known as ComPair. ComPair is a technology demonstrator for a gamma-ray telescope in the MeV range that is comprised of 4 subsystems: the double-sided silicon detector, virtual Frisch grid CdZnTe, CsI calorimeter, and a plastic-based anti-coincidence detector. The prototype CsI calorimeter is composed of thirty CsI logs, each with a geometry of $1.67 \times 1.67 \times 10 \ \mathrm{cm^3}$. The logs are arranged in a hodoscopic fashion with 6 in a row that alternate directions in each layer. Each log has a resolution of around $8 \%$ full-width-at-half-maximum (FWHM) at $662 \ \mathrm{keV}$ with a dynamic energy range of around $250\ \mathrm{keV}-30 \ \mathrm{MeV}$. A $2\times2$ array of SensL J-series SiPMs read out each end of the log to estimate the depth of interaction and energy deposition with signals read out with an IDEAS ROSSPAD. We also utilize an Arduino to synchronize with the other ComPair subsystems that comprise the full telescope. This work presents the development and performance of the calorimeter, its testing in thermal and vacuum conditions, and results from irradiation by $2-25 \ \mathrm{MeV}$ monoenergetic gamma-ray beams. The CsI calorimeter will fly onboard ComPair as a balloon experiment in the summer of 2023.

We summarize JWST's measured telescope performance across science Cycle 1. The stability of segments alignments is typically better than 10 nanometers RMS between measurements every two days, leading to highly stable point spread functions. The frequency of segment "tilt events" decreased significantly, and larger tilt events ceased entirely, as structures gradually equilibrated after cooldown. Mirror corrections every 1-2 months now maintain the telescope below 70 nm RMS wavefront error. Observed micrometeoroid impacts during cycle 1 had negligible effect on science performance, consistent with preflight predictions. As JWST begins Cycle 2, its optical performance and stability are equal to, and in some ways better than, the performance reported at the end of commissioning.

Ways of formation of azimuthal resonant patterns in circumstellar planetesimal disks with planets are considered. Our analytical estimates and massive numerical experiments show that the disk particles that initially reside in zones of low-order mean-motion resonances with the planet may eventually concentrate into potentially observable azimuthal patterns. The structuring process is rapid, usually taking ~100 orbital periods of the planet. It is found that the relative number of particles that retain their resonant position increases with decreasing the mass parameter $\mu$ (the ratio of masses of the perturbing planet and the parent star), but a significant fraction of the particle population is always removed from the disk due to accretion of the particles onto the star and planet, as well as due to their transition to highly elongated and hyperbolic orbits. Expected radio images of azimuthally structured disks are constructed. In the considered models, azimuthal patterns associated with the 2:1 and 3:2 resonances are most clearly manifested; observational manifestations of the 1:2 and 2:3 resonances are also possible.

Standard stellar evolution theory poorly predicts the surface abundances of chemical species in low-mass, red giant branch (RGB) stars. Observations show an enhancement of p-p chain and CNO cycle products in red giant envelopes, which suggests the existence of non-canonical mixing that brings interior burning products to the surface of these stars. The 12C/13C ratio is a highly sensitive abundance metric used to probe this mixing. We investigate extra RGB mixing by examining (1) how 12C/13C is altered along the RGB and (2) how 12C/13C changes for stars of varying age and mass. Our sample consists of 43 red giants spread over 15 open clusters from the Sloan Digital Sky Survey's APOGEE DR17 that have reliable 12C/13C ratios derived from their APOGEE spectra. We vetted these 12C/13C ratios and compared them as a function of evolution and age/mass to the standard mixing model of stellar evolution and to a model that includes prescriptions for RGB thermohaline mixing and stellar rotation. We find that the observations deviate from standard mixing models, implying the need for extra mixing. Additionally, some of the abundance patterns depart from the thermohaline model, and it is unclear whether these differences are due to incomplete observations, issues inherent to the model, our assumption of the cause of extra mixing, or any combination of these factors. Nevertheless, the surface abundances across our age/mass range clearly deviate from the standard model, agreeing with the notion of a universal mechanism for RGB extra mixing in low-mass stars.

A search has been made for 21 cm HI line emission in a total of 350 unique galaxies from two samples whose optical properties indicate they may be massive The first consists of 241 low surface brightness (LSB) galaxies of morphological type Sb and later selected from the HyperLeda database and the the second consists of 119 LSB galaxies from the UGC with morphological types Sd-m and later. Of the 350 unique galaxies, 239 were observed at the Nancay Radio Telescope, 161 at the Green Bank Telescope, and 66 at the Arecibo telescope. A total of 295 (84.3%) were detected, of which 253 (72.3%) appear to be uncontaminated by any other galaxies within the telescope beam. Finally, of the total detected, uncontaminated galaxies, at least 31 appear to be massive LSB galaxies, with a total HI mass $\ge$ 10$^{10}$ M$_{sol}$, for H$_0$ = 70 km/s/Mpc. If we expand the definition to also include galaxies with significant total (rather than just gas) mass, i.e., those with inclination-corrected HI line width W$_{50}$,cor > 500 km/s, this bring the total number of massive LSB galaxies to 41. There are no obvious trends between the various measured global galaxy properties, particularly between mean surface brightness and galaxy mass.

We present the analysis of 16 classical T Taur stars using LAMOST and TESS data, investigating spectral properties, photometric variations, and mass-accretion rates. All 16 stars exhibit emissions in H$\alpha$ lines, from which the average mass-accretion rate of $1.76\times10^{-9}~M_{\odot}yr^{-1}$ is derived. Two of the stars, DL Tau and Haro 6-13, show mass-accretion bursts simultaneously in TESS, ASAS-SN, and/or ZTF survey. Based on these observations, we find that the mass-accretion rates of DL Tau and Haro 6-13 reach their maximums of $2.5 \times 10^{-8}~M_{\odot}yr^{-1}$ and $2 \times 10^{-10}~M_{\odot}yr^{-1}$ during the TESS observation, respectively. We detect thirteen flares among these stars. The flare frequency distribution shows that the CTTSs' flare activity is not only dominated by strong flares with high energy but much more active than those of solar-type and young low-mass stars. By comparing the variability classes reported in the literature, we find that the transition timescale between different classes of variability in CTTSs, such as from Stochastic (S) to Bursting (B) or from quasi-periodic symmetric (QPS) to quasi-periodic dipping (QPD), may range from 1.6 to 4 years. We observe no significant correlation between inclination and mass-accretion rates derived from the emission indicators. This suggests that inner disk properties may be more important than that of outer disk. Finally, we find a relatively significant positive correlation between the asymmetric metric "M" and the cold disk inclination compared to the literature. A weak negative correlation between the periodicity metric "Q" value and inclination has been also found.

We characterize in detail the very dense $e^- e^+ \gamma$ plasma present during the Big-Bang Nucleosynthesis (BBN) and explore how it is perturbed electromagnetically by \lq\lq impurities, {\it i.e.\/}, spatially dispersed protons and light nuclei undergoing thermal motion. The internuclear electromagnetic screened potential is obtained (analytically) using the linear response approach, allowing for the dynamic motion of the electromagnetic field sources and the damping effects due to plasma component scattering. We discuss the limits of the linear response method and suggest additional work needed to improve BBN reaction rates in the primordial Universe. Our theoretical methods to describe the potential between charged dust particles align with previous studies on planetary and space dusty plasma and could have significant impact on interpretation of standard cosmological model results.

Pulsars are fast spinning neutron stars that lose their rotational energy via various processes such as gravitational and magnetic radiation, particle acceleration and mass loss processes. This dissipation can be quantified by a spin-down equation that measures the rate of change of the frequency as a function of the rotational frequency itself. We explore the pulsar spin-down and consider the spin-down equation upto the seventh order in frequency. This seventh order term accounts for energy loss due to the gravitational radiation caused by a current type quadrupole in the pulsar due to $r$-modes. We derive the rotational frequency due to the $r$-modes and find a solution in terms of the Lambert function. We also present an analytic exact solution for the period from the spindown equation and numerically verify this for the Crab pulsar. This analysis will be relevant for the detection of continuous gravitational waves by 3G ground based and space based gravitational wave detectors.

Ice is a major component of astrophysical environment - from interstellar molecular clouds through protoplanetary disks to evolved solar systems. Ice and complex organic matter coexist in these environments as well, and it is thought primordial ice brought the molecules of life to Earth four billion years ago, which could have kickstarted the origin of life on Earth. To understand the journey of ice and organics from their origins to becoming a part of evolved planetary systems, it is important to complement high spatial and spectral resolution telescopes such as JWST with laboratory experimental studies that provide deeper insight into the processes that occur in these astrophysical environments. Our laboratory studies are aimed at providing this knowledge. In this article we present simultaneous mass spectrometric and infrared spectroscopic investigation on how molecular ice mixtures behave at different temperatures and how this information is critical to interpret observational data from protoplanetary disks as well as comets. We find that amorphous to crystalline water ice transformation is the most critical phenomenon that differentiates between outgassing of trapped volatiles such as CO2 vs. outgassing of pure molecular ice domains of the same in a mixed molecular ice. Crystalline water ice is found to trap only a small fraction of other volatiles (<5%), indicating ice grain composition in astrophysical and planetary environments must be different depending on whether the ice is in amorphous phase or transformed into crystalline phase, even if the crystalline ice undergoes radiation-induced amorphization subsequently. Crystallization of water ice is a key differentiator for many ices in astronomical environments as well as in our Solar System.

Astronomical observations with gamma rays in the range of several hundred keV to hundreds of MeV currently represent the least explored energy range. To address this so-called MeV gap, we designed and built a prototype CsI:Tl calorimeter instrument using a commercial off-the-shelf (COTS) SiPMs and front-ends which may serve as a subsystem for a larger gamma-ray mission concept. During development, we observed significant non-linearity in the energy response. Additionally, using the COTS readout, the calorimeter could not cover the four orders of magnitude in energy range required for the telescope. We, therefore, developed dual-gain silicon photomultiplier (SiPM) boards that make use of two SiPM species that are read out separately to increase the dynamic energy range of the readout. In this work, we investigate the SiPM's response with regards to active area ($3\times3 \ \mathrm{mm}^2$ and $1 \times 1 \ \mathrm{mm}^2$) and various microcell sizes ($10$, $20$, and $35 \ \mu \mathrm{m}$). We read out $3\times3\times6 \ \mathrm{cm}^3$ CsI:Tl chunks using dual-gain SiPMs that utilize $35 \ \mu \mathrm{m}$ microcells for both SiPM species and demonstrate the concept when tested with high-energy gamma-ray and proton beams. We also studied the response of $17 \times 17 \times 100 \ \mathrm{mm}^3$ CsI bars to high-energy protons. With the COTS readout, we estimate (with several assumptions) that the dual-gain prototype has an energy range of $0.25-400 \ \mathrm{MeV}$ with the two SiPM species overlapping at a range of around $2.5-30 \ \mathrm{MeV}$. This development aims to demonstrate the concept for future scintillator-based high-energy calorimeters with applications in gamma-ray astrophysics.

Gamma-ray bursts produce afterglows that can be observed across the electromagnetic spectrum and can provide insight into the nature of their progenitors. While most telescopes that observe afterglows are designed to rapidly react to trigger information, the Transiting Exoplanet Survey Satellite (TESS) continuously monitors sections of the sky at cadences between 30 minutes and 200 seconds. This provides TESS with the capability of serendipitously observing the optical afterglow of GRBs. We conduct the first extensive search for afterglows of known GRBs in archival TESS data reduced with the TESSreduce package, and detect 11 candidate signals that are temporally coincident with reported burst times. We classify 3 of these as high-likelihood GRB afterglows previously unknown to have been detected by TESS, one of which has no other afterglow detection reported on the Gamma-ray Coordinates Network. We classify 5 candidates as tentative and the remainder as unlikely. Using the afterglowpy package, we model each of the candidate light curves with a Gaussian and a top hat model to estimate burst parameters; we find that a mean time delay of $740\pm690\,$s between the explosion and afterglow onset is required to perform these fits. The high cadence and large field of view make TESS a powerful instrument for localising GRBs, with the potential to observe afterglows in cases when no other backup photometry is possible.

I call attention to extraordinary features displayed by the genetically related long-period comet pair of C/1844 Y1 (Great Comet) and C/2019 Y4 (ATLAS). The issue addressed most extensively is the fragmentation and disintegration of the latter object, itself a thousands-of-years-old fragment. Of the four fragments of C/2019 Y4 recognized by the Minor Planet Center -- A, B, C, and D -- I confirm that B was the principal mass, which stayed undetected until early April. The comet's 2020 fragmentation is proposed to have begun with a separation of B and A near 22 January, when the nuclear condensation suddenly started to brighten rapidly. From late January to early April, only Fragment A was observed. The remaining Fragments C and D split off most probably from A in mid-March, but they too were detected only in April. A new fragment, E, is proposed to have been observed on three days. Further addressed are the issues of the orbital period and antitail of C/1844 Y1 and the extreme position of this pair among the genetically related groups/pairs of long-period comets.

Narrowband radio search for extraterrestrial intelligence (SETI) in the 21st century suffers severely from radio frequency interference (RFI), resulting in a high number of false positives, and it could be the major reason why we have not yet received any messages from space. We thereby propose a novel observation strategy, called MultiBeam Point-source Scanning (MBPS), to revolutionize the way RFI is identified in narrowband radio SETI and provide a prominent solution to the current situation. The MBPS strategy is a simple yet powerful method that sequentially scans over the target star with different beams of a telescope, hence creating real-time references in the time domain for cross-verification, thus potentially identifying all long-persistent RFI with a level of certainty never achieved in any previous attempts. By applying the MBPS strategy during the observation of TRAPPIST-1 with the FAST telescope, we successfully identified all 16,645 received signals as RFI using the solid criteria introduced by the MBPS strategy. Therefore we present the MBPS strategy as a promising tool that should bring us much closer to the first discovery of a genuine galactic greeting.

Observations from the James Webb Space Telescope (JWST) have unveiled several galaxies with stellar mass $M_*\gtrsim10^{10} M_\odot$ at $7.4\lesssim z\lesssim 9.1$. These remarkable findings indicate an unexpectedly high stellar mass density, which contradicts the prediction of the $\Lambda \rm CDM$ model. We adopt the Chevallier--Polarski--Linder (CPL) parameterization, one of the dynamic dark energy models, to probe the role of dark energy on shaping the galaxy formation. By considering varying star formation efficiencies within this framework, our analysis demonstrates that an increased proportion of dark energy in the universe corresponds to the formation of more massive galaxies at higher redshifts, given a fixed perturbation amplitude observed today. Furthermore, through elaborately selecting CPL parameters, we successfully explain the JWST observations with star formation efficiencies $\epsilon\gtrsim0.05$ at a confidence level of $95\%$. These intriguing results indicate the promising prospect of revealing the nature of dark energy by analyzing the high-redshift massive galaxies.

The ability to launch small secondary payloads to Mars on future science missions present an exciting opportunity for demonstration of advanced technologies for planetary exploration such as aerocapture. Over the years, several aerocapture technology demonstration missions have been proposed but none could be realized, causing the technology to become dormant as it is seen as too risky and expensive to be used on a science mission. The present study proposes a low-cost Mars aerocapture demonstration concept as a secondary payload, and could pave the way for future low-cost small interplanetary orbiter missions. The proposed mission heavily leverages the mission architecture and the flight hardware of the MarCO spacecraft for a low cost mission. The 35 kg technology demonstrator would launch as an ESPA secondary payload on a future Mars mission, and would be deployed from the upper stage soon after primary spacecraft separation. The vehicle then independently cruises to Mars, where it will perform aerocapture and insert a 6U MarCO heritage CubeSat to a 200 x 2000 km orbit. The mission architecture incorporates a number of cost saving approaches, and is estimated to fit within a 30M cost cap, of which 10M is allocated for technology development and risk reduction.

Small-scale eruptions could play an important role in coronal heating, generation of solar energetic particles (SEPs), and mass source of the solar wind. However, they are poorly observed, and their characteristics, distributions, and origins remain unclear. Here a mini coronal dimming was captured by the recently launched Solar Orbiter spacecraft. The observations indicate that a minifilament eruption results in the dimming and takes away approximately $(1.65\pm0.54)\times10^{13}$ g of mass, which also exhibits similar features as the sources of SEP events. The released magnetic free energy is of the order of $\sim10^{27}$ erg. Our results suggest that weak constraining force makes the flux rope associated with the minifilament easily enter a torus-unstable domain. We discuss that weak magnetic constraints from low-altitude background fields may be a general condition for the quiet-Sun eruptions, which provide a possible mechanism for the transport of coronal material and energy from the lower to the middle or even higher corona.

We perform the weak lensing mass mapping analysis to identify troughs, which are defined as local minima in the mass map. Since weak lensing probes projected matter along the line-of-sight, these troughs can be produced by single voids or multiple voids projected along the line-of-sight. To scrutinise the origins of the weak lensing troughs, we systematically investigate the line-of-sight structure of troughs selected from the latest Subaru Hyper Suprime-Cam (HSC) Year 3 weak lensing data covering $433.48 \, \mathrm{deg}^2$. From a curved sky mass map constructed with the HSC data, we identify 15 troughs with the signal-to-noise ratio higher than $5.7$ and address their line-of-sight density structure utilizing redshift distributions of two galaxy samples, photometric luminous red galaxies observed by HSC and spectroscopic galaxies detected by Baryon Oscillation Spectroscopic Survey. While most of weak lensing signals due to the troughs are explained by multiple voids aligned along the line-of-sight, we find that two of the 15 troughs potentially originate from single voids at redshift $\sim 0.3$. The single void interpretation appears to be consistent with our three-dimensional mass mapping analysis. We argue that single voids can indeed reproduce observed weak lensing signals at the troughs if these voids are not spherical but are highly elongated along the line-of-sight direction.

We show that it is possible to directly measure the formation time of galaxies using large-scale structure. In particular, we show that the large-scale distribution of galaxies is sensitive to whether galaxies form over a narrow period of time before their observed times, or are formed over a time scale on the order of the age of the Universe. Along the way, we derive simple recursion relations for the perturbative terms of the most general bias expansion for the galaxy density, thus fully extending the famous dark-matter recursion relations to generic tracers.

Lorentz invariance violation (LIV) is a proposed phenomenon where Lorentz symmetry is violated at high energies, potentially affecting particle dynamics and interactions. We use numerical simulations with the CRPropa framework to investigate LIV in gamma-ray-induced electromagnetic cascades, specifically studying how it impacts cascading electrons and photons undergoing pair production and inverse Compton scattering. Our detailed analysis of the simulation results, compared with existing theoretical models, reveals that LIV can significantly alter the behavior of both components of the cascade, photons and electrons, resulting in specific signatures in measured fluxes that could be observed in high-energy gamma-ray observations. These insights are crucial for ongoing searches for LIV and for the development of theoretical models incorporating LIV effects.

Distribution of stellar $\mathrm{H}\alpha$ chromospheric activity with respect to stellar atmospheric parameters (effective temperature $T_\mathrm{eff}$, surface gravity $\log\,g$, and metallicity $\mathrm{[Fe/H]}$) and main-sequence/giant categories is investigated for the F-, G-, and K-type stars observed by the LAMOST Medium-Resolution Spectroscopic Survey (MRS). A total of 329,294 MRS spectra from LAMOST DR8 are utilized in the analysis. The $\mathrm{H}\alpha$ activity index ($I_{\mathrm{H}{\alpha}}$) and the $\mathrm{H}\alpha$ $R$-index ($R_{\mathrm{H}{\alpha}}$) are evaluated for the MRS spectra. The $\mathrm{H}\alpha$ chromospheric activity distributions with individual stellar parameters as well as in the $T_\mathrm{eff}$ -- $\log\,g$ and $T_\mathrm{eff}$ -- $\mathrm{[Fe/H]}$ parameter spaces are analyzed based on the $R_{\mathrm{H}{\alpha}}$ index data. It is found that: (1) for the main-sequence sample, the $R_{\mathrm{H}{\alpha}}$ distribution with $T_\mathrm{eff}$ has a bowl-shaped lower envelope with a minimum at about 6200 K, a hill-shaped middle envelope with a maximum at about 5600 K, and an upper envelope continuing to increase from hotter to cooler stars; (2) for the giant sample, the middle and upper envelopes of the $R_{\mathrm{H}{\alpha}}$ distribution first increase with decrease of $T_\mathrm{eff}$ and then drop to a lower activity level at about 4300 K, revealing the different activity characteristics at different stages of stellar evolution; (3) for both the main-sequence and giant samples, the upper envelope of the $R_{\mathrm{H}{\alpha}}$ distribution with metallicity is higher for stars with $\mathrm{[Fe/H]}$ greater than about $-1.0$, and the lowest-metallicity stars hardly exhibit high $\mathrm{H}\alpha$ indices. A dataset of $\mathrm{H}\alpha$ activity indices for the LAMOST MRS spectra analyzed is provided with this paper.

The GAIA space mission is impacting astronomy in many significant ways by providing a uniform, homogeneous and precise data set for over 1 billion stars and other celestial objects in the Milky Way and beyond. Exoplanet science has greatly benefited from the unprecedented accuracy of stellar parameters obtained from GAIA. In this study, we combine photometric, astrometric, and spectroscopic data from the most recent Gaia DR3 to examine the kinematic and chemical age proxies for a large sample of 2611 exoplanets hosting stars whose parameters have been determined uniformly. Using spectroscopic data from the Radial Velocity Spectrometer (RVS) onboard GAIA, we show that stars hosting massive planets are metal-rich and $\alpha$-poor in comparison to stars hosting small planets. The kinematic analysis of the sample reveals that the stellar systems with small planets and those with giant planets differ in key aspects of galactic space velocity and orbital parameters, which are indicative of age. We find that the galactic orbital parameters have a statistically significant difference of 0.06 kpc for $Z_{max}$ and 0.03 for eccentricity respectively. Furthermore, we estimated the stellar ages of the sample using the MIST-MESA isochrone models. The ages and its proxies for the planet-hosting stars indicate that the hosts of giant planetary systems are younger compared to the population of stars harboring small planets. These age trends are also consistent with the chemical evolution of the galaxy and the formation of giant planets from the core-accretion process.

We investigate polarization spectra of hydrogen-rich core-collapse supernovae (Type~II SNe). The polarization signal from SNe contains two independent components: intrinsic SN polarization and interstellar polarization (ISP). From these components, we can study the SN explosion geometry and the dust properties in their host galaxies or in the Milky Way. In this first paper, using a new improved method, we investigate the properties of the ISP components of 11 well-observed Type~II SNe. As a result of our analysis, we find that 10 out of these 11 SNe showed a steady ISP component with a polarization degree $\lesssim 1.0$ \%, while one SN was consistent with zero ISP. As for the wavelength dependence, SN~2001dh (and possibly SN~2012aw) showed a non-Milky-Way-like ISP likely originating from the interstellar dust in their respective host galaxies: their polarization maxima were located at short wavelengths ($\lesssim4000$~\AA). Similar results have been obtained previously for highly reddened SNe. The majority of the SNe in our sample had too large uncertainties in the wavelength dependence of their ISP components to consider them further. Our work demonstrates that, by applying this method to a larger SN sample, further investigation of the ISP component of the SN polarization can provide new opportunities to study interstellar dust properties in external galaxies.

We investigate spectro-temporal properties for two black hole X-ray binary sources, MAXI J1535$-$571 and H 1743$-$322, during their hard and hard-intermediate states. For MAXI J1535$-$571, we analyze Swift/XRT, NuSTAR and NICER observations, specifically focusing on the occurrence of type-C Quasi-periodic Oscillations (QPOs). Regarding H 1743$-$322, we analyze multi-epoch observations of NICER and AstroSat, identifying a type-C QPO with centroid frequency ranging from 0.1--0.6 Hz. In both sources, we fit the spectra with a relativistic truncated disk and a power law component. In MAXI J1535$-$571, we also observe an additional relativistically smeared iron line. Through temporal and spectral analysis, we estimate the QPO centroid frequency and spectral parameters, such as the accretion rate and inner disc radii. We test the origin of type-C QPOs as relativistic precession frequency and dynamic frequency (i.e. the inverse of the sound crossing time $\frac{r}{c_s(r)}$). The dependence of QPO frequency on both the accretion rate and inner disc radii favours the QPO origin as dynamic frequency. We discuss the implications of these results.

We present spaxel-by-spaxel stellar population fits for the $\sim$10 thousand MaNGA datacubes. We provide multiple extension fits files, nominated as MEGACUBES, with maps of several properties as well as emission-line profiles that are provided for each spaxel. All the MEGACUBES are available through a web interface (https://manga.linea.org.br/ or this http URL). We also defined a final Active Galactic Nuclei (AGN) sample, as well as a control sample matching the AGN host galaxy properties. We have analysed the stellar populations and spatially resolved emission-line diagnostic diagrams of these AGNs and compared them with the control galaxies sample. We find that the relative fractions of young ($t \leq $56 Myr) and intermediate-age (100 Myr $\leq t \leq$ 2 Gyr) show predominantly a positive gradient for both AGNs and controls. The relative fraction of intermediate-age stellar population is higher in AGN hosts when compared to the control sample, and this difference becomes larger for higher [O III] luminosity AGNs. We attribute this to the fact that extra gas is available in these more luminous sources and that it most likely originates from mass-loss from the intermediate-age stars. The spatially resolved diagnostic diagrams reveal that the AGN emission is concentrated in the inner 0.5 $R_e$ (effective radius) region of the galaxies, showing that the AGN classification is aperture dependent and that emission-line ratios have to be taken together with the H$\alpha$ equivalent width for proper activity classification. We present a composite "BPT+WHAN" diagram that produces a more comprehensive mapping of the gas excitation.

The 2021 outburst of the symbiotic recurrent nova RS Oph was monitored with the Neutron Star Interior Composition Explorer Mission (NICER) in the 0.2-12 keV range from day one after the optical maximum, until day 88, producing an unprecedented, detailed view of the outburst development. The X-ray flux preceding the supersoft X-ray phase peaked almost 5 days after optical maximum and originated only in shocked ejecta for 21 to 25 days. The emission was thermal; in the first 5 days only a non-collisional-ionization equilibrium model fits the spectrum, and a transition to equilibrium occurred between days 6 and 12. The ratio of peak X-rays flux measured in the NICER range to that measured with Fermi in the 60 MeV-500 GeV range was about 0.1, and the ratio to the peak flux measured with H.E.S.S. in the 250 GeV-2.5 TeV range was about 100. The central supersoft X-ray source (SSS), namely the shell hydrogen burning white dwarf (WD), became visible in the fourth week, initially with short flares. A huge increase in flux occurred on day 41, but the SSS flux remained variable. A quasi-periodic oscillation every ~35 s was always observed during the SSS phase, with variations in amplitude and a period drift that appeared to decrease in the end. The SSS has characteristics of a WD of mass >1 M(solar). Thermonuclear burning switched off shortly after day 75, earlier than in 2006 outburst. We discuss implications for the nova physics.

A lower-than-solar elemental nitrogen content has been demonstrated for several comets, including 1P/Halley and 67P/C-G with independent in situ measurements of volatile and refractory budgets. The recently discovered semi-refractory ammonium salts in 67P/C-G are thought to be the missing nitrogen reservoir in comets. The thermal desorption of ammonium salts from cometary dust particles leads to their decomposition into ammonia and a corresponding acid. The NH$_{3}$/H$_{2}$O ratio is expected to increase with decreasing heliocentric distance with evidence for this in near-infrared observations. NH$_{3}$ has been claimed to be more extended than expected for a nuclear source. Here, the aim is to constrain the NH$_{3}$/H$_{2}$O ratio in comet C/2020 F3 (NEOWISE) during its July 2020 passage. OH emission from comet C/2020 F3 (NEOWISE) was monitored for 2 months with NRT and observed from GBT on 24 July and 11 August 2020. Contemporaneously with the 24 July 2020 OH observations, the NH$_{3}$ hyperfine lines were targeted with GBT. The concurrent GBT and NRT observations allowed the OH quenching radius to be determined at $\left(5.96\pm0.10\right)\times10^{4}$ km on 24 July 2020, which is important for accurately deriving $Q(\text{OH})$. C/2020 F3 (NEOWISE) was a highly active comet with $Q(\text{H}_{2}\text{O}) \approx 2\times10^{30}$ molec s$^{-1}$ one day before perihelion. The $3\sigma$ upper limit for $Q_{\text{NH}_{3}}/Q_{\text{H}_{2}\text{O}}$ is $<0.29\%$ at $0.7$ au from the Sun. The obtained NH$_{3}$/H$_{2}$O ratio is a factor of a few lower than measurements for other comets at such heliocentric distances. The abundance of NH$_{3}$ may vary strongly with time depending on the amount of water-poor dust in the coma. Lifted dust can be heated, fragmented, and super-heated; whereby, ammonium salts, if present, can rapidly thermally disintegrate and modify the NH$_{3}$/H$_{2}$O ratio.

We report the first detection in the interstellar medium of a C$_2$H$_5$O$_2$N isomer: $syn$-glycolamide (NH$_2$C(O)CH$_2$OH). The exquisite sensitivity at sub-mK levels of an ultra-deep spectral survey carried out with the Yebes 40m and IRAM 30m telescopes towards the G+0.693-0.027 molecular cloud have allowed us to unambiguously identify multiple transitions of this species. We derived a column density of (7.4 $\pm$ 0.7)$\times$10$^{12}$ cm$^{-2}$, which implies a molecular abundance with respect to H$_2$ of 5.5$\times$10$^{-11}$. The other C$_2$H$_5$O$_2$N isomers, including the higher-energy $anti$ conformer of glycolamide, and two conformers of glycine, were not detected. The upper limit derived for the abundance of glycine indicates that this amino acid is surely less abundant than its isomer glycolamide in the ISM. The abundances of the C$_2$H$_5$O$_2$N isomers cannot be explained in terms of thermodynamic equilibrium, and thus chemical kinetics need to be invoked. While the low abundance of glycine might not be surprising, based on the relative low abundances of acids in the ISM compared to other compounds (e.g. alcohols, aldehydes or amines), several chemical pathways can favour the formation of its isomer glycolamide. It can be formed through radical-radical reactions on the surface of dust grains. The abundances of these radicals can be significantly boosted in an environment affected by a strong ultraviolet field induced by cosmic rays, such as that expected in G+0.693-0.027. Therefore, as shown by several recent molecular detections towards this molecular cloud, it stands out as the best target to discover new species with carbon, oxygen and nitrogen with increasing chemical complexity.

SPIRou is a near-infrared spectropolarimeter and a high-precision velocimeter. The SPIRou Legacy Survey collected data from February 2019 to June 2022, half of the time devoted to a blind search for exoplanets around nearby cool stars. The aim of this paper is to present this program and an overview of its properties, and to revisit the radial velocity (RV) data of two multiplanet systems, including new visits with SPIRou. From SPIRou data, we can extract precise RVs using efficient telluric correction and line-by-line measurement techniques, and we can reconstruct stellar magnetic fields from the collection of polarized spectra using the Zeeman-Doppler imaging method. The stellar sample of our blind search in the solar neighborhood, the observing strategy, the RV noise estimates, chromatic behavior, and current limitations of SPIRou RV measurements on bright M dwarfs are described. In addition, SPIRou data over a 2.5-year time span allow us to revisit the known multiplanet systems GJ~876 and GJ~1148. For GJ~876, the new dynamical analysis including the four planets is consistent with previous models and confirms that this system is deep in the Laplace resonance and likely chaotic. The large-scale magnetic map of GJ~876 over two consecutive observing seasons is obtained and shows a dominant dipolar field with a polar strength of 30~G, which defines the magnetic environment in which the inner planet with a period of 1.94~d is embedded. For GJ~1148, we refine the known two-planet model.

The time scales of variability in active M dwarfs can be related to their various physical parameters. Thus, it is important to understand such variability to decipher the physics of these objects. In this study, we have performed the low resolution ($\sim$5.7\AA) spectroscopic monitoring of 83 M dwarfs (M0-M6.5) to study the variability of H$\alpha$ / H$\beta$ emissions; over the time scales from $\sim$0.7 to 2.3 hours with a cadence of $\sim$3-10 minutes. Data of a sample of another 43 late-type M dwarfs (M3.5-M8.5) from the literature are also included to explore the entire spectral sequence. 53 of the objects in our sample ($\sim$64\%) show statistically significant short-term variability in H$\alpha$. We show that this variability in 38 of them are most likely to be related to the flaring events. We find that the early M dwarfs are less variable despite showing higher activity strengths (L$_{H\alpha}$/L$_{bol}$ \& L$_{H\beta}$/L$_{bol}$), which saturates around $\sim$10$^{-3.8}$ for M0-M4 types. Using archival photometric light curves from TESS and Kepler/K2 missions, the derived chromospheric emission (\ha and \hb emission) variability is then explored for any plausible systematics with respect to their rotation phase. The variability indicators clearly show higher variability in late-type M dwarfs (M5-M8.5) with shorter rotation periods ($<$2 days). For 44 sources, their age has been estimated using StarHorse project and possible correlations with variability have been explored. The possible causes and implications for these behaviors are discussed.

Context. Stars in transition phases, like those showing the B[e] phenomenon and luminous blue variables (LBVs), undergo strong, often irregular mass ejection events. The prediction of these phases in stellar evolution models is therefore extremely difficult if not impossible. As a result, their effective temperatures, their luminosities and even their true nature are not fully known. Aims. A suitable procedure to derive the stellar parameters of these types of objects is to use the BCD spectrophotometric classification system, based on the analysis of the Balmer discontinuity. The BCD parameters ({\lambda}_1, D) are independent of interstellar extinction and circumstellar contributions. Methods. We obtained low-resolution spectra for 14 stars with the B[e] phenomenon and LBVs. Using the BCD method, we derived the stellar and physical parameters. The study was complemented with the information provided by the JHK colour-colour diagram. Results. For each star, the BCD system gives a complete set of fundamental parameters and related quantities such as luminosity and distance. We confirmed HK Ori, HD 323771 and HD 52721 as pre-main sequence HAe/B[e], AS 202 and HD 85567 as FS CMa-type, and HD 62623 as sgB[e] stars. We classified Hen 3-847, CD-24 5721, and HD 53367 as young B[e] stars or FS CMa-type candidates, and HD 58647 as a slightly evolved B[e] star. In addition, Hen 3-1398 is an sgB[e] and MWC 877, CPD-59 2854 and LHA 120-S 65 are LBV candidates. The stellar parameters of the latter two LBVs are determined for the first time. Conclusions. Our results emphasise that the BCD system is a highly valuable tool to derive stellar parameters and physical properties of B-type stars in transition phases. This method can be combined with near-IR colour-colour diagrams to determine or confirm the evolutionary stage of emission-line stars with dust disks.

The growing population of man-made objects with the build up of mega-constellations not only increases the potential danger to all space vehicles and in-space infrastructures (including space observatories), but above all poses a serious threat to astronomy and dark skies. Monitoring of this population requires precise satellite characterization, which is is a challenging task that involves analyzing observational data such as position, velocity, and light curves using optimization methods. In this study, we propose and analyze the application of two optimization procedures to determine the parameters associated with the dynamics of a satellite: one based on the Theory of Functional Connections (TFC) and another one based on the Nelder-Mead heuristic optimization algorithm. The TFC performs linear functional interpolation to embed the constraints of the problem into a functional. In this paper, we propose to use this functional to analytically embed the observational data of a satellite into its equations of dynamics. After that, any solution will always satisfy the observational data. The second procedure proposed in this research takes advantage of the Nealder-Mead algorithm, that does not require the gradient of the objective function, as alternative solution. The accuracy, efficiency, and dependency on the initial guess of each method is investigated, analyzed, and compared for several dynamical models. These methods can be used to obtain the physical parameters of a satellite from available observational data and for space debris characterization contributing to follow-up monitoring activities in space and astronomical observatories.

Metallicity is a fundamental physical property that strongly constrains galaxy formation and evolution. The formation of stars in galaxies is suppressed by the energy released from supernova explosions and can be enhanced by metal production. In order to understand the impact of this supernova feedback, we compare four different feedback methods, ejecting energy in thermal, kinetic, stochastic and mechanical forms, into our self-consistent cosmological chemodynamical simulations. To minimise other uncertainties, we use the latest nucleosynthesis yields that can reproduce the observed elemental abundances of stars in the Milky Way. For each method, we predict the evolution of stellar and gas-phase metallicities as a function of galaxy mass, i.e., the mass-metallicity relations. We then find that the mechanical feedback can give the best match to a number of observations up to redshift $z\sim3$, although the predicted gas-phase metallicities seem to be higher than observed at $z\ge 1$. The feedback modelling can be further constrained by the metallicities in distant galaxies with the James Web Space Telescope and those of a large sample with ongoing and future spectroscopic surveys.

Context. Galactic cosmic rays (GCRs) and solar particles with energies greater than tens of MeV penetrate spacecraft and instruments hosted aboard space missions. The Solar Orbiter Metis coronagraph is aimed at observing the solar corona in both visible (VL) and ultraviolet (UV) light. Particle tracks are observed in the Metis images of the corona. An algorithm has been implemented in the Metis processing electronics to detect the VL image pixels crossed by cosmic rays. This algorithm was initially enabled for the VL instrument only, since the process of separating the particle tracks in the UV images has proven to be very challenging. Aims. We study the impact of the overall bulk of particles of galactic and solar origin on the Metis coronagraph images. We discuss the effects of the increasing solar activity after the Solar Orbiter mission launch on the secondary particle production in the spacecraft. Methods. We compared Monte Carlo simulations of GCRs crossing or interacting in the Metis VL CMOS sensor to observations gathered in 2020 and 2022. We also evaluated the impact of solar energetic particle events of different intensities on the Metis images. Results. The study of the role of abundant and rare cosmic rays in firing pixels in the Metis VL images of the corona allows us to estimate the efficiency of the algorithm applied for cosmic-ray track removal from the images and to demonstrate that the instrument performance had remained unchanged during the first two years of the Solar Orbiter operations. The outcome of this work can be used to estimate the Solar Orbiter instrument's deep charging and the order of magnitude for energetic particles crossing the images of Metis and other instruments such as STIX and EUI.

Active Galactic Nuclei (AGN) are intensely accreting supermassive black holes at the centers of massive galaxies. Though these objects occupy little spatial extent of the galaxy itself, they are thought to have far reaching affects, impacting the galaxy's star formation, and possibly it's lifespan until it becomes 'red and dead'. Typical galaxies demonstrate that, over cosmic time, they tend to separate into a bimodal distribution of 'red and dead' or blue and star forming. We examine whether active galaxies evolve over cosmic time in a similar way, and whether this can reveal anything about the complexities of the relationship between an AGN and the host galaxy. We use the Stripe82X survey to identify 3940 X-ray AGN spanning z=0-2.5, and we measure the rest-frame UVJ colors of each galaxy. We classify AGN as star-forming or quiescent based on their location in a UVJ color diagram. We find that there is not a clear bimodal distribution between AGN in star forming and quiescent galaxies. Furthermore, the most luminous X-ray sources tend to lie in the star forming region, which may indicate a correlation between central engine activity and increased rates of star formation.

The origin and evolution of structure in the Universe could be studied in the Dark Ages. The highly redshifted HI signal between 30 < z < 80 is the only observable signal from this era. Human radio interference and ionospheric effects limit Earth-based radio astronomy to frequencies > 30 MHz. To observe the low-frequency window with research from compact steep spectrum sources, pulsars, and solar activity, a 200 km baseline lunar far-side radio interferometer has been much discussed. This paper conducts a preliminary site survey of potential far-side craters, which are few in number on the mountainous lunar far-side. Based on LRO LOLA data, 200 m resolution topographic maps of eight far-side sites were produced, and slope and roughness maps were derived from them. A figure of merit was created to determine the optimum site. Three sites are identified as promising. There is a need to protect these sites for astronomy.

Accurately estimating the C/O ratio of hot Jupiter atmospheres is a promising pathway towards understanding planet formation and migration, as well as the formation of clouds and the overall atmospheric composition. The atmosphere of the hot Jupiter WASP-43b has been extensively analysed using low-resolution observations with HST and Spitzer, but these previous observations did not cover the K band, which hosts prominent spectral features of major carbon-bearing species such as CO and CH$_{4}$. As a result, the ability to establish precise constraints on the C/O ratio was limited. Moreover, the planet has not been studied at high spectral resolution, which can provide insights into the atmospheric dynamics. In this study, we present the first high-resolution dayside spectra of WASP-43b with the new CRIRES$^+$ spectrograph. By observing the planet in the K band, we successfully detected the presence of CO and provide evidence for the existence of H$_2$O using the cross-correlation method. This discovery represents the first direct detection of CO in the atmosphere of WASP-43b. Furthermore, we retrieved the temperature-pressure profile, abundances of CO and H$_2$O, and a super-solar C/O ratio of 0.78 by applying a Bayesian retrieval framework to the data. Our findings also shed light on the atmospheric characteristics of WASP-43b. We found no evidence for a cloud deck on the dayside, and recovered a line broadening indicative of an equatorial super-rotation corresponding to a jet with a wind speed of $\sim$ 5 km s$^{-1}$, matching the results of previous forward models and low-resolution atmospheric retrievals for this planet.

The theory of transport of charged particles in cosmic magnetic fields is at the very center of the investigation of non-thermal phenomena in the universe, ranging from our local neighborhood to supernovae, clusters of galaxies or distant active galaxies. It is crucial to understand how particles get energized to non-thermal energies as well as to describe their motion from the sources to an observer or to another location in the universe. Here I summarize some essential, basic aspects of the theory and discuss some topics in the theoretical framework that are currently being developed. I will also discuss some simple applications of the theory of transport to particle acceleration and propagation in the Galaxy.

We present full-track high-resolution radio observations of the jet of the galaxy M87 at 8 and 15 GHz. These observations were taken over three consecutive days in May 2009 using the Very Long Baseline Array (VLBA), one antenna of the Very Large Array (VLA), and the Effelsberg 100 m telescope. Our produced images have dynamic ranges exceeding 20,000:1 and resolve linear scales down to approximately 100 Schwarzschild radii, revealing a limb-brightened jet and a faint, steep spectrum counter-jet. We performed jet-to-counter-jet analysis, which helped estimate the physical parameters of the flow. The rich internal structure of the jet is dominated by three helical threads, likely produced by the Kelvin-Helmholtz (KH) instability developing in a supersonic flow with a Mach number of approximately 20 and an enthalpy ratio of around 0.3. We produce a CLEAN imaging bias-corrected 8-15GHz spectral index image, which shows spectrum flattening in regions of helical thread intersections. This further supports the KH origin of the observed internal structure of the jet. We detect polarised emission in the jet at distances of approximately 20 milliarcseconds from the core and find Faraday rotation which follows a transverse gradient across the jet. We apply Faraday rotation correction to the polarisation position angle and find that the position angle changes as a function of distance from the jet axis, which suggests the presence of a helical magnetic field.

Cosmic ray acceleration at the termination shock of compact star clusters has recently received much attention, mainly because of the detection of gamma ray emission from some of such astrophysical sources. Here we focus on the acceleration of nuclei at the termination shock and we investigate the role played by proton energy losses and spallation reactions of nuclei, especially downstream of the shock. We show that for a rather generic choice of the mean gas density in the cavity excavated by the cluster wind, the spectrum of He nuclei is systematically harder than the spectrum of hydrogen, in a manner that appears to be qualitatively consistent with the observed and yet unexplained phenomenon of discrepant hardening. We also find that the spallation reactions of heavier nuclei are likely to be so severe that their spectra become very hard and with a low normalization, meaning that it is unlikely that heavy nuclei escaping star clusters can provide a sizeable contribution to the spectrum of cosmic rays at the Earth.

PG 1553+113 is a well-known blazar exhibiting evidence of a $\sim\! 2.2$-year quasi-periodic oscillation in radio, optical, X-ray, and $\gamma$-ray bands. We present evidence of a new, longer oscillation of $21.8 \pm 4.7$ years in its historical optical light curve covering 100 years of observation. On its own, this $\sim\! 22$-year period has a statistical significance of $1.9\sigma$ when accounting for the look-elsewhere effect. However, the probability of both the $2.2$- and $22$-year periods arising from noise is $\sim0.02\%$ ($3.5\sigma$). The next peak of the 22-year oscillation should occur around July 2025. We find that the $\sim\,$10:1 relation between these two periods can arise in a plausible supermassive black hole binary model. Our interpretation of PG 1553+113's two periods suggests that the binary engine has a mass ratio $\gtrsim 0.2$, an eccentricity $\lesssim 0.1$, and accretes from a disk with characteristic aspect ratio $\sim 0.03$. The putative supermassive black hole binary radiates nHz gravitational waves, but the amplitude is $\sim10-100$ times too low for detection by foreseeable pulsar timing arrays.

Clusters of galaxies, being the largest collapsed structures in the universe, offer valuable insights into the nature of cosmic evolution. Precise calibration of the mass of clusters can be obtained by extracting their gravitational lensing signal on the Cosmic Microwave Background (CMB) fluctuations. We extend and test here the performance achieved on cluster scales by the parameter-free, maximum a posteriori (MAP) CMB lensing reconstruction method, which has been shown to be optimal in the broader context of CMB lensing mass map and power spectrum estimation. In the context of cluster lensing, the lensing signal of other large-scale structures acts as an additional source of noise. We show here that by delensing the CMB fluctuations around each and every cluster, this noise variance is reduced according to expectations. We also demonstrate that the well-known bias in the temperature quadratic estimator in this regime, sourced by the strong non-Gaussianity of the signal, is almost entirely mitigated without any scale cuts. Being statistically speaking an optimal and blind lensing mass map reconstruction, the MAP estimator is a promising tool for the calibration of the masses of clusters.

Understanding how galaxies interact with the circumgalactic medium (CGM) requires determining how galaxies morphological and stellar properties correlate with their CGM properties. We report an analysis of 66 well-imaged galaxies detected in HST and VLT MUSE observations and determined to be within $\pm$500 km s$^{-1}$ of the redshifts of strong intervening quasar absorbers at $0.2 \lesssim z \lesssim 1.4$ with H I column densities $N_{\rm H I}$ $>$ $10^{18}$ $\rm cm^{-2}$. We present the geometrical properties (S\'ersic indices, effective radii, axis ratios, and position angles) of these galaxies determined using GALFIT. Using these properties along with star formation rates (SFRs, estimated using the H$\alpha$ or [O II] luminosity) and stellar masses ($M_{*}$ estimated from spectral energy distribution fits), we examine correlations among various stellar and CGM properties. Our main findings are as follows: (1) SFR correlates well with $M_{*}$, and most absorption-selected galaxies are consistent with the star formation main sequence (SFMS) of the global population. (2) More massive absorber counterparts are more centrally concentrated and are larger in size. (3) Galaxy sizes and normalized impact parameters correlate negatively with $N_{\rm H I}$, consistent with higher $N_{\rm H I}$ absorption arising in smaller galaxies, and closer to galaxy centers. (4) Absorption and emission metallicities correlate with $M_{*}$ and sSFR, implying metal-poor absorbers arise in galaxies with low past star formation and faster current gas consumption rates. (5) SFR surface densities of absorption-selected galaxies are higher than predicted by the Kennicutt-Schmidt relation for local galaxies, suggesting a higher star formation efficiency in the absorption-selected galaxies.

Studying the gravitational collapse of dust particles toward newly formed black holes has gained popularity following the observation of gravitational waves resulting from the merger of black holes. In this paper, we focus on modelling the descent of dust debris toward a black hole using a numerical code that incorporates relativistic hydrodynamics in the framework of General and Einstein-Gauss Bonnet gravity. We explore the influence of various parameters, such as the black hole's rotation parameter a and the EGB coupling constant alpha, on the curvature effects observed. Both parameters significantly impact the dynamics of the accretion disk formed around the black holes. Furthermore, we discuss the gravitational collapsing process in two distinct scenarios. It is also observed that the mass accretion rate is significantly influenced by these two parameters. The rate at which mass is accreted toward a black hole directly impacts the black hole's growth and evolutionary trajectory.

The paper re-examines the principal methodological questions, arising in the debate over the cosmological standard model's postulate of Dark Matter vs. rivalling proposals that modify standard (Newtonian and general-relativistic) gravitational theory, the so-called Modified Newtonian Dynamics (MOND) and its subsequent extensions. What to make of such seemingly radical challenges of cosmological orthodoxy? In the first part of our paper, we assess MONDian theories through the lens of key ideas of major 20th century philosophers of science (Popper, Kuhn, Lakatos, and Laudan), thereby rectifying widespread misconceptions and misapplications of these ideas common in the pertinent MOND-related literature. None of these classical methodological frameworks, which render precise and systematise the more intuitive judgements prevalent in the scientific community, yields a favourable verdict on MOND and its successors -- contrary to claims in the MOND-related literature by some of these theories' advocates; the respective theory appraisals are largely damning. Drawing on these insights, the paper's second part zooms in on the most common complaint about MONDian theories, their ad-hocness. We demonstrate how the recent coherentist model of ad-hocness captures, and fleshes out, the underlying -- but too often insufficiently articulated -- hunches underlying this critique. MONDian theories indeed come out as severely ad hoc: they do not cohere well with either theoretical or empirical-factual background knowledge. In fact, as our complementary comparison with the cosmological standard model's Dark Matter postulate shows, with respect to ad-hocness, MONDian theories fare worse than the cosmological standard model.

We find the conditions under which scale-invariant Einstein-Cartan gravity with scalar matter fields leads to an approximate conformal invariance of the flat space particle theory up to energies of the order of the Planck mass. In the minimal setup, these models, in addition to the fields of the Standard Model and the graviton, contain only one extra particle -- a massless dilaton. Theories of this type can pave the way for a self-completion all the way up the Planck scale and lead to rather universal inflationary predictions, close to those of the simplest Higgs-inflation scenario in the metric theory of gravity.

Upcoming neutrino telescopes promise a new window onto the interactions of neutrinos with matter at ultrahigh energies ($E_\nu = 10^7$-$10^{10}$ GeV), and the possibility to detect deviations from the Standard Model predictions. In this paper, we update previous predictions for the enhancement of the neutrino-nucleon cross-section for motivated leptoquark models and show the latest neutrino physics bound, as well as analyse the latest LHC pair production and Drell-Yan data, and flavour constraints (some of which were previously missed). We find that, despite the next generation of neutrino experiments probing the highest energies, they will not be enough to be competitive with collider searches.

Recent studies have shown that quasinormal modes suffer from spectral instabilities, a frailty of black holes that leads to disproportional migration of their spectra in the complex plane when black-hole effective potentials are modified by minuscule perturbations. Similar results have been found with the mathematical notion of the pseudospectrum which was recently introduced in gravitational physics. Environmental effects, such as the addition of a thin accretion disk or a matter shell, lead to a secondary bump that appears in the effective potential of black hole perturbations. Regardless of the environment's small contribution to the effective potential, its presence can completely destabilize the fundamental quasinormal mode and may potentially affect black hole spectroscopy. Here, we perform a comprehensive analysis of such phenomenon for Schwarzschild, Reissner-Nordstr\"om, Schwarzschild-de Sitter, and Reissner-Nordstr\"om-de Sitter black holes by considering the potential for a test scalar field with the addition of a tiny bump sufficiently away from the photon sphere. We find a qualitatively similar destabilization pattern for photon sphere, complex, scalar quasinormal modes in all cases, and a surprising spectral stability for dominant scalar, purely imaginary, de Sitter and near-extremal modes that belong to different families of the spectrum. For Reissner-Nordstr\"om-de Sitter black holes, we re-evaluate the validity of the strong cosmic censorship and find that the addition of a realistic bump in the effective potential cannot prevent its violation due to a combination of the spectral stability of dominant de Sitter and near-extremal modes for small cosmological constants and an ineffective migration of the photon sphere modes that dominate the late-time ringdown signal for sufficiently large cosmological constants.

We present the Completely Hackable Amateur Radio Telescope (CHART), a project that provides hands-on radio instrumentation and design experience to undergraduates while bringing accessible radio astronomy experiments to high school students and teachers. Here we describe a system which can detect 21-cm emission from the Milky Way which is optimized for cost and simplicity of construction. Software, documentation, and tutorials are all completely open source to improve the user experience and facilitate community involvement. We demonstrate the design with several observations which we compare with state-of-the-art surveys. The system is shown to detect galactic 21-cm emission in both rural and urban settings.

We compute the detailed energy spectra of axions with two-photon coupling produced in stellar cores over a wide range of stellar masses. We focus on main sequence stars and base our calculations on the stellar interior profiles from MESA, for which we provide simple fits in an appendix. The obtained stellar axion spectra, combined with recent models of star formation history and stellar initial mass function, enable us to estimate the properties of the diffuse axion background sourced by all the stars in the universe. The fluxes of this stellar axion background and its decay photons are subdominant to but can in principle be disentangled from those expected from the Sun and the early universe based on their different spectral and spatial profiles.

Vagnozzi et al. constrained the additional parameter of spacetimes with a photon sphere from the observation of the shadow of Sagittarius A* under the assumption that a distance to the Sagittarius A* and its mass parameter was estimated from other observations. They claimed that a Damour-Solodukhin wormhole with an additional parameter $\lambda$ is not an asymptotically-flat spacetime and that they gave the first robust observational constraint on the parameter $\lambda$ of the Damour-Solodukhin wormhole. However, they overlooked the fact that: (A) the Damour-Solodukhin wormhole spacetime is asymptotically flat, (B) the throat of the Damour-Solodukhin wormhole works as an effective photon sphere for $\lambda>\sqrt{2}/2$, and (C) not only a usual mass parameter but also the parameter $\lambda$ contributes the mass of the Damour-Solodukhin wormhole. Because of the overlook (C), we realize that their constraint on the parameter $\lambda$ is invalid. This is because their method corresponds to the following way: They estimated the mass parameter from the other observations under the assumption $\lambda=0$ even though the value of the parameter $\lambda$ strongly affects the determination of the mass parameter, and then, they used the value of the mass parameter to constrain $\lambda$ from the observation of the shadow. We conclude that we should constrain the mass parameter and $\lambda$ from the shadow observation and other observations without the assumption $\lambda=0$.

Evidence for a stochastic gravitational wave background in the nHz frequency band is recently reported by four pulsar timing array collaborations NANOGrav, EPTA, CPTA, and PPTA. It can be interpreted by gravitational waves from collapsing domain walls in the early universe. We assume such domain walls arising from the spontaneous breaking of a $Z_2$ symmetry in a scalar field theory, where a tiny $Z_2$-violating potential is required to make domain walls unstable. We propose that this $Z_2$-violating potential is radiatively induced by a feeble Yukawa coupling between the scalar field and a fermion field, which is also responsible for dark matter production via the freeze-in mechanism. Combining the pulsar timing array data and the observed dark matter relic density, we find that the model parameters can be narrowed down to small ranges.

We obtain stability criteria for diffusive inviscid multi-component Israel-Stewart hydrodynamics with and without background or dynamic electromagnetic fields. Our analysis is grounded on the maximum entropy principle, and it provides stability conditions that are valid around all thermodynamic equilibria, including rotating equilibria, charged equilibria, and equilibria in a background gravitational field. We prove that the electromagnetic part of the information current is stable and causal by construction and, therefore, the stability criteria found for Israel-Stewart theories of hydrodynamics automatically extend to similar formulations of magnetohydrodynamics.

We show that primordial black holes - in the observationally allowed mass window with $f_{\rm pbh}=1$ - formed from late nucleating patches in a first order phase transition imply upcoming gravitational wave interferometers will see a large stochastic background arising from the bubble collisions. As an example, we use a classically scale invariant $B-L$ model, in which the right handed neutrinos explain the neutrino masses and leptogenesis, and the dark matter consists of primordial black holes. The conclusion regarding the gravitational waves is, however, expected to hold model independently for black holes coming from such late nucleating patches.

Gravity theories that modify General Relativity in the slow-motion regime can introduce nonperturbative corrections to the stochastic gravitational-wave background~(SGWB) from supermassive black-hole binaries in the nano-Hertz band, while remaining perturbative in the highly-relativistic regime and satisfying current post-Newtonian~(PN) constraints. We present a model-agnostic formalism to map such theories into a modified tilt for the SGWB spectrum, showing that negative PN corrections (in particular -2PN) can alleviate the tension in the recent pulsar-timing-array data if the detected SGWB is interpreted as arising from supermassive binaries. Despite being preliminary, current data have already strong constraining power, for example they set a novel (conservative) upper bound on theories with time-varying Newton's constant at least at the level of $\dot{G}/G \lesssim 10^{-5} \text{yr}^{-1}$ for redshift $z=[0.1\div1]$. We also show that NANOGrav data are best fitted by a broken power-law interpolating between a dominant -2PN or -3PN modification at low frequency, and the standard general-relativity scaling at high frequency. Nonetheless, a modified gravity explanation should be confronted with binary eccentricity, environmental effects, nonastrophysical origins of the signal, and scrutinized against statistical uncertainties. These novel tests of gravity will soon become more stringent when combining all pulsar-timing-array facilities and when collecting more data.

We provide a mean curvature flow method for numerical cosmology and test it on cases of inhomogenous inflation. The results show (in a proof of concept way) that the method can handle even large inhomogeneities that result from different regions exiting inflation at different times.