Main

We present the discovery of AT 2024wpp ("Whippet"), a fast and luminous 18cow-like transient. At a redshift of z=0.0868, revealed by Keck Cosmic Web Imager spectroscopy of its faint and diffuse star-forming host, it is the fourth-nearest example of its class to date. Rapid identification of the source in the Zwicky Transient Facility data stream permitted ultraviolet-through-optical observations to be obtained prior to peak, allowing the first determination of the peak bolometric luminosity (2x10^45 erg/s), maximum photospheric radius (10^15 cm), and total radiated energy (10^51 erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-UV spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending >100 days post-explosion from the Very Large Telescope, Hubble Space Telescope, Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a powerful rapidly-accreting central engine blows a fast ( 0.15c) wind into the surrounding medium and irradiates it with X-rays. The high Doppler velocities and intense ionization within this wind prevent any identifiable features from appearing in the ejecta or in the surrounding circumstellar material, even in the far-ultraviolet. Weak H and He signatures do emerge in the spectra after 35 days in the form of double-peaked narrow lines. Each peak is individually narrow (full width  3000 km/s) but the two components are separated by  6600 km/s, indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.

The origin of non-thermal power-law distribution functions ubiquitously observed in astrophysical/space (e.g., the solar wind) and laboratory kinetic plasmas, is not well understood. Another puzzling phenomenon is temperature inversion in the solar corona. These two issues are deeply connected. We develop a self-consistent quasilinear theory (QLT) for electromagnetically driven kinetic plasmas, deriving a Fokker-Planck equation for the simultaneous relaxation of multiple species, with (i) a drive diffusion coefficient for the heating of dressed particles directly by the drive and indirectly by waves, and (ii) Balescu-Lenard diffusion and drag coefficients for internal turbulence and Coulomb collisions. Both electron and ion distributions relax towards a universal attractor with a $v^{-5}$ $(E^{-2})$ tail, akin to a $\kappa = 1.5$ distribution, under a super-Debye (but sub-Larmor) drive with a steep power-spectrum. This is an outcome of Debye screening: large-scale fields accelerate the unscreened, fast particles but not the screened, slow ones. The universality may be broken by shallow power-spectra and incomplete relaxation. Collisions cannot decelerate suprathermal particles, rendering a high $v$ tail immune to Maxwellianization. Such a tail may be generated in the solar corona by chromospheric convection despite collisional losses. The suprathermal particles escape sun's gravity (velocity filtration), inverting the temperature profile and raising it to $10^6$ K. A proper analysis of velocity filtration with a $\kappa \approx 1.5-2$ distribution inspired by QLT provides a reasonable fit to the spectroscopic data of heavy ions and explains the abrupt temperature rise, a consequence of the divergence of pressure in the $\kappa \to 1.5$ limit.

Gravitational wave spectral sirens can provide cosmological constraints by using the shape of the binary black hole (BBH) mass distribution (MD). However, the precision and accuracy of these constraints depends critically on the capturing all the MD features. In this work, we analyze 137 BBH events from the latest GWTC-4.0 with a novel data-driven semiparametric approach based on \textsc{Bspline} that adaptively places knots around the most informative structures in the MD, while keeping the dimensionality of the parameter space moderate. Our flexible models resolve three distinct peaks at $\sim10$, $18$, and $33\,\mathrm{M}_\odot$ and are statistically preferred over standard parametric models, with Bayes factors up to 226. Because these features are correlated with $H_0$, the semiparametric model yields, under different prior assumptions, 12%-21% improvement in the precision of $H_0$ relative to parametric models, providing $H_0 = 57.8^{+21.9}_{-20.6}\,\mathrm{km/s/Mpc}$ in the best case. Our results demonstrate that capturing the full complexity of the BBH mass distribution is essential for realizing the cosmological potential of spectral sirens as gravitational wave catalogs continue to grow.

It has long been thought that black hole accretion flows are driven by magnetohydrodynamic (MHD) turbulence, and there are now many general relativistic global simulations illustrating the dynamics of this process. However, many challenges must be overcome in order to predict observed spectra from luminous systems. Ensuring energy conservation, local thermal balance, and local ionization equilibrium, our post-processing method incorporates all the most relevant radiation mechanisms: relativistic Compton scattering, bremsstrahlung, and lines and edges for 30 elements and all their ions. Previous work with this method was restricted to black holes of $10 M_\odot$; here, for the first time, we extend it to $10^8 M_\odot$ and present results for two sub-Eddington accretion rates and black hole spin parameter 0.9. The spectral shape predicted for stellar-mass black holes matches the low-hard state for the lower accretion rate and the steep power law state for the higher accretion rate. For high black hole mass, both accretion rates yield power-law continua from $\sim 0.5 - 50$ keV whose X-ray slopes agree well with observations. For intermediate mass black holes, we find a soft X-ray excess created by inverse Compton scattering of low-energy photons produced in the thermal part of the disk; this mechanism may be relevant to the soft X-ray excess commonly seen in massive black holes. Thus, our results show that standard radiation physics applied to GRMHD simulation data can yield spectra reproducing a number of the observed properties of accreting black holes across the mass spectrum.

The context of the Sun in the galactic neighborhood is not well understood, especially when we compare its physical properties to those of nearby stars. Thereby, we still cannot fully comprehend whether or not the Sun is a typical star. This work aims to identify and characterize stars aligned with the solar evolutionary track that could represent it at the ZAMS and subgiant stages. We performed a spectroscopic analysis of 18 photometrically selected candidates using high-resolution and high-SNR spectra as well as the classical spectroscopic method, based on the excitation and ionization equilibria of Fe I and Fe II lines. Additionally, we derived evolutionary parameters using isochrones, and kinematic parameters. We also estimated chromospheric activity levels and performed age estimates through 3 additional independent methods: activity-age relations using the Ca II H $\&$ K and H$\alpha$ lines, and rotation periods estimated from TESS light curves. We identified three candidates that provide a good match to the Sun at $\approx$ 0.5 Gyr (HD 13531 and HD 61033) and subgiant (HD 148577) stages. Moreover, HD 197210 could be of interest when studying the Sun at $\approx$ 2 Gyr, when the Earth's atmosphere started having a significant amount of oxygen. Our selection method was successful and we were able to identify stars similar to the Sun at different evolutionary stages, which is essential for future research in the search of exoplanets and understand habitability, especially with the advent of the next generation of exoplanet-hunting instruments.

Detection and characterization of small-scale energetic events such as nanoflares and nanojets remain challenging owing to their short lifetimes, small spatial extent, and relatively low energy release, despite their potential role in coronal heating. Recent observations have identified nanojets as small-scale (length $\lesssim 6.6$ Mm, width $\lesssim 1$ Mm), fast ($\sim$ few 100 km s$^{-1}$), and short-lived ($\lesssim 30$ s) ejections associated with nanoflare-scale energies, providing evidence of magnetic reconnection at small spatial scales. However, the lack of synthetic diagnostics has limited the connection between magnetohydrodynamic (MHD) models and observations. In this Letter, we present synthetic observations of the coalescence of two flux ropes, leading to nanojet-like signatures from a numerical model obtained with the \texttt{MPI-AMRVAC} code. We report synthetic observables in Extreme-ultraviolet lines compatible with existing instruments such as SDO/AIA, and upcoming MUSE mission, and compare the synthetic observables with an existing observation of nanojets. The synthetic diagnostics of the emissivity maps, Doppler velocity, thermal, and non-thermal line broadening produce key observational properties, suggesting a plausible 3D scenario for nanojet generation where tiny flux ropes reconnect within loops. Our results provide predictions for the detectability of nanojets with current and future spectroscopic facilities, and establish a bridge between MHD modeling and observations.

Luminous fast blue optical transients (LFBOTs) are a growing class of enigmatic energetic transients. They show fast rises and declines, high temperatures throughout their evolution, and non-thermal emission in radio and X-rays. Their power source is currently unknown, but proposed models include engine-driven supernovae, interaction-powered supernovae, shock cooling emission, intermediate mass black hole tidal disruption events (IMBH TDEs), and Wolf-Rayet/black hole mergers, among others. AT2024wpp is the most optically luminous LFBOT to date and has been observed extensively at multiple wavelengths, including radio, optical, UV, and X-rays. We take models from multiple scenarios and fit them to the AT2024wpp optical, radio, and X-ray light curves to determine if which of these scenarios can best describe all aspects of the data. We show that none of the multiwavelength light curve models can reasonably explain the data, although other physical arguments favour a stellar mass/IMBH TDE of a low mass star and a synchrotron blast wave. We discuss how this scenario can be tested with late-time observations, and what other scenarios could possibly explain the broadband data.

A central magnetar engine is commonly invoked to explain energetic supernovae, which should have multiple signals in multiwavelength emission. Photoionization from the pulsar wind nebula (PWN) can create distinct spectroscopic signals in the nebular phase. Recent models suggest infrared emission, particularly from Ne II, can be prominent at late times. This work examines the cooling power of optical and infrared transitions to determine which lines contribute strongly to cooling and on what timescale. The models show infrared cooling becomes strong at $\sim$ 3 years post-explosion and dominates by 6 years, with [Ne II] 12.8$\mu$m being the strongest coolant. The fraction of total cooling in the infrared increases sharply once the PWN luminosity decreases below 10$^{40}$ erg s$^{-1}$, and this fraction also increases with increasing ejecta mass and decreasing average PWN photon energy. However, the emission from [Ne II] 12.8$\mu$m increases with increasing PWN luminosity and increasing ejecta mass. Cooling at 1 year is dominated by optical O and S lines, with infrared Ar, Ni, and Ne lines becoming strong at 3 years. Optical cooling is almost negligible at 6 years, with the supernova cooling almost entirely through mid- and far-infrared transitions. JWST spectroscopy with MIRI should be able to detect these lines out to $z \sim 0.1$. Supernovae with higher magnetic fields transition to infrared cooling on earlier timescales, while infrared-dominated supernovae should have strong emission from neutral atoms and emit strongly in radio at sub-decade timescales.

With the arrival of JWST observations of the TRAPPIST-1 planets, it is timely to reassess the contribution of tidal heating to their heat budget. JWST thermal phase curves could reveal endogenic heating through an anomalously high nightside temperature, providing an opportunity to estimate tidal heating. In this study, we revisit the tidal heating of these planets and propose a simple method to compute the tidal heating profile across a broad range of parameters. Our approach leverages a known formulation for synchronously rotating planets on low-eccentricity orbits and the fact that the profile shape depends solely on internal structure. We calculate the tidal heating contributions for all T-1 planets, with a particular focus on the impact of internal structure and eccentricity uncertainties on their total heat budget. Although the masses and radii of these planets are well constrained, degeneracies remain in their internal structure and composition. For volatile-poor planets of silicate-rock compositions, we investigate the role of core iron content by exploring a range of core sizes. For each structure, we compute the degree-two gravitational Love number, $k_2$, and the corresponding tidal heating profiles. We assume sub-solidus temperatures profiles that are decoupled from interior heat production, which means our estimates are conservative and likely represent minimum values. We find that the tidal heat flux for T-1b and c can exceed Io's heat flux, with uncertainties primarily driven by eccentricity. These high fluxes may be detectable with JWST. For T-1f to g, the tidal flux remains below Earth's geothermal flux, suggesting that tidal heating is unlikely to be the dominant energy source. For planets d and e, however, tidal heating likely dominates their heat budget, potentially driving intense volcanic and tectonic activity, which could enhance their habitability prospects.

The brown dwarf desert describes a range of orbital periods (<5 years) in which fewer brown dwarf-mass companions have been observed around Sun-like stars, when compared to planets and low mass stellar companions. It is therefore theorised that brown dwarf companions are unlikely to form or remain in this period range. The Gaia space telescope is uniquely sensitive to companions in this period range, making it an ideal tool to conduct a survey of the brown dwarf desert. In this study, we use Bayesian inference to analyse data from nearby (<200pc) Sun-like stars in Gaia's DR3 catalogue, assuming single companions. From this, we identify 2673 systems (2.41% of the sample) with possible brown dwarf companions in this period range. Accounting for observational biases, we find that 10.4+0.8-0.6% of nearby Sun-like stars have astrometric errors consistent with a brown dwarf-mass companion with a period less than 5 years, significantly higher than previous studies which reported occurrence rates of <1%. However, we acknowledge the limitations of DR3 and are unable to make a definitive statement without epoch data. By simulating epoch data with multiple companions, we find that, while some of the data can be explained by multiple low-mass brown dwarf companions and high-mass planets (>10MJ), high-mass brown dwarfs (>50MJ) in this period range are comparatively rare. Finally, we used our studies of the brown dwarf distribution to predict the number of companions in the brown dwarf desert we can expect to discover in DR4.

We investigate a possible origin for bursty radio emission observed on the active M dwarf V374 Peg, combining data-driven magnetic field modelling with archival radio light curves. We examine whether stellar prominence ejection can plausibly account for the observed radio bursts that have been attributed to electron cyclotron maser (ECM) emission. Our analysis shows that ejected prominences can produce the required energy range to drive the emission, and that modelled ECM visibility exhibits a rotational phase dependence consistent with the limited observational data (four observed bursts). The results support prominence ejection as a viable mechanism for ECM generation on V374 Peg and motivate further observational campaigns to constrain this process.

Full-disk observations from missions such as the SDO and SOHO have enabled comprehensive studies of solar oscillations and dynamics. Interpreting helioseismic and photospheric data is complicated by systematic center-to-limb variations. To explore the physical origin of these variations, we perform local 3D radiative hydrodynamic simulations that include effects of solar rotation to generate 24-hour synthetic time series of continuum intensity and Doppler velocity for nine viewing angles spanning from -75 to 75 degrees. The simulations reveal a systematic decrease in oscillation power toward the limbs and a pronounced East-West asymmetry that increases with frequency, primarily due to rotation-induced flows. With increasing angular distance from the disk center, the amplitudes and widths of the surface gravity (f) and resonant pressure (p) modes decrease. In contrast, the amplitudes of the corresponding pseudo-modes with frequencies above the acoustic cut-off frequency increase in the intensity power spectra but are suppressed in the velocity spectra. The local helioseismology ring-diagram analysis of the simulation data further demonstrates anisotropic broadening of the modes and distinct differences in background noise and pseudo-mode structure between the intensity and velocity data. These results indicate that the center-to-limb effects arise from both geometric projection and physical factors such as line-formation height and potential effects of the radial differential rotation. The findings provide a framework for correcting helioseismic observations and demonstrate that realistic 3D radiative hydrodynamic simulations are a powerful tool for disentangling geometric and physical biases in solar data.

Uranus and Neptune are characterized by anomalously tilted and multi-dipole magnetic fields, which poses substantial challenges for elucidating the internal mechanisms generating magnetic fields. Recent investigations confirmed that superionic H2O is thermodynamically stable and constitutes the dominant H2O phase within their icy mantles. In this study, we demonstrate that the superionic H2O ice exhibits a pronounced protonic thermoelectric effect, in which the maximum Seebeck coefficient within the interior of Uranus can reach approximately 620 uV/K, whereas that of Neptune is lower, within the range of 570-585 uV/K. Consequently, temperature gradients in the icy mantles can induce proton convection, which in turn drives magnetic field generation. Based on this novel mechanism, the disparities in magnetic field strength between Uranus and Neptune can be accounted for exclusively by their differing internal temperature gradients, and the predicted values are in agreement with observations.

We present a detailed timing analysis of the two high-frequency humps observed in the power density spectrum of Swift J1727.8–1613 up to 100 keV, using data from the Hard X-ray Modulation Telescope (Insight-HXMT). Our analysis reveals that the characteristic frequencies of the humps increase with energy up to $\sim30$ keV, followed by a plateau at higher energies. The fractional rms amplitudes of the humps increase with energy, reaching approximately 15\% in the 50-100 keV band. The lag spectrum of the hump is characterized primarily by a soft lag that varies with energy. Our results suggest that the high-frequency humps originate from a corona close to the black hole. Additionally, by applying the relativistic precession model, we constrain the mass of Swift J1727.8–1613 to $2.84 < M / M_{\odot} < 120.01$ and the spin to $0.14 < a < 0.43$ from the full-energy band dataset, using triplets composed of a type-C quasi-periodic oscillation and two high-frequency humps. When considering only the high-energy bands with stable characteristic frequencies, we derive additional constraints of $2.84 < M/M_{\odot} < 13.98$ and $0.14 < a < 0.40$.

Massive short-period binaries involving hot subdwarf stars (sdO/Bs) are rare but important to constraining pathways for binary star evolution. Moreover, some of the most promising candidate progenitor systems leading to Type Ia supernovae (SNe Ia) involve sdO/Bs. LAMOST J065816.72+094343.1 has been identified as such a candidate. To explore the nature and evolutionary future of LAMOST J065816.72+094343.1, we complemented archival spectroscopic data with additional time series spectra and high-resolution spectroscopy of the object. After combining these with photometric data, we determined the orbital parameters of the system and the mass of the companion. We solved the orbit of the system by analyzing 68 low- and medium-resolution spectra using state-of-the-art mixed local thermodynamic equilibrium (LTE) and non-LTE model atmospheres. Additionally, we gathered nine high-resolution spectra to determine atmospheric parameters and the projected rotational velocity of the sdOB. The inclination angle of the system was constrained assuming tidal synchronization of the sdOB, which was verified via analysis of the ellipsoidal variations in the TESS light curve. We determine LAMOSTJ065816.72+094343.1 to be a binary consisting of a massive $0.82 \pm 0.17 \mathrm{M}_{\odot}$ sdOB component with a $1.30^{+0.31}_{-0.26} \mathrm{M}_{\odot}$ unseen companion. Due to the companion's mass being very close to the Chandrasekhar mass limit and high for a white dwarf, it is unclear whether it is a white dwarf or a neutron star. We find the system to be in a close orbit, with a period of $P=0.31955193 \mathrm{d}$ and an inclination angle of $i = 49.6^{+5.2}_{-4.2} \mathrm{deg}$. While the exact nature of the companion remains unknown, we determine the system to either lead to a SN Ia or an intermediate mass binary pulsar, potentially after a phase as an intermediate-mass X-ray binary.

Short gamma-ray bursts (SGRBs) are thought to be primarily associated with binary neutron star (BNS) mergers. The SGRB population can therefore be scrutinized to look for signatures of the delay time between the formation of the progenitor massive star binary and the eventual merger, which could produce an evolution of the cosmic rate density of such events whose shape departs from that of the cosmic star formation history (CSFH). To that purpose, we study a large sample of SGRBs within a hierarchical Bayesian framework, with a particular focus on the delay time distribution (DTD) of the population. Following previous studies, we model the DTD either as a power-law with a minimum time delay or as a log-normal function. We consider two models for the intrinsic SGRB luminosity distribution: an empirical luminosity function (ELF) with a doubly broken power-law shape, and one based on a quasi-universal structured jet (QUSJ) model. Regardless of the chosen parametrization, we find average time delays $10\lesssim \langle \tau_\mathrm{d}\mathrm\rangle/\mathrm{Myr}\lesssim 800$ and a minimum delay time $\tau_\mathrm{d,min}\lesssim 350\,\mathrm{Myr}$, in contrast with previous studies that found long delay times of few Gyr. We demonstrate that the cause of the longer inferred time delays in past studies most likely resides in an incorrect treatment of selection effects.

TON 0599 (z=0.7247) belongs to the few flat spectrum radio quasars (FSRQs) detected in the very high energy (VHE, $E > 100$ GeV) gamma-ray band. Its redshift makes it currently one of the farthest VHE gamma-ray sources. It was detected for the first time with the MAGIC telescopes on 2017 December 15, and observed until December 29. The flux reached a maximum of about 50 per cent of the Crab Nebula flux above 80 GeV on the second night of observation, after which we witnessed a gradual decrease of the flux. The VHE gamma-ray spectrum connects smoothly to the one in the high energy ($E > 100$ MeV) band obtained from simultaneous observations with Fermi-LAT. It features a cut-off at energies around 50 GeV, indicating the location of the gamma-ray emission zone beyond the broad line region. In addition, we were able to follow the spectral evolution during the fading phase of the flare. Multiwavelength analysis based on observations in optical, near-infrared, and radio bands acquired by the Whole Earth Blazar Telescope (WEBT) Collaboration from November to March, as well as observations in X-ray and optical$-$UV bands with instruments on board the Swift satellite, shows strong correlation between different bands. We model the broadband emission with a simple one-zone leptonic model, where the high-energy peak is predominantly produced by external Compton (EC) scattering of photons from the dusty torus.

The slitless spectroscopic method employed by missions such as Euclid and the Chinese Space Station Survey Telescope (CSST) faces a fundamental challenge: spectroscopic redshifts derived from their data are susceptible to emission line misidentification due to the limited spectral resolution and signal-to-noise ratio. This effect systematically introduces interloper galaxies into the sample. Conventional strict selection not only struggles to secure high redshift purity but also drastically reduces completeness by discarding valuable data. To overcome this limitation, we develop an XGBoost classifier that leverages photometric properties and spectroscopic diagnostics to construct a high-purity redshift catalog while maximizing completeness. We validate this method on a simulated sample with spectra generated by the CSST emulator for slitless spectroscopy. Of the $\sim$62 million galaxies that obtain valid redshifts (parent sample), approximately 43% achieve accurate measurements, defined as $|\Delta z| \leq 0.002(1+z)$. From this parent sample, the XGBoost classifier selects galaxies with a selection efficiency of 42.3% on the test set and 42.2% when deployed on the entire parent sample. Crucially, among the retained galaxies, 96.6% (parent sample: 96.5%) achieve accurate measurements, while the outlier fraction ($|\Delta z|>0.01(1+z)$) is constrained to 0.13% (0.11%). We verified that simplified configurations which exclude either spectroscopic diagnostics (except the measured redshift) or photometric data yield significantly higher outlier fractions, increasing by factors of approximately 3.5 and 6.3 respectively, with the latter case also introducing notable catastrophic interloper contamination. This framework effectively resolves the purity-completeness trade-off, enabling robust large-scale cosmological studies with CSST and similar surveys.

The possibility to constrain cosmological parameters from galaxy surveys using field-level machine learning methods that bypass traditional summary statistics analyses, depends crucially on our ability to generate simulated training sets. The latter need to be both realistic, as to reproduce the key features of the real data, and produced in large numbers, as to allow us to refine the precision of the training process. The analysis presented in this paper is an attempt to respond to these needs by (a) using clusters of galaxies as tracers of large-scale structure, together with (b) adopting a 3LPT code (Pinocchio) to generate a large training set of $32\,768$ mock X-ray cluster catalogues. X-ray luminosities are stochastically assigned to dark matter haloes using an empirical $M-L_X$ scaling relation. Using this training set, we test the ability and performances of a 3D convolutional neural network (CNN) to predict the cosmological parameters, based on an input overdensity field derived from the cluster distribution. We perform a comparison with a neural network trained on traditional summary statistics, that is, the abundance of clusters and their power spectrum. Our results show that the field-level analysis combined with the cluster abundance yields a mean absolute relative error on the predicted values of $\Omega_{\rm m}$ and $\sigma_8$ that is a factor of $\sim 10 \%$ and $\sim 20\%$ better than that obtained from the summary statistics. Furthermore, when information about the individual luminosity of each cluster is passed to the CNN, the gain in precision exceeds $50\%$.

Planets with masses between Earth and Neptune often have radii that imply the presence of volatiles, suggesting that water may be abundant in their interiors. However, directly observing the precise water mass fraction and water distribution remains unfeasible. In our study, we employ an internal structure code MAGRATHEA to model planets with high water content and explore potential interior distributions. Departing from traditional assumptions of a layered structure, we determine water and rock distribution based on water-rock miscibility criteria. We model {wet planets} with an iron core and a homogeneous mixture of rock and water above it. At the outer regions of the planet, the pressure and temperature are below the rock-water miscibility point (the second critical point), causing the segregation of water and rock. Consequently, a shell of water is formed in the outermost layers. By considering the water-rock miscibility and the vapor state of water, our approach highlights the uncertainty in estimating the water mass fraction of detected exoplanets.

Pulsars are the most numerous class of Galactic gamma-ray sources detected by the Fermi Large Area Telescope (LAT). Young pulsars occasionally experience sudden timing discontinuities called glitches, characterized by rapid changes in rotational parameters, usually followed by a return to regular rotation. PSR J2021+4026 is unique among Fermi-LAT pulsars, exhibiting quasiperiodic switches between two states with varying spin-down rates approximately every 3-4 years, correlated with sudden changes in gamma-ray emission features. This study searched for gamma-ray emission variability in pulsars correlated with glitch occurrence. We introduced a novel approach to analyzing LAT gamma-ray pulsars through systematic examination of variability associated with spin-down rate changes. We tracked rotation and gamma-ray emission changes for seven promising glitches selected based on observed spin-down rate variations. Using 14 years of Fermi-LAT data, we conducted binned likelihood spectral analysis of data windows around selected glitch epochs. We improved best-fit parameter precision by incorporating likelihood weights calculated from diffuse background models, accounting for systematic error contributions. The phase-averaged flux and spectral parameters of analyzed pulsars showed no significant variation across investigated glitches. The 95% upper limits on relative flux change indicate the Vela pulsar flux is unchanging, with a 0.5% upper limit on relative change, making it promising for further searches. The connection between glitch dynamics and gamma-ray emission remains unclear, and PSR J2021+4026 remains unique in its gamma-ray variability properties. We conclude that comprehensive investigation of glitches is warranted to further unravel their underlying mechanisms.

Fast radio bursts (FRBs) are millisecond-duration transients of unknown origin, likely associated with compact astrophysical objects. We report evidence for a damped millisecond quasi-periodic structure in a non-repeat FRB 20190122C. The burst consists of eight closely spaced radio pulses separated by $\sim$1 ms, with pulse amplitudes exhibiting an exponential decay starting from the brightest component. Combined Gaussian fitting and time-series analysis reveal a quasi-periodic oscillation (QPO) at $\sim$1 kHz. The observed QPO is consistent with damped magnetospheric oscillations. Assuming an Alfvén wave origin, we estimate a surface magnetic field of $\sim 10^{12}$ G and a characteristic spin period of $\sim$1 s, favoring a low-field magnetar or young neutron star scenario. The absence of frequency drift and the presence of exponential damping disfavor a merger-driven origin. These results suggest the first detection of an exponentially decaying QPO in any FRB, marking a rare detection of coherent oscillatory behavior in FRBs.

Scorpius X-1 (Sco X-1) is a neutron star X-ray binary in which the neutron star is accreting rapidly from a low mass stellar companion. At radio frequencies, Sco X-1 is highly luminous and has been observed to have jet ejecta moving at mildly relativistic velocities away from a radio core, which corresponds to the binary position. In this Letter, we present new radio observations of Sco X-1 taken with the Karl G. Jansky Very Large Array. Using a fast imaging method, we find that the 10 and 15GHz data show a number of flares. We interpret these flares as the possible launching of fast jets ($\beta\Gamma$>2), previously observed in Sco X-1 and called ultra-relativistic flows, and their interaction with slower moving jet ejecta. Using the period between successive flares, we find that it is possible for the fast jets to remain undetected, as a result of the fast jet velocity being sufficiently high to cause the jet emission to be beamed in the direction of the motion and out of our line of sight. Our findings demonstrate that the ultra-relativistic flows could be explained by the presence of fast jets in the Sco X-1 system.

In this paper, we investigate how external photo-evaporation influences the formation, dynamical evolution and the resultant planetary architecture of multi-planet systems born in stellar clusters. We use a model of N-body simulations of multiple planet formation via pebble accretion coupled with a 1-D viscous disc subject to external photo-evaporation. We found that external photo-evaporation reduces the planet growth by reducing the pebble mass reservoir in discs containing multiple planetary embryos across a wide range of disc masses, and is particularly effective in suppressing planet growth in less initially massive discs (< 0.1 M$_{\odot}$). However, in more initially massive ($\geq$ 0.1 M$_{\oplus}$) discs planets lost due to planet-planet interactions dominate the outcome for final resultant total planet mass, masking the effects of external photo-evaporation in curbing the planet mass growth. In terms of the final resulting planetary architectures, the signature of external photo-evaporation is visible in less massive (< 0.1 M$_{\odot}$) discs, with fewer numbers and lower masses of planets surviving in discs irradiated with stronger external FUV radiation. External photo-evaporation also leaves a signature for the wide orbit (> 10 au) terrestrial planets (0.1 - 1 M$_{\oplus}$), with fewer planets populating this region for stronger FUV field. Finally, the 1st-order resonant pairs fraction decreases with stronger FUV radiation, although the resonant pairs occur rarely regardless of the FUV radiation environment, due to the small number of planets that survive gravitational encounters.

Temperature and luminosity are the two key diagnostics of a star, yet these cannot come directly from survey data, but must be imputed by comparing those data to models. SED fitting offers a high-precision method to obtain both parameters for stars where both their distance and extinction are well known. The recent publication of many all-sky or large-area surveys coincides the publication of parallaxes and 3D extinction cubes from the Gaia satellite, making it possible to perform SED fitting of truly large ($>10^8$) numbers of Galactic stars for the first time. The analysis of this data requires a high level of automation. Here, we describe the ongoing Gaia All-Sky Stellar Parameters Service (GASPS): the fitting of 240 million SEDs from Gaia DR3 and the extraction of temperatures and luminosities for the corresponding stars using the PySSED code. We demonstrate the quality of the initial results, and the promise that these data show, from wavelength-specific information such as the ultraviolet and infrared excess of each star, to stellar classification, to expansion of the project beyond our own Galaxy, and mineralogical mapping of the Milky Way's interstellar medium.

We analyse the association between the NEAs 2021 PH27 and 2025 GN1, which share similar heliocentric Keplerian elements and the same taxonomic classification. First, we confirm the spectral similarity by getting independent colours measurements of 2025 GN1 and confirming that they are both X-type. From numerical integration of the orbits up to 100 kyr in the past, taking into account relativistic corrections, we found that the two asteroids experienced five similar flybys with Venus, but none of them were closer than the Roche limit. The perihelion distance also reached values between 0.1 and 0.08 au about 17/21 kyr and 45/48 kyr ago, but still well outside the Roche limit with the Sun. So, the origin of the pair by tidal disruption of a progenitor rubble-pile asteroid appears unlikely. On the other hand, we found periods lasting several thousand years where the perihelion was below 0.1 au, and this can lead to thermal fracturing of the surface. We found that the rotation period of the primary and the mass ratio secondary/primary make the pair indistinguishable from the binary systems known among the NEAs, and the YORP effect can double the rotation period of 2021 PH27 in $150 \pm 50$ kyr. So it is plausible that the pair was formed by the rotational disintegration of a rubble-pile asteroid due to anisotropic gas emission or the YORP effect, which formed a binary system that later dissolved due to the internal dynamics of the pair. We are unable to give a value for the separation age; we can only say that it occurred more than 10.5 kyr ago and may have occurred between 17/21 kyr ago during the last and longer phase of lower perihelion distance. In this scenario, little meteoroids released in space due to the fragmentation event are still near the pair's orbit and can generate a meteor shower in Venus' atmosphere.

The models that most successfully reproduce the orbital architecture of the Solar System terrestrial planets start from a narrow annulus of material that grows into embryos and then planets. However, it is not clear how this ring model can be made consistent with the chemical structure of the inner Solar System, which shows a reduced-to-oxidized gradient from Mercury to Mars and a parallel gradient in the asteroid belt. We propose that there were two primary reservoirs in the early inner Solar System: a narrow, refractory enriched ring inside of 1 au, and a less massive, extended planetesimal disk outside of 1 au with oxidation states ranging from enstatite chondrites to ordinary chondrites. We show through a suite of N-body simulations that an inwardly sweeping secular resonance, caused by aerodynamic drag and perturbations from a mean-motion resonant Jupiter and Saturn, gathers the outer planetesimal disk into a narrow ring that migrates radially, forms Mars, and contributes oxidized material to proto-Earth. Remaining unaccreted planetesimals can be implanted into the asteroid belt as the parent bodies of aubrites and non-carbonaceous iron meteorites, while the most reduced material is not implanted and thus unsampled in the meteorite collection. This model explains the oxidation and isotopic gradients within the inner Solar System within the context of a low-viscosity, magnetic wind-driven disk.

The accelerated expansion of the Universe remains one of the central open problems in modern cosmology. While the $\Lambda$CDM model successfully describes a wide range of observations, the physical nature of dark energy is still unknown, motivating the study of alternative theories of gravity. Among these, $f(R)$ models provide a well-established extension of General Relativity, capable of reproducing a $\Lambda$CDM-like background evolution without introducing an explicit dark energy component. However, they can induce deviations in the growth of cosmic structures, making them testable through observables sensitive to cosmological perturbations. In this work, we use weak gravitational lensing to constrain several viable $f(R)$ gravity models. We analyze their impact on the matter power spectrum, as well as on the convergence and cosmic shear power spectra. Our analysis is carried out within a Bayesian framework using the \textit{Cobaya} code and its modified gravity extension, \textit{MGCobaya}, which enables consistent theoretical predictions and their comparison with current weak lensing and CMB lensing data. We find that standard cosmological parameters remain consistent with the $\Lambda$CDM scenario for all models considered, as expected from their background degeneracy. Nevertheless, we obtain non-trivial and model-dependent constraints on the characteristic parameters of several $f(R)$ theories.

High-density and high-Z crystals are a key element of most space-borne $\gamma$-ray telescopes operating at GeV energies (such as Fermi-LAT). The lattice structure is usually neglected in the development of a crystalline detector, although its effects on the energy deposit development should be taken into account, since the interactions of a high energy ($\sim$ GeV) photon or e$^\pm$ impinging along the axis of an oriented crystal are different than the ones observed in a fully isotropic medium. Specifically, if the angle between a photon (e$^\pm$) trajectory and the crystal axis is smaller than $\sim$ 0.1$^\circ$, a large enhancement of the pair production (bremsstrahlung) cross-section is observed. Consequently, a photon-induced shower inside an oriented crystal develops within a much more compact region than in an amorphous medium. Moreover, for photon energies above a few GeV and incidence angles up to several degrees, the pair-production cross-section exhibits a pronounced dependence on the angle between the crystal axis and the photon polarization vector. \\ In this work we show that these effects could be exploited to develop a novel class of light-weight pointing space-borne $\gamma$-ray telescopes, capable of achieving an improved sensitivity and resolution, thanks to a better shower containment in a smaller volume with respect to non-oriented crystalline detectors. We also show that an oriented tracker-converter system could be used to measure the polarization of a $\gamma$-ray source above few GeV, in a regime that remains unexplorable through any other detection technique. This novel detector concept could open new pathways in the study of the physics of extreme astrophysical environments and potentially improve the detector sensitivity for indirect Dark Matter searches in space.

The stellar spin-orbit angles of Neptune-sized planets present a primordial yet puzzling view of the planetary formation epoch. The striking dichotomy of aligned and perpendicular orbital configurations are suggestive of obliquity excitation through secular resonance – a process where the precession of a hot Neptune becomes locked onto a forcing frequency, and is slowly guided into a perpendicular state. Previous models of resonant capture have involved the presence of companion perturbers to the star-planet-disk system, but in most cases, such companions are not confirmed to be present. In this work, we present a mechanism for exciting Neptunes to polar orbits in systems without giant perturbers, where photo-evaporation is the self-contained mechanism. Photo-evaporation opens a gap in the protoplanetary disk at  1 au, and the inner disk continues to viscously accrete onto the host star, precessing quickly due to the perturbation of the outer disk. As the inner disk shrinks, it precesses more slowly, and encounters a resonance with the J2 precession of the Neptune, quickly exciting it to a polar configuration. While likely not applicable to more massive planets which trigger back-reactions onto the disk, this mechanism reproduces the obliquities of small planets in multiple respects.

Motivated by a number of X-ray observations of active galactic nuclei (AGNs) that exhibit a potential signature of ultra-fast inflows (UFIs), we consider in this work a scenario that UFIs can be physically identified as weakly-magnetized hydrodynamic accretion flows that is guided and channeled by poloidal magnetic field into low-to-mid latitude above the equatorial disk. In the context of general relativistic hydrodynamics (GRHD) under a weak-field limit in Kerr spacetime, we present a set of preliminary results by numerically calculating the physical property of GRHD flows (e.g. kinematics and density distribution) in an effort to simulate redshifted absorption line spectra. Our model demonstrates that such GRHD accretion off the equatorial plane (i.e. $v \gsim 0.1c$ where $c$ is the speed of light in the vicinity of AGN closer than $\sim 100$ \sw radii) can manifest itself as UFIs in the form of redshifted absorption signature assuming the observed characteristics such as column density of $N_H \sim 10^{23}$ cm$^{-2}$ and ionization parameter of $\log (\xi \rm{[erg~cm~s^{-1}])} \sim 3$ as also seen in recent multi-epoch {\it NuSTAR} observations among other data.

Observing supernovae (SNe) in the early Universe (z > 3) provides a window into how both galaxies and individual stars have evolved over cosmic time, yet a detailed study of high-redshift stars and SNe has remained difficult due to their extreme distances and cosmological redshifting. To overcome the former, searches for gravitationally lensed sources allow for the discovery of magnified SNe that appear as multiple images - further providing the opportunity for efficient follow-up. Here we present the discovery of "SN Eos": a strongly lensed, multiply-imaged, SN II at a spectroscopic redshift of z = 5.133 +/- 0.001. SN Eos exploded in a Lyman-{\alpha} emitting galaxy when the Universe was only  1 billion years old, shortly after it reionized and became transparent to ultraviolet radiation. A year prior to our discovery in JWST data, archival HST imaging of SN Eos reveals rest-frame far ultraviolet ( 1,300Å) emission, indicative of shock breakout or interaction with circumstellar material in the first few (rest-frame) days after explosion. The JWST spectroscopy of SN Eos, now the farthest spectroscopically confirmed SN ever discovered, shows that SN Eos's progenitor star likely formed in a metal-poor environment (<= 0.1 Z_{\odot}), providing the first direct evidence of massive star formation in the metal-poor, early Universe. SN Eos would not have been detectable without the extreme lensing magnification of the system, highlighting the potential of such discoveries to eventually place constraints on the faint end of the cosmic star-formation rate density in the very early Universe.

We present the detection of 2MASS J22282889-4310262 (2M2228), a T6/T6.5 brown dwarf, using the Karl G. Jansky Very Large Array (VLA) archival data observed at C band (4-8 GHz) over two observing epochs ($2\times96$ minutes). 2M2228 is detected at time and frequency averaged Stokes I and V peak flux densities of $67.3\pm4.9\ \mu\ \rm{Jy beam}^{-1}$ and $14.4\pm3.0\ \mu\text{Jy beam}^{-1}$ in the first epoch and $107.2\pm5.2\ \mu\rm{Jy\ beam}^{-1}$ and $-20.7\pm1.2\ \mu\text{Jy beam}^{-1}$ in the second epoch. This discovery constitutes the eighth and, notably, the most rapidly rotating T dwarf detected to date at radio wavelengths. Our observations reveal highly polarised bursts at fractional polarisation ratios $f_\text{c}>50$%. Using Stokes I light curves, we measure occurrence intervals of $\sim47$ and $\sim58$ minutes in the two observing epochs respectively with the first burst aligning within a half period timescale of the the previously measured mid infrared photometric period of $85.8\pm0.32$ minutes. We attribute the emission to the electron cyclotron maser emission (ECME) and constrain the magnetic field strength to $B\gtrsim1.4$ kG. We emphasise that the periods inferred are provisional considering the short observing durations. The combination of previously demonstrated atmospheric stability and newly detected radio emission in 2M2228 makes it a promising laboratory for testing magnetospheric currents-driven auroral models and for guiding future coordinated James Webb Space Telescope (JWST) and radio observations to probe the link between auroral activity and atmospheric dynamics in T-type brown dwarfs.

The long GRB 180728A, at a redshift of $z = 0.1171$, stands out due to its high isotropic energy of $E_{\gamma,iso} \sim 2.5 \times 10^{51}$ erg, in contrast with most events at redshift $z<0.2$. We analyze the properties of GRB 180728A's prompt emission, afterglow, and associated supernova SN 2018fip, comparing them with other GRB-SN events. This study employs a dense photometric and spectroscopic follow-up of the afterglow and the SN up to 80 days after the burst, supported by image subtraction to remove the presence of a nearby bright star, and modelling of both the afterglow and the supernova. GRB 180728A lies on the $E_{p,i}-E_{\gamma,iso}$ plane occupied by classical collapsar events, and the prompt emission is one of the most energetic at $z < 0.2$ after GRB 030329 and GRB 221009A. The afterglow of GRB 180728A is less luminous than that of most long GRBs, showing a shallow early phase that steepens around 5 hours (0.2 days). The GRB exploded in an irregular, low-mass, blue, star-forming galaxy, typical of low-z collapsar events. Because of the relatively faint afterglow, the light curve bump of SN 2018fip dominates the optical emission already after $\sim$3 days and is one of the best sampled to date. The strong suppression below $\sim$ 4000 angstrom and a largely featureless continuum in the early 6–9 days spectra favor aspherical two-component ejecta with a high-velocity collimated component ($> 20,000 km s^{-1}$), dominant early-on, and a more massive, low-velocity component, which dominates at much later epochs. Our findings indicate that asymmetries need to be considered in order to better understand GRB-SNe. In any case, SN 2018fip shares many characteristics with typical GRB-SNe. Its kinetic energy is below the common range of $10^{52}-10^{53}$ erg and does not correlate with the high energy of the GRB, highlighting the diversity of the GRB-SN energy budget partition.

Common envelope evolution (CEE) is a crucial phase in binary stellar evolution. Current global three-dimensional simulations lack the resolution to capture the small-scale dynamics around the embedded companion, while local wind-tunnel simulations always approximate the companion's orbital motion as linear rather than as rotation around the center of mass. We investigate how rotation, accretion, and stratification influence small-scale gas dynamics, gravitational drag and lift forces, and the spin-up rate of the companion. We perform three-dimensional local hydrodynamic simulations of a $0.2\, M_\odot$ compact companion plunging into the envelope of a $2\, M_\odot$ red giant in a reference frame rotating at the companion's orbital angular velocity, using the Athena++ code. The presence of stratification generates an inward-directed force, partially opposed by a rotation-induced outward lift force. Both the resulting inward directed force and the drag force, strongly influenced by stratification, would affect the evolution of the binary separation. We propose revised semi-analytical prescriptions for both drag and lift forces. Without accretion and for sufficiently small gravitational softening radii, a quasi-hydrostatic bubble forms around the companion, while accretion prevents its formation and converts kinetic energy into heat that could contribute to the envelope ejection. Drag and lift forces are only marginally affected by accretion. The companion spin-up rate varies non-monotonically in time, first increasing and then decreasing as it plunges deeper into the envelope. These results motivate future magnetohydrodynamic simulations to investigate how accretion, rotation, and stratification affect magnetic amplification, and how magnetic fields, in turn, influence mass and angular momentum accretion rates, as well as the drag and lift force exerted on the companion.

We present the IMRPhenomXE frequency-domain phenomenological waveform model for the dominant mode of inspiral-merger-ringdown non-precessing binary black holes in elliptical orbits. IMRPhenomXE extends the quasi-circular IMRPhenomXAS waveform model for the dominant $(\ell, |m|) =$ (2,2) modes to eccentric binaries. For the inspiral part, orbit-averaged equations of motion within the quasi-Keplerian parametrization up to third post-Newtonian order, including spin effects, are evolved, and the waveform modes are computed using the stationary phase approximation on eccentricity expanded expressions up to $\mathcal{O}(e^{12})$. The model assumes circularization at merger-ringdown, where it adopts the underlying quasicircular IMRPhenomXAS baseline. We show that IMRPhenomXE reduces to the accurate IMPhenomXAS model in the quasi-circular limit. Compared against 186 public numerical relativity waveforms from the Simulating eXtreme Spacetimes catalog with initial eccentricities up to $~0.8$, IMRPhenomXE provides values of unfaithfulness below $3\%$ for $72\%$ of simulations with initial eccentricities below 0.4. For larger eccentricities, the unfaithfulness degrades up to $\gtrsim 10\%$ due to the underlying small eccentricity expansions and additional modelling approximations. In terms of speed, IMRPhenomXE outperforms any of the existing inspiral-merger-ringdown eccentric waveform models. We demonstrate the efficiency, robustness, and modularity of IMRPhenomXE through injections into zero noise and parameter-estimation analyses of gravitational-wave events, showing that IMRPhenomXE is a ready-to-use waveform model for gravitational-wave astronomy in the era of rapidly growing event catalogs.

Sterile neutrinos offer a minimal and testable explanation for dark matter (DM), with their radiative decay actively searched for in X-ray observations. We show that cold sterile neutrino DM can be efficiently produced during reheating from inflaton decays with a tiny branching ratio, ${\rm BR}\lesssim 10^{-4}$. This production mechanism opens regions of parameter space where the active-sterile mixing is small enough to evade current X-ray constraints while reproducing the observed DM abundance. We systematically map the viable parameter space in terms of the sterile neutrino mass, mixing angle, inflaton mass, reheating temperature, and branching ratio. We further demonstrate that sterile neutrino DM can serve as a probe of inflationary reheating, with future X-ray observations capable of setting lower bounds on the reheating temperature several orders of magnitude above the existing bound from Big Bang Nucleosynthesis.

Near the 10 solar radius perihelion of Parker Solar Probe orbit 24, a confined region containing an enhanced plasma density of 25,000 particles per cubic centimeter and broadband electrostatic waves was encountered. The solar wind velocity of 200 kilometers per second and ion temperature of 25 eV were significantly reduced as compared to their values in the ambient solar wind. These anomalous plasma conditions were observed on closed magnetic field lines, as determined from observations of the suprathermal electron strahl. Because the polarity of the radial magnetic field did not change sign on the two sides of the crossing and the crossed region contained a double-peaked plasma structure, the spacecraft must have passed through the base of a pseudo-streamer whose structure extended out to 10 solar radii. In the plasma frame, an electric field as large as 400 millivolts per meter was detected during the crossing. The current associated with this electric field was less than one milliampere per square meter, corresponding to a drift velocity less than 2.5 kilometers per second. It also contained a turbulent plasma with density fluctuations divided by density as large as 0.3, suggesting that the resistive term in the generalized ohm's law was significant. Also, the density as a function of time had a non-zero slope when the electric field was non-zero, suggesting that the pressure gradient term also mattered. As compared to earlier remote sensing and theoretical results, it is surprising that the plasma in this pseudo-streamer had a remarkably low flow velocity and that the pseudo-streamer base extended out to 10 solar radii.

We study how the spin content of the thermal plasmas affects the propagation of gravitational waves in a radiation-dominated universe. As a simple but representative setup, we consider conformal scalar, Weyl fermion, and Maxwell fields that provide the background radiation, and we ask whether the resulting damping and phase shift of gravitational waves retain any memory of their spins. We revisit this question in a real-time quantum-field-theoretic framework, where the stress tensor splits into a background part, a dynamical (history-dependent) response, and local contact terms, with an additional on-shell projection fixed by the Friedmann equation. We find that the dynamical spin-dependent response arises on a short time scale characterized by the radiation temperature, which is exactly canceled by the local responses. As a result, the remaining long-time response is universal and consistent with kinetic theory in the hard thermal limit. Although the underlying mechanism exhibits strong spin dependence, it leaves no observable imprint on the large-scale effective dynamics of gravitational waves in this setup.

It is known that there exist theoretical limits on the mass of compact objects in general relativity. One is the Buchdahl limit for an object with an arbitrary equation-of-state that turns out to be the limit for an object with uniform density. Another one is the causal limit that is stronger than the Buchdahl limit and is related to the speed of sound inside an object. Similar theoretical limits on the mass of compact objects in deformed Hořava-Lifshitz (HL) gravity are found in this \paper. Interestingly, the both curves of the uniform density limit and the sound speed limit meet the horizon curve at the minimum of the horizon, where a black hole becomes extremal, i.e., $M=q$, considering the Kehagias-Sfetsos vacuum that is an asymptotic flat solution in the HL gravity.

In this work, we propose a novel approach for identifying, constructing, and validating precise and accurate universal relations for neutron star bulk quantities. A central element is simulation-based inference (SBI), which we adopt to treat uncertainties due to the unknown nuclear equation of state (EOS) as intrinsic non-trivial noise. By assembling a large set of bulk properties of non-rotating neutron stars across multiple state-of-the-art EOS models, we are able to systematically explore universal relations in high-dimensional parameter spaces. Our framework further identifies the most promising parameter combinations, enabling a more focused and traditional construction of explicit universal relations. At the same time, SBI does not rely on explicit relations; instead, it directly provides predictive distributions together with a quantitative measure of systematic uncertainties, which are not captured by conventional approaches. As an example, we report a new universal relation that allows us to obtain the radius as a function of mass, fundamental mode, and one pressure mode. Our analysis shows that SBI can surpass the predictive power of this universal relation while also mitigating systematic errors. Finally, we demonstrate how universal relations can be further calibrated to mitigate systematic errors accurately.

In cosmology, long-wavelength modes are related to large-gauge transformations (LGT), i.e. changes of coordinates that modify the physical geometry of the cosmological patch. These LGTs stand as bona-fide symmetries of cosmological perturbation theory with various applications, from consistency relations constraining cosmological correlators to non-linear conservation laws in the separate-universe approach. In this work, we revisit LGTs and derive two new results. First, we show that the global symmetries already identified in the literature can be extended to local infinite-dimensional symmetries. The associated generators depend on arbitrary functions of time, and generate low-multipole modes that modify the mean curvature energy and the angular momentum of the patch, demonstrating their physical nature. We propose to interpret these low-multipole soft modes as a new cosmological-frame ambiguity that needs to be fixed prior to evaluating cosmological observables. Second, we demonstrate that the adiabatic cosmological perturbations generated by LGTs deform but preserve all the explicit and hidden Killing symmetries of the background geometry. As such, long-wavelength modes stand as a concrete example of algebraically-special cosmological perturbations of Petrov-type O, and inherit the conformal group as isometries and a set of four deformed Killing-Yano tensors and their associated Killing tensors. This opens the possibility to study their effect on cosmological observables in a fully analytic manner.

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into “patches”. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.

Some young neutron stars, the magnetars, have ultra-strong magnetic fields, yet their inferred birth rate is comparable to the core-collapse supernova rate, challenging scenarios that require rare, extreme conditions. We propose that this discrepancy can be reconciled if both pulsars and magnetars pass through a dynamo process during the proto-neutron star (PNS) phase. We employ a shear-driven $\alpha$–$\Omega$ dynamo model that includes PNS contraction. The dynamo generically produces toroidal-dominated fields set mainly by the $\Omega$-effect. The evolution of the poloidal field is first dominated by flux conservation during collapse and then by the $\alpha$-effect. The saturated toroidal field depends strongly on the initial value of the shear, with a threshold at $q_0 \simeq 0.23$; below this, the poloidal field remains near the value obtained by the flux-conservation ($\approx 2.5\times10^{10}\,{\rm G}$). For the shortest initial periods, the model leads to magnetar-like strengths ($B_{\rm p} \simeq 10^{15}\,{\rm G}$, $B_\phi \simeq 10^{16}\,{\rm G}$), while for the slower rotators it yields ordinary pulsar fields ($B_{\rm p} \simeq 10^{12}\,{\rm G}$, $B_\phi \simeq 10^{14}\,{\rm G}$). We also argue that the central compact objects can acquire toroidal fields amplified solely by the $\Omega$-effect; lacking the $\alpha$-effect, their poloidal fields are not shaped by the dynamo effect.

We present PySCo, a fast and user-friendly Python library designed to run cosmological $N$-body simulations across various cosmological models, such as $\Lambda$CDM and $w_0w_a$CDM, and alternative theories of gravity, including $f(R)$, MOND and time-dependent gravitational constant parameterisations. PySCo employs Particle-Mesh solvers, using multigrid or Fast Fourier Transform (FFT) methods in their different variations. Additionally, PySCo can be easily integrated as an external library, providing utilities for particle and mesh computations. The library offers key features, including an initial condition generator based on up to third-order Lagrangian Perturbation Theory (LPT), power spectrum estimation, and computes the background and growth of density perturbations. In this paper, we detail PySCo's architecture and algorithms and conduct extensive comparisons with other codes and numerical methods. Our analysis shows that, with sufficient small-scale resolution, the power spectrum at redshift $z = 0$ remains independent of the initial redshift at the 0.1\% level for $z_{\rm ini} \geq$ 125, 30, and 10 when using first, second, and third-order LPT, respectively. Although the seven-point Laplacian method used in multigrid also leads to power suppression on small scales, this effect can largely be mitigated when computing ratios. In terms of performance, PySCo only requires approximately one CPU hour to complete a Newtonian simulation with $512^3$ particles (and an equal number of cells) on a laptop. Due to its speed and ease of use, PySCo is ideal for rapidly generating vast ensemble of simulations and exploring parameter spaces, allowing variations in gravity theories, dark energy models, and numerical approaches. This versatility makes PySCo a valuable tool for producing emulators, covariance matrices, or training datasets for machine learning.

We present optical and infrared observations from maximum light until around +800 days of supernova (SN) 2022jli, a peculiar stripped-envelope (SE) SN showing two maxima, each one with a peak luminosity of about $3 \times 10^{42}$ erg s$^{-1}$, separated by 50 days. The second maximum is followed by unprecedented periodic undulations with a period of $P \sim 12.5$ days. The spectra and the photometric evolution of the first maximum are consistent with the behaviour of a standard SE SN with an ejecta mass of $\sim 1.5$ $M_{\odot}$ and a radioactive $^{56}$Ni mass of $\sim 0.12$ $M_{\odot}$. The optical spectra after +400 days relative to the first maximum correspond to a standard SN Ic event, and at late times SN 2022jli exhibits a significant drop in the optical luminosity, implying that the physical phenomena that produced the secondary maximum have ceased to power the SN light curve. Among other potential scenarios, we discuss how the second maximum could be powered by a magnetar, while the light curve periodic undulations could be produced by accretion of material from a companion star onto the neutron star in a binary system. The near-infrared spectra shows clear first CO overtone emission from about +190 days after the first maximum, and it becomes undetected at +400 days. A significant near-infrared excess from hot dust emission is detected at +238 days, having been produced by either newly formed dust in the SN ejecta or a strong near-infrared dust echo. Depending on the assumptions of the dust composition, the estimated dust mass is $2-16 \times 10^{-4}$ $M_{\odot}$. The potential magnetar power of the second maximum can fit into a more general picture in which magnetars are the power source of SE super-luminous SNe, and could explain bumps, undulations, and late-time excess emission in SE SNe.

The diffuse Galactic gamma-ray emission is a very important tool used to study the propagation and interaction of cosmic rays in the Milky Way. In this work, we report the measurements of the diffuse emission from the Galactic plane, covering Galactic longitudes from $15^{\circ}$ to $235^{\circ}$ and latitudes from $-5^{\circ}$ to $+5^{\circ}$, in an energy range of 1 TeV to 25 TeV, with the Water Cherenkov Detector Array (WCDA) of the Large High Altitude Air Shower Observatory (LHAASO). After masking the sky regions of known sources, the diffuse emission is detected with $24.6\sigma$ and $9.1\sigma$ significance in the inner Galactic plane and outer Galactic plane, respectively. The WCDA spectra in both regions can be well described by a power-law function, with spectral indices of $-2.67\pm0.05_{\rm stat}$ in the inner region and $-2.83\pm0.19_{\rm stat}$ in the outer region, respectively. Combined with the Square Kilometer Array (KM2A) measurements at higher energies, a clear softening of the spectrum is found in the inner region, with change of spectral indices by $\sim0.5$ at a break energy around $30$ TeV. The fluxes of the diffuse emission are higher by a factor of $1.5-2.7$ than the model prediction assuming local CR spectra and the gas column density, which are consistent with those measured by the KM2A. Along Galactic longitude, the spatial distribution of the diffuse emission shows deviation from that of the gas column density. The spectral shape of the diffuse emission are possibly variation in different longitude region. The WCDA measurements bridge the gap between the low-energy measurements by space detectors and the ultra-high-energy observations by LHAASO-KM2A and other experiments. These results suggest that improved modeling of the wide-band diffuse emission is required.

The first year results of DESI (DR1) provide evidence that dark energy may not be quantum vacuum energy ($\Lambda$). If true, this would be an extraordinary development in the 25-year quest to understand cosmic acceleration. The best-fit DESI $w_0w_a$ models for dark energy, which underpin the claim, have strange behavior. They achieve a maximum energy density around $z\simeq 0.5 $ and rapidly decrease before and after. We explore physics-based models where the dark energy is a rolling scalar-field. Our four scalar-field models are characterized by one dimensionless parameter $\beta$, which in the limit of $\beta \rightarrow 0$ reduces to $\Lambda$CDM. While none of our models fit the DESI data significantly better than $\Lambda$CDM, for values of $\beta$ of order unity, they fit about as well as $\Lambda$CDM. We also consider the second data release from DESI (DR2), CMB data and supernovae data. The DR2 results are consistent with the DR1, and the combination of DESI, CMB and SNe favor $\beta = 0.23 - 0.95$, providing some evidence for a scalar-field explanation for dark energy. While the DESI data prefer $w_0w_a$ to a scalar field, the SNe data prefer a scalar field to $w_0w_a$, and together they favor a $w_0w_a$ model. We study the limits of $w_0w_a$ in describing dark energy, especially scalar field models, and also point out that the strange behavior of the best-fit DESI models could arise due to the matter density not varying as expected or an unaccounted for component of energy density in the Universe.

Both simulations and observations indicate that the so-called missing baryons reside in the intergalactic medium known as the warm-hot intergalactic medium (WHIM). In this study we employed the IllustrisTNG50-1 simulation to demonstrate that knowledge of the turbulence in the cosmic baryonic fluid is crucial for correctly understanding both the spatial distribution and the physical origins of the missing baryons in the Universe. First, we find that dynamical effects cause the gas to be detained in low-density and intermediate-density regions, resulting in high baryon fractions, and prevent the convergence of the gas in high-density regions, leading to low baryon fractions. Second, turbulent energy is converted into thermal energy, and the injection and dissipation of turbulent energy have essentially reached a balance from $z=1$ to $0$. This indicates that the cosmic fluid is in a steady state within this redshift range. Due to turbulent heating, as the redshift decreases, an increasing amount of warm gas is heated and converted into the WHIM, and some even into hot gas. We find that, compared with turbulence in the cosmic fluid, shocks are unimportant in intermediate-density regions and even negligible in high-density regions, both dynamically and thermodynamically. This finding accounts for the origin of the WHIM in terms of both dynamics and thermodynamics, calls into question the traditional view of shock-heating, and highlights the importance of turbulence in shaping the large-scale structure of the Universe, particularly in the evolution of galaxies and galaxy clusters. In addition to TNG50-1, we validated our key findings with TNG50-2, TNG100-1, WIGEON, and EAGLE simulations, demonstrating that the spatial resolution, box size, and sub-grid-physics variations do not affect our main conclusions.

We present the first assessment of the Ali Cosmic Microwave Background Polarization Telescope's (AliCPT) sensitivity to the reheating epoch after cosmic inflation, based on its ability to detect primordial gravitational waves. We consider three models of inflation, an $\alpha$-attractor T-model, RGI inflation and QCD-driven warm inflation. Assuming a fiducial value of $r=0.01$, we find that AliCPT-1, in its fully loaded focal plane detector configuration and combined with Planck, can provide measurements of the order of magnitude of the reheating temperature with an accuracy around $10\%$. For QCD-driven warm inflation this can be translated into a constraint on the inflaton coupling to gluons, which can be probed independently in axion search experiments. Our results constitute the first demonstration of AliCPT's ability to probe the initial temperature of the hot big bang and the microphysical parameter connecting cosmic inflation and particle physics.

Mass transfer (MT) in binary systems is a common evolutionary process that can significantly affect the structure, evolution, and final fate of both stars. In modeling MT hydrodynamics, it is usually assumed that the critical point of the flow, where the velocity exceeds the local sound speed, coincides with the inner Lagrange point (L1). However, in massive donors where radiative pressure dominates over gas pressure and the Eddington factor $\Gamma_\text{Edd}$ can approach or exceed unity, radiation-gas coupling can shift the critical point away from L1, altering the MT rate ($\dot{M}_\text{d}$). We investigate the effects of radiation on MT using time-steady radiative hydrodynamic equations and the von Zeipel theorem. We derive analytical expressions that closely approximate $\dot{M}_\text{d}$, algebraic solutions for simplified cases, and numerical results using a realistic equation of state. Two main differences emerge relative to traditional prescriptions for $\dot{M}_\text{d}$. First, for Roche-lobe-underfilling donors with $\Gamma_\text{Edd} \lesssim 1$, radiative momentum exchange leads to an exponential increase of $\dot{M}_\text{d}$ as a function of $1-\Gamma_\text{Edd}$. We provide a simple modification of existing prescriptions that captures this effect. Second, the photon tiring limit for super-Eddington outflows is much less restrictive near L1 than in spherical stars. We suggest that donors with super-Eddington, convectively inefficient subsurface layers can drive MT with $-\dot{M}_\text{d} \gtrsim 10^{-2}\,\text{M}_\odot\,\text{yr}^{-1}$ even before Roche-lobe overflow. We characterize the conditions for this new mode of super-Eddington-boosted MT and discuss its implications for binary evolution, including potential links to nonterminal outbursts of Luminous Blue Variables.

The Baryon Acoustic Oscillation (BAO) feature, imprinted in the transverse and radial clustering of dark matter tracers, enables the simultaneous measurement of the angular diameter distance $D_A(z)$ and the Hubble parameter $H(z)$ at a given redshift. Further, measuring the redshift space anisotropy (RSD) allows us to measure the combination $f_8(z)\equiv f\sigma_8(z)$. Motivated by this, we simultaneously study the dynamics of background evolution and structure formation in an abstract phase space of dynamical quantities: $ x = H_0 D_A/c$, $p = dx/dz$, and $f_8$. We adopt a semi-cosmographic approach, whereby we do not pre-assume any specific dark energy model to integrate the dynamical system. The Luminosity distance is expanded as a Padé rational approximation in the variable $(1+z)^{1/2}$. The dynamical system is solved by using a semi-cosmographic equation of state, which incorporates the dark matter density parameter along with the parameters of the Padé expansion. The semi-cosmographic $D_A(z), H(z)$ and $f\sigma_8(z)$, thus obtained, are fitted with BAO and RSD data from the SDSS IV. The reconstructed phase trajectories in the $3D$ $(x,p,f_8)$ space are used to reconstruct some diagnostics of background cosmology and structure formation. At low redshifts, a discernible departure from the $\Lambda$CDM model is observed. The geometry of the phase trajectories in the projected spaces allows us to identify three key redshifts where future observations may be directed for a better understanding of cosmic tensions and anomalies.

The masses of the white dwarfs in a binary carry information about previous mass-transfer phases. The core mass – radius relation of low-mass giants gives the size of the progenitor of a helium white dwarf at the moment it last filled its Roche lobe. Previously, we used this information for a few observed systems to propose a new mass-transfer type, based on an angular momentum balance. Our aim is to investigate if stable mass transfer instead of the angular momentum prescription is consistent with the observed double helium white dwarf masses. We reconstruct the progenitor evolution of observed double helium white dwarfs using the core mass – radius relation and evaluate if the periods at the start of the second phases of mass transfer are consistent with the outcome of stable mass transfer. More generally, we calculate the mass distribution of double helium white dwarfs for three different progenitors scenarios: double common envelope (with parameter $\alpha \lambda$), angular momentum prescription (with parameter $\gamma$) and stable mass transfer. We find that the observed systems are generally not consistent with stable mass transfer. Stable mass transfer leads to a tight correlation between the two white dwarf masses in a binary that is not consistent with the observed mass distribution. Double common envelope evolution is a particularly poor fit to the observations. The angular momentum prescription can populate the observed mass distribution, but not perfectly. We conclude that the first phase of mass transfer initiated on the red giant branch in low-mass systems does not generally proceed as stable mass transfer nor as common envelope, and thus is poorly understood. This may be related to the fact that for many observed binaries that have finished the first phase of mass transfer the orbit is eccentric, which is an unexpected outcome of mass transfer.

We investigate the impact of statistical inhomogeneity and anisotropy in primordial scalar perturbations on the scalar-induced gravitational waves (SIGW). Assuming inflationary quantum fluctuations originate from a coherent state, the resulting primordial scalar perturbations acquire a non-zero space-dependent mean, violating statistical homogeneity, statistical isotropy, and parity. As a consequence of statistical inhomogeneities, SIGW acquires distinct scale-dependent features in its correlation function. Statistical anisotropies further lead to possible parity violation and correlation between different polarization modes in the tensor perturbations. Therefore, detection of these signatures in the stochastic gravitational wave background would offer probes to the statistical nature of primordial scalar perturbations beyond the scales accessible to CMB observations.

We investigate the evolution of magnetized protoneutron stars (PNSs) through four schematic stages: neutrino trapped, deleptonization, neutrino transparent, and the final cold, catalyzed neutron star (NS). Using a quasi static approximation on the Kelvin Helmholtz timescale, we construct strongly magnetized configurations (magnetic field strengths up to 1e17 G) with the axisymmetric XNS 4.0 code, employing equations of state derived from relativistic mean field theory calibrated with the DDME2 parameter set. We analyze the evolution of the gravitational mass, equatorial radius, stellar deformation, magnetic flux, and the ratio of magnetic to gravitational binding energy as functions of thermodynamic and compositional changes. We find that increasing entropy per baryon and decreasing lepton fraction lead to higher core temperatures, which enhance magnetic deformation, flux confinement, and the magnetic to binding energy ratio. Magnetic field dissipation is most efficient during the deleptonization and neutrino transparent stages, and this process largely determines the observable magnetic field strength of the mature neutron star. This work provides the first general relativistic characterization of how the thermal and compositional evolution of protoneutron stars reshapes magnetic field deformation and energetics across poloidal, toroidal, and mixed field configurations at fixed baryonic mass.

The solar disk is a continuous source of GeV–TeV gamma rays. The emission is thought to originate from hadronic Galactic cosmic rays (GCRs) interacting with the gas in the photosphere and uppermost convection zone after being reflected by solar magnetic fields. Despite this general understanding, existing theoretical models have yet to match observational data. At the photosphere and the uppermost convection zone, granular convection drives a multi-scale magnetic field, forming a larger-scale filamentary structure while also generating turbulence-scale Alfvén wave turbulence. Here, we demonstrate that the larger-scale filamentary field shapes the overall gamma-ray emission spectrum, and the Alfvén wave turbulence is critical for further suppressing the gamma-ray emission spectrum below $\sim 100$ GeV. For a standard Alfvén wave turbulence level, our model's predicted spectrum slope from 1 GeV to 1 TeV is in excellent agreement with observations from Fermi-LAT and HAWC, an important achievement. The predicted absolute flux is a factor of 2–5 lower than the observed data; we outline future directions to resolve this discrepancy. The key contribution of our work is providing a new theoretical framework for using solar disk gamma-ray observations to probe hadronic GCR transport in the lower solar atmosphere.

In recent years, many wide orbit circumbinary giant planets have been discovered; some of these may have formed by gravitational fragmentation of circumbinary discs. The aim of this work is to investigate the lower mass limit for circumbinary disc fragmentation. We use the Smoothed Particle Hydrodynamics code SEREN, which employs an approximate method for the radiative transfer, to perform 3 sets of simulations of gravitationally unstable discs. The first set of simulations covers circumstellar discs heated by a single 0.7M$_{\odot}$ star (circumstellar model), the second set covers binaries with the same total stellar mass as the circumstellar model, attended by circumbinary discs with the same temperature profile (circumbinary fiducial model), and the third set covers circumbinary discs heated by each individual star (circumbinary realistic model). We vary the binary separation, mass ratio and eccentricity to see their effect on disc fragmentation. For the circumstellar disc model, we find a lower disc-to-star mass ratio for fragmentation of $\sim\,$0.31. For the circumbinary fiducial disc model we find the same disc-to-star mass ratio for fragmentation (but slightly lower for more eccentric, equal-mass binaries; 0.26). On the other hand, realistic circumbinary discs fragment at a lower mass limit (disc-to-star mass ratio of 0.17-0.26), depending on the binary properties. We conclude that circumbinary discs fragment at a lower disc mass (by $\sim 45\%$) than circumstellar discs. Therefore, gas giant planet around binaries may be able to form by gravitational instability easier than around single stars.

We report a weak-lensing (WL) mass measurement for the merging cluster Abell 754 and impose constraints on the merger trajectory. The trajectory analysis adopts a two-body model with a point-mass approximation and dynamical friction, refined using numerical simulations of major mergers and characterized by Euler angles. We first conduct WL analysis using the two-dimensional shear pattern from the Subaru HSC in combination with Suprime-Cam images to assist in color selection. The WL mass map shows a distinct double-peak structure located around the western and eastern brightest cluster galaxies as reported in the literature. The two-halo component analysis, which utilizes the 2D shear pattern over the cluster entire region and considers the lensing covariance matrix from uncorrelated large-scale structures, indicates mass values of $M_{200}^W=3.13_{-1.00}^{+1.53}\times10^{14}h_{70}^{-1}M_\odot$ and $M_{200}^E=6.41_{-1.97}^{+2.92}\times10^{14}h_{70}^{-1}M_\odot$. Thus, the eastern mass component associated with the X-ray tadpole-shaped gas is the main cluster. No substantial structural components are detected in the line-of-sight velocities of the member galaxies. Utilizing WL parameters, line-of-sight velocities, and X-ray information on morphology and kinematics, we determine an impact parameter of approximately 0.77 Mpc at an initial separation of 2 Mpc from the main cluster. The merger plane is inclined at about 20 degrees relative to the line-of-sight. Interestingly, this system is an off-axis, near-line-of-sight merger. This characteristic arises because the trajectory within the merger plane is altered during the pericenter passage, causing the apparent motion to transition from predominantly along the line-of-sight before the core passage to mainly within the plane of the sky afterward. This study will assist in conducting numerical simulations to understand the XRISM observations.

Understanding the three-dimensional evolution of coronal magnetic fields during solar flares remains challenging due to the lack of direct coronal field measurements. Here we combine data-driven MHD simulations of NOAA AR 11158 (Fan et al., 2024) with flare-ribbon and coronal-dimming observations to investigate realistic coronal magnetic-field evolution during an X-class flare. We introduce L-maps - maps of natural logarithm of magnetic field-line lengths - as a diagnostic tool to track the dynamics of simulated coronal magnetic structures. Variations in L-maps identify flare ribbons through field-line shortening and coronal dimmings through field-line lengthening. Comparison with SDO/AIA observations demonstrates strong morphological and temporal agreement, validating the simulated field evolution. Applying K-means clustering to the L-map temporal profiles, we distinguish three stages of coronal evolution: (1) slow pre-flare rise phase, (2) flare reconnection accompanied by CME rise, and (3) post-reconnection CME expansion. We detect a slow pre-flare rise phase of magnetic field lines rooted in ribbon footpoints and identify reconnection dimming - area of rapid expansion of active-region core magnetic field lines during flare impulsive phase due to reconnection. Our results show that L-maps provide a powerful and physically intuitive framework for bridging simulations and observations and for tracking the full three-dimensional evolution of coronal magnetic fields during flares.

The cosmological principle, asserting large-scale homogeneity and isotropy, underpins the standard model of cosmology. Testing its validity using independent astronomical probes remains crucial for understanding the global structure of the Universe. We investigate the angular distribution of Gamma-Ray Bursts (GRBs) using two of the most comprehensive all-sky datasets available, the BATSE (CGRO) and Fermi GBM catalogs, to test the isotropy of the GRB sky at large angular scales. We perform spherical harmonic decomposition of the GRB sky maps and estimate the dipole and quadrupole amplitudes. Statistical significance is evaluated by comparing the observed multipole amplitudes against distributions derived from 500 Monte Carlo realizations of isotropic skies. Our results show that the observed dipole amplitudes for both BATSE and Fermi GBM datasets lie within the $1\sigma$ region of their respective null distributions. However, the quadrupole amplitude in the raw, uncorrected BATSE and Fermi GBM skies appears elevated at $3.7\sigma$ and $3.0\sigma$, respectively. After incorporating the BATSE sky exposure function, this apparent quadrupole anisotropy vanishes, indicating that instrumental non-uniformities fully account for the signal in that case. Owing to the absence of a publicly available full-sky exposure model for Fermi GBM, the Fermi analysis is restricted to the raw sky distribution. Our method's reliability is validated through controlled simulations, which show it can detect the injected dipoles in BATSE-sized isotropic skies. These findings reinforce the statistical isotropy of the GRB sky and underscore the importance of accurate exposure corrections in cosmological anisotropy analyses.

Stellar and planetary magnetic fields play a crucial role in the habitability of a planet and the integrity of its atmosphere. The recently claimed detection of biosignatures, methane, carbon dioxide and dimethyl sulfide/disulfide, in the atmosphere of K2-18 b, a sub-Neptune orbiting an M dwarf star present an intriguing question regarding the stellar magnetic environment and the resistance of the planet's magnetosphere (if it exists) to erosion by magnetic activity from the host. To probe for radio emission from the system, we have conducted observations using the Karl G. Jansky Very Large Array (VLA) at S, C and X-bands (2-4, 4.5-7.5 and 8-10 GHz respectively) to search for coherent and incoherent radio emission. We detect no radio emission associated with incoherent emission mechanisms. We report $3\sigma$ Stokes I upper limits of $49.8\ \mu\rm{Jybeam}^{-1}$ at S-band, $17.7\ \mu\rm{Jybeam}^{-1}$at C-band and $18.0\ \mu\rm{Jybeam}^{-1}$ at X-band and an upper limit of the ratio of the radio to the total bolometric luminosity of $\log L_\text{R}/\log L_\text{bol}<-8.8$. We have also searched for short duration bursts associated with coherent emission mechanisms at C and X-bands . No signals above a $3\sigma$ significance threshold are detected. Although no signals are detected our radio observations offer constraints, albeit limited, on the stellar magnetic environment supporting recent X-ray observations indicating K2-18 is a very faint emitter. Our results also contextualise any planetary transmission spectra by providing constraints on the activity level of the host.

Gravitational scattering of small bodies (planetesimals) by a planet remains a fundamental problem in celestial mechanics. It is traditionally modeled within the circular restricted three-body problem (CR3BP), where individual particle trajectories are obtained via numerical integrations. Here, we use {Ö}pik's close-encounter framework to study the random walk of the orbital energy $x$ for an ensemble of test particles on planet-crossing orbits. We show that the evolution of each particle's orbital elements $(a, e, i)$ is fully encapsulated by the 3D rotation of the relative velocity vector $\bm{U}_\infty$, whose magnitude remains constant. Consequently, the system can be reduced to two degrees of freedom. By averaging over all possible flyby geometries, we derive explicit expressions for the drift and diffusion coefficients of $x$. We then solve the resulting Fokker–Planck equation to obtain a closed-form solution for the time evolution of the particle distribution. A characteristic scattering timescale naturally emerges, scaling as $(P_{p}/M_{p}^{2})/500$, where $P_{p}$ is the planet's orbital period and $M_{p}$ its mass ratio to the central star. The typical ejection speed of small bodies by a planet is estimated to be $3 v_p M_{p}^{1/3}$, where $v_p$ is the planet's orbital speed. Our analytical solution constitutes a universal law applicable to both the Solar System and exoplanetary systems, providing a computationally efficient alternative to costly $N$-body simulations for studying the orbital distributions and ejection of planetesimals and planets (e.g., Kuiper Belt, Oort Cloud, debris disks, interstellar objects, and free-floating planets).

A class of supernovae (SNe) termed `SN Ic-CSM' are characterized by late-time emergence of narrow emission lines of elements formed in the oxygen core of a massive star. A popular scenario is the interaction of the SN ejecta and O-rich circumstellar medium (CSM), i.e., Circumstellar Interaction (CSI). Uncovering the progenitor system of SNe Ic-CSM plays a critical role in understanding the final evolution of a massive star to a bare C+O star. In this Letter, we present observations of SN 2022esa which we show is an SN Ic-CSM. Surprisingly, a stable periodicity of  32 days is found in its light-curve evolution with a hint of a slowly increasing period over  200 days. We argue that the main power source is likely the interaction of the SN ejecta and O-rich CSM, while the energy input by the post-SN eccentric binary interaction within the SN ejecta is another possibility. In either case, we propose a massive Wolf-Rayet (WR) star as the progenitor, in a WR-WR or WR-BH (black hole) binary that will eventually evolve to a BH-BH binary. Specifically, in the CSI scenario, the progenitor system is an eccentric binary system with an orbital period of about a year, leading to the observed periodicity through the modulation in the CSM density structure. We also show that some other objects, superluminous SN I 2018ibb (a pair-instability SN candidate) and peculiar SN Ic 2022jli (the first example showing stable periodic modulation), show observational similarities to SNe Ic-CSM and may be categorized as SN Ic-CSM variants. Complemented with a large diversity in their light-curve evolution, we propose that SNe Ic-CSM (potentially linked to SNe Ibn/Icn) are a mixture of multiple channels that cover a range of properties in the progenitor star, the binary companion, and the binary orbit.

We present spatially resolved ALMA observations of the water line at 183 GHz in the disk around the Herbig star HD 100546. The water vapor emission peaks at the inner edge of the warm dust cavity, located  15 au from the central star. We attribute this to thermal desorption at the water snowline, shifted outward at the dust cavity wall directly heated by the intense radiation. This represents the first spatially resolved image of the water snowline using ALMA observations of the main water isotopologue in a protoplanetary disk. The water emission morphology peaking inside the first dust ring is consistent with previous ALMA detections of oxygen-bearing complex organic molecules in the disk, including thermally desorbed methanol. These findings signal that warm cavities of transition disks provide ideal targets to directly reconstruct the spatial distribution of water vapor and the snowline location with ALMA, and directly connect water vapor emission to ice desorption of complex organic species.

LISA can observe cosmological millihertz (mHz) gravitational wave (GW) backgrounds that may offer a decisive test for asteroid-mass primordial black hole (PBH) dark matter (DM). In standard scenarios, failing to detect a scalar-induced gravitational wave (SIGW) background would exclude the last viable window for PBH DM formed through critical collapse. We show that this conclusion becomes much weaker in the presence of astrophysical foregrounds and strongly non-Gaussian primordial density perturbations, by studying how these phenomena affect the link between SIGWs and PBHs, and reevaluate LISA's sensitivity to asteroid-mass PBHs. In addition, we analyse the interplay between PBHs and SIGWs to gain further insights into the nature of primordial non-Gaussianity. We find that uncertainties in $f_{\rm NL}$ can induce substantial uncertainties in the PBH abundance, which ultimately limits LISA's capacity to fully probe the asteroid-mass PBH DM window.

Compilation of papers presented by the VERITAS Collaboration at the 39th International Cosmic Ray Conference (ICRC), held July 14 through July 24, 2025 in Geneva, Switzerland.

Surviving rapid inward orbital migration is a crucial aspect of formation models for the Jupiter's Galilean moons. The primary aim of this study is to investigate the orbital migration of the Galilean moons by incorporating self-consistent solid dynamics in circumjovian disk models. We perform two-fluid simulations using the FARGO3D code on a 2D polar grid. The simulations model a satellite with the mass of a proto-moon, Europa, or Ganymede interacting with a circumjovian disk. The dust component, coupled to the gas via a drag force, is characterized by the dust-to-gas mass ratio ($\epsilon$) and the Stokes number ($T_s$). The effect of solids fundamentally alter the satellites' evolution. We identify a vast parameter space where migration is slowed, halted, robustly reversed -leading to outward migration-, or significantly accelerated inward. The migration rate is dependent on satellite mass, providing a natural source of differential migration. Solid dynamics provides a robust and self-consistent mechanism that fundamentally alters the migration of the Galilean moons, potentially addressing the long-standing migration catastrophe. This mechanism critically affects the survival of satellites and could offer a viable physical process to explain the establishment of resonances through differential migration. These findings establish that solid torques are a critical, non-negligible factor in shaping the final architecture of satellite systems.

We present a comprehensive analysis of TOI 864.01, a transit-like signal associated with the M-dwarf TIC 231728511. Utilizing the full baseline of TESS photometry (54 sectors), we recover a periodic signal with $P = 0.52067$ d and a shallow depth of $\sim$158 ppm. To assess the planetary nature of the candidate, we performed a rigorous vetting process combining centroid analysis, Bayesian model comparison, and false-positive probability calculations. While the low signal-to-noise ratio of the sub-Earth candidate yielded inconclusive formal statistical validation metrics (FPP) and Bayesian evidence ($\Delta \ln Z$), we demonstrate the planetary nature of the system through physical exclusion of false positive scenarios. The TRICERATOPS Nearby False Positive Probability (NFPP) of 0.0000, combined with centroid stability, rules out background contamination. Furthermore, we calculate that a stellar-mass companion at the derived orbital separation ($a \approx 5 R_\star$) would induce ellipsoidal variations of order $\gtrsim 5000$ ppm. The absence of such variations in the TESS photometry ($< 200$ ppm limit) physically precludes stellar binary scenarios. We derive a planetary radius of $R_p \approx 0.55 R_\oplus$, confirming TOI 864.01 as a physically vetted ultra-short-period sub-Earth.

We investigate the deflection of photons in the strong deflection limit within static and axisymmetric spacetimes possessing reflection symmetry. As the impact parameter approaches its critical value, the deflection angle exhibits a logarithmic divergence. This divergence is characterized by a logarithmic coefficient and a constant offset, which we express in terms of the coordinate-invariant curvature quantities evaluated at the unstable circular photon orbit. The curvature contribution is encoded in the electric part of the Weyl tensor, reflecting tidal effects, and the matter contribution is encoded in the Einstein tensor, capturing the influence of local energy and pressure. We also express these coefficients using the Newman–Penrose scalars. By exploiting the relationship between the strong deflection limit and the quasinormal modes, we derive a new expression for the quasinormal mode frequency in the eikonal limit in terms of the curvature scalars. Our results provide a unified and coordinate-invariant framework that connects observable lensing features and quasinormal modes to the local geometry and matter distribution near compact objects.

A relativistic self-gravitating equilibrium system with steady flow as well as spherical symmetry is discovered. The energy-momentum tensor contains the contribution of a current related to the flow and the metric tensor does an off-diagonal component to balance with the flow momentum. The presence of the off-diagonal component of the metric implies the radial motion of the reference frame, which gives rise to a problem how the relativistic effect is included in thermodynamic observables for such a general relativistic system. This problem is solved by taking an instantaneously rest frame in which geometric thermodynamic observables read as previously and giving them the special relativistic effect emerged from the inverse transformation to the original frame pointwise. The solution of the thermodynamic observables in accord with the laws of thermodynamics and the theory of relativity is presented. Finally the relativistic structure equations for the equilibrium are derived, from which the general relativistic Poisson equation as well as the heat conduction one are developed exactly.

In this paper, we explore parity violation in a scalar trispectrum from a dynamical Chern-Simons gravity theory. So far, a graviton-mediated diagram with two vertexes being of general relativity has been studied in this theory by taking into account the impact of a modified dispersion relation of gravitons on graviton's bulk propagators. We instead study a parity-odd trispectrum from both a graviton-mediated diagram, where one of the two vertexes originates from the Chern-Simons term, and a contact diagram by using the bulk propagators in general relativity. After computing the scalar-scalar-tensor cubic interactions and the scalar quartic ones originating from the Chern-Simons term, first we show that the resultant parity-odd trispectrum vanishes in the case of Bunch-Davies initial conditions, which is consistent with a no-go theorem for a non-vanishing parity-odd trispectrum. Then, we discuss a way to acquire a non-vanishing parity-odd trispectrum from the viewpoint of non-Bunch-Davies initial conditions.

In this paper, we systematically investigate the optical appearance of a Schwarzschild black hole illuminated by three geometrically thin accretion disk models under varying observational inclination angles. Based on the geometric relationship between the black hole and observer, we first divide the accretion disk into co-side and counter-side semi-disks. We then analyze light ray trajectories, and calculate the total number of orbits and transfer functions for both semi-disks. The results reveal distinct inclination-dependence of lensed regions on different semi-disks: as inclination increases, the lensed region contracts for the counter-side semi-disk while expanding for the co-side one. Furthermore, through explicit specification of the emission profiles of the three models, we present optical images for both optically thin and thick disk scenarios at different inclinations. The results demonstrate that: (i) the bright rings in all three models become progressively compressed and deviate from circularity as inclination increases; (ii) for thick disks, partial rings are obscured and the overall intensity is lower than thin disks. These results may advance our understanding of general black hole imaging processes and provide a new approach to test gravitational theories through optical morphology studies.

In the presence of an ultralight scalar or vector boson, a spinning black hole will be spun down through the superradiant instability. We use spin measurements from gravitational wave observations of binary black holes, in particular the heavy binary black hole merger event GW231123, along with the lower-mass GW190517 event, to constrain the existence of ultralight bosons. We disfavor scalars with masses in the range of $[0.55, 11]\times 10^{-13}$ eV and vectors in the range of $[0.11, 18]\times 10^{-13}$ eV, making only a conservative assumption that the black hole lifetimes are greater than $10^5$ years. The lower ends of these ranges, where the exclusion confidence is the highest, were not previously excluded by spin measurements from electromagnetic or gravitational wave observations. We map these constraints to axion and dark photon models with interactions.

We investigate the co-scattering mechanism for dark matter production in an EFT framework which contains new $Z_2$-odd singlets, namely two fermions $N_{1,2}$ and a real scalar $\chi$. The singlet scalar $\chi$ is the dark matter candidate. The dimension-5 operators play a vital role to set the observed DM relic density. We focus on a nearly degenerate mass spectrum for the $Z_2$ odd particles to allow for a significant contribution from the co-scattering or co-annihilation mechanisms. We present two benchmark points where either of the two mechanisms primarily set the DM relic abundance. The main constraint on the model at the LHC arise from the ATLAS mono-$\gamma$ search. We obtain the parameter space allowed by the observed relic density and the mono-$\gamma$ search after performing a scan over the key parameters, the masses $M_{N_{1,2}}, M_\chi$ and couplings $c_3^\prime, y^\prime_{11,22}$. We find the region of parameter space where the relic abundance is set primarily by the co-scattering mechanism while being allowed by the LHC search. We also determine how the model can be further probed at the HL-LHC via the mono-$\gamma$ signature.

GW200105_162426 is the first neutron star-black hole merger to be confidently confirmed through either gravitational-wave or electromagnetic observations. Although initially analyzed after detection, the event has recently gained renewed attention following a study [Morras et al. arXiv:2503.15393 ] that employed a post-Newtonian inspiral-only waveform model and reported strong evidence for orbital eccentricity. In this work, we perform a detailed analysis of GW200105 using state-of-the-art effective-one-body waveform models. Importantly, we present the first study of this event utilizing a physically complete model that incorporates both orbital eccentricity and spin precession across the full inspiral, merger, and ringdown stages, along with higher-order gravitational wave modes. Our results support the presence of eccentricity in the signal, with zero eccentricity excluded from the 99% credible interval, but yielding a mass ratio closer to the original LIGO-Virgo-KAGRA analysis, differing from the findings of [Morras et al. arXiv:2503.15393 ]. Additionally, similar to a previous eccentric-only analysis [de Lluc Planas et al. Astrophys. J. 995, 47 (2025).], we observe a multimodal structure in the eccentricity posterior distribution. We conduct targeted investigations to understand the origin of this multimodality and complement our analysis with numerical relativity simulations to examine how the inclusion of eccentricity impacts the merger dynamics.

In this work, we propose a novel realization of $\textit{type-I}$ cosmic strings arising from the spontaneous breaking of an extended gauge symmetry $SU(2)_R\times U(1)_{B-L}$ in the context of a low-scale split seesaw mechanism for neutrino mass generation. We demonstrate that the split seesaw framework, which explains the smallness of neutrino masses, naturally motivates a small scalar self-coupling $\lambda$. This intrinsically links the neutrino mass generation mechanism to the formation of $\textit{type-I}$ cosmic strings, where the gauge coupling dominates over the scalar self-coupling ($\beta\equiv\lambda/2g^2<1$). We explore the cosmological implications of these strings, including their gravitational wave signatures that are testable in current and future experiments. Our findings establish a compelling and testable connection between neutrino mass generation and cosmic string phenomenology in an underexplored region of parameter space.

We propose a minimal extension of the type-I seesaw model to realise leptogenesis from the co-annihilation of dark sector particles. The type-I seesaw model is extended with a singlet fermion and two singlet scalars charged under a $Z_{2}$ symmetry. The $Z_{2}$-odd singlet scalar is the dark matter candidate. Here the usual type-I seesaw mechanism generates neutrino mass, and a net lepton asymmetry is generated from the co-annihilation of the dark matter and the $Z_2$-odd singlet fermion. The $Z_{2}$-even singlet scalar is important in dark matter phenomenology. Successful leptogenesis is possible at TeV-scale, unlike the vanilla case. This minimal extension provides an elegant explanation of successful leptogenesis with direct connection to the dark matter abundance in the Universe.

In k-essence theories within general relativity, where the matter Lagrangian depends on a real scalar field $\phi$ and its kinetic term $X$, static and spherically symmetric compact objects with a positive-definite energy density cannot exist without introducing ghosts. We show that this no-go theorem can be evaded when the k-essence Lagrangian is extended to include a dependence on the field strength $F$ of a $U(1)$ gauge field, taking the general form ${\cal L}(\phi, X, F)$. In Einstein-scalar-Maxwell theories with a scalar-vector coupling $\mu(\phi) F$, we demonstrate the existence of asymptotically flat, charged compact stars whose energy density and pressure vanish at the center. With an appropriate choice of the coupling function $\mu(\phi)$, we construct both electric and magnetic compact objects and derive their metric functions and scalar- and vector-field profiles analytically. We compute their masses and radii, showing that the compactness lies in the range ${\cal O}(0.01)<{\cal C}<{\cal O}(0.1)$. A linear perturbation analysis reveals that electric compact objects are free of strong coupling, ghost, and Laplacian instabilities at all radii for $\mu(\phi)>0$, while magnetic compact objects suffer from strong coupling near the center.

Strong magnetic fields and plasmas are intrinsically linked in both terrestrial laboratory experiments and in space phenomena. One of the most profound consequences of that is the change in relationship between the frequency and the wave number of electromagnetic waves propagating in plasma in the presence of such magnetic fields when compared to the case without these fields. Furthermore, magnetic fields alter electromagnetic wave interaction with relativistic plasma waves, resulting in different outcomes for particle and radiation generation. For a relativistic plasma wave-based photon acceleration this leads to an increased frequency gain, and, thus, potentially to higher efficiency. The influence of a magnetic field leads to quantitative and qualitative change in the properties of photon acceleration, amplifying the increase in the electromagnetic wave frequency.

In this paper, we investigate periodic orbits of test particles around a deformed Schwarzschild black hole and the resulting gravitational waves. Firstly, we examine the properties of circular orbits and find that circular orbits could disappear when the deformation is large enough. Then, using an orbital taxonomy, we characterize various periodic orbits with a set of triples, which describes the zoom-whirl behaviours. We also calculate the gravitational waveform signals generated by different periodic orbits, revealing the influence of the deformation on the gravitational wave, which can be potentially picked up by future space-based detectors.