ALT EP241021a is a peculiar fast X-ray transient exhibiting a long X-ray plateau and an optical rebrightening, both challenging the traditional jet afterglow model. Whether its nature is a stellar explosion or a tidal disruption event (TDE) remains debated. Here we present late-time HST/WFC3 and Gemini-N/GMOS observations of its host galaxy at z=0.748. After ∼300 days post-trigger, the transient emission had faded below detection, revealing a dwarf disk galaxy with an effective radius Rₑ=1.7 kpc, a stellar mass M⋆∼3×10⁸M⊙, and a high star formation rate of ∼5 M⊙{ yr⁻¹}. Combined with previous very long baseline interferometry measurements, the transient can be located in the galactic disk with a projected physical offset of 0.95±0.13 kpc from the galaxy center. Host-subtracted optical light curves show that the rebrightening ceased at ∼47 days, followed by a sudden drop with a power-law index steeper than -3.3, coincident with a similar drop in the X-ray light curve. This synchronous drop

ALT Binary interaction can substantially alter massive-star evolution and pre-supernova structure, changing core-collapse outcomes and nucleosynthetic yields. We compare explodability and nucleosynthesis in 66 non-rotating, solar-metallicity single-star and binary-stripped progenitors spanning zero-age main-sequence (ZAMS) masses of 11-45 M⊙, using the spherically symmetric PUSH framework and nucleosynthesis post-processing. Both populations explode up to 22 M⊙, with binary stripping altering explodability at higher ZAMS masses. Successful explosions span similar energies (∼0.4-1.3 B) and remnant masses (∼1.4-2.0 M⊙). The largest nucleosynthetic differences occur at low ZAMS masses, particularly for material undergoing explosive O and Si burning. The ⁵⁶Ni yields and iron-group abundances broadly agree with observations of core-collapse supernovae and the metal-poor star HD 84937. When compared with calculations using time-dependent mixing-length theory and a two-parameter explodability cri

ALT We construct new finite-temperature, composition-dependent equation of state (EOS) tables for astrophysical simulations by implementing a recently developed energy-density functional. The functional is constrained by ab initio nuclear matter calculations and neutron-star observations. A distinguishing feature of this functional is a non-monotonic density dependence of the nucleon effective mass, with an increase beyond saturation density. Using these EOS tables, we investigate the impact of current uncertainties in nuclear matter properties on core-collapse supernova (CCSN) evolution with spherically symmetric simulations employing an effective treatment of convective mixing. The magnitude of the EOS effects depends on the progenitor compactness. Within current constraints, variations in incompressibility, symmetry energy, and high-density pressure produce only modest differences during the early post-bounce evolution. In contrast, the effective mass dependence has a much stronger infl

ALT High-energy outbursts from magnetars may be associated with crustal failures or quakes. The magnetoelastic modes of the star can be excited to large amplitudes in such a framework, providing a natural explanation for the quasi-periodic oscillations observed in the X-ray tails of some events. However, previous calculations of torsional modes have been carried out assuming an intact crust without accounting for the failure itself. We develop a code in this paper that solves the axial sector of the linearised Einstein-Maxwell-Euler equations in a cavity that hosts inelastic regions or 'plastic islands'. As crustal elements are displaced, shear stresses are tracked as a function of time to allow cells to dynamically switch from elastic to inelastic states. The presence of islands in the crust promotes phase mixing and, when reflected waves mix constructively, large sections fail collectively ('avalanche') if the initial kick is strong enough. Transient spectral features are observed as a r

ALT Synchrotron polarization is a powerful tool for diagnosing magnetohydrodynamic (MHD) turbulence, yet prior analyses are confined to the optically thin regime, neglecting the effects of synchrotron self-absorption (SSA). Here, we incorporate SSA into the radiative transfer of polarized synchrotron emission and employ 3D MHD turbulence simulations to investigate its impacts on polarization statistics. We show that SSA strongly modulates polarized intensity by suppressing its emission amplitude, steepening its low-frequency power-law slopes, and reducing scale-dependent anisotropy. Notably, SSA does not impede the recovery of the scaling slope of the magnetic turbulence. Our results extend the applicability of synchrotron polarization diagnostics to optically thick astrophysical environments, providing a theoretical foundation for interpreting multi-frequency radio polarization observations. This confirms that polarization statistical techniques remain effective for diagnosing MHD turbule

ALT Radiatively inefficient accretion flows (RIAFs) in low-luminosity active galactic nuclei (LLAGNs) are promising candidates for the PeV astrophysical diffuse neutrino background (DNB), but how the magnetically arrested disk (MAD) state affects their neutrino output and what fraction of LLAGNs are in this state remain unclear. We present a comprehensive study of diffuse neutrino emission from the inner accretion flows of LLAGNs in the MAD state, including all three flavors and both hadronuclear (pp) and photohadronic (pγ) production channels. Assuming that ∼ 5% of the accretion power is transferred to nonthermal protons, current IceCube data allow at most 2.3×10⁻³ of LLAGNs to have their inner accretion flows in a MAD state that can produce high-energy neutrinos. A lower fraction of the accretion power transferred to nonthermal protons would allow a proportionally larger fraction of such LLAGNs. Assuming that the comoving number density of low-excitation radio galaxies (LERGs) approximat

ALT Fast outflows are commonly observed in accreting black hole systems, yet their launching mechanism remains debated, especially when the gas is highly ionized and radiation line driving becomes inefficient. We investigate magnetically driven outflows from magnetically arrested discs (MADs) using a steady, axisymmetric magnetocentrifugal outflow model. The outflow equations follow the classical trans-magnetosonic MHD framework, while the disc structural scalings and outflow-base conditions are motivated by general relativistic magnetohydrodynamics (GRMHD) simulations. We solve for the trans-magnetosonic outflow solutions along prescribed large-scale poloidal magnetic field lines. The outflows launched from the inner disc are strongly accelerated and the formal Newtonian solutions can enter the mildly relativistic regime. The outflow velocity decreases systematically with increasing footpoint radius, producing a radially stratified outflow in which inner streamlines reach UFO-like velocit

ALT We present the discovery of supernova (SN) Ares, a strongly lensed supernova at z_spec=1.276±0.002 in a massive, triply imaged host galaxy behind the MACS J0308.9+2645 galaxy cluster. JWST/NIRSpec spectroscopy spanning the rest-frame optical to NIR of Ares reveals helium features at 5876 Å, 7065 Å, and 10830 Å, as well as Hα and Paβ. A comparison to local core-collapse SN spectra and light curves leads to a classification of SN Ares as a Type IIb supernova, the highest-redshift member of its class spectroscopically identified. A comparison to local SN IIb light curves provides a phase estimate for the spectrum of 34₋₉⁺¹⁰ rest-frame days post-radioactive peak, providing a unique view into a high-redshift stripped-envelope supernova in its late-photospheric evolution. A lens model of the cluster constructed using recent JWST data indicates that SN Ares is the first image to arrive and will reappear in two future images near the center of the cluster plane in ≳ 70 years, with predicted ma

ALT The mass and spin distributions of merging binary black holes offer clues to their formation pathways, which remain uncertain. In this work, we model the population of binary black holes using generic subpopulations with distinct mass-ratio, spin-magnitude, and spin-tilt distributions, whose relative contributions vary with primary mass. Using the 259 binary black holes in the fifth LIGO-Virgo-KAGRA catalog (GWTC-5), we resolve three subpopulations with low, medium, and high spins. The low-spin population dominates for primary masses near 35 M_odot, contributes roughly half of the binaries for primary masses of 10 M_odot, and favors nearly equal mass ratios overall; its spins are consistent with both black holes having negligible spin, with a log Bayes factor of log₁0B=6.1⁺⁰.²₋₀.₃ in favor of vanishing spins. The medium-spin population accounts for the other half of the population around primary masses of 10 M_odot and favors spin magnitudes χ_i ≈ 0.2 for both components, preferentiall

ALT We present a multiwavelength study of GRB 260924A at z=3.51±0.10 using Fermi, Swift, and ground-based optical and near-infrared observations. Its isotropic-equivalent gamma-ray energy, Eγ,ᵢₛₒ≃9.79×10⁵⁴ erg, places it among the most energetic GRBs observed. The prompt emission comprised two bright episodes separated by weaker activity. The X-ray afterglow ranked among the most luminous in our comparison sample at selected post-flare epochs, with a luminosity comparable to that of GRB 221009A at a rest-frame time of 3.5 ks. At a common redshift of z=1, the optical afterglow outshone GRB 221009A by approximately 2 mag at 0.3 d and 1 mag near 1 d. LAT emission extended to approximately 1100 s and showed an early excess above the subsequent decay. The highest-energy photon, 43.3 GeV, arrived at 82 s during the first episode; a 14.2 GeV photon arrived at 304 s between episodes. We describe the afterglow light curves through forward-shock synchrotron and synchrotron self-Compton (SSC) emissio

ALT The origin of the excess of GeV gamma-rays in the Milky Way's galactic center observed by Fermi-LAT has been an open question for nearly two decades. The two leading interpretations of this signal are that it is produced either by annihilating dark matter (DM), or arises from unresolved point sources, such as a novel population of millisecond pulsars. In both scenarios, uncertainties and limitations in the modeling of galactic diffuse gamma-ray emission, such as the steady-state approximation of cosmic ray (CR) propagation and assumption of an axisymmetric distribution of CRs, complicate the interpretation of the galactic center excess (GCE). Simulations with full magnetohydrodynamics (MHD) and CR transport can provide a new avenue for understanding the astrophysical phenomena that drive galactic diffuse gamma-ray emission. We utilize MHD simulations of Milky Way analogs with time-dependent, spectrally-resolved CR transport to reconstruct diffuse gamma-ray emission. Comparing instantan

ALT Optical and infrared GRB absorption spectroscopy provides valuable insight into host-galaxy properties across cosmic time. However, the star-forming region embedding the progenitor, on scales ≲ 100 pc is heavily ionized by the GRB emission, making X-ray spectroscopy the sole probe of its physical and chemical conditions. We characterize the GRB-embedding medium as a function of progenitor type and cosmic epoch via high-resolution X-ray spectroscopy. We extend our study to high-redshift GRBs to evaluate how effectively X-ray absorption signatures can distinguish between pristine, Pop III-, and Pop II-enriched environments. Using the time-dependent photoionization code TEPID, we self-consistently calculate the ionization structure of the absorber, the energies and the strengths of the resulting absorption lines. We analyze a flux-selected sample of GRBs showing strong evidence for time-dependent photoionization, and search for predicted narrow features in the RGS spectra. We also assess

ALT Pulsar timing arrays will soon be able to resolve the loudest supermassive black hole binaries contributing to the stochastic gravitational wave background at nanohertz frequencies. While the few decades of observations are typically not enough to see these binaries evolve in frequency, the so-called pulsar terms offer a glimpse into the past and can help us map out the frequency evolution of these binaries over tens of thousands of years. Measuring this long-term frequency evolution can allow us to look for deviations from a vacuum binary evolution due to various environmental effects. We develop a Fisher-matrix approach to calculate how precisely the frequency can be tracked over time in this manner, and demonstrate its use on a realistic near-future pulsar timing array with a 30-year baseline. We find that the environmental effects predicted by 2-dimensional hydrodynamic simulations of circumbinary disks are unlikely to be detectable in the circular binaries we considered, however,

ALT We present numerical magnetohydrodynamic (MHD) simulations of the interstellar medium in gravity-stratified boxes with the Piernik MHD code. The system contains thermal gas, spectrally resolved cosmic-ray (CR) nuclei within the CRESP algorithm, and spectrally unresolved CR protons. CR protons drive gas outflows and undergo Coulomb and hadronic losses. CR nuclei undergo Coulomb losses. We also include the spallation of primary Carbon by thermal gas atoms, thereby decaying Car- bon into secondary stable Boron isotopes. We use the resistive-MHD approximation as a subgrid model for unresolved turbulent magnetic dissipation in current sheets. We perform a parameter study of the magnetic diffusivity η. The Boron-to-Carbon ratio B/C and hadronic γ-ray luminosity density are computed as diagnostics. We find that non-zero magnetic diffusivity modifies the magnetic topology, leading to a more horizontal field in the halo, thereby accumulating CRs in the disk region and signifi- cantly increasing

ALT This paper examines the role of plasma compression regions ahead of interplanetary coronal mass ejections in the formation of Forbush effects decreases in cosmic ray intensity during the first phase. The aim of this study is to identify and quantify the relationship between the structure of the CME (specifically, the parameters of the compression region behind the shock front) and the nature of the observed Forbush effect. To this end, events with intensity decrease amplitudes greater than 5 percent were selected, and a theoretical model of cosmic ray behavior at the shock front was tested using modern analytical methods and mathematical models. Analysis of the results for two dozen events revealed satisfactory agreement between the theory and observations. The key reason for some discrepancies is the need to integrate the magnetic field over the particle gyro radius. The obtained data provide insight into the mechanisms of cosmic ray modulation in such environments.

ALT X-ray quasi-periodic oscillations (QPOs) were reported for 19 different observations of the atoll source 4U 1728- 34. Three of them reveal triplets of QPOs: a lower and a upper kHz QPOs and a low-frequency QPO. Even though they are discernible only after averaging we assume them to be simultaneous. We apply a separate model (formula) for each of the three frequencies of the observed QPOs and compose a system which contains three algebraic equations for the three unknown parameters - the mass and the specific angular momentum of the central neutron star, and the radius of the orbit of orgin of the given triplet of QPOs, which allows us to find the numerical values of the later. Error propagation formulas are applied for the obtaining of interval estimates of the parameters of the star. This is done through implicit function differentiation. The calculations are repeated with several different models for the kHz QPOs.

ALT We analyse what physical quantities of SN ejecta can be obtained from a single epoch of nebular JWST spectroscopy. We provide an analytical framework, which together with a grid of helium star SUMO spectral synthesis models allows the determination of these quantities for any stripped-envelope SN. Using the framework, we derive critical electron densities for major emission lines, finding values in the range 10⁵-10⁶ cm⁻³. This means formation under close to LTE conditions for 200 – 300 days. We obtain ionisation fractions of Ni and Co, as well as the temperature and filling factor of the Fe/He zone, the ⁵⁶Ni and stable nickel masses, the Ni/Fe ratio, and the optical depths τ[NᵢII]₆.₆₃₆μₘ and τ[CₒII]₁₀.₅₂μₘ. Besides these constraints from iron group elements, one can also obtain the filling factor of the carbon burning (O/Ne/Mg) zone from [Ne II] 12.81 μm, and the masses of Ar II and Cl I. We apply our methodology to a publicly available JWST spectrum of Type Ic SN 2024aecx. We find tha

ALT The recent discovery that microquasars operate as efficient particle accelerators brings back into focus the question as to whether their larger cousins, radio galaxies, also operate as efficient accelerators. We here discuss what we presently know about particle acceleration in radio galaxies, focusing particularly on the nearest such object, Centaurus A.

ALT Late light curves of neutron star mergers can contain substantial fission power while remaining compatible with different radioactive inventories. We develop a unified source attribution model in which a common bounded response formulation links nuclear heating, radiation transport and isotope identification. Within particle dependent deposition and gray photon escape, matched luminosity comparisons show how long alpha and fission responses become aligned. Explicit competing inventories then reproduce a light curve with a substantial ²⁵⁴Cf contribution, with smooth evolution of the beta luminosity response providing an important source of compensation. We derive optimization certificates and collective likelihood bounds that quantify the resulting limits on identification under specified source and ejecta constraints. We also introduce an energy conserving model with two radiation frequency groups to resolve the information carried by color at fixed total luminosity precision. Its exac

ALT We study the dynamical response of a hydrodynamic disk to an impulsive kick imparted to a central massive object, focusing on the global properties of the material that remains gravitationally bound. We construct a simple analytic model and show that the bound material can acquire a significant tilt—or even a retrograde rotation—if the kick is directed close to the disk midplane. We perform 3D numerical simulations and show that (1) the bound material relaxes to a torus-like circularized flow of which total mass and angular momentum is in fair agreement with the analytic estimate, and (2) in spite of nonlinear hydrodynamic effects, a highly tilted or retrograde disk can be sufficiently formed. The simulations additionally reveal a transient warp in the kicked disk, suggesting a kick as a formation mechanism of tilted or warped disks around compact objects. About 10% of the kinetic energy the bound material acquired from the kick is converted to the internal energy, while the exact conv