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

ALT Collapsar disks are proposed sources of r-process elements, but neutron-rich disk ejecta require gas to be both neutronized in the disk and ejected before accretion. The magnetic field that enables ejection also thickens the disk and accelerates the inflow, lowering both the density and the time available for weak processing. To compute the resulting neutronization, we evolve the electron fraction of the inflowing gas, adopting at each radius the temperature that maximizes the net neutronization rate for the local density and instantaneous composition. This yields a lower limit on Yₑ that is independent of the disk's thermal history. We adopt an optimistic unbinding radius of R_unb=10 rg for all magnetic fluxes capable of launching outflows. Combining this ejection condition with favorable assumptions of low black hole mass, ejection of midplane gas, and the upper end of the γ-ray burst (GRB) engine-power scale, which limits the accretion rate to Ṁ_BH≲0.4 M⊙ s⁻¹, gives a fiducial lower

ALT Horizon scale images probe the plasma dynamics and spacetime in the vicinity of accreting black holes. Interpreting these images requires models that connect image morphology to the structure of the underlying accretion flow. Disk misalignment is expected in many systems, yet most horizon scale image analyses assume that the emitting flow is aligned with the black hole spin. We investigate whether tilted accretion flows produce image features distinguishable from axisymmetric flows and whether their effects can be absorbed by changes in aligned model parameters. Using general relativistic magnetohydrodynamic simulations of tilted magnetically arrested disks spanning black hole spins a*=-0.9375 to 0.9375 and initial disk tilts 0° to 30°, we generate synthetic images and quantify their morphology through fits to an aligned, semi-analytic emission model. Using this approach, we show that high spin prograde models show little sensitivity to disk tilt, as the inner emitting flow aligns with

ALT We present a pedagogical introduction to the I-Love-Q relations within Newtonian gravity using an enthalpy-based formulation of stellar structure. Introducing the specific enthalpy converts Euler's equation into a first integral of hydrostatic equilibrium and recasts the equation of state as a relation between the mass density and the enthalpy. Together with Poisson's equation, these relations provide a unified description of spherical equilibrium and deformations induced by rotation and tides. We illustrate the formalism with polytropic equations of state and a relativistic free Fermi gas. In Newtonian gravity, slow uniform rotation and a weak tidal field excite the same linear quadrupolar response, yielding the exact identity Ī²Q̄/λ̄≡1 for the dimensionless (“bar”) observables—independently of the equation of state. This exact identity is distinguished from the approximate universality of the pairwise I-Love-Q relations, whose residual dependence on stellar structure is illustrated b

ALT Recently, the Five-hundred-meter-Aperture-Spherical-radio-Telescope (FAST) Galactic Plane Pulsar Snapshot (GPPS) survey discovers an extraordinary binary neutron star (BNS) system, PSR J0653+0443, possessing the highest known orbital eccentricity (e≈0.992) among Galactic BNSs (Yang et al., 2026), which provides a unique probe into the formation and evolution of BNSs. In this Letter, we perform compact binary population synthesis calculations with self-consistent neutron star spin evolution to model extremely eccentric BNS population detectable by the FAST GPPS survey, explicitly incorporating observational selection effects. We find that BNSs with e>0.99 constitute only ∼0.6% of the detectable population, with an expected detection number of λ_GPPS≈0.31 over the full planned footprint. Thus, although rare, systems as eccentric as PSR J0653+0443 are compatible with standard binary evolution. We further demonstrate that extremely eccentric BNSs arise preferentially from core-collapse sup

ALT We study toroidal structures formed by a charged, non-self-gravitating perfect fluid orbiting a Schwarzschild black hole immersed in a poloidal magnetic field. To obtain analytic and semi-analytic solutions, we assume a cold, rest-mass-dominated fluid with uniform specific charge and zero conductivity, so the current is purely convective. This regime is formally opposite to the ideal GRMHD limit. The total magnetic field comprises a prescribed asymptotically uniform external component and an approximate self-field associated with the azimuthal current in the torus. We represent the latter by a regularized dipole approximation to the field of an effective circular current loop. Neglecting the self-field, the method of characteristics yields a general implicit solution of the integrability condition for a function parametrizing the specific-angular-momentum profile. A separately obtained cylindrically dependent class recovers a solution from our earlier work. For the radially dependent c

ALT GRB 220706A exhibits X-ray flaring activity extending to 51 days after the trigger, along with a luminous optical thermal component emerging on a timescale of 10⁶ s. Such prolonged central-engine activity could be powered by a collapsar fed by an extended stellar envelope. However, a relativistic jet may struggle to break out of the extended envelope. These challenges motivate a tidal disruption event (TDE), although explaining both the early relativistic jet and the luminous late optical thermal emission within one TDE framework remains difficult. We investigate a TDE scenario in which shocks between stellar debris streams drive the early inflow of some debris, potentially carrying preexisting fossil magnetic flux toward the black hole (BH) and powering an initial relativistic jet via the Blandford-Znajek mechanism. The remaining debris circularizes into an accretion disk, whose thermal emission accounts for the late optical thermal component. For GRB 220706A, the optical timescale, l

ALT Population studies of fast radio burst (FRB) repetition typically model sources using a single distribution of steady, time-averaged burst rates, yet individual sources show significant departures from this assumption. Here we present FRB 20210601A, a source discovered by the Canadian Hydrogen Intensity Mapping Experiment FRB project (CHIME/FRB) that represents the most extreme such departure yet identified. The source produced at least nine bursts within a single 106.5 s interval – the highest instantaneous burst rate yet reported from a repeating FRB source at gtrsim 2 Jy ms fluences – yet remained otherwise undetected despite \sim 320 hr of exposure spanning 7 yr. The active interval occurred while the source was in a side-lobe of the CHIME/FRB digitized beams, implying an instantaneous burst rate gtrsim2.3× higher (gtrsim 21 bursts) at main-lobe sensitivity. The source's intense, brief burst storm flanked by apparent quiescence despite substantial exposure is unique among the CHIME

ALT We conducted a systematic spectral analysis of the X-ray flares of gamma-ray bursts (GRBs) observed by Swift/X-ray Telescope from 2005 April to 2015 March. The sample includes 521 flares from 206 GRBs. The GRBs cover the three subtypes: X-ray flashes (XRFs), X-ray-rich GRBs (XRRs), and classical GRBs (C-GRBs). We used a simple power-law model to fit the spectra during the flares, as well as to fit the preflare and postflare afterglow emissions, and obtained the parameters such as photon index and intrinsic hydrogen column density (N_H). By comparing the spectral characteristics of flares, prompt emission, and afterglow emission, and analyzing the temporal evolution of the X-ray flare spectra, we obtained the following main conclusions. (1) The spectrum during the flare phase is significantly harder than that of the preflare and postflare phases, while there is no obvious difference in the spectrum between the preflare and postflare phases. (2) The intrinsic N_H shows no significant cha