High Energy Astrophysical Phenomena
Adaptive proposals for nonparametric equation-of-state inference with RIFT: iterative Gaussian-process refinement in a compressed sequence representation
R. O'Shaughnessy and Z. Zhu
Nonparametric equation-of-state (EOS) inference evaluates the likelihood on a finite ensemble drawn from a prescribed functional prior. Reweighting that ensemble suffices for the binary
neutron stars detected so far, and loses effective sample size only once the likelihood concentrates — which needs third-generation catalogues, or extra electromagnetic and nuclear-theory information folded into the same target. We develop and validate an adaptive-proposal procedure that leaves the base prior fixed: data-informed generations are combined by multiple importance sampling and, where that degenerates at large catalogue size, by a calibrated Gaussian projection. We implement it in two representations — a compressed principal-component parametrization of the
neutron-
star sequence, whose draws need no stellar-structure solve, and a sound-speed parametrization with a differentiable Tolman–Oppenheimer–Volkoff solver — both on a constrained low-density-to-pQCD bridge. Because that anchor, and not the bridge, fixes the low-density prior, we rebuild the ensemble with a crust-plus-chiral-EFT anchor in place of the wide nuclear metamodel: the maximum-mass prior is unmoved, the radius gains a hard prior ceiling at the measured NICER value. GW170817 with the specified NICER and
radio factors gives the calibration-conditional $R(1.4\,M_\odot)=11.7\pm0.4$km; in a synthetic $1000$-event catalogue it reproduces the mean fixed-prior $\Lambda(1.4\,M_\odot)$ to $0.4$%, $1.5$ times wider, as the fixed archive's effective sample size falls from $\sim\!470$ to 22.
Read the full abstract ▾
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
SPECULATE: A synthetic spectral library, emulator and fitting package for accretion disc winds – Infrastructure and application to CVs
Austen G. W. Wallis, Christian Knigge, James H. Matthews et al. (+6 more)
Disc winds are critical components of accreting astrophysical systems and their observations can yield a wide variety of spectral line profiles. Yet, inferring disc wind parameters remains challenging: the underlying parameter spaces are high-dimensional and degenerate, while the radiative-transfer simulations are imperfect and computationally expensive. This paper tackles bridging this gap. Here, we present 'Speculate', an open-source framework for rapidly emulating and fitting observations with synthetic
accretion disc wind spectra, generated from the Monte Carlo radiative-transfer code Sirocco. Speculate includes the release of our cataclysmic variable (CV) training data, a library of 88,680 sparsely gridded Sirocco spectra spanning the ultraviolet and optical wave bands, a suite of pre-trained emulators, and its interactive Marimo user interface. Speculate compresses spectral grids using principal component analysis and then provides three approaches to interpolate the resulting latent representation: with a regular-grid interpolation, a neural network, or a Gaussian process. All three architectures enable Speculate to generate a Sirocco spectrum between $1-40\,\mathrm{ms}$, thereby enabling efficient inference. The first two support rapid $\chi^2$ optimisation. The Gaussian process utilises a
Bayesian inference engine coupled with a covariance-aware, flexible likelihood function, adapted and accelerated from the Starfish framework. This function helps absorb correlated discrepancies between simulations and data. Tests show all architectures reproduce unseen Sirocco spectra with broadly comparable accuracy and can recover their physical parameters. Subsequently, we apply Speculate to 5 representative nova-like CV spectra, reproducing several observed line features while also exposing mismatches where the current model grid omits relevant physics.
Read the full abstract ▾
All authors Austen G. W. Wallis, Christian Knigge, James H. Matthews, Knox S. Long, Madeleine-Mai Ward, Stuart A. Sim, Adam B. Hill, Amin Mosallanezhad, Nicolas Scepi
High Energy Astrophysical Phenomena
A spatially resolved view of Fast Radio Burst host metallicities with Integral-field Spectroscopy
Sunil Simha, Hsiao-Wen Chen, Wen-fai Fong et al. (+15 more)
Magnetar sources are the leading theory for Fast
Radio Burst (FRB) progenitors. If magnetars are indeed the dominant sources, we may thus expect any
metallicity preference for magnetar formation to be reflected in the FRB site in host
galaxies. Here, we leverage Integral Field Unit (IFU) spectroscopy to spatially resolve gas-phase
metallicity distribution in five FRB host
galaxies: FRB 20240210A, FRB 20240312D, FRB 20250227A, FRB 20211127I, and FRB 20250316A, at $z < 0.05$, including the FRB site, with the O3N2 index. We observed the first four sources with the newly commissioned Large Lenslet Array Magellan Spectrograph (LLAMAS) IFU on the Magellan
Telescopes and used archival Keck/KCWI data for FRB 20250316A. We find ISM
metallicity variations of at least 0.3 dex within individual hosts for the majority of the sample, with median values spanning $12 + log(O/H) \approx$ 8.5–8.7. At the burst sites, four have
metallicities of $12 + \log(O/H) \approx 8.5$–8.9, while the fifth has a
metallicity below 8.5. These findings reveal substantial
metallicity variations both among FRB host
galaxies and within the local environments of the bursts. Consequently, our study shows that longslit-based global estimates of host
galaxy metallicity do not always represent the true burst-site distributions. We therefore advocate for IFU follow-up of larger host samples to ultimately provide FRB-site-relevant observational constraints on
metallicity preferences for FRB occurrence.
Read the full abstract ▾
All authors Sunil Simha, Hsiao-Wen Chen, Wen-fai Fong, Sarah Hughes, Yuxin Dong, J. Xavier Prochaska, Nicolas Tejos, Tarraneh Eftekhari, Alexa C. Gordon, Stuart D. Ryder, Mawson W. Sammons, Alice P. Curtin, Victoria M. Kaspi, Adam E. Lanman, Calvin Leung, Kiyoshi W. Masui, Aaron B. Pearlman, Ryan M. Shannon
High Energy Astrophysical Phenomena
Investigating X-ray Emission from Radio-detected Broad- and Narrow-line Seyfert 1 Galaxies
Minhua Zhou, Minfeng Gu, Lei Xu et al. (+2 more)
Context: This paper presents a study of the X-ray emission for a sample of
radio-detected (RD-) broad- and narrow-line Seyfert 1
galaxies (NLS1s and BLS1s). Aims: To investigate the X-ray emission properties of early-stage
accretion activity or early jets in NLS1s. Methods: By fitting XMM-Newton X-ray spectra and combining with multi-band data from SDSS and FIRST, we conducted a statistical comparative study on the X-ray emission and multi-band correlations of NLS1s and BLS1s. Results: NLS1s and BLS1s show no significant difference in their soft X-ray blackbody temperatures, but NLS1s exhibit steeper hard X-ray
photon indices and optical-to-X-ray slopes ($\alpha_{\rm ox}$). Moreover, correlation analyses of various parameters reveal intrinsic differences in the X-ray emission between the two samples. For instance, at comparable optical luminosities, NLS1s exhibit a higher $ \alpha_{\rm ox} $ (i.e., weaker X-ray emission), marginally distinct dependencies between
radio luminosity and black hole mass in the fundamental plane, and different correlations between $\alpha_{\rm ox} $ and
radio loudness. Based on the relationship between UV luminosity and $\alpha_{\rm ox} $ in RQ-AGN, the estimated X-ray excess ($\Delta \alpha_{\rm ox} $) in both samples is positively correlated with
radio loudness. RQ-BLS1s generally display the X-ray excess, whereas RQ-NLS1s tend to show an X-ray deficiency. The Eddington ratio of RQ-NLS1s derived from X-ray luminosity is lower than that inferred from optical luminosity, further supporting their intrinsically weaker X-ray emission. Conclusions: These differences in X-ray emission between NLS1s and BLS1s may ultimately stem from the earlier evolutionary stage of NLS1s. Multivariate linear fits among
radio luminosity, X-ray luminosity, and
radio loudness for NLS1s and BLS1s support a multi-wavelength radiative connection associated with jets.
Read the full abstract ▾
All authors Minhua Zhou, Minfeng Gu, Lei Xu, Mai Liao, ZhengXue Chang
High Energy Astrophysical Phenomena
Chana: A GPU-Accelerated AMR GRRMHD Code
Tianshu Wang
This paper presents Chana, a GPU-accelerated, block-structured adaptive-mesh code for general relativistic magnetohydrodynamics, multigroup M1
neutrino transport, and dynamical spacetime
evolution using the Z4c formulation. Each physical module uses independently selected spatial discretizations and ghost-zone widths to balance accuracy and computational cost. Stiff radiation-matter interactions are treated implicitly, with Jacobians calculated analytically from the chain-rules. The code is written in C++20 and it uses MPI and Kokkos 5 for distributed-
memory and performance-portable parallelism. The code is validated through a number of GRMHD, radiation transport, and dynamic spacetime tests. For a representative core-collapse
supernova configuration with three
neutrino species and 12 energy groups per species, the code achieves approximately $1.1 \times 10^6$
cell updates per GPU second on NVIDIA A100 GPUs using four-stage RK4 integration. Weak-scaling efficiency remains above 85% up to 256 GPUs on Perlmutter.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Radial Modes of Hot Neutrino-Trapped Hybrid Stars
Peter B. Rau, Andrea Sabatucci and Armen Sedrakian
We study the fundamental radial oscillation mode of hot hadronic and hybrid
stars under conditions relevant to proto-
neutron stars and
neutron-
star merger remnants. The stellar backgrounds are constructed from finite-temperature equations of state with a covariant density functional for hadronic matter and three-flavor 2SC
quark matter at high density. We consider two isentropic configurations in both
neutrino-transparent matter and with trapped electron
neutrinos at fixed electron-lepton fraction. For trapped matter we compare a Gibbs-type construction with global electron-lepton-number conservation to a locally constrained Maxwell-type prescription; in both cases the fixed-
entropy stellar equation of state contains an extended coexistence region and no sharp interface requiring conversion rate-dependent junction conditions. We find that the fundamental radial frequency follows the corresponding purely hadronic sequence up to the onset of deconfinement and then decreases relative to it.
Neutrino trapping shifts this dynamical signature to larger stellar masses and central pressures, reflecting the delayed appearance of
quark matter. The Maxwell-type prescription moves the onset of deconfinement to still higher central pressure and produces a more rapid decrease of the mode frequency near the stability limit. We quantify the deconfinement effect through the fractional frequency shift between hybrid and hadronic
stars at equal gravitational mass. These results show that the fundamental radial mode provides a sensitive dynamical probe of the interplay among
entropy, lepton trapping, phase-transition construction, and
quark deconfinement in hot compact
stars.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Power-Law Injection Spectrum from an Ensemble of Reconnecting Current Sheets
Omar French
A collisionless, low-$\beta$
plasma undergoing strong sub-Alfvénic
turbulence is expected to form a broad hierarchy of reconnecting current sheets immersed in a strong guide
magnetic field. If the reconnecting field strength of a sheet scales with its length as a power law of index $\kappa$, and the number of sheets per unit interval of sheet length decreases as a power law of index $x$, the current-sheet ensemble injects nonthermal particles with a power-law energy spectrum $\propto \gamma^{-s}$, where $s = 1 + (x-2)/(1 + \kappa)$. The spectrum is hard ($s < 2$) when the longest sheets deliver most of the injected energy, which requires $x < 3 + \kappa$. Past numerical studies have measured $2 \lesssim x \lesssim 3.3$, and the scalings of intense current sheets support $\kappa \gtrsim 0$, resulting in $1 \lesssim s \lesssim 2.3$. This injection may yield flat or mildly steep
radio spectra in optically thin sources and hard ion spectra in the coronae of active galactic
nuclei.
Read the full abstract ▾
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Magnus: neutrino oscillation probabilities for any Hermitian Hamiltonian, any number of flavors, and any matter profile
Mauricio Bustamante
Interpreting
neutrino oscillation measurements requires computing the probability that a
neutrino born with one flavor is detected with another. In
vacuum and in matter of constant density, this probability has exact formulas. Where the density varies along the path, as in the Earth, the Sun, or a
supernova, it does not. There, the usual approaches either replace the profile by constant-density steps, whose error falls only as the square of their width, or integrate the
evolution equation with a general-purpose solver, which must shorten its steps to meet a tighter tolerance. Both become slow at high accuracy, yet an analysis needs the probability at many energies, directions, and parameter values. Each new experiment or model often requires writing and validating a new solver. We present Magnus, an open-source Python code that avoids these limitations. It uses the Magnus expansion, whose error falls as a high power of its step width and whose cost is set by how fast the density varies, not by how many oscillations the path holds. Magnus accepts any density profile, any number of flavors, and any Hermitian
Hamiltonian, such as those of non-standard interactions, sterile
neutrinos, Lorentz-invariance violation, and pseudo-Dirac
neutrinos. Where a cheaper route exists, it takes it automatically. For example, where the density varies slowly, as in the Sun, it follows the instantaneous eigenstates and applies the expansion only at resonances. Besides oscillating probabilities, Magnus returns phase-averaged ones, which describe solar and astrophysical
neutrinos. A typical probability takes a few milliseconds, and batched scans are one to two orders of magnitude cheaper per point. Among the public codes we compared, Magnus is the fastest at high accuracy on a varying profile. Magnus shifts the effort of studying a new experiment or model from writing a solver to specifying its physics.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Uncovering the Physical Origins of Black Holes in the Milky Way for Astronomical Surveys
Ilia Kiato, Pierson Lipschultz, Vicky Kalogera et al. (+5 more)
The observational landscape of stellar-mass black holes (BHs) in the Milky Way is expanding beyond X-ray binaries, with Gaia DR4 and Roman expected to open new windows onto BH populations. We use the binary population synthesis framework POSYDON to predict the present-day Galactic BH population and connect it to its evolutionary origins. We test the robustness of these predictions to uncertainties in binary
evolution and BH formation, including core-collapse mechanisms, natal kicks, common-envelope efficiency,
metallicity, and initial binary distributions. Across our models, we find that most Galactic BHs are isolated, with stellar mergers providing the largest contribution and binary disruptions the second largest. Among surviving binaries, detached BH-BH systems dominate. We identify a distinct, narrow feature at higher BH masses ($\simeq13\,\mathrm{M}_{\odot}$ in the fiducial model) produced by wind-driven
evolution of massive Wolf-Rayet progenitors. This feature is particularly prominent among detached BH-BH binaries and persists across variations in binary-
evolution and BH-formation physics, but depends strongly on
metallicity. At lower masses, these BH-BH systems predominantly originate from progenitors that undergo stable mass transfer before BH formation. Finally, for more direct observational applications, we embed the synthetic populations in a Galactic model, evolve their kinematics, perform first-order microlensing calculations for BH-BH lenses, and examine BH systems with luminous companions in the context of the Gaia BHs. In the latter, we uncover a robust stable-mass-transfer population largely absent in rapid population-synthesis predictions. These results provide an evolutionary framework for interpreting the emerging Galactic BH population across complementary observational channels.
Read the full abstract ▾
All authors Ilia Kiato, Pierson Lipschultz, Vicky Kalogera, Jeff J. Andrews, Max M. Briel, Abhishek Chattaraj, Seth Gossage, Philipp M. Srivastava
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
Optimal Photon Counting with Fast, Low Noise Astronomical Imagers
Jack T. Dinsmore, Christopher Layden, Roger W. Romani et al. (+9 more)
Measuring rapid astrophysical phenomena requires many short exposures, which suffer from repeated read noise. A variety of recent technologies are achieving sub-electron read noise, which enable rapid time-domain studies of faint sources. These data can be analyzed with traditional methods, but the ability to resolve individual electrons enables a new class of more precise,
photon-counting techniques. We present a
photon-counting method for sub-electron read noise detectors which delivers optimal statistical uncertainties. We focus on Complementary Metal-Oxide-
Semiconductor (CMOS) detectors and demonstrate our method on optical data collected by CMOS instrument "proto-Lightspeed," recently commissioned at the Magellan Clay
telescope at Las Campanas Observatory. The method can be applied to non-CMOS detectors as well, such as skipper CCDs and linear-mode avalanche photodiodes. The method substantially improves analysis of faint sources, increasing signal to noise ratios by up to $\sim 130\%$, which would require 5.3$\times$ more observing time to accomplish with data alone. As an example we show detections of four normal rotation-powered
pulsars with confirmed optical pulses, achieved in under two hours of total exposure. We provide the lightspeedpy pipeline for reducing proto-Lightspeed data with both
photon counting and standard techniques.
Read the full abstract ▾
All authors Jack T. Dinsmore, Christopher Layden, Roger W. Romani, Vera L. Berger, Kevin B. Burdge, Geoffrey Mo, Deepto Chakrabarty, Emma T. Chickles, Gabor Furesz, Juliana García-Mejía, Dave Osip, Jack Piotrowski
High Energy Astrophysical Phenomena
Pair echo model of CTAO/LST-1 signal from GRB 221009A
Andrii Neronov, Ievgen Vovk, Teneman Keita et al. (+1 more)
Interactions of very-high energy gamma-rays during their propagation through the intergalactic medium result in a delayed secondary “pair echo” signal. Detection of such pair echo can be used for measurements of intergalactic
magnetic fields (IGMF) in the voids of the Large Scale Structure of the Universe. We notice that a combination of data of LHAASO and CTAO/LST-1
telescopes on the gamma-ray burst GRB 221009A is consistent with the pair echo model. The LST-1 measurement of the source signal 1.33 days after the burst can be interpreted as the pair echo produced by very-high-energy gamma-rays propagating through intergalactic medium with
magnetic field of the strength log(B/G)=-16.2+/- 0.7, if its correlation length lambda_B is larger than 20 kpc. If the field correlation length is shorter than 20 kpc, the field strength estimate is modified upwards by a square root of (20 kpc / lambda_B). In the specific case of short correlation length IGMF that is relic from cosmological phase transitions, the pair echo model of the LST-1 signal implies the field strength in the 1e-14-1e-12 G range. Such
magnetic field parameters are consistent with all known constraints on IGMF, including the lower bounds from gamma-ray observations of active galactic
nuclei.
Read the full abstract ▾
All authors Andrii Neronov, Ievgen Vovk, Teneman Keita, Davide Miceli
High Energy Astrophysical Phenomena
Can Historic Measurements cast light on the Spectral Differences found between the Pierre Auger Observatory and the Telescope Array?
Quentin Luce and Alan A. Watson
The differences between the energy spectra reported by the Pierre Auger Observatory and the
Telescope Array Collaboration are well-known. In an effort to understand these differences, we have studied the residuals of the fluxes measured in early work at AGASA, Volcano Ranch and Haverah Park with reference to the spectrum reported by the Auger Collaboration. After an empirical adjustment to the energies in the region before the ankle, where fluxes from the two hemispheres are expected to be the same, it is found that historic data are in good agreement with measurements made at the Pierre Auger Observatory above 30 EeV. Thus, the tensions between the spectra measured by the
Telescope Array and the Auger Observatory remain.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Centaurus A: Opportunities to unveil particle acceleration with the CTAO
Cainã de Oliveira and Edivaldo Moura Santos
As the nearest
radio galaxy, Centaurus A (Cen A) has been observed across multiple wavelengths and over a broad range of angular scales, providing valuable insights into the functioning of
radio galaxies. However, despite being a known source of gamma rays, the physical mechanisms responsible for these high energy emissions remain unclear. In this study, we explore the capabilities of the Cherenkov
Telescope Array Observatory (CTAO) to provide insights into the origin of the gamma-ray emission from Cen A. Using simulated observations based on the CTAO Instrument Response Functions (IRF) for the Alpha Configuration of
telescopes, we investigate both the spectral and morphological domains to assess the observatory's potential to constrain competing models of particle acceleration in the kiloparsec-scale jet and the Southern Giant Lobe. For the jet, we explore CTAO observations with t=50 and 200h for different leptonic and hadronic origin scenarios for the very-high-energy gamma-ray emission. We show that longer observation campaigns (t=200h) would probe the presence of hard spectral components extending to tens of TeV. Morphological simulations demonstrate that CTAO can resolve the extended gamma-ray emission along the jet, discriminating between point-like and Gaussian spatial models within t=50h, assuming a known background model and an optimistic zenith angle $\vartheta=$20{\deg}. Under similar hypotheses, we studied the Giant Lobes evaluating both diffuse and filamentary emission templates for the S1 region detected by Fermi-LAT. We found that CTAO-South can be sensitive to hadronic scenarios with
proton energies extending beyond 10 TeV, for the Alpha Configuration and $\vartheta=$20{\deg}. Overall, our results indicate that CTAO observations of Cen A can provide a decisive step toward unveiling the mechanisms driving the high-energy emission and particle acceleration in
radio galaxies
Read the full abstract ▾
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Cherenkov Bursts are Memory Steps
Jann Zosso, Guangzi Xu and Vitor Cardoso
We show that the familiar Cherenkov burst from a finite superluminal charge track can be understood as a pair of interfering electromagnetic
memory transitions. Endpoint accelerations of the track produce opposite
memory steps in the transverse vector potential, such that the corresponding finite-frequency radiation is universally fixed, below the endpoint-acceleration-scale, by the
memory amplitude and the time for which the temporary
memory offset persists. As the Cherenkov direction is approached, the
memory amplitudes grow while their separation in observer time shrinks, until the two vector-potential steps overlap and their divergent contributions cancel into a finite Cherenkov burst. This perspective opens the door to using the Askaryan effect as a setting in which individual macroscopic
memory transitions may be resolved, providing a new experimental arena for
memory-linked infrared physics.
Read the full abstract ▾
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Detection of knots in the supernova type Iax remnant Pa 30
Tim Cunningham, Ilaria Caiazzo, John C. Raymond et al. (+1 more)
We present deep, narrowband Gemini North/GMOS images of the Pa 30 nebula that reveal rich small-scale structure in the ejecta filaments. In [S II], the number of detected filaments increases by about an order of magnitude compared to previous studies. The imaging further reveals that the filaments are not smooth radial streaks, but instead are composed of cascades of
knots or clumps. The images in [O III] yield the first confirmation that previously detected diffuse [O III] emission in fact originates from the same [S II] filaments. We measure a nebula center consistent with the position of the central
star, indicating that the remnant has not received a large transverse kick. The 3$\sigma$ upper limit on the velocity of the stellar kick is $\lesssim$100 km/s. Cross-sectional profiles of the filaments in [S II] and [O III] show a central peak on top of a nebular background, the latter being likely due to diffuse emission or unresolved filaments. The median [S II] width of 0.7” is slightly broader than the 0.50” seeing, providing some evidence of partially resolved filaments and implying a characteristic
knot diameter of ${\sim}10^{16}$ cm. The $\approx$1” widths measured in [O III] are consistent with the poorer seeing of the oxygen images. The discovery of this clumpy substructure provides a new observational constraint on models for the origin and
evolution of the remarkable filamentary ejecta of Pa 30.
Read the full abstract ▾
All authors Tim Cunningham, Ilaria Caiazzo, John C. Raymond, Scott J. Kenyon
High Energy Astrophysical Phenomena
Continuous Gravitational Waves from Thermo-Elastic Mountains in Ultraluminous X-ray Pulsars
Hong-Bo Li, Ziming Wang, Lijing Shao et al. (+1 more)
Fast-spinning, nonaxisymmetrically deformed
neutron stars (NSs) are promising targets for continuous gravitational-wave (CGW) searches with current and next-generation ground-based detectors. Ultraluminous X-ray
pulsars (ULXPs), characterized by super-Eddington
accretion and strong
magnetic fields, provide extreme environments in which substantial nonaxisymmetric deformations may develop. In this Letter, we investigate thermo-elastic mountains generated by magnetically induced temperature asymmetries in the accreted crusts of ULXPs. We connect the crustal thermal structure to an
accretion-column model and solve the full anisotropic heat-transport equation, extending previous perturbative treatments into the nonlinear, strongly magnetized regime. We find that the weak-field approximation begins to break down near $B_{\rm ref}\sim10^{13}\,{\rm G}$, beyond which nonlinear anisotropic heat transport significantly modifies the quadrupolar thermal response. The resulting thermal asymmetries generate substantial thermo-elastic mass quadrupoles at higher field strengths. Although the currently known ULXPs are unfavorable CGW targets because of their relatively slow
spins and, in most cases, large distances, our illustrative
spin-
evolution calculations show that a NS can enter the super-Eddington accretor phase with a
spin period of order $20\,{\rm ms}$. Such rapidly rotating Galactic ULXPs could lie within the projected sensitivities of next-generation detectors such as the Einstein
Telescope and
Cosmic Explorer. These results extend thermal-mountain physics into the strongly magnetized regime relevant to ULXPs and connect super-Eddington
accretion with prospective CGW observations.
Read the full abstract ▾
All authors Hong-Bo Li, Ziming Wang, Lijing Shao, Ren-Xin Xu
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.CO
Gravitational-wave background from supermassive black holes without merger trees: Tidally regulated mergers and direct inference from the NANOGrav 15 yr data
Shin'ichiro Ando
We present a semi-analytic framework that computes the gravitational-wave background (GWB) from supermassive black hole (SMBH) binaries by direct integration of an $N$-body-recalibrated extended Press-Schechter
accretion kernel, bypassing Monte Carlo merger trees entirely. The calculation is resolution-free and fast enough to be sampled directly against
pulsar-timing data with no emulator or precomputed model bank. Between
halo accretion and black-hole binary formation, we couple the satellite's simulation-calibrated tidal mass loss continuously to Chandrasekhar dynamical friction. Satellites below a sharp, nearly
redshift-independent mass-ratio threshold, $\xi \simeq 0.04$, are stripped faster than they sink and stall: their drag collapses onto the stellar core, and 38% of accreted satellites are unmerged by $z=0$. Combining this population model with per-binary stellar-hardening turnovers and eccentric spectra, we sample the five-parameter posterior directly against the NANOGrav 15 yr Hellings-Downs-correlated free spectrum, excluding the $15.8$ nHz bin, whose excess power a subsequent chromatic-noise reanalysis attributes to
pulsar noise. The data prefer a black-hole mass normalization $+0.31^{+0.20}_{-0.23}$ dex above the locally calibrated black-hole-bulge mass relation, consistent with earlier indications that the nanohertz background is loud relative to local SMBH calibrations and robust to the delay model, merger kernel, local mass calibration, and its
redshift evolution. The spectrum is compatible with, but does not require, eccentric binaries or dense stellar environments.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Energy-independent X-Ray Polarization in 4U 1630-47 in the Intermediate State from Spectroscopy and Polarimetry
Elena Seifina, Lev Titarchuk, Paolo Soffitta et al. (+4 more)
The IXPE mission enabled measurements of X-ray polarization in accreting binaries. The dependence of the X-ray polarization degree on the binary inclination and the optical depth of the emitting medium $\tau_0$ are the new important tools in X-ray Astronomy. We analyzed the black hole X-ray binary 4U~1630–47 as an example of one of the enigmatic sources in our
Galaxy. We consider spectral and polarimetric observations of outburst episodes from 4U~1630–47 observed with the IXPE and the NICER. We carefully investigated a time interval of the IXPE observations during which 4U~1630–47 was in a single spectral state (the intermediate state) and found that the polarization degree did not change significantly during this time interval with the
photon energy in the 2–8 keV range ($P\sim$ 6%). We interpreted this energy independence behavior in $P(E)$ as a result of the Comptonization (up-scattering) of soft
photons in the flat Compton cloud. We argued that the X-ray source broadband energy spectra can be reproduced by a physical model composed of the Comptonized component and iron-line (Gaussian) component. Spectral analysis using this model shows that during the intermediate state the 4U~1630–47 spectrum was characterized by a
photon index $\Gamma\sim 2.5$ and the electron temperature $kT_e\sim ~9 ~{\rm keV}$. In fact, this approach allows one to easily find the half-optical depth $\tau_0\sim 1.8$ of the Compton cloud in 4U~1630–47 applying the inclination $69\pm1^\circ$ and using the relation $(P,\cos(i),\tau_0)$ when solving the full radiative transfer equation for a flat Compton cloud by an iterative method. This approach is also accompanied by the fact that the polarization degree is independent of the
photon energy, which we demonstrate observationally, at least for 4U~1630–47 in the 2–8 keV range.
Read the full abstract ▾
All authors Elena Seifina, Lev Titarchuk, Paolo Soffitta, Lorenzo Marra, Fiamma Capitanio, Fabio Muleri, Anastasiia Emelianova
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Coherent radio bursts, polarity reversal, and quiescent emission from the M4V dwarf WW PsA
Jackson Mitchell-Bolton, Laura Driessen, Tara Murphy et al. (+6 more)
Coherent
radio emission from magnetically active M dwarfs is largely observed in two varieties:
stochastic solar-like bursts and beamed, rotationally modulated emission including auroral pulses. Detailed monitoring of these
stars is critical for probing the
plasmas and
magnetic fields driving the emission. We conducted a search for polarised
radio emission from
stars within 85 pc, covering $2.2\times10^4$ h of stellar dynamic spectra from the ASKAP Deep Investigation of Neutral Gas Origins (DINGO) survey. We report the discovery of coherent
radio bursts from the M4V dwarf WW PsA. In addition to quiescent emission, we detect three long-duration ($\gtrsim$30 min) bursts, each ~100% circularly polarised, in 283.3 h of data. We also report a fourth burst in an epoch not covered by our search, detected using the VASTER pipeline. One of the bursts features a polarity reversal midway through, based on which we favour the electron cyclotron maser (ECM) mechanism over
plasma emission. We tentatively propose the bursts are due to rotationally modulated ECM pulses of variable intensity. We infer the required physical properties of WW PsA, including a high obliquity $\beta = 74^{+6}_{-22}$ deg under an oblique rotator model.
Read the full abstract ▾
All authors Jackson Mitchell-Bolton, Laura Driessen, Tara Murphy, Joshua Pritchard, Barnali Das, Richard Dodson, Martin Meyer, Jonghwan Rhee, Yuanming Wang
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Gravitational-wave Echoes Beyond the Hubble Time from Quantum Black Holes
Che-Yu Chen, Naritaka Oshita and Yuki Yokokura
We investigate gravitational-wave echoes in a horizonless compact object model, a non-perturbative solution of the semi-classical Einstein equation that reproduces the
entropy-area law from the bulk structure. By employing a model of anisotropic fluids in classical general relativity (GR), we show that odd-parity gravitational waves are not reflected at the object's surface but are trapped inside due to the exponentially strong
redshift, and that the echo-delay time extremely exceeds the age of the Universe. Consequently, the echo signals are effectively unobservable, which is consistent with current null results from echo searches. We finally discuss how this
quantum black hole and the conventional classical black hole could be distinguished observationally.
Read the full abstract ▾
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
From the Milky Way to the Early Universe: How Metallicity Shapes the Formation of Double Neutron Stars
Abhishek Chattaraj, Jeff J. Andrews, Monica Gallegos-Garcia et al. (+9 more)
Among the compact binaries detected through gravitational wave (GW) emission, double
neutron stars (DNSs) hold the unique distinction of having well-characterized local analogs in the Milky Way. However, understanding their broader cosmological population remains challenging due to the complex
metallicity-dependent
evolution of their progenitors. Using the detailed binary population synthesis code POSYDON, we model DNS formation across a cosmological range of
metallicities. We find that while DNSs are predominantly formed through common envelope
evolution,
metallicity-dependent radial expansion and stellar wind mass loss bifurcates the pathway into distinct subchannels, producing systematically distinct merging populations at different
metallicities. Notably, our best representative Galactic models predict local merger rates in broad agreement with the latest GWTC-5 constraints, suggesting that the populations observed via
radio pulsar surveys and through GW emission need not be in tension. Contrary to previous studies, we demonstrate that the intrinsic merger efficiency increases toward low
metallicities, a trend robust across varying binary
evolution assumptions, although the magnitude and the underlying stellar processes driving this enhancement vary across
metallicity regimes. When convolved with the
cosmic star formation history, our models reveal that the majority of merging DNSs originate from progenitors in the range $\sim 0.1\,Z_\odot - Z_\odot$, with significant supersolar contributions. Furthermore, we show that weaker stellar winds at low
metallicities produce DNS mergers with systematically more symmetric mass ratios ($q \gtrsim0.9$). Additionally, we assess detectability within proposed configurations for third-generation GW observatories. Our study provides a framework for interpreting the cosmological DNS population in the upcoming multi-messenger era.
Read the full abstract ▾
All authors Abhishek Chattaraj, Jeff J. Andrews, Monica Gallegos-Garcia, Max M. Briel, Michael Zevin, Tassos Fragos, Emmanouil Zapartas, David R. Aguilera-Dena, Seth Gossage, Anarya Ray, Philipp M. Srivastava, Zepei Xing
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Unravelling the Nature of AT 2025abao: From Precursor to Final Fate
Zhuo Chen, Yingzhen Cui, Tianshu Wu et al. (+9 more)
Luminous red novae (LRNe) are potential signatures of common envelope
evolution (CEE), a critical yet poorly understood phase in compact binary formation. AT 2025abao, an LRN in the Andromeda
galaxy, originated from an asymptotic giant branch (AGB) progenitor and exhibited a prolonged pre-outburst transient. Lacking direct constraints on the companion, however, the system's evolutionary fate remains unclear. Here, we unravel the binary nature of AT 2025abao by modeling its complete
evolution, from precursor to final outcome. We show that the eight-year infrared precursor arises from a $\approx1.4^{+0.2}_{-0.3}\,M_{\odot}$ main-sequence companion inspiralling through the wind of a $\approx 6.9\,M_{\odot}$ AGB
star. As CEE commences, the companion plunges into the envelope and launches a shock. Radiation hydrodynamic modeling of this outburst constrains the total ejecta mass to $\approx 0.92\,M_{\odot}$ and energy to $\approx 1.25\times 10^{47}\,$erg, revealing that only $\approx 0.57\,M_{\odot}$ becomes unbound. Subsequent radiative transfer simulations successfully reproduce the evolving spectral energy distribution. Crucially, our models indicate the main-sequence companion and AGB core survive in an eccentric orbit without merging at least 400 days after CEE onset. AT 2025abao may therefore be the first observed CEE event caught forming a close compact binary, bridging a long-standing observational gap in compact binary formation.
Read the full abstract ▾
All authors Zhuo Chen, Yingzhen Cui, Tianshu Wu, Yongzhi Cai, Hongwei Ge, Andrea Reguitti, Minxuan Cai, Lulu Fan, Ji-An Jiang, Tinggui Wang, Zelin Xu, Jie Lin
High Energy Astrophysical Phenomena
A Physically Motivated Compact Parameterization of Neutron Star Atmosphere Emission for Thermal X-ray Pulse-Profile Modeling
Tong Zhao and Renxin Xu
Thermal X-ray pulse-profile modeling depends on the angular and spectral properties of
neutron star atmosphere emission. We construct a compact empirical approximation to the specific intensity using eight coefficients for the angular dependence and five for a normalized spectral kernel. The angular prescription is motivated by the formal solution of the radiative-transfer equation, while the spectral normalization preserves a specified bolometric flux. We calibrate this family to numerical atmosphere tables, focusing on return-current-heated and fully ionized hydrogen atmospheres. When incorporated into a semi-analytic pulse-profile model, the approximation reproduces profiles normalized by their phase-averaged flux to within approximately $4\%$ for antipodal hot spots and $5\%$ for non-antipodal hot spots in the tested heated-atmosphere configurations. We also analyze synthetic eXTP observations using different beaming prescriptions to test the conclusion in our previous work based on a linear description of the angular dependence of the emission. The comparisons suggest that the angular dependence of the intensity cannot be simply characterized by a linear function of the cosine value of the emission angle, because its detailed shape and energy dependence will affect the parameter inference. This parameterization can significantly increase the efficiency for analytic and numerical models, and provide a compact framework for examining how atmosphere assumptions affect
neutron star pulse profiles and the inferred stellar properties.
Read the full abstract ▾