High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
The ionizing properties of JWST's compact broad-line emitters
Sara Mascia, Jorryt Matthee, Alberto Torralba et al. (+4 more)
The recent JWST discovery of a numerous population of broad-line emitters (BLEs) at $z>4$ has reopened the question of whether sources other than faint
galaxies contributed significantly to
cosmic reionization. To assess this contribution, we present a systematic census of compact, blue broad-line emitters at $4\leq z\leq7$ selected from the DJA, designed to isolate sources in which the UV continuum and the broad-line emission originate from the same compact physical region. Starting from a parent sample of 4145
galaxies with NIRSpec/PRISM spectroscopy and NIRCam imaging, we apply criteria on broad Ha emission (FWHM$>2000$km s-1, detected at S/N$\geq5$, complete at $L_{Ha,broad}\geq10^{42.7}$erg s-1), blue continuum slopes ($\beta_{UV}\leq-1.5$, $\beta_{opt}<0.5$), and morphological compactness in both the rest-frame UV and optical, returning a final sample of 20 sources. This constitutes $\sim20%$ of the PRISM-selected broad-line sample, which is dominated by Little Red Dots (LRDs). We find that the compact blue BLEs display hot ionizing continua, high-ionization UV lines (CIV, NIV], HeII), and elevated Lya emitter fractions ($X_{Lya}=50-67%$) relative to
star-forming
galaxies and LRDs. Beyond their similar lack of X-ray emission, their optical spectra closely resemble those of LRDs. This suggests that compact blue BLEs extend this population towards lower column density envelopes, but with similar engines, rather than representing a physically distinct population. Using Sirocco to model physical configurations that reproduce the observed spectra, we find a high ionizing
photon production efficiency (log$\xi_{ion}\sim25.4$Hz erg-1) and a weighted average escape fraction $fesc\sim0.2$ for the bluest sources, and $\sim0.01$ for LRDs. This implies that broad-line sources do not dominate reionization globally, but given their luminosity, their contribution can dominate up to few Mpc scales.
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All authors Sara Mascia, Jorryt Matthee, Alberto Torralba, Jenny E. Greene, Anna-Christina Eilers, Edoardo Iani, Rohan P. Naidu
High Energy Astrophysical Phenomena
The GPSP Atlas: High-resolution Galactic Photon Survival Probability Atlas for Very-High- and Ultra-High-Energy Gamma-Ray Astronomy
Ekrem Oğuzhan Angüner
The emergence of Galactic PeV astronomy makes
photon–
photon ($\gamma\gamma$) absorption an increasingly important component of gamma-ray data analysis. In this work, the Galactic
Photon Survival Probability (GPSP) atlas is presented as the first Galactic framework describing gamma-ray survival probabilities over the full parameter space $P(l,b,d,E_\gamma)$ between 1 TeV and 10 PeV. The atlas is constructed using two independent GALPROP-based interstellar radiation field (ISRF) models, allowing direct assessment of ISRF-related systematics, and is released in a FITS format compatible with standard analysis frameworks. A novel gamma-ray survival phase space representation is introduced, extending 1D survival profiles into a 2D energy–distance framework that visualizes Galactic transparency and gamma-ray horizons. Using the full atlas, Galactic transparency and Galactic plane survival maps are constructed. These reveal that Galactic opacity is highly structured, with enhanced attenuation along spiral-arm tangent directions in the $\sim$100–300 TeV regime, while attenuation becomes nearly isotropic and
cosmic microwave background (CMB) dominated near PeV energies. The framework naturally accommodates attenuation calculations for extended and diffuse sources. The atlas is further extended to subluminal Lorentz invariance violation (LIV) scenarios through the GPSP-LIV atlas, incorporating LIV-modified pair production kinematics and cross sections. Sources emitting in the 2–3 PeV regime beyond gamma-ray horizons are identified as promising targets for probing LIV effects. Finally, practical applications are presented for the Galactic Center PeVatron and the Cygnus X-3 regions. The GPSP and GPSP-LIV atlases establish a publicly available foundation for studies of Galactic PeVatrons, diffuse gamma-ray emission, and fundamental physics searches in the emerging era of Galactic PeV astronomy.
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High Energy Astrophysical Phenomena
Thermal Stability of Radiation-Pressure-Dominated Accretion Disks Threaded by Net Vertical Magnetic Flux
Shahram Abbassi, Armin Memarian and Samik Mitra
The classical radiation-pressure instability predicts strong thermal variability in luminous black-hole
accretion disks, whereas most disk-dominated X-ray binary soft states remain comparatively stable. We examine whether net vertical
magnetic flux can weaken this instability through its contribution to the radial stress. The stability depends not only on the
equilibrium magnetic stress but also on how that stress changes during a thermal perturbation. We write the local stability condition in terms of the logarithmic heating response, $q_+<q_{+,\rm crit}$, which avoids specifying how the turbulent stress is divided into reference and net-flux components. For the illustrative closure $\delta=\zeta\sqrt{\bpol\btor}/\alpha$, $\etad=-d\ln\delta/d\ln H$ describes the response of the fractional stress correction, while $\Gnf=d\ln W_{\rm nf}/d\ln H$ describes the response of the additional net-flux stress itself. For an
accretion disk around a $10M_\odot$ black hole at $R=20\rg$ and $\Mdot=0.5\MEdd$, we adopt fixed local mass flux on the thermal timescale, $(\gamma,\gp)=(1,0)$, and $d\ln\zeta/d\ln H=0$. Marginal stability then occurs at $\bpol^{\rm crit}=0.0176$ for $\zeta=1$ and $0.1338$ for $\zeta=0.25$. These thresholds depend on the adopted stress closure and field-response prescription and should not be interpreted as universal
magnetic-pressure fractions. Fixed-$B_z$
equilibrium sequences, using a separate relation for the variation of $B_\varphi$ between steady states, show that increasing vertical field narrows the thermally unstable
accretion-rate interval but does not eliminate it for either $H/R<0.1$ or $H/R<0.2$. The relevant quantity for stabilization is therefore the thermal response of the stress associated with net vertical flux rather than the vertical
magnetic-pressure fraction alone.
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High Energy Astrophysical Phenomena
Measurement of spin-orbit misalignment in binary black holes via the total spin
Charles F. A. Gibson, Isha Anantpurkar and Javier Roulet
The degree of
spin-orbit
alignment in merging binary black holes is a powerful probe of their formation history. However, assessing
spin-orbit misalignment in individual events remains challenging, as most parameters commonly used to characterize precession tend to be poorly constrained. In this work, we introduce the angle between the total
spin and orbital angular momentum, $\theta_{LS}$, as an alternative measure of
spin-orbit misalignment. Using synthetic observations, we show that $\theta_{LS}$ retains more information to discriminate between the aligned- and isotropic-
spins hypotheses than commonly used alternatives, including $\chi_{\rm p}$. We then study this parameter on binary black hole mergers observed in the GWTC-5.0 catalog, and identify multiple events that are inconsistent with having aligned
spins. In several of the examples, this is not apparent from the posteriors of the effective
spin parameters ($\chi_{\rm p}$ or $\chi_\mathrm{eff}$) nor the individual
spin-orbit tilts ($\theta_1$ or $\theta_2$) alone, and thus had not been previously identified. We highlight GW241127_061008 as a compelling case for a second-generation merger, with a large, tilted primary
spin, unequal masses, and a large primary mass near the pair-instability-
supernova mass gap. Finally, we perform population inference using $\cos\theta_{LS}$ and confirm that the binary black hole population is inconsistent with either a purely isotropic or a purely aligned-
spin distribution, and requires substantial
spin-orbit misalignment.
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High Energy Astrophysical Phenomena
Supernova 1987A was a "failed supernova" twenty thousand years before its jet-driven explosion
Noam Soker
I show that the progenitor of
supernova (SN) 1987A faded substantially and became red for hundreds of years to observers in and near the plane of the equatorial ring, because the equatorial ring, which was formed by a binary interaction between the SN 1987A progenitor and a main-sequence companion that ejected material about 20,000 years before the explosion, obscured the progenitor. For a few hundred years, the luminosity for such hypothetical observers was mainly light scattered by the two outer rings, which amounted to ~5% of the progenitor luminosity. In present terms, this event would have been classified as a "failed
supernova" by these observers, although there was no core collapse, no black hole formation, and nothing failed. Rather, this event was a type II ILOT (intermediate-luminosity optical transient), in which equatorial ejecta temporarily obscured the central source. After a few hundred years, the outer rings became transparent, the inner ring became more transparent, and the SN 1987A progenitor brightened over a few thousand years to its normal luminosity for equatorial observers. This finding strengthens the claim that "failed
supernova" candidates are likely to be type II ILOTs. Although the binary interaction also spun up the core, the bipolar morphology of SN 1987A (its Keyhole) is misaligned with the triple-ring system. I use the jittering jets explosion mechanism (JJEM) to speculate on a scenario that might explain this misalignment. This study adds small but unique support to the claim that the JJEM is the primary explosion mechanism of CCSNe.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Dynamical Friction as Environmental Gravitational Self-Force
Sayak Datta
Dynamical friction (DF) and gravitational-wave radiation reaction are conventionally treated as distinct dissipative mechanisms acting on a compact object inspiraling through a matter environment. We show that DF is not an additional force but a term at order $q^2\epsilon$ in a covariant multiparameter expansion of the MiSaTaQuWa force equation that vanishes identically in the absence of a particle-induced perturbation of the environment's matter fields, where $q$ and $\epsilon$ are respectively the mass ratio and environmental parameter. As a test of this identification, we evaluate it in weak and adiabatic field limit, solving the polar density-perturbation equation sourced by the particle's own order-$q$
vacuum metric perturbation. The reduction reproduces the Chandrasekhar-Ostriker drag force and predicts two features in strong
gravity. An $\ell$-dependent splitting of the wake that only recombines into the Ostriker source in the weak-field limit, and a purely relativistic axial contribution with no Newtonian counterpart. This establishes dynamical friction as an intrinsic piece of self-force theory, extending to strong field, generic orbits, and generic environments, with direct consequences for extreme-mass-ratio inspiral waveform modeling for LISA.
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High Energy Astrophysical Phenomena
Quantum-Gravity-Inspired Effects in Neutron Stars: A Critical Map from Microscopic Assumptions to Observables
Randall Hell Vargas Pradinett
Claims that
neutron stars constrain
quantum gravity often compare models whose new physics enters at different stages of the stellar calculation. This article provides a critical map of three representative routes: generalized-uncertainty-principle deformations of microscopic thermodynamics, noncommutative-inspired modifications of the effective matter source, and higher-
curvature or scale-dependent modifications of gravitational dynamics. For each route we identify the quantity that is changed, the dimensionless parameter controlling the correction, and the consistency conditions required before masses, radii, or tidal deformabilities can be compared with observations. A deformed phase-space measure must be implemented in a thermodynamically consistent interacting equation of state; a smeared density must be completed by a conserved stress-energy tensor, generally with anisotropic pressure; and a gravitational effective field theory must remain within its derivative expansion and be applied consistently to both the
equilibrium background and tidal perturbations. Simple scale estimates show that coefficients of natural size suppressed by the Planck scale are negligible in
neutron stars. Observable effects consequently constrain model-dependent effective scales or enhanced couplings, not microscopic
quantum gravity directly. The resulting framework is intended to separate robust phenomenological bounds from effects produced by inconsistent implementations or by degeneracies with the high-density equation of state.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Global uniqueness of Kerr black hole spin and inclination from a segment of the critical curve
Kenta Hioki
High-resolution observations are expected to probe the
photon-ring structure of black hole images. The critical curve is the geometrically defined limiting locus on the observer's screen toward which successive higher-order
photon subrings accumulate. For a Kerr black hole, the shape of this limiting curve depends on the dimensionless
spin parameter $a$ and the inclination angle $i$. We investigate whether these parameters can be determined uniquely from a connected positive-length segment of the critical curve when the segment's position and orientation on the screen are unknown. For rotating non-extremal Kerr black holes with $0<a<1$ and $0<i\leq\pi/2$, we prove global uniqueness: if two such segments coincide as point sets after orientation-preserving rigid motions of the screen, then their Kerr parameter pairs coincide and the two rigid motions are identical. The proof uses an irreducible implicit
polynomial to show that a segment determines the full algebraic curve containing it and then recovers the parameter pair $(a,i)$ from rigid-motion invariants of that
polynomial.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
The Interplay of Magnetic Fields, Turbulence and Vorticity in Core-Collapse Supernovae
David Calvert, Michael Redle, Bibek Gautam et al. (+4 more)
The convective turbulent motion of the fluid below the shock in a core-collapse
supernova stretches and amplifies the
magnetic field of the progenitor
star. The energy contained in the field is sourced from the work done by the fluid on the field which comes at the expense of the fluid's kinetic and internal energy. In addition to the energy exchange with the fluid, the
magnetic field also has a back-reaction upon the fluid via a contribution to the baroclinic vector and thus affects the fluid vorticity. In this paper we explore the interaction of the
magnetic field with the fluid in core-collapse
supernovae using the ELEPHANT code with solar-
metallicity stars of 15 and 20 \msun zero-age main sequence mass and purely toroidal initial
magnetic fields of $B_0 = 0, 10^{10}, and 10^{12}$~G. We find that the
magnetic field in the gain region does not become so large that it alters the global dynamics above the 10% level in the early post-bounce
evolution. The turbulent kinetic energy of the fluid in the gain region is smaller in simulations with a strong initial
magnetic field, but the exact amount of reduction is uncertain due to limitations of the methods for measuring turbulent kinetic energy. The structure of the field in the simulations quickly becomes a tangled mass of flux ropes as soon as convection begins, which leads to a large
magnetic field contribution to the baroclinic vector that dominates over the hydrodynamic contribution. Although governed by very similar transport equations to the
magnetic field, the fluid vorticity and
magnetic field are always close to being randomly aligned at every stage of the
evolution. The enstrophy, which is seen to be closely associated with the turbulent kinetic energy, is found to be reduced in simulations with a strong initial
magnetic field supporting the inference that the
magnetic field reduces the amount of
turbulence in the fluid.
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All authors David Calvert, Michael Redle, Bibek Gautam, Carles J. Stapleford, Carla Frohlich, James P. Kneller, Matthias Liebendoerfer
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
The Bondi Dipole in Full Numerical Relativity: a Self-Accelerating Positive-Negative Mass Binary
Nikita M. Shirokov
Bondi showed in 1957 that bodies of opposite active gravitational mass self-accelerate: the negative chases the positive it repels, and the pair runs off together. We evolve this "Bondi dipole" in $3+1$ numerical relativity: two complex scalars share identical Klein-Gordon dynamics; only the phantom enters Einstein's equations with a minus sign – inertial and passive masses positive, active mass negative. Across a
matrix of thirty-four evolutions – runaway pairs, controls, and parameter scans – a mass-matched pair released at rest accelerates as a unit. The midpoint moves $3.00\pm0.01$ by $t=200$ with the separation held to 1%, and reaches a speed of $0.056c$ by $t=400$ with the acceleration steady to 2%; the total signed momentum holds at zero to $\lesssim 1$%. The force is
gravity on both of its axes: $a\propto d^{-2.03\pm0.01}$ over $d=8$ to $20$, $a\propto M^{0.97\pm0.06}$ over a factor $2.5$ in mass, and $a\,d^2/\bar{M}=1$ within 2.4% on the equal-mass ladder. Swapping the sectors inverts the acceleration to two parts in $10^5$; gauge, solver-depth and mesh variations move the drift by $\lesssim 0.01$% and box doubling by 4%; same-sign control pairs hold their centroids to $\lesssim 8\times10^{-4}$ even while merging. The runaway carries no detectable gravitational radiation: the signed dipole cannot radiate, the quadrupole's $\ddot{Q}$ is constant, and the measured $\ell=2$ amplitude falls as $r^{-4.8}$ – near zone, not flux. The phantom
star is, to our knowledge, the first asymptotically flat body of negative ADM mass evolved in numerical relativity; alone it survives to $t=1000$, slowly relaxing outward.
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High Energy Astrophysical Phenomena
A Broadband X-ray Analysis and Optical Counterpart Search of IC5052 ULX
Nabil Brice, Dominic J. Walton, Felix Fürst et al. (+10 more)
We present broadband X-ray spectral and timing analysis of the Ultra-luminous X-ray source (ULX) in IC5052 using simultaneous XMM-Newton and NuSTAR observations from 2022, supplemented by archival 2013 XMM-Newton data. A two-thermal component model, often interpreted as radially-segregated emission from a super-Eddington inner disc and its associated wind, provides a statistically acceptable fit but yields an implausibly high inner disc temperature of $k T_\mathrm{in} \approx 6.4$ keV, inconsistent with even super-Eddington disc models. Including an additional continuum component from either an
accretion column or a Comptonizing corona, as motivated by high S/N observations from other ULXs, provides comparable goodness of fit while allowing plausible inner disc temperatures. The
accretion column model yields $k T_\mathrm{in} \approx 1.2$ keV with the column contributing $F_\mathrm{col} \approx 62\%$ of total flux, while the Comptonizing corona model yields $k T_\mathrm{in} \approx 3.0$ keV with a scattered fraction $\sim 1$, assuming the hotter disc provides the seed
photons. Timing analysis initially challenges both scenarios: the
accretion column model places IC5052 ULX where prior results suggest pulsations may be detectable ($F_\mathrm{col} \sim 62\%$), yet none were detected, while the corona model appears inconsistent with its lack of observed short-timescale variability. However, incorporating spectral information relaxes these constraints, allowing both models to remain physically plausible for IC5052 ULX. Finally, using improved Chandra astrometry, we identified a candidate optical counterpart consistent with an evolved high mass donor. A discrepancy between the optical extinction and X-ray fitted absorption suggests localised X-ray absorption.
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All authors Nabil Brice, Dominic J. Walton, Felix Fürst, Daniel Stern, Amy H. Knight, Matteo Bachetti, Matthew J. Middleton, Alistair Pagan, Tim P. Roberts, Murray Brightman, Hannah P. Earnshaw, Fiona A. Harrison, Sean N. Pike
High Energy Astrophysical Phenomena
Assessing the Credibility of Gamma-Ray QPO Candidates in 41 TeV-Selected Blazars
Wen-Xin Yang, Yi Liu, Hong-Guang Wang et al. (+2 more)
We analyze quasi-periodic oscillation (QPO) candidates in the 0.1-100 GeV Fermi-LAT light curves of 41 TeV blazars with a conservative, multi-stage timing analysis combining FFT power spectra, red-noise Monte Carlo simulations, false-discovery-rate control, bootstrap period uncertainties, split-sample cross-validation, Lomb-Scargle and WWZ diagnostics, a detection-only sensitivity test, observingwindow checks, and injection-recovery experiments. A first-pass FFT search flags 16 sources above a raw 95% level and six strong candidates after data-quality and split-sample filtering, none satisfying a fully automated multi-method tier. Source-level significance is quantified with forward simulations that preserve the observed sampling and non-Gaussian flux distribution, treating the red-noise slope as a nuisance parameter and never assuming independence of periodogram powers. At simulation-selected reference slopes, only two of the 41 sources reach a raw source-level p < 0.05,only J1555.7+1111 reaches Benjamini-Hochberg significance, and none survives Benjamini-Yekutieli correction. No source survives the conservative slope envelope. Even J1555.7+1111, which the first-pass search flagged as significant but did not rank among its strong candidates, has a global p-value that rises to 7.5*10^-3 under the least favorable slope (~ 0.31 after the full-sample search), so it is not a robust detection. With substantial period uncertainties, a weak observing window, and limited injection-recovery sensitivity, we establish no robust gamma-ray QPO detection: a sampling-faithful red-noise treatment substantially contracts the candidate set, providing an explicit assessment of QPO credibility.
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All authors Wen-Xin Yang, Yi Liu, Hong-Guang Wang, Denis Bastieri, Jun-Hui Fan
High Energy Astrophysical Phenomena · Cross-listed from nucl-ex
Cluster emission and its impact on the r-process nucleosynthesis
Natalia Thomas, Silvia Bara, Thomas Elias Cocolios et al. (+20 more)
Cluster emission is an exotic decay mode between alpha-decay and fission, in which a parent
nucleus emits a cluster of nucleons heavier than an alpha-particle, but lighter than what is usually considered a fission fragment. The properties of cluster emission were investigated by analyzing five high-energy events detected in a spectrum of a mass A = 230 beam produced at ISOLDE (CERN). Under the assumption that these events were caused by cluster emission, the most likely parent-cluster pair responsible for the five high-energy events, was found to be $^{230}Ra$ emitting $^{22}O$, with a branching ratio of $(4.3$ +\- $1.9) \times 10^{-9}$. Four analytical formulas were used to estimate the partial half-lives of cluster emission for a group of
neutron-rich
nuclei. The decay rate was calculated for a selection of cluster
nuclei for each parent isotope. The rates of all decay channels of cluster emission per parent
nucleus were then included in calculations of the r-process nucleosynthesis in a
neutron star merger in order to study the possible impact of cluster emission on the r-process nuclear production. The resulting isotopic abundance distributions were compared to those calculated for a case in which cluster emission was not considered. It was found that the inclusion of cluster emission decay rates from the simple analytical formulas available nowadays does not influence the results of the r-process nucleosynthesis.
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All authors Natalia Thomas, Silvia Bara, Thomas Elias Cocolios, Stephane Goriely, Boris Andel, Andrei N. Andreyev, Alberto Camaiani, James G. Cubiss, Hilde De Witte, Zoe Favier, Michael Heines, Fedor Ivandikov, Jake D. Johnson, Jozef Klimo, Razvan Lica, Jozef Mišt, Chris Page, Riccardo Raabe, Adam Sitarčík, Viktor Van Den Bergh, Piet Van Duppen, Zixuan Yue, Ahmed Youssef
High Energy Astrophysical Phenomena
Probing the Three-Dimensional Structure of a Jet with Faraday Tomography
Sawera Gull, Masaya Kurogi and Keitaro Takahashi
Magnetic fields play a fundamental role in the dynamics and radiation of jets associated with active galactic
nuclei (AGNs), where they accelerate and collimate the relativistic
plasma and produce the observed synchrotron emission. Faraday
tomography is a powerful technique for probing the three-dimensional distribution of
magnetic fields and synchrotron-emitting
plasma along the line of sight, by reconstructing the Faraday Dispersion Function (FDF) from the observed polarization spectrum. To explore what aspects of AGN-jet structure can be revealed by Faraday
tomography, we construct a simple three-dimensional model of an AGN jet that captures its essential features, and compute the resulting FDF for a range of model parameters. The jet is represented as a cylindrical region of uniform thermal-electron density threaded by a coherent helical
magnetic field, to which a random turbulent component can optionally be added. The parameters varied include the inclination angle {\theta} between the jet axis and the line of sight, the wavenumber of the helical field, and the amplitude of the random
magnetic-field component. By systematically varying these parameters, we examine how the underlying
magnetic geometry and
turbulence are encoded in the observable Faraday and polarization structures. The main observational signatures identified by our model include top-bottom asymmetry across the jet, curved or double peaked FDF profiles and increasingly fragmented Faraday depth structure along longer lines of sight, providing potential diagnostics of large scale helical
magnetic fields and small scale turbulent components. These signatures providing a physical framework for interpreting future polarimetric observations of AGN jets from instruments such as LOFAR, MeerKAT, and the VLA.
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High Energy Astrophysical Phenomena
Fingerprints of thermal Comptonization in accreting neutron stars. Plasma-vacuum interplay in cyclotron lines and polarisation
E. Sokolova-Lapa, D. K. Maniadakis, J. J. R. Stierhof et al. (+11 more)
X-ray emission from accreting, strongly magnetised
neutron stars and its pulse-phase variability probe their
magnetic-field geometry,
spin orientation, and emission processes. Whether the radiation emerges mainly from a hot spot or column, and whether its properties are shaped by bulk or thermal Comptonization, remain debated across luminosity regimes. We aim to disentangle intrinsic emission from visibility effects and identify observables characteristic of thermal Comptonization in hot spots and columns. We therefore derived energy-dependent beam patterns and observable signatures without assigning the model to a luminosity regime, focusing on cyclotron-resonance and polarisation effects as tracers of anisotropy. To do so, we computed angle-dependent polarised broadband spectra, including the fundamental cyclotron line, for a homogeneous, self-emitting, magnetised Comptonizing
plasma over a broad parameter range. Accounting for light bending and projection, we obtained phase-dependent fluxes for different geometries and, for hot spots, observed linear polarisation. The beam patterns evolve with energy, driving pulse-profile changes. Near the cyclotron resonance,
plasma-
vacuum interplay produces a narrow central beam and side petals. Their visibility creates geometry-dependent dips, bumps, and M- and W-shaped structures in hot-spot pulsed fraction spectra, but only dips and bumps for columns. Thermally Comptonized cyclotron lines do not reliably trace
plasma temperature;
plasma-induced ellipticity and band averaging reduce observed soft-X-ray linear polarisation to 0-30%. Under typical X-ray
pulsar accretion-channel conditions, thermal Comptonization leaves robust energy-dependent anisotropic signatures. Energy-resolved pulse profiles, pulsed fraction spectra, and polarisation thus provide complementary diagnostics of
neutron star geometry, emission-region shape, and spectral formation.
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All authors E. Sokolova-Lapa, D. K. Maniadakis, J. J. R. Stierhof, E. Ambrosi, A. D'Aì, C. Ferrigno, N. Schettino, M. Middleton, A. Gúrpide, V. Grinberg, G. Lipunova, I. El Mellah, P. Kretschmar, J. Wilms
High Energy Astrophysical Phenomena
The First X-Ray Polarimetry of the Typical Accretion Disk Corona Source 4U 1822-37
WanYun Wu, Fei Xie and YuShan Ling
We report the first Imaging X-ray Polarimetry Explorer (IXPE) observations of the typical
accretion disk corona (ADC) source 4U 1822-37, covering 44 orbital cycles, together with simultaneous Swift-XRT data. The polarization degree (PD) of this source is found to be higher than typical low-mass X-ray binary (LMXB) values and exhibits a significant energy dependence. Within the 2–5~keV and 5–8~keV bands, PD remains constant, with average values of \(5.6\pm0.8\%\) and \(11.6\pm1.7\%\), respectively, and the difference is significant (\(>3\sigma\)). Orbital phase-resolved analysis reveals that during the companion eclipse, the PD in the 2–5~keV band drops from a significantly non-zero value to a level consistent with zero, while the polarization angle (PA) remains unchanged. In contrast, the PD in the 5–8~keV band shows a marginal rising trend, reaching \(21.3\pm6.1\%\), and the PA exhibits a periodic rotation of \(30^\circ\) before the eclipse. In addition, the PA rotates by \(40^\circ\) with increasing neutral absorption on a three-day timescale. These results suggest that the soft and hard emission in the 2–8~keV band may originate from regions with different spatial distributions, with the high PD implying a scattering contribution. The PA rotation is likely linked to scattering geometry asymmetries caused by a bulge or clumps.
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High Energy Astrophysical Phenomena
Molecular and Atomic Gas Associated with the Gamma Ray Supernova Remnant RCW 103
H. Inoue, Y. Asano, R. G. Bhuvana et al. (+15 more)
We present a study of the interstellar molecular and atomic gas associated with the gamma-ray
supernova remnant (SNR) RCW 103 using the Mopra $^{12}$CO($J$ = 1-0), Atacama Large Millimeter/submillimeter Array $^{13}$CO($J$ = 1-0), and the Australia
Telescope Compact Array & Parkes HI data. We find that CO clouds in the velocity range from $-58.7$ to $-43.5$ km s$^{-1}$ show a clear spatial correspondence with the X-ray shell of RCW 103, particularly extending from the northwestern to the southeastern regions. The position-velocity diagram of the CO emission reveals an expanding gas motion with an expansion velocity of $\Delta V \sim$$7.5$ km s$^{-1}$, which may have been produced by shock waves and/or stellar winds from the progenitor system. We estimate the total
cosmic-ray
proton energy to be $\sim$$3.0^{+1.1}_{-0.6} \times 10^{47}$ erg, adopting a total interstellar
proton density of $\sim$$810$ cm$^{-3}$. This value is more than an order of magnitude lower than those inferred for other gamma-ray emitting SNRs of comparable age. Given that a substantial amount of dense gas remains within the interior of RCW 103, where thermal X-ray emission is dominant, our results possibly suggest that a significant fraction of the shock energy may have been converted into thermal energy via gas heating, thereby reducing the efficiency of
cosmic-ray acceleration.
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All authors H. Inoue, Y. Asano, R. G. Bhuvana, R. Z. Alsaberi, R. Yamada, K. Tsuge, T. Murase, Y. Fukui, E. M. Reynoso, K. Tachihara, N. Izumi, M. Yamagishi, K. Furuya, N. Harada, K. Tokuda, G. Rowell, M. D. Filipović, H. Sano
High Energy Astrophysical Phenomena
X-ray Polarization of Inverse Compton Scattering by Thermal and Nonthermal Electrons
Boting Wang, Jirong Mao, Jieying Liu et al. (+1 more)
X-ray emission from
accretion-powered astrophysical systems is widely interpreted as inverse Compton (IC) scattering between energetic electrons and soft
photons. Besides the emitted intensity, the polarization of this radiation provides important information about the physical properties of the electrons involved. We investigate how different electron populations shape both the spectrum and polarization of IC emission in the X-ray band. We consider three electron populations: purely thermal, purely nonthermal power-law, and a hybrid population combining both components. We take both numerical simulations and semi-analytic calculations. We first attempt the cases for thermal and nonthermal electrons, respectively. We then focus on the hybrid population, which is expected to be realistic in high-energy object environments. For the case of hybrid electrons, the scattered emission separates into three energy regimes. At low energies ($\lesssim 0.1$ keV), it is dominated by thermal electrons; at high energies ($\gtrsim 4$ keV), it is governed by the nonthermal component. Between these limits, a transition band ($\sim 0.1$-$4$ keV) appears in which both components contribute. The degree of polarization varies smoothly across these regimes, and the behavior in the transition band directly traces the relative importance of thermal and nonthermal electrons. We further show that for partially polarized seed
photons, the scattered polarization scales linearly with the incident polarization while its frequency dependence remains unchanged. These results show that X-ray polarimetry provides a powerful diagnostic of the electron energy distribution in
accretion-powered systems.
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All authors Boting Wang, Jirong Mao, Jieying Liu, Fei Xie
High Energy Astrophysical Phenomena
Observations of ionized carbon towards the $\gamma$-ray-bright supernova remnant RX J1713.7-3946
A.R. Thakur, G.P. Rowell, R. Higgins et al. (+7 more)
The origin of Galactic
Cosmic Rays (CRs), particularly at sub-GeV energies, remains uncertain due to their difficulty in being traced. One possible tracer of low-energy CRs is ionised carbon ([C II]), which may be enhanced in regions affected by CR-induced ionisation. We present observations of [C II] 158 $\mu$m line emission across the $\gamma$-ray-bright
supernova remnant (SNR) RX J1713.7-3946 obtained with SOFIA. These data are compared with molecular and atomic gas from Mopra ($^{12}$CO), Nanten ($^{12}$CO) and SGPS (HI), and high-energy emission from TeV $\gamma$-ray H.E.S.S. and X-ray XMM-Newton. We find [C II] emission follows the atomic gas more closely than molecular gas, particularly in regions near the SNR shock front. Ratios of [C II] intensity to gas column density vary across the remnant, with peak values coinciding with regions of enhanced TeV $\gamma$-ray emission. To put the [C II] in a wider context, we examined pointings from the Herschel GOT C+ survey. Our analysis of the GOT C+ data shows no significant difference in the I[C II]/I[$^{12}$CO] ratio for observations towards
star formation regions, HII regions and SNRs. To assess the origin of carbon ionisation, we model [C II] emissivity using the photoionisation code CLOUDY. We find UV
photons and CRs can produce comparable levels of [C II] emission, assuming low-energy CRs (< 1 GeV) are accelerated and trapped within the SNR shock. These results highlight the potential of [C II] as a tracer of CR ionisation and the importance of combining multi-wavelength observations to probe CR interactions in SNRs.
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All authors A.R. Thakur, G.P. Rowell, R. Higgins, M. Burton, Y. Fukui, S. Einecke, H. Sano, G. Wong, M.D. Filipović, C. Braiding
High Energy Astrophysical Phenomena
The impact of circumstellar wind-blown bubbles on the dynamics of pulsar wind nebulae and supernova remnants
Lioni-Moana Bourguinat and Pierrick Martin
The core-collapse
supernova explosion of most massive
stars is followed by the development of a
supernova remnant (SNR) and
pulsar wind nebula (PWN) system whose
evolution is in part dictated by its surrounding environment. The latter is frequently assumed to be the typical interstellar medium (ISM). However, massive
stars emit powerful winds during their lifetime and carve extended circumstellar cavities known as wind-blown bubbles (WBBs). We investigated the impact of WBBs on the dynamics, energetics, and thermal X-ray emission of a SNR-PWN system. We performed numerical simulations of a 1D hydrodynamical analogue of the system, for different stellar progenitors and
pulsar parameters, in a WBB or ISM environment. The system initially expands to large sizes in the low-density interior of a WBB, until the SNR fills the entire bubble. The PWN grows to $\gtrsim10~\mathrm{pc}$ ($30~\mathrm{pc}$) after $\sim5~\mathrm{kyr}$ ($\sim25~\mathrm{kyr}$) for a $M=8~\mathrm{M}_\odot$ ($M=20~\mathrm{M}_\odot$) progenitor, $5-6$ times larger than in an ISM environment. The impact of the SNR on the massive outer shell of the WBB generates a strong reflected shock that efficiently returns energy to the inner parts of the system. At late times, after a strong compression of the PWN by an order of magnitude in size, back-and-forth shock crossings of the cavity maintain the SNR at very high temperatures and drive a vigorous reverberation of the PWN, with changes in radius by up to $3-4$. In this stage, the PWN is on average $2-4$ times larger than in an ISM environment and contains up to an order of magnitude more energy. Thermal radiation from the system occurs in few very localised emission bursts, as low-velocity shocks are transmitted across the bubble shell when it is hit by blast waves. WBBs offer a possible explanation for the large sizes of many PWNe and the non-detection of their parent SNRs.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Searching for Solar-Basin Axionlike-Particle Decay with XMM-Newton Blank-Sky Observations
Bo Zhang, Chi Zhang, Lei Lei et al. (+4 more)
Axion-like particles (ALPs) bound in the solar gravitational field form the so-called ALP solar-basin. Since the two-
photon decay of non-relativistic particles is approximately isotropic, this population can be searched for using observations in the anti-solar direction. In this work, we propose a search strategy for narrow decay-line signals from the ALP solar basin using XMM-Newton blank-sky observations (XMM-BSOs) stacked spectra data taken in directions opposite to the Sun. By jointly fitting the signal and background model, we obtain limits on $g_{a\gamma\gamma}^{95}$ in the mass range $m_a=1.4\text{--}16~{\rm keV}$, with typical sensitivities of $g_{a\gamma\gamma}\sim10^{-10}\text{--}10^{-11}~{\rm GeV}^{-1}$. We have implemented the first anti-solar search for the solar basin, demonstrating that this strategy can exploit the stacked exposure of a large number of X-ray observations and provide a scalable analysis framework for future searches.
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All authors Bo Zhang, Chi Zhang, Lei Lei, Yang Yu, Guan-Shen Wang, Bing-Yu Su, Lei Feng
High Energy Astrophysical Phenomena
Spatially resolved spectral properties of M87* on event horizon scales
Shan-Shan Zhao, Ru-Sen Lu, Rocco Lico et al. (+2 more)
The supermassive black hole at the center of the nearby
radio galaxy M87 (M87*) is a
prime target for studying black hole physics. Spatially resolved spectral measurements on event-horizon scales can reveal the origin of the emission and probe the
plasma and gravitational environment in the immediate vicinity of the black hole. Here, we present an analysis of spectral properties based on nearly simultaneous high-resolution images at 3.5 mm (86 GHz) and 1.3 mm (230 GHz), obtained in 2018 with the Global Millimeter VLBI Array (GMVA) including ALMA and the Greenland
Telescope, and the Event Horizon
Telescope (EHT). We obtain the first spatially resolved spectral-index map ($S_\nu \propto \nu^\alpha$) within the compact region ($\leq 100\,\mu$as). We further detect a robust radial gradient with a modest rise in the inner $\lesssim 20~\mu$as (slightly inside the 1.3 mm ring), followed by a systematic decline at larger radii. The spectral index transitions from positive to negative values near $\sim 30~\mu$as, close to the 3.5 mm ring radius, consistent with frequency-dependent synchrotron opacity in the innermost
accretion flow. These results provide new observational constraints that can help discriminate between models of the horizon-scale emission and the launching of relativistic jets in M87*.
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All authors Shan-Shan Zhao, Ru-Sen Lu, Rocco Lico, Yuh Tsunetoe, Sijia Peng
High Energy Astrophysical Phenomena
Linking high-mass X-ray binaries to binary compact object mergers in Milky Way-like galaxies
Felipe Vivanco Cádiz, M. Celeste Artale, Nicola Masetti et al. (+5 more)
High-mass X-ray binaries (HMXBs) constitute a potential intermediate phase connecting massive stellar binaries to the formation of coalescing binary compact objects (BCOs). Yet, the specific circumstances that allow HMXBs to later develop into merging BCOs are still under debate. In this study, we focus on wind-fed HMXBs and investigate this link by generating synthetic catalogs with the population-synthesis code SEVN and assigning them to a sample of 66 Milky Way-like
galaxies. Using stellar particles drawn from the TNG50 cosmological simulation, we assign HMXBs according to particle mass, age, and
metallicity, and follow their subsequent
evolution to BCOs. In this way, our approach provides a realistic framework for modelling HMXBs in the Milky Way by explicitly accounting for the varied
metallicities and spatial distributions of binary systems. Our method recovers the spatial distribution inferred from the observed properties of Galactic HMXBs: their positions follow the spiral arms and agree with the measured radial profile. The age distribution aligns well with observations and shows that BH-HMXBs tend to be younger than NS-HMXBs. We find that the fraction of HMXBs that evolve into merging BCOs within a Hubble time for BH-HMXBs is ~0.2-3.2% (or ~0.3-5.4% when restricting to 10^35 <= L_X <= 10^40 erg s^-1), while for NS-HMXBs is ~3.6-23.4% (or ~3.5-26.0% with the same luminosity cut). We show that common envelope (CE) episodes and natal-kick magnitudes are the primary processes determining the number of merging systems. Successful BCO mergers are typically produced by systems that experienced significant orbital hardening (early CE), whereas stable mass transfer often yields wide, non-merging binaries unless extreme eccentricities are induced by kicks.
Metallicity plays a secondary but important role by modulating compact-remnant masses and wind-driven orbital widening.
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All authors Felipe Vivanco Cádiz, M. Celeste Artale, Nicola Masetti, Gaston Escobar, Giuliano Iorio, Ankit Kumar, Boyuan Liu, Michela Mapelli