High Energy Astrophysical Phenomena
Polarization Transport and Polarized Images of a Rotating Braneworld Black Hole
Wen-Hao Deng, Qing-Quan Jiang, Kai Lin et al. (+1 more)
We investigate polarized synchrotron emission from an optically thin
accretion flow around a rotating braneworld black hole, focusing on how higher-dimensional
gravity modifies
photon propagation and polarization transport. We integrate the null-geodesic and parallel-transport equations for the polarization four-vector and, within a common emissivity and
magnetic-field prescription, examine the effects of tidal charge, black-hole
spin, observer inclination, and prograde or retrograde orbital motion. We analyze the linearly polarized intensity, electric-vector position angle (EVPA), Stokes parameters, the joint $Q$–$U$ polarization-state space, and the cumulative net linear polarization degree, and compare representative braneworld configurations with Kerr and Kerr–Newman spacetimes. Within the parameter range considered, tidal charge and
spin do not generate a qualitatively new large-scale polarization morphology. Instead, they primarily reorganize the polarized intensity, orientation, and polarization-state distribution in the strong-field region near the shadow boundary and
photon ring. Viewing inclination controls the dominant projected morphology, while high inclinations enhance projection and Doppler asymmetries and make the distinction between prograde and retrograde flows more pronounced. The Stokes components and their joint state space expose local bending, stretching, and trajectory concentration that are less apparent in intensity images. The cumulative net linear polarization degree decreases with increasing cumulative radius, and larger tidal charge or
spin lowers its amplitude for the representative models considered. Together, these complementary polarization observables provide a potential route for separating spacetime, viewing-geometry, and
accretion-flow effects and for constraining braneworld tidal charge with horizon-scale polarimetry.
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All authors Wen-Hao Deng, Qing-Quan Jiang, Kai Lin, Pei Wang
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
A Systematic Study of Resonance-Driven Flux Modifications in Extreme-Mass-Ratio Inspirals
Edoardo Levati, Lennox S. Keeble and Alejandro Cárdenas-Avendaño
Transient orbital resonances can introduce phase-dependent corrections to the
evolution of extreme-mass-ratio inspirals (EMRIs), potentially altering their long-term dynamics and emitted gravitational-wave signals. In this work, we quantify the resonance-induced modifications to the energy, axial angular momentum, and Carter constant fluxes and compute the corresponding resonance coefficients across a broad region of the orbital parameter space. Using the publicly available $\texttt{pybhpt}$ code, we solve the Teukolsky equation in the frequency domain to coherently combine the degenerate radial and polar harmonics that arise at resonance. We analytically derive a selection rule governing the relative radial-polar phase dependence of the resonant flux modifications. We argue that the relative strength of the resonant flux modifications reflects a balance between
symmetry-induced cancellations and the degree to which the resonant orbit samples the underlying two-dimensional orbital phase space. For the dynamically important $3{:}2$ and $2{:}1$ resonances, we also characterize how the resonance coefficients vary with the primary black-hole
spin, orbital eccentricity and inclination. Our results constitute the largest set of Teukolsky-based resonance coefficients calculated to date and provide essential input for future studies of transient orbital resonances in EMRIs.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
Convolutional Neural Network for Extraction of $n = 1$ Photon Ring of Black Holes
Courtney Duong, Frank Myhre and Joseph R. Farah
Very-long-baseline interferometry (VLBI) may enable direct imaging of fine, event-horizon scale black hole structures such as the
photon ring. In particular, the $n=1$
photon subring encodes information about black hole
spin in its radial profile and azimuthal brightness modulation, making it a key proxy for spacetime properties. However, the $n=1$ subring overlaps with emission from the $n=0$ subring in observations, requiring isolation of the $n=1$ subring for measurements. We present a convolutional neural network (CNN) capable of extracting the $n=1$ subring from composite images containing $n=0$ and $n=1$ subrings. We simulate $111,000$ $m$-ring images with eht-imaging to train and validate the CNN. The CNN accurately recovers the radial and angular brightness profiles of the $n=1$ subring with a mean normalized cross correlation (NXcorr) of $\sim0.99$. The CNN provides a detection capability by predicting no false positives when input images lack a $n=1$ subring. We perform feature extraction with ringfit to show that the CNN-predicted $n=1$ subring accurately recovers the ground truth radial profiles and azimuthal brightness modulation, demonstrating the CNN's capability to extract
spin-sensitive features. We further test the CNN on black hole images generated by KerrBAM and general relativistic magnetohydrodynamic (GRMHD) simulations, finding that it recovers the overall $n=1$ subring radial profiles while exhibiting discrepancies in the recovered intensity profiles. These results demonstrate the potential of deep learning methods to isolate the $n=1$ subring from overlapping emission, providing a framework for analyzing future high resolution black hole images from proposed VLBI missions such as the Black Hole Explorer (BHEX).
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High Energy Astrophysical Phenomena
Multi-scale variability in the optical afterglow of GRB 251013C from high-cadence LAST observations
R. Konno, E. O. Ofek, S. Garrappa et al. (+8 more)
Context. Optical afterglows of gamma-ray bursts (GRBs) are often described by smooth power-law decays, but deviations such as
flares and rebrightenings provide important constraints on the underlying emission processes. Aims. We investigate the temporal variability of the optical afterglow of GRB 251013C using high-cadence observations, and assess the origin of the observed variability. Methods. We analyze continuous optical observations obtained with the Large Array Survey
Telescope (LAST), complemented by publicly available X-ray data from Swift-XRT. The optical light curve is modeled using a power-law decay with superposed variability components, and contemporaneous optical and X-ray measurements are used to constrain the broadband spectrum. Results. The optical light curve shows pronounced variability on multiple timescales, including broad rebrightening episodes with $\Delta t \sim t$ and superposed faster fluctuations with $\Delta t/t < 1$. The main rebrightening exhibits a structured rise with a clear steepening prior to the peak. The fast variability comprises asymmetric fast-rise, slow-decay features whose durations increase with peak time. The optical flux lies on the extrapolation of the X-ray spectrum, and the spectrum hardens by the same amount whether measured within the X-ray band or from optical to X-ray. Conclusions. We favor a refreshed external-shock interpretation for the main rebrightening. The broadband spectrum and post-peak decay are consistent with slow-cooling synchrotron emission in a wind-like medium. The spectral hardening requires a newly dominant, harder electron population, while the faster optical variability indicates structure within the refreshed ejecta or shocked region.
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All authors R. Konno, E. O. Ofek, S. Garrappa, O. Teboul, E. Waxman, S. Ben-Ami, D. Kovaleva, A. Krassilchtchikov, D. Polishook, E. Segre, E. A. Zimmerman
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Using Machine Learning to Model Stellar Collisions in our Galactic Center
Tristan C. Sand, Sanaea C. Rose, Elena González Prieto et al. (+9 more)
Direct collisions in the inner pc of the Galactic center can alter the orbits and properties of
stars. The outcome of a collision depends on a number of parameters, including the masses and ages of the
stars, the impact parameter, and the initial relative velocity. We utilize the newly developed $\verb|collAIder|$, a machine learning tool developed to predict the outcomes of stellar collisions, to bridge 3D hydrodynamic simulations of stellar collisions with a dynamical model of the Galactic center. Our results show a substantial population of stripped
stars, $\sim$$10\%$ of the initial stellar population, produced by mass loss during high-speed collisions. Stellar mergers are less frequent, with about $5\%$ of the
stars experiencing a collision-induced merger. We also find that high-speed, nearly head-on collisions can completely disrupt the
stars. These destructive collisions are usually preceded by 10 or more collisions, which gradually reduce the mass of the
star before it is ultimately destroyed. We estimate that mass loss during stellar collisions injects roughly $(2.5-8)\times 10^5$ M$_\odot$ of gas into the surrounding environment. Most of this gas is injected into the inner $0.1$ pc and about $90\%$ is retained within the cluster and may be accreted onto the supermassive black hole.
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All authors Tristan C. Sand, Sanaea C. Rose, Elena González Prieto, James C. Lombardi, Jr., Charles F. A. Gibson, Fulya K{\i}roğlu, Kyle Kremer, Christopher E. O'Connor, Enrico Ramirez-Ruiz, Frederic A. Rasio, Tjitske Starkenburg
High Energy Astrophysical Phenomena
A Magnetic Unification of Merging Supermassive Black Hole Binaries
Mark J. Avara, David O'Neill and Zoltán Haiman
The detection of an electromagnetic (EM) transient from a supermassive black hole binary (SMBHB) merging within a gaseous environment will constitute a multi-messenger milestone. Numerical simulations of these systems have mostly been performed in 2D with a constant viscosity parameter representing turbulent and
magnetic stresses. These simulations predict a steep drop in
accretion rate and X-ray luminosity at merger, followed by a slow recovery. However, 3D-GRMHD and 3D-MHD simulations have shown only a modest reduction in
accretion rate and a fast post-merger recovery. We present a new 2D pseudo-Newtonian framework with physically motivated prescriptions for
stochastic viscosity, relativistic apsidal precession, and large-scale
magnetic fields. When suitably calibrated, this 2D framework accurately captures key 3D-GRMHD behavior, demonstrating that it can be used to explore binary
accretion without the high computational cost of 3D-GRMHD simulations. We find that the merger signatures are most sensitive to the strength of the
magnetic field, with a drop in the
accretion rate at merger progressively less pronounced for stronger fields. Post-merger
evolution is determined by both magnetization and relativistic precession of orbiting gas, yielding rapid recovery of
accretion. For low-magnetization disks, recovery is driven by self-intersection shocks, and the dip at merger is followed by a distinct second dimming. Large-scale
magnetic fields of increasing magnitude lead to magnetically arrested disk (MAD) behavior which disturbs the merging system progressively earlier before merger, and longer after. Our results unify the EM signatures of the merger of embedded coplanar SMBHBs, and provide novel observational constraints on their intrinsic magnetization.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Reconnection of Gravitational Fields
Luca Comisso and Felipe A. Asenjo
In a tetrad formulation of general relativity, an ideal Ohm-type condition for the gravitational field implies the conservation of gravitational fluxes and the preservation of the connectivity of gravitational field sheets. We investigate the consequences of departures from ideal gravitational
evolution by developing a theory of gravitational reconnection, defined as a change in the connectivity of gravitational field sheets arising from the breakdown of the ideal frozen-in
evolution of the gravitational field. We derive quantitative measures of the gravitational reconnection rate, show that gravitational reconnection alters the energy-momentum exchange between the gravitational and matter sectors, and determine how it modifies the
evolution of gravitational helicity. Our results provide a quantitative framework for describing changes in gravitational connectivity and their consequences in dynamical spacetimes.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Frozen-In Gravitational Fields
Felipe A. Asenjo, Maricarmen A. Winkler and Luca Comisso
Spacetime can undergo complex nonlinear
evolution, as governed by the Einstein field equations, and a central challenge is to understand the
geometric structures that arise, persist, and interact throughout its
evolution. Using a formulation of Einstein equations that parallels nonlinear electrodynamics of continuous media, we show that general relativity admits gravitational field connections—two-surfaces and associated field lines whose connectivity is maintained by the spacetime dynamics. This gravitational frozen-in behavior is enabled by an ideal Ohm-type condition for the gravitational field. We further show that the same framework naturally leads to a conserved “gravitational
magnetic” flux. A conserved gravitational helicity also emerges, with a clear topological interpretation in terms of gravitational field-line structures. These results identify well-defined topological constraints on admissible spacetime
evolution and provide an organizing principle underlying the nonlinear dynamics of spacetime.
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High Energy Astrophysical Phenomena
Early NIR echo and the time variable mass loss history of Type IIn SN 2024kgi
Naveen Dukiya, Kuntal Misra, Andrea Pastorello et al. (+30 more)
We present a comprehensive analysis of the long-term photometric and spectroscopic monitoring campaign of the Type IIn
Supernova (SN) 2024kgi. The SN reaches at peak an $r$-band absolute magnitude of $-19.81 \pm 0.06$ mag and a bolometric luminosity of $\sim 2 \times 10^{43}$ erg s$^{-1}$. We observe a break in the lightcurve at day $\sim 312$, after which the luminosity decline changes from $t^{-1.0}$ to $t^{-4.5}$, likely due to the shock sweeping the dense CSM. We introduce a semi-analytical lightcurve modeling approach for CSM-interaction in transients that accounts for variable
diffusion time. We hence estimate a CSM mass of $2.34^{+11.8}_{-1.6} M_{\odot}$ and with a density profile $\rho_{csm} \propto r^{-2.74}$, indicating progressively increasing mass loss toward the SN explosion. The ejecta signatures emerge as broad H, He, and Ca II triplet lines, at day $\sim 80$, much earlier than expected from a spherically symmetric CSM, suggesting asymmetry in the CSM. After the lightcurve break, the H lines exhibit a wavelength-dependent deficit in the red-wing flux, indicating new dust formation in the ejecta and/or in the post-shock gas. We observe an NIR excess from day $\sim 40$ onwards. We attribute the early NIR excess before the lightcurve break solely to the NIR echo from pre-existing dust, as there are no other indications for new dust formation. The late-time NIR excess likely has contributions from both the preexisting and newly formed dust. The steady increase in mass loss, slow CSM velocity, and asymmetric CSM favor a binary interaction-induced mass loss.
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All authors Naveen Dukiya, Kuntal Misra, Andrea Pastorello, Andrea Reguitti, Anjasha Gangopadhyay, Aravind P. Ravi, Brian Hsu, Noah Franz, David J. Sand, Nathan Smith, Jennifer E. Andrews, Moira Andrews, K. Azalee Bostroem, Collin Christy, Monalisa Dubey, Joseph R. Farah, Archana Gupta, Estefania Padilla Gonzalez, Emily Hoang, D. Andrew Howell, Curtis McCully, Darshana Mehta, Megan Newsome, Jeniveve Pearson, Nicolas Meza Retamal, Jeonghee Rho, Manisha Shrestha, Bhagya Subrayan, Giacomo Terreran, Lina Tomasella, Stefano Valenti, Giorgio Valerin, Kathryn Wynn
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Gravitational wave signatures of subsolar neutron star formation in collapsar disks
Vishal Baibhav, Valerio De Luca, Loris Del Grosso et al. (+3 more)
Standard models for stellar core collapse predict the birth of
neutron stars with masses exceeding a solar mass. In the collapsar model, a rapidly rotating massive
star collapses to a black hole surrounded by a dense,
neutrino-cooled
accretion disk, whose outer regions may in some cases fragment into
neutron-rich clumps that collapse to form subsolar-mass
neutron stars. These disk-formed objects can then merge either with one another or, following possibly hierarchical
evolution, with the central black hole. In this work, we characterize the gravitational-wave signatures of these binaries, focusing on distinctive features of the collapsar environment: Doppler and other phase modulations from orbital motion about the central black hole, gas-driven migration in the disk, and tidal interactions during inspiral. We show that the combination of anomalously low component masses with these environmental imprints produces unique waveform signatures that can distinguish the collapsar channel from other subsolar merger scenarios. Current and next-generation detectors have good prospects for identifying the intrinsic properties of such objects and, if subsolar mergers are discovered, for testing and constraining the collapsar formation pathway.
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All authors Vishal Baibhav, Valerio De Luca, Loris Del Grosso, Emanuele Berti, Brian D. Metzger, Lam Hui
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Quarkyonic matter suppresses neutron-star $g$ modes and reverses their mass trend
Probit J Kalita and Bharat Kumar
Gravity (g) modes are the only
neutron-
star oscillations that report on the composition of dense matter rather than on its stiffness, and work on hybrid
stars has established that a first-order
quark transition raises their frequency. Quarkyonic matter does the opposite.
Quark-nucleon chemical
equilibrium is maintained by the strong interaction, so the
quarks acquire no thermodynamic freedom on an oscillation period and $c_s^2-c_e^2$ reduces to a positive-definite quadratic form in the lepton gradients alone. The nucleon momentum shell stiffens both sound speeds together instead of separating them, so the buoyancy factor collapses by a factor of 9.5 to 19 at an early transition and the core is left only weakly stratified. Solving the $l=2$ relativistic Cowling problem for ten equations of state that share one isoscalar sector, seven quarkyonic and three nucleonic controls at matched
symmetry-energy slope, we found the g-mode confined to the nucleonic shell outside the core, with the horizontal flow that it lives on excluded from the core while the core is displaced almost rigidly. Its frequency falls from 158-522 Hz across the controls to $81-254$~Hz across the quarkyonic models, and by 14% at 1.4$M_\odot$ for the matched pair at $L=50\mev$; more important than the shift, it decreases with mass where the controls rise. Writing each frequency as the dynamical frequency $(GM/R^3)^{1/2}$ times a dimensionless remainder separates structure from composition. The $f$ and $p_1$ trends prove to be inherited from the mass–radius relation; the $g_1$ remainder, constant to $2-9\%$ along a nucleonic sequence, falls by a quarter to a third along a quarkyonic one and departs by a factor of two from the nucleonic $g$-mode relation at fixed compactness and $L/K_0$. These are Cowling values, lower bounds at the ten-per-cent level, and the sign of the trend survives a correction of that size.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Universal $Z^{2/3}/\sqrt{Q_\alpha}$ Scaling Law in Alpha Decay from Nuclei to Neutron-Star Mergers
Hisham Anwer, B. Salah and A. R. Abdulghany
We establish a universal scaling law for $\alpha$-decay half-lives based on the variable $X_a = Z^a/\sqrt{Q_\alpha}$, which collapses experimental and theoretical data spanning over twenty orders of magnitude onto a single linear correlation. Global optimization over the complete set of even-even $\alpha$ emitters reveals a uniquely sharp optimum at $a \simeq 2/3$. This exponent is theoretically motivated by the leading
geometric scaling of heavy
nuclei and emerges quantitatively from the correlated nuclear systematics, driven by the correlated $(Z, Q_\alpha)$
manifold of the nuclear chart. Strikingly, five structurally distinct semi-empirical models and an independent microscopic WKB calculation, when independently optimized with respect to the exponent $a$, yield values clustered around $2/3$, while the corresponding $a=2/3$ correlations remain highly linear without refitting the original model parameters. This emergent scaling law implies smooth variations of decay times along the heavy $r$-process path. We demonstrate analytically that, given a roughly uniform distribution of this variable, the scaling law naturally supports a quasi-power-law radioactive heating rate ($\dot{\epsilon} \propto t^{-1.24}$), consistent with full network calculations. Furthermore, integrating these scaling predictions directly into nuclear source terms for radiative-
diffusion models yields multimessenger observables that accurately reproduce the kilonova AT2017gfo associated with the gravitational-wave event GW170817, demonstrating that the $Z^{2/3}/\sqrt{Q_\alpha}$ scaling coordinate provides a robust tool for modeling the radioactive engines of
neutron-
star mergers.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Event Detection and Finite-Grid Effects at an Imposed Absorbing Boundary in Newtonian Black Hole Orbit Integrations
Gregory M Davis
Numerical classification of black-hole orbits can depend on how prescribed inner capture or absorbing boundaries are implemented. This study investigated how discrete evaluation of such a boundary affects orbit classification. Massless particles were integrated about an isolated Newtonian point mass and initialized at periapsis with an absorbing boundary at rsink = 104RS. Because the Keplerian periapsis q is constant, the expected classification can be analytically determined. A classifier omitting evaluation at initialization can miss particles that already satisfy the removal criterion, but evaluation at t = 0 reproduced the analytic classification on every sampled grid. As the grid resolution increased, the inferred critical periapsis approached the imposed sink radius. These results demonstrate that an apparent critical periapsis can depend on both the imposed boundary and its numerical evaluation, emphasizing the need to distinguish numerical effects from genuine dynamical thresholds.
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High Energy Astrophysical Phenomena
PEARLS: NuSTAR and XMM-Newton Extragalactic Survey of the JWST North Ecliptic Pole Time-Domain Field IV: X-Ray Variability Analysis
Ross Silver, Francesca Civano, Xiurui Zhao et al. (+31 more)
NuSTAR and XMM-Newton have observed the James Webb Space
Telescope (JWST) North Ecliptic Pole (NEP) Time-Domain Field (TDF) for almost five contiguous years starting in 2019. In that time, the NEP X-ray survey has accumulated 3.5 Ms and 228 ks of quasi-simultaneous NuSTAR and XMM-Newton observations, respectively. This paper presents variability results for the 112 NuSTAR and 453 XMM-Newton sources detected in this field, based solely on the X-ray photometric data. Four NuSTAR sources and 11 XMM-Newton sources varied in at least one band at >=99% confidence. The sources with
redshift measurements show a relationship between luminosity and variability with 74% of variable sources brighter than 5x the sensitivity limit of the survey. This is supported by about 1/3 of sources with more than 400 counts detected being variable and only 4 sources with fewer counts showing variability. Variability timescales are not well determined, but variability amplitude tends to be larger on longer timescales.
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All authors Ross Silver, Francesca Civano, Xiurui Zhao, Samantha Creech, S. P. Willner, Christopher N. A. Willmer, Rogier A. Windhorst, Haojing Yan, Anton M. Koekemoer, Rosalia O'Brien, Rafael Ortiz III, Rolf A. Jansen, Gibson B. Bowling, Payaswini Saikia, W. Peter Maksym, Nico Cappelluti, Francesca Fornasini, Massimo Ricotti, Timothy Carleton, Seth H. Cohen, Rachel Honor, Jake Summers, Jordan C. J. D'Silva, Sibasish Laha, Dan Coe, Christopher J. Conselice, Jose M. Diego, Simon P. Driver, Brenda Frye, Norman A. Grogin, Madeline A. Marshall, Nor Pirzkal, Aaron Robotham, Russell E. Ryan Jr
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Ruling out nucleonic direct Urca cooling in low-mass neutron stars using nuclear data
Gabriele Montefusco, Pietro Klausner, Marco Antonelli et al. (+3 more)
Connecting nuclear experiments to
neutron star composition requires controlling the extrapolation of experimental information beyond the densities probed in the laboratory. We combine a broad set of nuclear structure observables and INDRA-FAZIA isospin-transport data within a
Bayesian inference of the dense matter equation of state (EoS). To limit uncontrolled extrapolation to high density, we employ a flexible asymptotically causal metamodel whose
neutron star posteriors are comparable to those obtained with agnostic EoS models. The nuclear structure information is propagated through its full multidimensional distribution of correlated nuclear matter parameters, while the density-dependent INDRA-FAZIA likelihood is evaluated directly along each sampled metamodel
symmetry energy curve. These two sources of laboratory information give compatible constraints on the
symmetry energy, and their combination preserves agreement with finite nuclear observables. When combined with ab initio chiral effective field theory calculations and astrophysical observations, all these constraints substantially improve the determination of central
proton fractions in low-mass
neutron stars, while leaving larger uncertainties for massive
stars. Within the adopted nucleonic metamodel, the reduced probability of large
proton fractions strongly disfavors electronic direct-Urca onset at or below $1.4\,M_\odot$: its posterior probability falls from $\sim20\%$ with chiral and astrophysical constraints alone to below $1\%$ when the laboratory information is included.
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All authors Gabriele Montefusco, Pietro Klausner, Marco Antonelli, Caterina Ciampi, Diego Gruyer, Francesca Gulminelli
High Energy Astrophysical Phenomena
Magnetar magnetothermal evolution with Landau-quantized electrons: enhanced Joule heating due to free electron diamagnetism and the magnetar heating problem
Peter B. Rau
Magnetars are systematically more luminous than other
neutron stars. Previous studies suggest that supporting such high luminosities requires a heat source beyond standard Ohmic dissipation– the “magnetar heating problem”. We previously demonstrated using periodic box simulations that de Haas–van Alphen (dHvA) oscillations of the Landau quantization-induced magnetization in a
neutron star could repeatedly generate large-gradient field components that undergo rapid Ohmic dissipation. Using the QMFM finite volume code developed for this purpose, we perform axisymmetric 2.5D electron magnetohydrodynamics plus thermal
evolution simulations of a realistic
neutron star crust, including all Landau quantization effects, to quantify this enhancement to field dissipation and heating of the
star. We show that Landau quantization effects generate strong, small-scale
magnetic field structures whose dissipation can heat the field-confined equatorial hot spot beyond its temperature in the absence of Landau quantization. Enhanced heating is greatest for weaker initial fields $B\sim10^{14}$ G, for which
magnetic energy is dissipated 30% faster: in this case, the crust cools sufficiently for the dHvA oscillations to reach large amplitudes. For the stronger fields $\gtrsim B\sim5\times10^{14}$ G required to power the most luminous magnetars, the enhancement is modest, as dissipation of these fields heats the crust sufficiently to thermally suppress dHvA oscillations. In cases where heating is significantly enhanced, most of the heat goes into increasing the
neutrino luminosity, and surface
photon luminosity is only slightly increased. For the simple crust-confined fields that we simulated, Landau quantization-enhanced Joule heating is thus insufficient to explain the magnetar heating problem.
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High Energy Astrophysical Phenomena
Luminosity Signatures of Dark Sector Particles from Black Hole Evaporation in Neutron Stars
Ioannis Dalianis and Anastasios Irakleous
Microscopic black holes may form at the centers of
neutron stars through the accumulation and collapse of dark matter. While Standard Model particles produced by Hawking evaporation are efficiently absorbed by the dense stellar medium, sufficiently weakly interacting and long-lived particles can escape and subsequently decay into high-energy
neutrinos,
photons, or charged particles, providing an indirect probe of Hawking radiation. We examine the joint energy–angular distribution of these secondary particles, incorporating mediator propagation, energy-dependent decay, and relativistic decay kinematics. For relativistic mediators, the normalized energy-integrated angular profile becomes approximately independent of the black hole temperature, with its characteristic extent controlled primarily by the combination $c\tau_S/D$ of the mediator lifetime and source distance, as the boost enhancement of the decay length is compensated by relativistic beaming. We demonstrate the viability of this mechanism and illustrate its phenomenology with gravitationally coupled scalars, dark
photons, dark-$Z$
bosons, and heavy neutral leptons. Comparing with monochromatic mediator production from dark matter annihilation, we find that the energy-integrated angular profiles can be nearly degenerate, while the energy spectra and energy-resolved angular distributions remain distinct. These complementary spectral and angular signatures provide targets for high-energy
neutrino and gamma-ray searches.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
A New Probe of Strongly-Interacting Dark Sector using Neutrino Telescopes
Jose A. Macias Cruz, Christopher V. Cappiello, P. S. Bhupal Dev et al. (+1 more)
A confining dark sector modeled after
quantum chromodynamics provides a well-motivated framework for strongly-interacting dark matter. We show that dark vector
mesons in a confining dark sector can be resonantly produced in high-energy
neutrino scattering on the
cosmic neutrino background, generating a distinctive absorption feature in the
cosmic neutrino energy spectrum. Unlike conventional attenuation effects, this feature directly reflects the mass spectrum of dark resonances and can therefore serve as a spectroscopic signature of a strongly-interacting dark sector. We find that a broad range of dark-sector parameter space is within the reach of future
neutrino telescopes, including IceCube-Gen2
Radio. Our proposal thus turns the
cosmic neutrino background into a target for discovering dark-sector resonances, while simultaneously providing a novel probe of dark sector interactions with
neutrinos.
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All authors Jose A. Macias Cruz, Christopher V. Cappiello, P. S. Bhupal Dev, Suchita Kulkarni
High Energy Astrophysical Phenomena
Jet variability in small mass ratio supermassive black hole binaries
Jay V. Kalinani, Manuela Campanelli, Michail Chabanov et al. (+4 more)
We present three-dimensional general relativistic magnetohydrodynamic simulations of a precessing supermassive black hole binary with mass ratio q=1/7, embedded in a circumbinary disk. We investigate how dynamics within the binary cavity launch and shape a relativistic jet to thousands of gravitational radii. The primary black hole dominates both
accretion and jet power, while the smaller black hole repeatedly crosses and shocks the inner
accretion flow. These passages of the secondary drive magnetized gas alternately into the upper and lower jet funnels, producing disturbances that propagate outward as quasi-periodic outflows. Although the inner flow is perturbed twice per orbit, each jet lobe shows one dominant outflow per orbit. On longer timescales, the jet precesses, reverses its
magnetic handedness, and undergoes two weak phases. The first results from a reorientation of the primary
spin and is followed, after the jet recovers, by a reversal in the circulation of the projected
magnetic field. The second weak phase occurs as the secondary's orbit becomes nearly coplanar with the circumbinary disk, reducing the gas and
magnetic flux reaching the primary. Together, these results connect cavity dynamics to large-scale jet variability and predict a set of correlated jet signatures whose relative timing and causal ordering may provide stronger evidence for a small-mass-ratio supermassive black hole binary than any one feature alone.
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All authors Jay V. Kalinani, Manuela Campanelli, Michail Chabanov, Maria Chiara de Simone, Carlos O. Lousto, Helvi Witek, Yosef Zlochower
High Energy Astrophysical Phenomena
Particle Acceleration in Stratified 2D MRI Turbulence: From Reconnection to First- and Second-Order Fermi and Shear Acceleration
Astor Sandoval, Mario Riquelme and Jorge Cuadra
Low-luminosity
accretion disks around black holes are weakly collisional, potentially enabling nonthermal particle acceleration. Local two-dimensional particle-in-
cell simulations of the stratified magnetorotational instability (MRI) in pair
plasmas by Sandoval et al. (2024; hereafter S24) revealed nonthermal populations with maximum energies proportional to the scale-separation ratio $\omega_{c,0}/\Omega_0$, where $\omega_{c,0}$ and $\Omega_0$ are the initial particle cyclotron and Keplerian frequencies, respectively. We identify the acceleration mechanisms involved and quantify their scale-separation dependence. Acceleration occurs primarily within large-scale current sheets associated with an MRI dynamo. Particles are initially injected by non-ideal electric fields during reconnection driven by plasmoid splitting, attaining energies independently of scale separation. They subsequently undergo rapid first-order Fermi-like acceleration occurring within converging flows between newly formed, separating plasmoids. During this stage, energies grow at a rate proportional to the instantaneous non-relativistic cyclotron frequency, independently of $\omega_{c,0}/\Omega_0$. This fast acceleration rate implies a maximum energy proportional to $\omega_{c,0}/\Omega_0$. Particles then continue interacting repeatedly with plasmoids, undergoing slower, predominantly second-order Fermi acceleration, with a subdominant contribution from shear acceleration. This stage increases particle energies by only a factor of a few over several orbits, regardless of $\omega_{c,0}/\Omega_0$. The combination of these three stages implies a maximum energy proportional to $\omega_{c,0}/\Omega_0$, explaining the scaling found by S24 and suggesting that the MRI may accelerate particles to ultrarelativistic energies in low-luminosity disks. Testing these results in three dimensions remains an important next step.
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High Energy Astrophysical Phenomena
Multi-wavelength Behaviour and Lepto-hadronic Modeling of PKS 0215+015 Around the Epoch of IceCube-220225A
Athira M Bharathan and Markus Böttcher
The detection of high-energy astrophysical
neutrinos has opened a new avenue for identifying
cosmic particle accelerators. Blazars, active galactic
nuclei (AGN) with relativistic jets oriented close to the observer's line of sight, are promising sites of hadronic interactions capable of producing PeV-scale
neutrinos. We investigate the flat-spectrum
radio quasar (FSRQ) PKS~0215+015 ($z \simeq 1.715$), positionally consistent with the IceCube-220225A
neutrino event of estimated energy $\sim$154~TeV. We combine Fermi-LAT $\gamma$-ray data with Swift-XRT and Swift-UVOT observations to characterise the source around the
neutrino epoch. PKS~0215+015 exhibited pronounced $\gamma$-ray, X-ray and optical activity in early 2022, consistent with a disturbance propagating along the jet. We construct broadband spectral energy distributions (SEDs) for the flaring interval and model them using leptonic and lepto-hadronic frameworks. The SED is well reproduced by a leptonic model comprising synchrotron, synchrotron self-Compton and external Compton emission, indicating that electron processes dominate. A co-accelerated
proton population remains radiatively subdominant but requires a
proton kinetic luminosity roughly two orders of magnitude above equipartition with the
magnetic field. The predicted
neutrino flux is well below that implied by a single IceCube-220225A-like detection. Independent analysis of short-term $\gamma$-ray variability yields an emission-region size consistent with the SED fit, supporting the model's physical self-consistency. We discuss the temporal and energetic plausibility of the association between PKS~0215+015 and IceCube-220225A and implications for future multimessenger studies of high-
redshift FSRQs.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.CO
Biases from Astrophysical Environmental Effects in Standard-Siren Cosmology
Ioannis Liodis, Rodrigo Vicente, Soumen Roy et al. (+1 more)
Next-generation ground based gravitational wave detectors will enable precision standard-siren cosmology, making systematics increasingly important. We investigate how line-of-sight acceleration, as may arise for compact binaries in dense astrophysical environments, biases measurements of the Hubble constant $H_0$. We simulate a catalogue of 50 binary
neutron star bright sirens with known host
redshifts, assuming the signals have been impacted by line-of-sight acceleration and analysing them with
vacuum waveforms. Unmodelled line-of-sight acceleration biases the inferred luminosity distances and shifts the individual $H_0$ posteriors systematically towards lower values. Consequently, combining events narrows the posterior around a biased value rather than averaging away the systematic, even when the acceleration signs are assigned randomly. For our 50-event catalogues, affected fractions of approximately $10\%$ at $|a_\parallel|/c=10^{-6}\,\mathrm{s^{-1}}$, or $30\%$ at $|a_\parallel|/c=10^{-7}\,\mathrm{s^{-1}}$, produce offsets exceeding three posterior standard deviations in at least one quarter of the realisations. Considering larger catalogues further increases the significance of the effect. Our results indicate that environmental effects may constitute an important systematic for precision standard-siren cosmology and should be incorporated into future population analyses.
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All authors Ioannis Liodis, Rodrigo Vicente, Soumen Roy, Samaya Nissanke
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM
IceCube Upgrade status and perspectives
Anna Eimer
The IceCube
Neutrino Observatory instruments one cubic kilometer of deep-glacial ice between 1450 m and 2450 m below the surface at the geographic South Pole to detect
neutrinos via Cherenkov radiation of relativistic charged particles produced in their interactions. This detector is responsible for a number of key observations in
neutrino astrophysics, which include the discovery of a high-energy astrophysical
neutrino flux and, more recently, the galactic plane. During the austral summer of 2025/26, five new strings equipped with new photosensor designs were deployed as a dense infill in the middle of the existing detector. The science goals of this detector are twofold: Firstly, given the higher photocathode density, an improved atmospheric
neutrino event selection and reconstruction at a few GeV can be achieved for enhanced capabilities to study
neutrino oscillations. Secondly, novel calibration devices will improve the knowledge of the optical properties of the glacial ice and the detector response. These new calibration results will be applied to archival IceCube data, improving angular and spatial resolution of all detected astrophysical
neutrino events. The IceCube Upgrade also serves as a first step towards the next-generation
neutrino telescope at the South Pole, called IceCube-Gen2.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Companion masses of Gaia DR3 AstroSpectroSB1 binaries: a Bayesian forward-modelling framework
Prasid Sandave and Raghuveer Garani
Gaia Data Release 3 (DR3) has substantially expanded the study of unresolved binaries by providing combined astrometric and spectroscopic orbital solutions for a large sample of non-single
stars. We present a
Bayesian forward-modelling framework for estimating companion masses in Gaia DR3 AstroSpectroSB1 systems. The method samples the physical parameters of each binary, predicts the corresponding astrometric Thiele-Innes constants and spectroscopic orbital coefficients, and evaluates their likelihood using the full covariance
matrix published by Gaia. An external prior on the primary mass is incorporated to resolve the remaining degeneracy between the component masses and orbital inclination in single-lined systems. We apply this framework to 1035 AstroSpectroSB1 systems with primary-mass estimates drawn from the Gaia DR3 astrophysical\_parameters table. Of these, 760 systems also have Gaia-reported estimates for both component masses and are used as a validation sample. The remaining 275 systems constitute an inference sample for which the mass of the fainter, unresolved companion is estimated. For systems with well converged posteriors, the inferred parameters reproduce the Gaia orbital observables, while the companion masses recovered for the validation sample are consistent with the Gaia estimates. In the inference sample we find 113 well converged systems for which the companion masses are meaningfully inferred. We find that the population is dominated by ordinary
stars, together with a smaller high-mass tail that may contain massive white dwarfs or other compact-object candidates. Our framework provides a scalable approach for converting Gaia AstroSpectroSB1 solutions into companion-mass posterior distributions, identifying promising systems for targeted follow-up, and preparing for the larger and more precise orbital samples anticipated with Gaia DR4.
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