High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Rotating Weyssenhoff fluids in linearized Einstein-Cartan theory
Emmanuele Battista, Salvatore Capozziello and Francesco Giovinetti
The Weyssenhoff fluid expands the ordinary perfect-fluid description of general relativity by taking into account the intrinsic
spin of its constituent particles. Within the linearized regime of Einstein-Cartan theory, we investigate the exterior geometry produced by isolated slowly rotating Weyssenhoff fluids, i.e., sources endowed with both macroscopic and microscopic angular momenta. Our work represents an extension of the foundational analysis of Arkuszewski, Kopczyński and Ponomariev, which was restricted to the static fluid configuration. Under the assumptions of stationarity and axial
symmetry, we derive the explicit expression for the linearized stress-energy tensor of the source and obtain the corresponding metric through a multipole expansion. The ensuing solution exhibits a generalized Lense-Thirring structure, with both the gravitoelectric and gravitomagnetic sectors affected by the
quantum spin and macroscopic rotation. We also discuss some phenomenological implications of the model, including the gyroscope precession and the Sagnac effect, along with potential experimental probes of the predicted corrections.
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High Energy Astrophysical Phenomena
Spectral and Polarization Properties of Coherent Radio Emission from Relativistic Magnetized Pair Plasma Shocks
Yuanhong Qu, Joonas Nättilä and Lorenzo Sironi
Fast
radio bursts (FRBs) are millisecond-duration
radio transients whose emission mechanism remains an open question. The so-called synchrotron maser instability in relativistic magnetized shocks is a leading candidate for FRBs produced outside the compact object magnetosphere, yet its spectral and polarization predictions have not been systematically explored. We present three-dimensional particle-in-
cell simulations of relativistic magnetized pair
plasma shocks with upstream magnetization $\sigma > 1$ and bulk Lorentz factor $\gamma_0 = 10$, assuming a plane-parallel shock geometry and neglecting radiative cooling, and compute the spectra and polarization of the precursor maser emission for an arbitrary line of sight. For on-axis observers aligned with the shock-propagation direction, the X-mode dominates the emission. The O-mode power increases at off-axis viewing angles and is primarily associated with currents parallel to the upstream background
magnetic field. Assuming a spherical shock, we find full-width-at-half-maximum fractional bandwidths of $\Delta\nu/\nu_0\simeq0.57$ and $0.82$ for $\sigma=3$ and $6$, respectively. For highly magnetized shocks, the intrinsic emission bandwidth accounts for most of the spectral width, while high-latitude contributions provide additional broadening. The integrated emission remains highly linearly polarized near the spectral peak, with a nearly constant polarization angle due to the dominance of the X-mode. Our results suggest that synchrotron maser emission can produce spectra with bandwidths and high linear polarization degrees compatible with observations of some non-repeating FRBs, and may provide testable signatures for distinguishing shock-powered FRBs from other emission mechanisms.
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High Energy Astrophysical Phenomena
Infrared Cavity Surrounding T Pyxidis: Evidence of a Nova Super-remnant?
Michael W. Healy-Kalesh and Matthew J. Darnley
Nova super-remnants (NSR) are shell-like structures spanning tens of parsecs that are predicted to grow around all recurrent novae as a result of repeated ejecta sweeping up the surrounding material. After the first NSR was discovered in the Andromeda
Galaxy around M31N 2008-12a, a number of Galactic NSRs have been uncovered, as has the first NSR in the Large Magellanic Cloud. Here we report an apparent infrared cavity surrounding the Galactic recurrent nova, T Pyxidis, which we suggest may be a nova super-remnant and discuss the implications.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
A tidal disruption event in a quasar at redshift 7.19
S. Fujimoto, Q. Fei, G. B. Brammer et al. (+41 more)
We report a long-lived nuclear transient in GNz7q, a red
quasar at $z=7.19$ powered by a $\sim3\times10^{7}\,M_\odot$ black hole and hosted by a compact, dusty starburst
galaxy. The transient was identified in more than two decades of imaging with HST, Spitzer, and JWST. After a rapid rise, the source faded smoothly by $\Delta m\simeq1.1$ mag in the rest-frame ultraviolet over $\sim2$ rest-frame yr, with coherent, wavelength-dependent
evolution across 1–5 $\mu$m that places GNz7q above the 99.9th percentile of the SDSS
quasar variability distribution and is absent at $z\gtrsim5$. The duration and energetics disfavor superluminous
supernovae, and
stochastic quasar variability reproduces the multi-band
evolution with a probability of $\lesssim10^{-5}$. A panchromatic model combining a thermal continuum with a $t^{-5/3}$ decline reproduces the light curves, yielding a peak bolometric luminosity of $\simeq3\times10^{45}$ erg s$^{-1}$ and a radiated energy of $\simeq1.5\times10^{53}$ erg, which imply the tidal disruption of a
star of a few solar masses and place the event among the most energetic tidal disruption events (TDEs) known. A redshifted, extremely broad Balmer-line component in independent JWST/NIRSpec spectroscopy is consistent with a transient, non-virialized broad-line region. JWST/MIRI photometry further reveals delayed mid-infrared emission from $\simeq1500$ K dust at a sub-parsec radius, consistent with a dust echo of the
flare. The relatively low black-hole mass and dense
star-forming
nucleus of GNz7q are conditions under which TDEs are expected to be most efficient. These observations provide a time-domain view of episodic black-hole fueling and its dusty nuclear environment 700 million years after the Big Bang. Wide-field surveys with Roman and Euclid in the near-infrared, complemented by LSST at lower
redshifts, may uncover such transients in large numbers.
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All authors S. Fujimoto, Q. Fei, G. B. Brammer, K. Inayoshi, V. Kokorev, L. C. Ho, R. Li, F. Walter, V. Bromm, L. Colina, P. Dayal, S. L. Finkelstein, M. Ginolfi, Z. Liu, G. C. K. Leung, G. E. Magdis, J. Matthee, R. P. Naidu, P. Oesch, M. Onoue, P. G. Pérez-González, D. Watson, J. Álvarez-Márquez, J. Antwi-Danso, Y. Asada, G. Barro, C. M. Casey, J. Chisholm, S. Gillman, R. Marques-Chaves, J. P. U. Fynbo, T. R. Greve, I. Labbe, R. A. Meyer, F. Rizzo, A. Robbins, R. Schneider, C. L. Steinhardt, S. Toft, A. Trinca, F. Valentino, R. Valiante, M. Vestergaard, M. Xiao
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
SN Helios: A Multiply Imaged Type II Supernova Opening Time-Delay Cosmography beyond redshift of 3
Seiji Fujimoto, Conor Larison, Justin D. R. Pierel et al. (+64 more)
We report the discovery and spectroscopic confirmation of SN Helios, a strongly lensed, multiply imaged Type II
supernova (SN) at $z=3.34$ behind the
galaxy cluster RXC J0018.5+1626. The transient was identified as a red F150W-dropout source (F277W = 26.1 mag) in JWST/NIRCam imaging taken on 2026 July 3 for the VENUS survey, with no counterpart in 2024 December imaging. Director's Discretionary Time observations on 2026 August 17 added second-epoch NIRCam imaging and a deep NIRSpec prism spectrum. The spectrum shows a strong, spectrally resolved H$\alpha$ emission line (FWHM $\approx 7900$ km/s) with a P-Cygni absorption blueshifted by 8800 km/s, together with corresponding H$\beta$ and He I $\lambda$10830 features, establishing a hydrogen-rich photosphere at $z=3.34$. Template fits classify SN Helios as a Type II SN, and light-curve comparisons with well-studied local SNe II yield a phase of $27.5\pm2.8$ rest-frame days past B-band maximum. Independent cluster lens models magnify the observed image by $\mu\approx 10$-20 and predict another image within $\simeq 2$-6 yr, offering a rare opportunity for a time-delay measurement of $H_{0}$ with a source at $z>3$. The host
galaxy is undetected in deep rest-frame ultraviolet and optical imaging, in emission lines, and in ALMA 2 mm dust continuum, leaving a heavily obscured counterpart unlikely. Its de-lensed $M_{\rm UV}\gtrsim -13$ places it far below blank-field limits and adds support to an elevated core-collapse rate per unit
star formation in ultra-faint
galaxies. Without the multi-epoch data, SN Helios would masquerade as a convincing $z\approx 16$ Lyman-break
galaxy, with
galaxy-template fits strongly disfavoring any low-
redshift solution even with multiple medium bands. Its spectrum thus provides an empirical SED template with which high-
redshift searches can vet similar dropout candidates.
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All authors Seiji Fujimoto, Conor Larison, Justin D. R. Pierel, Lukas J. Furtak, Masamune Oguri, Adi Zitrin, Jose M. Diego, Keren Sharon, David A. Coulter, Gabriel Brammer, Vasily Kokorev, Chelsea Nash, Pedram Abedi, Christa DeCoursey, Armin Rest, Andreas L. Faisst, Brenda L. Frye, Tiger Yu-Yang Hsiao, Kohei Inayoshi, Kotaro Kohno, Jorryt Matthee, Matteo Messa, Yoshiaki Ono, Fengwu Sun, Eros Vanzella, Rogier A. Windhorst, Abdurro'uf, Aadya Agrawal, Joseph F. V. Allingham, Yoshihisa Asada, Hakim Atek, Maruša Bradač, Larry D. Bradley, Mateusz Bronikowski, Dan Coe, Christopher J. Conselice, Pratika Dayal, Eiichi Egami, Michael Engesser, Gavin Scott Farley, Qinyue Fei, Ori D. Fox, Yoshinobu Fudamoto, Miriam Golubchik, Yuichi Harikane, Gourav Khullar, Tomokazu Kiyota, Paulo A. A. Lopes, Ray A. Lucas, Guillaume Mahler, Ashish Kumar Meena, Rohan P. Naidu, Gautham Narayan, Gaël Noirot, Pascal A. Oesch, Masami Ouchi, José María Palencia, Massimo Pascale, Luke Robbins, M. R. Siebert, Roberta Tripodi, Francesco Valentino, Darach Watson, Hayley Williams, Hiroto Yanagisawa, Erik Zackrisson, Anita Zanella
High Energy Astrophysical Phenomena
Machine Learning $\beta$-decay Half-lives and Their Application to $r$-Process Observables
Mengke Li, Flora Wang, Jonathan Engel et al. (+3 more)
Accurately modeling $\beta$-decay half-lives of highly
neutron-rich
nuclei is a critical challenge for understanding $r$-process nucleosynthesis and the resulting kilonova light curves. We introduce a data-driven approach to model $\beta$ decay that uses Mixture Density Networks (MDNs) trained on the latest experimental measurements to extrapolate the half-lives of
neutron rich
nuclei. Unlike standard deterministic regression, the MDN directly parameterizes the probability distribution of the half-lives, providing intrinsic (aleatoric) uncertainty. We contrast the intrinsic uncertainty of a single model with the range of models produced by using random variations of the input training data samples. While all models show excellent agreement with experimental data, we find that varying the training data sets produces a wide range of extrapolations, particularly along data-poor regions such as the $N=126$ isotonic chain. We then propagate a selection of model results into $r$-process network calculations to evaluate their impact on isotopic abundances. Finally, by coupling the resulting isotopic abundances with thermalization efficiencies, we translate the effective nuclear heating rates into bolometric light curves. We compare the ranges of outcomes produced from the intrinsic uncertainty of a single model to those produced by multiple independent models trained on different training data sets.
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All authors Mengke Li, Flora Wang, Jonathan Engel, Matthew Mumpowe, Rebecca Surman, Nicole Vassh
High Energy Astrophysical Phenomena
Interaction of stellar dipole and disk magnetic fields in accretion-ejection systems
Somayeh Sheikhnezami and Sarah Aslani
We study jet formation from a magnetically diffusive, sub-Keplerian
accretion disk threaded by different
magnetic field configurations. We present two dimensional, axisymmetric MHD simulations in spherical coordinates employing the PLUTO code. Our results show that the reference simulation, in which the disk is threaded by an initial large scale poloidal
magnetic field, reaches a quasi steady state and produces a well collimated jet.Both kinetic and
magnetic torques are significant and evolve smoothly over time. The
accretion process is established smoothly, with about 26% of the accreting material being delivered into the outflow. Alternatively, applying a purely stellar dipolar
magnetic field produces weak and unstable outflows, characterized by inefficient angular momentum transport and strongly suppressed
accretion. Additionally, in simulations where the stellar dipolar
magnetic field is present alongside the disk's initial poloidal
magnetic field, the disk
magnetic field predominantly stabilizes the system. It also facilitates angular momentum transport from the disk and sustains a significant outflow mass flux. Furthermore, we performed additional simulations that explicitly include an inner gap associated with the disk truncation region. These simulations were designed as a robustness test of the treatment of the innermost disk region and confirm that our main conclusions are not sensitive to the presence of this gap. Overall, our findings demonstrate that although the magnitude of stellar dipole plays an important role in the
evolution of the
accretion-ejection structure, the large scale poloidal
magnetic field threading the disk is essential for launching and sustaining a stable and well collimated magnetized jet.
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High Energy Astrophysical Phenomena
Mass and spin properties of black-hole mergers reveal formation in triples
Jakob Stegmann and Aleksandra Olejak
Deciphering the formation channels of the observed binary black hole mergers remains a central open problem in gravitational-wave astronomy. With hundreds of detections, the inferred distribution of masses and
spins reveals a rich diversity which is difficult to reconcile with traditional formation scenarios from isolated binary
stars or dense stellar environments. Here, we consider the large fraction of massive progenitor
stars found in hierarchical triples and investigate black hole mergers driven by gravitational perturbations from tertiary companions. Simulations of their dynamics and stellar
evolution reproduce key features of the merger population, including: i) a sharp primary mass peak at $m_1\sim10\,\rm M_\odot$ dominating the population; ii) substantial fractions of systems with large
spin-orbit angles within and beyond the peak, matching the skewed distributions of the
spin parameters $\chi_{\rm eff}$ and $\chi_p$; iii) a mass-ratio distribution favouring equal masses with matching slopes. We further predict a sharp decline of mergers near $m_1\sim30\,\rm M_\odot$, coincident with the location of inferred features that may signal another channel dominating the high-mass tail. Our models of hierarchical triples demonstrate, for the first time, a formation scenario which simultaneously reproduces the principal properties inferred for the low-mass bulk of binary black hole mergers.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
Saturation Mechanism of Cosmic Ray Streaming Instabilities with a Shell Distribution
Mohamad Shalaby, Rouven Lemmerz and Christoph Pfrommer
Cosmic rays (CRs) drive galactic winds and regulate
galaxy growth while contributing to heating the central cooling
plasma in dense
galaxy clusters, making the nonlinear saturation of the instabilities that govern their transport a problem of central importance in astrophysics. Using fully kinetic particle-in-
cell (PIC) simulations, we find that the streaming instability driven by CRs with a shell momentum distribution saturates through gyro-phase bunching around driven Alfvén waves. Fluid-PIC (FPIC) simulations with both ideal and Landau closures reproduce the PIC saturation amplitude, and the same gyro-phase bunching mechanism, indicating that nonlinear Landau damping (NLLD) does not determine the saturation level at our simulation parameters ($v_{\rm A} = 0.01c$, $n_{\rm CR}/n_i = 0.01$). Notably, the CR ions fully isotropize in the Alfvén-wave frame in all simulations, including the FPIC run with an ideal closure in which NLLD is entirely absent, showing that this isotropization does not require NLLD. We additionally confirm, using the FPIC ideal closure, that this saturation amplitude is unchanged across a tenfold increase in domain size, indicating that the mechanism is local rather than dependent on domain-scale processes. Together, these results indicate that, at least in this regime, NLLD is not the dominant saturation mechanism for the CR streaming instability, in tension with common assumptions built into CR transport models used in
galaxy formation and interstellar medium simulations. Whether this conclusion extends to the lower CR densities and Alfvén speeds characteristic of the interstellar medium remains an open question that we address in an upcoming work.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
Non-linear dynamo waves in magnetized shear flows: a candidate mechanism for the solar cycle
Uddipan Banik
Large-scale
magnetic reversals in
planets,
stars, and
accretion disks require a non-linear theory coupling the
magnetic field to its sustaining flow. We derive exact non-linear solutions to incompressible magnetohydrodynamics in background rotational shear, with large-scale velocity and
magnetic fields linear in position (affine form). They reveal a cyclic feedback between meridional circulation, shear,
magnetic tension, induction, and the Coriolis force. The steady-circulation reversal orbit, or dynamo wave, periodically reverses all
magnetic components and supports slower modulations. In the solar near-surface shear layer (NSSL), moderate shear permits stable 11-year reversals with poleward speeds of 8-12 m/s and poloidal and toroidal amplitudes of 4-11 G and 2.2-3.8 kG near 1 Mm depth, in reasonable agreement with regional observations. At stronger shear, an 88-year reversal exhibits a 203-207-year modulation, reproducing the Gleissberg and Suess-de Vries activity timescales but requiring weaker poloidal fields. Such reversals, however, remain observationally unestablished. At tachocline density, an 11-year reversal and the inferred return flow require toroidal fields of hundreds of kilogauss over a broad shear range, exceeding large-scale-field reconstructions but partly permitted by seismic upper limits. This favors a shallow NSSL origin for a local cycle, while leaving open the issue of a global dynamo. Toroidal dominance prolongs the cycle because shear acting on a weak poloidal field changes only a small fraction of the stronger toroidal field per rotation. Balancing the weak
magnetic torque against advection and the Coriolis force also requires slow circulation, which gradually turns the poloidal field and reverses toroidal induction. Efficient poloidal regeneration would shorten this delay. A long solar cycle therefore favors a primarily shear-driven dynamo.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Metastable Neutron Stars as Transient-Rate Detectors of Heavy Dark Matter
Ziwen Yin and Hong-Yi Zhang
Metastable
neutron stars can undergo catastrophic conversion to
quark-containing
stars when a localized energy deposition nucleates a critical bubble. We show that dark-matter-induced conversions can be constrained by the present transient rate of the
neutron star population, rather than by the survival of any individual hadronic
star as often assumed in previous literature. Population depletion makes the present transition rate nonmonotonic: weak triggering produces few transitions, whereas sufficiently rapid triggering predominantly converts
stars formed in the past. Consequently, transient observations can exclude a finite interval of interaction rates, qualitatively different from conventional one-sided survival bounds. Using the beaming-corrected short gamma ray burst rate as a
benchmark, we derive constraints on dark matter annihilation, decay, inelastic particle scattering, and elastic scattering of macroscopic dark matter, including parameter space not covered by existing probes. Transient demographics thus provide a new population level probe of dark sector interactions and the phase structure of ultradense matter.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
The third law of black hole thermodynamics and the mass-to-charge ratio of scalar fields
Shahar Hod and Tsvi Piran
Kehle and Unger have recently shown that self-gravitating charged classical scalar fields can collapse to form extremal Reissner-Nordström (eRN) black holes in finite time, thus violating the third law of thermodynamics (TLT). Reall has subsequently proved that the formation of an eRN black hole in gravitational collapse is impossible if the mass-to-charge ratio of the field exceeds unity, $m/e\geq1$. In the present compact paper we
conjecture, using
quantum considerations, that the Reall bound is not sharp. In particular, we point out that the electric field of a charged system with charge $Q$ will spontaneously polarize the
vacuum in the regime $(eQ/\hbar)^2>(mQ/\hbar)^2+1/4$, thereby creating pairs of charged particles that discharge the black hole and ensure the
quantum validity of the TLT in this regime. Motivated by the TLT, we
conjecture that the classical Reall bound can be strengthened such that classical considerations would prevent eRN black holes from forming dynamically in the regime $m/e\geq\sqrt{1-\big({{\hbar}/{2eQ}}\big)^2}$, where
quantum polarization effects are unable to protect the TLT.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Stiffness corrections for f-mode neutron star universal relations
Isaac G. Chu and Carolyn A. Raithel
Excitations of the
neutron star (NS) fundamental mode (f-mode) during a binary NS inspiral or from a glitching
pulsar can produce gravitational waves (GWs) that will be detectable with the next generation of detectors, opening the door to GW asteroseismology of
neutron stars. There exist approximately equation-of-state (EOS)-insensitive, or "universal," relations that relate the f-mode to other NS properties. These universal relations have typically been identified with relatively small, selective EOS samples. To more thoroughly explore the parameter space, we examine the f-modes for a large sample of piecewise-parametric EOSs by solving the linearized fluid perturbation equations for the f-mode frequency and damping time in full general relativity. We utilize our sample to evaluate the EOS-sensitivity of previously-proposed universal relations (URs) for both the f-mode frequency and damping time. We find that URs that depend on combinations of only NS mass and radius have significant residuals, as previously reported; but that these residuals are strongly correlated with the overall stiffness of the EOS. We account for this residual dependence on the EOS by introducing linear correction terms that depend on the characteristic radius predicted by the EOS and the slope of the mass-radius curve at intermediate masses. To assess the impact of our new correction terms on observables, we consider the case of GW emission due to a glitch in a Vela-like
pulsar and demonstrate that the predicted signal-to-noise ratio for such an event is over/under-estimated by up to ~10% when using an existing, single-parameter UR, but is recovered nearly exactly with our improved 3-parameter UR. In contrast, we find that URs between the f-mode and tidal deformability exhibit only minimal EOS-dependent correlations in their residuals and overall remain highly EOS-insensitive.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Extending multi-messenger constraints on neutron star matter through the inclusion of direct Urca cooling
M. Dio Danarianto, Guilherme Grams, Thibeau Wouters et al. (+1 more)
The properties and behavior of strongly interacting matter at extreme densities can not only be determined through terrestrial experiments or through theoretical considerations, but also astrophysical observations of
neutron stars (NSs) and binary
neutron star systems become increasingly important to obtain complementary information. In light of these findings, we perform a
Bayesian study inferring the NS equation of state (EoS) by incorporating constraints from the direct Urca (dUrca) process, thereby including information on matter composition in addition to traditionally used macroscopic observables. We implement a self-consistent treatment of $\beta$-
equilibrium and charge neutrality in the jester framework, including the calculation of the
proton fraction and the onset of nucleonic dUrca in the presence of electrons and
muons. We combine constraints from chiral effective field theory, astrophysical measurements of NS masses, radii, and tidal deformabilities, and observations of rapidly and slowly cooling
neutron stars. The dUrca constraint seems to be in favor of stiffer EoSs, but –at the current stage– has only a minor impact on macroscopic NS properties once we include other nuclear and astrophysical constraints. In contrast, the dUrca information provides a constraint on the composition of canonical-mass NSs favoring a higher
proton fraction inside the
star, illustrating the complementary information carried by cooling observations. Our results demonstrate the potential of incorporating composition-sensitive observables into multimessenger inference and provide a step toward a more comprehensive treatment of dUrca constraints with microscopically motivated EoS models.
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All authors M. Dio Danarianto, Guilherme Grams, Thibeau Wouters, Tim Dietrich
High Energy Astrophysical Phenomena
A Helical Trajectory Interpretation of a Multi-wavelength Event in a Blazar S5 0716+714
Zhihao Ouyang, Jingyu Wu, Hubing Xiao et al. (+9 more)
Relativistic jets in blazars exhibit strong variability across multiple timescales, but the connection between temporal variability and the
evolution of jet structures remains poorly understood. In this work, we investigate the $\gamma$-ray variability of the BL Lac object S5 0716+714 from July 2014 to June 2015 and explore its possible connection with the parsec-scale jet
evolution. We identify an escalating periodic oscillation (EPO) in the $\gamma$-ray light curve, characterized by a sequence of successive flux enhancements with progressively increasing temporal separations. Combining Fermi-LAT data with contemporaneous 43 GHz Very Long Baseline Array (VLBA) observations, we find a temporal association between the EPO and the downstream propagation of a superluminal
knot. A helical trajectory model simultaneously fitting the $\gamma$-ray variability and the two-dimensional VLBA component positions reproduces the observed flux modulation and component motion. These results suggest that
geometric Doppler modulation caused by the changing viewing angle of a moving jet component provides a possible explanation for the observed EPO. This work provides a framework of connecting blazar variability to the
knot evolution of relativistic jets.
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All authors Zhihao Ouyang, Jingyu Wu, Hubing Xiao, Zhijian Luo, Zhu Chen, Shaohua Zhang, Liang Chen, Jianzhen Chen, Marina Manganaro, Luis C. Ho, Junhui Fan, Chenggang Shu
High Energy Astrophysical Phenomena
Exceptional Gamma-Ray Flaring Activity of the Blazar S4 0954+65 in Early 2025
Zhihao Ouyang, Jingyu Wu, Hubing Xiao et al. (+11 more)
S4 0954+65 (4FGL J0958.7+6534) is a TeV-detected blazar at a
redshift of $z = 0.3694 \pm 0.0011$, classified as an intermediate-synchrotron-peaked BL Lac object. In early 2025, it entered an exceptional $\gamma$-ray high state. We aim to investigate the origin and physical properties of the exceptional 2025
flare, and to constrain the emission processes responsible for this flaring activity. We performed a multi-wavelength analysis using $\gamma$-ray, X-ray, optical/UV,
radio, and 43 GHz Very Long Baseline Array (VLBA) observations. We examined multi-band correlations with the z-transformed discrete correlation function (zDCF), analyzed the spectral
evolution and parsec-scale jet kinematics, and modeled the broadband spectral energy distributions (SEDs). The $\gamma$-ray variations lead the optical and
radio emission by 3.22 days and possibly 18.26 days, respectively, while no significant correlation is found between the $\gamma$-ray and X-ray emission. The $\gamma$-ray spectra show a harder-when-brighter behavior, consistent with enhanced particle acceleration during the active state. A similar spectral trend is also observed in the X-ray band, where the
photon index is anti-correlated with flux. During the major $\gamma$-ray
flare, VLBA images reveal the emergence of a new superluminal
radio knot from the core, whose extrapolated ejection time is consistent with the peak of the $\gamma$-ray
flare. The temporal and structural
evolution during the 2025
flare is consistent with a shock-in-jet scenario, in which a newly emerging disturbance propagates downstream and drives the
flare. Broadband SED modeling shows that a leptonic synchrotron self-Compton plus external Compton model with dusty
torus seed
photons reproduces the multi-wavelength observations with physically plausible parameters. A lepto-hadronic interpretation remains possible but requires substantially higher jet power.
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All authors Zhihao Ouyang, Jingyu Wu, Hubing Xiao, Lili Yang, Shangchun Xie, Shaohua Zhang, Zhijian Luo, Jianzhen Chen, Jianguo Wang, Mingjun Liu, Qinyu Wu, Huaqing Cheng, Wenda Zhang, Junhui Fan
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR
A Multiwavelength View of $\rho$ Oph II: Disentangling the Variability of the Multi-Star Component C
Sean J. Gunderson, Walter W. Golay, Jackson Codd et al. (+8 more)
We present a multiwavelength analysis of the
star $\rho$ Oph C, covering X-ray, optical, near-infrared, and
radio observations to test for the presence of interferometrically-detected cool
star companions. The X-ray observations from Chandra, XMM-Newton, and NuSTAR show
flare-like events lasting minutes or days in time and spectral properties consistent with those of cooler
stars instead of the primary
magnetic B
star. The near-infrared data is also consistent with the proposed trinary system properties due to the presence of CO-band heads. After removing the primary B
star's rotation, the optical data from TESS shows a residual signal at the level of 0.8 mmags, matching the variations expected from cool
stars in orbit around a bright B
star. Finally, multi-epoch
radio data reveals that $\rho$ Oph C exhibits significant large scale flux variations that are atypical for a
magnetic massive
star. Taken as a whole, the multi-epoch and -wavelength data presents a consistent picture of $\rho$\,Oph\,C as a rare trinary system composed of a hot
star and two cool
stars.
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All authors Sean J. Gunderson, Walter W. Golay, Jackson Codd, David P. Huenemoerder, Felipe Navarete, Christiana Erba, Alexandrea Moreno, John M. Cannon, Richard Ignace, Pragati Pradhan, the MACRO consortium
High Energy Astrophysical Phenomena
Observational signatures of warped accretion flows in tidal disruption events
Andrew Mummery and Eliot Quataert
We analyze the possible observational signatures and
evolution of global warps in the
accretion flows produced in tidal disruption events. These warps are driven by Lense-Thirring torques resulting from the misalignment of the disk's rotation axis and the black hole's
spin axis. In a previous paper we argued that these global warps should be generically present in TDE
accretion flows as they enter a late-time thin disk phase of
evolution. We isolate three possible observational signatures of warps: (i) anomalous (reddened) late time optical colors, resulting from irradiative heating of the warped outer disk by the inner flow, (ii) delayed X-ray rises, resulting from the inner disk being slowly revealed to a distant observer as the warped flow gradually aligns with the
spin axis, and (iii) reverberation of turbulent X-ray
flares into optical/UV frequencies as the inner disk heats the outer disk during a flaring state. We present preliminary observational evidence that all three effects may have already been observed in TDE systems. Observations of TDEs may well offer the cleanest astronomical signatures of the strong-
gravity effects which cause disk warping, and provide unique constraints on the poorly understood
evolution of warped
accretion disks.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Multi-messenger and multi-band signal from first-order phase transitions in proto-neutron stars
Christian Ecker, Mauro Giliberti and Luciano Rezzolla
A first-order phase transition (PT) alters a compact
star on two scales: globally, via growth of a
quark-matter core, and microscopically, via collision of
quark bubbles, driving a simultaneous gravitational-wave (GW) emission in the kHz and MHz bands. Using a constrained ensemble of model-agnostic equations of state, we follow the
accretion-driven
evolution of proto-
neutron stars through the PT and compute the resulting multi-band GW signal. The correlations found between the kHz emission and the MHz burst could help constrain nuclear matter and the physics of the PT. A delayed
neutrino burst should accompany the signal, with the delay set by the details of the PT, thus providing a
prime multi-messenger source.
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High Energy Astrophysical Phenomena
AGN winds and outflows: from accretion-disc scales to the host galaxy
Delphine Porquet
Ultra-fast outflows (UFOs), launched from the inner
accretion disc in active galactic
nuclei (AGN), are among the
prime candidates for driving AGN feedback in their host
galaxies. Determining their physical properties and energetics is therefore essential for assessing their impact on
galaxy evolution. This review highlights recent observational progress, with particular emphasis on the groundbreaking insights enabled by high-resolution X-ray spectroscopy. The first X-Ray Imaging and Spectroscopy Mission (XRISM)/Resolve observations of AGN winds have revealed that the innermost UFOs are kinematically structured and inhomogeneous. In the archetypal
quasar PDS 456, these observations have led to a substantial upward revision of the inferred mass outflow rate, momentum flux and kinetic power. Complementary UV, optical, IR and mm observations trace the ionised, atomic and molecular phases of AGN-driven outflows from parsec to galactic scales. However, the physical coupling between the
accretion-disc wind and the galactic outflows remains one of the major unresolved questions in AGN feedback. Building on the pioneering XRISM results, NewAthena's X-ray Integral Field Unit (X-IFU) will characterise the physical properties and energetics of
accretion-disc winds with unprecedented precision from the local Universe up to
cosmic noon, while complementary multi-wavelength observations with facilities such as the Extremely Large
Telescope (ELT), James Webb Space
Telescope (JWST), Atacama Large Millimeter/submillimeter Array (ALMA), and Square Kilometre Array (SKA) will determine whether and how their energy and momentum are transferred to the host
galaxy.
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High Energy Astrophysical Phenomena · Cross-listed from physics.comp-ph
Monte Carlo sampling of first-order QED processes in laser and pulsar plasmas
Verneri Sarjomaa and Joonas Nättilä
Monte Carlo sampling of strong-field
quantum electrodynamics processes underpins simulations of high-intensity
laser experiments and of astrophysical compact-object magnetospheres. Sampling an event requires the total rate of the process together with the cumulative probability that determines how energy is partitioned between the produced particles. Simulations typically tabulate both in advance and invert the tabulated probability numerically. Here we replace this procedure with elementary-function approximations for synchrotron radiation and the nonlinear Breit–Wheeler process. For each process, we approximate the auxiliary function that sets the total rate, as well as the cumulative probability, with Padé approximants chosen so that the inversion reduces to a quartic equation. This yields the sampled
quantum parameter—electron $\chi_e$ or
photon $\chi_\gamma$—in closed form. The approximations and the particle spectra sampled from them agree with the exact results to within $1\%$. The procedure requires no lookup tables, no interpolation, and no numerical root finding, and can be inserted directly into radiative particle-in-
cell codes.
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High Energy Astrophysical Phenomena
Comparative spectro-temporal study between 1A 1246$-$588 and 4U 0614$+$091 using AstroSat
Suchismito Chattopadhyay, Soma Mandal and Ranjeev Misra
We present a comparative broadband spectro-temporal study of the ultra-compact X-ray binary (UCXB) candidates 1A 1246$-$588 and 4U 0614$+$091 using AstroSat observations. Spectral modelling shows that the spectrum of 1A 1246$-$588 is well described by thermal Comptonization and a soft thermal disk component. We identify a candidate narrow quasi-periodic oscillation (QPO) at $993\pm4$ Hz with a single-detector significance of $ ~ 3.7\sigma$, tentatively consistent with the upper kHz QPO previously reported from this source. An independent cross-instrument check does not confirm this feature, and we therefore treat it as a tentative, unconfirmed signature rather than a secure detection. In contrast, across the 4 observations, 4U 0614$+$091 evolves from a Comptonization-dominated hard state to a thermally dominated soft state, with the electron temperature decreasing from ~ 19 keV to ~2.3 keV, while the disk and blackbody temperatures increase. This
evolution is accompanied by an increase in the disk contribution to the total flux from ~ 18% to ~ 50% and the appearance of an Fe emission line near 6.97 keV in the soft state. The inner disk radius remains approximately constant at ~13- 15 $R_g$, suggesting that the observed
evolution is driven primarily by changes in the thermal properties of the
accretion flow rather than substantial variations in disk truncation. When the source is in its hardest state, it displays the richest timing behaviour, with variability components spanning from ~ 12 Hz to nearly 1 kHz, whereas the softer observations are dominated by low frequency variability, along with a persistent component near ~140 Hz and a prominent ~ 100 Hz feature in O4. These results suggest that progressive cooling of the Comptonizing corona, along with enhanced thermal emission from the disk and boundary layer, play a key role in shaping the spectral and timing
evolution of 4U 0614$+$091.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
A Census of Stellar-mass Black Holes in the Milky Way with POPKIN. I. Isolated Black Holes
Jian-Guo He, Yong Shao, Yu-Dong Nie et al. (+5 more)
Gravitational-wave observations have revealed hundreds of stellar-mass black holes, yet only about two dozen are known in the Milky Way, almost all in binaries. We present POPKIN, a Python framework that couples single- and binary-
star evolution with Galactic orbital dynamics to trace black-hole progenitors from the zero-age main sequence to the present-day isolated black-hole (IBH) population. Across ten models varying the
supernova (SN) prescription, mass-transfer efficiency, and common-envelope ejection efficiency, the total IBH abundance is controlled primarily by the SN prescription. Our fiducial model, with a recently proposed
metallicity- and stripping-history-dependent SN prescription, predicts $\sim4\times10^7$ IBHs in the
Galaxy, including $\sim8\times10^4$ within $1\,\rm{kpc}$ of the Sun; alternative SN prescriptions predict $\sim(1-2)\times10^8$ IBHs. The fiducial model yields a bimodal mass distribution, peaking near $9\,M_{\odot}$ and $20\,M_{\odot}$, with a deficit at $13-17\,M_{\odot}$. This distinguishes it from alternative prescriptions, some of which populate the $2-5\,M_{\odot}$ mass-gap region. Non-kicked IBHs follow nearly circular orbits near the Galactic plane, with typical peculiar velocities of $20-30\,\rm{km\,s^{-1}}$, whereas kicked systems undergo stronger radial migration and span a broader velocity range. We estimate $\sim5\times10^3$ accreting IBHs with $F_{\rm X}>10^{-14}\,\rm{erg\,s^{-1}\,cm^{-2}}$, nearly all non-kicked; this estimate is sensitive to the adopted radiative-efficiency and hot-flow treatments. For a Roman-like bulge survey, our fiducial model predicts $\sim360$ intrinsic IBH microlensing events over five years in a $1.70\,\rm{deg^2}$ effective area, before survey-selection effects. We propose that long-timescale microlensing events from IBHs can strongly constrain the SN physics governing stellar-mass black hole formation.
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All authors Jian-Guo He, Yong Shao, Yu-Dong Nie, Gui-Yu Wang, Xiao-Tian Xu, Chen Wang, Xiao-Jie Xu, Xiang-Dong Li
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
Binary-pulsar Timing: A 3D Solar-System Accelerometer and Unknown-Source Probe
Zheng-Long Wang, Zi-Qing Xia, Bo Zhang et al. (+1 more)
The acceleration of the Solar System barycenter (SSB) offers a unique precision probe of the local gravitational environment, enabling searches for otherwise invisible gravitating sources such as
Planet Nine and nearby (primordial) black holes. Using the binary-
pulsar timing measurements, we develop an analysis framework that combines the line-of-sight differential accelerations of 26 binary
pulsars to jointly reconstruct the three-dimensional acceleration of the SSB and place directional upper limits. Across three smooth Galactic-potential baselines, the residual acceleration is consistent with zero. We obtain directional 95% upper limits of $0.198$, $0.262$, and $0.693~\mu\mathrm{as}\,\mathrm{yr}^{-1}$ over 50%, 75%, and all sampled directions, respectively. These limits are tighter by factors of 3.5, 3.6, and 1.6 than a matched Gaia EDR3
benchmark and improve previous
pulsar constraints by more than an order of magnitude. We further extend the framework to the full SSB–
pulsar two-endpoint response, enabling direct position-dependent mass constraints on unknown gravitational sources. A $10\,M_\odot$ object is excluded within 0.39, 0.34, and 0.21 pc over the same sky fractions. Our unknown-mass limits surpass the tidal-equivalent INPOP19a reference beyond 0.2 pc by about an order of magnitude over most of the sky at 1 pc.
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All authors Zheng-Long Wang, Zi-Qing Xia, Bo Zhang, Yi-Zhong Fan
High Energy Astrophysical Phenomena
SN 2025aedz: A typical short-plateau type IIP supernova with rapid post-peak decline
Bo Wang, Luhan Li, Chengyuan Wu et al. (+5 more)
Type IIP
supernovae (SNe IIP) are the most common subclass of core-collapse SNe in observations. However, SNe IIP with short plateaus of the order of tens of days are rarely observed. The progenitors for this kind of SN can help to address the red supergiant issue in stellar
evolution. In this article, we report optical photometry and spectroscopy of SN\,2025aedz, a rapidly post-peak declining SN IIP with a typical short plateau. It exhibits a peak absolute magnitude of $M_r=-17.16\pm0.03$\,mag. The $r$-band light curve shows a steep early post-peak decline of $\sim5\,\mathrm{mag}\,(100\,\mathrm{d})^{-1}$ followed by a relatively short plateau, with a plateau duration of $\sim50\pm3$\,d. The overall spectral
evolution is consistent with that of normal SNe~IIP, showing a blue continuum with prominent Balmer P-Cygni profiles during the photospheric phase, followed by the gradual strengthening of hydrogen and metal lines as the ejecta cools down, although the metal lines remain weak and the expansion velocities decline rapidly. SN\,2025aedz is similar to the short-plateau SN\,2018gj in its overall
evolution, whereas its pronounced early decline resembles that of SN\,2023ufx, which has the shortest plateau duration known so far. The radioactive tail of the bolometric light curve implies a synthesized $^{56}$Ni mass of $\sim0.03\pm0.01\,M_\odot$. Motivated by the steep early decline, we performed radiation hydrodynamic simulations by exploring different circumstellar material configurations to reproduce its early bolometric light curve. These simulations indicate that SN\,2025aedz originated from a progenitor with a relatively low-mass hydrogen envelope, possibly produced through enhanced mass loss or binary interaction, while the steep early decline is likely explained by additional luminosity from circumstellar interaction.
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All authors Bo Wang, Luhan Li, Chengyuan Wu, Jujia Zhang, Yongzhi Cai, Yize Dong, Xuefei Chen, Zhanwen Han
High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA
Stellar Collisions from Self-consistent Stellar Dynamics Around Growing Supermassive black Holes
Fupeng Zhang and Pau Amaro Seoane
The centers of
galaxies harbor the densest stellar environments, where a massive black hole (MBH) accelerates
stars to such high velocities that direct collisions can result in high-energetic phenomena, such as gravitational wave sources, kilonovae, and
supernova-like transients. These collisions can reshape the cluster's density profile and release gas that can be subsequently accreted by the MBH. However, the evolving rates of such phenomena from self-consistent dynamics around mass-growing MBHs remain largely unexplored. In this work, we simulate nuclear
star clusters (NSCs) across a range of masses and density profiles by employing the GNC Monte Carlo code, that self-consistently models stellar dynamics and the subsequent
accretion of released gas. We find that stellar collisions flatten the density cusp in the innermost regions ($r \lesssim 10^{-3}-10^{-2}$ pc) within $\sim 0.1-1$ Gyr. While high initial collision rates in steep cusps quickly decline due to stellar depletion, the interplay between collisions and MBH growth is important only in massive NSCs ($M_\star \sim 10^9 M_\odot$). As MBH grows, increased stellar velocities shift the balance toward destructive collisions of which relative velocities can be $\gtrsim 2500 {\rm \,km\,s^{-1}}$. Consequently, present-day destructive collision rates in massive clusters remain high ($10^{-4}\sim 10^{-3}{\rm yr}^{-1}$), whereas they are smaller in Milky Way-like NSCs or negligible in smaller NSCs. Our results highlight a crucial synergy between stellar dynamics and MBH growth, identifying massive
galaxies as
prime targets for observing transients from destructive stellar collisions.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Learning Inspiral-Merger-Ringdown Waveforms from a Post-Newtonian Baseline
Arghya Chattopadhyay and Shilpa Kastha
Modeling the full inspiral-merger-ringdown signal requires combining analytically controlled inspiral physics with the nonlinear strong-field information supplied by numerical relativity. We represent the numerical relativity contribution beyond an analytic inspiral waveform as residual amplitude and phase corrections. Retaining the leading-order frequency-domain amplitude and the $3.5$ Post-Newtonian TaylorF2 phase, we use a Kolmogorov-Arnold network to learn these residual corrections from SXS waveforms. After training, the learned corrections are stored as explicit spline functions, so waveform evaluation no longer requires the network itself. On $75$ simulations excluded from training and model selection, the model achieves a median flat-noise mismatch of $2.7\times10^{-5}$. Our results demonstrate a machine learning driven waveform modeling strategy in which numerical relativity augments, rather than replaces, analytically known waveform structure.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Constraining the Quadratic-mode Amplitude Coupling in GW250114
Yuxin Yang, Changfu Shi and Yi-Ming Hu
Detecting quadratic quasi-normal modes in black hole ringdowns would provide evidence for nonlinear gravitational dynamics, while measuring their properties would enable tests of the corresponding predictions of general relativity. Specifically, second-order black hole perturbation theory predicts that their amplitudes scale with the product of the amplitudes of their parent linear modes, with a coupling coefficient that depends on the
spin of the remnant black hole. This mode-specific coupling coefficient has not yet been directly measured from gravitational wave data. Here, we use
Bayesian inference on the GW250114 ringdown, modeled with the $220$, $221$, and $220\times220$ modes, to infer the amplitude-coupling coefficient of the $220\times220$ mode. The inferred coefficient is consistent with predictions from numerical relativity fits and second-order perturbation theory; no comparison shows a deviation exceeding $1.3 \sigma$. Although the current data cannot distinguish among these
spin-dependent predictions, this measurement establishes a basis for more stringent observational tests of nonlinear gravitational dynamics in black-hole ringdowns.
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High Energy Astrophysical Phenomena
DETECT: Real-Time Identification of Transients with DESI Spectroscopic Redshift
Yu-Hsing Lee, Ting-Wan Chen, Ze-Ning Wang et al. (+10 more)
Wide-field surveys now report thousands of transients per month, while spectra are obtained for only a few per cent of them. We present DETECT (DESI–Transient Event Cross-matching Tool), a pipeline that turns each Transient Name Server (TNS) alert into a distance-informed candidate within an hour by placing it in the context of the Dark Energy Spectroscopic Instrument (DESI) archive. DETECT cross-matches every new report against the 22 million spectra of DESI EDR and DR1 through a HEALPix index, associates the transient with a host
galaxy by a directional-light-radius rule whose morphology-dependent thresholds are calibrated on 4,474
supernovae with known
redshifts (92.5% completeness, 0.4% wrong hosts), and passes ambiguous cases to a reviewer through a web interface. With a validated host
redshift it derives the peak absolute magnitude, the projected offset and basic host properties of each event, and ranks it for spectroscopic follow-up. Applied retrospectively to ~1.2x10^5 TNS reports from 2020–2024, DETECT recovers a spectroscopic host for 15% of them, from these we build a Gold Sample of ~5,400 well-sampled light curves whose luminosity distributions by class reproduce those of untargeted surveys. Because the absolute magnitude is known at discovery, intrinsically overluminous events stand out immediately: in the prospective 2025 run this is how the lensed superluminous
supernova SN~2025wny was flagged within hours of its report, and how faint, fast-declining kilonova candidates were screened against model grids and archival photometry. DETECT shows how an archival spectroscopic survey can make host
redshifts a routine part of transient triage ahead of the Rubin Observatory's LSST.
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All authors Yu-Hsing Lee, Ting-Wan Chen, Ze-Ning Wang, Sheng Yang, Limeng Deng, Chuan-Jui Li, K. C. Chambers, Thomas de Boer, Chien-Cheng Lin, Thomas B. Lowe, Paloma Mínguez, Gregory S. H. Paek, Richard Wainscoat
High Energy Astrophysical Phenomena
Recurrent double-peaked $\gamma$-ray sub-flares in PKS 1424-418
Na Wang, Tong Liu and Jingran Xu
We report a hint of recurrent double-peaked $\gamma$-ray sub-
flares in PKS~1424–418 during two similar major active epochs, MJD 56117–56498 and MJD 59669–59978. The candidate double-peaked sub-
flares show a characteristic intra-subflare peak separation of $\sim 11.8$ d and a neighbouring-subflare spacing of $\sim 67$ d. Red-noise Monte Carlo tests indicate that the candidate recurrent double-peaked morphology is not easily reproduced by
stochastic variability alone, with false-alarm probabilities of $p_{\rm a}=0.0216$ and $p_{\rm b}=0.0006$ for the two active epochs, respectively. In the simulations of the entire Fermi Large Area
Telescope (LAT) light curve, no red-noise realisation reproduces both epoch-like structures. The spectral energy distribution (SED) modelling shows similar radiative properties for the two peaks of one double-peaked candidate, while changes in the Doppler factor appear to play an important role in the flaring activity. Together with the previously reported near-zero lag between the millimetre and $\gamma$-ray emission, these results suggest that the recurrent activity may be associated with the compact mm/sub-mm core region. We discuss a possible structured-jet scenario in which a single disturbance propagates through a chain of quasi-stationary recollimation shocks. In this picture, repeated interactions between the disturbance and the shock structure may qualitatively account for both the double-peaked sub-
flare profiles and the observed $\sim 11.8$ d and $\sim 67$ d time-scales. Further active epochs are required to determine whether this similarity represents a recurrent long-term behaviour.
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