Peer Revenue Fully funded

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics High Energy Astrophysical Phenomena

astro-ph.HE Watch High Energy Astrophysical Phenomena

Monday 31 August

High Energy Astrophysical Phenomena

TeV Gamma Rays and Neutrinos from Winds Driven by Radiatively Inefficient Accretion Flows of Low-Luminosity Active Galactic Nuclei

Nobuyuki Sakai, John F. Beacom and Kohta Murase

Recently, the Large High Altitude Air Shower Observatory (LHAASO) reported the first TeV gamma-ray detection from a low-luminosity active galactic nucleus (LLAGN) lacking a strong jet. This source, NGC 4278, is one of the nearest LLAGNs that can be studied in detail as a template for more distant objects. Most previous studies have focused on the month-scale-variable gamma-ray activities, seeking to explain them with weak jets. We focus instead on NGC 4278's quiet-period emission, proposing a different mechanism based on a wind launched from a radiatively inefficient accretion flow (RIAF). In particular, we model particle acceleration at a wind-driven shock and calculate the resulting multimessenger emission. To match the TeV gamma-ray fluxes reported by LHAASO in the quiet period, our model requires a wind power of $\lesssim2\times10^{43}~\mathrm{erg~s^{-1}}$ with a spectral index of injected cosmic rays of 2.0. We show that this is achievable through Bondi accretion of the ionized gas observed on the 100-pc scale, for a shallow accretion profile. We discuss the testability of our wind-driven shock scenario with multimessenger observations. As another important application, we extend our model to Sgr A*, the nearest LLAGN, and show that its TeV gamma-ray emission is reproduced with reasonable parameters. Our results suggest that RIAF-driven winds may be a generic emission mechanism in LLAGNs, making this class a potentially important population of both gamma-ray emitters and cosmic-ray accelerators.
Read the full abstract

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

NS-UNO: Neutron Star EoS Inference from an Unconstrained Number of Observations

Valéria Carvalho, Márcio Ferreira, Michał Bejger et al. (+1 more)

Future multimessenger observations of neutron stars (NS) are expected to substantially increase both the number and precision of astrophysical constraints on the equation of state (EoS) of dense matter. This motivates inference frameworks capable of accommodating a variable, non fixed number of observations while preserving the posterior information associated with each measurement. In this work, we introduce NS-UNO, a Neural Posterior Estimation framework for NS EoS inference designed to accommodate an Unconstrained Number of Observations (UNO). NS-UNO combines a hierarchical DeepSets model with a conditional normalising flow, enabling a single trained model to perform inference from mass-radius observation sets of varying size, with each observation represented by a set of posterior samples. We demonstrate accurate and well calibrated posterior reconstructions using a model trained jointly on piecewise polytropic and non-parametric Gaussian process EoS ensembles. The reconstruction improves as observations probe a broader range of NS masses, while remaining robust to variations in the number and precision of the observations. The model also generalises to EoSs outside the families used during training. Finally, we qualitatively demonstrate the framework on current multimessenger constraints from NICER and GW170817. NS-UNO provides a flexible and scalable approach to NS EoS inference, naturally suited to the increasingly diverse observational datasets expected from next generation multimessenger astronomy.
Read the full abstract

All authors Valéria Carvalho, Márcio Ferreira, Michał Bejger, Constança Providência

High Energy Astrophysical Phenomena

Cascades from ultra-high-energy neutrinos

Gaetano Di Marco, Rhorry Gauld, Rafael Alves Batista et al. (+2 more)

Neutrinos produced at the highest energies can interact with cosmic neutrino and radiation backgrounds during their propagation to Earth. The many available $\nu\nu$, $\nu\bar{\nu}$, and $\nu\gamma$ channels can lead to their absorption or energy redistribution, whilst the leptonic and hadronic final states may feed secondary fluxes of neutrinos, protons, and electromagnetic particles through the decay or hadronisation of the heavy leptons, bosons, and quarks produced. We present a framework to characterise these propagation effects in detail, \texttt{$\nu$propa}, an extension of the CRPropa Monte Carlo code that interfaces with event generators and to dedicated computations of the relevant cross sections. It also treats flavour oscillations in vacuum. Using this code, we investigate sources at high redshifts ($z = 10$), and find a strong absorption of the prompt flux beyond~$\sim 10^{21} \; \text{eV}$, although the copious secondary neutrinos partially compensate this depletion, also contributing to the spectrum at lower energies. The framework is designed to study scenarios of cosmological neutrino production beyond~EeV energies such as superheavy dark matter, cosmic strings, and primordial black holes, and to yield reliable predictions for the forthcoming neutrino observatories.
Read the full abstract

All authors Gaetano Di Marco, Rhorry Gauld, Rafael Alves Batista, Alfonso García-Soto, Miguel Á. Sánchez-Conde

High Energy Astrophysical Phenomena

ALMA Observations of DEM L241/LMC P3 in the Large Magellanic Cloud: Evidence for the Formation of Cool Molecular Jets Driven by a Microquasar

Yasuo Fukui, Bhuvana G. R., Hidetoshi Sano et al. (+17 more)

We present ALMA observations of DEML 241/LMC P3, the most luminous $\gamma$-ray binary consisting of a compact object and an O star, in CO emission. We have found an one-sided jet-like CO feature of 8 pc length and 1 pc width, which accompanies another weaker CO jet candidate with slightly different orientation. The one-sided CO jet exhibits striking alignment with LMC P3, suggesting that the jet was driven by LMC P3. We have determined kinetic temperature of the CO jet to be significantly high at 33$-$60 K as compared with $\sim$15 K in the nearby non-jet CO cloud whereas no radiative heat source is found. We interpret that the high temperatures are due to shock heating of a microquasar jet driven by the $\gamma$-ray binary, where the compact object has an accretion disk fed by the O star winds. The CO jet matches existing predictions from magneto-hydrodynamical simulations, which show that CO jet can form from the interaction of the microquasar jet and an ambient ISM cloud. These results provide strong evidence that CO jets are a signature sculptured by microquasar jets, lending support for mass accretion in LMC P3 as the $\gamma$-ray origin. The results suggest a second case of CO jets potentially driven by a microquasar along with the CO jets in the microquasar candidate HESS J1023-575 recently identified in the Milky Way. Further, our results suggest the use of sub-mm observations for identifying microquasars, opening a new possible window for their discovery and study.
Read the full abstract

All authors Yasuo Fukui, Bhuvana G. R., Hidetoshi Sano, Kisetsu Tsuge, Rami Z. E. Alsaberi, Rin Yamada, Yuya Asano, Aya Bamba, Miroslav Filipovic, Charles Law, Norikazu Mizuno, Toshikazu Onishi, Paul Plucinsky, Gavin Rowell, Manami Sasaki, Piyush Sharda, Hiromasa Suzuki, Kengo Tachihara, Kazuki Tokuda, Yumiko Yamane

High Energy Astrophysical Phenomena

SNAD: enabling discovery in the era of big data

Maria Pruzhinskaya, Emille E. O. Ishida, Konstantin Malanchev et al. (+8 more)

In the era of wide-field surveys and big data in astronomy, the SNAD team is exploiting the potential of modern datasets for discovering new, unforeseen, or rare astrophysical objects and phenomena with machine learning (ML). The SNAD pipeline was built under the hypothesis that, although automatic ML algorithms have a crucial role to play in this task, the scientific discovery is only completely realized when such systems are designed to boost the impact of domain knowledge experts. Our key contributions include the development of the Coniferest Python library, which offers implementations of two active learning algorithms with an “expert in loop”, and the creation of the SNAD Transient Miner, facilitating the search for specific types of transients. We have also developed the SNAD Viewer, a web portal that provides a centralized view of individual objects from the Zwicky Transient Facility's (ZTF) data releases, making the analysis of potential anomalies more efficient. Finally, when applied to ZTF data, our approach has resulted in more than a hundred new supernova (SN) candidates, along with a few other non-catalogued objects, such as red dwarf flares, superluminous SNe, RS CVn type variables, and young stellar objects.
Read the full abstract

All authors Maria Pruzhinskaya, Emille E. O. Ishida, Konstantin Malanchev, Anastasia Lavrukhina, Etienne Russeil, Timofey Semenikhin, Sreevarsha Sreejith, Emmanuel Gangler, Matwey Kornilov, Vladimir Korolev, Alina Volnova

High Energy Astrophysical Phenomena

Hunting the nature of the Seyfert 1 galaxy GRS 1734-292: can it be a gamma-ray emitter?

Luigi Foschini

It has been proposed that the radio-weak Seyfert galaxy GRS 1734-292 is the counterpart of 3EG J1736-2908 and of the nearby Fermi/LAT source. I examine this identification, considering that the radio weakness could result from free-free absorption of a relativistic jet. An association with the EGRET detections is plausible, whereas the latest Fermi/LAT localization no longer favors GRS 1734-292. New observations, especially at radio frequencies of tens of GHz, would help to settle the issue.
Read the full abstract

High Energy Astrophysical Phenomena

SN 2019cqc: A Hydrogen-rich Superluminous Supernova Showing Electron-Scattering Signatures

Dinesh Hebbar, Rupak Roy, Matt Nicholl et al. (+15 more)

Hydrogen-rich superluminous supernovae without narrow emission lines (SLSNe-II) are rare transients whose powering mechanisms remain debated, particularly the role of circumstellar medium (CSM) interaction. We present photometric and spectroscopic observations of SN 2019cqc to investigate its power source and progenitor mass loss. We model the lightcurve using MOSFiT with the csm and csmni models to constrain the explosion and CSM parameters. SN 2019cqc peaked at $M_g = -20.21 \pm 0.07$ and emitted $\sim 1.7 \times 10^{50}\,\mathrm{erg}$ of energy in the form of radiation. Photometric and spectroscopic modeling indicates that CSM interaction dominates in both scenarios, with best-fit CSM and ejecta masses of $\sim 4.5~ M_\odot$ and $\sim 32~ M_\odot$, respectively. The inferred CSM properties imply an extreme eruptive mass loss at a rate of $\sim 0.2--0.3 ~M_\odot\,\mathrm{yr^{-1}}$ in the years preceding the core collapse, consistent with a variable progenitor of luminous blue variable progenitor. We observe a persistent blueshifted asymmetry in the H$\alpha$ emission line. At early times ($\lesssim +110$~d), this is attributed to electron scattering with bulk Velocity of ejecta, while the profile at late epochs ($\gtrsim +402$~d onward) suggests the subsequent formation of dust in the ejecta. Additionally, we identify a distinct, short-lived feature at $\sim$ 4600 Å , likely a blend of ionized C III/N III lines powered by the interaction of the SN-shock with the extended atmosphere.
Read the full abstract

All authors Dinesh Hebbar, Rupak Roy, Matt Nicholl, Jesper Sollerman, Joseph P Anderson, Mariusz Gromadzki, D. Andrew Howell, Tuomas Kangas, Seppo Mattila, Daichi Hiramatsu, Avishay Gal-Yam, Edo Berger, K. Azalee Bostroem, Ting-Wan Chen, Joseph Farah, Sebastian Gomez, Curtis McCully, Jeonghee Rho

Sunday 30 August

High Energy Astrophysical Phenomena

Advancing Fundamental Physics and Cosmology with high-resolution X-ray imaging

Sara Turriziani, Herman L. Marshall, Daryl Haggard et al. (+4 more)

Black Holes are the key to solving many unanswered questions in fundamental physics: in particular, the very extreme properties shown by supermassive black holes at the centers of galaxies make them obvious candidates for testing gravity theories in the strong-field regime. Since X-rays are generated by matter under extreme physical conditions, ultra-high resolution X-ray imaging (uXRI) will directly image the region near the event horizon of black holes in X-rays, similar to the Event Horizon Telescope in the radio band, enabling unprecedented tests of General Relativity and alternative theories of gravity near supermassive black holes. On the other hand, clusters of galaxies hold the potential of unveiling many unknowns in cosmology. uXRI will unlock this potential by probing small-scale plasma properties in the intracluster medium, providing the missing link required to establish galaxy clusters as reliable tools for high-precision cosmology. Moreover, uXRI will enable mapping of Dark Matter from galaxy cluster dynamics via proper motion measurements. Finally, uXRI will open a new field of precision X-ray astrometry, allowing for measuring pulsar parallaxes to support nanoHertz gravitational wave searches.
Read the full abstract

All authors Sara Turriziani, Herman L. Marshall, Daryl Haggard, Scott Randall, Mayura Balakrishnan, Tom Maccarone, Nicole Ford

High Energy Astrophysical Phenomena

Vortex pinning and the elastic response of neutron-star crusts - I. Axisymmetric loading

Elia Giliberti and Gabriele Cambiotti

Vortex pinning is central to the standard interpretation of pulsar glitches, but the mechanical load exerted by a pinned vortex array on the solid crust has received less attention than the angular-momentum reservoir itself. We calculate the axisymmetric elastic response of a continuously stratified neutron-star crust to this load using realistic SLy4 and BSk21 stellar backgrounds and composition-dependent Coulomb shear moduli. The superfluid-crust lag sets the Magnus force, while the mesoscopic pinning force of Seveso et al. (2016) provides a local upper bound. At low lag the response is linear; progressive local saturation then produces a broad transition and a finite high-lag envelope. The stress maximum is robustly located at the deep crustal boundary towards the rotation axis, although the local Magnus force vanishes on-axis, showing that the localization is produced by global elastic-gravitational redistribution. Realistic elasticity changes the stress amplitude by 10-20 per cent relative to the common mu=10^-2 P prescription and reverses the SLy4-BSk21 ordering. At a Vela-motivated lag of 10^-2 rad s^-1, the maximum strain is only 3.1 x 10^-5 (SLy4) and 4.7 x 10^-5 (BSk21), remaining below 1.4 x 10^-4 on the formal plateau. A 1.2-2.0 solar-mass scan changes the stress amplitude by only about 20 per cent and leaves the deep-polar localization unchanged. Pinning therefore supplies a structured and astrophysically relevant crustal pre-stress, but cannot by itself break an initially relaxed crust.
Read the full abstract

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.CO

Spheroidal Resampling Analysis of High-Redshift Gamma-Ray Burst Spatial Densities

Istvan Horvath, Zsolt Bagoly, Lajos G. Balazs et al. (+6 more)

Gamma-ray bursts (GRBs) are bright transient sources that can be observed at high redshift. They can therefore be used as tracers of the distant large-scale structure, although the GRB redshift sample is sparse and affected by strong selection effects. We analyze the three-dimensional distribution of 542 GRBs with spectroscopic redshifts. The method extends our earlier spherical-window search by replacing spherical counting volumes with axisymmetric spheroids. The angular positions of the observed GRBs are kept fixed in the Monte-Carlo null samples, while the redshifts are shuffled within each Galactic hemisphere. In the Northern Galactic hemisphere, the overdensity associated with the Hercules–Corona Borealis Great Wall remains significant for a range of spheroidal shapes. This supports the stability of the previously reported signal and shows that it is not only a consequence of using spherical counting volumes. In the Southern Galactic hemisphere, the same method finds no structure with comparable significance. A small candidate grouping is present, but its significance is only marginal, and it is sensitive to the small number of events. We conclude that spheroidal resampling is a useful check of GRB overdensity searches, but the physical nature of any candidate structure still requires confirmation with independent tracers such as galaxy or quasar samples.
Read the full abstract

All authors Istvan Horvath, Zsolt Bagoly, Lajos G. Balazs, Jon Hakkila, Janos Horvath, Sandor Pinter, Istvan I. Racz, Peter Veres, Bendeguz Koncz

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

The multi-frequency radio light curve of the sub-pc SMBH binary candidate PG 1302-102

Sayan Basu, Roger P. Deane and Keith W. Bannister

Supermassive black hole binary (SMBHB) candidates with sub-parsec (sub-pc) orbital separations are rare, high-value systems, thought to be the dominant sources of the recently detected nanoHertz (nHz) gravitational wave (GW) background. Alongside pulsar-timing-array searches for localized nHz GW sources from SMBHBs, an increasing number of candidates have been identified from synoptic surveys of large quasar optical light curves over increasingly long baselines. The optical light curve of the quasar PG~1302-102 at a redshift of $z=0.278$ exhibits a pronounced, smoothly varying periodic signal of ~5.2 years over approximately 20 years. Although the cause of this periodicity remains debated, a plausible explanation is a binary system of two SMBHs with a sub-pc separation. At this close distance, the $10^{8.3-9.4} M_{\odot}$ nuclear black holes in PG 1302-102 are expected to merge within $\sim$$10^{5}$ yr solely due to GW emission. We present a multi-frequency radio light curve analysis of PG~1302-102 spanning a $\sim$19-year baseline, with observations between 2005 and 2024 drawn from the Australian Telescope Compact Array (ATCA). The ATCA radio light curve is highly variable at 5.5~GHz but shows no significant evidence of the periodicity seen at optical wavelengths. However, we report fractionally stronger evidence of periodicity in the in-band spectral index time-series at 5.5~GHz, with a period consistent with the optical periodicity. Furthermore, the recently reported change in optical periodicity is also present in the radio in-band spectral index light curve. These two results suggest that radio and optical periodicity may be physically coupled despite very different emission mechanisms. We argue that this radio-optical coupling reinforces the SMBHB interpretation, despite the optical periodicity change, and provides an intriguing case study ahead of the LSST-SKAO era.
Read the full abstract

High Energy Astrophysical Phenomena

Photon–Dark Matter Elastic Scattering: An Effective-Operator Scan and First Operator-Resolved Sensitivity Estimates from the Galactic Halo

Trinity Rosebud Stenhouse, Asli Acar, Mikhail Bashkanov et al. (+3 more)

Elastic photon–dark matter scattering attenuates gamma-ray spectra along a line of sight, probing the same operators as dark matter annihilation to photons but at a rate linear, rather than quadratic, in dark matter density. We consider Standard Model gauge-invariant effective operators of mass-dimension 5 to 7, suppressed by a cutoff scale $\Lambda$, coupling scalar, Majorana or Dirac dark matter to the photon. The leading operators with non-vanishing real-photon amplitudes enter at dimension-5 for Dirac dark matter and dimension-7 for Majorana dark matter. In the electroweak-doublet dipole portal, the inelastic splitting invoked to evade direct detection also closes the CMB annihilation bound, leaving attenuation the only one of the three photon-sector probes that survives. Applying this to a pixel-level reanalysis of 17 years of Fermi–LAT Pass~8 data toward the Galactic centre, we derive the first operator-resolved sensitivity estimates for photon–dark matter scattering from the Galactic halo: $\Lambda \simeq 0.32~\mathrm{GeV}$ for the dimension-5 Dirac dipoles, $0.21~\mathrm{GeV}$ for the dimension-6 scalar Rayleigh operator and $0.79$–$1.06~\mathrm{GeV}$ for the dimension-7 Rayleigh family. The reach is weak: it lies below the EFT-validity threshold across the cold dark matter mass range, and is superseded on the dipole plane by CMB and direct-detection constraints. The framework is calibrated against pseudo-experiments, and recomputes the sensitivity for any instrument that provides a per-bin spectrum with uncertainties and a line-of-sight column density.
Read the full abstract

All authors Trinity Rosebud Stenhouse, Asli Acar, Mikhail Bashkanov, Frank F. Deppisch, Chamkaur Ghag, Dan P. Watts

Saturday 29 August

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

How much of the black hole ringdown is sourced within the light ring?

Mark Ho-Yeuk Cheung

Not much. It has been proposed that applying a rational filter to a black hole ringdown gravitational waveform reveals a direct wave component sourced near the event horizon. By solving the Teukolsky equation for a point particle plunging into a Kerr black hole, I show that the maximum amplitude of the waves sourced within the prograde light ring is $\lesssim 10\%$ that of those sourced by the full trajectory no matter if the waves are filtered or not. This agrees with the interpretation of quasinormal modes as waves orbiting the light ring and the direct wave as the power of these modes redistributed in time. Therefore, both quasinormal modes and direct waves are more a probe of the light ring than the near-horizon region. For GW250114, I estimate that the component of the waves sourced within the light ring have a signal-to-noise ratio $\rho \lesssim 1$ measured after the peak of the filtered waves.
Read the full abstract

High Energy Astrophysical Phenomena

Rapid Energy Dissipation by Colliding Waves in Strongly Magnetized Plasmas

Tianshu Wu, Xinyu Li and Yangyang Cai

Rapid dissipation of magnetic energy in highly magnetized environments around neutron stars and black holes is a key open question in high-energy astrophysics. We develop a general kinetic picture of counter-propagating wave collisions in magnetized pair plasmas for arbitrary polarizations and find that magnetic energy can be dissipated on the wave-crossing timescale. The two magnetohydrodynamical conditions on the field invariants, $I_1\equiv B^2-E^2>0$ and $I_2\equiv \mathbf{E}\cdot\mathbf{B}=0$, can be spontaneously violated during the collision. Parallel electric fields develop to screen nonzero $I_2$ with little energy loss, consistent with the evolution described by Force-Free Electrodynamics. When magnetic dominance is lost, strong particle energization is triggered, dissipating magnetic energy on the wave-crossing timescale. This dynamical process yields a rapid dissipation channel of magnetic energy and provides a kinetic pathway to high-energy emission.
Read the full abstract

High Energy Astrophysical Phenomena

Evidence for an accretion-driven subpopulation of black holes in GWTC-5.0

Zacharias Roupas

We report Bayesian evidence for a subpopulation of black holes, grown via accretion during the gaseous birth-stage of star clusters, in the cumulative GWTC-5.0 released by the LIGO-Virgo-KAGRA collaboration. This accretion channel predicts a saturating spin–mass relation, with low spins at low masses, rising continuously with mass through all intermediate spin values, to high spins at high masses. We test this prediction directly against the component spins of the catalogue. We single out 10 events with positive support and many others with weaker support across the whole component-mass range of the catalogue. We identify a preferred mass scale $m^t=20.7^{+11.6}_{-1.2}\,M_\odot$ (90% credibility) separating regimes with different accretion-mixture fractions, with $\ln B=5.5$. Above this inferred scale, the evidence for an accretion-driven subpopulation is strongly concentrated, reaching a natural log Bayes factor of $16.6$ against the LVK fiducial spin population.
Read the full abstract

High Energy Astrophysical Phenomena

Little Red Dots as Shock-Powered High-Energy Neutrino Sources

Tyco Mera, Chris Ashall, Shunsaku Horiuchi et al. (+3 more)

Little Red Dots (LRDs) are compact, high-redshift sources whose physical nature remains uncertain. Their optical spectra bear many similarities to Type IIn supernovae (SNe IIn), motivating a scenario in which their emission is powered by shocks interacting with dense surrounding material. We investigate whether such interactions can power LRDs and contribute to the diffuse high-energy neutrino intensity measured by IceCube. In our simplified model, a fast central-engine outflow drives a shock through dense surrounding material before stalling near the LRD photosphere, while some material continues to flow through the shock. We explore parameter ranges motivated by SNe IIn and the observed and inferred properties of LRDs, finding solutions with shock luminosities from 2.2e43 to 3.5e44 erg/s. Using an analytical framework for cosmic-ray acceleration and hadronic interactions in dense shock environments, we calculate the resulting high-energy neutrino emission and integrate it over the cosmological LRD population. For our fiducial SNe IIn-based cosmic-ray parameters, the average predicted contribution below 2e5 GeV increases from about 0.2% for the lowest-luminosity quintile to about 2% for the highest-luminosity quintile, while an illustrative higher-efficiency case reaches about 13% of the IceCube diffuse neutrino intensity. The incompleteness of the current LRD census and uncertainties in their physical nature limit constraints on the cosmic-ray parameters and the distribution of L_s. Larger LRD samples, together with improved physical models and a full population-synthesis study, will be required to constrain the total LRD contribution to the diffuse neutrino background.
Read the full abstract

All authors Tyco Mera, Chris Ashall, Shunsaku Horiuchi, Rohan Naidu, Kyle Medler, Peter Hoeflich

Friday 28 August

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

A Unified Treatment of the Self-Force Problem

Beka Modrekiladze, Ira Z. Rothstein and Jordan Wilson-Gerow

This paper introduces formalism, based on worldline effective field theory, which allows one to systematically calculate the gravitational self-force on a compact object immersed in an environment with non-vanishing stress energy. Using the closed time path integral we present a universal effective action that can be used to calculate the equations of motion of a compact object due to its interaction with the environment to any order in the relevant expansion parameters, the relative importance of which depends upon the choice of environment. We show that the leading order equations of motion can be universally written in terms of the retarded two-point function of the stress-energy tensor for the environment. The resulting action can be used to calculate both dissipative (dynamical friction) and conservative forces in a completely relativistic fashion. We demonstrate the utility of the result by calculating the dissipative force due to dust, an inviscid fluid, and a coherent field. Our results agree with those previously derived in the literature. We furthermore show that the famous “Coulomb Log" found by Chandrasekhar should be interpreted as a renormalization group log due to a UV divergence that renormalizes the dissipative part of the in-in action. We then prove that this log is universal in the Newtonian limit in that its value is universal, for a generic class of environments and trajectories. This log is the leading log in an RG flow in the dissipative action that has yet to be explored.
Read the full abstract

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM

Lynx2030 Science Analysis Group: Final Report

Lynx2030 Science Analysis Group: Simon R. Bandler, Laura W. Brenneman, Nico Cappelluti et al. (+50 more)

The Lynx2030 Science Analysis Group (SAG) was convened to reassess the scientific goals and technical drivers of the Lynx mission concept amid a rapidly evolving astrophysics landscape. Building on the original Lynx Concept Study, the SAG examined how recent discoveries, emerging facilities, and advances in instrumentation influence the scientific opportunities for a next-generation flagship X-ray observatory. Through focused working groups, the SAG investigated the scientific impact of enhanced capabilities: (i) improved angular resolution, (ii) broader bandpass coverage, (iii) an enhanced microcalorimeter, (iv) new capabilities and observing modes, and (v) larger fields of view. Across a broad range of topics, from the formation of the first black holes and the evolution of galaxies to the baryon cycle, compact objects, stellar explosions, multi-messenger astrophysics, and the dynamic high-energy Universe, the SAG finds that the scientific motivation for a Lynx-class observatory remains compelling and, in many areas, has significantly strengthened over the past decade, prominently through JWST's discovery of the "Little Red Dots", likely massive accreting black holes in infant galaxies whose nature is fundamentally an X-ray question. This report shows that modest extensions beyond the original Lynx design reference mission can unlock transformative science while preserving the observatory's core architecture. Powerful current and future facilities such as Roman, Rubin, JWST, SKA, ngVLA, LISA, and NewAthena highlight the unique role a high-angular-resolution, high-throughput X-ray observatory would play in the multi-wavelength and multi-messenger ecosystem of the 2030s and beyond. The findings of the Lynx2030 SAG confirm Lynx's central vision: an unprecedented view of the hot and energetic Universe, enabling discoveries that will define high-energy astrophysics in the coming decades.
Read the full abstract

All authors Lynx2030 Science Analysis Group: Simon R. Bandler, Laura W. Brenneman, Nico Cappelluti, Daniel Castro, Steven R. Ehlert, W. Peter Maksym, Fabio Pacucci, Scott W. Randall, Grant R. Tremblay, John ZuHone, Steven W. Allen, Antara R. Basu-Zych, Akos Bogdan, Joel N. Bregman, Tamta Burduli, Thomas Connor, Sanskriti Das, Casey DeRoo, Stephen DiKerby, Paul A. Draghis, Martin Elvis, Giuseppina Fabbiano, Ralf K. Heilmann, Jimmy A. Irwin, Amruta Jaodand, Margarita Karovska, Vinay L. Kashyap, Anthony A. Kerr, Caroline Kilbourne, Ralph Kraft, Jiangtao Li, Labani Mallick, Herman L. Marshall, Michael L. McCollough, Anna Ogorzałek, Frederik Paerels, Daniel Patnaude, Paul Plucinsky, David Pooley, Frederick S. Porter, Daniele Rogantini, Roger Romani, Helen R. Russell, Kazuhiro Sakai, Mark Schattenburg, Dan A. Schwartz, Malgorzata Sobolewska, Paolo Soffitta, Alexey Vikhlinin, Daniel R. Wilkins, Scott Wolk, Ka-Wah Wong, Irina Zhuravleva

High Energy Astrophysical Phenomena

Anomalous horizontal track-like events at the HAWC observatory: candidate neutrino-induced charged leptons from the Pico de Orizaba volcano

Hermes León Vargas and Andrés Sandoval

Two track-like events with exceptionally large charge deposits, pointing back to the region of maximum overburden ($>18$ km.w.e.) of the Pico de Orizaba volcano, were reported by the HAWC Collaboration in a search for Earth-skimming neutrinos. Using exclusively published information, including the published Monte Carlo charge distributions and the scattered-muon background model, we show that these events are kinematically inconsistent with all identified backgrounds. A conservative energy-conservation bound places the in-tank energy deposit of the candidates above $\approx$190–210~GeV, with a worst-case minimum of 122–136~GeV, in either case exceeding the 100~GeV maximum of the scattered-muon background model. Calibration systematics derived from the published simulations act unidirectionally, pushing the implied deposits into the multi-TeV regime. Direct atmospheric muons require $E_\mu \gtrsim 0.67$~PeV to penetrate the overburden and contribute $4.5\times10^{-5}$ expected events ($\lesssim 10^{-3}$ under the largest possible prompt-charm flux); collinear muon bundles are excluded by five independent arguments. Conversely, the neutrino hypothesis predicts identifiable events precisely in the observed charge window ($10^{3}$–$10^{4}$ photoelectrons) and in the highest-overburden analysis region, both observed. The two track-like events imply a rate that exceeds the conventional atmospheric neutrino flux expectation at the 2.1–2.5$\sigma$ level. The charges of the observed candidates require an emerging lepton above about 20~TeV; the published calibration does not bound the energy from above. These would constitute the first neutrino candidates detected in Mexico and the first obtained with the Earth-skimming volcano technique.
Read the full abstract

High Energy Astrophysical Phenomena

A Self-Sustaining Black Hole Engine Powered by the Tidal Disruptions of Stars

James Guillochon and Avi Loeb

Tidal disruption events (TDEs) strongly prefer host galaxies undergoing, or recovering from, a burst of star formation, implying that a rare minority of galaxy types produces most events. The required per-galaxy rates, as high as $10^{-2}$ gal$^{-1}$ yr$^{-1}$, are hard to achieve through stellar relaxation alone. Molecular clouds surrounding nuclear clusters help set the relaxation rate, offering a path to higher rates. We show that (post-)starburst galaxies, whose nearby prototypes contain large molecular gas reservoirs, are likely in a self-sustaining cycle: an enhanced disruption rate compresses the surrounding clouds through momentum injected by the unbound debris, the denser clouds compress the cluster, and the cluster disrupts stars faster still. The runaway is arrested only when stars begin to collide. Solving for the steady state, the rate saturates at $1.4\times10^{-2}(M_{\rm h}/10^{6}M_\odot)^{-0.84}$ yr$^{-1}$, two orders of magnitude above the canonical rate at $10^{6}M_\odot$, with a normalization uncertain by a further two orders of magnitude through the stellar collision rate. Three independent requirements — that tidal debris outweigh AGN feedback, that the molecular clouds fit within the disk that holds them, and that the cusp be no denser than observed nuclei — bound the flattening of the stellar cusp to $0.18 \lesssim f_\ast \lesssim 0.25$. Because no engine can run below a threshold black hole mass, holes seeded beneath it stay dark until accretion carries them across, switching on after $\sim 1$ Gyr and offering a natural explanation for the late peak recently measured in the TDE delay time distribution. The nucleus is buried under $A_V \simeq 50$ whatever its geometry, so most such disruptions should be hidden from optical surveys and emerge instead in the infrared.
Read the full abstract

High Energy Astrophysical Phenomena

A Terrestrial Gamma-ray Flash with an Asymmetric Footprint Observed at the Pierre Auger Observatory

The Pierre Auger Collaboration, John Ortberg, David M. Smith et al. (+1 more)

The Pierre Auger Observatory, a $3000km^2$ detector array that sits 1400m above sea level in Argentina, has the ability to map the entire footprint of Terrestrial Gamma-ray Flashes (TGFs), which are short, intense bursts of gamma rays associated with lightning. This is in contrast to the vast majority of TGF detections that only occur in a single detector in space. In this paper we leverage this capability to perform two important analyses on an event from 2007, chosen for its large footprint and high signal quality. First, we triangulate the source of the TGF to $2.3\pm0.5$km height above ground level using the arrival time of the gamma rays themselves at the detector array, independently of any information regarding the lightning channel. With the source position established, we can analyze the spatial distribution of the TGF on the ground with respect to that source. Not only do we find that one side of the TGF footprint shows an order of magnitude higher flux than the other, but we also find an asymmetric azimuthal structure consisting of two clear peaks in intensity. These peaks are offset by about $120^o$ from each other. This azimuthal structure is not possible under the traditional uniform electric-field model of a TGF. Using Geant4 simulations of collimated beams of the relativistic runaway electron-avalanche spectrum, we attempt to reconstruct the source geometry of the TGF and find that it likely had significant components in the $\theta > 75^o$ range, where $\theta$ is the off-nadir angle.
Read the full abstract

All authors The Pierre Auger Collaboration, John Ortberg, David M. Smith, Joseph Dwyer

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Strongly coupled quark matter in neutron stars and their mergers

Konstantin Maslov, Ralf Rapp, Joaquin Grefa et al. (+2 more)

The discovery of the strongly-coupled quark-gluon plasma (sQGP) in high-energy heavy-ion collisions has revealed remarkable properties of matter at high temperature, with transport coefficients close to conjectured bounds from quantum field theory at strong coupling. The high sQGP collision rates imply very large energy uncertainties and the melting of quasiparticle structures. Deploying quantum many-body theory based on the self-consistent $T$-matrix approach for the sQGP at high temperature, we investigate its manifestation at high baryon density and low temperature, as present in neutron stars and their mergers. We constrain the chemical-potential dependence of the quark interaction kernel using first-principles information from Quantum Chromodynamics on baryon-number susceptibilities. Very large collisional widths persist at large density and are found to relegate superconducting phases to rather small temperatures. Instead, a strongly coupled diquark liquid prevails in the thermodynamics under the conditions relevant to neutron-star mergers. At lower densities, the diquarks take over from the single-quark contributions, suggesting a pathway toward hadronization. Our results are consistent with observational constraints on the equation of state of neutron stars, corroborating the presence of strongly coupled quark matter in the interior of these objects.
Read the full abstract

All authors Konstantin Maslov, Ralf Rapp, Joaquin Grefa, Veronica Dexheimer, Claudia Ratti

High Energy Astrophysical Phenomena

Decisive evidence for a global cosmic-ray feature in gamma-ray data

Fernando Valenciano, Pedro De la Torre Luque, Daniele Gaggero et al. (+1 more)

We analyze 17 years of Fermi-LAT data to study the diffuse $\gamma$-ray emission along the Galactic plane and its connection to cosmic-ray (CR) propagation. Accounting for correlated instrumental systematics, we find decisive evidence for a spectral break at $\sim20-30$ GeV, present across the inner Galactic disk, with a preference of $\Delta\chi^2=39.78$ ($4.44 \sigma$ global). The energy and amplitude of this feature are in striking agreement with the spectral feature observed in local CR nuclei, indicating that it is a global property of the Galactic disk rather than a local phenomenon. The measured slope change, $\Delta\gamma \simeq 0.20$, is consistent with local CR data and with expectations from a transition in the CR diffusion regime from Kolmogorov to Kraichnan turbulence. Our results provide strong evidence that diffuse $\gamma$-ray emission along the Galactic disk is dominated by $\pi^0-$decay emission up to a hundred GeV. These findings provide key insights into the origin of the CR spectral hardening and the propagation of CRs throughout the Galaxy, and illustrate how this multimessenger approach can be used to probe the origin of features in the CR spectra, such as the long-studied CR Knee.
Read the full abstract

All authors Fernando Valenciano, Pedro De la Torre Luque, Daniele Gaggero, Jorge Martin Camalich

High Energy Astrophysical Phenomena

Galactic Science with Ultra-High Angular Resolution X-ray Imaging

Paul A. Draghis, Jeremy Hare, Mayura Balakrishnan et al. (+8 more)

Milli- to micro-arcsecond X-ray imaging will open a new observational regime for Galactic astrophysics by resolving physical scales that are inaccessible to current X-ray observatories. This white paper highlights the science enabled by such capabilities across four broad questions: how particles are accelerated, how stars die, how accretion is fueled, and what populations of X-ray sources inhabit the Galaxy. Ultra-high angular resolution will enable many new studies, such as resolving shocks and jets, measuring proper motions, parallaxes, and binary orbits, and providing secure multiwavelength counterpart identifications in crowded environments such as the Galactic Center and globular clusters. Combined with high-time-resolution observations, these measurements will connect variability and transient events to the physical structures in which they originate, while coordination with gravitational-wave, neutrino, $\gamma$-ray, radio, optical, and infrared facilities will provide spatial information needed to identify and characterize multi-messenger sources. In addition to defining the science cases, this paper presents a curated list of compelling targets spanning various angular resolutions and outlines the complementary specifications necessary to maximize the scientific outcome. Accomplishing these science goals will require an instrument with high angular resolution, precise astrometry, substantial collecting area, sufficient spectral and timing resolution, and high dynamic range imaging capabilities.
Read the full abstract

All authors Paul A. Draghis, Jeremy Hare, Mayura Balakrishnan, Poshak Gandhi, Tyler Holland-Ashford, Margarita Karovska, Thomas Maccarone, Herman L. Marshall, Mark Reynolds, Malgosia Sobolewska, Ryan Tanner

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.CO

AXIS Could Have Accessed Dark Matter Decays

Joshua W. Foster, Inci Karaaslan, Gordan Krnjaic et al. (+1 more)

The Advanced X-ray Imaging Satellite (AXIS) was a mission concept designed to improve upon the sensitivity and spatial resolution of the Chandra X-ray Observatory and XMM-Newton. Although AXIS was not selected for implementation, the concept study defined a mature instrument design with low-background, arcsecond imaging over the $0.3$-$10$ keV energy range, a large effective area, and a wide field of view. These capabilities provide a useful benchmark for the dark matter decay sensitivity of future X-ray observatories. We estimate the reach of a future AXIS-like instrument for narrow photon lines from decaying keV-scale dark matter, including axion-like particles and sterile neutrinos. For Galactic center observations, we find projected lifetime sensitivities of order $10^{31}$ s, improving upon existing limits by up to an order of magnitude over part of the keV mass range.
Read the full abstract

All authors Joshua W. Foster, Inci Karaaslan, Gordan Krnjaic, Nimrod Shapir

High Energy Astrophysical Phenomena

A Similarity Theorem and Its Breakdown in Atomic Black Hole Accretion

Marcus DuPont

Atomic gas in a point-mass potential possesses an exact similarity that survives time dependence, two-body atomic microphysics, and a specified class of radiation and feedback laws. At fixed ambient temperature and composition, $M_\bullet\mapsto\lambda M_\bullet$ and $n_\infty\mapsto\lambda^{-1}n_\infty$ enlarge radii and times by $\lambda$ while preserving dimensionless profiles, optical depths, Eddington ratios, and variability. Here $M_\bullet$ is the central mass, $n_\infty$ the ambient number density, and $\lambda>0$ the scale factor. We prove this rescaling unique within the class. The symmetry also locates its boundary during rapid growth. Define the fractional mass gained in one Bondi time as $\epsilon_{\rm grow}=\dot M_\bullet t_{\rm B}/M_\bullet$, where $\dot M_\bullet$ is the retained rate and $t_{\rm B}$ the Bondi time. This quantity equals $\dot R_{\rm B}/c_\infty$, the expansion speed of the Bondi radius $R_{\rm B}$ in units of the ambient sound speed $c_\infty$; hence $\epsilon_{\rm grow}=1$ is sonic dilation. A retained law $\dot M_\bullet\propto M_\bullet^p$ with $p>0$ reaches this boundary after a finite increase in mass and leaves at most $(p\epsilon_0)^{-1}$ additional Bondi times, where $\epsilon_0$ is the initial loading. If retained, the canonical hyper-Eddington example has already crossed. Independently, no nontrivial stationary growing profile preserves both the atomic similarity and its self-consistent flux. The theorem therefore unifies radiating Bondi and feedback-regulated scalings and identifies where a relaxed fixed-mass continuation loses control.
Read the full abstract

High Energy Astrophysical Phenomena

Exploring the sensitivity of in-ice radio detectors to cosmic ray mass composition

Nathaniel Alden, Marissa Boucher, Cosmin Deaconu et al. (+2 more)

In-ice radio detectors have been developed primarily for the detection of high-energy neutrinos via the Askaryan effect, but have recently been shown to also be sensitive to cosmic ray air showers impacting the ice sheet. Using CORSIKA 8 to simulate impacting air showers, we find that the lateral width of the in-ice cascade is sensitive to the atomic mass of the primary cosmic ray. The width of the shower core is accessible through the shape of the Askaryan radio spectrum, while the amplitude encodes the total in-ice charge excess. Using these two observables, we show that in-ice radio detectors can be used to measure cosmic ray mass composition in the region above $10^{17}$eV if the in-ice receivers are placed to adequately sample the Askaryan emission pattern. We also show that the in-ice core width is highly, but not exactly, correlated with the depth of maximum particle count ($\mathrm{X}_{\mathrm{max}}$), the most commonly used observable for reconstructing cosmic ray mass composition.
Read the full abstract

All authors Nathaniel Alden, Marissa Boucher, Cosmin Deaconu, Abigail Vieregg, Philipp Windischhofer

High Energy Astrophysical Phenomena

Distinct Modes of Pulsar Glitch Activity Revealed by the Waiting-Time–Amplitude Morphology

Wen-Tong Liu, Wei-hua Wang, Xia Zhou et al. (+1 more)

Pulsar glitches display diverse behaviors. They are commonly labeled as "Vela-like" or "Crab-like," yet these qualitative categories do not provide reproducible quantitative boundaries. We constructed an objective classification scheme based on the joint distribution of backward waiting time $\Delta t_{-}$ and fractional glitch amplitude $\Delta\nu/\nu$. A sample of 349 glitches from 22 pulsars was compiled by cross-matching the Jodrell Bank and ATNF glitch databases. For each source, we used two-dimensional kernel density estimation (KDE) together with highest-density regions (HDRs) to derive geometric descriptors, including the HDR area, anisotropy ratio, and out-of-HDR fraction. Hierarchical clustering of the KDE–HDR descriptors revealed two morphology classes independent of visual inspection. In this convention, the Compact class is associated with small HDR areas, elevated anisotropy, and limited peripheral occupancy. The Extended class is associated with broader HDR occupancy and stronger low-density extensions. We found that bootstrap resampling and hyperparameter sensitivity tests confirmed this partition for most sources. Nevertheless, two prolific pulsars (PSR J0537-6910 and PSR J1341-6220) were found to occupy intermediate positions. Logistic regression identified the mean backward waiting time $\langle\Delta t_{-}\rangle$ as the strongest class predictor (in-sample $\mathrm{AUC}=0.88$; leave-one-out $\mathrm{AUC}_{\mathrm{CV}}=0.59$, reflecting the limited sample size). Additionally, a parallel analysis using $\Delta t_{+}$ recovered the same two-class structure but with reduced stability. The data suggest that the Compact class is consistent with near-complete reservoir depletion, whereas the Extended class reflects partial, avalanche-like releases. As a result, short-term measurements of $G$ in Extended-class pulsars may underestimate the true crustal superfluid fraction.
Read the full abstract

All authors Wen-Tong Liu, Wei-hua Wang, Xia Zhou, Fei-fei Kou

High Energy Astrophysical Phenomena

Relativistic outflows power a quasi-periodic eruption: constraints on energetics, mass loss, and emission mechanisms

Joheen Chakraborty, Erin Kara, Wenbin Lu et al. (+17 more)

Quasi-periodic eruptions (QPEs) are recurring bursts of X-ray radiation originating from supermassive black holes (SMBHs). They are an unprecedented type of structured, high-amplitude SMBH variability, but the physical origins of their regularity, timescales, energetics, and emission are uncertain. We present new XMM-Newton observations of the QPEs in ZTF19acnskyy/"Ansky", constituting the deepest observations of individual bursts in any source thus far. The X-ray spectra reveal time-evolving P Cygni profiles comprising blueshifted absorption and redshifted emission from L-shell transitions of Fe XIX-XXIV, with column densities $N_H\sim 10^{22-23}$ cm$^{-2}$ and bulk velocities of $|v_w/c|\sim 0.2$, indicating relativistic mass ejections during each eruption. We construct a time-dependent analytical model of a wind turning on to self-consistently compute its evolving luminosity and ionization properties, and find that the light curve and spectral lines can be simultaneously produced by a wide-angle outflow with $\dot{M}\sim 10^{-9}-10^{-8}\,M_\odot$ s$^{-1}$ kinetically powering the X-rays with an efficiency of $L_X/\dot{E}_K\sim 0.1$. For a covering fraction $f_\Omega\sim0.5$, each eruption ejects $\sim 10^{-3}\,M_\odot$ and $\gtrsim 10^{49}$ erg of kinetic energy, setting an upper bound on the QPE lifetime of $\lesssim1000$ bursts if the underlying mass reservoir is $\sim1 M_\odot$, and implying that the bursts may result in detectable multiwavelength signatures of reverberation and feedback. These measurements provide new quantitative constraints on QPE energetics, emission mechanisms, and the mass/energy they recycle into their circumnuclear environments, as well as an observational probe for direct comparison with physical models and hydrodynamical simulations of QPEs.
Read the full abstract

All authors Joheen Chakraborty, Erin Kara, Wenbin Lu, Brian D. Metzger, Peter Kosec, Riccardo Arcodia, Itai Linial, Olivia Aspegren, Ehud Behar, Sudip Bhattacharyya, Margherita Giustini, Lorena Hernandez-Garcia, Daniel Kasen, Giovanni Miniutti, Frits Paerels, Erwan Quintin, Claudio Ricci, Daniele Rogantini, Paula Sanchez-Saez, Fatima Zaidouni

High Energy Astrophysical Phenomena

Reassessing the contribution of long-GRB high-energy afterglows to the isotropic gamma-ray background after GRB 221009A

S.V. Troitsky

Very-high-energy photons from gamma-ray bursts (GRBs) are absorbed by the extragalactic background light and partly reprocessed into the GeV band. We update previous estimates of the long-GRB contribution to the Fermi-LAT isotropic gamma-ray background (IGRB), using a time-integrated high-energy afterglow template of GRB 221009A, anchored by GeV-TeV data, together with an explicitly specified scaling with prompt energy and beaming. Despite the observed multi-TeV afterglow, the cascade component reaches only 1.6e-4 of the IGRB. Including direct GeV emission raises the maximum fraction to 1.1e-3, but makes the result more dependent on the population-averaged broadband template. Variations of the extragalactic background light, propagation implementation, intrinsic spectral cutoff, and population prescription do not change the conclusion: the multi-TeV detection of GRB 221009A does not make long GRBs a significant source of the IGRB.
Read the full abstract