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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 14 September

High Energy Astrophysical Phenomena

Hardware-aware quantum attention for fast radio burst identification

Li He, Xuan Yang, Feng Xiong et al. (+10 more)

Fast radio bursts (FRBs) are millisecond-duration extragalactic pulses whose discovery requires searches over large signal-parameter spaces and the rejection of candidate sets dominated by radio-frequency interference and noise. Integrating quantum processors into FRB searches requires a workflow connecting telescop data to hardware-compatible models. Here we develop a pipeline that converts raw search-mode PSRFITS data into dynamic-spectrum segments and identifies FRB-like signals using a hybrid Quantum Vision Transformer (QViT). On labelled FAST data, the selected QViT achieves a mean accuracy of 94.00% and recall of 98.30%, with similar performance to a compact classical Vision Transformer. Recall reaches 97.11% on an FRB source excluded from training and model selection. Real-device execution on 82 segments yields a mean simulator-hardware Hellinger fidelity of 0.9161 +/- 0.0074. The workflow connects raw telescope data to quantum-assisted identification and provides an experimental basis for assessing the measurement requirements that must be addressed before survey-scale deployment.
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All authors Li He, Xuan Yang, Feng Xiong, Songbo Zhang, Qiuhao Chen, Yuchen He, Yunxiang Yang, Jun Lu, Claudio Furtado, Amilcar R. Queiroz, Xinping Deng, Yang Wu, Xuefeng Wu

Astrophysics of Galaxies

The driving mode of turbulence in disc galaxy simulations with adaptive mesh refinement

James Watt, Christoph Federrath, Thorsten Tepper-Garcia et al. (+2 more)

Turbulence is a key ingredient in controlling the structure of the interstellar medium (ISM) and star formation, yet we still lack a detailed understanding of its drivers in galaxies. Previous idealised simulations of turbulence employ a stochastic forcing field to drive turbulence. The geometry of this forcing field - whether it is predominantly solenoidal or compressive - is a key parameter governing how turbulence shapes the ISM density distribution and regulates the star formation rate. The turbulence driving parameter ($b$) quantifies the relative contribution of compressive versus solenoidal driving.. Therefore, accurate knowledge of the driving parameter is essential for understanding and predicting star formation, and for sub-grid modelling of ISM physics and the star formation rate. In this work, we introduce an algorithm to measure the turbulence driving parameter in adaptive mesh refinement (AMR) simulations of galaxies. We focus our analysis on a synthetic Large Magellanic Cloud (LMC), present-day analogue with a total mass $M \approx 10^{11}\,\mathrm{M}_\odot$. We find that turbulence is driven primarily solenoidally ($b<0.4$) within the inner $\sim4\,\mathrm{kpc}$ of the galaxy, and becomes increasingly compressive with $b>0.4$ towards the outskirts, $R\gtrsim4.5\,\mathrm{kpc}$. The volume-weighted median across the disc, $b\simeq0.4$, is consistent with the natural mixture of driving modes. We further find that $b$ is weakly correlated with the strength of shear, in that solenoidal driving tends to be associated with regions of higher shear, as expected for the more central parts of galaxies. These trends persist over $\sim\!2\,\mathrm{Gyr}$ of the galaxy's evolution.
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All authors James Watt, Christoph Federrath, Thorsten Tepper-Garcia, Oscar Agertz, Joss Bland-Hawthorn

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Inelastic Dark Matter at LZ from Radiative Dirac Neutrino Mass Paradigm

Pankaj Borah, Satyabrata Mahapatra and Newton Nath

The LUX-ZEPLIN (LZ) experiment has reported a high-energy nuclear recoil candidate, LZ230616, at $E_R = 248 \pm 23_{\rm stat} \pm 23_{\rm sys}\,$keV, which is difficult to reconcile with elastic scattering of halo dark matter (DM). Endothermic inelastic scattering offers a natural explanation, but it rests on a nucleon coupling that is off-diagonal rather than diagonal. We show that this feature arises automatically within a radiative Dirac neutrino mass framework. The Standard Model is extended by three right-handed neutrinos (RHNs), a pair of vector-like neutral fermions for each generations, and a scalar sector comprising an inert doublet and a real singlet, governed by a $\mathcal{Z}_2 \times \mathcal{Z}_4$ symmetry. The $\mathcal{Z}_2$ symmetry stabilizes the DM, while the $\mathcal{Z}_4$ symmetry forbids the tree-level Dirac Yukawa coupling together with all renormalizable Majorana mass terms, thereby allowing the generation of Dirac neutrino masses at the one-loop level through a softly broken scalar trilinear coupling `$\kappa$'. Since the neutral dark-sector fields can be expressed in terms of real scalar mass eigenstates, the $Z$ boson couples to them purely off-diagonally and elastic $Z$-mediated scattering is absent identically rather than simply suppressed. The singlet–doublet mixing induced by `$\kappa$' governs both the inelastic rate and the one-loop Dirac neutrino mass, which therefore vanish as $\kappa \to 0$. We find that DM masses in the few hundred GeV to TeV range, with splittings of $\mathcal{O}(340-360)\,$ keV, simultaneously reproduce the observed relic abundance, account for the LZ event and yield neutrino masses of the correct order, while respecting elastic direct-detection limits and all relevant theoretical and experimental constraints. A substantial part of the surviving parameter space lies within reach of DARWIN.
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Astrophysics of Galaxies

Nexus-CDM: Isolated Galaxy Simulations with Cosmologically Evolving Dark-Matter Halos I. Method and Validation

Thor Tepper-García, Joss Bland-Hawthorn, Oscar Agertz et al. (+1 more)

Galaxy evolution can be modelled in two complementary ways. Standalone simulations place a single galaxy in isolation, evolving it under controlled initial conditions without the surrounding cosmic web. This approach offers high resolution and computational efficiency, making it well suited to disentangle specific physical processes (e.g. feedback and disc instabilities) and testing them cleanly, though at the cost of ignoring environmental context, gas accretion from the broader large-scale structure, and the hierarchical assembly that feeds real galaxies over cosmic time. Cosmological simulations, by contrast, form galaxies self-consistently within an expanding universe, capturing large-scale structure formation, mergers, gas inflows, and environmental effects such as tidal stripping and ram-pressure. This realism comes at a steep computational cost, requiring coarser resolution or simplified sub-grid physics for star formation and feedback. Here, we explore a new paradigm that combines the relative merits of both methods – what we call the Nexus-CDM framework. This approach naturally incorporates galaxy mass growth, which is absent from existing standalone simulations, reinforcing the limitations of static halo models used in galaxy formation and evolution research. The viability of the framework is demonstrated in an idealised setup, where it successfully reproduces the formation and subsequent evolution of a realistic stellar disc. We present some early results, in particular, discs form readily in a gravitational potential with a shallow central gradient, contrary to recent claims.
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All authors Thor Tepper-García, Joss Bland-Hawthorn, Oscar Agertz, Christoph Federrath

High Energy Astrophysical Phenomena

Optical spectroscopy of the VHE flat-spectrum radio quasar PKS 0903-57

E. Kasai, P. Goldoni, C. Boisson et al. (+5 more)

We report new optical spectroscopic results for the gamma-ray blazar PKS~0903$-$57. The optical properties of this source have historically been complicated to establish, due to a bright foreground star separated from the blazar by only 0.67$^{\prime\prime}$. During its strong high-energy (HE) and very high-energy (VHE) gamma-ray flaring period between 2020 and 2022, the Southern African Large Telescope and Very Large Telescope (VLT) took spectra of its optical counterpart. Photometric monitoring with the Rapid Eye Mount (REM) telescope complemented the observations. The observational results were inconclusive. A major improvement was achieved with a repeat of the VLT observations in 2024 using a 0.5$^{\prime\prime}$ slit under excellent seeing conditions. This led to the detection of five narrow emission features in the spectra, yielding a robust redshift measurement of $z$ = 0.2621 $\pm$ 0.0006. We also detected a broad symmetric H$\alpha$ emission component with a full width at half maximum of 4020 $\pm$ 30 km/s in the spectra. Non-thermal jet emission was found to dominate the continuum, supporting the classification of PKS~0903$-$57 as a flat-spectrum radio quasar. Another interesting observation was a significant velocity displacement of $\sim$1500~km/s between the broad H$\alpha$ line and its corresponding narrow line. Such a displacement may be associated with unusual dynamics in the broad-line region or accretion flow, a system containing two supermassive black holes, or a recoiling black hole produced following a supermassive black-hole merger. Building on these results, we carried out additional VLT, REM, and Swift observations towards the end of 2024 and during 2025. We present in this paper the preliminary results from the analysis of these new data.
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All authors E. Kasai, P. Goldoni, C. Boisson, S. Pita, W. Max-Moerbeck, F. D'Ammando, B. Rajput, M. Backes

Cosmology and Nongalactic Astrophysics

Forecasting Coupled Dark Energy Parameters with the One-Loop Galaxy Power Spectrum

Bilal Tüdes and Luca Amendola

We forecast constraints on the parameters of the coupled dark energy model using DESI and Euclid data with the one-loop galaxy power spectrum. We investigate the distinguishability of our model from the zero-coupling scenario at the $1\sigma$ level and explore how the parameter constraints depend on the fiducial coupling $\beta_{\rm fid}$, the fixed potential slope parameter $\nu$, the maximum wavenumber $k_{\max}$, and different prior choices. We find that the inclusion of mildly non-linear scales improves the constraints on the coupling by roughly a factor of five. Then, we address the question of which is the minimum value of $\beta$ that can be distinguished from zero at $1\sigma$. We find that for our reference case $k_{\rm max}=0.2 h/$Mpc, $\beta=0.15$ lies roughly $1\sigma$ above zero. In the most optimistic case with $k_{\rm max}=0.3 h/$Mpc and including a Planck prior on $\Omega_{m0}$, this value can be reduced to $0.05$. These values are substantially larger than the current constraints on $\beta$, but the latter have been obtained assuming $\beta$ to be constant from at least the decoupling epoch to today, while we only employ late-time data. We conclude therefore that only models that allow for time-varying couplings can be detected with late-time datasets.
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High Energy Astrophysical Phenomena

Measurement of Cosmic-Ray Density in the Spiral Arms toward Galactic Anticenter

Jia-hao Liu, Bing Liu and Rui-zhi Yang

Using nearly 17 years of Fermi-LAT data, we analyzed the diffuse gamma-ray emission associated with different spiral arms of the Milky Way in the ranges $l = 105^\circ$ to $145^\circ$ and $b = -5^\circ$ to $5^\circ$. The gamma-ray emissions from these spiral arms all exhibited clear pion-bump features, which can be well explained by a power-law spectrum of cosmic-ray protons. The spectral indices corresponding to the three distinct spiral arms – the Local Arm, the Perseus Arm, and the Outer Arm – are found to be approximately $-2.75$, $-2.55$, and $-2.80$, respectively. The energy densities of the cosmic rays above 10 GeV are estimated to be all around 0.2$\rm~eV~cm^{-3}$. We further compared our results with previous studies, which have established various propagation models predicting that cosmic ray density decreases and spectra soften with increasing Galactocentric radius. We found higher densities and harder spectral indices than predicted in the outer Galaxy, suggesting possible contributions from a larger halo, slower magnetic field decay, or a combination of these and other effects. In particular, the spectral hardening observed in the Perseus Arm may be attributed to locally enhanced cosmic-ray acceleration.
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Astrophysics of Galaxies

Tracing Stellar Populations through the Mg-Al Anti-Correlation in Gaia-ESO Globular Clusters

H. Sinclair-Wentworth, C. C. Worley, P. Jofre et al. (+2 more)

Context. Globular clusters (GCs) are fragments of the chemical history and evolution of the Milky Way. Their notable intra-cluster abundance variations have been used to characterise chemical trends and stellar populations. However, the origins of these populations and GCs in general are still largely unknown. Aims. Our aim is to explore the origin of the stellar populations belonging to 14 GCs making use of their abundances derived from the Gaia-ESO Survey (GES) spectra. In particular, we use the Mg-Al anti-correlation to separate the populations. Methods. The GES spectra were revisited to derive additional homogenous chemical abundances for Mg and Al. A Gaussian Mixture Model (GMM) was applied to the [Mg/Al] distribution for each cluster to define a threshold between the two main populations. Results. Eight clusters imply the presence of Mg-Al anti-correlations and dual populations. We find there is a regime transition near [Fe/H] approximately -1.4, where, the Mg-Al anti-correlation disappears at higher metallicity. Several clusters, regardless of their Mg-Al anti- correlation behaviour, exhibit metallicity spreads (e.g., NGC 2808, NGC 6752) and s-process variations (e.g., NGC 7078, NGC 1851), suggesting complex enrichment histories. Conclusions. The presence and spread of the Mg-Al anti-correlation depend on cluster mass and metallicity, with metal poor and/or massive clusters exhibiting the clearest anti-correlation. This work demonstrates additional abundances that can be retrieved from Gaia-ESO Survey spectra and provides further insight into the chemistry of multiple stellar populations within GCs. These findings highlight the chemical complexity of GCs and the need for large, homogeneous datasets to trace their formation histories.
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All authors H. Sinclair-Wentworth, C. C. Worley, P. Jofre, J. Schiappacasse-Ulloa, L. Magrini

Cosmology and Nongalactic Astrophysics

Field-Level Baryon Acoustic Oscillation Reconstruction of the DESI DR1 Luminous Red Galaxies with Linear Field Transformer (LiFT)

Liam Parker, Uroš Seljak, Adrian E. Bayer et al. (+2 more)

We present the first application of neural field-level baryon-acoustic oscillation (BAO) reconstruction to real spectroscopic survey data. We develop Linear Field Transformer (LiFT), a 3D vision transformer that takes as input the observed galaxy field, its standard reconstruction, and a set of context channels encoding local line of sight, survey coverage, and redshift, and learns to correct standard reconstruction toward the linear density field. We construct a forward-modeling pipeline to produce mock lightcones similar to the DESI Data Release 1 (DR1) luminous red galaxy (LRG) sample, and train LiFT on these. We validate LiFT on held-out simulations, as well as on additional mocks which differ in gravity solver, halo finder, HOD, cosmology, and fiber-assignment history, as well as on mocks analyzed with a distorted distance-redshift relation; ultimately, we find unbiased dilation parameters with consistently tighter constraints than standard reconstruction. Applied to the DESI DR1 LRGs, LiFT improves errors on $\alpha_{\rm iso}$ by 13%, 24%, and 30% and on $\alpha_{\rm AP}$ by 5%, 22%, and 30% relative to the DESI DR1 standard reconstruction analysis in the LRG1, LRG2, and LRG3 bins respectively; meanwhile, our DR1 central values remain consistent with DR1 and DR2. This equates to a factor of 1.2, 1.7 and 2.0 increase in Figure of Merit (or effective survey volume) if one were to only use standard reconstruction. Ultimately, these results establish LiFT as a validated, survey-ready tool for current and upcoming galaxy surveys.
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All authors Liam Parker, Uroš Seljak, Adrian E. Bayer, Richard Feder, David Valcin

Sunday 13 September

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Gravitating sources with zero energy density in cosmology

Özgür Akarsu, Cihad K{\i}br{\i}s, Burcu Öztürk et al. (+1 more)

A cosmological source can have identically zero comoving energy density and still gravitate through its pressure. This differs from an energy density passing through zero at an isolated time. Maintaining zero density with nonzero pressure requires energy exchange in a nonstatic FLRW universe. We construct proportional-pressure and constant-pressure backgrounds, including steady-state, bouncing, recollapsing, and $\Lambda$CDM expansion histories, and relate them to creation pressure, bulk viscosity, and time-dependent vacuum descriptions. Scalar fields can realize zero density along a trajectory; imposing it as an identity on a timelike $P(X,\phi)$ domain selects $P=A(\phi)\sqrt{X}$, locally a signed potential-free cuscuton for nonzero $A$. We formulate linear perturbations without dividing by the vanishing background density. For a nondegenerate $P(X,\phi)$ scalar with a timelike field gradient, zero density and negative pressure cannot coexist with positive kinetic and gradient coefficients when the interaction leaves its principal kinetic structure unchanged. Two models couple the scalar to number-conserving dust through a field-dependent mass. The proportional-pressure trajectory is a homogeneous saddle and has no growing power-law dust mode on its accelerating branch in the matter-sourced quasistatic subhorizon approximation. A distinct constant-pressure model reproduces the $\Lambda$CDM expansion history, but in the same approximation the dust mode that initially grows during matter domination reaches a maximum at low redshift and then decays. These restrictions apply to the stated scalar class and models. Exact Bianchi I solutions demonstrate separately conserved zero-density sources supported by anisotropic stress. An inverse-pressure construction distinguishes the density of an interacting constituent from an inferred dark-energy density that may cross zero.
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All authors Özgür Akarsu, Cihad K{\i}br{\i}s, Burcu Öztürk, N. Merve Uzun

High Energy Astrophysical Phenomena

Bayesian Inferences on Analytical Equations of State Approximations of Neutron Stars

Arijit Das and Sourav Roy Chowdhury

Equations of state (EoS) for dense matter are commonly provided in tabulated pressure-energy density relations, complicating numerical implementation and potentially compromising thermodynamic consistency. In this work, we propose a piecewise-continuous analytical form with a common parametrization capable of representing a broad class of dense matter EoSs. We validate this parametrization against tabulated EoSs from the CompOSE and LALSimulation repositories. Following the initial deterministic fitting, we employed two distinct Bayesian approaches: one based on synthetic EoSs generated by adding noise to the fitted EoS and another based on multi-messenger measurements of neutron-star masses and tidal deformabilities. In both approaches, the initial best-fit parameters are used as reference values. For the considered EoSs, spanning from very soft to very stiff, the resulting fits reproduce the tabulated EoSs and the associated macroscopic neutron-star observables in the repositories with sufficient accuracy. The inferred parameters exhibit strong correlations arising from the continuity conditions imposed at the segment boundaries. These correlations persist in the low- and intermediate-density segments under multi-messenger inference but become weak in the core, reflecting the limited constraining power of current observations at high densities. The ability of a single functional form to describe EoSs derived from different microscopic frameworks, together with the recurrence of similar parameter correlations, suggests that diverse dense matter EoSs may share a common underlying structure.
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Earth and Planetary Astrophysics

Second Generation Planet Formation in Post-AGB Discs - II: Dust Coagulation and Core Accretion

Ali Pourmand, Orsola De Marco, Devika Kamath et al. (+1 more)

Observations have established that the circumbinary discs formed around post-asymptotic giant branch (post-AGB) binaries have striking similarities to protoplanetary discs around young stars. In this study, we examine the feasibility of the different stages of growth in the core accretion framework of planet formation in post-AGB discs, in order to assess whether planet formation is possible in these systems. We find that dust coagulation up to mm sizes is possible within the lifetimes of post-AGB discs, consistent with observations. We then investigate the subsequent growth of planetesimals through pebble and planetesimal accretion. If the streaming instability operates in these discs, the resulting planetesimals formed in higher-mass post-AGB discs ($M_{\rm disc}\sim0.1M_\odot$) can enter rapid pebble accretion and reach their isolation mass within the estimated disc lifetime. By contrast, in lower-mass post-AGB discs ($M_{\rm disc}\sim0.01M_\odot$), planetesimal accretion is too inefficient to produce substantial further growth. We also show that the larger aspect ratios of post-AGB discs compared to protoplanetary discs around young stars imply high pebble isolation masses and therefore potential formation of rocky planets with masses extending up to Jupiter masses. After assessing gas accretion and concurrent migration in these discs, we conclude that second generation planet formation in post-AGB discs is theoretically possible within their estimated lifetimes ($10^4$–$10^5$yr) provided that local dust-to-gas ratio enhancements and sufficiently high disc masses are achieved.
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All authors Ali Pourmand, Orsola De Marco, Devika Kamath, Daniel J. Price

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Boosted or Inelastic? Discriminating Interpretations of the LZ 248 keV Event

Satyabrata Mahapatra and Partha Kumar Paul

The LUX-ZEPLIN experiment has reported a single nuclear recoil candidate at $E_R = 248 \pm 23(\mathrm{stat}) \pm 23(\mathrm{sys})$~keV, disfavouring the background-only hypothesis at a global significance of $2.6\sigma$. The difficulty such an event poses is not the recoil energy itself but the absence of any accompanying excess at low energy as elastic scattering of halo dark matter yields a monotonically falling spectrum, and supplying the required momentum transfer $q \simeq 246$~MeV already demands $m_\chi \gtrsim 79$~GeV. We confront the event with the two kinematically distinct mechanisms that evade this limitation, endothermic inelastic dark matter, in which a mass splitting $\delta \sim \mathcal{O}(100)$~keV forbids low-energy recoils and boosted dark matter, in which a light relativistic flux supplies the momentum, treating both with the same model-independent scalar–scalar, pseudoscalar–scalar and pseudoscalar–pseudoscalar effective operators. The two scenarios prove spectrally distinguishable. The inelastic spectra sit near the observed energy for every operator, placing only $6$–$17\%$ of events below 150~keV, whereas the boosted spectra depend critically on the operator: the scalar and pseudoscalar–scalar interactions place $99\%$ and $92\%$ of their events below 150~keV, while the pseudoscalar–pseudoscalar interaction places $75\%$ above it. Momentum dependence is thus essential to the boosted interpretation, but in the inelastic case it trades against the splitting, the preferred $\delta$ decreasing monotonically from $\mathcal{O}_{ss}$ to $\mathcal{O}_{ps}$ to $\mathcal{O}_{pp}$. Because the scenarios differ across the whole high-energy window, a handful of additional events would separate them, placing the question within reach of the full LZ exposure.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Stability and Structural Properties of Hot Quark Stars within Perturbative QCD

Tousif Raza and Tyler Gorda

The hypothesis of strange quark matter (SQM) and the possible existence of strange stars have been extensively investigated within the thermodynamic bag model, typically employing the free Fermi gas approximation with or without perturbative QCD corrections at zero temperature, where quark confinement is modeled by the bag pressure. In this work, based on the perturbative inclusion of quark mass effects, we develop a thermodynamically consistent equation of state (EOS) for SQM at finite temperature, incorporating perturbative corrections up to $\mathcal{O}(\alpha_s)$ in the strong coupling constant $\alpha_s$ while ensuring full adherence to the Maxwell relations. These corrections are essential for accurately describing hot quark stars potentially formed during core-collapse events. We present results for both fixed and running couplings, using a phenomenological model to include the breakdown of the perturbative running of $\alpha_s$ at low momenta. Our results demonstrate that incorporating finite-temperature perturbative QCD corrections leads to SQM configurations that fall within the absolute stability window, with equilibrium energies per baryon lying below that of iron, the most tightly bound nucleus. Our EOS supports compact stars with masses exceeding $1.4\,M_\odot$ (and above $2\,M_\odot$ for some values of the bag constant), in agreement with current astrophysical constraints from pulsar and gravitational-wave observations.
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Earth and Planetary Astrophysics

WINERED Detects a Strong Atmospheric Outflow on the Sub-Neptune GJ 3090b

Shreyas Vissapragada, Zifan Lin, Annabella Meech et al. (+12 more)

Sub-Neptunes are the most common short-period ($P<100$ d) planets known. A major goal for the field is to build a comprehensive understanding of their compositions and evolutionary histories, and an important tool for achieving this goal is metastable helium (He$^*$) transmission spectroscopy, which traces atmospheric escape. In this paper, we report the detection of He$^*$ in the atmosphere of the sub-Neptune GJ 3090b at high spectral resolution. We observed two consecutive transits of this planet with Magellan II/WINERED, and detected peak He$^*$ absorptions during transit of $2.033\pm0.086\%$ (23.6$\sigma$) and $1.619\pm0.122\%$ (13.3$\sigma$), respectively. The first transit was affected by a stellar flare near egress while the second transit was unaffected. The signal is variable in amplitude and deeper than anticipated by the JWST/NIRISS observations of Ahrer et al. (2025). We do not observe a significant Doppler shift, and the signal has a FWHM of $25$ km s$^{-1}$, implicating photoevaporation. Our outflow modeling suggests that $Z_\mathrm{atm}\lesssim100\times$ solar, as the observed He$^*$ amplitudes are challenging to achieve in a metal-rich atmosphere. To match the muted transmission spectra from JWST and VLT/CRIRES+, GJ 3090b's lower atmosphere is likely covered by aerosols. Finally, we found that GJ 3090b has an atmospheric lifetime of $\sim300$ Myr, much shorter than previously reported. This adolescent ($\sim1$ Gyr) sub-Neptune is currently in a transformative phase of photoevaporative evolution.
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All authors Shreyas Vissapragada, Zifan Lin, Annabella Meech, Collin Cherubim, Leonardo A. Dos Santos, Aaron Householder, Krishna Kanumalla, Mercedes Lopez-Morales, Andrew McWilliam, William Misener, Ava Morrissey, Morgan Saidel, Jessica J. Spake, Johanna Teske, Nicole L. Wallack

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

Full set of scenarios of high energy collision in the Schwarzschild background and kinematic censorship

A. V. Toporensky, P. Gusin, A. Radosz et al. (+1 more)

We consider collisions between particles moving freely in the Schwarzschild background. We suggest classification of scenarios that lead to unbounded energy output in the center of mass frame. Although this is forbidden in the exterior of a black hole, the phenomenon becomes possible with account of white hole region and mirror universe in the complete space-time diagram. Also, we scrutinize collisions in the vicinity of the bifurcation point and reveal the role of resting observers in the inner region beyond the horizon. In some scenarios $E_{c.m.}$ not only diverges but becomes seemingly infinite that is, as a matter of fact, impossible according to the principle of so-called kinematic censorship. We resolve a corresponding paradox and argue, why this principle remains valid.
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All authors A. V. Toporensky, P. Gusin, A. Radosz, O. B. Zaslavskii

Cosmology and Nongalactic Astrophysics

Bayesian Inference of the Tip of the Red Giant Branch: I. One-Dimensional Analysis

James D. Gibbon and Daniel J. Mortlock

The tip of the red giant branch (TRGB) is a relative distance measure that can be used, as part of a cosmic distance ladder, to infer the Hubble constant. We present a Bayesian framework for TRGB inference that incorporates selection effects and propagates per-star flux uncertainties, modelling the observed catalogue as a realisation of an inhomogeneous Poisson point process which includes the RGB and contamination from the asymptotic giant branch (AGB). We derive expressions for the predicted TRGB uncertainty in terms of the photometric noise, stellar density fainter than the tip, and the ratio of the AGB to AGB+RGB number densities, $r$. We validate these results using synthetic data from a simplified luminosity function. Applying the full model to synthetic catalogues, we find that the dependence on $r$ is the strongest of the three, and that reliable inference requires $r\lesssim0.5$; otherwise, the posterior can be multimodal, and the TRGB cannot reliably be identified. We then fit data from 11 Hubble Space Telescope fields of the calibrator galaxy NGC 4258. We find intrinsic field-to-field scatter of $\tau=0.067^{+0.023}_{-0.017}$ mag (beyond the measurement noise), and a galaxy-level, extinction-corrected TRGB magnitude of $25.324 \pm 0.026$ in the F814W filter. Combining this with the maser distance modulus to NGC 4258 of $29.397 \pm 0.032$ mag, we determine the absolute magnitude of the TRGB to be $M_{\mathrm{F814W}}^{\mathrm{TRGB}} = -4.073 \pm 0.026$ (tip) $\pm 0.032$ (dist), consistent with, but brighter than, other recent analyses of the same data.
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Astrophysics of Galaxies

PRISMS. GHZ1. A standard tale of galaxy evolution with atypical ionizing conditions at $z=9.878$

Borja Pérez-Díaz, Marco Castellano, Javier Álvarez-Márquez et al. (+33 more)

[Abridged] The first operating years of the James Webb Space Telescope (JWST) have revealed a surprising number of $z \gtrsim 10$ UV-bright objects, many of them characterized by their compactness, anomalous chemical abundance patterns and complex ISM physics (e.g. N-enhanced systems). To assess whether these objects are a phase of early galaxy evolution or a peculiar population, it is essential to understand the physics of systems without anomalous abundance patterns in this epoch. We present a detailed analysis of GHZ1 ($z=9.878$), a moderately ($\mu = 1.715$) lensed UV-bright ($M_{UV} = -20.07$) galaxy in the Abell2744 field, characterized by an extended size ($R_{e} \sim 410$ pc). These properties, which contrast with the properties of many of the N-enhanced galaxies, make GHZ1 an excellent laboratory to assess what are the major drivers of early galaxy evolution and the origin of the differences. By means of JWST spectroscopic observations from NIRSpec (PRISM-CLEAR configuration) and the MIR/LRS, we analyzed the full UV and optical emission from GHZ1. We used a spectro-photometric SED fitting to characterize the stellar evolution and the emission line spectra to constrain its chemical enrichment. We find that GHZ1 is among the most massive systems at $z\sim 10$ (log(M$_{\star}$ [M$_{\odot}$]) = 9.17$_{-0.26}^{+0.27}$), with a moderate amount of dust attenuation ($A_{V} = 0.21_{-0.12}^{+0.12}$~mag) and ongoing star formation (with a median SFR $= 8.75_{-1.72}^{+1.71}$ M$_{\odot}\cdot$yr$^{-1}$ over the last 10 Myr). Its chemical enrichment patterns (12+log(O/H) = $7.81_{-0.11}^{+0.12}$, log(C/O) = $-0.66_{-0.13}^{+0.13}$, log(N/O)$< -1.04$) are consistent with a standard evolution dominated by primary production from massive stars. We also derive an H$\alpha$/H$\beta$ Balmer ratio below Case B predictions. We speculate that [...].
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All authors Borja Pérez-Díaz, Marco Castellano, Javier Álvarez-Márquez, Luis Colina, Lorenzo Napolitano, Sarah Kendrew, Alejandro Crespo Gómez, Stefano Carniani, Shouyi Wang, Fan Zou, Abdurro'uf, Arjan Bik, Karina Caputi, Román Fernández-Aranda, Adriano Fontana, Yoshinobu Fudamoto, Macarena García-Marín, Mahmoud Hamed, Yuichi Harikane, Takuya Hashimoto, Jakob M. Helton, Tiger Y.-Y. Hsiao, Danial Langeroodi, Ruqiu Lin, Rui Marques-Chaves, Göran Östlin, Pablo G. Pérez-González, Enrico Piconcelli, Carlota Prieto-Jiménez, Pierluigi Rinaldi, Guido Roberts-Borsani, Bruno Rodríguez del Pino, Paola Santini, Tommaso Treu, Ana Varo-O'Ferrall, Jorge Zavala

High Energy Astrophysical Phenomena

First results on the search for the Galactic Center Excess in the sub-GeV band with the emulsion telescope in GRAINE 2023

Yuya Nakamura, Shigeki Aoki, Takashi Azuma et al. (+34 more)

(Please check the paper for full abstract.) The Galactic Center Excess (GCE) is an unexplained excess of gamma-ray emission from the Galactic Center. The GRAINE experiment aims to reveal the origin of the GCE using an emulsion gamma-ray telescope with high angular resolutions of 1 deg at 100 MeV and 0.1 deg at 1 GeV. In this study, we search for the GCE in a small region near the Galactic Center using the GRAINE 2023 flight data. In particular, rather than focusing on the spectral peak of the GCE at 2 GeV, we focused on the energy range below 300 MeV, where the spectral differences between the dark matter annihilation and millisecond pulsar scenarios are more pronounced. We searched for the GCE within 1 deg of the Galactic Center in the 75–300 MeV energy range. Although no significant excess was observed, we obtained an upper limit on the GCE flux of 1.70*10^-7 GeV cm^-2 s^-1 at the 2 sigma confidence level for the 1deg-radius ROI centered on the Galactic Center, based on a direct observation of the narrow region around the Galactic Center. This observation requires high angular resolution and represents a unique result from GRAINE. The obtained upper limit is consistent with the GCE flux near the Galactic Center, which was estimated from existing Fermi-LAT observations using a wide ROI and assuming an NFW profile. Although the current upper limit constrains some models, the available statistics are still insufficient to distinguish between the dark matter annihilation and millisecond pulsar scenarios, and both remain consistent with the current results. We also estimated the projected sensitivity of future GRAINE experiments based on the present observation and demonstrated their potential to probe the origin of the GCE by comparing the projected sensitivity with the predicted GCE spectra.
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All authors Yuya Nakamura, Shigeki Aoki, Takashi Azuma, Hirotaka Hayashi, Yudai Isayama, Atsushi Iyono, Takumi Kato, Tsuyoshi Kawahara, Kohichi Kodama, Ryosuke Komatani, Masahiro Komatsu, Masahiro Komiyama, Hideyuki Minami, Kunihiro Morishima, Fumiya Murakami, Shogo Nagahara, Naotaka Naganawa, Mitsuhiro Nakamura, Tomoaki Nakamura, Noboru Nakano, Toshiyuki Nakano, Kazuma Nakazawa, Miyuki Oda, Kazuhiro Okamoto, Hiroki Rokujo, Osamu Sato, Kai Shimizu, Amon Suganami, Yuki Sugi, Kou Sugimura, Satoru Takahashi, Ikuya Usuda, Saya Yamamoto, Jun Yamashita, Mayu Yamashita, Shoma Yoneno, Masahiro Yoshimoto

Astrophysics of Galaxies

Euclid: Data Release 1 (DR1) – Fornax-7, an ultra-faint companion to the Fornax dwarf spheroidal galaxy? A remote star cluster or dwarf satellite of the Fornax dSph

T. Saifollahi, A. Lançon, A. M. N. Ferguson et al. (+165 more)

We report the discovery of an ultra-faint stellar system in the vicinity of the Fornax dwarf spheroidal (dSph) galaxy in Euclid DR1. This system, which we designate Fornax-7, is located $1.1$ deg from the centre of the Fornax dSph at about $145$ kpc, corresponding to a projected distance of $\sim 2.8$ kpc assuming the distance of the Fornax dSph. We characterise Fornax-7 using constraints from its colour-magnitude diagram (CMD), luminosity function (LF), and integrated optical colours from ground-based data. These observables are modelled jointly through a forward-modelling framework to constrain its distance modulus, stellar population properties, and total stellar mass. Assuming a low metallicity of $-2.2 \leq {\rm [M/H]} \leq -2.0$, similar to known ultra-faint systems around the Milky Way and the LMC, we derive a distance modulus consistent with that of the Fornax dSph. We estimate an age of $(10.4\pm1.9)$ Gyr and infer a stellar mass of $170^{+50}_{-62}$ solar masses. Relaxing the metallicity constraint and allowing for a wider range that covers the metallicity of the known old Fornax globular clusters (GCs), we find a metal-poor population but with a higher metallicity ${\rm [M/H]}=-1.4\pm0.3$, while the age, distance modulus, and mass remain mostly the same. These results suggest a likely physical association with the Fornax dSph. Fornax-7 may represent either an extremely remote star cluster associated with Fornax, a dwarf satellite of Fornax (i.e., a "satellite of a satellite"), or an independent ultra-faint satellite in the outer halo of the Milky Way. In all cases, it constitutes an exceptional system probing the lowest-mass regime of galaxy and star cluster formation, and the structure of dwarf galaxy haloes. Deeper photometric and spectroscopic follow-up observations are required to confirm both the nature of the system and its dynamical connection to Fornax.
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All authors T. Saifollahi, A. Lançon, A. M. N. Ferguson, P. Boldrini, M. Gatto, J. M. Howell, N. F. Martin, A. C. Robin, F. Annibali, M. Baes, E. Balbinot, G. Battaglia, M. Bellazzini, Michele Cantiello, M.-R. L. Cioni, C. Crociati, V. Dornan, P.-A. Duc, A. Genina, C. M. Gutierrez, R. Habas, P. Jablonka, S. S. Larsen, M. Libralato, F. R. Marleau, D. Martínez-Delgado, S. Martocchia, D. Massari, F. Niederhofer, J. D. Sakowska, M. Urbano, L. R. Bedin, M. Griggio, A. Mohandasan, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, M. Bolzonella, E. Branchini, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, M. Cropper, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, M. Frailis, E. Franceschi, M. Fumana, L. Gabarra, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, S. Kermiche, A. Kiessling, B. Kubik, K. Kuijken, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, M. Magliocchetti, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, M. Meneghetti, E. Merlin, G. Meylan, P. Monaco, A. Mora, M. Moresco, C. Moretti, L. Moscardini, R. Nakajima, C. Neissner, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, W. J. Percival, V. Pettorino, A. Pezzotta, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, I. Risso, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, M. Schirmer, P. Schneider, A. Secroun, E. Sihvola, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, S. Toft, R. Toledo-Moreo, F. Torradeflot, A. Tsyganov, I. Tutusaus, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, A. Zacchei, F. M. Zerbi, I. A. Zinchenko, E. Zucca, J. García-Bellido, K. Tanidis

Solar and Stellar Astrophysics

Stripped helium stars in UV

L.R. Yungelson, A.G. Kuranov and A.V. Mishakina

The model of Galactic population of stripped helium stars, the remnants of $5 \lesssim M/M_\odot \lesssim 24$ primary components of close binaries after RLOF is presented. These stars emit in the UV range of the spectrum and may be observed by detectors aboard planned "Spektr-UV" (WSO-UV) space telescope. For the current star formation rate in the Galaxy 2$\mathrm {M_\odot yr^{-1}}$, the estimate of the number of 1 to 7 $M_\odot$ objects with $T_{\rm eff} \gtrsim$25,000\,K ranges from 14700 to 28500. The number of 2 to 7 $M_\odot$ objects is 3200 to 5500. The main evolutionary factor influencing the estimate is possible formation of common envelopes and merger of components in them. Detection of candidate stripped helium stars by UV-excess is hampered by the dominance of main-sequence companions to stripped helium stars in the combined spectra of binaries. This effect of observational selection may reduce the number of candidate stripped helium stars potentially detectable by photometry to $\lesssim 1000$.
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High Energy Astrophysical Phenomena

First Light of Neutron Star Mergers: Off-axis Cocoon Cooling X-ray Emission from Short Gamma-Ray Burst Jets

Jian-He Zheng and Wenbin Lu

Neutron star mergers (NSMs) are confirmed gravitational wave sources. Identifying an early electromagnetic counterpart for these events is therefore crucial for rapid localization and multimessenger follow-up. However, the associated Gamma-Ray Bursts (GRBs) are highly collimated and are therefore easily missed by off-axis observers. An early, less beamed counterpart is essential for identifying the majority of mergers. In this Letter, we investigate the cooling emission from jet-driven cocoons produced by short gamma-ray burst jets propagating through merger ejecta. We perform hydrodynamic simulations and radiative post-processing to calculate the early X-ray emission over a wide range of viewing angles. We find that the mildly relativistic cocoon produces bright soft X-ray transients for off-axis observers, with luminosities of $10^{46-48}{\rm erg\,s^{-1}}$ and durations of a few to ten seconds. The X-ray spectra are quasi-thermal with characteristic temperatures of $0.1$–$1\,{\rm keV}$. For observers at $\theta_{\rm v}=10^{\circ}$, the cocoon emission is detectable by Einstein Probe (EP) out to $z\simeq 0.3$. For nearby events like GW170817, it remains detectable up to $\theta_{\rm v}\simeq 45^{\circ}$. The predicted detection rate for EP is $0.5\,{\rm yr^{-1}}$ in the canonical model. In future multimessenger campaigns, rapid UV/optical/IR follow-up of such X-ray triggers can subsequently identify the associated kilonova and jet afterglow emission, which will confirm the origin.
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High Energy Astrophysical Phenomena

NICER neutron stars with dark energy and dark matter: effects on the inferred equation of state

Nathan Rutherford, Chanda Prescod-Weinstein and Anna Watts

[Abridged] In this work, we compare neutron stars where dark energy or dark matter are present in the core, contrasting them against purely baryonic stars with the same central energy density. From this comparison, we find that the dark energy models are more constrained by neutron star observations than the dark matter models, suggesting that neutron stars can place strong constraints on dark energy parameters. We consider four configurations: purely baryonic neutron stars described by a piecewise polytropic (PP) equation of state (EoS), baryonic stars admixed with bosonic or fermionic asymmetric dark matter (ADM) cores, and stars with a dark energy core and baryonic shell, where the dark energy is described by the modified Chaplygin dark fluid (MCDF). Using the masses and radii of PSR J0740$+$6620, PSR J0437$-$4715, and PSR J0030$+$0451, we employ Bayesian inference to investigate how accounting for bosonic/fermionic ADM and MCDF cores affects the inferred neutron star properties. We find that MCDF cores, more than PP and ADM admixed models, substantially broaden neutron star mass-radius and pressure-energy density posterior distributions. Moreover, the MCDF EoS parameters can be tightly constrained. While bosonic and fermionic ADM cores decrease the inferred maximum mass, their posteriors strongly coincide with those of the PP model for ADM mass-fractions $F_\chi \leq 5\%$. These results demonstrate that current mass-radius observations cannot rule out MCDF cores, but they can constrain the MCDF parameter space to narrow regions. ADM admixed neutron stars, however, remain observationally identical to purely baryonic stars for all explored mass-fractions, even with improved mass-radius uncertainties. This suggests that mass-radius measurements alone are insufficient to detect ADM core inside neutron stars and that independent astrophysical or particle physics probes will be required.
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Astrophysics of Galaxies

The Connection between Halo Assembly History and the Stellar Distribution I: The Central Stellar Mass - Richness Plane

Shuo Xu, Song Huang, Alexie Leauthaud et al. (+4 more)

Recent observations suggest intrinsic links between the stellar components of massive halos and their assembly histories. Using massive halos with $\log[M_{\rm halo}/M_\odot] \geq 13.0$ from the IllustrisTNG-300 simulation, we explore differences in secondary halo properties between samples selected by central galaxy stellar mass and satellite richness. For group-like masses, we find that halos selected by the outskirts stellar mass of their central galaxies between 50 and 100 kpc ($M_{\star,[50,100]}$) have similar halo mass distributions to those selected by intrinsic satellite richness ($\lambda_{10, R_{200}}$), but differ significantly in assembly history: $M_{\star,[50,100]}$-selected halos are more concentrated and formed earlier. At higher masses ($\sim10^{14}~M_\odot$), intrinsic richness becomes the better halo-mass proxy, but only when projection effects are ignored. We find that the difference-set test selects comparable halo-mass samples most effectively when the two proxies have similar scatter. Projection effects and baryonic physics do not alter the main trends but remain important caveats for observational applications. Our findings show that the central stellar mass-richness plane is a powerful tool for selecting halos with particular accretion histories, offering new insights into the galaxy-halo connection in the era of deep imaging and precision lensing surveys such as Euclid and LSST.
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All authors Shuo Xu, Song Huang, Alexie Leauthaud, Benedikt Diemer, Katya Leidig, Conghao Zhou, Carlo Cannarozzo

Astrophysics of Galaxies

Nitrogen-Loud Quasars from the Dark Energy Spectroscopic Instrument. II. Broad-Line Region Metallicity and Relative Nitrogen Enrichment

Shuo Zhai, Wei-jian Guo, Yong-Jie Chen et al. (+3 more)

Whether the unusually strong nitrogen emission in nitrogen-loud (N-loud) quasars reflects high overall metallicity, enhanced nitrogen abundance relative to other elements, or both has long been debated. We analyze the broad-line region (BLR) abundances of 121 N-loud quasars at $2.13 \leq z \leq 3.90$ selected from the Dark Energy Spectroscopic Instrument Data Release 1 and construct a control sample of normal quasars matched in redshift, continuum luminosity, and virial black hole mass. Within the N-loud sample, metallicities inferred from N V/C IV span $\sim 3$-$50\,Z_\odot$ and are systematically higher than those inferred from the nitrogen-independent (Si IV+O IV])/C IV and Al III/C IV diagnostics, which agree closely and mainly span $\sim 1$-$20\,Z_\odot$. Compared with the matched controls, the N-loud quasars show systematically higher metallicities in both N V/C IV and (Si IV+O IV])/C IV, with median values approximately three times those of the controls. Notably, the discrepancy between the metallicities inferred from N V/C IV and (Si IV+O IV])/C IV becomes more pronounced toward the high-metallicity end of the N-loud sample, suggesting additional nitrogen enrichment beyond the overall metal enrichment. Together, these results indicate that N-loud quasars have both high overall BLR metallicity and enhanced relative nitrogen abundance, suggesting that relative nitrogen abundance is at least partially decoupled from overall metallicity. N-loud quasars therefore provide a high-metallicity laboratory for understanding how nuclear environments can produce unusual abundance patterns and offer a complementary view of how nitrogen enrichment arises across cosmic time.
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All authors Shuo Zhai, Wei-jian Guo, Yong-Jie Chen, Haining Li, Jian-Min Wang, Gang Zhao

Solar and Stellar Astrophysics · Cross-listed from hep-ph

Probe of Solar Neutrino Magnetic Moments through Spin-Flavor Precession: Resonance Structure and Antineutrino Appearance

Pouya Bakhti, Sudip Jana, Chui-Fan Kong et al. (+2 more)

We investigate solar-neutrino spin–flavor precession (SFP) induced by magnetic moments in the three-active-flavor framework. For Majorana neutrinos, SFP can convert solar neutrinos into antineutrinos of different active flavors. In the Dirac case, SFP instead produces sterile right-handed states and can lead to the disappearance of active neutrinos. Using the full $6\times6$ Hamiltonians and GS98 and AGSS09 solar profiles, we examine propagation-eigenvalue crossings at $B_\perp=0$ and the projected magnetic couplings between the corresponding states. For normal mass ordering and $1\leq E_\nu/\mathrm{MeV}\leq20$, we confirm the absence of finite-density Majorana crossings. A magnetically coupled Dirac crossing emerges above approximately $12~\mathrm{MeV}$ but involves only a subdominant electron-flavor component, limiting resonant disappearance. Nonresonant Majorana conversion nevertheless offers a distinctive lepton-number-violating solar $\bar\nu_e$ signal, motivating our sensitivity study for the Jinping Neutrino Experiment. For a proposed $3~\mathrm{kt}$ detector operating for five to ten years, we project a 90% C.L. sensitivity of $P(\nu_e\to\bar\nu_e)\simeq(0.85-1.3)\times10^{-5}$. In the $\mu_{12}$-only benchmark, optimistic solar-core transverse magnetic fields of $B_\perp=7-10~\mathrm{MG}$ imply a reach of $|\mu_{12}|\simeq(2.3-4.1)\times10^{-13}\,\mu_B$, numerically below existing direct-scattering limits and commonly quoted stellar-cooling bounds. This could enable Jinping to provide one of the most stringent projected terrestrial sensitivities to Majorana transition magnetic moments.
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All authors Pouya Bakhti, Sudip Jana, Chui-Fan Kong, Seodong Shin, Seokhoon Yun

High Energy Astrophysical Phenomena

Evolution of the High-Energy Excess in Swift J1727.8-1613 during Its 2023 Flare State

Xiao Fan, Bei You, Yi Long et al. (+2 more)

We investigate the evolution of the high-energy excess in Swift J1727.8-1613 during its 2023 flare state using joint Insight-HXMT and INTEGRAL/ISGRI observations covering 2-500 keV. Fits to the broadband spectra with a model including thermal Comptonization and disk reflection leave systematic positive residuals above ~150 keV. Adding a power-law component improves the fits and yields photon indices of 2.08-2.61, demonstrating that the high-energy excess beyond the thermal Comptonization continuum is present throughout the flare state. We also show that all spectra can be well described by the hybrid Comptonization model eqpair, without requiring any additional high-energy component. The fitting results indicate that the energy supply to the electrons transitions from predominantly thermal heating to non-thermal acceleration, and that the electron injection spectrum steepens abruptly near the onset of the flare state. During this evolution, the radio spectral index changes from approximately zero to negative values, accompanied by the ejection of three transient jet knots. Based on this temporal association, we discuss a possible connection between the increase in non-thermal power indicated by our spectral analysis and the ejection of the transient jet.
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All authors Xiao Fan, Bei You, Yi Long, Han He, Liang Chen

High Energy Astrophysical Phenomena

High-energy spectral cutoffs in the prompt emission of Fermi gamma-ray bursts: bulk Lorentz factors, emission radii, and a cutoff-peak energy relation

Yuan-Yuan Zuo and Yuan-Chuan Zou

The high-energy end of the gamma-ray burst (GRB) prompt spectrum carries information on the physical conditions of the relativistic outflow, but the number of well-characterized spectral cutoffs is small. We present a systematic search for high-energy spectral cutoffs in the time-integrated prompt spectra of 139 GRBs observed by Fermi between 2008 July and 2025 December, selected to have broadband coverage either through a LAT detection or through bright BGO emission. Joint GBM, LLE, and LAT spectra over $T_{90}$ are fitted with four empirical models and compared using the Bayesian information criterion, yielding 106 bursts with well-constrained cutoff energies $E_c$. An empirical two-component Gaussian mixture model applied to $\log_{10}(E_c/\mathrm{MeV})$ separates a low-$E_c$ group from the main distribution at $E_c=2.12$ MeV; the 77 bursts lying firmly above this boundary are interpreted within the internal $\gamma\gamma$ pair-opacity framework. Combining $E_c$ with wavelet-based minimum variability timescales (median $0.119$ s), we infer bulk Lorentz factors of $11.7$ to $2.78\times10^{3}$ (median 145) and emission radii of $\sim10^{13}$ to $10^{15}\,\mathrm{cm}$. Neither the $\Gamma$-$L_{\mathrm{iso}}$ nor the $\Gamma$-$E_{\mathrm{iso}}$ relation is statistically significant for the full sample, whereas the 27 bursts with measured redshifts show a moderate $\Gamma$-$L_{\mathrm{iso}}$ correlation with a slope of $0.36_{-0.23}^{+0.22}$. We further find a strong rest-frame correlation between the cutoff and peak energies, $E_{c,z}\propto E_{p,z}^{2.15_{-0.97}^{+0.96}}$, for the 26 bursts with measured redshifts, which persists after controlling for redshift.
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Solar and Stellar Astrophysics

Presence of Solar Neutral Atom Corona and Coronal Heating

Z.Q. Qu, R.Y. Zhou, H. Su et al. (+3 more)

By analyzing slit scanning spectral data obtained during 2024 total solar eclipse, presence of neutral atom corona is revealed along with a hidden inner F-corona detected within heights below half a solar radius. The inner F-corona is found to be essentially different from the Fraunhofer corona formed by dust scattering beyond about 2.3 solar radius heights. The two new kinds of the solar corona are deduced from the intensity difference between the spectral line intensity distribution and their adjacent continuum one acquired during the totality. Through analysis of the recorded spectra ranging from 516.0nm to 540.7nm, the relative depths of strong Fraunhofer lines are found to be changed among the neighboring lines from one place to another and from the photospheric lines acquired before the eclipse. Thus the resonant scattering is regarded to be responsible for the changes. Furthermore, shown in the reconstructed maps at selected spectral lines, the detected inner F-corona is found spreading globally and the neutral atom scattering acts as its dominant source. Both of their distribution patterns generally depend on specific lines and show considerably asymmetrical diffusions. The outward neutral fluxes are observed to be mainly hindered in regions of coronal magnetic loops with roughly estimated concentration above $10^{-5}$. Thus it can play a key role in global coronal heating via Cowling dissipation in these widely spread coronal loops, like heating in Tokamak by neutral beam injection(NBI). The Cowling dissipation can give a consistent interpretation of heating from the chromosphere to the corona. Thus the neutral atom corona is not only a new gradient of the solar corona but also the missed factor critical for concatenating together these coronal heating mechanisms.
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All authors Z.Q. Qu, R.Y. Zhou, H. Su, Y. Liang, L. Chang, X.M. Cheng

Solar and Stellar Astrophysics

Thermodynamic exchange and mode stability in strongly nonadiabatic radial pulsations

Jan Zalewski

We apply the quadratic balance relation for linear nonadiabatic pulsations to radial modes of a sequence of post-AGB envelope models covering $3.52\leq\log(T_{\rm eff})\leq4.6$. The relation separates the thermodynamic exchange power $\mathcal{P}_{\rm ex}$, response power $\mathcal{P}_{\rm rsp}$, and surface contribution $\Delta B$, and introduces an effective norm through $\mathcal{P}_{\rm ex}+\Delta B=2\gamma\chi_{\rm eff}\mathcal{E}_{\rm kin}$, where $\gamma$ is the mode growth rate. For nearly adiabatic modes $\chi_{\rm eff}$ is close to unity, whereas in strongly nonadiabatic pulsations the compression and horizontal area deformation contributions can make it change magnitude or even reverse its sign. In the cooler models, a broad family of overtone modes has $\chi_{\rm eff}<0$ and is damped despite positive thermodynamic exchange power. For these modes the response power supplies the opposing damping. Conversely, two low frequency modes in the hotter models are excited over a range of effective temperatures, even though their thermodynamic exchange power is negative. Their instability is produced by the positive response power. Strange modes generally have $\chi_{\rm eff}>0$, apart from a narrow boundary-sensitive transition during which a cold strange mode transforms into an ordinary p-mode. The excited low frequency solution with $\chi_{\rm eff}<0$ persists with a finer numerical mesh and such modes are found under the alternative outer boundary formulations examined, although their frequencies are boundary condition dependent. Thus, for strongly nonadiabatic pulsations, the sign of the thermodynamic exchange power alone does not determine mode stability.
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