High Energy Astrophysical Phenomena
Indirect Dark Matter Detection in the Multi-Messenger Era: Experiments, Systematics, Anomalies, and Prospects for Discovery
Muad Ghaith and Khaled Obaideen
Indirect searches for dark matter (DM) span gamma rays, charged
cosmic rays,
neutrinos, X-rays,
radio emission, the
cosmic microwave background (CMB), and the 21~cm signal, but reported constraints and anomalies vary in evidential strength. This critical review synthesizes peer-reviewed literature from January 2000 through October 2026 using a structured search strategy. We assess observations through a framework linking particle interactions and
halo source terms to propagation or cosmological energy deposition, instrumental response, background modeling, and statistical inference. Fermi-LAT observations of dwarf spheroidal
galaxies provide robust GeV-scale
benchmarks for DM annihilation, whereas Galactic-center searches offer higher expected signals but depend more on foregrounds and
halo profiles. Charged-
cosmic-ray measurements are precise but limited by propagation and source uncertainties, while
neutrino searches offer complementary sensitivity through solar capture, directional and flavor information, and high-mass annihilation or decay. Several widely discussed signals, including the 3.5~keV line, 511~keV emission, the Galactic-center GeV excess, charged-particle features, cluster
radio excesses, and candidate gamma-ray lines remain inconclusive because of limited independent confirmation, uncertain target scaling, spectral degeneracies, or background-modeling limitations. Cosmological observations provide complementary constraints from CMB energy-injection limits and 21~cm measurements of the intergalactic medium. Artificial intelligence increasingly supports reconstruction and inference but requires rigorous calibration and domain-shift validation. The strongest case for DM discovery would require statistically consistent evidence across independent targets, instruments, or messengers, under common particle-physics parameters, and with well-characterized uncertainties.
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High Energy Astrophysical Phenomena
An end-to-end experimental pipeline for automated track identification for paleo-detectors
Claudio Galelli, Alessandro Testi and Lorenzo Caccianiga
Paleo-detectors aim to exploit the damage tracks left in natural minerals by
cosmic messengers over geological times to reconstruct past fluxes of energetic particles. For
cosmic rays, the expected signal is abundant, and the tracks are micron-scale, so they can be revealed by etching and read out with conventional optical microscopy; what remains challenging is turning a bulk sample into a calibrated track-length spectrum that can be quantitatively confronted with theoretical predictions. In this work we present the experimental pipeline we developed for this purpose within the INFN PRImuS experiment, from sample preparation and automated multi-focus microscopy to track recognition with OptimusPrimus, a two-stage machine-learning
algorithm, and to a forward-folding model that propagates
geometric sectioning, etching and the measured detection response into simulated spectra. The pipeline was built and validated on chemically etched obsidian where the recovered track-length distribution is statistically compatible with expert annotation. In parallel, we developed and characterized a dry argon-
plasma etching protocol for halite, an evaporite mineral of particular interest as a low-background
cosmic-ray paleo-detector. Since every stage of the pipeline is mineral-agnostic, with only the trained networks and the detection response to be re-derived from annotated data, we are now applying it to
plasma-etched halite with the aim of identifying
cosmic-ray-induced tracks.
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Astrophysics of Galaxies
A Quest for Changing-State AGNs
Kasra Mokhtarpour and Vicki Sarajedini
We use Gaia Data Release 3 (DR3) light curves to identify photometrically selected changing-state active galactic
nucleus (CSAGN) candidates. We employ unsupervised deep learning and anomaly detection methods to identify unusual patterns of variability in the light curves of 872,228 AGNs with known variability. We find that 8,504 light curves show anomalous behavior. Among these, 682 sources show evidence for two-state photometric behavior during the Gaia DR3 observing baseline. These 682 CSAGN candidates were selected using an automated statistical pattern recognition approach based on Gaussian mixture models (GMMs) to identify sources whose magnitude distributions are consistent with two preferred brightness levels, substantially reducing the need for human visual inspection in selecting the CSAGN candidates. The candidates tend to have fainter absolute magnitudes and lower
redshifts than the non-anomalous Gaia variable AGN sample, suggesting that some may be accreting at lower rates. Our approach builds a large candidate sample with less reliance on human visual selection. Follow-up observations of these sources can help identify what drives changing-state transitions and clarify their connection to
accretion-disk physics and supermassive black hole (SMBH) fueling.
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Cosmology and Nongalactic Astrophysics
Self-Interacting Dark Matter: From Particle Physics Theories to Structure Formation Simulations
Martin Rosenlyst, Vinh Tran, Oliver Zier et al. (+7 more)
We present a unified theory-to-simulation framework for self-interacting dark matter (SIDM), combining a self-contained introduction to its particle-physics foundations and representative
benchmark models with an explicit, systematic mapping to simulation inputs and validated numerical implementations in the moving-mesh code AREPO-2. We characterize representative elementary and composite dark-sector models through their particle content,
symmetries, interactions, production mechanisms, and constraints. We then establish an explicit mapping from their microscopic properties to the inputs required for structure-formation simulations, including modifications to cosmological initial conditions, internal-state mass splittings and populations, reaction networks, velocity- and angle-dependent cross sections, dissipative energy loss, and decay rates and recoil kinematics. Building on the efficient, scalable SIDM infrastructure introduced in our companion work, we implement isotropic and anisotropic self-scattering with constant or velocity-dependent cross sections, multi-state and inelastic reactions, and dissipative scattering, as well as a dedicated DM decay module. We validate the implementations through beam-
lattice deflection experiments, thermalization and uniform-box decay tests, isolated-
halo gravothermal core-collapse simulations, and cosmological box and zoom-in simulations. The tests reproduce analytical predictions and published inelastic and dissipative
benchmarks, with agreement across numerical schemes. The resulting framework provides a common reference for researchers across disciplines and a practical route from microscopic dark-sector theories to nonlinear astrophysical predictions beyond standard isotropic, elastic SIDM.
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All authors Martin Rosenlyst, Vinh Tran, Oliver Zier, Xuejian Shen, Mark Vogelsberger, Thejs Brinckmann, Mads T. Frandsen, Jesús Zavala, Frederik Holt Dihver Christensen, Mikkel Theiss Kristensen
Astrophysics of Galaxies
Unveiling the Hot Interstellar Medium in Nearby Galaxies with eROSITA
Roman Laktionov, Manami Sasaki, Elias Kyritsis et al. (+9 more)
Diffuse X-ray emission in
galaxies originates from stellar-feedback-heated gas and unresolved compact sources. We investigate its thermal component and the scaling of X-ray luminosity with
star formation rate (SFR), including
galaxies with very low SFRs. We analyzed eROSITA/SRG data from the four all-sky surveys (eRASS:4) for a blind, volume-limited sample of 140
galaxies within 25 Mpc from the Updated Nearby
Galaxy Catalog (Karachentsev et al. 2013), cross-matched with HECATEv2 (Kyritsis et al. 2026b). Early-type
galaxies were analyzed separately, while
star-forming
galaxies were divided into low-, medium-, and high-specific-SFR (sSFR) subsamples. We modeled the integrated X-ray spectra with thermal
plasma and power-law components, stacked spectra for each subsample, and derived total and thermal X-ray luminosities. The stacked spectra show a stronger soft thermal component at high sSFR, whereas low-sSFR and early-type
galaxies are increasingly dominated by the harder non-thermal continuum. For
star-forming
galaxies, the total 0.5-8 keV luminosity follows $\log L_X \sim 39.5 + 0.9\log\mathrm{SFR}$, with an intrinsic scatter of about 0.9 dex. The 0.5-2 keV thermal luminosity follows $\log L_X \sim 38.7 + 1.1\log\mathrm{SFR}$, with an intrinsic scatter of about 0.7 dex. The thermal luminosity remains well correlated with SFR down to $\sim 10^{-5}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$ and is consistent with previous relations for
star-forming
galaxies. By contrast, the flatter and more scattered total X-ray luminosity-SFR relation suggests that unresolved X-ray binaries likely dominate at low SFR, while thermal X-ray emission remains a robust tracer of stellar feedback.
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All authors Roman Laktionov, Manami Sasaki, Elias Kyritsis, Andreas Zezas, Steven Hämmerich, Fiona Knies, Jörn Wilms, Frank Haberl, Martin G. H. Krause, Ashley Coombs, Philipp Weber, Aafia Zainab
Instrumentation and Methods for Astrophysics
Initial Performance Tests of MASTA for Wide-Field Narrowband Imaging
Mingxuan Xu, Jiang-Tao Li, Li Ji et al. (+2 more)
Wide-field narrowband imaging provides an efficient approach for mapping low-surface-brightness line emission over large angular scales. We present initial performance tests of Multi-Application Survey
Telescope Array (MASTA) for narrowband imaging. Using commissioning data obtained with the QHY461 and COSMOS-8K cameras, we characterize the basic reduction procedure, photometric calibration, image quality, and point-source detection limits. The measured surface-brightness and point-source detection limits become deeper with increasing exposure time, roughly following the expected background-limited scaling. Under the current observing and reduction conditions, the COSMOS-8K camera generally reaches deeper surface-brightness limits, particularly in the red filters, while QHY461 has smaller pixel size and provides better sampling of the
telescope point spread function (PSF). As demonstrations, we perform continuum subtraction for the nearby
galaxy M106 and the
supernova remnant Cygnus Loop using adjacent narrowband filters and reveal the H{\alpha} and [O III] structures in M106 and filamentary structures in the Cygnus Loop. We further compare the MASTA surface brightness H{\alpha} map of M106 with an independent SITELLE measurement. After accounting for [N II] contamination and the wavelength-dependent response of the 6544 Å filter in the f /1.7 converging beam, the corrected median ratio is 0.973. These tests indicate that MASTA is a promising facility for wide-field narrowband imaging. Further improvements in calibration frames, including flux calibration, field-dependent bandpass characterization, and spatially varying PSF modeling and matching will be required for quantitative studies of diffuse ionized gas.
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All authors Mingxuan Xu, Jiang-Tao Li, Li Ji, Chen Zhang, Yantian Zhu
High Energy Astrophysical Phenomena
Double Detonations on a Moving Mesh with $\texttt{Cattails}$: Characterizing Early Reddening in SNe Ia
Dillon Hasenour, Paul Duffell and Abigail Polin
Type Ia
supernovae are useful as cosmological distance indicators and are significant sources of chemical enrichment in
galaxies, but much about their origins remains uncertain. The double detonation explosion mechanism is one promising model for these transients. We present a suite of thermonuclear hydrodynamic double detonation models of sub-Chandrasekhar mass white dwarfs spanning thin to thick helium shells. Thin shell models produce light curves and spectra consistent with normal Type Ia
supernovae, and thicker shell models have early time luminosity bumps from radioactive ashes in the shell and early reddening in color sometimes observed in peculiar Type I
supernovae. The reddening is due to line blanketing from heavy elements produced in the shell detonation encompassing the central emission. We perform the computations using $\texttt{Cattails}$, a moving mesh nuclear hydrodynamics code introduced in this work. After carrying out subsequent radiative transfer calculations using the $\texttt{Sedona}$ code, we relate the time of early reddening to the mass of the initial helium shell. We also consider how the relation changes as a function of total mass as well as how the peak brightness depends on the total mass. Finally, we provide a series of fitting functions that can be used to estimate the mass of the shell consistent with an observation of reddening in the early color
evolution of a type Ia
supernova.
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Astrophysics of Galaxies
Evidence for Hierarchical Turbulent Scaling in Nearby Star-Forming Galaxies
Luna Maria Scipio, Fernando A. N. Santos and Jay Armas
We find recurring signatures of intermittency in molecular-gas velocities from cloud to galactic scales. In 31 selected
galaxies from PHANGS-ALMA, velocity-centroid exponents through sixth order show nonlinear order dependence and nearly linear relations between consecutive exponents across
galaxies. Positive estimated offsets from single-exponent scaling occur in all 52
galaxies with a valid power law fit and 99 of 100 clouds. A generalized She-Leveque hierarchy accommodates these signatures, supporting a hierarchical description of turbulent scaling in molecular gas across these environments.
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Solar and Stellar Astrophysics
TESS flares and chromospheric variability in the Pleiades, the Hyades, and Praesepe
A. Görgei, K. Vida, B. Seli et al. (+5 more)
Magnetic activity is a result of the interaction between rotation and dynamo processes in cool
stars with outer convection zones. Since open cluster members share a common age, distance, and chemical composition, they provide an opportunity to study the
magnetic activity of cool
stars in a controlled astrophysical context. We used 120s cadence observations from the Transiting
Exoplanet Survey Satellite (TESS) to study the
flare activity of
stars in three open clusters with different ages: the Pleiades (100 Myr), the Hyades (700 Myr) and Praesepe (700 Myr). We used the Ohio State Multi-Object Spectrograph (OSMOS) at MDM Observatory with the goal of identifying coronal mass ejections (CMEs) in the Pleiades and Praesepe. We investigated the flaring characteristics of the cluster members using the TESS light curves: we identified the
flares, then divided the
dataset into different categories based on the effective temperature and light curve amplitude. We calculated the
flare energies and investigated the
flare frequency distributions. We studied the dynamic spectra of the H$\alpha$ line and its environment to search for indication of CMEs. The power-law indices of the
flare frequency distributions obtained in our analysis span the 1.8-2.8 range. We found the highest
flare rates in the Pleiades for all investigated spectral types. Our results show that the
flare rate of M dwarfs is similar in the Pleiades and the Hyades while for K-type
stars the
flare rate in the Pleiades is an order of magnitude higher. Our analysis reveals that the
flare rate in M
stars changes with their effective temperature: the rate is highest for T$_{eff}$ $\sim$3200-3300 K -coinciding with the transition between partially and fully convective
stars - with smooth decrease in
flare rate towards cooler and hotter M dwarfs. We used the MDM/OSMOS spectra to place an upper limit on the CME rate.
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All authors A. Görgei, K. Vida, B. Seli, K. Oláh, P. Sági, B. Schmercz, R. M. Roettenbacher, Zs. Kővári
Cosmology and Nongalactic Astrophysics
A census of Dark Energy Survey Year 3 redMaPPer galaxy clusters in a high exposure eROSITA All Sky Survey region
P. A. Giles, A. K. Romer, J. Pilling et al. (+64 more)
We present the cross-match of
galaxy clusters detected by redMaPPer using the first three years of Dark Energy Survey (DESY3RM) operations, and the first release of the eROSITA-All Sky Survey (eRASS1) taken by eROSITA on board the Spectrum Roentgen Gamma
telescope. We define a sky region ($60^{\circ}<{\rm R.A.}<90^{\circ}$ and $-58^{\circ}<{\rm Dec}<-48^{\circ}$) whereby the mean eRASS1 exposure time of clusters falling within this footprint is $\sim$2.5 times longer than the mean exposure time of the full eRASS1–DESY3RM overlap. Limiting to a
redshift range $0.2 < z < 0.65$ and redMaPPer estimated richnesses to $>$50, we obtain a sample of 57 clusters. We match these clusters to the cluster catalogue constructed for the eRASS1, finding 45 clusters with a match and 12 with no match in the catalogue. X-ray properties of the 12 unmatched clusters are estimated via a forced photometry analysis. We investigate the form of the luminosity-richness relation, finding the relation using the full 57 cluster sample is statistically consistent with using only the 45 matched clusters, and will require the deeper data of future eRASS releases (or dedicated X-ray follow-up) to explore further potential differences. Using external data from XMM, ACT and SPT, we find detections of 5 of the 12 unmatched clusters, indicating the presence of virialised gas. Finally, we found the 12 unmatched clusters occupy a higher
redshift range and lower richness range (compared to the matched clusters), and find no evidence for an underlying physical reason for the lack of X-ray emission.
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All authors P. A. Giles, A. K. Romer, J. Pilling, R. Wilkinson, D. J. Turner, T. Jeltema, A. Farahi, M. E. Ramos-Ceja, F. Balzer, M. Kluge, S. Grandis, E. Bulbul, M. Hilton, S. Bhargava, E. Aljamal, A. E. Evrard, E. W. Upsdell, P. T. P. Viana, A. Abdulghafour, M. Aguena, S. S. Allam, O. Alves, F. Andrade-Oliveira, D. Bacon, D. Brooks, R. Camilleri, A. Carnero Rosell, J. Carretero, M. Costanzi, L. N. da Costa, J. De Vicente, S. Desai, P. Doel, C. Doux, B. Flaugher, J. Frieman, J. Garc, M. Gatti, D. Gruen, G. Gutierrez, S. R. Hinton, D. L. Hollowood, K. Honscheid, K. Kuehn, O. Lahav, S. Lee, J. L. Marshall, J. Mena-Fernández, F. Menanteau, R. Miquel, R. C. Nichol, R. L. C. Ogando, A. A. Plazas Malagón, S. Samuroff, E. Sanchez, D. Sanchez Cid, M. Smith, M. E. da Silva Pereira, M. Soares-Santos, E. Suchyta, M. E. C. Swanson, C. To, D. L. Tucker, V. Vikram, A. R. Walker, N. Weaverdyck, J. Weller
Cosmology and Nongalactic Astrophysics
The XMM Cluster Survey: Cross-Calibration of eROSITA and XMM using Dark Energy Survey Y3 Galaxy Clusters
J. E. Pilling, D. J. Turner, P. A. Giles et al. (+9 more)
We present the cross-calibration of the eROSITA and XMM
telescopes, using
galaxy clusters detected by redMaPPer from the first three years of Dark Energy Survey observations (DESY3RM). We use the X-ray: Generate and Analyse (XGA) Python module to measure eROSITA properties, and validate our methodology using a deep pointed eROSITA CAL-PV observation of A3158, and a sample of 119 clusters from the expanded HIgh FLux
Galaxy Cluster Sample (eeHiFLUGCS). Next, we construct a sample of DESY3RM clusters matched to XMM observations analysed by the XMM Cluster Survey (XCS), and to clusters in the first release of the eROSITA All-Sky Survey (eRASS1). This produced a sample of 114 DESY3RM clusters with both XMM and eROSITA detections. Our resulting X-ray temperatures determined from eROSITA were compared to eRASS1 catalogue values, showing consistency between the two analyses. Comparisons between XMM and eROSITA temperatures reveal a systematic offset, with XMM temperatures 28$\pm$7% higher on average. Finally, we fit $L_{\rm X,soft}$-$\lambda_{\rm RM}$ and $T_{\rm X}$-$\lambda_{\rm RM}$ scaling relations for both eROSITA and XMM using the same cluster sample, finding minimal differences in the $L_{\rm X,soft}$-$\lambda_{\rm RM}$ relation but a clear normalisation offset in the $T_{\rm X}$-$\lambda_{\rm RM}$ relation, particularly for the highest richness systems. This study will enable future work combining eROSITA and XMM observatories for DESY3RM clusters.
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All authors J. E. Pilling, D. J. Turner, P. A. Giles, A. K. Romer, R. Wilkinson, P. J. Rooney, M. Hilton, S. Bhargava, J. Hall, R. Wang, A. Abdulghafour, B. J. Maughan
Astrophysics of Galaxies
Environmental Dependence of Satellite Planarity and Orbital-Pole Coherence around Milky Way Analogues in a Hydrodynamical Cosmological Simulation
Peng Wang, Yu Luo, Jiang Chang et al. (+2 more)
We examine whether the unusual spatial flattening and orbital-plane coherence of the Milky Way's classical satellites are connected to the
Galaxy's location in the
cosmic web. We compare the 11 classical satellites with the 11 most massive satellites of 11,922 Milky Way-mass hosts in the TNG300-1 hydrodynamical simulation. We measure flattening with both the simple inertia tensor (SIT), which retains radial information, and the reduced inertia tensor (RIT), which isolates angular anisotropy. Orbital-plane coherence is characterized by the minimum opening angle containing the axes of the eight most coplanar satellite orbits. For the Milky Way, we find $(c/a,b/a)=(0.183,0.558)$ for SIT and $(0.364,0.736)$ for RIT, together with an eight-orbit opening angle of $21.9^\circ$. The corresponding fractions of simulated systems at least as extreme are $4.94\%$, $12.28\%$, and $5.04\%$, respectively. We describe the environment using the velocity-shear tensor smoothed on $2\,h^{-1}\mathrm{Mpc}$ and compare the full sample with Local Group-like pairs, systems whose shear
eigenvalues match those reconstructed for the Local Group, and hosts in
knots, filaments, sheets, and voids. Among the well-sampled environmental subsets, the shape and opening-angle distributions differ only weakly. Although the
cosmic web imprints preferred orientations on host
spins and satellite orbital-plane axes, the Milky Way combines orientations that are uncommon in the simulation. We conclude that the present-day
cosmic-web environment alone does not substantially increase the occurrence of Milky Way-like satellite configurations. This result does not rule out an origin in anisotropic
accretion, since neither the present-day web class nor its shear
eigenvalues fully encodes the assembly history of an individual satellite system.
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All authors Peng Wang, Yu Luo, Jiang Chang, Xi Kang, Shi Shao
Solar and Stellar Astrophysics
An Intermediate-orbit Brown Dwarf Confirmed with Astrometry+Radial Velocity Joint Analysis, and the Eccentricity Distribution of Brown Dwarfs Across Different Locations
Lei Ren, Tianjun Gan, Yifan Xuan et al. (+5 more)
Intermediate-orbit ($\sim 1$ AU) brown dwarfs with absolute mass measurements are essential for understanding the
evolution of substellar objects. Although such systems remain rare, their number is now being enlarged thanks to astrometry. Here, we present the absolute mass measurements for HD 203771B, a massive brown dwarf orbiting a K dwarf ($M_\ast=0.79\pm0.08\ M_\odot$) with a period of 1140 days on an eccentric ($e\approx0.5$) and inclined ($i\approx 130^{\circ}$) orbit. Through joint analysis of (1) radial velocities and Gaia two-body solution, as well as (2) radial velocities, Hipparcos Intermediate Astrometric Data and two-epoch Gaia astrometry, we obtain true companion masses of $74.20^{+3.46}_{-3.64} M_{\mathrm{J}}$ and $69.03^{+4.99}_{-4.95} M_{\mathrm{J}}$, respectively, agreeing with each other within $1\sigma$. Taking a sample of 159 brown dwarfs with absolute mass measurements from different detection techniques, we investigate their eccentricity distributions across different semi-major axis ranges by fitting a Beta distribution. We find that the peak of eccentricity distribution tends to gradually shift toward lower values from wide orbits ($a>20$ AU) to intermediate ($1<a<20$ AU) and inner ($0.1<a<1$ AU) regions. Such trend is plausibly due to disk friction during orbital
evolution. Together with obliquity studies showing that brown dwarfs are mostly aligned, our result suggests that brown dwarfs may migrate inward through quiescent coplanar disk-driven processes.
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All authors Lei Ren, Tianjun Gan, Yifan Xuan, Shude Mao, Shigeru Ida, Guang-yao Xiao, Fabo Feng, Enric Pallé
Instrumentation and Methods for Astrophysics
Institutional broadening of the Japanese astronomy and astrophysics research community during 1996-2025
Hideaki Fujiwara
Using bibliometric data from publication records, we investigate the institutional broadening of Japanese astronomy and astrophysics over 1996-2025. The number of Japan-affiliated publications increased from 588 to 2,156, and the number of unique participating Japanese institutions increased from 123 to 227, indicating a nominal broadening of the institutional base. However, institution-publication links remained concentrated among leading institutions, and the effective number of institutions, a frequency-weighted diversity measure, increased more gradually than the number of unique participating institutions. These results show that Japanese astronomy and astrophysics broadened institutionally, but not through a complete equalization of institutional participation. The observed change is best interpreted as an expansion of the participating institutional base around a persistent core of leading institutions.
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Earth and Planetary Astrophysics
An updated view of Jupiter's UV main auroral emission: large-scale analysis of UV and particle data from Juno's first 60 orbits
Linus Head, Denis Grodent, Bertrand Bonfond et al. (+9 more)
The properties and origins of Jupiter's UV main auroral emission are, at present, not yet fully understood, particularly the extent to which its two distinct zones, the Zone-I and Zone-II aurora, originate from a common source. In this work, remote-sensing and in-situ data from the Juno spacecraft are used to investigate and produce maps of the average properties of the main emission over Juno's first 60 orbits. It is found that the peak in mean energy of electrons precipitating in the main emission is consistently poleward of the energy-flux (or brightness) peak, in both hemispheres and at all local times, and is co-located with the statistical location of the Zone-II aurora. Evidence is presented that the flux-energy relationship of the main emission is adequately characterised by theoretical power laws describing electron acceleration from quasi-static potentials or Alfvénic
turbulence and that it shows a modulation with ionospheric electron density consistent with theoretical predictions. Finally, the average energy spectra of precipitating electrons in the Zone-I aurora remain power-law-like between an energy flux of 1 and 100 mW m$^{-2}$, whereas the average Zone-II spectra develop a distinct “plateau” or “flattop” shape beyond an energy flux of $\sim$5 mW m$^{-2}$. Our results provide some evidence that the Zone-I and Zone-II aurorae are phenomenologically distinct, and the consequences of this interpretation for future investigation of the main emission are discussed.
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All authors Linus Head, Denis Grodent, Bertrand Bonfond, Nicholas Kruegler, Ali Sulaiman, George Clark, Bilal Benmahi, Guillaume Sicorello, Julie Vinesse, Thomas Greathouse, Rohini Giles, Barry Mauk
Cosmology and Nongalactic Astrophysics · Cross-listed from stat.ML
$\texttt{NFDiag}$: High-dimensional MCMC Convergence Diagnosis with Normalizing Flows
Kutay Nazl{\i} and Elena Sellentin
Accurately assessing the convergence of Monte Carlo Markov Chains is crucial for ensuring their validity in
Bayesian inference problems. However, convergence assessment in high dimensions is known to be difficult, due to most convergence diagnostics becoming insensitive beyond a few dozen parameters. Conventional convergence statistics analyze marginal distributions which in high dimensions neglects increasing levels of information from the joint and conditional probability distributions. Thus we propose $\texttt{NFDiag}$, which taps into the information of the full multivariate joint posterior with a normalizing flow (NF). Our convergence diagnostic thereby also analyzes information from conditional distributions. In other words, by working in the full multivariate space, it is sensitive with respect to the geometry of the chain in high dimensions. Our diagnostic utilizes that NFs assume independent and identically distributed (iid) training samples, which is a testable assumption that will be violated by a non-converged or strongly correlated chain. Our diagnostic trains NFs on separate parts of a chain, and then assesses whether these correspond to the same multivariate target distribution. We test our diagnostic in up to 250 dimensions, and demonstrate it is universal and unbiased, and detects problematic chain quality also when Gelman-Rubin $\hat{R}$ and the multivarite effective sample size do not.
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High Energy Astrophysical Phenomena
The Thousand-Pulsar-Array programme on MeerKAT - XX. Co-existing interacting periodicities and polarization modulation in PSR J1901-0906
Jui-An Hsu, Patrick Weltevrede, Geoff Wright et al. (+3 more)
We present a comprehensive analysis of the complex subpulse modulation in PSR J1901-0906 using data from the Thousand-
Pulsar-Array (TPA) programme. Our analysis reveals the coexistence of three distinct periodicities in the subpulse modulation of both profile components, which obey a beat relation. We also detect additional spectral beat features caused by the modulation of these co-existing periodicities by investigating the
Fourier phase correlation in two-dimensional fluctuation spectra. Moreover, the single-pulse polarization states are shown to be modulated and synchronized with the three co-existing periodicities observed in total intensity. Such synchronization has been reported for only a small number of
pulsars, but this discovery marks the only one where this synchronization involves multiple co-existing periodicities. The modulation beats are similar to, yet more complex than, the beat system previously identified in PSR J1514-4834 with higher-order harmonics playing a significant role. The coexistence of the observed beat-like periodicities in PSR J1901-0906 implies that they are not independent, but rather originate from an underlying, interconnected physical system within the
pulsar magnetosphere. Building upon the same
geometric framework previously applied to PSR J1514-4834, we demonstrate that a feedback system with interacting rotating carousels successfully reproduces the complex subpulse modulations observed in PSR J1901-0906 and naturally explains the beat relations.
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All authors Jui-An Hsu, Patrick Weltevrede, Geoff Wright, Michael J Keith, Aris Karastergiou, Xiaoxi Song
Astrophysics of Galaxies
Identifying the principal mechanism of star formation feedback
Chong Li, Rouyu Li, Keping Qiu et al. (+27 more)
Feedback from massive
stars regulates the formation of next-generation
stars and
planets and thus shapes the
evolution of
galaxies, yet observational evidence capable of determining which mechanism dominates the feedback process has long been lacking. Here,we present a large-scale HI survey toward Orion A$.$ With an unprecedented sensitivity and superior resolution, FAST (Five-hundred-meter Aperture Spherical
radio Telescope) reveals a well-defined heart-shaped expanding HI bubble, enshrouding the well-known "Veil" bubble of ionized gas. The photoionization-driven and wind-driven gas expands at 10.9 and 13.8 kilometers per second, respectively, with a kinetic energy ratio of 1:2 assuming a spherical
symmetry and a uniform HI-to-H2 ratio. This first direct comparison within a single bubble shows that radiation does not dominate the feedback process as predicted by classical theories; instead, stellar winds contribute a comparable share of the injected kinetic energy.
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All authors Chong Li, Rouyu Li, Keping Qiu, Marko Krco, Di Li, Hongchi Wang, Xin Lyu, Yan Duan, Min Fang, Xuepeng Chen, Lile Wang, Haoran Feng, Shuinai Zhang, Miaomiao Zhang, Shaobo Zhang, Yue Cao, Yao Wang, Yan Gong, Fujun Du, Zhiwei Chen, Yang Su, Yuehui Ma, Yuchen Xing, Yinghui Zheng, Tianwei Zhang, Shu Niu, Chenrui Li, Jiawei Liu, Zhijun Zhang, Yulian Guo
Solar and Stellar Astrophysics
Aditya-L1 and SDO Observations of a Confined X-Class Flare with an EUV Late Phase: Thermal and Nonthermal Emission, Magnetic Topology, and Flux Rope Confinement
Vishwa Vijay Singh, Bhuwan Joshi and N.P.S. Mithun
We study a long-duration, confined X2.0-class solar
flare exhibiting three distinct episodes of HXR emission, along with an accompanying EUV late phase. A key highlight of this work is the novel observations from the high-resolution solar X-ray spectrometers SoLEXS and HEL1OS onboard Aditya-L1, providing insights into the
evolution of thermal and non-thermal emissions. Simultaneous EUV observations from AIA/SDO in hot channels, combined with multi-band X-ray light curves, reveal a two-stage confined eruption of a large MFR, separated by $\sim$10~minutes. The first stage corresponds to an M4.6
flare, while the overall event reaches X2.0 on the GOES scale. During the first phase,
magnetic reconnection beneath the large EUV hot channel causes
plasma heating to $\sim$19~MK, with a non-thermal spectral index of $\sim$4.3. In the second phase, characterized by external reconnection and confinement of the MFR hot channel, the temperature increases to $\sim$22~MK, accompanied by further hardening of the spectral index to $\sim$3.9. Despite pronounced non-thermal signatures and enhanced particle acceleration, the MFR fails to erupt through the overlying coronal loops because of the strong strapping force exerted by the large overlying coronal loops. Importantly, the stalled eruption, together with reconnection in the higher overlying loops, results in enhanced heating within a closed
magnetic configuration, with temperatures peaking at up to $\sim$15~MK during the late phase. The paper also provides the first observations of detectable non-thermal X-ray emission during the early EUV late phase, albeit briefly, providing direct evidence for reconnection-induced heating, likely occurring in the higher overlying coronal loops.
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Cosmology and Nongalactic Astrophysics
CosmoAgent: AI Agent for Theoretical Cosmology
Stephon Alexander, Loukas Gouskos, Savvas M. Koushiappas et al. (+2 more)
We present CosmoAgent, an agentic AI framework using large
language models (LLMs) to search for dark-energy and modified-
gravity models. We define a covariant grammar that allows LLM
agents to explore the space of modified-
gravity Lagrangians. An in-house computational pipeline derives the equations of motion, solves the background dynamics, and evaluates the likelihood using late-time expansion data, including the DES 5-year type Ia
supernova sample and the DESI Data Release 2 BAO measurements. Theories are ranked by the Akaike Information Criterion (AIC) to balance simplicity and likelihood. We benchmarked 8 frontier LLMs from ChatGPT, Claude, Gemini, Kimi, DeepSeek, and Qwen, and all LLMs are able to find theories with a lower nominal AIC than flat $\Lambda$CDM, with a best improvement of $\Delta$AIC = -3.328. Seven recover quadratic quintessence. Exploratory searches also return induced-
gravity and scalar-Gauss-Bonnet structures. The modest AIC improvements do not establish an observational preference for these models over flat $\Lambda$CDM. The code is publicly available at wsunamoutlook-prog/AI-Modified-
Gravity.
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All authors Stephon Alexander, Loukas Gouskos, Savvas M. Koushiappas, Cooper Niu, Wenrong Sun
High Energy Astrophysical Phenomena
Blackbody evolution and circumstellar medium properties of broad-lined H-rich superluminous supernovae
Tuomas Kangas, Takashi Nagao, Uliana Pylypenko et al. (+2 more)
Broad-lined H-rich superluminous
supernovae (SLSNe II) tend to show signs of interaction, including a UV excess compared to a blackbody function. However, a quantitative analysis of the CSM configuration and the UV excess has so far not been performed for most of the literature sample. Additionally, SN 2023gpw showed signs of asymmetry in its peculiar blackbody and spectral
evolution, raising the question of whether similar properties can be found in other SLSNe II. We aim to characterize the circumstellar environment of SLSNe II by searching for signs of asymmetry, quantifying the UV excess, and investigating any IR echoes produced by dust. Diversity among SLSNe II is also explored. We fit blackbody functions to the SEDs of SLSNe II to quantify the UV excess luminosity and its
evolution. We use this to investigate mass-loss rates required to produce the excess through interaction. We also investigate the line profiles in SLSN II at late times and compare line velocities to the blackbody radius
evolution. We examine public WISE IR images and place constraints on IR echoes. We find mass loss rates of $\sim10^{-4}$ to $\sim0.03\, \mathrm{M_\odot}$~yr$^{-1}$ when assuming all interaction luminosity emerges in the UV, i.e., conservative lower limits for the total mass loss rate. Radii calculated from line velocities in late-time spectra are mostly too large for a spherical interaction photosphere, only compatible with the blackbody radius
evolution if the CSM is non-spherical with a low filling factor. This is in some cases supported by a mismatch between spectroscopic and blackbody expansion velocities. Considerable diversity is seen in the sample, probably as a result of different viewing angles and CSM masses. WISE images seem too shallow to observe IR echoes in SLSNe II beyond $z\sim0.1$, but in the nearest event, SN 2020jhm, a likely IR echo is detected, suggesting pre-existing dust.
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All authors Tuomas Kangas, Takashi Nagao, Uliana Pylypenko, Steve Schulze, Lin Yan
Astrophysics of Galaxies
Nearly pristine gas in a galaxy 1 billion years after the Big Bang
Sarah E. I. Bosman, Frederick B. Davies, Louise Welsh et al. (+22 more)
Excitation of carbon and oxygen ions is the primary mechanism by which collapsing gas clouds dissipate heat to form new
stars. At early
cosmic times, in
galaxies with chemically pristine gas, many
stars are expected to have masses far larger than the mass of our sun due to the deficit in these elements. We searched for ultra-metal-poor
galaxies using their spectroscopic absorption signatures in front of bright background
quasars, employing the new GHOST high-resolution spectrograph. Here we report the discovery of the first
galaxy containing a reservoir of neutral hydrogen gas with
metallicity below the ultra-metal-poor threshold: with a measured carbon-to-hydrogen ratio 11,000 times lower than the Sun, it is the most pristine ever found by a factor of four. UMP-DLA-1 is the only known
galaxy with measured carbon and oxygen abundances too low to enable efficient formation of
stars with solar mass or below. The low
metallicity alone therefore guarantees a top-heavy stellar population, providing a direct view of the chemical composition imprinted by massive low-
metallicity stars that perished long before the present day: an elevated oxygen-to-carbon ratio. The abundance pattern of UMP-DLA-1 is likely a close representation of the atomic yields of first- or early second-generation
stars.
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All authors Sarah E. I. Bosman, Frederick B. Davies, Louise Welsh, Emanuele P. Farina, Prakash Gaikwad, Benedetta Spina, Barun Maity, Ryan Cooke, Klaudia Protušová, Valentina D'Odorico, Eduardo Bañados, James S. Bolton, Rebecca L. Davies, Xiaohui Fan, Martin G. Haehnelt, Joseph F. Hennawi, Tahlia J. Hill, Seyeon Hwang, Vid Iršič, Laura Keating, Girish Kulkarni, Samuel Lai, Emma V. Ryan-Weber, Lasse Seyberlich, Molly Wolfson
Cosmology and Nongalactic Astrophysics
Sensitivity of calibration-free DESI DR2 BAO–supernova constraints to a distance-duality tilt
Stéphane Fay, Mikel Artola and Leandros Perivolaropoulos
Recent measurements from DESI baryon acoustic oscillations (BAO) have reported a moderate preference for dynamical dark energy, challenging the standard $\Lambda$CDM paradigm. Nonetheless, such a trend could reflect a tension between the shape and the offset of the Hubble diagrams predicted by current BAO and Type Ia
supernovae (SN) data, which may underpin a possible breakdown of the
cosmic distance duality relation (CDDR) linking luminosity distances $D_{\rm L}$ and angular-diameter distances $D_{\rm A}$. We explore this possibility by parametrizing deviations from this relation as $\eta(z) \equiv D_{\rm L} / [{(1+z)}^2 D_{\rm A}] = \alpha{(1+z)}^\varepsilon$, and investigate how the preference for a Chevallier-Polarski-Linder (CPL) dynamical dark energy is modified once $\varepsilon \!\neq\! 0$ is allowed. Using DESI DR2 and uncalibrated SN data (Pantheon$+$, DES-Dovekie, Union3, and Union3.1), we find that allowing $\varepsilon$ to vary freely in both $\Lambda$CDM and CPL reduces the CPL preference with respect to $\Lambda$CDM by a larger amount than the addition of spatial
curvature $\Omega_k$; only Union3.1 exhibits comparable reductions. We also find that the preference reduction is robust to alternative $\eta(z)$ parametrizations, and that the $\eta(z)$ constraints remain stable under the removal of BAO tracers or low-
redshift cutoffs for Pantheon$+$, whereas the DES-Dovekie preference largely disappears once $z < 0.1$ SN are removed. In a separate calibrated analysis, illustrative Planck sound-horizon and SH0ES absolute-magnitude priors give $\alpha \simeq 0.942 \pm 0.014$, quantifying the normalization mismatch under those assumptions. We also map the CDDR violation onto
photon-loss and varying-$G$ scenarios, concluding that the cosmological constraints are much weaker than existing constraints on these physical mechanisms.
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Solar and Stellar Astrophysics
SiO Maser Line-width Diagnostics of AGB Stars and Red Supergiants: The RSG-adjacent Region in the FWZI–Luminosity Plane
Qiu-Yu Tao, Jun-ichi Nakashima, Yong Zhang et al. (+3 more)
We investigate whether SiO maser line profiles can distinguish asymptotic giant branch (AGB)
stars from red supergiants (RSGs) and identify unusual AGB-classified sources near the RSG regime. We compiled 2,956 detected SiO maser spectra for 1,551 objects and constructed reference samples of 1,068 O-rich AGB
stars and 36 RSGs. The full width at zero intensity (FWZI) was reliably measured for 1,020 AGB
stars and 32 RSGs. AGB
stars are concentrated at narrow line widths: 81.5% have FWZI <10 km s^-1, whereas 81.2% of RSGs have FWZI >15 km s^-1 and none has FWZI <10 km s^-1. Infrared two-color diagrams provide only partial separation. Combining FWZI with luminosities based primarily on quality-filtered Gaia/Bailer-Jones distances, with independent literature distances for several RSGs, reveals a weak tendency for wider SiO maser lines at higher luminosities but no clean boundary. We therefore define an empirical RSG-adjacent region in the FWZI-luminosity plane, 15 <= FWZI <= 26.6 km s^-1 and 3.9 <= log(L/L_sun) <= 4.9, to characterize the high-luminosity, broad-line tail of the AGB-classified sample. Ten sources fall within this region. Using infrared SEDs, DUSTY fits, OH/H2O maser information, and variability, we find that six are most naturally interpreted as luminous AGB-like objects, two warrant follow-up to assess possible high-initial-mass AGB, RSG-like, or SAGB-related interpretations, and two are less securely constrained because of poor DUSTY fits. The RSG-adjacent region is therefore a physically mixed screening space, not a definitive classification box, for selecting high-priority follow-up targets.
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All authors Qiu-Yu Tao, Jun-ichi Nakashima, Yong Zhang, Zehao Zhang, Jia-Yong Xie, Chang Liu
Solar and Stellar Astrophysics
From the QBO to Rieger-type periods: Explaining extreme solar events by tidally triggered magneto-Rossby waves
F. Stefani, G.M. Horstmann, G. Mamatsashvili et al. (+1 more)
It has recently been demonstrated that the occurrence of extreme solar events is governed by a phase-stable period close to 1.723 years (629.29 days). According to our previously developed tidally-synchronized solar dynamo model, this is one of the periods resulting from two-
planet spring tides exerted by the tidally dominant
planets Venus, Earth and Jupiter, which trigger magneto-Rossby waves in the solar tachocline. Overall, the squared sum of these three waves incorporates nine periods ranging from 59 to 629 days. Using a standard Rayleigh test, we demonstrate that all nine of these periods can be identified in the data on extreme solar events. For the latter, we use a combination of 72 ground-level enhancement (GLE) events with various X-
flare data, the number of which increases when the threshold is successively lowered from X10 to X1. To identify the spectral peaks, it is necessary to analyze the sidebands that emerge due to the modulation with the longer-term periods such as the 11-year Schwabe cycle and the third harmonics of the Hale cycle. In this framework, the seminal Rieger period of 154 days is re-interpreted as the lower sideband of 146 days which is the quarter of the synodic period of Venus and Earth.
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All authors F. Stefani, G.M. Horstmann, G. Mamatsashvili, T. Weier
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Nonequilibrium framework for first-order phase transitions
Jie Liu and Ligong Bian
The first-order phase transition is central to electroweak baryogenesis and gravitational wave generation, yet thermal
equilibrium effective potential analyses cannot describe the real-time non-
equilibrium dynamics of the phase transition process. We use the Schwinger-Keldysh closed-time-path formalism of real-time finite-temperature field theory to study these effects. For the $\phi^6$ model, we derive the effective action and the corresponding Langevin equation. We further extend the formalism to the two scalar fields case, obtaining the coupled Langevin equations. These results provide a theoretical framework for the bubble nucleation simulation of the non-
equilibrium phase transition process, laying the foundation for reliable predictions of baryogenesis and gravitational wave signals.
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Solar and Stellar Astrophysics
Grand minima and intermittency in near-critical convection-driven dynamos
P. J. Käpylä
Context: Solar magnetism exhibits long-term variations on timescales of decades to centuries. Aims: The main aim is to study how the supercriticality of the dynamo affects the variability of
magnetic fields on timescales relevant to the Sun. Methods: Three-dimensional rotating magnetohydrodynamic simulations in a spherical wedge geometry are used to produce self-consistent convection-driven dynamos. The supercriticality of the dynamo is controlled by varying the
magnetic diffusivity. Results: The main result is that long-term variability of the dynamo increases with decreasing supercriticality of the dynamo and that cases nearest to the onset of dynamo action show extended grand minima-like periods of low activity. The simulations fall in three classes where the least supercritical cases show the largest variations of
magnetic activity and where the flow including differential rotation is almost unaffected by the
magnetic field. In the cases with the highest supercriticality the
magnetic field is permanently strong and differential rotation permanently quenched, both having relatively little temporal variation. In an intermediate regime both the
magnetic fields and differential rotation exhibit strong anticorrelated fluctuations. Conclusions: The occurrence of grand minima in the Sun has been conjectured to be due to a weakly supercritical dynamo. The current results support this idea and suggest that the absence of grand minima in earlier global dynamo simulations is because their large-scale dynamos were too supercritical. Furthermore, the current results suggest that the effect of the
magnetic field on differential rotation is negligible if the average rms-field is less than about 2~kG.
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High Energy Astrophysical Phenomena
Direct Observational Constraint on Upstream Magnetic Field Amplification Reveals the Particle Acceleration Limit in a Supernova Remnant
Yuya Kawabata, Takaaki Tanaka, Hiromasa Suzuki et al. (+1 more)
The origin of Galactic
cosmic rays up to the knee energy (PeV) remains a long-standing open question in astrophysics.
Supernova remnant shocks are leading candidates for accelerating particles to PeV energies, yet this requires strong
magnetic field amplification in the upstream region to confine the highest energy particles. Despite its importance, the upstream
magnetic field strength has long lacked direct observational constraints. Here we report the observation of numerous synchrotron X-ray hotspots extending into the upstream of the
supernova remnant RX J1713.7$-$3946 in archival Chandra data. These hotspots show spatial and temporal properties consistent with synchrotron emission from secondary electrons produced by hadronic interactions between accelerated
protons and dense molecular clumps. Using the spatial extent of these upstream hotspots as a physical scale, we estimate the
proton diffusion length to be $\sim 1~\mathrm{pc}$. This measurement provides a constraint on the upstream
magnetic field strength of $\sim 10~\mu\mathrm{G}$, which is consistent with recent simulations of Bell-instability-driven
magnetic field amplification. Our results indicate that the current amplification is insufficient to reach PeV energies, explaining the observed TeV gamma-ray spectral cutoff and providing a diagnostic for assessing PeVatron capability in stellar shocks.
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All authors Yuya Kawabata, Takaaki Tanaka, Hiromasa Suzuki, Tsuyoshi Inoue
Instrumentation and Methods for Astrophysics
Deep learning methods for gamma event selection in TAIGA-IACT image analysis in stereo-mode
E. O. Gres, A. P. Kryukov, P. A. Volchigov et al. (+6 more)
In astrophysical complex TAIGA there are four Imaging Atmospheric Cherenkov
telescopes (IACTs), located at a distance of 300-500 m from each other, due to which extensive air showers (EAS) generated by
cosmic and gamma radiation are recorded by a single
telescope or by multiple
telescopes simultaneously (stereo-mode). The analysis of EAS images from two or more Cherenkov
telescopes together is of particular interest, since for this approach the reconstruction of physical parameters of the primary gamma ray is much more accurate than in mono-observations. However, the gamma-ray event reconstruction strongly depends on the quality of the
hadron background suppression of the classifier, therefore, the gamma event selection stage is one of the important ones in the further analysis of IACT data. We propose and study several neural network methods for gamma event selection in joint TAIGA-IACT image analysis. Neural network methods we suggested involves a single-stage analysis of IACT images from two
telescopes, while the second method considers the formation of autoencoder-derived essential features that contain the EAS physical parameters, including the type of primary particle.
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All authors E. O. Gres, A. P. Kryukov, P. A. Volchigov, A. P. Demichev, J. J. Dubenskaya, D. P. Zhurov, S. P. Polyakov, E. B. Postnikov, A. J. Razumov
Astrophysics of Galaxies
Galaxy Clusters from the DESI Legacy Imaging Surveys. IV. Alignment of Member Galaxy Orientations at z < 0.5
Zhaobin Chen, Yizhou Gu, Shufei Liu et al. (+2 more)
Using DESI photometric catalog data, we systematically analyze the spatial
alignment of
star-forming
galaxies (SFGs) and quiescent
galaxies (QGs) in clusters. The results reveal that, in both brightest central
galaxy (BCG)
alignment (BA) and satellite
alignment (SA), the
alignment signals of SFGs and QGs exhibit opposite trends in several aspects. For the BA signal, SFGs show stronger
alignment in cluster outskirts, whereas QGs exhibit stronger
alignment in inner regions. For the SA signal, both SFGs and QGs exhibit nearly isotropic signals in outer regions, while in inner regions they show opposite signals. In addition, the BA signal depends on cluster richness and QG fraction, and is more pronounced in mature clusters. Specifically, QGs show a stronger BA signal overall, which increases with luminosity and axis ratio, whereas SFGs show a weaker BA signal with no significant dependence on these parameters. The BA signal also exhibits a strong dependence on satellite
galaxy color, which is independent of morphology. We confirm this by analyzing the BA signal in two populations: red disk and blue elliptical
galaxies. However, neither BA nor SA shows a significant dependence on
redshift at z < 0.5. In summary, these findings reflect how
galaxy transport along
cosmic filaments drives cluster
evolution: early-stage SFGs fall into clusters along filaments, and during cluster relaxation, their spatial orientations are reshaped by gravitational potentials and tidal forces, weakening BA signal and enhancing SA signal. In contrast, QGs, as early cluster members, exhibit a more pronounced anisotropic distribution and maintain relatively stable spatial orientations.
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All authors Zhaobin Chen, Yizhou Gu, Shufei Liu, Hu Zou, Qirong Yuan