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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 9 March

Astrophysics of Galaxies

The Average Age Map of the Galactic Bulge

Jialu Nie, Martín López-Corredoira, Chao Liu et al. (+2 more)

The Galactic Bulge, as the center of the Galaxy, is the closest laboratory for studying galaxy formation and evolution. However, its study faces significant challenges due to heavy dust extinction. This paper is devoted to deriving the average age of the Galactic Bulge and investigating its spatial distribution. We utilize a high-precision PSF-fitting photometric catalogue in the $J$ and $K_{\mathrm{s}}$ bands observed by VISTA to study the average stellar ages within the Bulge. Red giant stars are employed as tracers, with their average distances determined using red clump stars as references. The average ages are fitted with stellar models. Our analysis reveals a systematic age gradient across the Galactic Bulge ($2^{\circ} < |b| < 8^{\circ}$). The mean stellar age increases significantly with galactic latitude, shifting from a younger population ($\sim 4.69^{+0.97}_{-0.81}$ Gyr) prevalent near the plane to a predominantly older population ($\sim 10.48^{+0.93}_{-0.85}$ Gyr) at higher latitudes. We hypothesize that the young stellar population at low latitudes is predominantly composed of a pseudo-bulge formed via disk/bar processes (incorporating contributions from recent star-forming activity in the Galactic center), whereas the older stellar population is associated with spheroidal bulges generated through early-stage collapse or accretion of debris from merged dwarf galaxies.
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All authors Jialu Nie, Martín López-Corredoira, Chao Liu, Hai-feng Wang, Iulia Simion

High Energy Astrophysical Phenomena

High-Energy Neutrino Emission in NGC1068 driven by Turbulent Magnetic Reconnection

Luana Passos-Reis, Elisabete M. de Gouveia Dal Pino, Juan C. Rodríguez-Ramírez et al. (+1 more)

Astrophysical neutrinos from Active Galactic Nuclei (AGN) offer a unique window into high-energy particle acceleration in obscured environments. The nearby Type II Seyfert galaxy NGC 1068 is a compelling example, exhibiting evidence of a high-energy neutrino excess without an associated TeV $\gamma$-ray counterpart. This suggests that hadronic processes may occur within an inner, magnetically dominated region, where the TeV emission is suppressed by $\gamma \gamma$ absorption and reprocessed via electromagnetic cascades in the dense, obscured environment. Building on our framework, which establishes turbulence-driven magnetic reconnection as the main driver for particle acceleration in this source, we present a refined lepto-hadronic model based on de Gouveia Dal Pino & Lazarian (2005) and Kadowaki et al. (2015). In these proceedings, we adopt a conservative inner disk radius compared to our previous results, moving the acceleration region further from the innermost stable circular orbit. We estimate the high-energy neutrino emission from hadronic and photo-hadronic processes, constrained by the acceleration timescale for first-order Fermi acceleration within the turbulent current sheet. The estimated model reproduces the IceCube neutrino flux excess, providing an essential technical complement and validation for our forthcoming comprehensive publication.
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All authors Luana Passos-Reis, Elisabete M. de Gouveia Dal Pino, Juan C. Rodríguez-Ramírez, Giovani H. Vicentin

Cosmology and Nongalactic Astrophysics

Symmetry-Protected Momentum Exchange between Dark Matter and Dark Energy

Mohid Farhan

We present a particle physics motivated realization of interacting dark energy in which a radiatively stable dark energy sector couples to weakly interacting massive particle dark matter through pure momentum exchange. The dark energy field arises as a pseudo-Nambu-Goldstone Boson from a complex scalar singlet charged under a softly broken global $U(1)_S$, while dark matter is identified with an inert scalar doublet stabilized by a discrete $Z_4$ symmetry. This symmetry structure allows renormalizable dark matter-dark energy portal operators; however, requiring the dark energy field to emerge as a radiatively stable pseudo-Nambu-Goldstone Boson necessitates their absence, leaving derivative interactions as the leading coupling. As a result, energy transfer between the dark sectors is absent at the background level, while momentum exchange modifies the evolution of cosmological perturbations. We implement the resulting interacting dark energy model self-consistently in the Boltzmann code CLASS and study its impact on the growth of structure. We find that, despite sizeable momentum exchange, the suppression of the clustering amplitude $\sigma_8$ saturates above the level required to fully resolve current low-redshift tensions. Our results demonstrate that symmetry-protected, momentum-exchange-only dark sector interactions possess an intrinsic limit on structure suppression, providing a theoretically controlled benchmark for interacting dark energy scenarios.
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High Energy Astrophysical Phenomena

Discovery of a 36-minute long-period transient ASKAP J142431.2-612611

Joshua Pritchard, Tara Murphy, Dougal Dobie et al. (+13 more)

We report the discovery of a new long-period radio transient, ASKAP J142431.2-612611, with a 36 minute period, identified in the Australian SKA Pathfinder Evolutionary Map of the Universe survey. We detected pulsed emission from ASKAP J142431.2-612611 over a period of eight days during follow-up observations with the Australia Telescope Compact Array, after which the source appears to have switched off. No optical or near-infrared counterpart is detected in archival surveys or in targeted Gemini South FLAMINGOS-2 observations. During its active state, the source exhibits a stable pulse profile with fractional polarisation consistent with 100%, evolving from elliptically to linearly polarised and tracing a well-defined great-circle trajectory on the Poincaré sphere. We show that this behaviour is consistent with fully linearly polarised intrinsic emission modified by propagation through a linearly polarised birefringent medium. This discovery expands the known population of long-period transients and highlights the intermittent nature of their activity. We discuss the implications for proposed models of long-period transients and outline future observations needed to constrain the origin of their intermittency and polarisation properties.
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All authors Joshua Pritchard, Tara Murphy, Dougal Dobie, Emil Lenc, Akash Anumarlapudi, Manisha Caleb, Sophia Grainger, Natasha Hurley-Walker, David L. Kaplan, Samuel J. McSweeney, Jackson Mitchell-Bolton, Kovi Rose, Rahul Sengar, Ziteng Wang, Jayde Willingham, Andrew Zic

Sunday 8 March

Astrophysics of Galaxies

Here Be SDRAGNs - Spiral Galaxies Hosting Large Double Radio Sources

Jean Tate, William C. Keel, Michael O'Keeffe et al. (+16 more)

We present a sample of large double radio sources hosted by spiral galaxies (Spiral Double Radio Active Galactic Nuclei, SDRAGNs). Candidates were selected during Radio Galaxy Zoo, and refined using Sloan Digital Sky Survey images. The most promising were targeted in the Zoo Gems Hubble Space Telescope program, yielding images for 36 candidates. We assess the likelihood of each spiral galaxy being the genuine host of the radio emission finding 15 new high-probability SDRAGNs. SDRAGN hosts are seen preferentially close to edge-on. SDRAGNs predominantly show FR II radio structures and optical pseudobulges. Accounting for sample selection effects, the radio-jet axes lie preferentially near the poles of the galaxy disks; we find a constant probability distribution for intrinsic pole-jet angles < 30 degrees, ramping to zero at 60 degrees. We have obtained optical spectra for all these new SDRAGNs. Among both previous and new SDRAGN samples, 8/25 show Seyfert 2 signatures, 6/25 show central star formation, and 5/25 show LINER emission strong enough to indicate AGN or shock ionization, broadly similar to radio galaxies in elliptical hosts with the addition of star formation (diluting or masking weak AGN signatures). SDRAGNs include FR II sources seen at unusually low radio power, and preferentially occur in significant galaxy overdensities on 1-Mpc scales. Our "false alarms" - systems where HST data show the spiral to not be the actual host galaxy - include radio sources seen through large parts of foreground spiral disks, potentially useful for Faraday-rotation studies of disk magnetic fields.
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All authors Jean Tate, William C. Keel, Michael O'Keeffe, O. Ivy Wong, Heinz Andernach, Julie K. Banfield, Alexei Moiseev, Aleksandrina Smirnova, Arina Arshinova, Eugene Malygin, Elena Shablovinskaya, Roman Uklein, Stanislav Shabala, Ray Norris, Brooke D. Simmons, Rebecca Smethurst, Ivan Terentev, Chris Molloy, Victor Linares

Solar and Stellar Astrophysics

BlackGEM observations of compact pulsating stars: Mode identification for the DOV PG 1159-035 using multi-colour photometry

P. Ranaivomanana, C. Johnston, M. Uzundag et al. (+10 more)

While space-based telescopes offer unparalleled precision for asteroseismology, ground-based observations remain crucial for identifying compact pulsator candidates and enabling their pulsational study through multi-colour photometry. The BlackGEM telescope array significantly enhances the detection and characterisation possibilities for compact pulsators that tend to be much fainter than dwarf or giant pulsators. Using BlackGEM multi-colour photometry of the hot pre-white dwarf PG 1159-035, we demonstrate its capability to detect short, multi-periodic pulsations with amplitudes down to a few milli-magnitudes. The primary aim of this study is to establish the feasibility of pulsation mode identification in hot subdwarfs and white dwarfs via mode amplitude-ratio analysis derived from BlackGEM multi-colour observations. Pulsation frequencies were extracted from our target using iterative pre-whitening analysis. To validate our data-driven mode identification concept using multi-colour photometry, we used the well-studied hot pre-white dwarf PG 1159-035, with previously identified pulsation modes, as a prototypical object that served for validation. The pre-whitening analysis using BlackGEM's standard q-, u-, and i-band light curves of PG 1159-035 revealed pulsation frequencies of l=1 and l=2 modes, consistent with values obtained from the literature. Subsequent amplitude ratio calculations resulted in discernible distributions for the l=1 and l=2 modes. The future assembly of more BlackGEM amplitude ratios for well-known white dwarfs with already identified modes will lead to density estimators suitable for identifying newly detected modes in known or as-yet-undiscovered pulsators. Our proof-of-concept study paves the way for large-scale asteroseismic analyses of optically faint compact pulsating stars using ground-based facilities, such as BlackGEM.
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All authors P. Ranaivomanana, C. Johnston, M. Uzundag, P.J. Groot, T. Kupfer, S. Bloemen, P.M. Vreeswijk, J.C.J. van Roestel, D.L.A. Pieterse, J. Paice, A. Kosakowski, G. Ramsay, C. Aerts

Earth and Planetary Astrophysics

Post-perihelion Coma Composition of the Interstellar Comet 3I/ATLAS from Optical Spectroscopy

Ruining Zhao, Xiliang Zhang, Bin Yang et al. (+4 more)

We present multi-epoch optical spectroscopy of the interstellar comet 3I/ATLAS obtained between December 2025 and January 2026 (heliocentric distances 1.8-3.3 au), yielding post-perihelion production rates and mixing ratios for CN, C$_3$, C$_2$, CH, and gaseous metals (Fe I and Ni I). Our results show that the coma is less depleted in C$_2$ after perihelion than before, indicative of subsurface activation or compositional heterogeneity. The outgassing profiles reveal a pronounced perihelion asymmetry: CN and metal production rates decline more gradually outbound than inbound, consistent with the reported behavior of H$_2$O and implying a change in the comet's activity pattern across perihelion. Despite being metal-rich relative to its H$_2$O content, 3I follows the metal-CO correlation observed in comets of diverse origins, suggesting that gaseous metal release is more closely linked to a CO-bearing volatile reservoir than to H$_2$O, potentially in the form of metal carbonyls. In addition, the [O I] $\lambda6300$ emission shows a significant residual after subtracting the expected contributions from H$_2$O, CO$_2$, and CO, which may reflect systematic uncertainties in the photodissociation yields of those molecules or a contribution from additional oxygen-bearing parents.
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All authors Ruining Zhao, Xiliang Zhang, Bin Yang, Xiangyu Fan, Shu Wang, Yang Huang, Jifeng Liu

High Energy Astrophysical Phenomena

Inefficiency of chiral dynamos in protoneutron stars and the early universe

Valentin A. Skoutnev and Andrei M. Beloborodov

The chiral plasma instability (CPI) has been invoked as a possible mechanism for generating primordial magnetic fields in the universe and ultrastrong fields in neutron stars. We investigate chiral dynamos where the chirality imbalance is pumped by a source on a timescale $t_0$ and show that the CPI rate $\gamma$ is limited to $\gamma_0/(1+{\cal Q}^2)$, where ${\cal Q}= (\gamma_0 t_0)^{1/3}$ and $\gamma_0$ corresponds to models with instantaneously created chirality imbalance $(t_0=0)$. We then find that chiral flipping with rate $\Gamma_{\mathrm f}$ hinders the chiral dynamo if $\Gamma_{\mathrm f} >\gamma_0/(1+{\cal Q}^2)$ and completely suppresses it if $\Gamma_{\mathrm f} >\gamma_0/(1+{\cal Q}^{3/2})$. Realistic $t_0$ typically give ${\cal Q}\gg 1$, which makes the dynamo greatly vulnerable to suppression by chiral flipping. The suppression is strong in protoneutron stars and may be (barely) avoided near the electroweak transition in the early universe.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Scattering from compact objects: Debye series and Regge-Debye poles

Mohamed Ould El Hadj

We investigate elastic scattering by a compact, horizonless body in curved spacetime, considering a massless scalar wave incident on a static, spherically symmetric, uniform-density star of radius $R$ and mass $M$ with a Schwarzschild exterior. We introduce an exact Debye-series decomposition of the scattering matrix, in the spirit of Debye expansions in Mie scattering. This decomposition separates direct surface reflection from contributions involving transmission into the interior and subsequent propagation, and admits a natural trajectory interpretation. We then determine the associated Regge-Debye pole spectrum in the complex angular-momentum plane. For neutron-star-like tenuities ($R>3M$), the spectrum exhibits two pole families: a surface-wave branch associated with the surface matching condition and a broad-resonance branch associated with the interior regularity condition. For ultracompact objects ($R<3M$), the surface-wave branch persists, while the interior-resonance sector splits into broad- and narrow-resonance branches. We next reconstruct the scattering amplitude from the Debye partial-wave contributions and find excellent agreement with direct partial-wave calculations. Finally, we develop complex angular-momentum representations order by order in the Debye series, making explicit how the pole families and non-pole sectors contribute to each Debye term. In the neutron-star-like regime, we find a genuine competition between Regge-Debye pole sums and branch-cut contributions, and show that, at high frequency, the rainbow-like enhancement already arises from the first interior-transmission contribution and is dominated by the interior-resonance Regge-Debye poles. By contrast, in the ultracompact regime, the Debye amplitudes are overwhelmingly pole dominated.
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Earth and Planetary Astrophysics

Dust distribution in circumstellar disks harboring multi-planet systems. II. Super-thermal mass planets

V. Roatti, G. Picogna and F. Marzari

Theoretical formation models and exoplanet detection surveys indicate that systems with multiple giant planets are common. We investigate how multiple super-thermal mass planets embedded in a circumstellar disk shape the dust distribution and examine the consequences for interpreting disk substructures and inferring planetary properties. We perform two-dimensional hydrodynamical simulations with a modified PLUTO code, treating dust as Lagrangian particles in a wide range of sizes. We analyze systems with two planets of different masses and orbital separations, comparing them to the single-planet scenario. We generate synthetic ALMA continuum maps using RADMC-3D and compute the relative impact velocities of dust particles to assess potential limitations to grain growth. Dust morphologies in multi-planet systems cannot be described as a simple superposition of single-planet gaps. Secular planetary perturbations can generate multiple dust traps and asymmetric structures, while also exciting significant eccentricities in dust particle orbits. As a consequence, the locations and widths of dust rings and gaps depend on the size of the particles, the masses of the planet, and the orbital configurations. Synthetic continuum images may hide gaps carved by multiple planets, thereby complicating the interpretation of observed substructures. In addition, eccentricities induced in dust orbits lead to stronger gas drag, reducing the Stokes number for a given particle size, and the enhanced relative velocities associated with eccentric orbits can further suppress grain growth, promoting fragmentation and replenishment of small dust grains.
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Solar and Stellar Astrophysics

Hydrogen photoionization in a magnetized medium: the rigid-wavefunction approach revisited

René D. Rohrmann

Realistic modeling of stellar spectra requires accurate radiative opacity coefficients. Owing to the fragmentary nature of existing data from rigorous quantum-mechanical calculations, photoionization coefficients based on the rigid-wavefunction approximation remain the only practical option for studies of magnetic white dwarfs. Although variants of this approach have been widely used in spectral analyses for decades, a complete and explicit treatment of degeneracy-level breaking has not previously been presented. In this work, we provide a comprehensive description of this procedure, including explicit expressions for the photoionization probability of individual bound-free transitions as functions of magnetic field strength and radiation polarization. We also evaluate the occupation numbers of bound states in a magnetized gas under ionization equilibrium, enabling the calculation of absolute photoionization opacities. Because high-lying atomic states are strongly perturbed by the magnetic field and ultimately dissolved, substantial modifications of the monochromatic absorption are found even for fields below 10 MG–a regime where fully rigorous quantum calculations are numerically demanding and have not yet been applied. Over a wide range of magnetic field strengths, pronounced dichroic features appear in the hydrogen continuum absorption.
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Earth and Planetary Astrophysics

WD 1054-226 revisited: a stable transiting debris system

J. Korth, A. J. Mustill, H. Parviainen et al. (+24 more)

A growing number of white dwarfs (WDs) exhibit one or more signs of remnant planetary systems, including transits, infrared excesses, and atmospheric metal pollution. WD 1054-226 stands out for its unique, highly structured, and persistent photometric variability. We aim to investigate the long-term stability and nature of the periodic signals observed in WD 1054-226 to better understand the origin and evolution of its transiting material. We analyse all available TESS light curves from Sectors 9, 36, 63, and 90 using Lomb-Scargle (LS), Box-Least-Squares (BLS), and Gaussian process (GP) periodogram analyses. We complement these with multiband, high-cadence ground-based photometry from LCOGT, MuSCAT2, ALFOSC, and ProEM to test for colour dependence and confirm the periodicities. We confirm the persistence of the previously-reported 25.01 h and 23.1 min periodicities over a six-year baseline. The 25.01 h signal shows some temporal evolution, while the 23.1 min dips are highly coherent on long timescales. A transient 11.4 h feature, previously reported, is detected only in early TESS sectors and is absent in recent data. No significant colour dependence is found in the ground-based observations. The stability of both the 25.01 h and 23.1 min signals indicates a long-lived, dynamically sculpted debris structure around WD 1054-226. The lack of colour dependence implies high optical depth, consistent with an opaque, edge-on debris ring rather than an optically thin dust population. This makes WD 1054-226 a key laboratory for testing models of remnant planetary systems around white dwarfs.
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All authors J. Korth, A. J. Mustill, H. Parviainen, E. Villaver, J. W. Kuehne, V. J. S. Béjar, Y. Hayashi, N. Abreu García, T. Kagetani, K. Kawauchi, L. Livingston, M. Mori, G. Morello, N. Watanabe, I. Fukuda, K. Ikuta, I. Bonilla-Mariana, E. Esparza-Borges, G. Fernández-Rodríguez, A. Fukui, S. Geraldía-González, J. González-Rodríguez, K. Isogai, N. Narita, E. Palle, A. Peláez-Torres, M. Sánchez-Benavente

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

Gravitational waves from warm inflation in the weak dissipative regime

Orlando Luongo, Tommaso Mengoni and Paulo M. Sá

Previous work on the gravitational-wave background generated in a two-scalar-field cosmological model, in which warm inflation and the dark sector are unified within a single framework, has shown that the resulting spectrum could be potentially detectable by planned next-generation gravitational-wave observatories. In this work, we extend this analysis to the weak dissipation regime of warm inflation, highlighting how the features of the inflationary scenario play a crucial role in the production of gravitational waves. The full gravitational-wave energy spectrum is calculated using the formalism of continuous Bogoliubov coefficients. By comparing our results with those obtained in the strong dissipation regime and with the sensitivity curves of future detectors, we find that the weak dissipation regime improves the prospects for observational detection.
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Instrumentation and Methods for Astrophysics

An Attempt to Search for Unintended Electromagnetic Radiation from Starlink Satellites with the 21 Centimeter Array: Methodology and RFI Characterization

Xupiao Yang, Qijun Zhi, Yanbin Yang et al. (+6 more)

The rapid expansion of low-Earth-orbit (LEO) megaconstellations introduces new risks to radio astronomy from unintended electromagnetic radiation (UEMR). In this work, we present an attempt to search for UEMR from Starlink satellites using the 21 Centimeter Array (21CMA). Because the sensitivity of a single pod observation is limited, we focus on developing a robust observing and detection pipeline. Using Two-Line Element (TLE) data, we predict satellite transit times to guide the observations, and we define entry into the field of view (FoV) as an apparent declination greater than $85^{\circ}$ with respect to the 21CMA. We analyze the system equivalent flux density (SEFD) and the resulting single-pod sensitivity limits, which explain the detection of emission originating from the ORBCOMM satellites, rather than any detectable broadband UEMR in our dynamic spectra. To validate the methodology, we developed a Python package, orbdemod, to demodulate ORBCOMM downlink signals in our data. The recovered satellite ID agrees with the satellite predicted by our maximum-declination analysis, thereby validating the accuracy of our transit prediction and identification framework. Furthermore, via modulation power spectrum analysis, we show that the impulsive broadband bursts are produced by power line arcing near the array rather than by satellite UEMR.
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All authors Xupiao Yang, Qijun Zhi, Yanbin Yang, Quan Guo, Juhua Gu, Jianfeng Wang, Yan Huang, Yun Yu, Feiyu Zhao

High Energy Astrophysical Phenomena

A jet formation model for astrophysical objects

Chun Xu

We propose a unified model for jet formation applicable to active galactic nuclei, young stellar objects, and X-ray binaries. In this model, the binding energy released from the accretion disk is primarily stored as turbulence rather than being radiated away, leading to the formation of advection-dominated accretion flows. Near the central object, a thick accretion disk with funnel-like structures develops. Within the turbulent flows, the smallest stable blobs can be accelerated beyond the escape velocity through the combination of two mechanisms - the Gaussian-like velocity distribution within the turbulence and a mechanism involving the combined effects of inward pressure force and angular momentum conservation.These rapidly moving blobs may exit through the funnels, collectively forming two opposing jets. This model predicts that jets originate from the innermost region of the thick disk surrounding the central object. The formation of jet is directly related a parameter \eta that describes the energy fraction stored in turbulence in units of the binding energy of local Keplerian energy. \eta > 0.5 is a minimal condition for jet to form. This model can be extended to account for jet formation in active galactic nuclei, young stellar objects, X-ray binaries, and other analogous astronomical systems.
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Solar and Stellar Astrophysics

New Way to Date Globular Clusters: Brown Dwarf Cooling Sequences

Roman Gerasimov

As the oldest building blocks of our Galaxy, globular clusters retain the archaeological footprint of the early stellar environments. Accurate absolute ages of globular clusters are required to interpret this ancient record. Existing dating techniques often produce precise but discordant ages, suggestive of systematic errors in excess of 1 Gyr. The James Webb Space Telescope (JWST) has unlocked a new dating method that leverages the cooling behavior of previously unobservable brown dwarf members. With a largely independent set of systematic errors, this new method provides a new consistency test for more established methodologies. I present a likelihood-based histogram-free method to derive globular cluster ages from multi-band JWST photometry of cluster members near and below the hydrogen-burning limit. By applying the method to a large set of simulated observations, I establish that formal age errors (i.e. errors based on measurement uncertainties alone) under 0.2 Gyr are attainable for nearby globular clusters. I also evaluate the significance of associated systematic effects, including the chemical heterogeneity of globular clusters (multiple populations), unresolved binary systems and uncertainties in brown dwarf cooling rates. As with other methods of age determination, systematic effects dominate the error budget (in selected cases, by over an order of magnitude), but may be reduced with more sophisticated analysis. Finally, I provide a lookup table for determining the number of observations, exposure times and temporal baselines required to estimate the age of a given cluster to a prescribed precision.
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High Energy Astrophysical Phenomena

Catching TeV emission from GRB 221009A and alike with LHAASO, LACT and SWGO

Yunlei Huang, Sujie Lin, Soebur Razzaque et al. (+2 more)

Gamma-Ray Bursts (GRBs) are the most energetic electromagnetic explosions in the universe. Recently, the Large High Altitude Air Shower Observatory (LHAASO) reported the breakthrough observation of GRB 221009A with gamma-ray energies beyond 13 TeV. This discovery, together with the previous GRB detection well above 100 GeV, confirms the production of very-high-energy (VHE, $\gtrsim 100$ GeV) radiation which might be a common component of all bright GRBs. It is reasonable to expect that bright GRBs are important targets for ground-based gamma-ray experiments. In this work, we estimate the detection rate for current and upcoming ground-based gamma-ray observatories including LHAASO, Large Array of Imaging Atmospheric Cherenkov Telescopes (LACT) and the Southern Wide-field Gamma-ray Observatory (SWGO) under two emission models with GRB~221009A as the template: first, that they all share the same intrinsic VHE spectral shape; second, they have the same environmental parameter and electron spectral index, governing their synchrotron self-Compton (SSC) emission. Using the long GRB luminosity and redshift distribution function obtained from the Fermi-GBM GRB samples, and accounting for the cosmological effects and extra-galactic background light (EBL) absorption, we derive the expected VHE flux at Earth. The sensitivity analysis for LHAASO, the upcoming LACT, and SWGO to evaluate their detection potential across specific redshift and luminosity ranges has been performed. The corresponding 5$\sigma$ detection rates of 221009A-like GRBs for the two emission models are: LHAASO, 0.04-0.05 yr$^{-1}$; LACT, 0.03-0.06 yr$^{-1}$; SWGO, 0.2-0.4 yr$^{-1}$. These rates can vary by up to $\approx 24\%$ due to different EBL models.
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All authors Yunlei Huang, Sujie Lin, Soebur Razzaque, Lili Yang, Zijie Huang

Cosmology and Nongalactic Astrophysics

Study of the cosmological tensions and DESI-DR2 in the framework of the Little Rip model

Safae Dahmani, Imad El Bojaddaini, Amine Bouali et al. (+2 more)

We present an analysis that investigates the $H_0$ and $S_8$ tensions by considering a dark energy model. The latter is a late-time model characterized by a future abrupt event known as the Little Rip (LR) model and characterised by one extra parameter, $\beta$, compared to the standard model, $\Lambda$CDM. To test this approach, we perform a statistical analysis by the MCMC method using the most recent observational data. We obtain a positive correlation in ($H_0$, $\beta$) plane. We also note that the Hubble tension is less than $3\sigma$ when using early measurements, i.e., Cosmic Microwave Background (CMB) data, and when combining it with Baryon Acoustic Oscillation (BAO) data, but it is no longer so when we combine early and late measurements (i.e. PantheonPlus (PP)). In addition, we test the model with DESI-DR2 combined with CMB and recent SNIa measurements. We notice that our model shifts toward the quintessence field. For a complete statistical analysis, we use the Akaike Information Criteria and Bayesian analysis of the evidence. According to Bayes factors, we find that the LR model provides an improved fit only to CMB data.
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All authors Safae Dahmani, Imad El Bojaddaini, Amine Bouali, Ahmed Errahmani, Taoufik Ouali

Saturday 7 March

Earth and Planetary Astrophysics

Forecasting Catastrophe: Constraints on the Fomalhaut Main Belt Planetesimal Population from Observed Collisional Remnants

Arin M. Avsar, Kevin Wagner, Dániel Apai et al. (+2 more)

Catastrophic planetesimal disruptions offer a unique opportunity to study and characterize large planetesimal populations in exoplanetary systems that are not currently detectable by modern observatories. The unexpected discovery of a second collision event in the Fomalhaut system raises important questions about the planetesimal population and dynamical state inside the Fomalhaut main belt that led to two collisions in 20 years. We present a statistical model developed and applied to the archetypal Fomalhaut system to provide new constraints on the bulk properties of the planetesimals in Fomalhaut's main belt. Utilizing the constraints provided by the spatially resolved Fomalhaut cs1 and cs2 collision events, we retrieve the belt parameters that best reproduce the observed collision rate while remaining consistent with the system's age and dust mass. Our best-fit model suggests a total main belt mass of 200-360 $M_{\oplus}$, with the transition from a collisionally evolved to a primordial planetesimal population occurring at a radius of $115_{-10}^{+30}$ km and a maximum planetesimal radius of $380_{-202}^{+643}$ km. We estimate a catastrophic collision rate of $0.086_{-0.048}^{+0.067}$ collision events per year for planetesimals with radii $\ge$ 100 km in the region interior to the main belt. Our findings show that further observable collisions are likely, motivating continued monitoring of Fomalhaut and other nearby debris disks.
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All authors Arin M. Avsar, Kevin Wagner, Dániel Apai, Christopher Stark, Isabel Rebollido

High Energy Astrophysical Phenomena

A Reproducible Black Hole-Neutron Star Merger Gallery Example for the Einstein Toolkit

Rahime Matur, Beyhan Karakaş, Roland Haas et al. (+3 more)

Black hole-neutron star mergers are important sources of gravitational waves and potential electromagnetic counterparts, but publicly available numerical relativity configurations for these systems remain limited. In this work, we present a fully reproducible black hole-neutron star merger simulation performed exclusively with official Einstein Toolkit thorns and configured to target the detected event GW230529. We evolve the system at three resolutions, with finest grid spacings of $162$, $222$, and $310$~m, and assess the numerical robustness of the resulting dynamics and gravitational wave signal. The entire setup, from initial data to a parameter file with some of the analysis scripts, is publicly released as a new Einstein Toolkit gallery example and is distributed as part of the Hypatia release, establishing a reference black hole-neutron star merger configuration within the Einstein Toolkit.
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All authors Rahime Matur, Beyhan Karakaş, Roland Haas, Ian Hawke, Nils Andersson, Steven R. Brandt

Instrumentation and Methods for Astrophysics

Broadband Searches for Extraterrestrial Technological Intelligence: a New Strategy To Find Nearby Alien Civilizations

B. Zuckerman

One of the most interesting questions that astronomy can hope to answer is: are we alone in our Milky Way galaxy? A detection of an electromagnetic (EM) signal generated by an extraterrestrial technological intelligence, or the presence in our solar system of an alien probe, would answer this question in the negative. Purposeful interstellar communication is a 2-way street - the transmitting and receiving technological intelligences (TIs) both need to do their parts. As the receiving TI, our EM search programs should incorporate a model of what a transmitting TI is likely to be doing. Published searches for extraterrestrial technological intelligence (SETI) have generally not done so and thus have often been suboptimally designed. We propose an improved search technique that more closely corresponds to astronomical surveys that have been undertaken for reasons that have nothing to do with SETI. Published non-SETI radio and optical surveys are sufficiently extensive that they already supply meaningful constraints on the prevalence of nearby purposely communicative alien civilizations. Purposeful communication can also include the sending of spaceships (probes). The absence of evidence for alien probes in the solar system suggests that no alien civilization has passed within ~100 lt-yr of Earth during the past few billion years.
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High Energy Astrophysical Phenomena

Flip-flop states in X-ray binaries and changing-state AGN

Thomas J. Maccarone, Jessie Runnoe, Gregoire Marcel et al. (+4 more)

We show that the flip-flop transitions in X-ray binaries (rapid cycling between different spectral states which are sometimes seen near the global state transition) show a series of analogies to the changing state phenomena (rapid changes in the emission line properties that seem to be driven by changes in the central engine) in active galactic nuclei (AGN). Specifically, (1) the timescales for the transitions scale approximately linearly with mass and (2) both phenomena occur at a few percent of the Eddington luminosity. Because most accretion physics is expected to be scale-free, it is likely that these represent two manifestations of the same phenomena. Demonstrating this would allow the use of a much wider range of observational techniques, on a much wider range of characteristic timescales, and provide a clearer pathway toward understanding these rapid transitions than is currently available. We discuss potential means to establish the connection more firmly, and to use the combination of the observational advantages of both classes of systems to develop a better understanding of the phenomenon.
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All authors Thomas J. Maccarone, Jessie Runnoe, Gregoire Marcel, Emilia Jaervelae, Douglas Buisson, Unnati Kashyap, Federico M. Vincentelli

Astrophysics of Galaxies

To What Extent Are Star Cluster Ages Encoded in Their Environments? Exploring the Spatial Distribution of Age-Related Information with PHANGS-HST Imaging and Convolutional Neural Networks

Javier Viaña, Janice C. Lee, Andrew Vanderburg et al. (+12 more)

The environments around star clusters evolve as stellar feedback reshapes the interstellar medium and dynamical processes reorganize the structure of the surrounding stellar field. As approximately single-age populations, star clusters can serve as clocks to trace these environmental changes. In this exploratory study, we test whether convolutional neural networks (CNNs) can identify age-dependent changes in cluster environments. We take cluster ages as given from basic SED fitting of five-band UV-optical aperture photometry from the PHANGS (Physics at High Angular resolution in Nearby GalaxieS) HST survey. We first show that CNNs can be trained on image cutouts centered on clusters to recover ages directly from imaging. This demonstration provides the foundation for this study, which examines whether the information used by CNNs to predict age is coherent and physically meaningful. We perform controlled image occlusion experiments as an explainable AI method. These show that the CNNs extract age-predictive environmental cues in the absence of cluster light and when information on SED shape is removed by combining the five filters into one image. We find that reliance on environmental information increases at the youngest (<10 Myr) and oldest (>1 Gyr) ages, where clusters can exhibit similarly red colors. Our results are consistent with the long-recognized picture that cluster environments evolve systematically with age. We demonstrate that this information is encoded at a level detectable by machine-learning and recoverable from broadband imaging. This establishes a path for using new techniques to connect image-based age inference to the physical evolution of cluster environments.
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All authors Javier Viaña, Janice C. Lee, Andrew Vanderburg, John F. Wu, M. Jimena Rodríguez, Remy Indebetouw, Médéric Boquien, Ralf S. Klessen, Sophia Rivera, Erik Rosolowsky, Oleg Y. Gnedin, Daniel A. Dale, Kirsten L. Larson, David A. Thilker, Gagandeep Anand

Solar and Stellar Astrophysics

Understanding the formation and eruption of sigmoidal structure through data-driven modeling of magnetic evolution in solar active region 13500

P. Vemareddy, S. Nair and S. Gosain

We investigate the magnetic origin of the coronal mass ejection (CME) that occurred on November 28, 2023, at 19:50UT from active region (AR) 13500 located near the solar disk-center. The eruption was associated with an S-shaped sigmoidal structure formed by the inner AR polarities along a sheared polarity inversion line, while the outer polarities evolved through proper motions. During November 26-28, the AR exhibited a decrease in net magnetic flux while progressively injecting magnetic helicity and energy into the corona toward the eruption onset, highlighting the key role of helicity-injection in triggering eruptions. To simulate this magnetic evolution, we employed a data-driven magnetofrictional (MF) simulation starting 2.8 days prior to the eruption. The energy input for the model was constrained using the observed energy injection through an ad-hoc parameter. The initial potential-field configuration gradually evolved into a sheared-arcade and eventually developed into a twisted flux rope (FR) over the observed time-scale. Proxy emission maps based on electric currents show remarkable morphological agreement between the simulated and observed sigmoidal structure. The average FR-core twist increasingly builds-up leading the FR to initiate slow-rise motion of FR top from 50Mm until its eruption onset at 80Mm. Importantly, the ratio of current-carrying to total relative-helicity increased from 0.13 at FR formation to 0.30 at eruption, when the FR core entered the torus-unstable regime, suggesting an association between torus-instability and a threshold helicity ratio. These results demonstrate that data-driven MF simulations can successfully reproduce the evolving coronal magnetic configuration and may provide a robust tool for assessing the eruptive potential of ARs, particularly the helicity ratio.
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Earth and Planetary Astrophysics

High nitrogen and carbon isotopic ratios in the interstellar comet 3I/ATLAS

C. Opitom, J. Manfroid, D. Hutsemékers et al. (+13 more)

Interstellar objects provide a unique opportunity to further our understanding of the planetary formation process by studying in detail material formed around another star. Their ices contain precious clues about the environment and conditions prevailing in their home system. As fractionation processes can be sensitive to the temperature and radiation environment, isotopic ratios are powerful tracers of the origin and evolution of different species. While isotopic ratios have been measured in solar system comets, previously detected interstellar objects have been too faint to measure isotopic ratios. Here we report the measurement of two ratios in 3I/ATLAS from observations of the CN molecule: $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N. We report $^{12}$C/$^{13}$C=$147^{+87}_{-40}$ and $^{14}$N/$^{15}$N=$343^{+454}_{-124}$. The $^{14}$N/$^{15}$N is higher than the value of $\sim$~150 usually measured for solar system comets, close to the values measured in the interstellar medium, pre-stellar phases or the outside of protoplanetary discs. The $^{12}$C/$^{13}$C is marginally higher than the values usually measured for solar system comets and in the interstellar medium. These measurements could indicate an origin of 3I in the outer disc around an older low-metallicity star.
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All authors C. Opitom, J. Manfroid, D. Hutsemékers, E. Jehin, M. M. Knight, K. Aravind, L. Ferellec, D. Bodewits, V. V. Guzmán, M. Cordiner, R. C. Dorsey, F. La Forgia, M. Lippi, B. P. Murphy, C. Snodgrass, M. Bannister

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

Shadows and Polarization Images of a Four-dimensional Gauss-Bonnet Black Hole Irradiated by a Thick Accretion Disk

Xiao-Xiong Zeng, Huan Ye, Muhammad Israr Aslam et al. (+1 more)

We adopt a general relativistic ray-tracing approach to study the shadows and polarization images of spherically symmetric Gauss-Bonnet (GB) black holes enveloped by geometrically thick accretion flows. Specifically, we adopt a phenomenological RIAF-like model and an analytical Hou disk model. In the RIAF-like model, increasing the GB coupling parameter $\lambda$ reduces both the size and brightness of the higher-order image, while increasing $\theta$ alters the shape of the higher-order image and obscures the horizon's outline. The main difference between isotropic and anisotropic emission is that the latter produce distortion of the high-order image in the vertical direction, leading to an elliptical morphology. For the Hou disk model, due to specific regions being geometrically thinner with the conical approximation, the high-order images are narrower with the increase in $\lambda$ than the RIAF model. While increasing $\theta$ enhances the brightness of the direct images outside the higher-order images, but hardly changes the size of the higher-order images, which is in sharp contrast to the RIAF model. Meanwhile, the Hou disk produces polarization patterns that trace the brightness configuration and are affected by $\lambda$ and $\theta$, reflecting the intrinsic structure of spacetime. These results illustrate that intensity and polarization in thick-disk models provide probes of GB black holes and near-horizon accretion dynamics.
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All authors Xiao-Xiong Zeng, Huan Ye, Muhammad Israr Aslam, Rabia Saleem

Astrophysics of Galaxies

Fuzzy Dark Matter and the Impact of Core–Halo Diversity on Its Particle Mass Constraints

Dafa Wardana, Kohei Hayashi, Masashi Chiba et al. (+1 more)

We investigate how diversity in the core–halo mass relation and the inclusion of higher-order velocity moments affect constraints on the fuzzy dark matter particle mass ($m_\psi$) inferred from the internal kinematics of dwarf galaxies. Using stellar line-of-sight velocities and projected positions for eight Milky Way dwarf spheroidal galaxies, we model their dark matter halos as solitonic cores embedded within outer Navarro–Frenk–White envelopes. We apply both second- and fourth-order Jeans analyses to derive the posterior distribution of $m_\psi$. Our results show that there are two ranges of $m_\psi$ consistent with the observed kinematics: $\log_{10}(m_\psi/\mathrm{eV}) = -19.72^{+0.64}_{-0.56}$, and a narrower low-mass window $\log_{10}(m_\psi/\mathrm{eV}) = -21.81^{+0.39}_{-0.26}$, both within the 68% credible intervals. The latter becomes prominent only when core–halo diversity is taken into account, which highlights the sensitivity of the inferred fuzzy dark matter particle mass constraints to our understanding of the core–halo relation. Future observations, providing larger stellar samples and more precise kinematic measurements, will be essential for clarifying the allowed parameter space of fuzzy dark matter.
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All authors Dafa Wardana, Kohei Hayashi, Masashi Chiba, Elisa G. M. Ferreira

Solar and Stellar Astrophysics

Polarimetric Tomography Applied to Synthetic Multi-Spacecraft White-Light Images: Observing Coronal Mass Ejections in 3D

David Barnes, Erika Palmerio, Tanja Amerstorfer et al. (+7 more)

A discrete tomography method has been developed that is able to reconstruct three-dimensional coronal mass ejection (CME) density structure. We test the method by producing synthetic coronagraph imagery for three events using the CORona–HELiosphere (CORHEL) model. We combine images from different numbers of observing spacecraft and we perform the method separately using polarimetric and non-polarimetric reconstructions, as a means to test their relative effectiveness. We show that increasing the number of observing spacecraft consistently reduces the mean relative absolute error (MRAE) between the simulated and reconstructed density. Furthermore, the MRAE is generally lower when using polarimetric reconstructions compared to non-polarimetric reconstructions. Methods applied to localise the CME front work well for all spacecraft configurations, and are improved when using polarimetric, over non-polarimetric, reconstructions. The presence of a CME front can be identified with an accuracy of $(72\pm9)\%$, $(70\pm8)\%$ and $(52\pm12)\%$ for CME1, CME2 and CME3 via polarimetric reconstructions using only three spacecraft at L1, L4 and L5. The radial position of the CME front can be constrained to a high level of precision when using polarimetric reconstructions using the same three spacecraft; $0.003\pm0.004$\,au, $0.004\pm0.005$\,au and $0.005\pm0.004$\,au for CME1, CME2 and CME3, respectively. We expect that at least four spacecraft are required in order to derive accurate information about 3D CME structure. We find no strong evidence of improvement when including out-of-ecliptic observers, but that their inclusion increases the volume of space within which the inversion can be performed.
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All authors David Barnes, Erika Palmerio, Tanja Amerstorfer, Eleanna Asvestari, Luke Barnard, Maike Bauer, Jasa Calogovic, Greta Cappello, Phillip Hess, Christina Kay

High Energy Astrophysical Phenomena

A Delayed Radio Flare Traces Kinetic Energy Injection in the SMBHB Candidate SDSS~J143016.05+230344.4

Tao An, Ailing Wang, Yingkang Zhang et al. (+12 more)

SDSS~J143016.05+230344.4 ($z=0.08105$) has been proposed as a candidate pre-coalescence supermassive black hole binary and shows remarkable multiwavelength variability. Its radio evolution provides a direct probe of the compact emitting region and of the physical origin of the late-time activity. We aim to localize the variable radio emission, characterize its spectral evolution, and constrain whether the radio brightening is produced by a newly emerging compact component, external absorption, or dissipation in a structured circumnuclear environment. At all epochs, the radio emission is dominated by a single unresolved milliarcsecond core with $T_{\rm B} \gtrsim 10^{7}$ K, constraining the variable emission to $\lesssim 0.3$ pc. The broadband spectra require two synchrotron self-absorbed components: a persistent low-frequency component with $\nu_{\rm p,steady} \approx 0.74$ GHz and $S_{\rm p,steady} \approx 1.22$ mJy, and a flare component whose turnover evolves from $(6.35 {\rm GHz}, 0.18 {\rm mJy})$ in 2022 February-May to $(8.61 {\rm GHz}, 0.38 {\rm mJy})$ in 2022 December, and then to $(5.83 {\rm GHz}, 0.25 {\rm mJy})$ in 2023 March-April. The flare contribution at 15 GHz reaches $\sim 80\%$ and matches the near-epoch VLBI recovery fraction, showing that the high-frequency brightening arises from a newly formed compact synchrotron component. A second brightening of the 15.2 GHz VLBI core is detected between 2023 September and 2024 February, while the source remains unresolved. Equipartition scalings imply characteristic radii of $\sim 5 \times 10^{-4}$ pc for the flare and $\sim 9 \times 10^{-3}$ pc for the steady component, and indicate a steep inner circumnuclear density profile, $n \propto R^{-1.7}$. The delayed radio flare is best explained by dissipation in an outflow or jet-base disturbance propagating through a structured circumnuclear medium.
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All authors Tao An, Ailing Wang, Yingkang Zhang, Lei Yang, Xinwen Shu, Fabao Zhang, Ning Jiang, Tinggui Wang, Huan Yang, Zhen Pan, Liming Dou, Zhijun Xu, Zhenya Zheng, Ruqiu Lin, Xiaofeng Li

Cosmology and Nongalactic Astrophysics

The Impact of Dark Matter on Gravitational Wave Detection by Space-based Interferometers

Yuezhe Chen, Pan-Pan Wang, Bo Wang et al. (+2 more)

The existence of dark matter is supported by multiple astrophysical observations, yet its particle nature remains unknown. The development of gravitational wave astronomy, especially with future space-based detectors such as LISA, provides new opportunities to study the interactions between dark matter and compact-object systems. This review summarizes the main dark matter candidates and their macroscopic distributions, and highlights three mechanisms through which dark matter can affect gravitational wave observations: (1) modifications to compact-object orbits and the dynamics of systems such as extreme mass-ratio inspirals, including dark matter spikes, dynamical friction, and potential perturbations; (2) gravitational lensing effects induced by the spatial distribution of dark matter, altering waveform amplitudes and phases; and (3) direct couplings between ultralight dark matter fields and detectors. As low-frequency gravitational wave detection techniques are proposed and continue to develop, these effects may offer a novel avenue for probing the properties of dark matter, and combining precise waveform modeling with multi-messenger observations could reveal insights into its microscopic structure.
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All authors Yuezhe Chen, Pan-Pan Wang, Bo Wang, Rui Luo, Cheng-Gang Shao