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Physics Astrophysics

astro-ph Watch Astrophysics

Sunday 29 March

High Energy Astrophysical Phenomena

A Tale of Two Jets: Double Relativistic Outflows from Close Binary GRB Progenitors

He Gao

Gravitational wave astronomy has revealed that close binaries with compact companions are widespread. Long GRBs (LGRBs) from massive star collapse face persistent challenges in achieving the rapid core rotation required by the collapsar model. Binary interaction via tidal spin-up offers a natural solution; recent population synthesis studies suggest a substantial fraction of LGRBs may originate from close binaries with a compact companion. In this scenario, supernova ejecta from the primary can be accreted by the companion, potentially launching a second relativistic jet after a delay set by the binary separation. We develop a comprehensive model for these double-jet systems, analyzing the dynamics of the second jet and its interaction with the first. The resulting observational signatures depend critically on the Lorentz factor ratio, the alignment angle, and the time delay. For aligned jets, two regimes arise: a fast second jet producing multiple gamma-ray triggers with distinct spectral/polarization evolution, and a slow second jet where its emission appears as an X-ray flare followed by an afterglow plateau from energy injection. For misaligned jets, the observed signal ranges from normal GRBs with late-time radio structures to fast X-ray transients followed by off-axis rebrightening. These features have observational parallels in existing GRB data. High-resolution radio interferometry with SKA, time-resolved polarimetry with eXTP, and multi-wavelength surveys with Einstein Probe and SVOM will test these predictions, providing constraints on the evolution of close massive binaries as progenitors of GRBs and gravitational wave sources.
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Earth and Planetary Astrophysics

$\texttt{Exoformer}$: Accelerating Bayesian atmospheric retrievals with transformer neural networks

L. Pagliaro, T. Zingales, G. Piotto et al. (+2 more)

Computationally expensive and time-consuming Bayesian atmospheric retrievals pose a significant bottleneck for the rapid analysis of high-quality exoplanetary spectra from present and next generation space telescopes, such as JWST and Ariel. As these missions demand more complex atmospheric models to fully characterize the spectral features they uncover, they will benefit from data-driven analysis techniques such as machine and deep learning. We introduce and detail a novel approach that uses a transformer-based neural network ($\texttt{Exoformer}$) to rapidly generate informative prior distributions for atmospheric transmission spectra of hot Jupiters. We demonstrate the effectiveness of $\texttt{Exoformer}$ using both simulated observations and real JWST data of WASP-39b and WASP-17b within the TauREx retrieval framework, leveraging the nested sampling algorithm. By replacing standard uniform priors with $\texttt{Exoformer}$-derived informative priors, our method accelerates nested-sampling retrievals by factor of 3-8 in the tested cases, while preserving the retrieved parameters and best-fit spectra. Crucially, we ensure that the retrieved parameters and the best-fit models remain consistent with results from classical methods. Furthermore, we confirm the statistical consistency of the two retrieval approaches by comparing their log-Bayesian evidence, obtaining absolute values of each Bayes factor $|\Delta\log{Z}|<5$, i.e., with no strong preference following common scales for either model. This hybrid approach significantly enhances the efficiency of atmospheric retrieval tools without compromising their accuracy, paving the way for more rapid analysis of complex exoplanetary spectra and enabling the integration of more realistic atmospheric models.
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All authors L. Pagliaro, T. Zingales, G. Piotto, I. Giovannini, G. Mantovan

Cosmology and Nongalactic Astrophysics

Model-independent test of the cosmic distance duality relation with recent observational data

Xing Wu

We test the cosmic distance duality relation (CDDR) using two model-independent methods. Method I is based on the PAge parametrization, which characterizes the expansion history in terms of the cosmic age. Parametrizations of possible CDDR violations are constrained using observational data from Type Ia supernovae (SN), baryon acoustic oscillations (BAO), cosmic chronometers, and gamma-ray bursts (GRB), including the latest PantheonPlus and DES Dovekie SN samples and DESI DR2 BAO data. The results support the validity of the CDDR within $1\sigma$. Different combinations of data sets are further explored to assess the impact of various probes and calibration choices, demonstrating the robustness of this conclusion. Although GRB data extend to higher redshifts, their constraining power is significantly weaker than that of the other low-redshift probes. The PantheonPlus and DES Dovekie samples yield consistent results. Method II uses a non-parametric Gaussian process reconstruction of the luminosity distance from SN data, combined with BAO measurements to construct the observed CDDR violation and constrain its parametrizations. The results are consistent with those from Method I, and we find no evidence for a violation of the CDDR.
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Earth and Planetary Astrophysics

Closeby Habitable Exoplanet Survey (CHES). V. Planetary Parameters Derived from Angular Separation Variations

Dongjie Tan, Jianghui Ji, Chunhui Bao et al. (+11 more)

The Closeby Habitable Exoplanet Survey (CHES) aims to achieve microarcsecond-level astrometry of about one hundred nearby FGK-type stars within 10 parsecs to detect Earth-like planets. Such precision exceeds the capability of absolute astrometry relying on Gaia catalogs, whose positional accuracy degrades over time due to error propagation from stellar motion and epoch offsets, limiting their use in microarcsecond-level detection. Traditional relative astrometry depends on positional components along right ascension and declination, requiring precise knowledge of field rotation and satellite attitude, which introduces additional errors. To address this, we propose a new relative measurement model based solely on variations in the length of angular separation between the target and reference stars, independent of direction. The model incorporates effects such as proper motion, parallax, radial velocity, light aberration, gravitational lensing, and planetary perturbations, enabling reconstruction of planetary orbits and masses. This approach enhances measurement stability and precision, providing a framework that is not entirely dependent on the Gaia catalog and suitable for CHES and other future high-accuracy astrometric missions.
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All authors Dongjie Tan, Jianghui Ji, Chunhui Bao, Xiumin Huang, Guo Chen, Su Wang, Yao Dong, Jiacheng Liu, Zi Zhu, Haitao Li, Junbo Zhang, Liang Fang, Dong Li, Lei Deng

Astrophysics of Galaxies

Study of Integrated Far-ultraviolet Emissions from Galactic Globular Clusters using AstroSat/UVIT observations

Sonika Piridi, Ranjan Kumar, Divya Pandey et al. (+1 more)

We used observations obtained with the Ultraviolet Imaging Telescope on board the AstroSat satellite to measure the integrated far-ultraviolet (FUV) and optical (V) magnitudes of 30 Galactic globular clusters (GCs). We classified the UV-bright evolved stellar populations of the GCs using FUV$-$V versus FUV color-magnitude diagrams (CMDs) and BaSTI-IAC isochrones and subsequently quantified their contributions to the total integrated FUV emissions. We found that the horizontal branch (HB) and post-HB (post-HB) stars contribute $\sim 40\%-45$% to the total FUV emission of GCs, while the contribution of blue straggler stars is only $\sim$3%. The HB stars especially dominate the UV budget of the metal-poor clusters. The observed spread in FUV-optical color in the color-color diagram supports the phenomenon that the UV upturn of early-type galaxies is due to the evolved stars. We studied for the first time the variation of integrated FUV magnitudes and colors with several cluster parameters in the core, intermediate, outer, and tidal regions, such as the fraction of second-generation stars, helium mass fraction, HB morphology, and mass of the GCs. We found that the GCs with a higher second-generation star fraction, helium mass fraction, and cluster mass are brighter in all the regions. The GCs with bluer HB morphologies also have brighter and bluer FUV magnitudes in the core and intermediate regions. Metal-poor GCs show significantly bluer FUV$-$optical colors, consistent with a stronger contribution from hot evolved stars.
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All authors Sonika Piridi, Ranjan Kumar, Divya Pandey, Ananta C. Pradhan

Earth and Planetary Astrophysics

Quantifying Building Blocks of Life in Planetary Analog Materials: Implications for Prebiotic Chemistry and Biosignature Identification

Xiaoou Luo, Chao He, Zhengbo Yang et al. (+5 more)

Building blocks of life such as amino acids, nucleobases, and fatty acids are central to prebiotic chemistry and represent key targets in the search for planetary biosignatures. In planetary materials, biomolecules typically occur at trace levels within complex matrices, posing substantial analytical challenges, particularly for quantitative characterization. Here we develop a gas chromatography tandem mass spectrometry method that enables robust qualitative and quantitative analysis of 56 prebiotically relevant molecules. The method is applied to a Titan aerosol analog and, for the first time, to a Martian gypsum analog from the Qaidam Basin, revealing diverse inventories of amino acids, nucleobases, and fatty acids in both samples. In the Titan aerosol analog, the first detection of phenylalanine and an extensive inventory of fatty acids, together with elevated nucleobase abundances, offers new insights into atmospheric photochemical synthesis of prebiotic molecules. In the Martian analog sample, amino acids are detectable and exhibit pronounced biotic abiotic contrasts in abundance patterns relative to those observed in the Titan aerosol analog, whereas fatty acids show more overlapping abiotic and biotic signatures, highlighting the potential of amino acids as robust biosignatures. These results provide quantitative constraints on prebiotic chemical evolution and underscore the utility of GC-MS-MS for biosignature identification in planetary exploration.
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All authors Xiaoou Luo, Chao He, Zhengbo Yang, Yingjian Wang, Ziyao Fang, Yu Liu, Sai Wang, Haixin Li

Earth and Planetary Astrophysics

A Possible Mechanism to Explain the Prograde Equatorial Jet of a Jupiter-like Gaseous Giant

Yuchen Lian, Pengshuo Duan and Dali Kong

Gaseous giants are characterized by their deep atmospheres, which lack clear boundaries with their interiors; therefore, their internal states could directly influence atmospheric dynamics. So far, most modeling studies have considered deep convection as the primary mechanism by which the interior influences atmospheric dynamics. In this work, we propose another possible mechanism that might crucially determine the appearance of gaseous giants' atmospheric cloud-top jet winds, tracing them to a typical hydromagnetic wave (the so-called equatorial Magnetic-Archimedes-Coriolis wave) generated within the stably stratified, strongly magnetized helium rain layer. The associated thermal perturbations can propagate upward through the convective molecular hydrogen envelope, eventually affecting the atmospheric thermal structure - the zonal inhomogeneities that are conducive to the formation of the eastward atmospheric equatorial jet (super-rotation). Our results have important implications for understanding the equatorial dynamics of gaseous giants. This mechanism could also help explain the equatorial westward jets (sub-rotation) observed on Uranus and Neptune, which lack the helium rain layers.
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Astrophysics of Galaxies

Catching the Nebular Needle in a Polluted Haystack: Line-emission Signatures from Population III-forming Pockets around Massive Galaxies at the End of Reionization

Alessandra Venditti, Luca Graziani, Raffaella Schneider et al. (+10 more)

Finding the first generation of (Population III or Pop III) stars is one of the most ambitious and exciting challenges of astrophysics. JWST opened concrete prospects for their detection during the Epoch of Reionization (EoR), where increasing evidence suggests that residual Pop III formation may persist, even within pristine pockets of high-mass halos, due to inhomogeneous enrichment. However, the identification of Pop III stars within globally enriched environments will be challenging. We investigate the detectability of a subdominant Pop III component in/around massive ($M_\star \gtrsim 10^9 ~\mathrm{M_\odot}$) galaxies at $z \approx 6.5 - 9$ from the dustyGadget cosmological simulation suite, and the confusion arising from second-generation (Pop II) stars in their surroundings. We find that young ($\lesssim 1$ Myr), massive ($M_\mathrm{III} \sim 6 \times 10^5 ~\mathrm{M_\odot}$) Pop III clusters forming within these galaxy environments are responsible for strong HeII1640 line emission ($L_\mathrm{HeII1640} \gtrsim 10^{41} ~\mathrm{erg \, s^{-1}}$), which would be detectable with $\approx 10 (50)$ h of medium-resolution observations with NIRSpec/IFU at $z \approx 6 (10)$. These bright luminosities cannot be produced by standard Pop II populations alone. On the other hand, the dominant Pop II component within massive “hybrid” Pop III hosts powers strong metal line emission ($L_\mathrm{[OIII]5007} \gtrsim 10^{42} ~\mathrm{erg \, s^{-1}}$), indicating that the detection of metal lines alone cannot exclude the presence of Pop IIIs in high-$z$ galaxy environments. We further discuss candidate selection strategies based on Ly$\alpha$, H$\alpha$ and H$\beta$ emission, and how spatially resolved observations may enable the detection of isolated, pristine pockets in the outskirts of massive halos.
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All authors Alessandra Venditti, Luca Graziani, Raffaella Schneider, Volker Bromm, Julian B. Munoz, Claudia Di Cesare, Rosa Valiante, Antonello Calabrò, Roberto Maiolino, Steven L. Finkelstein, Massimiliano Parente, Matteo Saggini, John Chisholm

2603.27582 · 29 Mar · 27 pages, 9 figures, 2 tables. Accepted for publication in APJ. Summary of changes: added estimate of Pop III number density in/around M*>1e9 Msun galaxies and discussion of implications of Pop III searches in large-scale overdensities in Sec. 4.2; added comparison with HeII emission from WRs from Cassata+13 and Visbal+15 in App. B; model clarifications; reference updates; minor figure updates

Abstract PDF $GLXY ×4$STAR ×3$HALO ×2

Saturday 28 March

Cosmology and Nongalactic Astrophysics

Inverse non-metricity in $f(Q)$ gravity: cosmology and observational constraints

Luís Atayde, Simão Marques Nunes and Noemi Frusciante

We study a minimal modified gravity scenario in the symmetric teleparallel (non-metricity) formulation, focusing on an inverse non-metricity term with $f(Q)=Q+M^4 Q^{-1}$. The model does not introduce additional free parameters relative to $\Lambda$CDM, but modifies the late-time expansion and linear growth via an enhanced effective gravitational coupling. We identify key signatures: an enhanced matter power spectrum and CMB lensing, alongside a reduced late-time ISW effect and a shift in CMB peak positions. We confront the model with CMB data alone and in combination with BAO, RSD, SNIa, and DES large-scale structure data, considering both fixed minimal neutrino mass and varying $\Sigma m_\nu$. We find that the model typically prefers higher $H_0$ than $\Lambda$CDM, alleviating the $H_0$ tension, while its boosted growth tends to increase clustering amplitudes unless offset by larger neutrino masses when $\Sigma m_\nu$ is free. Overall, CMB-only data provide at most weak statistical support compared to $\Lambda$CDM, whereas late-time measurements impose tight restrictions that largely remove any improvement, positioning this model as a minimal yet strongly constrained alternative to dark energy.
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Earth and Planetary Astrophysics · Cross-listed from physics.space-ph

Turbulent dynamo in the terrestrial magnetosheath

Zoltán Vörös, Owen Wyn Roberts, Yasuhito Narita et al. (+10 more)

Dynamo action refers to energy exchange processes through which magnetic fields are generated at the expense of kinetic energy of the plasma flows. Dynamos can generate magnetic fields across scales larger or smaller than the flows themselves. Multi-scale dynamo processes underpin magnetic phenomena from planetary cores to stellar and galactic environments, while also shaping turbulent magnetic fields at smaller scales. Yet, experimental validation of dynamo action has remained largely confined to laboratories. Here we report evidence for a turbulent dynamo in the terrestrial magnetosheath. Observations reveal the predicted spatial topology of stretched and folded magnetic fields, compressive effects, and pressure anisotropy instabilities essential for magnetic field amplification. Our findings also highlight the central role of turbulent dynamos in energy conversion and structure formation within collisionless plasma turbulence. The observed energy exchange signatures indicate that the magnetosheath may serve as a natural testbed for validating dynamo theories and simulations.
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All authors Zoltán Vörös, Owen Wyn Roberts, Yasuhito Narita, Emiliya Yordanova, Rumi Nakamura, Adriana Settino, Daniel Schmid, Martin Volwerk, Cyril L. Simon Wedlund, Ali Varsani, Luca Sorriso-Valvo, Philippe-A. Bourdin, Árpád Kis

Instrumentation and Methods for Astrophysics

Enhancing Water Cherenkov Detector Arrays through multiPMT Modules

D. Ambrosino, R. Colalillo, V. M. Grieco et al. (+6 more)

Water Cherenkov Detectors (WCDs) are pivotal in various scientific fields, including neutrino physics, gamma-ray astronomy, and cosmic-ray research. The detection sensitivity and precision of these detectors crucially rely on photomultiplier tubes (PMTs) to capture Cherenkov radiation produced by charged particles moving faster than the speed of light in water. In recent years, employing multiPMT modules has emerged as a promising strategy to enhance large volume water and ice Cherenkov detector performance. In this work we explore the use of a multiPMT module in small WCD units, arranged in arrays as typically used to detect Extensive Air Showers (EAS). We outline a possible configuration and present the advantages it can offer for data analysis, as demonstrated through dedicated simulations. We investigate the potential of multiPMTs in capturing the features of the Cherenkov light distribution originated by single muons and discuss its possible application for muon tagging in WCD arrays.
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All authors D. Ambrosino, R. Colalillo, V. M. Grieco, F. Guarino, L. Lavitola, F. Sansone, M. Tambone, L. Valore, M. Waqas

Solar and Stellar Astrophysics

Assessing VBz variations during CME propagation: a preparatory study for the HENON mission using EUHFORIA

G. Prete, A. Niemela, S. Poedts et al. (+21 more)

Coronal mass ejections (CMEs) are among the main drivers of space weather hazards. In this context, HENON is a new space mission designed to carry out observations in the solar wind upstream of the Earth, aiming to provide timely alerts for hazardous perturbations propagating towards the Earth. HENON will orbit Earth on a distant retrograde orbit, approximately 0.082 AU upstream of the Earth when it is on the Sun-Earth line. The measurements taken by HENON will allow us to determine plasma and magnetic field parameters with a lead time of several hours with respect to the Lagrangian point L1. We assess the VB_z parameter variations (the product of solar wind speed V and southward magnetic field B_z) along the HENON orbit. Given its role as a primary driver of geomagnetic activity, we analyse how these measurements change with respect to Earth's position to evaluate HENON's forecasting potential. We used the FRi3D CME model of the EUHFORIA simulation code to characterize the initial properties of the CME. FRi3D allows us to set the CME magnetic field as a magnetic flux rope. From the simulation results, we evaluated the VB_z parameter at nine virtual spacecraft positions along the planned HENON orbit. The heliocentric longitudes of the virtual spacecraft range from about -6.9{\deg} to 6.9{\deg}, while the geocentric longitudes vary from -60{\deg} to +60{\deg} in steps of 15{\deg}. The initial direction of propagation of the CME central apex is either along the Sun-Earth line or at heliocentric longitudes of {\pm}30{\deg}. We find that with the proposed orbital parameters, the values of the VBz parameter along the HENON orbit are sufficiently similar to those measured in the vicinity of the Earth to be useful for space weather forecasts. HENON enables reliable VB_z estimates 2-8 hours in advance, improving space weather forecasting and protection of critical infrastructure and satellites.
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All authors G. Prete, A. Niemela, S. Poedts, G. Zimbardo, S. Cicalò, M. F. Marcucci, M. Laurenza, M. Stumpo, S. Landi, M. Sangalli, L. Provinciali, D. Monferrini, D. Calcagno, V. Di Tana, R. Walker, F. Pecora, G. Nisticò, V. Carbone, F. Chiappetta, A. Greco, F. Lepreti, F. Malara, S. Perri, S. Servidio

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

Particle-antiparticle perturbation superhorizon crossing: baryogenesis, leptogenesis, magnetogenesis and darkogenesis

She-Sheng Xue

During the reheating epoch, gravitationally produced superheavy particle-antiparticle pairs undergo quantum oscillations. Perturbations in their relative densities cross out the horizon, leading to an asymmetry of particles and antiparticles inside the horizon. Massive particles decay into light baryons and leptons, thereby explaining baryogenesis and leptogenesis, whose charged components must generate a nontrivial electric current, thereby producing a primordial magnetic field (magnetogenesis). As a result, the baryon (lepton) number-to-entropy ratio and the primordial magnetic field bound are consistent with observational data. We also discuss darkogenesis, the origin of dark matter and anti-dark matter asymmetry.
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High Energy Astrophysical Phenomena

XRISM spectroscopy of a crowded Galactic center region – I. Disentangling the sources in the field of view

Maxime Parra, Kai Matsunaga, Shifra Mandel et al. (+16 more)

The Galactic center is a complex and crowded region hosting the supermassive black hole Sgr A*, numerous accreting compact objects, and diffuse X-ray emission. This paper presents the first in a series of studies analyzing the XRISM observation of the X-ray transient MAXI J1744-294/Swift J174540.2-290037, located $\sim18''$ from Sgr A*. The observation, conducted in March 2025, along with XMM-Newton and NuSTAR coverage, aimed to investigate the Fe emission features of MAXI J1744-294 during its outburst. However, the region surrounding the source is heavily contaminated by X-ray emission from various diffuse and point sources, including strong line contributions from the supernova remnant Sgr A East and the Galactic center X-ray emission (GCXE). Additionally, the nearby neutron star low-mass X-ray binary (NS-LMXB) AX J1745.6-2901 was also in outburst during the XRISM observation, further complicating the spectral analysis. This study focuses on disentangling the contributions of these overlapping sources by robustly modeling the background contamination and spatial-spectral mixing. We describe the methodologies, region selection, and data reduction techniques applied to the different instruments. Two complementary approaches – empirical and physical modeling – are employed to characterize diffuse emission and point-source contributions. The results provide a foundation for the detailed spectral analysis of MAXI J1744-294, AX J1745.6-2901, and the surrounding interstellar medium (ISM), which will be presented in subsequent papers. This study highlights the challenges and robust solutions for analyzing XRISM/Resolve data from crowded regions in conjunction with other X-ray telescope data.
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All authors Maxime Parra, Kai Matsunaga, Shifra Mandel, Kaya Mori, Hideki Uchiyama, Masayoshi Nobukawa, Tahir Yaqoob, Takayuki Hayashi, Misaki Mizumoto, Shinya Yamada, Megumi Shidatsu, Paul A. Draghis, Efrain Gatuzz, John A. Tomsick, Charles J. Hailey, Chichuan Jin, Benjamin Levin, Gabriele Ponti, Mark Reynolds

High Energy Astrophysical Phenomena

XRISM spectroscopy of a crowded Galactic center region – II. Narrow emission lines in the Black Hole candidate MAXI J1744-294/Swift J174540.2-290037

Maxime Parra, Shifra Mandel, Kai Matsunaga et al. (+13 more)

Narrow, highly ionized X-ray emission lines in black hole low-mass X-ray binaries (BH-LMXBs) are rare and have been observed in only a few sources, during unusual, heavily obscured accretion states. We report on a detailed high-resolution spectral analysis of emission line features from the first XRISM observation of a BH-LMXB candidate in a bright soft state, MAXI J1744-294/Swift J174540.2-290037, in the central parsec region of our galaxy. The source was observed as part of an extensive, coordinated multi-wavelength campaign on its recurring X-ray outburst in early 2025. By carefully modeling the contributions of multiple point sources and diffuse emission within the XRISM/Resolve field of view, and combining these data with broadband X-ray coverage from XMM-Newton and NuSTAR (Paper I), we identified a narrow ($\sigma \sim 500-1000$ km s$^{-1}$), static emission component intrinsic to the system. This component likely arises from a highly ionized (log $\xi \gtrsim 5.5$) photoionized plasma in the inner disk atmosphere, and is accompanied by a weak, narrow Fe I K$\alpha$ line at 6.4 keV. We also detected at least three narrow emission features at atypical energies between 6.7 and 7.1 keV. The lack of corresponding rest-frame atomic transitions points toward highly ionized blueshifted Fe lines with outflow velocities of $-1300$ to $-6000$ km s$^{-1}$, which we model with multiple layers of photoionized or collisional plasma. We explore scenarios in which these unprecedented features are produced by multiple phases in a jet and/or a disk wind, and discuss potential similarities between MAXI J1744- 294 and the exotic microquasar SS 433.
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All authors Maxime Parra, Shifra Mandel, Kai Matsunaga, Kaya Mori, Ryota Tomaru, Efrain Gatuzz, Paul A. Draghis, Megumi Shidatsu, Hideki Uchiyama, Masayoshi Nobukawa, Tahir Yaqoob, Charles J. Hailey, Chichuan Jin, Benjamin Levin, Gabriele Ponti, Mark Reynolds

High Energy Astrophysical Phenomena

XRISM spectroscopy of a crowded Galactic center region – III. S, Ar and Ca ISM Absorption Features in the spectrum of MAXI J1744-294

Efrain Gatuzz, Maxime Parra, Muhammet F. Hasoglu et al. (+7 more)

We present a comprehensive study of X-ray absorption by sulfur (S), argon (Ar), and calcium (Ca) in the interstellar medium (ISM) along the line of sight to the low-mass X-ray binary MAXI J1744$-$294, using high-resolution XRISM Resolve spectra complemented by Chandra HETG data. The analysis employs an updated ISMabs model, incorporating newly computed $R$-matrix photoabsorption cross-sections for Ca I$-$Ca III, and existing cross-sections for higher ionization states. We find that S and Ar are predominantly in low-ionization states, with S II and Ar II dominating the cold and warm ISM phases, while higher-ionization species are constrained by upper limits. Calcium is primarily detected in low-ionization states, consistent with strong depletion into dust grains, with only marginal contributions from highly ionized ions. Using the measured ionic column densities, we infer hydrogen column densities of $N_{\rm H} \sim 1.1$-$1.3 \times 10^{23}\,\mathrm{cm^{-2}}$ from S and Ar, while the Ca-based value, tracing the neutral ISM, is in agreement with these estimates, highlighting the consistency across different tracers. Our results demonstrate the diagnostic power of combining multiple elements to probe ISM ionization structure, elemental depletion, and dust composition, and provide the first X-ray constraints on calcium absorption in the interstellar medium.
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All authors Efrain Gatuzz, Maxime Parra, Muhammet F. Hasoglu, Thomas W. Gorczyca, Shifra Mandel, Kaya Mori, Kai Matsunaga, Hideki Uchiyama, Masayoshi Nobukawa, Megumi Shidatsu

High Energy Astrophysical Phenomena

Systematic Study of Forward and Reverse Shock Afterglow Emission from Two-Component Jets

Olzhas Mukazhanov, Ernazar Abdikamalov and Paz Beniamini

Two-component jets are frequently invoked to explain complex features in gamma-ray burst (GRB) afterglows, such as late-time rebrightening and chromatic breaks. While many studies fit these models to individual events, a systematic exploration mapping the broader parameter space, particularly the reverse shock contribution, is currently lacking. To address this, we present a comprehensive systematic analysis of two-component jet signatures using numerical modeling with the VegasAfterglow code. Our modeling shows that observable rebrightenings in the forward shock require the wing to carry substantially more energy, while for the reverse shock the energies can be comparable. Because the two components can occupy different spectral regimes, spectral breaks may arise when the wing emission overtakes the core. When the wing's initial velocity is high, relativistic beaming can render its emission invisible to the on-axis observer. As the flow decelerates, the resulting debeaming produces a steeper rise in the observed emission, reaching temporal slopes as steep as about $4.5$ and peaking shortly after the core jet break. In this case, the wing masks the core's break, leaving only a single late-time break. Slower wings that are not initially beamed away do not obscure the core, allowing the observer to see two distinct jet breaks. At late times, the decaying post-jet-break slopes are unaffected and limited to temporal slopes of about $-p$. Additionally, the forward shock dominates the emission across most of the parameter space, while the reverse shock contributes noticeably only under conditions of high magnetization and long engine durations.
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Earth and Planetary Astrophysics

Constraining the presence of exotrojans in hot Jupiter systems using TTV observations from TESS

Zixin Zhang, Wenqin Wang, Xinyue Ma et al. (+8 more)

Co-orbital bodies (Trojans) share a 1:1 mean-motion resonance with a planet. Although Trojans are common in the Solar System, none has yet been confirmed in an exoplanetary system. Hot Jupiters are not expected to retain primordial co-orbitals efficiently, but their deep and frequent transits make them favorable targets for observational constraints using transit timing variations (TTVs). As part of the ExoEcho project, we analyze TESS photometry for 260 confirmed hot Jupiters with published RV-based masses to search for TTV signals compatible with Trojan companions. We derive transit times and compare the observed residuals with co-orbital models computed with REBOUND N-body simulations. Accounting for the degeneracy between Trojan mass and libration amplitude, we place upper mass limits on possible companions over a range of typical libration amplitudes. For a representative libration amplitude of 15 deg, we rule out exotrojans more massive than 1 Earth mass in 130 systems, corresponding to about 50% of the sample. A more conservative chi-square analysis that incorporates observational uncertainties raises this threshold to 3 Earth masses. We further combine these limits with dynamical-stability constraints for the 1:1 resonance to exclude unstable configurations. Our results provide population-level constraints on massive exotrojans in short-period systems and establish a framework for future high-precision searches with missions such as PLATO and ET (Earth 2.0).
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All authors Zixin Zhang, Wenqin Wang, Xinyue Ma, Zhangliang Chen, Yonghao Wang, Cong Yu, Shangfei Liu, Yang Gao, Baitian Tang, Dichang Chen, Bo Ma

Cosmology and Nongalactic Astrophysics

Exploring Late-Time Cosmic Acceleration in VCDM Cosmology

Sai Swagat Mishra, Soumya Kanta Bhoi and P.K. Sahoo

In this work, we have considered a minimally modified gravity theory that effectively reproduces VCDM-like behavior to investigate its cosmological implications. The model parameters are constrained using a combination of CC, RSD, DESI BAO DR2, and Union3 datasets. The model parameters are constrained using an MCMC framework, ensuring a robust estimation of credible intervals. We examine both background and perturbation-level observables, analyzing the Hubble parameter, deceleration parameter, effective equation of state, distance modulus, and the growth rate of cosmic structures through the \(f\sigma_8(z)\) observable. Our results show that the model successfully reproduces the observed expansion history, featuring a smooth transition in the Hubble evolution around \(z \simeq 0.3\), and consistent behaviour of cosmological parameters. The model outperforms \(\Lambda\)CDM in the statistical comparisons for the full dataset combination (CC+RSD+DESI DR2+Union3). These results highlight the potential of minimally modified gravity theories with VCDM-like dynamics as consistent and competitive alternatives to the standard cosmological paradigm.
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Solar and Stellar Astrophysics

Orbital Contraction of Post-Common-Envelope Binaries with a Circumbinary Disk

Shigeyuki Karino and Kenji Nakamura

Tight and compact binary systems, such as double neutron star binaries, are believed to undergo a common envelope evolution phase, resulting in strongly bound orbits. During this phase, the outer layers of the primary star are expelled, resulting in orbital shrinkage. However, a part of the expelled material may remain as a circumbinary disk, which can further influence subsequent orbital evolution. In this study, we investigated orbital evolution in the presence of a circumbinary disk within a simplified framework by assuming that orbital contraction and disk dissipation occur over the viscous timescale. The results showed that the orbit of the binary system after the common envelope evolution phase was further contracted by up to $\sim 17 \%$ due to the presence of the circumbinary disk, irrespective of the disk's mass and structure. This additional orbital contraction following the common envelope evolution phase may have significant implications for the formation rate of double neutron star binaries that merge within a cosmic timescale.
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High Energy Astrophysical Phenomena

Irregular Repeating Tidal Disruption Events due to Diffusive Tides

Shu Yan Lau, Ethan McKeever and Hang Yu

A repeating partial tidal disruption event (rpTDE) is typically modeled as a star on a bound orbit that is partially disrupted by a massive black hole (MBH) at each pericenter passage. For disruption to occur, the pericenter distance must be close to or within the characteristic tidal radius, such that the tidal field overcomes the star's binding force and triggers mass loss. However, a binary with a pericenter distance several times the tidal radius can build up its tidal perturbation over multiple orbits via a diffusive process, eventually triggering a nonlinear instability that ejects mass and powers an eruption. This leads to repeated, stochastic disruptions. In this Letter, we propose that such a mechanism can produce a subclass of rpTDEs with large variations in recurrence time (e.g., J0456-20), which we dub “diffusive-tide rpTDEs”. We show that diffusive tidal growth can occur for a white dwarf or main-sequence star orbiting a MBH when the pericenter distance is a few times the tidal radius, provided that the orbital period is shorter than the tidal energy dissipation timescale. These diffusive-tide rpTDEs may account for a significant fraction of the rpTDE population.
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High Energy Astrophysical Phenomena

The cold molecular gas regulates the activity of active galactic nuclei in massive galaxies

Yongyun Chen, Qiusheng Gu, Luis.C Ho et al. (+8 more)

The physical quantities that directly regulate AGN feedback in massive galaxies remain poorly understood. Observations of molecular gas surrounding AGNs suggest that this gas serves as a fuel source for AGN activity. Accordingly, we study the relationship between AGN activity and molecular gas properties. In this study, we analyze a large sample of nearby AGNs with available measurements of molecular gas mass, radio luminosity, and \oiii~luminosity. Our results show that radio luminosity and \oiii~luminosity exhibit stronger correlations with molecular gas mass than with other physical parameters such as black hole mass, stellar mass, and bulge mass. Moreover, when controlling for the correlations between radio luminosity, \oiii~luminosity, and molecular gas mass, the relationships between these luminosities and other key physical parameters become significantly weaker or disappear entirely. This suggests that, of all the properties we have considered, it is the molecular gas mass that is most tightly correlated with radio and \oiii~luminosity, and may thus be the most important driver of nuclear activity.
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All authors Yongyun Chen, Qiusheng Gu, Luis.C Ho, Junhui Fan, Feng Yuan, Tao Wang, Zhifu Chen, Dingrong Xiong, Xiaoling Yu, Xiaotong Guo, Nan Ding

Earth and Planetary Astrophysics

Small Body Dynamics with SBDynT: Proper Elements and Chaos Analysis

Dallin Spencer, Kat Volk, Darin Ragozzine et al. (+1 more)

The Small Body Dynamics Tool (SBDynT) is software written for the community of Solar System small body researchers to perform dynamical classification, characterization, and investigation. SBDynT provides advanced simulation analysis capabilities that make it straightforward to determine mean motion resonance occupation, proper orbital elements, and a variety of stability indicators. These calculations can be performed for small bodies that are known, newly discovered, or simulated; observational uncertainties can be incorporated through the use of dynamical clones. In this paper, we describe the methods for producing proper orbital elements and stability indicators, which serve as essential tools for characterizing dynamical stability and long-term evolution. Through extensive validation, we demonstrate that this code offers a robust open-source framework for investigating the dynamics of Solar System small bodies with high accuracy. We also aim for computational efficiency allowing SBDynT to provide dynamical information for the several-fold increases in small bodies expected in the LSST era.
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All authors Dallin Spencer, Kat Volk, Darin Ragozzine, Renu Malhotra

Astrophysics of Galaxies

A MeerKAT view of the Neutral Atomic Gas in Stephan's Quintet

K. Rajpurohit, E. O'Sullivan, G. Schellenberger et al. (+7 more)

We present new MeerKAT 21cm spectral line observations of the neutral hydrogen gas in the compact galaxy group Stephan's Quintet (HCG 92). These data provide a significantly improved view of the atomic gas distribution and kinematics in the group. New features include the first detections of HI associated with member galaxies NGC 7319 and NGC 7320C, the identification of an additional high-velocity HI component associated with SQ-A, and the detection of additional HI at low velocities filling much of the area of the NGC~7318B disk. We also find HI in the previously detected gas bridge linking NGC 7319 and NGC 7318B, and a new northern bridge linking NGC 7319 to the SQ-A star-formation region. We detect HI with a wide range of velocities along the line of sight through the northern half of the famous shock ridge, including in the 6200-6500$\rm\,km\,s^{-1}$ velocity range occupied by shocked H$\alpha$ emission. We examine the morphology and velocity structure of the HI and consider the origins of different components, finding some evidence that while the gas associated with NGC 7318B has been disturbed by its collision with the group, it may still retain a component of disk rotation. We find no gaseous connection between the tidal tails and NGC 7320C, but reaffirm the close connection between the shocked gas in the ridge (traced by X-ray, radio continuum and warm H$_2$ emission) and the southern tidal tail. Based on the integrated spectrum, we find a total HI mass in the group of 3.5$\pm$0.4$\times$10$^{10}\,M_{\odot}$, higher than the VLA estimate and comparable to FAST.
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All authors K. Rajpurohit, E. O'Sullivan, G. Schellenberger, J. M. Vrtilek, L. P. David, S. Giacintucci, P. N. Appleton, C. K. Xu, C. Cheng, T. Deb

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

Layered dark structure with a Structuring Field: A $Z_4$-symmetric Inert Doublet-Singlet realization and implications for the $S_8$ tension

Marriam Naeem and Mohid Farhan

We introduce the Layered Dark Sectors with a Structuring Field (LDS-SF), a structured cosmological framework where the internal architecture of a multi-component dark sector naturally generates scale-dependent growth of structure. In this framework, the characteristic scale dependence is derived from the dominant eigenvalue, $\lambda(k)$, of the dark sector's perturbation matrix. This structurally-driven mechanism modifies structure growth while preserving the standard $\Lambda$CDM background expansion and General Relativity. We provide a minimal realization of this framework within a two-component DM $Z_4$-symmetric Inert Doublet Singlet Model ($Z_4$-IDSM). By integrating out the heavy inert doublet mediator, we derive a contact-interaction Effective Field Theory (EFT) for a 60~GeV singlet dark matter candidate. This interaction manifests macroscopically as an effective sound speed $c_s^2$, which we map to the LDS-SF eigenmode evolution. We implement this system into the CLASS Boltzmann code, employing a late-time activation function that projects virialized halo properties into the linear perturbation framework. We also compute the relic density using micrOMEGAs to further stress-test the relic abundance predictions of viable parameters. Our numerical analysis demonstrates that while the model remains indistinguishable from $\Lambda$CDM at the era of recombination, it introduces a targeted suppression of the matter power spectrum at late times ($z < 10$) and small scales ($k > 0.1~h/\text{Mpc}$). Confronting the model with Planck CMB, BAO, and growth-rate measurements, we find three instances of couplings that successfully alleviate the $S_8$ tension, bringing the predicted amplitude into $1\sigma$ agreement with weak-lensing data from KiDS-1000 and DES. This work establishes LDS-SF as a mathematically consistent and observationally viable extension of standard cosmology.
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Earth and Planetary Astrophysics

Origins of Compact Mean-Motion Resonances: Evidence for Long-Range Migration and the Case of Kepler-36

Konstantin Batygin and Alessandro Morbidelli

The observed census of resonant extrasolar planets spans a tantalizing display of orbital architectures, ranging from familiar 2:1 and 3:2 mean-motion commensurabilities to nearly co-orbital configurations characterized by period ratios close to unity. While mean-motion resonances are widely recognized as signposts of convergent disk-driven migration, the process through which the most compact systems are established remains puzzling, since resonance capture must repeatedly fail at a series of first-order commensurabilities before finally succeeding at a high resonant index. Motivated by this discrepancy, here we develop an analytic theory that fuses the stability-based resonance capture criterion with the conventional paradigm of active accretion disks and the standard model of type-I migration. Within this framework, we derive an expression for the stellocentric radius of resonance capture, $r_{\rm{c}}$, and show that it depends only on the product of the disk viscosity parameter, $\alpha$, and the opacity-contributing small-grain mass fraction, $f_\mu$. Applying this formalism to Kepler-36 - the most compact known resonant system with a 7:6 period ratio - we find that resonance locking could not have been established near the disk's inner edge. Instead, capture must have occurred at $r_{\rm{c}}\approx 1-4$ AU, implying orbital decay of the planetary pair by approximately an order of magnitude. Viewed in this light, compact resonant architectures provide the clearest evidence for long-range migration among sub-Jovian planets. Moreover, the emerging picture is fully consistent with formation models in which super-Earths accrete within localized rings of planetesimals at orbital distances comparable to those that gave rise to the terrestrial planets of the Solar System.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Optimized numerical evolution of perturbations across sharp background trajectory turns in multifield inflation

Guillermo F. Quispe Peña, Johor D. Peñalba Quispitupa and José T. Gálvez Ghersi

Features in the primordial power spectrum require numerical methods that are both accurate and scalable across the wide class of multifield inflationary models that produce them. Sharp turns in the background trajectories, induced by either potential or geometric effects, render these computations particularly challenging. In this work, we introduce an efficient method for evolving primordial scalar fluctuations, requiring time steps comparable to those used for the background evolution. We demonstrate that the method accurately tracks perturbations through rapidly turning trajectories in arbitrary field-space geometries, enabling systematic exploration of spectral features across diverse multifield scenarios. Our approach scales robustly to large numbers of degrees of freedom, providing a reliable computational framework for probing regimes that significantly depart from slow-roll or slow-turn dynamics.
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High Energy Astrophysical Phenomena

Comparison between axisymmetric numerical magnetohydrodynamical simulations and self-similar solutions of jet-emitting disks

N. Zimniak, C. Zanni and J. Ferreira

Turbulent accretion disks threaded by a large-scale vertical field near equipartition can drive tenuous and fast self-confined jets. Self-similar solutions of these jet-emitting disks (JEDs) have been known for a long time and provide the distributions of all physical quantities, from the turbulent disk to the asymptotic regime of ideal magnetohydrodynamic (MHD) jets. However, a thorough comparison with time-dependent numerical simulations has never been achieved, mostly because mass-loss rates found in simulations were always larger than those found analytically. This tension may have cast doubt on the analytical approach, the numerical one, or both. Our goal is to bridge the gap between these two complementary approaches and settle this long-standing issue. We performed 2.5D (axisymmetric) simulations of resistive and viscous accretion disks described by the same parameter sets as analytical JED solutions. The results demonstrate an almost perfect agreement between the numerical and analytical solutions, thereby resolving the previously observed tension. The simulations also confirm that JEDs behave as dynamical attractors: starting from different initial conditions, the system consistently converges toward the expected steady-state solution. This work demonstrates that self-similar solutions provide valuable insights into accretion-ejection physics. However, as 2.5D numerical simulations which rely on alpha-prescriptions, they strongly depend on the assumptions made for turbulent terms. In contrast, 3D simulations capture the turbulence, but become prohibitively expensive when modeling large-scale astrophysical systems. We advocate for the use of global 3D simulations to investigate turbulence and to derive physically motivated prescriptions for use in 2.5D studies.
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Friday 27 March

Earth and Planetary Astrophysics · Cross-listed from physics.soc-ph

The new Geological Age that never was or the multiple layers of the Transientocene

Orfeu Bertolami

Since its humble origins, humans have left imprints on the face of the planet. From the profound transformation unleashed by the Neolithic Revolution, about 12000 years ago, till the present, humans have reshaped the planet significantly. From the second half of the XX century, the impact on the atmosphere, biosphere, cryosphere, hydrosphere and upper lithosphere is so overwhelming that a new geological age, the Anthropocene, was proposed to consider the extent of these transformations. However, despite the ubiquitous nature of the changes in course, the International Union of Geological Sciences rejected in March 2024 formalizing the Anthropocene as a new geological epoch. This controversial decision implies that geologists are not quite convinced that human activities have reached the level of an encompassing new geological age. Nevertheless, it is beyond any doubt that there is no single spot on the planet where the signs of the transformations ensued by the human activities are not felt. Furthermore, the interconnection of the human activities has reached a level of entanglement that it makes the Anthropocene an inescapable feature of our present and immediate future. Thus, more important than framing our present condition in a way that it can be recognised by geologists in the future, is the understanding that by its very nature, the Anthropocene is a condition that is continuously being reshaped to the point that we should instead regard our time as a Transientocene, a time of significant and multidimensional transformations.
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Astrophysics of Galaxies · Cross-listed from physics.space-ph

Analytical Scaling of Relativistic Drag in the Interstellar Medium

Lucky Gangwar

This paper develops an analytical framework for the retarding forces on macroscopic spherical probes travelling through the interstellar medium (ISM) at relativistic speeds (0.1c to 0.99c). Integrating the aberrated momentum flux of both baryonic and radiative fields yields scaling laws that expose what this work calls the Magnitude Paradox: relativistic inertia (gamma^3) keeps a probe's speed nearly constant across parsec-scale distances, yet the same gamma^2 boost to the effective baryonic cross-section drives extreme thermal loading on the hull – a relativistic correction that becomes significant only above beta > 0.5c and was not quantified in prior work focused on the Starshot regime (beta approx. 0.2c). The central conclusion is that ISM drag is not a kinematic problem – a probe will not be slowed to a stop – but a thermodynamic one: the forward surface faces energy deposition rates that no passive material can survive. A closed-form crossover condition is also derived separating the baryonic- and radiative-dominated regimes, showing that for any macroscopic probe in the galactic disk, total radiative drag is negligible by many orders of magnitude.
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