High Energy Astrophysical Phenomena
Magneto-Active Environments in Pulsar Binaries with the MeerKAT Telescope: I. Pulsar sample and their basic properties
Jaikhomba Singha, Dongzi Li, Marisa Geyer et al. (+6 more)
Eclipsing
pulsar binaries and binaries with a high mass companion are ideal systems for studying and understanding the properties of
plasma in magneto-ionic environments. In this work, the first paper of a series, we present MeerKAT observations of three
pulsar binaries: the high-mass binary PSR J1740$-$3052, the black widow PSR J2051$-$0827 and the redback PSR J1748$-$2446A (Terzan~5A). With the help of MeerKAT's high-sensitivity polarimetric observations, we characterise the properties of these sources, including the linear/circular polarization, dispersion measure (DM), rotation measure (RM) and scattering time. The two eclipsing millisecond
pulsars exhibit strong orbital-phase-dependent propagation effects and we observe $\sim$2 eclipses in these systems during our observations. PSR J1740$-$3052 is a binary system with a 231 d orbital period. The relatively large separation results in a smooth RM variation, enabling us to resolve its variation timescale and constrain the small-scale
magnetic structure. A gradual RM variation is observed over $\sim$1500 s, occurring near periastron. This behaviour implies a
magnetic spatial scale of $\sim$0.003 AU in the companion wind, assuming a relative velocity of $\sim$250 km s$^{-1}$. The linear polarisation intensity profiles of PSR J2051$-$0827 show shape variations as a function of frequency, with a stronger leading component emerging at lower frequencies. We observe signatures of the propagation effect in the polarisation properties of PSR J1748$-$2446A during eclipse ingress and egress. This could arise from Faraday Conversion or multipath propagation of the
pulsar signal and requires detailed analysis.
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All authors Jaikhomba Singha, Dongzi Li, Marisa Geyer, Maciej Serylak, Federico Abbate, Senate Lekomola, Robert Main, Andrea Possenti, Amanda Weltman
Cosmology and Nongalactic Astrophysics
Revealing the neutrino mass through persistent homology of the cosmic web
Jiaqi Wang, Willem Elbers, Carlos S. Frenk et al. (+4 more)
Cosmological constraints on
neutrino mass offer a promising avenue for advancing our understanding of both fundamental particle physics and the
evolution of
cosmic large-scale structure. To overcome challenges associated with traditional probes of
neutrino mass, particularly degeneracies with other parameters, we consider topological summaries of the
cosmic web based on the formalism of persistent homology. We introduce persistence strips, a novel representation that segments Betti curves by topological persistence, effectively condensing two-dimensional persistence diagrams into a set of one-dimensional curves. Applied to the FLAMINGO suite of cosmological simulations, these topological descriptors demonstrate pronounced sensitivity to
neutrino mass. By constructing an emulator spanning a 10-dimensional $w_0 w_a\text{CDM} +\nu$ cosmological parameter space that includes parameters degenerate with
neutrino masses in conventional approaches, assuming a volume of only $(350 \, \mathrm{Mpc})^3$, we obtain
neutrino mass constraints with an uncertainty of $0.05 \, \mathrm{eV}$ for the total matter field and $0.13 \, \mathrm{eV}$ for the dark matter-only field, with the strongest constraints coming from void
topology. Persistence strips exhibit roughly twice the constraining power of unbinned Betti curves and, through their multi-scale, environment-dependent sensitivity, systematically break degeneracies between
neutrino mass and other cosmological parameters. We pinpoint the precise physical origin of the signal, identifying two equally important contributions: sensitivity to the
neutrino mass fraction, which is highest in underdense regions, and the impact of
neutrinos on the distribution of dark matter. Our findings highlight the particular promise of applying topological statistics to weak
lensing measurements, which directly probe the total matter distribution.
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All authors Jiaqi Wang, Willem Elbers, Carlos S. Frenk, Shaun Cole, Xiaohu Yang, Ian G. McCarthy, Rien van de Weygaert
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
X-ray Response of the Fully-Depleted, p-Channel SiSeRO-CCD
Julian Cuevas-Zepeda, Joseph Noonan, Claudio Chavez et al. (+6 more)
We present an X-ray characterization of a fully depleted, 725 $\mu$m thick p-channel SiSeRO-CCD. Measurements with a $^{55}$Fe source yield an energy resolution of $54 \pm 0.9$ eV ($14.6 \pm 0.25 e^{-}$) at 5.9 keV for single-pixel events, indicating that the SiSeRO amplifier preserves the intrinsic charge resolution of the CCD under multi-sample non-destructive readout. Characterization with a $^{241}$Am source extends the response to higher-energy
photons, with reconstructed spectral features observed between 9-26 keV and the 59.5 keV $\gamma$ emission. These measurements, together with a
muon-derived
diffusion calibration, show that charge transport and
diffusion are consistent with interactions spanning the full sensor depth. These results demonstrate that the SiSeRO-CCD simultaneously achieves sub-electron noise performance and efficient charge collection in a thick, fully depleted silicon detector. This combination enables X-ray spectroscopy across a broad energy range while maintaining sensitivity to faint signals.
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All authors Julian Cuevas-Zepeda, Joseph Noonan, Claudio Chavez, Miguel Sofo-Haro, Nathan Saffold, Juan Estrada, Kevan Donlon, Chris Leitz, Steve Holland
High Energy Astrophysical Phenomena
GECAM discovery of a peculiar magnetar X-ray burst (MXB 221120) from SGR J1935+2154 associated with a fast radio burst
Wen-Jun Tan, Yue Wang, Chen-Wei Wang et al. (+50 more)
Fast
radio bursts (FRBs) are enigmatic
cosmic transients of millisecond duration observed in the
radio band. The identification of FRB-associated magnetar X-ray bursts (MXBs) from
galactic magnetar SGR J1935+2154 suggests that at least a fraction of FRBs can be produced from magnetar activity. However, the sample size of FRB-associated MXBs is still very small. Here we report a bright and peculiar FRB-associated MXB from SGR J1935+2154 detected by GECAM on November 20, 2022, dubbed MXB 221120. We find that both temporal and spectral properties of MXB 221120 exhibit distinctive features. Its light curve could be generally described by a single FRED function with superposition of several narrow pulses. Interestingly, we identify a possible QPO feature with center frequency of ~18 Hz in this MXB. The time-integrated spectrum is best fitted by a blackbody model with temperature (kT ) of 18.6 keV, rendering it the first thermal spectrum FRB-associated MXB from SGR J1935+2154. Compared to other MXBs with single emission episode, MXB 221120 has longer duration and higher blackbody temperature, making it an outlier in the burst sample. These results indicate that MXB 221120 may be produced by a special mechanism with extreme physical conditions.
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All authors Wen-Jun Tan, Yue Wang, Chen-Wei Wang, Shao-Lin Xiong, Xiao-Bo Li, Shuang-Nan Zhang, Ce Cai, Wang-Chen Xue, Peng Zhang, Bo-Bing Wu, Zheng-Hua An, Ming Gao, Ming-Yu Ge, Ke Gong, Dong-Ya Guo, Hao-Xuan Guo, Long-Fei Hao, Yue Huang, Yu-Xiang Huang, Ke-Jia Lee, Bing Li, Kui-Cheng Li, Xin-Qiao Li, Jia-Cong Liu, Xiao-Jing Liu, Ya-Qing Liu, Xiang Ma, Wen-Xi Peng, Rui Qiao, Yang-Zhao Ren, Li-Ming Song, Xi-Lei Sun, Jin Wang, Jin-Zhou Wang, Ping Wang, Xiang-Yang Wen, Shuo Xiao, Lun-Sheng Xie, Heng Xu, Sheng Yang, Shu-Xu Yi, Qi-bin Yi, Zheng-Hang Yu, Li-Da Zhang, Fan Zhang, Hong-Mei Zhang, Jin-Peng Zhang, Yan-Qiu Zhang, Zhen Zhang, Xiao-Yun Zhao, Yi Zhao, Chao Zheng, Shi-Jie Zheng
Instrumentation and Methods for Astrophysics
A research roadmap for assessing the feasibility of warming Mars
E. S. Kite, A. Essunfeld, M. H. Hecht et al. (+22 more)
This roadmap outlines research pathways to determine whether Mars could be warmed with non-biological methods. It does not presuppose that warming Mars is desirable; its purpose is to identify what would need to be true for Mars to be warmed, what it would cost, and what could go wrong. Three complementary research tracks appear promising. Solid-state greenhouse membranes offer local warming, aiding water harvesting, food production, and oxygen supply near human bases. Orbiting reflectors can warm key sites such as bases and CO$_2$-ice reservoirs, although a large combined area would be required. Strengthening Mars' natural greenhouse effect might warm large regions or the globe, although many aspects remain to be worked out. Each approach carries scientific and technical risks that research must address. Near-term priorities are on-Earth testing of key parameters that will determine whether engineered aerosol warming is realistically possible, assessing whether exponential production of bioplastic habitats is possible, and designing at-Mars process experiments. In the near term, the research proposed here is closely aligned with and supports research needed to understand Mars' atmosphere and volatile
evolution and hazards to human explorers. The main external uncertainty is whether or not launch costs continue to fall. This is early-stage research, and we discuss key near-term decision points, alternative pathways, and payoffs if research outcomes are negative. We also outline build-out pathways if research succeeds and demand exists. Relatively modest research investments would keep open the option of extending life beyond Earth as Mars' scientific exploration continues.
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All authors E. S. Kite, A. Essunfeld, M. H. Hecht, M. A. Mischna, R. Wordsworth, H. Mohseni, A. Boies, N. Averesch, S. Ansari, M. I. Richardson, E. A. DeBenedictis, D. Stork, A. L. Bamba, C. J. Handmer, C. Jourdain, R. Ramirez, C. E. Mason, A. Kling, A. S. Braude, A. Dumitrescu, S. P. Worden, J. Cumbers, N. Lanza, R. Quayum, C. S. Cockell
Cosmology and Nongalactic Astrophysics
Consistency relations of amplitude and phase fluctuations of gravitational waves magnified by strong gravitational lensing
Yuta Nakazono and Teruaki Suyama
We discuss the amplitude and phase fluctuations of gravitational waves due to wave optics
lensing in the presence of both a strong lens and cosmological weak lenses. By applying the
geometric optics approximation to the strong lens and treating the weak
lensing potential perturbatively, we obtain the amplification factor up to the second order in the weak
lensing potential. Additionally, we establish a methodology to systematically evaluate the weak
lensing effects based on diagrammatic rules. Based on the derived amplification factor, we evaluate the statistics of the fluctuations and demonstrate that the consistency relations originally established in the absence of a strong lens still hold in exactly the same form when a strong lens is present. The physical origin of these relations is also discussed. Furthermore, we demonstrate that for the mean of the weak
lensing signal, both the magnification of the signal and the shift of the Fresnel scale to larger scales occur, consistent with the behavior observed in the variance.
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Cosmology and Nongalactic Astrophysics
Nonminimally coupled quintessence with sign-switching interaction
Jia-Qi Wang, Rong-Gen Cai, Zong-Kuan Guo et al. (+3 more)
We propose a new nonminimally coupled quintessence model to account for the late-time dark energy dynamics indicated by recent Dark Energy Spectroscopic Instrument (DESI) measurements. Within this framework, the quintessence density begins to decrease only when it starts to dominate the Universe, which naturally accounts for the late-time onset of dark energy weakening. The coupling also induces a sign change in the effective energy transfer between dark matter and dark energy during
cosmic evolution. While the scalar field itself remains canonical and never crosses the phantom divide, the modified
evolution of the dark matter density gives rise to an effective crossing behavior in the observationally inferred dark energy sector. Compared with both $\Lambda\mathrm{CDM}$ and $w_0w_a\mathrm{CDM}$ models, our model is favored more strongly by current cosmological data. This work may provide a promising avenue for understanding the observational late-time weakening of dark energy and the origin of its dynamics.
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All authors Jia-Qi Wang, Rong-Gen Cai, Zong-Kuan Guo, Yun-He Li, Shao-Jiang Wang, Xin Zhang
Astrophysics of Galaxies
SDSS J153231.80+420342.7: a triple black hole candidate with a close binary black hole
Qi Zheng, YiWen Jiang, Xue-Guang Zhang et al. (+1 more)
We report a triple black hole candidate with a close binary black hole (BBH) in the blue
quasar SDSS J153231.80+420342.7 (=SDSS J1532) at a
redshift of 0.209. It shows double-peaked profiles in all narrow emission lines, which can be a signature of a dual AGN. If the double-peaked features are produced by a dual AGN, the estimated physical separation between the two cores is about 3 kpc. Alternative interpretations to the double-peaked profiles involving rotating disk-like narrow line region (NLR) and AGN-driven
outflow models are also discussed for the double-peaked features. Besides, SDSS J1532 shows optical quasi-periodic oscillations (QPO) of about 0.6 yr from the ZTF and CSS light curves, with time duration longer than 14 years, which may indicate a binary black hole with about 1 mpc separation. Two alternative explanations, the disk precession and the jet precession models, are also discussed. The current results cannot completely rule out alternative models for the characteristics of spectrum and light curves. As a candidate for triple black hole with two cores in kpc scale and a close BBH in milli-pc scale in SDSS J1532, it may be going through a critical period in its
evolution.
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All authors Qi Zheng, YiWen Jiang, Xue-Guang Zhang, Qirong Yuan
Instrumentation and Methods for Astrophysics · Cross-listed from cs.CL
AstroConcepts: A Large-Scale Multi-Label Classification Corpus for Astrophysics
Atilla Kaan Alkan, Felix Grezes, Sergi Blanco-Cuaresma et al. (+5 more)
Scientific multi-label text classification suffers from extreme class imbalance, where specialized terminology exhibits severe power-law distributions that challenge standard classification approaches. Existing scientific corpora lack comprehensive controlled vocabularies, focusing instead on broad categories and limiting systematic study of extreme imbalance. We introduce AstroConcepts, a corpus of English abstracts from 21,702 published astrophysics papers, labeled with 2,367 concepts from the Unified Astronomy Thesaurus. The corpus exhibits severe label imbalance, with 76% of concepts having fewer than 50 training examples. By releasing this resource, we enable systematic study of extreme class imbalance in scientific domains and establish strong baselines across traditional, neural, and vocabulary-constrained LLM methods. Our evaluation reveals three key patterns that provide new insights into scientific text classification. First, vocabulary-constrained LLMs achieve competitive performance relative to domain-adapted models in astrophysics classification, suggesting a potential for parameter-efficient approaches. Second, domain adaptation yields relatively larger improvements for rare, specialized terminology, although absolute performance remains limited across all methods. Third, we propose frequency-stratified evaluation to reveal performance patterns that are hidden by aggregate scores, thereby making robustness assessment central to scientific multi-label evaluation. These results offer actionable insights for scientific NLP and establish
benchmarks for research on extreme imbalance.
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All authors Atilla Kaan Alkan, Felix Grezes, Sergi Blanco-Cuaresma, Jennifer Lynn Bartlett, Daniel Chivvis, Anna Kelbert, Kelly Lockhart, Alberto Accomazzi
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Localized Steps toward ACT-Favored Inflation
Kai-Ge Zhang, Chengjie Fu, Jian-Feng He et al. (+1 more)
Recent ACT measurements favor a scalar spectral index larger than the Planck value, posing a challenge to many single-field slow-roll inflation models. We show that a smooth, localized step in the inflaton potential can shift the predicted scalar spectral index and tensor-to-scalar ratio by displacing the field value at which the CMB pivot scale exits the horizon. This mechanism can move monomial and, in particular, plateau-like attractor models toward the ACT-favored region, whereas the induced shift remains insufficient in natural inflation. We derive semi-analytical expressions for the step-induced remapping and quantify the associated effective e-fold shift, finding that it can be comparable to, and in some cases exceed, the shift allowed by conservative reheating uncertainties.
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All authors Kai-Ge Zhang, Chengjie Fu, Jian-Feng He, Zong-Kuan Guo
Solar and Stellar Astrophysics
Multiplicity of Massive stars in the Milky Way (M3W). I. Project description, UNWIND, application to GLS 11 448, and DIB catalog
J. Maíz Apellániz, R. C. Gamen, G. Holgado et al. (+8 more)
(ABRIDGED BUT NOT TOO FAR) Multiplicity is ubiquitous among massive
stars and its understanding is constrained by the sample of well-determined orbits. The immediate goal of M3W is to significantly increase the number of massive multiple systems with well-determined orbits and masses. We will address issues such as multiplicity statistics, the mass function in clusters and the field, the properties of binaries with compact companions and gravitational-wave progenitors, the origin and characteristics of runaways and their 3-D motions, the use of apsidal motion as a probe of
stellar interiors, and the mass discrepancy between different methods (evolutionary, spectroscopic, and Keplerian). In this first paper, we present the project; describe the data and tools that will be used, including the disentangling UNWIND tool; analyse the very massive twin binary system GLS 11 448; and briefly introduce some of the following papers of the series. We present a new orbit for GLS 11 448, using UNWIND to obtain for the first time disentangled spectra for the full 3820-11 000 $\mathring{A}$ range for an OB spectroscopic binary. We derive the
stellar parameters, making new
stellar lines available for the study of O
stars. The Aa and Ab components of GLS 11 448, both classified as O3.5 II(f*), are the two most massive O
stars ever detected according to the evolutionary masses of 70$\pm$10 M$_\odot$ and 76$\pm$11 M$_\odot$ determined in this paper. We also report the first-ever detection of the interstellar He I 10 830 triplet in absorption in an OB-
star sightline. As a by-product of the ISM model derived for UNWIND using GLS 11 448 and five other standard
stars, we present the most detailed diffuse-interstellar-band (DIB) library ever built, with a total of 631 DIBs in the 4000-17 100 $\mathring{A}$ range, of which 37 are fitted with multiple-Gaussian profiles and 119 had never been identified before.
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All authors J. Maíz Apellániz, R. C. Gamen, G. Holgado, S. Rosu, J. I. Arias, S. Simón-Díaz, A. Pellerin, M. Abdul-Masih, E. Madero Fuentes, J. A. Molina-Calzada, R. H. Barbá
High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph
Triggering physical plasmoids in forming current sheets: conditions and diagnostics
Hubert Baty
We investigate the conditions for triggering the plasmoid instability in a dynamically forming current sheet in the resistive magnetohydrodynamic framework, using a pseudo-spectral code applied to the Orszag-Tang
vortex at Lundquist number $S \sim 10^5$. Following García Morillo & Alexakis (2025), we use the power spectrum of the current density $E_J(k)$, complemented by the vorticity spectrum $E_\omega(k)$, to assess the convergence of our simulations, and show that this diagnostic remains valid even in the presence of physical plasmoids, allowing us to unambiguously distinguish them from spurious ones. We then show that physical plasmoids can be triggered in a well-resolved spectral simulation when three conditions are simultaneously met: a perturbation applied near the time of maximum current density, with amplitude above a critical threshold $\varepsilon_c \sim 10^{-5}$ for our numerical scheme, and with spectral content containing the unstable wavenumbers. These conditions are confirmed using continuous noise injection, which yields similar results at amplitudes one to two orders of magnitude lower. The resulting growth rates and plasmoid numbers are in good agreement with the theory of \citet{Comisso2017}. These results resolve the apparent paradox raised by García Morillo & Alexakis (2025) and also clarify the role of numerical noise in the triggering of the plasmoid instability.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
The Axion Helical Misalignment Mechanism
Wei Chao and Chang-Jie Dai
Understanding
axion production in the early Universe remains a pivotal challenge, given the
axion as a compelling cold dark matter candidate. Conventional misalignment scenarios often overlook the possibility that a large initial
axion velocity can fundamentally reshape the subsequent
evolution of the
axion field. In this letter, we provide a comprehensive analysis of how
primordial magnetic fields impact the
axion relic abundance. By accounting for the
axion coupling to the Chern-Simons term of the hypercharge gauge field, the equation of motion of the
axion is recast as a driven oscillator equation. This modification effectively shifts the onset of
axion oscillations, leading to a significant reevaluation of the final relic abundance, a novel effect we term the
axion helical misalignment mechanism. Furthermore, in the presence of
primordial chiral asymmetries, the
chiral magnetic effect (CME) emerges as a critical driver of
axion dynamics. The interplay between the
axion field and the CME not only profoundly influences the
evolution of Standard Model
chiral fermions but also provides a viable pathway for generating the observed
baryon asymmetry of the Universe.
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Cosmology and Nongalactic Astrophysics
No evidence for dynamical dark energy from the Combo correlation of GRBs
Marco Muccino, Massimo Della Valle, Luca Izzo et al. (+1 more)
Recently, the Dark Energy Spectroscopic Instrument (DESI) collaboration has presented results indicating that dark energy may exhibit dynamical behavior. Calibrated gamma-ray burst (GRB) correlations can be employed to verify or reject a time-
evolution of the dark energy (DE) equation of state, $\omega(z)$, up to
redshifts $z\sim 9$. We use the most updated catalog of GRBs fulfilling the Combo correlation and improve its calibration employing three catalogs of type Ia
supernovae at
redshifts $z\leq0.075$ and the Bézier interpolation of the Hubble rate, as an alternative to the cosmographic series that fails to be constraining at high
redshifts. To test the
evolution of $\omega(z)$, we adopt a model-independent,
redshift-binned DE parametrization. In both the calibration and the DE reconstruction analyses the impact of the spatial
curvature on the results is explored. The calibrated Combo correlation yields a Hubble constant $H_0\sim70$ km/s/Mpc which alleviates the existing Hubble tension and is broadly consistent with current measurements, although the uncertainties prevent a high-precision measurement. Regarding the reconstruction of $\omega(z)$ of DE, spatially curved scenarios are disfavored and, despite the apparent ”phantom” behavior at $z\lesssim0.55$ due to the limited statistics caused by the shortage of nearby events, at $z>0.55$ the analysis provides statistically robust evidence in favor of the cosmological constant scenario. The Combo correlation alleviates the Hubble tension and shows no significant evidence in favor of dynamical DE. This suggests that GRBs, as distance indicators, are broadly consistent with the current
cosmic distance ladder.
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All authors Marco Muccino, Massimo Della Valle, Luca Izzo, Orlando Luongo
Instrumentation and Methods for Astrophysics
Geant4-IcyMoons: Simulating Electron Interaction Physics in Irradiated Astrophysical Ices
Gideon Yoffe, Jacques Pienaar, Ioanna Kyriakou et al. (+4 more)
Energetic particles continuously process water ice across astrophysical and planetary environments, from interstellar clouds and comets to icy planetary surfaces. Interpreting the resulting observables requires a physically grounded description of the underlying interactions, both to identify radiation-driven signatures and to distinguish them from superimposed chemical, thermal, and microphysical effects. We present Geant4-IcyMoons, an extension of Geant4-DNA developed for irradiated water ice and, ultimately, for materials embedded within it. In this study, we model the elastic and inelastic interactions of electrons with amorphous and hexagonal ice. For the first time, this enables a transport-ready Monte Carlo simulation of electron irradiation in water ice, linking incident-particle environments to the
evolution of icy surfaces. We apply this framework to Jupiter's moon Europa as a representative case of electron bombardment of an icy surface. We show that, on the trailing hemisphere, the stronger low-energy electron bombardment confines much of the deposited energy to the upper $\lesssim 0.1$ cm, whereas on the leading hemisphere, the more energetic incident population drives deposition patterns to depths of tens of centimeters. This may contribute to the observed lens-like enrichment of radiolysis products centered on the equator of the trailing hemisphere. This work lays the foundation for treatments of ion irradiation and radiation chemistry in water ice and embedded materials.
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All authors Gideon Yoffe, Jacques Pienaar, Ioanna Kyriakou, Dimitris Emfietzoglou, Sébastien Incerti, Hoang Tran, Yohai Kaspi
High Energy Astrophysical Phenomena
Gaussian Process Inference of Stochastic Magneto-Active Dynamics and Viscosity in Swift J1727.8-1613
Lijuan Dong, Dahai Yan, Zihan Yang et al. (+4 more)
Linking X-ray variability to the underlying magnetohydrodynamic (MHD) dynamics of black hole X-ray binaries remains challenging. We systematically investigate the
stochastic and oscillatory variability of the black hole X-ray binary candidate Swift J1727.8$-$1613 during its 2023 outburst using Gaussian process (GP) regression applied to Insight-HXMT multi-band light curves. The variability is modeled with a physically motivated composite kernel comprising one stochastically driven damped simple harmonic oscillator (SHO) and two damped random walk (DRW) components. The SHO term robustly recovers quasi-periodic oscillations (QPOs) with frequencies $\nu_0 \sim 0.07$–$5$ Hz, consistent with the fundamental Alfvén mode of a contracting magnetically confined disk–coronal cavity. The quality factor rises from $Q \sim 3$ to $Q \sim 10$, suggesting increasing coherence of the
magnetic cavity. We also find an anti-correlation between QPO frequency and the short DRW damping timescale, supporting our proposed
stochastic magneto-active dynamics scenario. Associating the short and long DRW timescales with the local turbulent turnover and thermal adjustment timescales, respectively, we infer an effective viscosity parameter of $\alpha \approx 0.1$, supporting a strongly magnetized
accretion flow. Strikingly, near the onset of relativistic jet ejection around MJD 60206, both relaxation timescales collapse toward the 0.1 s sampling limit, suggesting a rapid reorganization of the disk internal energy balance immediately before jet launching. Our results establish GP inference as a powerful route to connecting X-ray timing observables with the dynamical state of black hole
accretion flows.
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All authors Lijuan Dong, Dahai Yan, Zihan Yang, Haiyun Zhang, lin Xie, Qingcui Bu, Lian Tao
Astrophysics of Galaxies
Spectropolarimetry of the changing-look active galactic nucleus NGC 1566 and its potential link to supermassive black hole binaries
F. Marin, V. H. Sasse, J. Biedermann et al. (+4 more)
The AGN NGC~1566 is known to present dramatic and regular spectral shape changes, associated with the appearance and disappearance of broad emission lines. The underlying mechanism responsible for such changes is yet to be identified, but occultation, eccentric
accretion disks, turbulent disk-dominated broad line regions (BLRs) or binary supermassive black holes have been hypothesized. Because the scenarios used to explain the variable spectral shapes of NGC~1566 each have a specific
geometric configuration, we used the VLT/FORS2 instrument to obtain nine 3500-10\,000~Å\, polarized spectra of the source between August 2 and September 21, 2025. We caught the AGN in a type-2 state, i.e., without any broad component in total nor polarized fluxes. Its low and wavelength-independent polarization degree (and angle) above 4000~Å\, argues against occultation of the BLR and is consistent with a significant weakening or disappearance of the BLR. The polarized spectrum reveals a strong rise of polarization in the blue band, likely echoing the 2018 outburst of the AGN. The temporal variability of the total flux continuum but the steadiness of the line profiles demonstrate that the object is viewed close to pole-on, irrespective of its spectral type at the time of observation. Relative to archival data, NGC 1566 shows significant variability in polarization degree, angle, and wavelength dependence. Even more surprisingly, NGC~1566 behaves opposite to the basic predictions of the unified model: its polarization angle is perpendicular to the AGN polar axis and its polarization degree is higher when in a brighter, type-1 phase. The results reported above contradict occultation and binary supermassive black hole hypotheses, rather supporting
accretion-driven photoionization/structural changes in the internal
accretion flow and the BLR.
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All authors F. Marin, V. H. Sasse, J. Biedermann, D. Hutsemékers, R. C. Fernandes, D. Porquet, V. Oknyansky
Instrumentation and Methods for Astrophysics
CORSIKA 8: A General Framework for Particle Cascade Simulations
J.M. Alameddine, J. Albrecht, A.A Alves Jr. et al. (+34 more)
The simulation of extensive air showers and particle cascades in general is a cornerstone of modern astroparticle physics. For more than two decades, CORSIKA, currently in version 7, has been one of the most widely used tools for this purpose. However, its architecture reflects design constraints of an earlier computing era, as well as increasingly limiting extensibility, maintainability, and adaptability to modern experimental requirements. CORSIKA 8 is a complete redesign of the original CORSIKA code, implemented in modern C++ and based on contemporary software engineering principles. It introduces a modular and extensible simulation framework with explicit handling of units, flexible geometry, and environment descriptions. In this paper, we present the design philosophy and core architecture of CORSIKA 8, describe the implementation of electromagnetic and hadronic shower physics, and validate air shower simulations against CORSIKA 7. The results demonstrate good agreement at the few-percent level for key observables, confirming the physics fidelity of CORSIKA 8. We also showcase new use cases that were beyond the capabilities of version 7, such as the simulation of cross-media showers and particle cascades in ice, including
radio-signal propagation
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All authors J.M. Alameddine, J. Albrecht, A.A Alves Jr., J. Ammerman-Yebra, L. Arrabito, D. Baack, A. Coleman, C. Deaconu, H. Dembinski, D. Elsässer, R. Engel, A. Faure, A. Ferrari, C. Gaudu, C. Glaser, M. Gottowik, D. Heck, T. Huege, K.H. Kampert, N. Karastathis, J. Lazar, L. Nellen, D. Parello, T Pierog, R. Prechelt, R. Privara, M. Reininghaus, W. Rhode, F. Riehn, M. Sackel, P. Sampathkumar, A. Sandrock, A. Schmidt, J. Soedingrekso, R. Ulrich, P. Windischhofer, B. Yue
Solar and Stellar Astrophysics
Asteroseismic Diagnostics for Red Giants with Kepler: Measuring epsilon and Small Frequency Separations in 16,000 Stars
Yingxiang Wang, Timothy R. Bedding, Yaguang Li et al. (+4 more)
Asteroseismic studies of red
giants have primarily relied on two global parameters: the large frequency separation (Dnu) and the frequency of maximum power (numax). Meanwhile, the p-mode phase shift (epsilon) and small frequency separations (dnu01, dnu02), which offer additional constraints on
stellar interiors, remain underexplored due to measurement challenges. Here we develop an automated pipeline based on collapsed echelle diagrams and apply it to about 16,000 Kepler red
giants, jointly measuring Dnu, epsilon, dnu01, and dnu02 and assembling the largest homogeneous catalogue of these quantities to date, together with updated Dnu values and formal internal uncertainties. Using this catalogue, we quantify evolutionary trends across the red-
giant branch and core-helium-burning phase. We find that dnu02/Dnu stays nearly constant for RGB
stars and, for core-helium-burning
stars, organises into two sequences that are systematically offset but partially overlap, broadly separating
stars in the red-clump and secondary-clump regimes. We also trace the mass- and
metallicity-dependent helium-flash transition. Meanwhile, epsilon follows a single Dnu-epsilon relation common to both evolutionary phases. Comparisons with
stellar-
evolution models reveal systematic offsets in epsilon and dnu01, which we interpret as signatures of near-surface and outer-envelope modelling deficiencies. These comparisons further suggest that dipole-mode small separations are sensitive to mode-dependent surface terms in evolved
stars. Overall, our results demonstrate that epsilon and the small separations provide important diagnostics of core structure, convective-boundary mixing, and helium ignition that are complementary to those provided by Dnu and numax alone. The resulting catalogue offers a reference for testing and calibrating future
stellar-
evolution models.
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All authors Yingxiang Wang, Timothy R. Bedding, Yaguang Li, Yifan Chen, Courtney L. Crawford, Daniel Huber, K. R. Sreenivas
Astrophysics of Galaxies
Milky-Way-like stars in a galaxy core 8 billion years ago revealed by gravitational lensing
Quirino D'Amato, Filippo Mannucci, Alessandro Sonnenfeld et al. (+40 more)
The assembly of
stellar-dominated cores in elliptical
galaxies is key to understanding how
cosmic structures evolved. Gravitational
lensing offers unique insights into the nature of their
stars. We report the discovery of the smallest known quadruply lensed
quasar (radius ~0.2"), whose
lensing galaxy at
redshift 1.055 (5.5 billion years after the Big Bang) features a
lensing mass of only ~2x10^10 M_sun. A
Bayesian analysis, based on the system's exceptional properties and standard scaling relations, allowed us to sample the central
galactic initial mass function with unmatched accuracy and in a previously uncharted regime in terms of mass and
redshift. We found it consistent with the Milky Way one, while excluding bottom-heavy functions. This suggests that the core either grew slowly or underwent early disruptive events altering its
stellar build-up, in contrast with the classical view that bulges form rapidly and remain unchanged by later interactions.
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All authors Quirino D'Amato, Filippo Mannucci, Alessandro Sonnenfeld, Martina Scialpi, James W. Nightingale, Cristiana Spingola, Stefano Zibetti, Alessandro Marconi, Piero Rosati, Cosimo Marconcini, Guido Agapito, Anna Gallazzi, Enrico Di Teodoro, Gloria Andreuzzi, Francesco Belfiore, Elena Bertola, Caterina Bracci, Stefano Carniani, Elisa Cataldi, Avinanda Chakraborty, Matteo Ceci, Claudia Cicone, Anna Ciurlo, Giovanni Cresci, Alessandra De Rosa, Elisa Di Carlo, Anna Feltre, Michele Ginolfi, Isabella Lamperti, Bianca Moreschini, Emanuele Nardini, Michele Perna, Elisa Portaluri, Khatun Rubinur, Paolo Saracco, Paola Severgnini, Vincenzo Testa, Giulia Tozzi, Giacomo Venturi, Lorenzo Ulivi, Cristian Vignali, Maria Vittoria Zanchettin, Antonio Pepe
High Energy Astrophysical Phenomena
The Real and Pseudo Dispersion Measures of FRB~20220912A
Yi Feng, Dengke Zhou, Y.-K. Zhang et al. (+5 more)
Fast
radio bursts (FRBs) are millisecond-duration
radio transients. As they propagate through the interstellar medium, they interact with free electrons, resulting in dispersion. The corresponding dispersion measure (DM) is referred to as the real DM (DM$_{\rm real}$). In practice, however, the dispersion measure derived from modeling (DM$_{\rm model}$) is often contaminated by intrinsic burst morphology, giving rise to a pseudo DM component (DM$_{\rm pseudo} = {\rm DM}_{\rm model} - {\rm DM}_{\rm real}$). In this work, we focus on the highly active repeating FRB~20220912A and utilize its microshots – extremely short-duration (typically tens of microseconds), broadband emissions – to investigate its DM$_{\rm real}$ and DM$_{\rm pseudo}$. We adopt two assumptions: first, that FRB~20220912A resides in a non-magneto-ionic environment and that its DM$_{\rm real}$ variation is smaller than $10^{-2}$\,pc\,cm$^{-3}$ over a few years; and second, that microshots have a negligible intrinsic morphological time delay. By identifying two new microshots and combining them with previously reported ones, we find that all four microshots exhibit remarkably consistent DM values over a one-month timescale, with an average of $219.380 \pm 0.004\,\mathrm{pc\,cm^{-3}}$. We define this value as the DM$_{\rm real}$ of FRB~20220912A. We further show that bright, narrow bursts with a width of less than 2\,ms also yield DM estimates consistent with the microshot-based DM$_{\rm real}$. A survey of five repeating FRBs reveals that DM$_{\rm pseudo}$ is a common phenomenon, with variations typically spanning a range of approximately $10\,\mathrm{pc\,cm^{-3}}$ at 1.2\,GHz. These findings highlight the importance of accounting for morphological contributions in DM interpretation and demonstrate that microshots and narrow bursts are powerful tools for probing DM$_{\rm real}$.
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All authors Yi Feng, Dengke Zhou, Y.-K. Zhang, D. Li, Jianhua Fang, Jiaying Xu, Chenyuan Xu, Jintao Xie
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Interior geometry of black holes as a probe of first-order phase transition
Zi-Qiang Zhao, Zhang-Yu Nie, Shao-Wen Wei et al. (+2 more)
Traditional diagnostics of black hole phase transitions rely on thermodynamic quantities defined at the event horizon or asymptotic boundary. Here, we demonstrate that the near-singularity geometry offers a sharp, independent probe of both first-order phase transitions and supercritical crossover. For scalarized AdS black holes exhibiting a first-order phase transition, the Kasner exponent $p_t$, which characterizes the approach to the singularity, undergoes a dramatic transformation. On one side of the transition, $p_t$ oscillates strongly with temperature, reflecting violent interior dynamics. On the other side, it becomes a smooth, monotonically varying function. These two distinct behaviors converge as the critical point is approached. Beyond the critical point, in the supercritical region, $p_t(T)$ develops a distinct extremum, defining a Kasner crossover line that is entirely independent of traditional thermodynamic (Widom line) or dynamic (Frenkel line) criteria. Our work establishes the near geometry of singularity of scalarized black hole as a novel class of diagnostics for phase transitions, revealing that a change in the macroscopic thermodynamic state fundamentally reshapes the deepest interior structure of spacetime.
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All authors Zi-Qiang Zhao, Zhang-Yu Nie, Shao-Wen Wei, Jing-Fei Zhang, Xin Zhang
High Energy Astrophysical Phenomena
The impact of the eROSITA bubbles on Galactic cosmic-ray transport
Benedikt Schroer
We propose that the observed spectral hardening in
Galactic cosmic ray fluxes is governed by macroscopic
Galactic outflows, such as the eROSITA bubbles, rather than microphysical variations in their scattering properties. Employing a phenomenological transport model, we show that an advective
outflow boundary naturally reproduces the $300\,$GV hardening in secondary-to-primary ratios. Global fits to precision AMS-02 data yield an effective local inner
halo boundary of $\sim 5\,$kpc and an
outflow speed of $\sim 360\,$km/s, in striking agreement with independent multi-wavelength kinematic constraints of the eROSITA
outflows. This interpretation provides a testable alternative to breaks in the effective
diffusion coefficient, without increasing the number of free parameters.
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Solar and Stellar Astrophysics
SN2024abfl: A Low-Luminosity Type IIP Supernova at the Low-Mass End of Core Collapse
Luhan Li, Jujia Zhang, Zeyi Zhao et al. (+8 more)
We present optical photometric and spectroscopic observations of the low-luminosity (LL) Type IIP
supernova SN\,2024abfl. The distance to its host
galaxy is highly uncertain, with independent estimates of $9.5^{+2.3}_{-2.4}$ Mpc and $15.0^{+8.9}_{-1.9}$ Mpc. Even adopting the larger distance, the inferred plateau luminosity is only $\sim 10^{41}\rm erg\,s^{-1}$, placing SN 2024abfl at the extreme faint end of SNe IIP population. Its light curve exhibits a long-lasting plateau of approximately 110 days. The spectra show exceptionally low expansion velocities, with the \FeII\, velocity of $\sim1200\,\rm km\,s^{-1}$ at 50 days after the explosion, significantly lower than the typical values of $\sim2000-5500\,\rm km\,s^{-1}$ observed in SNe IIP, placing SN\,2024abfl among the slowest-expanding LL SNe IIP. Bolometric modeling yields a synthesized $^{56}$Ni mass of $\sim0.002-0.004\,\rm M_\odot$, though this estimate remains subject to significant uncertainty owing to the poorly constrained distance. Considering the plateau color and duration, the magnitude drop from plateau to tail, and the progenitor luminosity, we favor a low-mass core-collapse origin for SN\,2024abfl.
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All authors Luhan Li, Jujia Zhang, Zeyi Zhao, Liping Li, Xiaofeng Wang, Liyang Chen, Zeyi Wang, Jingxiao Luo, Zhengwei Liu, Zhanwen Han, Bo Wang
Solar and Stellar Astrophysics
Heating of a plasma sheet in nonequilibrium ionization with nonthermal electrons
Jin-Yi Lee, John C. Raymond, Katharine K. Reeves et al. (+4 more)
A flux rope eruption on September 10, 2017 provides unique observations of the
plasma sheet beneath the rising flux rope. The
plasma sheet is likely in a nonequilibrium state in terms of both ionization and the electron distribution function. We trace the
evolution of a blob in the
plasma sheet using observations from the Atmospheric Imaging Assembly onboard the
Solar Dynamics Observatory. We investigate the heating of
plasma sheet material in the presence of non-Maxwellian electron distributions and nonequilibrium ionization. Our models compute time-dependent ion fractions, incorporating impulsive heating to various peak temperatures, continuous heating rates, and kappa values that represent the non-Maxwellian distribution. The statistically preferred models constrain the effective impulsive heating temperature to above 20~MK. High-temperature solutions are permitted only for very low kappa values, indicating that suprathermal electrons play a significant role. Impulsive heating dominates the energy budget, with continuous heating contributing approximately 6%-50% of the initial impulsive energy input.
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All authors Jin-Yi Lee, John C. Raymond, Katharine K. Reeves, Chengcai Shen, Stephen Kahler, Yong-Jae Moon, Yeon-Han Kim
Solar and Stellar Astrophysics
Spectroscopic Case Studies of Four Long-duration Transition-region Explosive Events
Yi'an Zhou, Xiaoli Yan, Zhike Xue et al. (+3 more)
This work presents a detailed spectroscopic case study of four long-duration transition-region (TR) explosive events (EEs) observed in NOAA Active Region 13213 on 2023 February 10 using the Interface Region Imaging Spectrograph. The dynamic spectral
evolution of each event is tracked through multicomponent Gaussian fitting of the Si IV 1403 Å line profiles. Three recurrent spectral morphologies are identified and characterized: bilateral wing enhancement, exclusive red-wing enhancement, and exclusive blue-wing enhancement, among which bilateral enhancement is the most common in the studied cases. Throughout their lifetimes of 20-25 minutes, these events display sustained and evolving bidirectional flows, with high-velocity components ($|v|$ > 100 km $s^{-1}$) emerging in late phases. These spectral signatures are interpreted as evidence of ongoing or recurrent
magnetic reconnection, where bilateral profiles correspond to bidirectional
outflows, and exclusive wing enhancements represent
geometric or evolutionary phases of the same process. In contrast, cotemporal
flare ribbons and loop structures exhibit pronounced, unidirectional
redshifts. This study underscores that significant non-Gaussian wing enhancement, rather than exclusively high speed, constitutes a defining spectroscopic signature of EEs, and provides detailed kinematic constraints on the dynamics of such TR EEs.
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All authors Yi'an Zhou, Xiaoli Yan, Zhike Xue, Liheng Yang, Jincheng Wang, Zhe Xu
Astrophysics of Galaxies
Diverse lifestyles of bar-like galaxies and their coevolution with the brightest galaxy in the most massive cluster of TNG50
Ewa L. Lokas
Clusters can provide propitious environments for bar formation in
galaxies. This work studies the formation and
evolution of 15 bar-like
galaxies in the most massive cluster of the TNG50 simulation from the IllustrisTNG suite. The selection includes
galaxies from the last simulation output from well-resolved subhalos with a strongly prolate
stellar component. Eleven
galaxies form or strongly enhance their bars during a pericenter passage around one or more progenitors of the brightest cluster
galaxy (BCG). Two form their bars early as a result of minor mergers, one via an interaction with another massive
galaxy, and one via disk instability. The bar formation times differ considerably, ranging between 3-11 Gyr. The lengths of the bars also differ, ranging between 2-6 kpc, and do not correlate with the amount of
tidal forcing experienced. All
galaxies have at least one pericenter passage around a BCG progenitor, but the number of interactions varies strongly and is reflected in the different amount of mass stripping the
galaxies experience. Most bar formation events take place before the BCG is fully formed. In three cases, they occur just before different progenitors of the BCG merge. For six bar-like
galaxies, the merger events leading to the final formation of the BCG cause significant changes of their orbits. Their diverse evolutionary histories illustrate the different paths to bar formation in clusters and emphasize the complex nature of the process, which includes coevolution with BCG progenitors.
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Cosmology and Nongalactic Astrophysics
Estimates of the Dynamic Characteristics of Binary Systems for Traversable Wormholes Search
I. A. Moiseev and O. S. Sazhina
The paper presents simulated detectability of traversable wormholes (WHs) in wide binary astrophysical systems without
accretion (dormant binary systems) and in the
Galactic center. The wormhole spacetime is represented as a gluing of two asymptotically flat Schwarzschild spacetimes, without specifying the detailed geometry of the throat. We consider a traversable WH candidate as a compact object in a binary system, whose companion
star is perturbed by a massive object on an elliptical orbit on the other side of the WH throat. In the case of a supermassive BH as WH candidate the perturbing acceleration is analyzed and compared with the
stochastic gravitational influence of surrounding
stars. For dormant wide binary systems, we analyze the radial velocity perturbations and their distinguishability from triple-system scenario. Under the model assumptions and the considered observational sampling, radial velocity perturbations are detectable in simulations with an observational accuracy of 1.5 km/s for all considered observation time spans. For a more conservative accuracy of 10 km/s, the spectral analysis methods become statistically significant after $\approx17$ years of simulated data accumulation. The spectral and non-parametric methods significantly reduce the required accumulation time compared to matched-filtering applied in isolation.
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Solar and Stellar Astrophysics · Cross-listed from physics.flu-dyn
Small-Scale Dynamo for Full Spectrum of Hydrodynamic Turbulence in Kazantsev Model
Leonid Kitchatinov
A method is proposed for computing coefficients in the Kazantsev equation of small-scale dynamo for the full spectrum of hydromagnetic
turbulence comprising the inertial range together with the range of viscous dissipation. The dynamo equation with so-defined coefficients is solved numerically for
magnetic (Rm) and hydrodynamic (Re) Reynolds numbers from $10^2$ to $10^8$. The threshold value ${\rm Rm}_c$ for onset of dynamo increases initially with Re but then saturates at a constant value of ${\rm Rm}_c \simeq 300$ for ${\rm Re}\geq 10^5$. In the case of small Prandtl number Pm = Rm/Re << 1, the field growth rate is also small and depends logarithmically on Rm. In this case, the
magnetic energy spectrum peaks around the scale of Ohmic dissipation, which decreases with increasing Pm. The decrease stops at the scale of viscous dissipation while the growth rate increases sharply when Pm approaches the value of one. The increase in the growth rate proceeds to ${\rm Pm} > 1$ but slows down and then saturates at a value somewhat below the inverse lifetime of most short-living eddies. An explanation of the results is proposed.
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Cosmology and Nongalactic Astrophysics
Cosmological Constraints on the Generalized Uncertainty Principle from Redshift-Space Distortions
Andronikos Paliathanasis
We investigate the imprints of the Generalized Uncertainty Principle on cosmological scales by using
redshift-space distortion measurements in combination with background cosmological data to determine constraints on the deformation parameter $\beta$. We consider the modified Poisson bracket related to the existence of a minimal length, which leads to a modified Raychaudhuri equation for the standard $\Lambda$CDM model and gives rise to a phenomenological one-parameter dynamical dark energy scenario. Through this modification, we can reveal the effects of the minimal length on the late-time structure of the universe. We employ the $f$ and $f\sigma_8$ measurements of the growth rate combined with background data, including
cosmic chronometers,
baryon acoustic oscillations and Type Ia
supernova observations. The observational constraints reveal a systematically negative value for the deformation parameter $\beta$, with the $\Lambda$CDM limit lying within the 95% credible interval. When
supernova data are included, the Akaike Information Criterion indicates weak-to-strong support in favour of the GUP-modified model depending on the SNIa catalogue, while the
Bayesian evidence suggests a weak preference.
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