Cosmology and Nongalactic Astrophysics
Testing the CCC+TL cosmology with cosmic-chronometer measurements of the Hubble parameter
Rajendra P. Gupta
In a recent paper, it was shown that the Covarying Coupling Constants and Tired Light (CCC+TL) hybrid model yields the Hubble parameter $H(z)$ that is substantially different from its measured value using differential aging of quiescent
galaxies as
cosmic chronometers (CC). It was claimed that the fit of the CCC+TL model to the $H(z)$ data results in a best-fit value for the parameter $\alpha$, defining the strength of the co-variation of the constants, disagreeing with that for the SN~Ia data at the $\sim 6\sigma$ level. In this paper we re-examine the assumptions underlying such a comparison.
Cosmic-chronometer measurements are designed to be independent of cosmological priors, but they nevertheless rely on
stellar population synthesis models, isochrones, and age-dating calibrations developed within standard
stellar-
evolution physics. Therefore, even before introducing any specific correction factor, the present CC compilation cannot be regarded as a model-independent falsification of CCC+TL without recomputing the relevant
stellar population models in that framework. In the absence of such a recalculation, we ask a more limited question: what type and magnitude of modification to the effective differential-age relation would be sufficient to remove the claimed tension? We show that a phenomenological factor of the form $\sim (1+z_t)^{-3}$ with $z_t$ being the TL contribution to the observed
redshift, motivated by the scaling of gas cooling times for
galaxy formation in the CCC+TL framework compared to $\Lambda\text{CDM}$, is sufficient to reduce the apparent discrepancy in $\alpha$ to $\sim 0.13\sigma$. Since $z_t = 0$ for the
stellar model primarily developed from local
stellar observations, the
stellar-aging methods may be unable to verify $\sim (1+z_t)^{-3}$ dependence.
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Instrumentation and Methods for Astrophysics
Reassessment of ammonia self- and air-broadened half-widths in the HITRAN database
Ali Elkhazraji
Accurate NH3 pressure-broadening parameters are essential for reliable line-by-line simulations in atmospheric sensing, combustion diagnostics, and planetary/
exoplanet studies. Current HITRAN NH3 self- and air-broadened half-widths rely largely on the Nemtchinov rotational correlation and database rules that clamp or assign default values beyond the validated range, limiting the representation of measured rotational trends, especially at high J”. Here, published NH3 self- and air-broadened Lorentz half-widths were compiled and reassessed to develop updated HITRAN-ready empirical correlations. The
dataset includes 1317 self-broadened and 1231 air-broadened widths at, or reduced to, 296 K across multiple bands, branches, and rotational states. The analysis shows that linewidths are governed mainly by rotational dependence rather than branch, band, or vibration-inversion effects. Weighted, positivity-constrained third-degree
polynomial fits were developed for gamma_self and gamma_air as functions of the branch-dependent index m and K”. The new correlations reduce the MAPE from 10.95% to 6.80% for air broadening and from 23.61% to 10.89% for self broadening relative to HITRAN2024. Comparisons with PNNL and pure-NH3 spectra further confirm improved absorption simulations, providing a physically constrained replacement for the current HITRAN NH3 broadening treatment.
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High Energy Astrophysical Phenomena
Fast targeted gravitational-wave followup search for compact binary mergers using GSTLAL pipeline
Leo Tsukada, Noah Zhang, Surabhi Sachdev et al. (+4 more)
We present a novel method to conduct targeted gravitational-wave searches for compact binary mergers using the GstLAL inspiral pipeline. By incorporating sky localization and timing information from external electromagnetic triggers, we enhance the sensitivity of the search for sub-threshold gravitational-wave signals associated with events such as short gamma-ray bursts. Our approach modifies the standard likelihood ratio ranking statistic to include a sky localization prior, allowing for a more focused analysis on specific regions of the sky. We demonstrate the effectiveness of this method through injection studies, comparing the performance of the targeted search against the standard all-sky search configuration. The results show a significant improvement in detection efficiency for signals consistent with the provided sky location and timing, while maintaining control over false alarm rates. This targeted search framework enables rapid follow-up of electromagnetic transients, facilitating multi-messenger astronomy efforts in the era of advanced gravitational-wave detectors.
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All authors Leo Tsukada, Noah Zhang, Surabhi Sachdev, Shomik Adhicary, Chad Hanna, Prathamesh Joshi, Divya Singh
High Energy Astrophysical Phenomena
Crust glass formation reveals the neutron star birth properties in IGR J17480-2446
D. A. Baiko and A. I. Chugunov
IGR J17480-2446 is a low-mass X-ray binary, harboring an exceptional accreting
pulsar (a
neutron star) with an unusual
spin frequency of 11 Hz and a very slow post-outburst crust cooling. The former may imply that it is observed at an early stage of recycling, while the latter was shown to indicate the presence in the outer crust of a low thermal conductivity layer, possibly made of glass. Here we argue that the glass layer formation is a natural result of
accretion induced failure of pristine cold
crystal crust. This allows us to determine the mass of the accreted material as $\Delta M \approx 2.4\times 10^{-6}~M_\odot$, confirming very early
accretion stage for this
neutron star. An analysis of
spin and thermal state reveals a peculiar set of
neutron star birth properties which is commonly associated with `recycled'
neutron stars, i.e.\ those that have been experiencing prolonged periods of
accretion from a companion. We speculate that such birth properties may represent the outcome of
neutron star formation in an electron-capture
supernova.
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High Energy Astrophysical Phenomena
Multiwavelength variability of the high-energy neutrino candidate PKS 0735+178 over three decades
T. Mufakharov, Yu. Sotnikova, V. Vlasyuk et al. (+12 more)
We present the multiwavelength variability of the BL Lac object PKS 0735+178, associated with the high-energy
neutrino event IC211208A. The light curves cover the
radio (1-230 GHz), optical, and
Fermi-LAT $\gamma$-ray bands over a $\sim$30 years time-scale. The light curves are correlated, with delays from 0 to 1200 days increasing towards lower frequencies, consistent with emission from an opacity-stratified jet. The bright
flare after the IC211208A event indicates emission from a compact, optically thick region with enhanced activity and more efficient particle acceleration. Short optical and $\gamma$-ray bursts have been detected very close to the
neutrino event, within a few days. The $\sim$12-day lag between the $\gamma$-ray and optical emissions is detected for the first time, suggesting that the emission regions are not co-spatial. A characteristic variability time-scale of $\sim$10-11 yr is robustly detected in the
radio-mm bands ($\geq3\sigma$), while the optical and $\gamma$-ray data show weaker, shorter-period signals. The independent constraints from the VLBI core-shift measurements and
radio time delays yield consistent estimates of the jet geometry and disturbance propagation, supporting variability governed by jet propagation effects. The long-term modulation is consistent with a slow variation in energy release at the jet base, while individual
flares arise from shocks propagating downstream. Jet precession may contribute to the long-term modulation; however, the required viewing angles are inconsistent with the VLBI constraints, indicating that precession alone cannot explain the observed variability.
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All authors T. Mufakharov, Yu. Sotnikova, V. Vlasyuk, D. Kudryavtsev, A. Pushkarev, A. Mikhailov, M. Khabibullina, Yu. Kovalev, Y. Kovalev, A. Popkov, A. Erkenov, O. Spiridonova, T. Semenova, P. Tsybulev, D. Nezamov
Cosmology and Nongalactic Astrophysics
The local ultraviolet signature of Type Ia supernova environments from HST and MUSE
Lluís Galbany, Cullen Abelson, Alaa Alburai et al. (+17 more)
The local environment of a Type Ia
supernova (SN~Ia) traces the local
stellar-population age (a statistical proxy for the progenitor age),
star formation,
dust, and chemical enrichment that may influence both its light-curve properties and its standardized luminosity. We assemble a homogeneous explosion-site
dataset to test how near-ultraviolet (UV) imaging combined with optical integral-field spectroscopy improves the characterization of SN~Ia environments and their connection to SN~Ia observables. We analyze 340 low-
redshift SN~Ia explosion sites observed with HST/WFC3 in F275W together with matched VLT/MUSE spectroscopy. For each site we measure local photometry and extract a 1~kpc-aperture spectrum, model the
stellar continuum with STARLIGHT in a joint UV+optical fit, derive local
stellar and gas-phase properties, and fit the SN light curves with sncosmo/SALT3-NIR. UV emission is detected at 235 of the 337 sites with valid HST imaging. The UV- and H$\alpha$-based
star-formation-rate surface densities are strongly correlated, with the UV estimates systematically higher by about 0.5 dex. Including the UV constraint in the STARLIGHT fit shifts local luminosity-weighted ages toward older values by a median of $+0.20$ dex for UV detections and $+0.45$ dex for UV non-detections, showing that UV data help break age–
dust–
metallicity degeneracies and substantially alter and tighten the inferred local
stellar-population ages within the adopted modelling framework. Consistently, F275W$-r$ is very strongly correlated with the joint-fit
stellar age. Within the 169-SN~Ia calibration sample, the joint
stellar age, the H$\alpha$ specific
star-formation rate (sSFR), and the UV sSFR all correlate strongly with the SALT3 stretch parameter $x_1$, with significances above $6.8\sigma$. (abridged)
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All authors Lluís Galbany, Cullen Abelson, Alaa Alburai, Joseph P Anderson, Yago Ascasibar, Chris Ashall, Carles Badenes, Chris Burns, Èlia Diéguez Gurnés, Albert García Soto, Claudia P. Gutiérrez, Eric Y. Hsiao, Hanindyo Kuncarayakti, Andrew J. Levan, Jospeh Lyman, Mark M. Phillips, Sebastian F. Sánchez, Ramon Sanfeliu, Maximilian Stritzinger, Danny Steeghs
Instrumentation and Methods for Astrophysics
Distributed Peer Review at ALMA: An Empirical Comparison with Panel-Based Review
John M. Carpenter and Andrea Corvillón
Large astronomical observatories are increasingly adopting distributed peer review (DPR) to manage growing proposal volumes, yet empirical comparisons with panel-based systems remain limited. Beginning in 2021 (Cycle 8), the Atacama Large Millimeter/submillimeter Array (ALMA) transitioned to DPR for the majority of proposals, with DPR applied to nearly all proposals from Cycle 9 onward. Under DPR, each Principal Investigator (PI) designates a reviewer to evaluate a set of proposals without collective discussion. This study analyzes over 20,000 proposals and 160,000 reviews spanning 13 cycles to assess the impact of this change. We find that DPR largely reproduces the systematic ranking trends observed in panel evaluations across PI demographics, technical characteristics, and scientific areas, consistent with panel outcomes both before and after discussion. Scientific diversity among the top-ranked proposals is similar between DPR and post-discussion panel rankings. Individual proposal ranks show substantial dispersion under both DPR and panel assessments prior to discussion, with discussion only partially reducing this variance. The observed dispersion therefore reflects intrinsic variation in reviewer judgments rather than a byproduct of the distributed process itself. In Cycle 12, reviewers rated the majority of DPR written comments as high or adequate quality, with no dependence on reviewer career stage. However, 10% of reviews were rated as low quality, highlighting the challenge of maintaining quality standards across the approximately 16,000 reviews produced each cycle. Overall, our results indicate that DPR reproduces the population-level ranking structure obtained in panel review, despite differences in review mechanics and the role of discussion.
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Instrumentation and Methods for Astrophysics
Deep RL for Fast Long-Horizon Operations Scheduling on NASA's Carruthers Geocorona Observatory Mission
Alex Zhang, Jackson Craig and Lara Waldrop
Spacecraft operations scheduling is a highly constrained, long-horizon combinatorial optimization problem that traditionally relies on heuristics, constraint programming, or manual planning. We present a scalable deep reinforcement learning framework developed and deployed for NASA's Carruthers Geocorona Observatory mission. Our framework introduces a macro-action abstraction known as activity blocks coupled with dynamic action-masking to navigate the intractably large search space and strictly enforce complex power, thermal, and instrument constraints. The resulting architecture generates globally feasible schedules with overwhelming probability, establishes operational trust, and executes a full training cycle in under six hours, circumventing the need for policy robustness by enabling rapid, on-demand retraining. Further, resulting schedules outperform baseline heuristics in scheduled science quality. The deep reinforcement learning framework was deployed as the default operational scheduler for the Carruthers Geocorona Observatory mission from the outset of the mission, demonstrating that deep reinforcement learning can be trusted for real spacecraft operations under complex, evolving constraints.
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Cosmology and Nongalactic Astrophysics
Dark Matter as an Inflationary Relic in Warm Inflation
Swagat S. Mishra, Umang Kumar, Suratna Das et al. (+1 more)
Warm inflation is usually expected to completely deplete the inflaton condensate by dissipating its energy into radiation. We show that this expectation fails in a simple and observationally viable regime. In a strongly dissipative warm inflationary scenario, the dissipative ratio, $Q=\Upsilon/(3H)$, can fall rapidly after the end of inflation as the system approaches radiation domination, thereby suppressing further energy transfer to the thermal bath. This leads to a residual inflaton condensate, which subsequently evolves as an effectively non-dissipative scalar field. For potentials with a stable quadratic minimum, this remnant inflaton manifests as a cold dark matter component. We establish this mechanism for the minimal renormalizable potential, with a dissipative coefficient $\Upsilon\propto T^3$. In this case, current cosmological data allow strong dissipation while leaving the inflaton mass weakly constrained by inflationary observables. The observed dark matter abundance then fixes its mass to be $m \approx 0.02\,{\rm MeV}$, while larger masses overclose the Universe. The transition to matter-like scaling occurs well before BBN, avoiding a long-lived inflaton dark radiation component. Relic inflaton dark matter therefore turns the post-inflationary dynamics of warm inflation into a new late time constraint on its parameter space.
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All authors Swagat S. Mishra, Umang Kumar, Suratna Das, Varun Sahni
Astrophysics of Galaxies
Measuring Magnetic Field Strengths in Galactic Star-forming Regions via the Zeeman Effect with the SKA
Tyler L. Bourke, Tao-Chung Ching, Laura Fissel et al. (+14 more)
Magnetic fields thread the interstellar medium from the largest to the smallest scales and play an important role in molecular cloud
evolution and
star formation. Quantifying this requires measurements of the field strengths, and the most direct way to measure them is via the Zeeman effect in spectral lines. The effect is subtle for the typical field strengths expected from theory, from a few $\mu$G in diffuse molecular clouds to a few 10s of mG in dense
star-forming regions, and detections are scarce. Existing measurements of
magnetic field strength suggest dense clouds and cores are marginally supercritical (cannot prevent collapse, but can inhibit it), but may be biased due to small sample sizes. Zeeman effect measurements tracing different scales and densities within molecular clouds can reveal the variation of field strengths, providing critical measurements to address the question of whether
star formation is primarily regulated by
magnetic fields or
turbulence on different scales. Observations with SKA precursors such MeerKAT and FAST are beginning to increase the number of Zeeman effect detections in nearby
star-forming regions. The SKA will extend their reach to many regions within our
Galaxy that are best representative of where most
stars form, while zooming in on the densest
star-forming regions, providing a statistical basis for the role of
magnetic fields in molecular cloud
evolution and
star formation. We present predictions and plans for Zeeman effect observations with the SKA
telescopes, demonstrating the significant advances they will provide for studies of
magnetic fields in molecular clouds.
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All authors Tyler L. Bourke, Tao-Chung Ching, Laura Fissel, James A. Green, Jihye Hwang, A. M. Jacob, Boy Lankhaar, Emmanuel Momjian, Kate Pattle, A. P. Sarma, Mehrnoosh Tahani, Chenoa D. Tremblay, Timothy Robishaw, Tomoya Hirota, Kristen L. Thompson, Keping Qiu, Aaryaa Premanand
Cosmology and Nongalactic Astrophysics
Phantom-Divide Crossing in Exponentially Coupled Quintessence and the Role of Neutrino-Mass Freedom
Jincheng Wang, Hongwei Yu and Puxun Wu
We investigate a quintessence dark-energy model with an exponential potential and an exponential coupling to cold dark matter (CDM), hereafter referred to as the CQ-EXP model, using Planck CMB, DESI BAO, and DES-Dovekie
supernova observations. We also examine how variations in the
neutrino mass sector affect the constraints. When the
neutrino mass sum is fixed at $\sum m_\nu=0.06$ eV, the data favor a coupling between quintessence and CDM, with the coupling parameter $\beta$ deviating from zero at more than $3\sigma$. In particular, the observations favor the $\beta<0$ branch, where the energy transfer between the two dark sectors changes sign and the effective equation of state (EoS) of dark energy crosses the phantom divide, $w=-1$. When the effective
neutrino mass parameter $\sum m_{\nu,\mathrm{eff}}$ is treated as a free parameter, the data show a preference for negative values of $\sum m_{\nu,\mathrm{eff}}$. This additional freedom weakens the preference for the coupling between quintessence and CDM and leads to nearly identical values of $\chi^2_{\rm min}$ for the CQ-EXP models with $\beta>0$ and $\beta<0$, corresponding respectively to models without and with phantom-divide crossing in the effective EoS. Both values are slightly larger than that obtained in the $w_0w_a$CDM model, indicating that the CQ-EXP model cannot be statistically distinguished from the $w_0w_a$CDM model with the data considered here. Therefore, when $\sum m_\nu$ is fixed, current observations favor the CQ-EXP model with phantom-divide crossing. In contrast, when negative values of $\sum m_{\nu,\mathrm{eff}}$ are allowed, a CQ-EXP dark energy without crossing $w=-1$ can also provide an effective explanation of the latest observations.
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Astrophysics of Galaxies
Complex organic molecules in the young hot core RCW 120 S2
M. S. Kirsanova and A. A. Farafontova
We analyse physical and chemical structure of the hot molecular core RCW120 S2, based on high-sensitivity (2-4 mK) APEX observations at 1.3 mm. The analysis reveals a rich molecular inventory, including complex organic molecules (COMs) such as CH$_3$OH, CH$_3$CHO, CH$_3$OCHO and CH$_3$OCH. We derive gas temperatures (20-300 K), H$_2$ densities (10$^4$-10$^7$cm$^{-3}$), and molecular column densities. The detected emission probes a radially stratified envelope, with cooler (<= 60 K) and less dense (10$^4$-10$^5$cm$^{-3}$) outer layers traced by SO, SO2, and c-C$_3$H$_2$, while warmer (60-100 K) and denser (10$^5$-10$^7$cm$^{-3}$) inner regions are traced by H$_2$CO, OCS, and low-excitation CH$_3$CN. The hot gas (<= 100 K) exhibits broad (8-10 km/s) lines from high-excitation CH$_3$OH, CH$_3$CN, HDO, and CH$_3$OCH$_3$. Relative molecular abundances of COMs generally agree with astrochemical hot-core models, while methanol appears underabundant and CH$_3$CN overabundant compared to predictions. We attribute these discrepancies to the need for interferometric observations at intermediate spatial scales to resolve the core's true filling factor and radial gradients.
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High Energy Astrophysical Phenomena
Fast Optical Variability of the TeV Blazar PKS 1725+123 Observed by SVOM-VT and Insights from Multi-wavelength Follow-up Observations
Shuo-Yu Liu, Yu-Wei Yu, Ji-Shun Lian et al. (+29 more)
PKS 1725+123 is a flat-spectrum
radio quasar (FSRQ) with a
redshift of $z=0.586$. The detection of this object in the TeV band was reported by the MAGIC
telescopes and H.E.S.S. in August 2025. Subsequently, we promptly initiated Target-of-Opportunity observations using the Space-based multi-band astronomical Variable Objects Monitor (SVOM) satellite. By analyzing the observational optical data from SVOM-VT and comprehensively examining the
Fermi-LAT and Swift-XRT observational data, it was found that the source is in a high-flux state across the optical, X-ray, and GeV $\gamma$-ray bands around the time of the TeV detections. Its optical flux reaches a historically unprecedented high level and shows significant variability on timescale as short as minutes. The variability is accompanied by changes in the color index, exhibiting a bluer when brighter behavior during the high-flux state. Based on the simultaneous multi-wavelength data, we construct the broadband spectral energy distribution (SED) of the source in the high-flux state. PKS 1725+123 demonstrates a remarkably high synchrotron peak frequency, which is distinctly different from that of other FSRQs. We propose a two-zone spine-sheath jet model to reproduce this SED. The optical–X-ray emission is generated by the synchrotron process of the relativistic electrons within a compact zone. The inverse Compton (IC) scattering processes of the same electron population contribute to the low-energy end of the
Fermi-LAT spectrum, while the high-energy end of the
Fermi-LAT spectrum is ascribed to the IC scattering of the synchrotron
photons within the compact zone by the higher-energy electrons in an extended region.
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All authors Shuo-Yu Liu, Yu-Wei Yu, Ji-Shun Lian, Xin-Ke Hu, Alexis Coleiro, Zhu-Heng Yao, Li-Ping Xin, Jing Wang, Hua-Li Li, Zi-Qi Wang, Jin Zhang, Floriane Cangemi, Bertrand Cordier, Antoine Foisseau, Olivier Godet, Andrea Goldwurm, Diego Gotz, Sebastien Guillot, Xu-Hui Han, Ning Jiang, Cyril Lachaud, Sebastien Le Stum, En-Wei Liang, Pierre Maggi, Yu-Lei Qiu, Jerome Rodriguez, Lian Tao, Jian-Yan Wei, Chao Wu, Liang Zhang, Shuang-Nan Zhang, Shi-Jie Zheng
High Energy Astrophysical Phenomena
Intraday Optical Variability of BL Lacertae during its Highly Active 2020-2024 Phase
A. Takey, Ergün Ege, B. M. Mihov et al. (+12 more)
We present an analysis of the intraday flux and spectral variability of BL Lacertae from 2020 September 30 to 2024 December 7, covering its highest recorded brightness and low, intermediate, and high flux states. Our study involved 62 nights of multi-band (BVRI) optical monitoring using four ground-based
telescopes located in Egypt, Türkiye, and Bulgaria. We assessed intraday flux variability using the power-enhanced F-test and the nested ANOVA test. Significant variability was detected in 88 out of 117 light curves, consistent with previous studies of this object during active epochs. The maximum variability amplitude is 44.5 per cent in the B band. Spectral analysis reveals a bluer-when-brighter trend during intraday
flares, supporting a synchrotron origin for the variable emission. For a subset of well-sampled
flares, we model their profiles with a double exponential function, deriving rise and decay time-scales, thereby constraining the characteristic times of particle acceleration and cooling processes within the relativistic jet. Assuming a turbulent jet model, we determined limits on the radii and
magnetic field strengths of the emitting regions. We detected soft time lags for a multi-band
flare and from their analysis, derived the Doppler factor and
magnetic field strength of the corresponding emitting region. Our long-term, high-cadence study confirms that BL Lacertae was in an exceptionally active phase during the 2020-2024 period, with intraday variability being a common phenomenon. The results underscore the dynamic nature of the jet emission region and provide valuable observational constraints for models of blazar variability and jet physics.
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All authors A. Takey, Ergün Ege, B. M. Mihov, E. G. Elhosseiny, Aykut Ozdonmez, Murat Tekkesinoglu, Hüseyin Er, Aditi Agarwal, L. S. Slavcheva-Mihova, M. Emir Kenger, M. S. Rizk, I. Zead, F. I. Elnagahy, W. A. Badawy, S. K. J. Pacif
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Determining Kerr black hole spin and inclination from a segment of the critical curve in black hole images
Kenta Hioki, Umpei Miyamoto and Tomohiro Harada
We present a method for determining the
spin parameter $a/M$ and inclination angle $i$ of a non-extremal Kerr black hole from segments of the critical curve identified in black hole images. Although the critical curve itself is not directly observable, higher-order
photon rings accumulate near it, and in realistic observations localized portions of the resulting brightness enhancement may be available for identifying segments of the critical curve. We introduce standardized segments of the critical curve and define three observables that characterize their geometry. We show that these observables uniquely determine $(a/M,i)$, together with an auxiliary parameter $r_{nl}\in[0,1]$ specifying the location of the identified segment along the critical curve, within the domain considered. Thus, even a segment of the critical curve contains sufficient
geometric information to constrain the black hole
spin and inclination without reconstructing the full critical curve. The framework is naturally suited to realistic observations and may be extended to more general rotating black hole spacetimes.
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Solar and Stellar Astrophysics
Effect of surface magnetic fields on limb darkening in main-sequence stars
N. Kostogryz, A. I. Shapiro, V. Witzke et al. (+5 more)
Context.
Stellar limb darkening encodes the thermal and radiative structure of
stellar photospheres and is a key ingredient in modeling transit light curves and transmission spectra. It was recently shown that
stellar surface
magnetic fields modify limb darkening in
stars with near-
solar fundamental parameters, and that only
magnetic models can reproduce high-precision transit observations for such
stars. However, for
stars with non-
solar fundamental parameters, the magnitude of the
magnetic effect on limb darkening remain unconstrained. Aims.We aim to investigate how surface magnetism affects
stellar limb darkening across a range of fundamental parameters and to provide the community with center-to-limb spectra of
stars at different magnetization levels. Methods. We use the MPS-ATLAS code to compute synthetic spectra from 3D radiative magnetohydrodynamic box-in-a-
star simulations performed with the MURaM code. These simulations self-consistently capture photospheric magneto-convection without relying on ad hoc parameterizations. We perform calculations for main-sequence
stars at
solar metallicity with effective temperatures in the range Teff = 3200 - 6800 K. For
stars with
solar effective temperature we also consider metal-poor, M/H = -1.0, and metal-rich, M/H = 0.5, cases. Results. We show that the magnitude of the
magnetic effect depends strongly on
stellar fundamental parameters, increasing toward hotter and more metal-rich
stars. Overall, limb darkening is significantly affected by
magnetic fields in K, G, and F
dwarfs, while the effect becomes negligible in M-
dwarfs. We release a public database of synthetic spectra at 10 disk positions.
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All authors N. Kostogryz, A. I. Shapiro, V. Witzke, T. Bhatia, S. K. Solanki, I. Kuhlemann, V. Vasilyev, Y. C. Unruh
Solar and Stellar Astrophysics
Prediction of Solar Flares Using Photospheric Magnetic Field Parameters with Deep Learning
Yash Chaudhary, Jason T. L. Wang, Chunhui Xu et al. (+2 more)
Solar flares, particularly those of the M- and X-class, have a significant impact on human life because of their potential to disrupt critical infrastructure and communication systems on Earth. Accurate prediction of
solar flares is crucial for mitigating these risks, but the black-box nature of conventional deep learning models used in
flare prediction limits their trustworthiness and interpretability. In this paper, we propose a new approach to
solar flare prediction using photospheric
magnetic field parameters or features with deep learning. To improve model interpretability, we integrate explainable artificial intelligence (XAI) techniques, including SHapley Additive exPlanations (SHAP) and partial dependence plots (PDPs), into our prediction framework. XAI methods provide transparency by analyzing the importance and interactions of features used by our model. Specifically, SHAP values offer a global and local understanding of the features, while PDPs provide insights into feature-level trends. These techniques demonstrate the potential of XAI in deploying AI-driven solutions in high-impact applications such as
solar flare prediction, paving the way for more informed decision-making in
solar physics and space weather studies.
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All authors Yash Chaudhary, Jason T. L. Wang, Chunhui Xu, Yan Xu, Sen Zhang
Solar and Stellar Astrophysics
The efficiency per free-fall time as a ratio of the Star Formation Rate to the gas-infall rate in collapsing cores: dependence on the core definition, accretion, and radial structure
Fabián Quesada-Zúñiga, Manuel Zamora-Avilés, Enrique Vázquez-Semadeni et al. (+3 more)
A parameter used to characterise
star formation activity in MCs is the efficiency per free-fall time, $\epsilon_{\rm ff}$, although commonly referred to as an efficiency, it is formally the ratio between the
star formation rate (SFR) and the gas-infall rate. Here we numerically study the collapse of cores and define $\epsilon_{\rm ff}\equiv\langle\dot{M}_\star\rangle/(M_{\rm core}/\tau_{\rm ff})$, where $\langle\dot{M}_\star\rangle$ is the average SFR, $M_{\rm core}$ is the gas mass within the core (as the gas
cells above a density threshold), and $\tau_{\rm ff}$ is the free-fall time of the core gas. We perform simplified numerical experiments of the gravitational collapse of an isolated core, varying the initial mean number density ($n_0=100$ and $1000~\rm cm^{-3}$) and adopting closed/open BCs to (dis)allow fresh gas
accretion into the domain. The simulations start with a slight central Gaussian overdensity that evolved into a power-law profile, $n\propto r^{-p}$ with $p\to2$. As the collapse proceeds, a sink particle forms in the center of the core. We find that both the BCs and the adopted core definition modify the measured core properties and, consequently, the inferred $\epsilon_{\rm ff}$. Low-density models have less mass available, and their
accretion histories are therefore much more sensitive to the choice of BCs, while high-density runs, with their larger mass reservoirs, maintain similar
accretion histories regardless of the BCs. In all models, after sink formation, $\epsilon_{\rm ff}$ rises and then remains relatively stable while
accretion continues to replenish the core's mass, but increases once the gas reservoir is exhausted. Somewhat counterintuitively, $\epsilon_{\rm ff}$ is higher in the low-mass cores, since the larger gas infall rates onto the high-mass cores compensate for their higher SFR. We conclude that the inferred $\epsilon_{\rm ff}$ depends sensitively on both the adopted core definition and external mass supply
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All authors Fabián Quesada-Zúñiga, Manuel Zamora-Avilés, Enrique Vázquez-Semadeni, Gilberto C. Gómez, Aina Palau, Javier Ballesteros-Paredes
Cosmology and Nongalactic Astrophysics
Optimization of Tessellation-based Statistics: Void Statistics
Yu Liu, Cheng Zhao, Yu Yu et al. (+2 more)
Tessellation methods are extensively employed in the analyses of
cosmic large-scale structure (LSS). However, these techniques are highly sensitive to perturbations in both densities and positions of points, often leading to substantial rearrangements of tessellation configurations. As a result, considerable additional statistical errors are introduced in various tessellation-based statistics, thereby weakening their cosmological constraints. In this work, we identify this issue and propose an efficacious measurement scheme through subsampling and averaging to enhance the stabilities of tessellation-based statistics. As a case study, we apply the new scheme to measure multiple primary void statistics [i.e., void size function (VSF), void two-point correlation function (VTCF), and void power spectrum (VPS)] in two distinct classes of voids, based on Delaunay and Voronoi tessellations, respectively. We notice that the statistical uncertainties in void statistics can be predominantly attributed to tessellation instabilities. Through rigorous testing, we demonstrate that the proposed method can substantially eliminate these scatters to deeply mine the statistical power of void statistics. Specifically, we find that our method can dramatically boost the signal-to-noise ratios (SNRs) of void
Baryon Acoustic Oscillations (BAOs) and significantly improve the constraining power of void statistics on cosmological parameters. These findings showcase enormous application potentials of our new method in maximizing extraction of cosmological information from
galaxy surveys. Importantly, our method is simple yet highly potent with broad applicability, hopefully evolving into a standard framework for measuring tessellation-based statistics in the future.
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All authors Yu Liu, Cheng Zhao, Yu Yu, Zhejie Ding, Jean-Paul Kneib
Earth and Planetary Astrophysics
The panchromatic JWST dayside spectrum of WASP-121 b reveals a refractory-rich formation
K. Angelique Kahle, Paul Mollière, Laura Kreidberg et al. (+16 more)
One path to understand how
planets form is to link their present-day atmospheric composition to predictions from
planet formation models. For the hottest
planets, the abundances of refractory species can provide a useful formation tracer, complementing the traditionally used C/O and overall
metallicity. Here we investigate the refractory abundance in the atmosphere of the ultra-hot Jupiter WASP-121 b, combining new JWST MIRI/LRS observations with archival NIRSpec/G395H and NIRISS/SOSS data to obtain a panchromatic dayside emission spectrum from 0.6 to 12 $\mu$m. Our
retrieval analysis detects the refractory tracer SiO gas at high confidence, in addition to previously detected volatile species. The atmosphere is enriched in volatile and refractory species, with enhanced refractory-to-volatile ratios of Si/O=$3.54^{+0.86}_{-0.69}$x
stellar and Si/C=$3.05^{+1.12}_{-0.80}$x
stellar, relative to new
stellar abundance constraints from ESPRESSO data. In addition, we confirm the depletion of TiO and the need for an additional source of reflected light opacity with a
geometric albedo of $0.22\pm0.03$. The retrieved dayside temperature profile has a strong inversion layer, with a more complex structure than standard parameterizations can accommodate, and an eclipse map analysis indicates a small eastward hotspot offset of $4.8^{+2.7\circ}_{-2.8}$. Comparing our results with models of
planet formation, we find that the measured enrichment pattern was shaped by
accretion from multiple reservoirs, either through a mixture of solid and gas
accretion interior to the water ice line or through continued solid
accretion during inward migration from farther out in the disk. Finally, we model the
planet's dynamical history and find that it could reach its current high-obliquity orbit as a consequence of a post-formation dynamical event, such as
planet-
planet scattering or von Zeipel-Lidov-Kozai cycles.
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All authors K. Angelique Kahle, Paul Mollière, Laura Kreidberg, Bertram Bitsch, Mara Attia, Silke S. Dainese, Nicholas Storm, Daniel Valentine, Thomas M. Evans-Soma, H.J. Hoeijmakers, Stefan Pelletier, Ludmila Carone, Cyril Gapp, Yoav Rotman, Sophia R. Vaughan, D. A. Christie, Louis-Philippe Coulombe, Christiane Helling, Thomas Henning
High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph
Plasma Flow Generation and Particle Acceleration from Expanding Magnetic Bubbles
Yang Zhang, Brandon K. Russell, Geoffrey Pomraning et al. (+9 more)
Impulsive
plasma dynamics in the laboratory are often driven by rising electric currents, yet their quantitative
plasma response has not been well established. By means of fully kinetic particle-in-
cell simulations and
laser-driven capacitor-coil experiments, we show that a rising current expels
plasma, forming an expanding
magnetic bubble and accelerating particles. The expansion front velocity scales with the Alfvén speed determined by the
magnetic field at its inner edge and the
plasma density at its outer edge. This mechanism establishes impulsive current drive as a fundamental way that generates
plasma flows and accelerates particles in laboratory
plasmas, with potential relevance to astrophysics.
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All authors Yang Zhang, Brandon K. Russell, Geoffrey Pomraning, Lan Gao, Xiaocan Li, Adam Stainer, William Daughton, Chuanfei Dong, Liang Wang, Peiyun Shi, Kian Orr, Hantao Ji
High Energy Astrophysical Phenomena
Do Prompt Gamma-ray Burst Fireball Composition Impact on Afterglow Emission? Cases Study for Long GRBs 080916C/090902B and Short GRBs 090510/130603B
Yu Gan, Ren-Jie Xiong, Zi-Qi Wang et al. (+3 more)
Broadband observations with the
Fermi mission reveal that a large fraction of gamma-ray burst (GRB) spectra are dominated by non-thermal emission, while a small fraction are dominated by thermal/quasi-thermal emission, likely indicating the difference in jet composition among GRB. By selecting two typical long GRBs (080916C and 090902B) and two short GRBs (130603B and 090510), we present a comparative analysis to investigate whether the composition of
prompt GRB jets influences the afterglow emission for bursts originating from both massive
star collapse and compact binary mergers. Incorporating emission from both primary and cascade electron populations, we fit the multi-wavelength afterglow lightcurves of these GRBs with the standard forward shock model and analyze the particle acceleration and radiation physics of the jets. Our results show that the afterglow lightcurve
evolution with the characteristic parameters is not related to the composition of the GRB fireball but rather depends on the ambient medium density. The early UV-optical afterglows of the two long GRBs are dominated by synchrotron emission from cascaded $e^{\pm}$ pairs produced via the $\gamma\gamma$ annihilation process, whereas this is not the case for the two short GRBs. These results suggest that the internal energy of the fireball is converted into jet kinetic energy during the
prompt phase, and that the fireball composition leaves no detectable footprint on the afterglow jet. Instead, the density of the ambient medium plays an essential role in shaping the afterglow emission.
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All authors Yu Gan, Ren-Jie Xiong, Zi-Qi Wang, Qi-Yu Yan, Liang-Jun Chen, Xiao-Li Huang
Cosmology and Nongalactic Astrophysics
Dark Energy in the DESI Era: A Brief Review of Evidence, Beyond-$\Lambda$CDM Interpretations, and Tensions
Tian-Nuo Li, Guo-Hong Du, Hao Wang et al. (+3 more)
Recent
baryon acoustic oscillation measurements from DESI provide important new clues for reassessing whether the standard $\Lambda$CDM model offers a sufficient description of the late-time expansion history of the Universe. When combined with
cosmic microwave background and type Ia
supernova data, these measurements show an apparent departure from the $\Lambda$CDM model, commonly described as dynamical dark energy (DDE) with equation of state crossing the phantom divide (i.e., quintom behavior). This review examines the current status of the DESI-motivated indications for DDE and their possible implications for physics beyond $\Lambda$CDM. We discuss how the strength of the preference for DDE depends on the adopted parametrization and
dataset combination, and how residual systematics or internal tensions among
datasets may affect its interpretation. At the background level, several mechanisms beyond $\Lambda$CDM can produce similar expansion histories. We therefore further discuss how the same effective departure from $w=-1$ may arise from physically distinct scenarios, including interacting dark energy, non-minimally coupled
gravity, and non-standard dark matter. Meanwhile, these different new-physics interpretations may have different implications for current cosmological tensions, especially those involving $H_0$, $S_8$, and $\sum m_\nu$. In conclusion, the question posed by DESI is not merely whether dark energy evolves with time, but rather how, within the framework of precision cosmology, to disentangle new physics scenarios from systematic errors.
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All authors Tian-Nuo Li, Guo-Hong Du, Hao Wang, Yun-He Li, Jing-Fei Zhang, Xin Zhang