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Physics Astrophysics

astro-ph Watch Astrophysics

Sunday 17 May

High Energy Astrophysical Phenomena

Precise and Rapid Parameter Inference of Kilonova with Conditional Variational Autoencoder

Surojit Saha and Albert K.H Kong

The coalescence of binary neutron stars in the GW170817 event led to the generation of gravitational waves, accompanied by the electromagnetic counterpart known as a kilonova (KN). Since then, it has been a prime topic of interest, as it has provided much insight into multi-messenger astronomy. Apart from existing methods for parameter estimation, we propose an alternative technique for it, utilizing the strength and flexibility of a conditional variational autoencoder. Publicly available light curves are used as training data, conditioning on the corresponding physical parameters for a chosen model; after training, we carry out rapid parameter inferences. As this approach approximates the likelihood through variational inference, it yields results more efficiently. Through this innovative approach, we demonstrated that the total time, from training to parameter inference, is under $\approx3$h. We showed that for a given KN light curve, we can rapidly perform parameter inference based on the required model.
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Astrophysics of Galaxies

From inter-filamentary gas to filaments and hubs: gas flows in the Mon R2 hub-filament system

Jihye Hwang, Doris Arzoumanian, Yoshito Shimajiri et al. (+5 more)

Hub-filament systems (HFSs) play an important role in the formation of massive stars and star clusters. Although the velocity structures along dense filaments have been studied, the gas kinematics in the low density inter-filament regions has not been investigated. We use $^{13}$CO ($J$ = 1–0) and C$^{18}$O ($J$ = 1–0) observations obtained with the Nobeyama 45 m telescope to study the gas dynamics towards the Monoceros R2 (Mon R2) HFS. From the $^{13}$CO and C$^{18}$O data, tracing low- and high-density gas, respectively, we identify velocity coherent structures and divide them into filaments (Fs) and inter-filamentary regions (IFs). We estimate velocity gradients ($\Delta v$) and mass accretion rates ($\dot{M}$) along ($\parallel$) and across ($\perp$) the Fs and IFs. The mean ratio of $\dot{M}_\parallel$ to $\dot{M}_\perp$ in Fs is 6.8, while that in IFs is 1.5. These results show that the overall gas within both Fs and IFs flows directly into the hub and the gas flows faster along the Fs than the IFs. In addition, we found that at least 30% of the gas mass in the IFs may flow towards the Fs replenishing the latter with new matter. Our study reveals the importance of considering the total gas mass reservoir, both low- and high-density, infalling into the hub and promoting the formation of massive stars, which are preferentially located in the hub of Mon R2.
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All authors Jihye Hwang, Doris Arzoumanian, Yoshito Shimajiri, Masahiro N. Machida, Shu-ichiro Inutsuka, M. S. N. Kumar, Shingo Nozaki, Kazuki Tokuda

Solar and Stellar Astrophysics

The Deep Learning-Based Dual-Branch Multimodal Fusion Model for Solar Flare Prediction

Limin Zhao, Xingyao Chen, Xiaoshuai Zhu et al. (+2 more)

Solar flares are intense eruptive events caused by the rapid release of magnetic energy, often impacting Earth's space environment through electromagnetic radiation and high-energy particles. Accurate flare prediction is critical for space weather forecasting. However, many existing deep learning approaches often rely on single-modal inputs or shallow feature fusion, limiting their ability to capture complementary information. In this study, we propose a dual-branch multimodal fusion deep learning model for predicting 24-hour solar flares. The model integrates magnetograms and magnetic parameters through cross-attention mechanisms, followed by cross-scale interactions at the feature level to enhance multi-scale representation. It is designed to perform both binary prediction of $\geqslant$ C-class flares and multi-class classification of C, M, and X-class flares. To ensure rigorous evaluation, we employ a stratified group five-fold cross-validation scheme to preserve class representativeness and adopt a splitting-before-sampling strategy based on NOAA active region numbers to prevent data leakage. Experimental results show that the model achieves a TSS of 0.661 and an HSS of 0.658 for binary $\geqslant$ C-class prediction, while notably attaining a TSS of 0.780 and an HSS of 0.775 for X-class flares in the multi-class task. Compared with existing approaches, the model demonstrates superior performance in predicting intense X-class flares, effectively suppresses the false alarm rate, and exhibits strong generalization capability.
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All authors Limin Zhao, Xingyao Chen, Xiaoshuai Zhu, Dong Zhao, Yihua Yan

High Energy Astrophysical Phenomena

Understanding corona and disk evolution in black hole X-ray binaries through a comprehensive study of their broadband variability and QPO characteristics

Biki Ram and Manoneeta Chakraborty

The shape of the power spectrum of the black hole low-mass X-ray binary evolves systematically over different spectral states during an outburst. Therefore, the power colours (ratio of the variability amplitude at different frequency ranges) and the hue parameter, quantifying the power spectral shape, can be utilised to identify the spectral states of the system. We present the comprehensive power colour analysis and subsequent identification of spectral states using the entire archival data (2016-2024) from AstroSat. We detected 29 QPOs (quasi-periodic oscillations), along with several associated harmonics and shoulders, and investigated their properties as a function of hue. We examined the evolution of the QPO RMS variability and time lag, along with hue and QPO frequency. We report a sign change in the average QPO time lag around the QPO frequency of ~2 Hz for high inclination sources, during the hard-to-hard intermediate state transition. At lower frequency, the hard lags showed an increasing trend reaching up to ~36 ms, but the soft lags above 2 Hz remained confined within ~10 ms, suggesting an evolution to a compact corona. Conversely, for low inclination sources, no such transition was found. Furthermore, for high inclination sources, the harmonic lag remains unaffected during state transition, in contrast to the QPO lag behaviour. Our results are consistent with a transition from an elongated jet-like corona to a compact corona and reveal vital clues about the dynamical evolution of the corona and disk.
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High Energy Astrophysical Phenomena

Radio Emission from Fast Blue Optical Transients Powered by Trans-relativistic Shocks in Confined Circumstellar Material

Liang-Duan Liu, Jia-Sen Zhang, Zhao-Sheng Zhang et al. (+1 more)

Fast blue optical transients (FBOTs) are luminous, rapidly evolving explosions whose radio emission provides a sensitive probe of shock interaction and the circumstellar material (CSM) surrounding the progenitor. However, the origin of their diverse radio light-curve morphologies, especially the very steep post-peak declines seen in several well-sampled events, remains unclear. We present a forward-shock synchrotron model in which mildly relativistic ejecta interact with a dense but radially confined CSM. The CSM is described by a broken power-law density profile, and the radio emission is modeled by including both synchrotron self-absorption and external free-free absorption. Applying this framework to multi-frequency radio observations of a representative sample of FBOTs, we show that their radio diversity can be explained by shock propagation through a finite CSM shell. The early radio evolution is regulated by absorption, while the rapid post-peak fading marks the forward shock's transition from the dense inner CSM into a more tenuous outer environment. The inferred shock velocities are trans-relativistic, $v_{\rm sh}\sim0.1$–$0.5c$. The radio-emitting CSM requires high mass-loading rates, $\dot{M}\sim10^{-4}$–$10^{-3}\,M_{\odot}\,{\rm yr}^{-1}$, but modest total CSM masses, $M_{\rm CSM}\sim10^{-4}$–$10^{-2}\,M_{\odot}$. These properties point to brief episodes of enhanced mass loss in the final years to decades before explosion, rather than long-lived steady winds. Our results provide a dynamically consistent interpretation of FBOT radio emission and establish radio light curves as a diagnostic of the immediate pre-explosion mass-loss history of FBOT progenitors.
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All authors Liang-Duan Liu, Jia-Sen Zhang, Zhao-Sheng Zhang, Yun-Wei Yu

Solar and Stellar Astrophysics

A growth of early superhump: Multi color observation of the WZ Sge star TCP J23580961+5502508

Ryosuke Sazaki, Makoto Uemura, Tatsuya Nakaoka et al. (+1 more)

We report optical and near-infrared photometry of a WZ Sge-type dwarf nova, TCP J23580961+5502508, during its 2022 superoutburst, obtained using the 1.5-m Kanata telescope. Our observation detected early superhumps on three consecutive nights which included the rising phase toward the peak of the outburst. The early superhumps exhibited a profile dominated by the primary maximum during the first two days, while a prominent secondary minimum appeared on the third day. We reconstructed the structure of the accretion disk from multi-color light curves using the early superhump mapping. The accretion disk has a prominent flaring structure on the leading side of the disk during the first two days. An additional flaring structure emerged on the opposite side on the third day, forming a two-armed pattern that can be interpreted within the framework of the 2:1 resonance model. The reconstructed disk structure in the first two days suggests the presence of an additional mechanism operating during the initial stage of early superhump development.
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All authors Ryosuke Sazaki, Makoto Uemura, Tatsuya Nakaoka, Ryo Imazawa

Astrophysics of Galaxies

HI Observations of Baryon-Dominated Dwarf Galaxy Candidates

Atharva Mirashi, Abhinav Narayan, K. Keerthi et al. (+7 more)

We present resolved HI observations of six dwarf galaxies drawn from a sample of baryon-dominated dwarf galaxy (BDDG) candidates previously identified using global HI spectra from ALFALFA and optical inclinations from SDSS, both of which suffer from systematic uncertainties in irregular dwarf galaxies. Using uGMRT interferometric observations, we obtain high-resolution HI cubes that enable more reliable determination of their geometry, circular velocity, and dynamical mass. We find that optical axial ratios systematically underestimate true disc thickness, inflating inclinations and underestimating rotation velocities in earlier work. Our HI-derived axial ratios and kinematic position angles yield larger inclination corrections and hence larger dynamical masses. Four of these galaxies, UGC 6438, UGC 7983, AGC 191707, and AGC 733302, appear dark-matter deficient. The latter three of these four exhibit high baryon enhancement efficiency factor (ratio of baryon mass accumulated by a halo to the maximum expected value for its halo mass) exceeding 50%, with AGC 191707 appearing formally super-efficient. Only UGC 9500 and AGC 220901 are consistent with being dark-matter dominated. Two of these high-efficiency dwarf galaxies lie in relatively isolated environments, showing no clear signatures of tidal disturbance or stripping, making their dark-matter deficiency difficult to reconcile with standard $\Lambda CDM$ expectations for low-mass halos. Our results underscore the importance of resolved HI kinematics in confirming genuine BDDGs and suggest that more such systems may exist. Identifying a larger sample is essential for assessing their implications for baryon-halo coupling and structure formation within the $\Lambda CDM$ paradigm.
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All authors Atharva Mirashi, Abhinav Narayan, K. Keerthi, Saurabh Kadawla, Harshal Raut, Narendra Nath Patra, Nirupam Roy, Prerana Biswas, Mousumi Das, Juliana Saponara

High Energy Astrophysical Phenomena

Identifying observable MeV lines from the decays of weak and main $r$-process isotopes in mergers

Maude Lariviere, Nicole Vassh, Yanwen Deng et al. (+2 more)

We consider predictions for the MeV gamma-ray spectrum emitted by the $\beta$ decays of freshly synthesized isotopes from a neutron star merger at timescales of relevance for post-merger (days) and remnant (years) emission. We develop a search algorithm to identify observable spectral peaks and then determine if a specific isotope has a dominant emission line producing the spectral feature. We predict emission spectra using nucleosynthesis calculations which consider nuclear models with distinct masses, $\beta$-decays, and fission properties as well as variations on main ($A>130$) and weak ($A<130$) $r$-process astrophysical conditions. We tabulate all lines from decaying isotopes that our procedure identifies and provide the predicted range in time over which each line could be visible. We find that Rh-106 presents a unique opportunity to distinguish between main and weak $r$-process emission, as our calculated spectrum above $\sim 1$ MeV for an event dominated by the weak $r$ process is identical to the Rh-106 emission spectrum from $\sim$ 0.2 to $\sim$17 years. We further find emission from species such as Hf-181, Ta-182, Ta-184, and Re-188 offers the potential to be able to distinguish between nuclear models. We investigate whether the 2.6 MeV strong gamma-ray line from Tl-208 is predicted to be robustly observable across calculation variations on both timescale of days and years. We find Tl-208 to consistently shine through on the order of years, though it can face competition from Ga-72 and La-140 at early times ($\sim$ days). We additionally highlight numerous isotopes of interest for observation and nuclear experiment.
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All authors Maude Lariviere, Nicole Vassh, Yanwen Deng, Xilu Wang, Rebecca Surman

Cosmology and Nongalactic Astrophysics

Constraints on Self-Interacting Fuzzy Dark Matter from the Stellar Kinematics of the Dwarf Galaxy Leo II

Yi Zhao, Yu-Ming Yang, Xiao-Jun Bi et al. (+1 more)

The one-parameter fuzzy dark matter (FDM) model has faced increasingly stringent constraints from both Lyman-$\alpha$ forest observations and local measurements of dwarf galaxies. A natural extension to mitigate these limits is the inclusion of FDM self-interactions. In this study, we derive constraints in the two-dimensional parameter space $(m_a, f_a)$ using the dark matter density profile inferred from a Jeans analysis of the stellar kinematics in the dwarf galaxy Leo II, which has previously been employed to constrain non-interacting FDM. We find that, for a fixed particle mass $m_a$, attractive (repulsive) self-interaction leads to a more concentrated (more diffuse) FDM density profile relative to the non-interacting case, thereby improving (worsening) agreement with the Jeans analysis results. Our results indicate that, for either attractive or repulsive SI with strength $f_a^{-1}\lesssim 10^{-14}\,\mathrm{GeV}^{-1}$, the $95\%$ confidence-level lower limits on $m_a$ lies within the range $(1-10)\times10^{-22}\,\mathrm{eV}$, although the precise bounds depend to some extent on the statistical method employed. This analysis simultaneously constrains the two parameters $(m_a, f_a)$ without relying on assumptions about cosmological or galaxy evolution histories, and thus offers a complementary probe to existing constraints.
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All authors Yi Zhao, Yu-Ming Yang, Xiao-Jun Bi, Peng-Fei Yin

Saturday 16 May

Earth and Planetary Astrophysics

Towards a Foundation Model for the Martian Atmosphere

Sujit Roy, Udayshankar Nair, Yuling Wu et al. (+16 more)

The martian atmosphere hosts dynamical phenomena ranging from planet-encircling dust storms to mesoscale orographic clouds and nocturnal low-level jets. General circulation model show capability to simulate these phenomena, but is computationally expensive at resolution needed to resolve mesoscale features. While assimilation of satellite remote sensing observation enable forecasting capabilities using such models, observation record is often sparse, short and fragmented across instrument generators. These constraints motivate the development of a data-driven foundation model for the Martian atmosphere. Foundation models live in a complex design landscape. There is an interplay between the available data, the physics of the underlying processes and corresponding developments in AI. Even though the idea of a foundation model is to address multiple use cases in a data- and compute-efficient manner, it is important to have a clear picture what applications can sensibly addressed by a single model. The purpose of this paper is to elucidate this design landscape. We discuss available data ranging from atmospheric retrievals to reanalysis datasets as well as existing physical models. Moreover, we identify a wide range of candidate downstream applications. Finally, we consider relevant recent developments in artificial intelligence (AI) that can be leveraged in this context. Here, we put a particular emphasis on AI models for atmospheric physics, data-driven approaches to data assimilation as well as methods to work in a limited data setting.
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All authors Sujit Roy, Udayshankar Nair, Yuling Wu, Georgios Priftis, Liping Wang, Anastasia Georgiou, Anne Jones, Björn Lütjens, Johannes Schmude, Campbell Watson, Rachel A. Slank, Ankur Kumar, Anirbit Mukherjee, Procheta Sen, Ramin Lolachi, Haonan Chen, Manil Maskey, Juan Bernabé-Moreno, Rahul Ramachandran

High Energy Astrophysical Phenomena

Multimission Observations of GS 1354-64 during the 2025-2026 Outburst: First Results

Dipak Debnath, Hsiang-Kuang Chang, Subham Srimani et al. (+1 more)

The Galactic transient black hole GS 1354-64 recently showed a new outburst, which has been continuously monitored by MAXI, NuSTAR and Insight-HXMT missions. The ongoing $2025$–$2026$ outburst shows a slow rise with an unusually short period ($\sim 3$~days) of X-ray flare of peak flux $\sim 1.4$~Crab, followed by another relatively weak flare of intensity $\sim 0.8$ Crab. The source was observed to evolve through “canonical” spectral states in a hardness-intensity diagram (HID) during rising phase of the outburst, but the subsequent outburst profile during this study, the source did not follow the reverse trend of the HID. A rapid evolution of quasi-periodic oscillation (QPO) frequencies ($\sim 0.07-4$ Hz) is observed during hard and intermediate spectral states without any signature of QPOs in the soft state. The evolution of the observed low frequency QPOs shows a monotonically increasing (rising phase) signature as well as decreasing (decay phase) one, these are further studied with the propagating oscillatory shock model to understand the nature of the evolution of the shock wave responsible for the origin of the observed QPOs. The broadband energy spectra from NuSTAR ($3-70$ keV) and Insight-HXMT ($2-60$ keV) are well described by thermal (diskbb) and reflection (relxill) model components, indicating a strong signature of a relativistic reflection feature. Using “canonical” observations of a softer state, we found the source to be maximally rotating with $a_k \sim 0.998$ and inclination angle to be as $i \sim 63^\circ - 70^\circ$, which are consistent with earlier reports.
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All authors Dipak Debnath, Hsiang-Kuang Chang, Subham Srimani, Anuj Nandi

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

Evaluation and Modeling of Pneumatic Percussive Drill for Martian Subsurface Access

Luis Phillipe Tosi, Marcel Veismann, Kristopher Sherrill et al. (+2 more)

Deep subsurface access on Mars could enable sampling of ancient lacustrine deposits, volatile-rich horizons, and other geologic targets beyond the reach of current shallow drilling systems. This study evaluates a wireline pneumatic rotary-percussive drill concept that uses compressed atmospheric CO2 as both the actuation and transport fluid. The architecture combines a pneumatically driven hammer, magnetic flapper-valve, and incremental bit-indexing mechanism in a compact bottom-hole assembly for low-power deployment. We develop a reduced-order model of the hammer and chamber dynamics that captures coupled pressure, flow, and impact behavior during each strike. The model is compared with benchtop percussion experiments and used to interpret hammer velocity, displacement, strike timing, and impact energy. A modified testbed is then used to drill Martian rock simulants spanning weaker sandstone and stronger Saddleback basalt cases, linking drilling response to operating pressure and material properties. The experiments show repeatable percussive impacts and mechanical specific energy values from 74 to 360 MJ/m3, with lower values in weaker simulant and higher values in stronger basalt. The results indicate that the system is most effective in a percussion-dominant mode with bit geometry matched to available impact energy. Together, the architecture study, validated model, and drilling experiments support the wireline pneumatic drill as a candidate for low-power deep drilling on Mars, while identifying remaining work in robustness, cuttings removal, and full-system integration.
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All authors Luis Phillipe Tosi, Marcel Veismann, Kristopher Sherrill, Marcello Gori, Scott Perl

Solar and Stellar Astrophysics

On the Nature of Candle-Flame-Shaped Solar Flares and Sub-Alfvénic Supra-Arcade Plasma Downflows

Ivan Oparin, Sabastian Fernandes, Bin Chen et al. (+4 more)

Certain solar flares exhibit a distinctive candle-flame or cusp-shaped feature above the bright flare arcade visible in extreme ultraviolet (EUV) and X-ray channels sensitive to high-temperature plasma. The presence of a cusp-like structure is generally regarded as a key piece of morphological evidence for magnetic reconnection to power explosive energy release in solar flares. In addition, downward-propagating plasma flows above the flare arcade have often been interpreted as outflows driven by magnetic reconnection. However, the relationship between the observed candle-flame-shaped morphology and the underlying magnetic field geometry for reconnection remains unclear. Likewise, the observed speed of the plasma downflows has been found to be too low compared to the upstream Alfvén speed predicted by reconnection theories. With the help of a recently developed three-dimensional magnetohydrodynamics (MHD) model, we examine the locations where magnetic topology changes from antiparallel to closed (Y-points) in a candle-flame-shaped flare, compare the observational emission features with synthetic EUV images generated from the model, and analyze their time evolutions. We also investigate the role of projection effects and line-of-sight integration in the measurements of plasma downflow speeds. Our analysis reveals that the Y-points do not necessarily coincide with the apparent cusp tip. Also, the apparent speeds of the supra-arcade downflows, as derived from tracks in the time-distance plots, underestimate the true Alfvén speeds in the reconnection inflow region by at least a factor of 2 up to an order of magnitude.
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All authors Ivan Oparin, Sabastian Fernandes, Bin Chen, Chengcai Shen, Xiaocan Li, Fan Guo, Sijie Yu

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

An EFT Map of Axion Dark Radiation from Reheating

Yong Xu

Light, weakly coupled sectors can retain information about the cosmological background in which they are produced. We study light axions produced during reheating and their contribution to dark radiation, $\Delta N_{\rm eff}$. We develop a shift-symmetric EFT in which an inflaton-dependent axion kinetic term systematically organizes the leading production channels. The same kinetic function generates both direct inflaton decay and inflaton annihilation from the oscillating inflaton background. Direct decay is described by an invisible inflaton branching fraction, while annihilation is a genuinely reheating-sensitive source controlled by a coherent combination of Wilson coefficients. We derive the contribution to $\Delta N_{\rm eff}$ from both channels and show that they scale oppositely with the reheating temperature: the decay contribution falls as $T_{\rm rh}^{-2}$, whereas the annihilation contribution grows approximately as $T_{\rm rh}^{4/3}$. Their crossing is missed by treatments that keep only one production channel. We translate current and projected $\Delta N_{\rm eff}$ sensitivities into constraints on the Wilson coefficients of the kinetic function, obtaining a two-dimensional EFT map of axion dark radiation from reheating. This map can imply both lower and upper bounds on the reheating temperature, showing that light axion relics can turn dark radiation measurements into constraints on reheating.
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Earth and Planetary Astrophysics · Cross-listed from eess.SP

A reversed solar illumination dependence of unintended emission from Starlink Direct-to-Cell satellites at 72-234 MHz with the EDA2

Haofan Dong, Houtianfu Wang, Hanlin Cai et al. (+1 more)

Second-generation Starlink Direct-to-Cell (DTC) satellites carry an additional payload for direct cellular phone connectivity whose unintended electromagnetic radiation (UEMR) at sub-300 MHz frequencies has not been individually characterised. We reanalyse 112,534 detections from 1,806 Starlink satellites observed with the Engineering Development Array version 2 (EDA2) at 21 frequencies between 72.685 and 234.375 MHz (Grigg et al. 2025), separating 175 DTC and 1,623 Ku-only v2-Mini comparison satellites via the McDowell General Catalogue (McDowell 2020). DTC satellites emit a range-corrected flux density 1.45x that of the Ku-only comparison (Cliff's delta = +0.30, p = 2.6e-11). At 230.469 MHz the XX detection fraction reaches 0.811 against a 0.481 baseline (p ~ 1e-274), and 11 of 21 frequency channels show Benjamini-Hochberg-significant polarisation anomalies. The DTC population is brighter in eclipse than in sunlight (illuminated/eclipsed flux density ratio 0.47) while the Ku-only comparison shows the opposite sense (1.18); the reversal persists across altitude, sub-satellite latitude, frequency, and launch-epoch matching. The reversal strongly disfavours UEMR mechanisms that scale monotonically with instantaneous solar photocurrent and favours an active on-board source whose effective duty cycle is larger at lower equilibrium temperature. Within the 230.469 MHz coarse channel, fine-channel inspection isolates the excess to a single ~24 kHz bin near 230.627 MHz, tail-driven and absent at five control channels. Three falsifiable mechanism-discrimination tests show this feature is not coincident with the LOFAR-resolved Bassa et al. (2024) clock fundamentals, is unresolved at the EDA2 24 kHz resolution, and is heterogeneously expressed across the v2-Mini fleet rather than driven by a few permanently bright units or by uniform thermal scaling.
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All authors Haofan Dong, Houtianfu Wang, Hanlin Cai, Ozgur B. Akan

Earth and Planetary Astrophysics

A Framework for Applying the Loeb-Turner $\alpha$-Slope Test to Archival Photometry of Trans-Neptunian Objects

Omer Eldadi and Abraham Loeb

Reflected sunlight from a solar-system body produces a flux at Earth that scales as the heliocentric distance to the negative fourth power, whereas self-luminous emission scales as the negative second power. This difference defines the Loeb–Turner $\alpha$-slope test, a photometric technosignature diagnostic applicable to any solar-system body observed at multiple heliocentric distances. Of 22 (observatory $\times$ band) analysis bins for Pluto in the Minor Planet Center (MPC) archive, none recovers the reflected-sunlight flux–distance slope predicted when photometry is restricted to a single instrument and band. The archive cannot cleanly execute the $\alpha$-slope test on the brightest, most-observed trans-Neptunian object. We formalize a six-criterion eligibility pipeline (Q1–Q6) for the Loeb & Turner technosignature test and apply it to every numbered TNO. Of 8,606 candidate bins (KBO $\times$ observatory $\times$ band), 1,089 pass Q1–Q3 and 186 additionally pass Q4–Q6, splitting into 53 consistent with reflected sunlight ($\alpha = -4$), 24 with self-luminous emission ($\alpha = -2$), and 109 anomalous. The anomalous bins exhibit slopes steeper than $\alpha = -4$ or shallower than $-2$, consistent with uncorrected per-instrument calibration offsets rather than any single physical mechanism. All 24 self-luminous-like bins originate from Pan-STARRS PS1/PS2; no other observatory contributes any. This indicates a per-instrument calibration systematic. The Rubin Observatory's ten-year survey will deliver uniform single-instrument calibration on a roughly threefold larger sample and either resolve the test at $>10\sigma$ on hundreds of TNOs or, by reproducing the same clustering, falsify the calibration-systematic interpretation.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Direct On-Wafer Measurements of Noise Parameters in C- and X-bands at $T=4$ K

Daniil Frolov, Jean-Olivier Plouchart and Utku Soylu

This paper describes the setup and the results of the direct on-wafer measurements of a FET noise parameters obtained with a source-pull method at temperatures down to T=4K and in the 5-12 GHz frequency range. The setup consists of a cryostat with wafer probes, two reflectometers, a programmable impedance generator, wideband isolators and bias tees and low noise preamplifier, all cooled to cryogenic temperatures, allowing to perform a full vector error-corrected wafer-level measurements of the discrete transistors and amplifier dies. The setup and its calibration procedure are designed in a such way that allows simultaneous calibration, S-parameters, noise parameters and I-V curve measurements of several FETs all in one cooldown. Using the described setup we perform first measurements of 14nm FinFETs and also measure noise parameters of an LNA based on these FETs. Resulting noise temperature values are compared against those obtained using independent and alternative measurement techniques.
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High Energy Astrophysical Phenomena

Jet-Structure Imprint on the Curvature Tail of Gamma-Ray Burst Prompt Emission

Zhen-Yu Yan, Xiao-Hong Zhao, Hendrik J. van Eerten et al. (+7 more)

Even though the prompt emission of gamma-ray bursts (GRBs) is highly beamed, high-latitude emission still produces a distinct light curve break after the intrinsic emission ceases and the edge of the jet comes into view. This curvature effect offers a direct probe of the jet structure during the prompt phase. To uncover the geometric structure of the GRB jet encoded in the prompt light-curve evolution, we develop a numerical model that calculates synchrotron light curves from structured jets to interpret the observed break. We apply this model to the prompt emission of GRB 230307A, which displays a rare late-time break. Our analysis demonstrates that simple spherical outflow and top-hat jet models are inadequate to reproduce the light curve. Instead, the observations are best described by a power-law wing jet with a uniform core ($\theta_{\rm core}=0.0147$ rad) and a surrounding power-law wing. Our results demonstrate that the break in late-time prompt emission can be a powerful diagnostic of GRB jet structure.
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All authors Zhen-Yu Yan, Xiao-Hong Zhao, Hendrik J. van Eerten, Jun Yang, Jiang-Chuan Tuo, Shu-Xu Yi, Chen-Wei Wang, Wen-Jun Tan, Shao-Lin Xiong, Bin-Bin Zhang

Earth and Planetary Astrophysics

Systematic KMTNet Planetary Anomaly Search. XIII. Complete Sample of 2021 Prime Field Planets

In-Gu Shin, Jennifer C. Yee, Weicheng Zang et al. (+39 more)

The Systematic KMTNet Planetary Anomaly Search series was conducted using the KMTNet data archived from $2016$ to $2019$. From this first phase of the series, we reported a total of $50$ planetary systems hidden in the data archive, which represent about $35\%$ of the total microlensing planets discovered from $2016$ to $2019$, demonstrating that this semi-machine-based search is a crucial channel for building a complete microlensing planet sample. We continue this series for $2021$ and beyond to expand the microlensing planet sample. In this work for the $2021$ KMTNet high-cadence fields (Prime fields), we find seven hidden planetary systems and three planet candidates. These new planets represent about $33\%$ of the total microlensing planets discovered within the Prime fields observed during the $2021$ bulge season. While the by-eye search is the primary channel for detecting microlensing planets (i.e., two-thirds of microlensing planet discoveries), this work clearly shows that a systematic search series is still necessary for constructing a complete microlensing planet sample. Such a sample is essential for conducting unbiased statistical studies of planet demographics in our Galaxy. Datasets for all the events used for analyses in this work are publicly available: doi:10.5281/zenodo.21472225.
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All authors In-Gu Shin, Jennifer C. Yee, Weicheng Zang, Cheongho Han, Andrew Gould, Shude Mao, Chung-Uk Lee, Yoon-Hyun Ryu, Ian A. Bond, Takahiro Sumi, Michael D. Albrow, Sun-Ju Chung, Kyu-Ha Hwang, Youn Kil Jung, Yossi Shvartzvald, Hongjing Yang, Sang-Mok Cha, Dong-Jin Kim, Seung-Lee Kim, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Richard W. Pogge, Fumio Abe, David P. Bennett, Aparna Bhattacharya, Ryusei Hamada, Yuki Hirao, Stela Ishitani Silva, Shota Miyazaki, Yasushi Muraki, Kansuke Nunota, Greg Olmschenk, Cl'ement Ranc, Nicholas J. Rattenbury, Yuki K. Satoh, Daisuke Suzuki, Takuto Tamaoki, Sean K. Terry, Paul. J. Tristram, Aikaterini Vandorou, Hibiki Yama

High Energy Astrophysical Phenomena

Nonlinear electrodynamics in magnetars: systematic effects on radius constraints and timing analysis

Gabriel A. Porto, Jonas P. Pereira, Eduardo Bittencourt et al. (+1 more)

Magnetars are among the most extreme laboratories in the universe, harboring surface magnetic fields reaching $10^{15}$~G. At these supercritical scales, Maxwell's linear electrodynamics is superseded by Nonlinear Electrodynamics (NLED). While vacuum birefringence has provided initial observational evidence for these effects, its broader impact on photon propagation remains largely unexplored. In this work, we demonstrate that NLED significantly alters photon propagation in the vicinity of magnetars, deviating light from standard null-geodesics. We estimate that neglecting these corrections leads to relative errors in inferred stellar radii by means of ray-tracing techniques of approximately $10\%$. Furthermore, we find that NLED induces a systematic minimal travel-time delay of approximately $350~n$s, a value that already far exceeds the $100$~ns temporal resolution of missions like NICER. These results are critical for the interpretation of X-ray pulse profiles from current and future observatories, such as eXTP, which rely on high-precision light-bending and timing models to determine neutron-star masses and radii. Finally, our results underscore the role of magnetars as a vital window into the physics of superdense matter and supercritical fields, and we briefly highlight other astrophysical observables–such as glitches and antiglitches–that may be affected by NLED.
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All authors Gabriel A. Porto, Jonas P. Pereira, Eduardo Bittencourt, Elda Guzmán-Herrera

Astrophysics of Galaxies

PEARLS: JWST Counterparts of Micro-Jy Radio Sources in the NEP Time Domain Field. II. All Four Spokes

S. P. Willner, Hansung B. Gim, Maria del Carmen Polletta et al. (+18 more)

JWST/NIRCam observations in the North Ecliptic Pole Time Domain Field (TDF) identify 4.4 micron counterparts for 206 of 211 radio sources with S(3 GHz) \gapprox 5 micro-Jy in a 65arcmin^2 field. One of the remaining radio sources is likely to be a radio lobe of a nearby Seyfert galaxy, and the four radio sources without counterparts could be spurious. All but five counterparts are brighter than magnitude 23.5 AB at 4.4 micron. A simple position match with radius 0.3 arcsec would have identified 198 of the counterparts but only in a 4.4 micron catalog created with aggressive deblending of multiple peaks within an object's brightness distribution into distinct catalog sources. The properties of the radio-host galaxies are mostly consistent with those found in Paper 1: the median redshift is 1.14, and the radio emission, calculated taking into account the non-linear dependence of radio luminosity on star-formation rate, is consistent with a star formation origin in ~79% of the sample. For the other ~21%, the radio flux could come from star formation hidden behind dust or from an active galactic nucleus. One difference from other studies of radio-source counterparts is that 66% of the radio hosts show at least one indication of an AGN's presence. The presence of AGN and of hidden star formation could be elucidated by monitoring for source variability, and the TDF is the field most suited to such observations.
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All authors S. P. Willner, Hansung B. Gim, Maria del Carmen Polletta, Gibson B. Bowling, Seth H. Cohen, Vicente Estrada-Carpenter, Anton M. Koekemoer, Rosalia O'Brien, Alex Pigarelli, Christopher N. A. Willmer, Rogier A. Windhorst, Rolf A. Jansen, Rafael Ortiz III, Jake Summers, William Cotton, Francesca Civano, Norman A. Grogin, W. P. Maksym, Payaswini Saikia, Ross M. Silver, Xiurui Zhao

Astrophysics of Galaxies

The ${}^{13}\mathrm{CO}(2{-}1)/^{12}\mathrm{CO}(2{-}1)$ Line Ratio from 100 Molecular Clouds in the Large Magellanic Cloud

Dia Kalra, Erik Rosolowsky, Adam Leroy et al. (+1 more)

We analyze the line ratio of the $^{13}$CO (2-1) to $^{12}$CO (2-1) rotational transitions observed from new ALMA observations of 100 Giant Molecular Clouds (GMCs) that span the Large Magellanic Cloud. We measure a median line ratio of $^{13}\mathrm{CO}(2{-}1)/^{12}\mathrm{CO}(2{-}1) = 0.078$ with $68\%$ of the sample falling between 0.058 and 0.107. A regression analysis confirms a nearly linear relationship across two orders of magnitude in line luminosity. Moreover, we find that the inclusion of $(L_{\text{FIR}})$ from Young Stellar Objects as a predictor variable of the line ratio significantly improves the quality of the fit, with clouds hosting IR-bright YSOs having relatively brighter $^{13}$CO emission. This analysis indicates that active star forming molecular clouds have different internal conditions than more quiescent clouds.
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All authors Dia Kalra, Erik Rosolowsky, Adam Leroy, Remy Indebetouw

Solar and Stellar Astrophysics

Red novae, their progenitors, and remnants

Tomasz Kaminski and Nadejda Blagorodnova

Red novae or luminous red novae are a class of optical transients that have emerged over the past two decades. They occupy an intermediate luminosity regime between classical novae and supernovae and are characterized by cool, slowly expanding ejecta and a pronounced evolution toward red, dust-enshrouded remnants. These events are now widely interpreted as the outcome of binary coalescence involving non-compact stars, providing a rare opportunity to directly observe the dynamical phases of stellar mergers and their immediate aftermath. Observational studies of red novae provide a glimpse into the still poorly understood physics of unstable mass transfer and common-envelope evolution in binary stars, responsible for the formation of high-energy astrophysical phenomena, compact binary systems, and gravitational wave sources. In this review, we synthesize current observational knowledge of red novae, including their outburst properties, population characteristics, and long-term remnants. Observations of light curves, spectra, and circumstellar environments reveal a complex interplay between mass ejection, collisions, radiative processes, and dust formation. Archival detections of red novae progenitors show a diversity of systems, ranging from low-mass contact binaries to massive evolved stars, with a notable representation of post-main-sequence stars. We examine current efforts to predict red nova outbursts and establish robust event rates, both of which remain challenging. The growing sample of extragalactic transients suggests that the brightest red novae may be even more frequent than core-collapse SNe in the local Universe, underscoring their importance for binary evolution and stellar population studies. Finally, we outline future prospects, including the impact of large-scale time-domain surveys and the potential connection between stellar mergers and gravitational-wave sources.
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Astrophysics of Galaxies

Determination of the best dark matter profile for the Milky Way with Gaia DR3 using Bayesian Model Comparison

Aryan Singh and Shantanu Desai

We carry out a Bayesian model comparison analysis to determine the dark matter model that best describes the Milky Way rotation curve, using four recent compilations of rotation-curve velocities with the Gaia data. We compare these data using three different baryonic models along with seven different dark matter models. Within the adopted modeling framework and Gaia-based rotation curve datasets, we find that the Einasto profile provides the preferred phenomenological fit compared to the NFW profile} across most combinations of datasets and baryonic models. We also find that the cored dark profiles are preferred over the (cuspy) NFW profile. We also test MOND using three different interpolating functions and find that, within the implementations considered, the models provide poorer fits than the preferred dark matter profiles. Finally, among the different baryonic models considered, none is decisively favored over the others.
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Cosmology and Nongalactic Astrophysics

Circular polarization of the cosmic microwave background induced by the optical Magnus effect on gravitational lensing

Yusuke Nishida

Polarization of the cosmic microwave background (CMB) brings out information not only on the early universe but also on the late-time large-scale structure via weak gravitational lensing. Here, we show that circular polarization is induced in principle from CMB temperature fluctuations when the optical Magnus effect is incorporated into gravitational lensing. This is a consequence of the transverse shift of a trajectory of light depending on its helicity that requires right-handed and left-handed components at the same observation point to be sourced from different points of the surface of last scattering. Whereas the resulting circular polarization is found far beyond the scope of current detection, our work establishes the optical Magnus effect on gravitational lensing as a new fundamental mechanism to produce circular polarization of CMB.
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Astrophysics of Galaxies

Magnetised CGM Gas at z~1 revealed by SPICE-RACS

Sunil Malik, S. P. O'Sullivan, A. J. M. Thomson et al. (+17 more)

Magnetic fields are expected to permeate the circumgalactic medium (CGM) of galaxies, yet direct constraints at high redshift remain limited by the lack of high-quality Faraday rotation measure (RM) data. Using the RMs from SPICE-RACS DR2 combined with the DESI DR1 quasar catalogue, we compile the largest sample to date of 2483 quasar sightlines with associated RMs, including 612 with intervening Mg II absorbers tracing foreground galaxies and 1871 control sightlines without Mg II absorbers. After subtracting the Galactic RM contribution and restricting the analysis to sightlines with low Milky Way HI column density and H$\alpha$ intensity, we obtain a foreground-cleaned sample of 757 quasars (191 Mg II / 566 control) spanning redshifts $0.13<z<3.45$. In this foreground-cleaned sample, Mg II sightlines exhibit a $4.5\sigma$ excess in the residual RM dispersion of $4.13 \pm 0.91~\mathrm{rad\,m^{-2}}$ relative to the control sample, at a median absorber redshift of $z\sim1.14$. This implies model-dependent CGM magnetic field strengths of $\sim0.4 - 0.8\, \mu$G over projected radii of $20 - 150$ kpc. This indicates that substantial CGM magnetisation was already established by $z\sim1$, enabling new constraints on the growth and amplification of magnetic fields in galaxy halos over cosmic time.
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All authors Sunil Malik, S. P. O'Sullivan, A. J. M. Thomson, C. S. Anderson, C. Van Eck, L. Rudnick, Amit Seta, B. M. Gaensler, Y. K. Ma, Takuya Akahori, D. Alonso-López, M. Brüggen, E. Carretti, S. W. Duchesne, T. J. Galvin, G. Heald, O. Hlinka, A. Khadir, S. A. Mao, R. Omae

Astrophysics of Galaxies

The Rapid ASKAP Continuum Survey VII: Spectra and Polarisation In Cutouts of Extragalactic Sources (SPICE-RACS) Second Data Release – Unveiling the Magnetised Sky

Alec J.M. Thomson, Timothy J. Galvin, Stefan W. Duchesne et al. (+18 more)

We present the second data release (DR2) of Spectra and Polarisation in Cutouts of Extragalactic sources from RACS (SPICE-RACS). SPICE-RACS DR2 is derived from the third low-band epoch of the Rapid ASKAP Continuum Survey (RACS-low3) and covers the entire sky from the South celestial pole up to a declination of $+49^\circ$; approximately 87.5% of the celestial sphere. We produce 'cutout' spectral cubes in Stokes $I$, $Q$, $U$ around 4 million radio sources and extract spectra towards 5 million radio components. Across our observed band of 799.5–1087.5 MHz we find an $rms$ noise of $\sim200\mu\mathrm{Jy/PSF}$, an angular resolution of $\sim15''$, and residual wide-field instrumental polarisation on the order of 0.1%. After de-duplication, our polarisation catalogue contains the detection of $2.5\times10^5$ ($3.4\times10^5$) Faraday rotation measures (RM) for components with a linearly polarised signal above $8\sigma$ ($6\sigma$). This places SPICE-RACS DR2 as the largest single RM catalogue ever produced by nearly an order of magnitude; the number of RMs in our catalogue alone is $\sim5$ times larger than every previous RM catalogue combined. Our resulting RM grid has an areal density of $6.7^{+1.8}_{-1.7}\mathrm{deg}^{-2}$, providing an effective 'resolution' of $\sim23'$, and reveals striking features across the sky. The broad-band RMs have a median uncertainty of $\sim2\ \mathrm{rad\ m}^{-2}$, and include complexity metrics and information from the time domain. The breadth and quality of the SPICE-RACS DR2 dataset will enable a new generation of RM science. Further, SPICE-RACS will provide an ideal reference for forthcoming deep polarisation surveys such as the ASKAP POSSUM survey. All of our data products are publicly available on the CSIRO Data Access Portal (DAP) and the CSIRO ASKAP Science Data Archive (CASDA).
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All authors Alec J.M. Thomson, Timothy J. Galvin, Stefan W. Duchesne, Emil Lenc, George Heald, Ondrej Hlinka, Sunil Malik, Craig S. Anderson, Erik Osinga, Lerato Baidoo, N. M. McClure-Griffiths, Sebastian Hutschenreuter, Shane P. O'Sullivan, Takuya Akahori, B. M. Gaensler, J. P. Leahy, Y. K. Ma, Vanessa A. Moss, L. Rudnick, C. L. Van Eck, J. L. West

High Energy Astrophysical Phenomena

SN 2023dbc in M108: Optical and Near-Infrared Observations of a Highly-Obscured, Moderately Energetic Stripped-Envelope Supernova

Masayuki Yamanaka, Takahiro Nagayama, Akari Kumano et al. (+4 more)

We present near-infrared (NIR) and optical observations of the highly reddened and moderately energetic Type Ib supernova (SN) 2023dbc, covering a period from 2 to 136 days after the explosion. By comparing its color evolution, specifically in $r-JHK_{\mathrm{s}}$ and $i-JHK_{\mathrm{s}}$, with those of broad-lined Type Ic (Ic-BL) and Type IIb SNe, we estimate a significant extinction of $A_{V}=4.1\pm0.1$\,mag toward the SN. The extinction-corrected peak absolute magnitudes are $M_{J} = -16.8\pm0.2$\,mag, $M_{H} = -16.8\pm0.2$\,mag, and $M_{K_{\mathrm{s}}} = -17.0\pm0.2$\,mag. The SN exhibited an $r$-band rise time of 14.9 days. The spectra display broad features indicative of high expansion velocities; the He~i line velocity was measured at $16,000\,\mathrm{km\,s^{-1}}$ at $t=-4$\,d. Its spectral profile is broader than those of typical moderately energetic Type Ib SNe, yet narrower than those of Type Ic-BL SNe, placing it in an intermediate category. Based on the light-curve timescale and velocity, we estimate a kinetic energy of $E_k = (4.1\pm0.7) \times 10^{51}$\,erg, an ejecta mass of $M_{\mathrm{ej}} = 2.3\pm0.7\,M_{\odot}$, and a radioactive $^{56}\mathrm{Ni}$ mass of $(3.8\pm0.1) \times 10^{-2}\,M_{\odot}$. An analysis using a two-component model suggests a steep density profile in the outer layer contrasted with a dense inner core, which implies ejecta asphericity. The low $^{56}\mathrm{Ni}$ mass is consistent with a partial fallback scenario. We conclude that SN 2023dbc originated from an aspherical explosion with partial core fallback, arising from a progenitor ($M_{\mathrm{ini}} \simeq 15\,M_{\odot}$) that had retained its helium envelope within a binary system.
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All authors Masayuki Yamanaka, Takahiro Nagayama, Akari Kumano, Devendra Kumar Sahu, Avinash Singh, Hrishav Das, G. C. Anupama

High Energy Astrophysical Phenomena

Simulation study of the cosmic ray Sun shadow with a time-dependent solar magnetic field model

Jie Xia, Ming-Yang Cui, Qiang Yuan et al. (+3 more)

During the propagation of cosmic rays in the solar system, the Sun will block those particles and form a shadow whose position and depth are very important probe of the magnetic fields in the Sun's corona, in the interplanetary space, and the Earth's vicinity. In this work we carry out Monte Carlo studies of the Sun shadow, with a novel approach to take into account daily variations of the coronal and interplanetary magnetic field models. This treatment is suitable for studies of short-term variations of the Sun shadow, which become detectable by the Large High Altitude Air Shower Observatory (LHAASO) experiment. Two different coronal magnetic field models, the Potential Field Source Surface (PFSS) and Current Sheet Source Surface (CSSS) models, with observational time-varying photospheric magnetic fields as boundary conditions, are studied in this work. The interplanetary magnetic fields are then derived using the Parker spiral model based on the coronal ones. Furthermore, both the coronal and interplanetary magnetic field strengths are corrected using the Parker Solar Probe (PSP) measurements. We compare the simulation results with the daily observations of Sun shadow by LHAASO in 2021, and find that the CSSS model generally shows better consistency of the displacement of the Sun shadow than the PFSS model.
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All authors Jie Xia, Ming-Yang Cui, Qiang Yuan, Yi Zhang, Guang-Lu Shi, Li Feng

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

Warm inflation in Weyl geometric gravity

Runhua Huang, Tiberiu Harko, Shi-Dong Liang et al. (+2 more)

We investigate the warm inflationary scenario in the Weyl geometric gravity theory, in which the action is constructed by adding matter to the simplest conformally invariant gravitational action in Weyl geometry. The $\tilde{R}^2$ theory can be formulated equivalently as a linear theory supplemented by an additional scalar degree of freedom originating from higher-order curvature terms, with the equations of motion obtained via variational methods. We investigate the cosmological implications of the theory by considering the warm inflationary scenario of the early evolution of the Universe, in which radiation, the inflaton field, and the Weyl vector coexist. We consider the widely studied linear dissipation coefficient model along with a quartic potential, and investigate the influence of the Weyl vector term on the dynamics. We have performed numerical computations for different coupling models, and we have successfully developed a warm inflationary model in which the Universe transitions naturally from an inflationary epoch to a radiation-dominated era. The relevant cosmological observables have been calculated and compared with the latest observational constraints from the ACT data.
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All authors Runhua Huang, Tiberiu Harko, Shi-Dong Liang, Hong-Hao Zhang, Lei Ming