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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 27 April

Cosmology and Nongalactic Astrophysics

A sound-horizon-free measurement of the Hubble constant from DESI DR2 baryon acoustic oscillations using artificial neural networks

Gaurav N. Gadbail and Kazuharu Bamba

We present a model-independent, sound-horizon-free measurement of the Hubble constant $H_0$ using baryon acoustic oscillation tracers from the Dark Energy Spectroscopic Instrument Data Release 2. The function reconstructions are performed using the artificial neural network method, which is a completely data-driven approach that avoids the mild $\Lambda$CDM prior dependence. Our approach is based on the distance duality relation and combines three complementary observational probes, such as Type\,Ia supernovae, cosmic chronometer, and DESI DR2 BAO – without requiring any knowledge of the sound horizon scale $r_d$ or any assumption about the absolute luminosity of SNe\,Ia. We obtain a joint constraint of $H_0 = 71.5\pm2.2$\,km\,s$^{-1}$\,Mpc$^{-1}$ at 68% confidence for 1000 bootstrap realisations and 4096 neurons, which is consistent with the TRGB result and the SH0ES measurement within $0.6\sigma$, consistent with the Planck 2020 result within $2\sigma$. Our results favor a higher value of $H_0$ compared to the Planck CMB inference, adding independent support for the reality of the Hubble tension.
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Instrumentation and Methods for Astrophysics

LStein: A new approach to visualizing sparse 2.5-dimensional data

Lukas Steinwender, Anais Möller and Christopher J. Fluke

Visualization of high-dimensional data is crucial to retrieve all the knowledge that is contained within a dataset. Effective and informative presentation of three-dimensional data via a two-dimensional medium is challenging, especially if the dataset more closely resembles a 2.5-dimensional (2.5D) entity due to sparse sampling. We present LStein (Linking Series to envision information neatly), a novel visualization approach implemented in Python, in an attempt to solve this challenge. Inspired by the astrophysical application of displaying photometric timeseries in multiple passbands with minimal loss of information, we compare our method to traditional approaches. While astronomy – specifically multi-passband visualization for lightcurves obtained with the Rubin Observatory – serves as the principal driver for the design, we demonstrate that LStein can be used in any context with 2.5D datasets from radio astronomy to machine learning hyperparameter search visualization. LStein provides a complementary visualization to traditional techniques. LStein can be installed from GitHub (https://github.com/TheRedElement/LStein).
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Instrumentation and Methods for Astrophysics

The Operation Control System for the Tianlai Experiment

Jixia Li, Fengquan Wu, Shijie Sun et al. (+2 more)

The Tianlai 21cm intensity mapping experiment is located at the Hongliuxia Observing Station, which is a remote site with excellent electromagnetic environment. To facilitate the operation of the Tianlai experiment while reducing the required human power and travel cost, we have designed the system to be remotely controllable from the start. In this paper, we present the basic design of the operation control system, including the control network, and the controlling mechanisms for the power switch, the steering of the dish antenna, the analog and digital components of the array, and the operation of the array. In the design of this system of operation control, we emphasize the following points: online accessible, simplicity, flexibility, strict control of electromagnetic interference (EMI) and security. The various devices are connected in a local area network (LAN), and one can control them remotely by securely logging into a server on the LAN and issue commands. We describe the functions of the programs designed for the control. Similar design and the various hardware and software components may also be applicable or of reference value to other remote observing stations.
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All authors Jixia Li, Fengquan Wu, Shijie Sun, Yougang Wang, Xuelei Chen

Cosmology and Nongalactic Astrophysics

Reconstructing the cosmic expansion with a generalized q(z) parameterization: A decelerating Universe from late-time constraints

Tomás Verdugo, Alberto Hernández-Almada, Miguel A. García-Aspeitia et al. (+2 more)

We present a generalized phenomenological parameterization of the deceleration parameter $q(z)$ that incorporates an effective radiative component (ERC) in addition to a localized late-time contribution. The proposed framework extends previous two-parameter $q(z)$ reconstructions by explicitly regulating the high-redshift behavior while preserving the late-time transition dynamics. We constrain the free parameters $(h, q_0, z_c, z_e)$ using late-time observational data from cosmic chronometers (CC), Pantheon+ Type Ia supernovae (SNIa), H\,ii galaxies (HIIG), and intermediate-luminosity quasars (QSO). For the full data combination (CC+SNIa+HIIG+QSO), we obtain $q_0 = -0.25^{+0.04}_{-0.04}$ and a transition redshift $z_T \simeq 0.80$, indicating a currently accelerating Universe with a transition occurring earlier than in the $\Lambda$CDM model. Within the redshift range probed by the data, the reconstructed $q(z)$ deviates from the $\Lambda$CDM trend, suggesting a possible reduction of the late-time acceleration. Furthermore, the reconstruction favors a relatively high value of the Hubble parameter, $h = 0.729 \pm 0.006$. The ERC remains weakly constrained by late-time data but ensures a smooth and monotonic evolution of $q(z)$, $j(z)$, and $w_{\rm eff}(z)$ across a wide redshift range. Within the observed interval, the model effectively reproduces the late-time behavior of the previous parametrization, while providing a controlled extension toward early epochs. Our results show that current low- and intermediate-redshift data are compatible with a reduced late-time acceleration.
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All authors Tomás Verdugo, Alberto Hernández-Almada, Miguel A. García-Aspeitia, Juan Magaña, Verónica Motta

Astrophysics of Galaxies

East Asian VLBI Network astrometry toward the star-forming region G040.96+02.48 in the Extreme Outer Galaxy

Xianjin Shen, Zehao Lin, Nobuyuki Sakai et al. (+18 more)

Accurate astrometric measurements for star-forming regions located on the far side of the Milky Way remain scarce. In this work, we present the astrometric results for a 22\,GHz water maser associated with star-forming region G040.96+02.48 located on the far side of the Milky Way, using the East Asian VLBI Network. The target water maser's proper motion was determined to be ($\mu_{\alpha}\cos\delta, \mu_{\delta}$) = ($-2.06_{-0.51}^{+0.53}$, $-2.95_{-0.44}^{+0.45}$)~mas~yr$^{-1}$. The derived three-dimensional kinematic distance to the star-forming region is 20.2$\pm$3.2\,kpc, placing it slightly outside the Outer Scutum$-$Centaurus Arm. The corresponding vertical height of 872$\pm$139\,pc indicates a significant warp of the outer Galactic disk, which is in good agreement with the latest precessing warp model. Moreover, the resulting peculiar motions reveal a complex kinematic pattern, characterized by a large outward radial velocity of $-32\pm$18\,km~s$^{-1}$. Our observations substantially expand the valuable sample of star-forming regions with accurate astrometric measurements in the Extreme Outer Galaxy.
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All authors Xianjin Shen, Zehao Lin, Nobuyuki Sakai, Ye Xu, Shuaibo Bian, Yuanwei Wu, Yan Sun, Dejian Liu, Jingjing Li, Bo Zhang, Shuangjing Xu, Tomoaki Oyama, Chungsik Oh, Wu Jiang, Lang Cui, Pengfei Jiang, Guanghui Li, Mareki Honma, Se-Jin Oh, Zhi-Qiang Shen, Na Wang

Earth and Planetary Astrophysics

Uncovering the Rapidly Evolving Orbits of the Dynamic TOI-201 System

Ismael Mireles, Solène Ulmer-Moll, Donald Liveoak et al. (+47 more)

Studying planetary interactions in exoplanet systems informs theories of planet formation and evolution, providing essential context for understanding our own solar system. We combine spectroscopy, transit photometry, transit timing variations, and astrometry to characterize the TOI-201 system. The co-transiting system consists of a super-Earth, warm Jupiter, and massive companion at 5.8, 53, and 2900 day orbital periods, respectively. We perform dynamical simulations to study the past and future of the system. von-Zeipel-Kozai-Lidov oscillations emerge as the most plausible scenario to explain the outer companion's high orbital eccentricity, with planet-planet scattering a possible but less likely contender. Due to non-zero mutual inclinations between the planets, the system is visibly evolving on very short timescales, with the current co-transiting configuration ending in 200 years.
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All authors Ismael Mireles, Solène Ulmer-Moll, Donald Liveoak, Diana Dragomir, Judith Korth, Alexander Venner, Karen A. Collins, Amaury H.M.J. Triaud, Tristan Guillot, Antoine Petit, Theron Carmichael, Sarah Millholland, Tim Hallatt, Hannu Parviainen, Hugh P. Osborn, David Rapetti, Thomas A. Baycroft, Siddharth Bhatnagar, François Bouchy, Radka Dancikova, Pedro Figueira, Monika Lendl, Stéphane Udry, Peter Wheatley, Lyu Abe, Abdelkrim Agabi, Matteo Beltrame, Philippe Bendjoya, Vincent Deloupy, Djamel Mékarnia, François-Xavier Schmider, Olga Suárez, Khalid Barkaoui, Keith Horne, Felipe Murgas, Enric Palle, Richard P. Schwarz, Ramotholo Sefako, Avi Shporer, Gregor Srdoc, Chris Stockdale, Francis P. Wilkin, Joel D. Hartman, Lauren A. Sgro, Thiam-Guan Tan, Jon M. Jenkins, Attila Bódi, David Havell, Darren Rivett, Ian Transom

Earth and Planetary Astrophysics

A distant brown dwarf coplanar to a warm Jupiter and a hot super-Earth

Matías I. Jones, Luca Naponiello, Trifon Trifonov et al. (+21 more)

In transiting planetary systems, in which planetary sizes are accurately determined from transit observations, the presence of transit-timing variations (TTVs), especially when combined with radial velocity (RV) data, provides powerful constraints on masses and orbital eccentricities. Together, these measurements offer crucial insights into system architecture, formation mechanisms and dynamical evolution. We present long-term RV and transit/TTV monitoring of the relatively young star (age approximately 1 Gyr) TOI-201, revealing an exceptional multi-planet system composed of a hot super-Earth (SE) size planet transiting every 5.8 days, a warm Jupiter (WJ) on a 53-day orbit and an eccentric (e = 0.62) low-mass brown dwarf (BD) on an approximately 8-year orbit, with an estimated mass of about 16 Jupiter masses. The BD is the longest-period transiting substellar object ever characterized by means of RVs and the only one known to be coplanar with inner planets. The architecture of this system suggests that the SE was formed isolated and in the innermost region of the gaseous disk. On the other hand, the orbital configuration of the outer companions suggests a nearly in situ formation of both objects, with the WJ forming in a dense inner disk. Alternatively, the BD might have formed farther out and migrated inward, while increasing its eccentricity owing to interactions with the disk.
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All authors Matías I. Jones, Luca Naponiello, Trifon Trifonov, Rafael Brahm, Gabriele Pichierri, Lorena Acuña-Aguirre, Robert J. De Rosa, Marcelo Tala Pinto, Aldo S. Bonomo, Luigi Mancini, Alessandro Sozzetti, Yared Reinarz, Alessandro Morbidelli, Néstor Espinoza, Giovanni Rosotti, Eric L. Nielsen, Stefan Y. Stefanov, Thomas Henning, Andrés Jordán, Jan Eberhardt, Artie Hatzes, Leonardo Vanzi, Jan Janik, Petr Kabath

High Energy Astrophysical Phenomena

GRRMHD Simulations of State Transitions in Non-Jetted Tidal Disruption Events

Brandon Curd, Safira Heridia, Aviyel Ahiyya et al. (+1 more)

Circularization of the stream material into a debris cloud during tidal disruption events (TDEs) was recently demonstrated in one of the most accurate long duration TDE simulations to-date. The cooling envelope model (CEM) provides a description of the circularized debris cloud and its emission over time well beyond circularization across different disruption parameters. In the CEM, sub-Eddington accretion rates occur early in TDEs and the debris has a shallow density profile of roughly $\rho \propto r^{-1}$, with Eddington accretion only being achieved after several months. To explore the late stages of the CEM, we perform general relativistic radiation magnetohydrodynamics (GRRMHD) simulations of magnetized tori adapted from the near Eddington phase of the CEM for a $1M_\odot$ star disrupted around a $10^7 M_\odot$ black hole (BH). We find that the disk becomes thermally unstable within 17.1-46.5 days depending on the spin of the BH. Thermal spectra show a soft X-ray excess prior to collapse, with a nearly two order of magnitude decline in X-ray luminosity upon disk collapse. Furthermore, the evolution of the blackbody radius and temperature of our models are correlated with the spin of the black hole. The spectral properties and soft X-ray luminosity in our models are similar to the TDE AT2021ehb, which is a non-jetted TDE with late X-rays and a state transition after $\approx 271$ days.
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All authors Brandon Curd, Safira Heridia, Aviyel Ahiyya, Richard Anantua

Sunday 26 April

Astrophysics of Galaxies

With arms wide open: a VLT/MUSE view of the mechanisms driving unwinding spiral arms in cluster galaxies

Augusto E. Lassen, Benedetta Vulcani, Jacopo Fritz et al. (+13 more)

The environmental mechanisms driving unwinding spiral arms in cluster galaxies remain debated. While earlier studies attributed it mainly to gravitational interactions, recent works suggest that RPS alone can induce unwinding. We present a VLT/MUSE spatially resolved analysis to investigate the mechanisms responsible for spiral-arm unwinding in two galaxies, UG101 and UG103, drawn from a larger sample. They are selected as tidal and RPS-driven candidates, respectively, based on the proximity of close neighbors. We estimate the galactocentric radius at which tidal forces, from a companion or the cluster potential, become relevant ($R_{\mathrm{tid}}$). We examine gas and stellar kinematics, exploiting their different responses to gravitational and hydrodynamical perturbations. SINOPSIS is used to map stellar populations in age bins and constrain unwinding timescales. For UG101, we find $R_{\mathrm{tid}} \sim 1.5 R_e$, while the unwound features extend beyond this radius. UG101 shows irregular stellar and gas kinematics; its rotation curve indicates similar motions, although the gas is truncated on one side and extended on the other. For UG103, neither the closest companion nor the cluster appear capable of triggering unwinding. UG103 displays regular stellar but disturbed gas kinematics, with truncation on the disk side likely facing the ICM wind and gas extended in the opposite direction. Stellar population maps show the emergence and unwinding of the spiral arms in UG103 on timescales consistent with its cluster infall time ($\sim 1.6$ Gyr). We conclude that unwinding in UG101 and UG103 is primarily driven by tidal interactions and RPS, respectively, although a combined effect cannot be excluded for UG101. Our methodology provides a framework to identify the mechanisms driving unwinding in cluster galaxies from spatially resolved properties.
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All authors Augusto E. Lassen, Benedetta Vulcani, Jacopo Fritz, Bianca M. Poggianti, Antonino Marasco, Yara Jaffé, Marco Gullieuszik, Alessia Moretti, Mario Radovich, Rory Smith, Stephanie Tonnesen, Neven Tomičić, Koshy George, Alessandro Ignesti, Luka Matijević, Eric Giunchi

High Energy Astrophysical Phenomena

Alfven-winged pulsar

Maxim Lyutikov

Detecting possible electromagnetic precursors to the gravitational signal from merging compact objects is challenging, but it can reveal intricate physical properties of the merging stars through their gravitational and electromagnetic interactions. We demonstrate, using 3D Particle-In-Cell simulations, that a neutron star moving through the magnetosphere of a merging companion generates a complicated system of dissipative currents, a relativistic analogue of planetary Alfven wings. Generated electric currents carry a large fraction of the electromagnetic power intersected by the neutron star. These currents may lead to the generation of beamed, pulsar-like coherent radio and high-energy emission. Orbital modulation will produce a nearly periodic signal, an Alfven-winged pulsar.
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Earth and Planetary Astrophysics

Probabilistic Spectral Reconstruction of Trans-Neptunian Objects from Sparse Photometry: A Framework for Taxonomy, Survey Optimization, and Outlier Detection

Hsing Wen Lin, Larissa Markwardt, Kevin J. Napier et al. (+3 more)

Near-infrared (near-IR) spectroscopy provides critical constraints on the surface composition of trans-Neptunian objects (TNOs), but spectroscopic observations remain limited compared to broadband photometry. We develop a probabilistic latent-space framework to quantify how much spectral information is retained in sparse photometric measurements. Using a principal component representation trained on a sample of near-IR spectra, we model the spectral manifold of TNOs and perform Bayesian inference in this reduced space to reconstruct full spectra from photometry while propagating uncertainties. Leave-one-out cross-validation demonstrates that the dominant modes of spectral variability are low-dimensional: 4 to 5 principal components capture the structure relevant for taxonomic classification, while 8-10 components improve spectral reconstruction fidelity and uncertainty calibration. For most objects, the reconstructed spectra achieve empirical credible-interval coverage of 95 percent across wavelength. This suggests the diversity of near-IR spectral shapes is governed by structured, correlated surface processes rather than stochastic variation. Practically, we apply this framework to survey optimization, quantifying the information content of JWST/NIRCam filters to identify optimal configurations (e.g., F090W, F115W, F410M, F460M) for TNO taxonomy. Additionally, we demonstrate the pipeline's capability to detect and reconstruct rare spectral types, such as the peculiar Neptune Trojans 2006 RJ103 and 2011 SO277, by allowing constraining photometry to select low-probability intermediate models from the continuous topological manifold. Ultimately, this framework bridges the gap between sparse photometry and spectroscopy, providing a statistically rigorous tool to map the compositional structure of minor planets in upcoming large-scale surveys.
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All authors Hsing Wen Lin, Larissa Markwardt, Kevin J. Napier, Fred C. Adams, Renu Malhotra, David W. Gerdes

Astrophysics of Galaxies

A GLIMPSE of the 99%: a census of the faintest galaxies during the epoch of reionization and its implications for galaxy formation models

Hakim Atek, Iryna Chemerynska, Lukas J. Furtak et al. (+19 more)

We present a comprehensive study of the galaxy UV luminosity function (UVLF) at $z=6-9$ leveraging deep JWST observations from the GLIMPSE survey. Thanks to gravitational lensing, we probe the UVLF to an unprecedented depth of $M_{\text{UV}} = -12$ mag, approximately three magnitudes deeper than previous robust constraints. Our UVLF determination incorporates a rigorous end-to-end uncertainty framework, including statistical and systematic lensing uncertainties. We find that the $z \sim 7$ UVLF continues to rise steeply with a faint-end slope of $\alpha = -1.98_{-0.05}^{+0.06}$. Crucially, our data show no clear evidence of a turnover down to \muv $= -12.3$. The persistence of this faint population provides stringent constraints on galaxy formation models and cosmological simulations that predict an early flattening of the luminosity function due to radiative feedback or star-formation thresholds. Furthermore, post-JWST models specifically calibrated to match the UV-bright excess at $z > 10$ generally fail to reproduce the observed evolution toward lower redshifts and fainter magnitudes, highlighting a significant tension in our current understanding of early galaxy assembly. We derive a comoving ionizing emissivity at $z=7$ of log($n_{\mathrm ion}$ / s$^{-1}$ Mpc$^{-3}$) $\approx 50.85$, which suggests that faint galaxies dominate the ionizing budget, providing enough photons to maintain reionization even in a highly clumped IGM ($C_{\text{HII}} = 5$). As our detection of faint galaxies effectively rules out a luminosity function truncation at $M_{\text{UV}} \geq -15$, these results emphasize the need to either accurately characterize the ionizing properties of the global, low-mass galaxy population at $z > 6$, or to refine physical models of intergalactic medium clumping and its redshift evolution to maintain consistency with the observed reionization timeline.
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All authors Hakim Atek, Iryna Chemerynska, Lukas J. Furtak, Johan Richard, John Chisholm, Vasily Kokorev, Michelle Jecmen, Damien Korber, Ryan Endsley, Richard Pan, Arghyadeep Basu, Jeremy Blaizot, Rychard Bouwens, Meriam Ezziati, Sylvain Heurtier, Kristen. B. W. McQuinn, Marcie Mun, Julian B. Munoz, Pascal Oesch, Joakim Rosdahl, Alberto Saldana-Lopez, Seiji Fujimoto

High Energy Astrophysical Phenomena

SCAT Data Release 1: 1812 optical spectra of 1331 transients

Michael A. Tucker, Mark E. Huber, Benjamin J. Shappee et al. (+19 more)

We present the first data release (DR1) of the Spectroscopic Classification of Astronomical Transients (SCAT) survey, covering the first $\approx 5$ years of observations (March 2018 - January 2023). DR1 includes 1812 spectra of 1331 transients, which we sort into broad spectroscopic classes including supernovae (SNe), transients originating in galactic nuclei, and stellar variability. We collect multi-filter light curves from imaging surveys and fit them with phenomenological models to estimate peak brightnesses and the time of explosion/first-light. Extragalactic transients are matched to candidate host galaxies, and we compare host-galaxy luminosities and projected offsets by SN type. SNe appear to be a reliable way to augment the redshift coverage of nearby ($z\lesssim 0.1$) galaxies in tandem with dedicated redshift surveys. We present new redshifts for roughly half of the SN host galaxies, most of which are low-luminosity dwarfs similar to the Magellanic Clouds ($M_r \gtrsim -18$ mag). This set of transient spectra, light curves, luminosities, redshifts, and host galaxies offers an excellent testbed for real-time photometric/light curve classification pipelines in the modern era of deep and large-area surveys. We conclude with a brief discussion of the provided data products and status of the SCAT survey.
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All authors Michael A. Tucker, Mark E. Huber, Benjamin J. Shappee, Jason T. Hinkle, Willem B. Hoogendam, Charlotte R. Angus, Chris Ashall, Katie Auchettl, Kenneth C. Chambers, Dhvanil D. Desai, Aaron Do, Joseph Ghammashi, Catherine J. Grier, Joanna Herman, Thomas de Jaeger, Jodie Kiyokawa, Miranda Y. Kong, Thomas B. Lowe, Eugene A. Magnier, Anna V. Payne, Sara Romagnoli, David Rubin

Instrumentation and Methods for Astrophysics

Beyond the Final Label: Exploiting the Untapped Potential of Classification Histories in Astronomical Light Curve Analysis

Zhuoyang Zhou, Alex I. Malz, Chad M. Schafer et al. (+3 more)

The Legacy Survey of Space and Time (LSST) on the Vera C. Rubin Observatory will generate a massive collection of time series (light curves) of the measured flux of transient and variable astronomical objects. With each new flux observation, light curve classifiers need to generate updated probability distributions over candidate classes, which will then be shared with the global community for the purpose of identifying interesting targets for follow-up observations as well as less time-sensitive analysis applications. Using the synthetic light curves and classification results of participating classifiers from the Extended LSST Astronomical Time-series Classification Challenge (ELAsTiCC), we investigate a novel framework to enhance existing light curve classifications by incorporating their classification histories and the temporal evolution of these histories. To demonstrate the potential of this approach, we introduce a model that combines a recurrent neural network and an additive attention module, which shows improved classification accuracy and more balanced precision-recall performance compared to existing classifiers from the challenge. Furthermore, at this stage, most, if not all, of the existing classifiers are evaluated by their final classification results on complete light curves; we propose new metrics that evaluate the stability, accuracy, and early classification performance of a classifier's predictions when using limited data by considering the Wasserstein distance between the temporally evolving classification probability distributions. Our metrics offer a more comprehensive perspective for model assessment by supplementing classical methods such as the confusion matrix and precision-recall.
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All authors Zhuoyang Zhou, Alex I. Malz, Chad M. Schafer, Konstantin Malanchev, Guillermo Cabrera-Vives, Christopher Hernández

Solar and Stellar Astrophysics

The Diagnostic Disagreement and the Closure Failure of the Quiet-Sun Corona Are the Same Relative Entropy

Victor Edmonds

In the weakly collisional quiet-Sun corona, the electron distribution departs from Maxwellian, and “the electron temperature” is not single-valued: two standard diagnostics differ by a stable factor $R \approx 2.4$ across the solar cycle. We show this departure is a single relative entropy whose two orthogonal components are the EUV–radio diagnostic disagreement and the failure of the local conductive closure. By the generalized Pythagorean identity for Bregman divergences, the relative entropy of the $\kappa \approx 2.5$ distribution from its radio-diagnostic Maxwellian projection ($1.20$ nats) partitions with no cross-term into two components. The first is the energy-matched closure deficit ($0.32$ nats), the information discarded by the local Spitzer–Härm closure (Edmonds 2026c), which itself has no convergent form across $\kappa \in [2,3]$. The second is the inter-projection diagnostic gap ($0.876$ nats), what the EUV and radio diagnostics disagree by and a closed-form function of $R$ within the shape envelope. Closure failure and diagnostic disagreement are therefore the same relative entropy in two orthogonal coordinates: together they account for the corona's full departure from Maxwellian. The physical heat flux that survives is non-local and tail-dominated. Any mechanism that sets this $\kappa$ must act on the suprathermal tail, operate non-locally, and fix $\kappa$ to the observed band; of the standalone candidates only velocity filtration (Scudder 1992) meets the first two, and whether it, or anything, fixes $\kappa$ is the open problem we leave posed.
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High Energy Astrophysical Phenomena

A Unified Explanation of Gamma-Ray and Neutrino Spectra from Astrophysical Sources Based on the Gluon Condensation Model

Jiangyuan Qian, Jintao Wu and Jianhong Ruan

The advent of multi-messenger astronomy has provided abundant information for understanding the acceleration and particle-production mechanisms of cosmic rays. In this work, we present a unified study of cosmic gamma-ray and neutrino spectra within the Gluon Condensation (GC) model. Derived from Quantum Chromodynamics (QCD), the GC model predicts that, in high-energy hadronic processes, gluons may condense near a critical momentum, leading to a dramatic enhancement in secondary-pion production and imprinting a characteristic broken power-law feature on the gamma-ray spectrum. Within this framework, we first derive the neutrino spectrum corresponding to the GC scenario and then investigate three astrophysical sources with both gamma-ray observations and neutrino candidate signals: the active galactic nuclei TXS 0506+056 and NGC 1068, and the supernova remnant G54.1+0.3. Using the GC model, we fit the observed gamma-ray spectra of these sources and predict their corresponding neutrino spectra. Our results show that the gamma-ray spectra of TXS 0506+056 and NGC 1068 are well described by the GC model, and that the predicted neutrino spectra are consistent with IceCube observations within uncertainties; in particular, clear relations are found between their relative magnitudes. For SNR G54.1+0.3, however, the GC-predicted neutrino spectrum exhibits continuous hardening after the break, deviating from the typical power-law behavior expected for cosmic-ray secondaries and thus disfavoring a common GC origin. This study represents the first systematic attempt to correlate gamma-ray and neutrino spectra within the GC framework, offering a new perspective on multi-messenger emission from high-energy astrophysical sources.
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Solar and Stellar Astrophysics

Magnetic Activity Cycles and Rotation in Planet-hosting and Non-hosting Solar-type Stars

Amina Boulkaboul, Alessandro Sozzetti, Caroline Soubiran et al. (+1 more)

We analyze periodicities in radial velocity (RV) measurements and magnetic activity indicators (S-index and BIS) for 767 Gaia RV standard stars to distinguish between stellar activity and planetary signals. Significant RV periods were detected in only 359 of these stars. Rotation and magnetic cycle periods are identified through iterative periodogram analysis. Among stars with confirmed planets, $28.2\%$ exhibit RV signals that coincide with activity indicators, compared to $21.3\%$ among stars without planets; however, statistical tests show this difference is not statistically significant. Several RV signals previously attributed to planets, such as those in HIP7240, HIP28460, and HIP48331, are instead likely caused by stellar activity, emphasising the importance of using multiple diagnostics to assess RV variability. We report rotation periods in 125 stars, including 30 new estimates, and detect magnetic activity cycles in 127 stars, 95 of which are new. We further investigate the relationship between rotation and magnetic cycle periods in the context of stellar dynamo theory. The full sample reveals a continuous distribution in the $P_{\rm rot}/P_{\rm cyc}$, Rossby number diagram, lacking the classical division into active and inactive branches and instead showing a negative slope, in contrast to some earlier studies. Interestingly, stars with planetary companions exhibit a steeper trend (slope of $-1.049 \pm 0.078$) compared to non-hosts ($-0.654 \pm 0.056$), suggesting that the presence of planets may subtly influence the host star's magnetic behaviour.
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All authors Amina Boulkaboul, Alessandro Sozzetti, Caroline Soubiran, Yassine Damerdji

Astrophysics of Galaxies

The Vertical Structure and Asymmetry of Mg ii-enriched Gas in the Milky Way Disk

Xiaochuan Jiang, Taotao Fang and Shulan Yan

The physical properties of Milky Way Mgii-bearing gas remain poorly constrained due to the saturation of the near-UV doublet. We utilize the weaker Mgii $\lambda\lambda$1239, 1240 doublet from 482 archival HST/COS extragalactic sightlines to probe this cool gas phase. We identify 43 low-velocity absorbers ($|v_{\rm LSR}|<40\ {\rm km\ s^{-1}}$), yielding a covering fraction ($C_f$) of $32\pm5\%$ for $\log N_{\rm MgII} > 15$. We find that $C_f$ follows an exponential decay relative to equivalent width thresholds, marking a transition from a diffuse medium to localized, dense structures (e.g., cold neutral medium cores). The steep decline of the distribution at high column densities likely reflects the saturation of the turbulent log-normal spectrum and dust depletion. By integrating stellar data, we derive a Mgii scale height $h_{\rm MgII} = 0.12\pm0.02\ \rm\ kpc$ and mid-plane density $n_{0,\rm MgII} = (3.9\pm0.4)\times 10^{-6}\ \rm cm^{-3}$. A pronounced north-south asymmetry exists, with the northern hemisphere displaying a significantly higher mid-plane density ($n_{0,n} \approx 4.7 \times 10^{-6}\ \rm cm^{-3}$) than the south ($3.2 \times 10^{-6}\ \rm cm^{-3}$). This discrepancy suggests that the northern interstellar medium is more spatially concentrated and clumpy, whereas the southern gas is more ubiquitously distributed with a lower average density. These results indicate that Mgii is tightly confined to the disk, governed by a unified depletion law and restricted vertical extent.
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Astrophysics of Galaxies

Two Exciting High-redshift Galaxy Candidates Turn Out to Be Two Exciting Ultra-cool Brown Dwarfs

Maruša Bradač, Chris Willott, Yoshihisa Asada et al. (+37 more)

From the onset of observations of JWST we have discovered unexpectedly luminous galaxies at redshifts $z>10$ and as high as $z=14$. With their discovery, the question immediately followed as to where their progenitors are, since such progenitors should be within reach of existing surveys. However, the discovery of several bright candidates at $z>15$ may indicate further discrepancies between pre-JWST model predictions and current observations. Progenitors of the bright $z\sim 14$ galaxies should be visible at redshifts as high as $z\sim 20-30$, showing in the data as F277W and F356W dropouts. We identify two such candidates in the Bullet Cluster JWST data; however, subsequent NIRSpec follow-up data show spectra that can be well fit with Y dwarf templates with temperatures ${272\mbox{--}351\mbox{K}}$ and ${445\mbox{--}525\mbox{K}}$ (using ATMO2020 and Sonora Elf Owl models) and distances of $\sim 150\mbox{--}650\mbox{pc}$. The first is one of the lowest-temperature brown dwarfs known, and the lowest-temperature brown dwarf detected spectroscopically outside the solar neighborhood. With additional NIRCam imaging taken $\sim 1$ year later, we also detect their proper motions of $(49 \pm 8)\,\mbox{mas/yr}$ and $(24 \pm 3)\,\mbox{mas/yr}$, further indicating that at least some F277W and F356W dropouts are sub-stellar cold Milky Way objects such as brown dwarfs.
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All authors Maruša Bradač, Chris Willott, Yoshihisa Asada, Loïc Albert, Gregor Rihtaršič, Anishya Harshan, Jon Judež, Nicholas S. Martis, Andrea Ferrara, Kevin Hainline, Abdurro'uf, Joseph F. V. Allingham, Volker Bromm, John Chisholm, Dan Coe, Guillaume Desprez, Jose M. Diego, Andreas L. Faisst, Seiji Fujimoto, Lukas J. Furtak, Tiger Yu-Yang Hsiao, Kohei Inayoshi, Anton M. Koekemoer, Vasily Kokorev, Brian C. Lemaux, Paulo A. A. Lopes, Ray A. Lucas, Danilo Marchesini, Vladan Markov, Gaël Noirot, Richard Pan, Scott W. Randall, Johan Richard, Luke Robbins, Ghassan T. E. Sarrouh, Marcin Sawicki, Tim Schrabback, Roberta Tripodi, Eros Vanzella, Rogier A. Windhorst

Cosmology and Nongalactic Astrophysics

CLASH-VLT: The Fifth Force in Chameleon Gravity from Joint Lensing and Kinematics Cluster Mass Profiles

Lorenzo Pizzuti, Federico Rivano, Keiichi Umetsu et al. (+1 more)

We present a high-precision joint gravitational-lensing and kinematic analysis of nine massive galaxy clusters from the CLASH and CLASH-VLT surveys to test chameleon screening gravity and its $f(R)$ sub-class at Mpc scales. We investigate the dependence on the assumed parametrization of the total cluster mass profile by adopting three models, namely Navarro–Frenk–White (NFW), Burkert, and Hernquist. When cuspy models (NFW or Hernquist) are assumed in the general chameleon framework, the combined constraints from the nine clusters are fully consistent with General Relativity (GR), excluding large regions of the modified-gravity parameter space (the coupling constant $\mathcal{Q}$ and the background chameleon field $ \phi_\infty$), providing one of the tightest bounds on general chameleon models with clusters to date. In contrast, adopting a Burkert profile – disfavored by lensing data – leads to a mild ($\sim 2\sigma$) departure from the GR expectation in joint analysis. When considering the $f(R)$ sub-case, we obtain a bound on the background scalaron field of $|f_R| \lesssim \mathrm{2-5}\times 10^{-5}$ (95% C.L.) for NFW and Hernquist models, in agreement with current constraints at cosmological scales, and an apparent deviation from standard gravity of $\log_{10}|f_R| = -4.7 \pm 1.2$ for the Burkert case. We investigate the impact of systematics in the kinematical analysis, showing that the tension is mitigated when clusters exhibiting clear dynamical disturbance are excluded from the sample. [...[ The upcoming generation of wide-field lensing surveys and spectroscopic follow-up programs will enable similar analyses on substantially larger samples, offering the prospect of tightening cluster-based constraints on gravity and the dark sector.
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All authors Lorenzo Pizzuti, Federico Rivano, Keiichi Umetsu, Andrea Biviano

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Physics informed operator learning of parameter dependent spectra

Haohao Gu, Sensen He, Hanlin Song et al. (+6 more)

Spectral problems governed by differential operators underpin a wide range of physical systems, yet remain computationally challenging because their spectra depend sensitively on continuous parameters and often demand repeated evaluations across parameter space. Here we present $\texttt{DeepOPiraKAN}$, an open source physics informed neural network architecture for spectral analysis. By combining operator learning with enhanced optimization stability, it captures the underlying parameter-to-spectrum mapping in a single model, avoiding repeated spectral solutions at isolated points in parameter space. As a representative and stringent benchmark, we apply this framework to the computation of quasinormal modes of Kerr black holes. A single trained network accurately resolves modes with $(\ell,m)\in \{(2,0),(2,1)\}$ and overtones up to $n=7$ across the full spin range, achieving relative errors of $\mathcal{O}(10^{-6})$ for the fundamental mode and gradually increasing to $\mathcal{O}(10^{-4})$ for higher overtones, benchmarked against the Leaver's method. This level of accuracy is already significant for black hole spectroscopy and practical ringdown modelling for current and future observatories. More broadly, these results highlight the potential of $\texttt{DeepOPiraKAN}$ as a general and scalable framework for parameter dependent spectral problems across complex physical systems.
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All authors Haohao Gu, Sensen He, Hanlin Song, Bo Liang, Zhenwei Lyu, Xiaoguang Hu, Minghui Du, Peng Xu, Bo-Qiang Ma

High Energy Astrophysical Phenomena

The Deep Newtonian Regime in Late-Time Blast Waves: Inevitable Transition and Distinct Flux Signatures

Sk. Minhajur Rahaman, Jonathan Granot and Paz Beniamini

In many astrophysical transients, outflows drive shocks into the ambient medium, accelerating electrons to non-thermal energy distributions that produce broadband synchrotron emission. At late times, even initially collimated relativistic jets evolve into quasi-spherical Newtonian blastwaves. As the shock decelerates, the post-shock internal energy per particle decreases; below a critical velocity $\beta_{\rm DN} \approx 0.2$, only a fraction $\xi_e < 1$ of electrons are accelerated to relativistic energies, defining the deep Newtonian (DN) regime. We develop a unified analytic framework for synchrotron emission in this phase, applicable to both single-velocity and stratified ejecta. For gamma-ray burst afterglows in a uniform medium, the DN transition occurs at $t_{\rm DN} \approx 3.7\,E_{51}^{1/3} n_0^{-1/3}$~yr, yielding a shallower decay by $\delta\alpha = 6(p-2)/5$ relative to standard Newtonian predictions. For kilonova remnants ($E_0 = 10^{50.5}$~erg, $M_{\rm ej} = 0.1\,M_\odot$), the DN phase begins prior to deceleration; neglecting it underestimates radio flux by factors of $\sim 3$–$5$ during coasting and even more thereafter. Magnetar-boosted remnants ($E \sim10^{52}$~erg) should reach $\sim$\,10\,–\,100\,$\mu$Jy at 3~GHz at $\sim$\,40\;Mpc, though limits on GW170817 already disfavor a long-lived millisecond magnetar. In core-collapse supernovae in a wind medium ($\rho\!\propto\!r^{-k}$), the peak luminosity remains constant during coasting, while $\nu_{\rm pk} \propto t^{-1}$; for SN~2023ixf, we find $k = 1.29 \pm 0.14$. The DN spectral energy distribution typically satisfies $\nu_m\!<\!\nu_{\rm sa}\!<\!\nu_c$, peaking at sub-GHz frequencies where LOFAR and SKA-low are most sensitive. Even non-detections place robust constraints on ambient density and outflow energetics.
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Instrumentation and Methods for Astrophysics

High-Precision Ground Characterization of Test-Mass Magnetic Properties for the Taiji Gravitational Wave Mission via a Physics-Informed Neural Framework

Chang Liu, Qiong Deng, Huadong Li et al. (+12 more)

Taiji is a gravitational wave detection mission in space initiated by the Chinese Academy of Sciences, which will open the millihertz window through a heliocentric triangular constellation of three drag-free spacecraft. Its ultimate sensitivity is determined partly by the residual acceleration noise of the gravitational reference sensors (GRS), within which the coupling between the test-mass and the fluctuating environmental magnetic field constitutes one of the key stray-force contributions. Following the path established by the LISA and TianQin teams, high-precision ground characterization of remanent magnetic moment $\vec{m}_r$ and volume susceptibility $\chi$ of the test masses is a central step in the Taiji pre-launch test program. A persistent challenge for this characterization is the non-stationary, colored background noise inherent to torsion-pendulum facilities, which systematically biases classical Ordinary Least Squares (OLS) and Kalman filter (KF) estimators. We propose an AI-enhanced Differentiable Weighted Least Squares (AI-WLS) framework that fuses a dilated one-dimensional residual network, acting as a dynamic noise evaluator, with a fully differentiable analytical physical solver. This architecture preserves the exact linear mapping from the magnetic parameters to the torque response while autonomously identifying and suppressing contaminated data segments. Validated on real measured noise from the Changchun Institute of Optics, Fine Mechanics and Physics torsion-pendulum facility developed for Taiji, which achieves a torque sensitivity of order $10^{-13}\,\mathrm{N\cdot m\,Hz^{-1/2}}$, the AI-WLS framework bounds the maximum absolute estimation errors at $4.46\times 10^{-10}\,\mathrm{A\cdot m^2}$ for $\vec{m}_r$ and $7.8\times 10^{-8}$ for $\chi$, satisfying Taiji's ground-test requirements on all these parameters simultaneously.
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All authors Chang Liu, Qiong Deng, Huadong Li, Liwei Yang, Xiaodong Peng, Ziren Luo, Yuzhu Zhang, Chen Gao, Xiaotong Wei, Minghui Du, Zihao Xiao, Peng Xu, Bo Liang, Zhi Wang, Li-e Qiang

High Energy Astrophysical Phenomena

Hyperaccreting Neutron Stars inside Massive Envelopes: The Implausibility of Thorne-Żytkow Objects

Patrick Chi-Kit Cheong, David Radice and Christopher L. Fryer

The evolution of neutron stars (NSs) embedded within massive stellar envelopes is a critical phase in binary stellar evolution, potentially leading to the formation of Thorne-Żytkow Objects (TŻOs) or catastrophic collapse. We present the first fully coupled general relativistic hydrodynamics (GRHD) simulations of hypercritical accretion onto NSs that simultaneously incorporate grey two-moment (M1) neutrino transport and an $\alpha$-chain nuclear reaction network. By investigating four distinct progenitor evolutionary stages, we resolve the complex interplay between intense neutrino cooling, multidimensional fluid dynamics, and nuclear feedback. Our results show that while vigorous convection is triggered in the post-shock region, the global energy budget is primarily governed by neutrino cooling, which effectively balances the accretion power. Crucially, even though our M1 transport scheme captures neutrino absorption and localized heating, the efficient cooling sink and high ram pressure of the infalling envelope prevent the formation of any core-collapse supernova-like explosion. We find that all nucleosynthetically processed material ($T > 5$~GK) remains strictly gravitationally bound, challenging the assumption that these systems contribute significantly to galactic nucleosynthetic yields via convective dredge-up. The lack of sustained outflows and the persistent hypercritical accretion rates suggest that embedded NSs will rapidly exceed the Tolman-Oppenheimer-Volkoff mass limit on timescales of minutes to hours. We conclude that these systems are not stable TŻOs, but are rather transient precursors to catastrophic black hole formation and potential central engines for high-energy transients.
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Cosmology and Nongalactic Astrophysics

The open-Universe signal: A model artifact rather than genuine curvature

Peng-Ju Wu

Recent late-Universe observations suggest an open Universe. If confirmed, such a departure from spatial flatness would carry profound implications for our understanding of cosmic inflation and the ultimate fate of the Universe. Motivated by this intriguing result and the release of new data, we revisit the question using baryon acoustic oscillation measurements from DESI DR2, multiple Type Ia supernova samples, refined strong gravitational lensing time-delay analyses, and the most up-to-date cosmic chronometer data. We find that within the $\Lambda$ cold dark matter ($\Lambda$CDM) paradigm, the combined data still prefer an open Universe with $\Omega_K=0.049\pm0.037$. However, this preference vanishes in extensions to $\Lambda$CDM, where the data instead favor a flat Universe. The model comparison shows that for $\Lambda$CDM, introducing new physics is preferred over merely allowing spatial curvature, and flat $\Lambda$CDM extensions perform better than their curved counterparts. We therefore argue that the mild open-Universe signal is an artifact of limited model flexibility, rather than a genuine feature of late-Universe observations.
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Saturday 25 April

Earth and Planetary Astrophysics

Direct Imaging Constraints on Binary Planets and Exomoons around Epsilon Indi A b

Matson Garza, Mary Anne Limbach, Rachel Bowens-Rubin et al. (+6 more)

Epsilon Indi A b is a directly imaged $\sim6 M_{\rm Jup}$ exoplanet orbiting a nearby (3.6 pc) K-dwarf at $\sim 30$ AU. We analyze archival JWST/MIRI 15 $\mu$m coronagraphic imaging of this planet to search for directly imaged satellites orbiting Eps Ind A b. Within the planet's Hill sphere (radius $R_H \approx 2.3$ AU or $1.3 \lambda/D$), we compare single- and double-PSF models using Bayesian evidence. We find that a double-PSF (binary planet) fit is preferred. This apparent preference can most plausibly be explained by systematics, although follow-up observations would be required to fully rule out a binary planet interpretation. We construct a contrast curve of the exoplanet after removing this feature, demonstrating sensitivity to companions as faint as $0.03\times$ the F1550C flux of Eps Ind A b (equivalent to $T = 130$ K, $1.3 M_{\rm Jup}$) at large separations (>2 AU). We also demonstrate sensitivity to brighter companions $0.2\times$ the F1550C flux of Eps Ind A b (equivalent to $T = 180$ K, $2.5 M_{\rm Jup}$) down to separations of 0.52 AU (1.3 pixels; $0.29 \lambda/D$; 144 mas). This study demonstrates that JWST/MIRI can directly detect exomoons or binary planets inside the Hill sphere of directly imaged exoplanets orbiting neighboring stars.
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All authors Matson Garza, Mary Anne Limbach, Rachel Bowens-Rubin, Matthew De Furio, Elisabeth C. Matthews, Kyle Franson, Sarah C. Millholland, Logan A. Pearce, Andrew Vanderburg

Cosmology and Nongalactic Astrophysics

STVG-MOG Cluster Dynamics and the Cosmological $1/r^2$ Force Law from Pairwise kSZ Data

John W. Moffat

We investigate whether Scalar-Tensor-Vector Gravity in its weak-field modified gravity form can account for the cluster-scale inverse-square force law inferred from recent kinematic Sunyaev-Zeldovich measurements of cluster pairwise motions. The starting point is the X-COP cluster fit of STVG-MOG, for which a representative baryonic cluster mass $M\sim 10^{15}M_\odot$ together with parameters $\alpha\sim 9.11$ and $\mu\sim 0.196~{\rm Mpc}^{-1}$ provides a successful description of cluster dynamics without particle dark matter. We extrapolate this fit to the separation range $30$ to $230~{\rm Mpc}$, relevant for the pairwise kSZ analysis. Since the Yukawa transition length $\mu^{-1}\simeq 5.1~{\rm Mpc}$ is much smaller than these separations, the STVG-MOG acceleration law reduces to an effective inverse-square form. This explains why the theory can satisfy the observed Newtonian behavior while remaining distinct from MOND-like long-distance modifications. We derive the corresponding pairwise velocity curve and show that, after fitting a single overall kSZ amplitude, the extrapolated STVG-MOG prediction reproduces the measured trend of the pairwise kSZ data. The analysis shows that the X-COP cluster fit and the cosmological-scale kSZ force-law result are mutually consistent within STVG-MOG.
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Instrumentation and Methods for Astrophysics

ArchGEM: an Advanced Data Analysis Tool for Analyzing Scattered Light Noise in LIGO

Kaylah McGowan, Shania Nichols, Siddharth Soni et al. (+4 more)

Scattered light is one of the most common sources of non-stationary noise at low frequencies in Advanced LIGO detectors. It appears as arch-like features in time-frequency spectrograms, produced when stray light reflects from moving surfaces and recombines with the main interferometer beam. In this study, we present ArchGEM, an automated framework for identifying and characterizing these arches and recovering the physical properties of the scattering surfaces. ArchGEM combines a prominence-based peak-finding method with a Gaussian Mixture Model clustering approach to capture a range of scattered-light morphologies across different detector conditions. We apply ArchGEM to scattered light glitches across Advanced LIGO observing runs O3 (2019–2020) and O4 (2023–2024). We find that the average frequency distributions of this noise span 15–25 Hz in O3a and O4, but increase to 20–40 Hz during O3b. Typical inferred surface velocities are 0.2–0.5 $\mu$m/s, and inferred surface displacements are 0.1–0.3 $\mu$m. The Gaussian Mixture Model performs most consistently for complex or overlapping features, with mean frequency offsets within 5 Hz of the Gravity Spy baseline. Our results show that ArchGEM provides a practical tool for detector characterization by linking observed spectrogram features to the motion of scattering surfaces and helping guide future mitigation of scattered light noise in current and next-generation interferometers. By quantifying the temporal and spectral behavior of scattered light, ArchGEM provides a robust framework for diagnosing noise sources and guiding targeted mitigation strategies in future detector upgrades.
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All authors Kaylah McGowan, Shania Nichols, Siddharth Soni, Chayan Chatterjee, Gabriela Gonzalez, Kelly Holley-Bockelmann, Karan Jani

Cosmology and Nongalactic Astrophysics

Testing Scalar Field Dark Matter models in M31 galaxy through the Rotation Curve analysis

Gulnara Suliyeva, Kuantay Boshkayev, Talgar Konysbayev et al. (+2 more)

We explore the viability of scalar field dark matter halo models through the rotation curve analysis of the Andromeda galaxy (M31), taking into account a realistic description of its baryonic structure. The mass model includes a stellar disk described by the Freeman profile and two alternative bulge configurations: a classical single de Vaucouleurs bulge and a two-component structure consisting of inner and main bulges modeled by exponential sphere profiles. The dark matter halo is modeled using three scalar field motivated models: fuzzy dark matter (FDM), Bose-Einstein condensate and multistate scalar-field dark matter. The model parameters are determined through the Levenberg-Marquardt nonlinear least-squares fitting, and the relative performance of the models is evaluated using the Bayesian Information Criterion which allows a direct comparison with previous phenomenological halo studies performed for the same galaxy. We find that the two-bulge baryonic configuration ensures a better statistical description of the M31 rotation curve, independently of the adopted halo model. The results also suggest that, within scalar field dark matter scenarios, smooth cored halos, such as FDM, provide the most consistent description of the M31 kinematics.
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All authors Gulnara Suliyeva, Kuantay Boshkayev, Talgar Konysbayev, Yergali Kurmanov, Guldana Rabigulova

Solar and Stellar Astrophysics

Deflection of a Filament Eruption with Three Parallel Flare Ribbons via Reconnection at an X-Point

Xiaomeng Zhang, Jinhan Guo, Yang Guo et al. (+2 more)

On 2024 May 6, Active Region 13663 produced an X4.5-class flare associated with a filament eruption that exhibited remarkable rotation and deflection dynamics. This study aims to investigate two key aspects of this event: the formation mechanisms of the complex flare ribbon structures and the physical drivers behind the observed filament deflection. We conduct a data-constrained magnetohydrodynamic simulation using the zero-beta approximation to reconstruct the filament's evolution. Through detailed analysis of quasi-separatrix layers (QSLs) and their comparison with observed flare ribbons, we establish crucial connections between magnetic topology and flare morphology. First, our simulation successfully reproduces key observational features of the eruption. Then, we connect the flare ribbon morphology with calculated QSLs. Finally, we find filament deflection resulting from localized reconnection at the X-point, as evidenced by Lorentz force decomposition. We demonstrate that reconnection above two current channels of opposite helicity governs the eruption dynamics, with magnetic pressure gradients driving flux rope deflection while magnetic tension force simultaneously restraining arcade ascent. The event features a "sandwich" magnetic configuration including double parallel polarity inversion lines with strong shear component. We suggest that this particular configuration could serve as a plausible formation mechanism for the observed parallel three-ribbon structure. In addition, the evolution of QSLs and flare ribbons provides clear evidence of reconnection between two flux ropes.
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All authors Xiaomeng Zhang, Jinhan Guo, Yang Guo, Mingde Ding, Brigitte Schmieder