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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 1 December

Instrumentation and Methods for Astrophysics

Revisiting wideband pulsar timing measurements

Abhimanyu Susobhanan, Avinash Kumar Paladi, Réka Desmecht et al. (+28 more)

In the wideband paradigm of pulsar timing, the time of arrival of a pulsar pulse is measured simultaneously with the corresponding dispersion measure from a frequency-resolved integrated pulse profile. We present a new method for performing wideband measurements that rigorously accounts for measurement noise. We demonstrate this method using observations of PSR J2124$-$3358 made as part of the Indian Pulsar Timing Array experiment using the upgraded Giant Metre-wave Radio Telescope, and show that our method produces more realistic measurement uncertainty estimates compared to the existing wideband measurement method.
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All authors Abhimanyu Susobhanan, Avinash Kumar Paladi, Réka Desmecht, Amarnath, Manjari Bagchi, Manoneeta Chakraborty, Shaswata Chowdhury, Suruj Jyoti Das, Debabrata Deb, Shantanu Desai, Churchil Dwivedi, Himanshu Grover, Jibin Jose, Bhal Chandra Joshi, Shubham Kala, Fazal Kareem, Kuldeep Meena, Sushovan Mondal, K Nobleson, Arul Pandian B, Kaustubh Rai, Adya Shukla, Manpreet Singh, Aman Srivastava, Mayuresh Surnis, Hemanga Tahbildar, Keitaro Takahashi, Pratik Tarafdar, Kunjal Vara, Vaishnavi Vyasraj, Zenia Zuraiq

Instrumentation and Methods for Astrophysics

Kratos-polrad: Novel GPU system for Monte-Carlo simulations with consistent polarization calculations

Haifeng Yang and Lile Wang

Polarized radiation serves as a vital diagnostic tool in astrophysics, providing unique insights into magnetic field geometries, scattering processes, and three-dimensional structures in diverse astrophysical scenarios. To address these applications, we present Kratos_polrad, a novel GPU-accelerated Monte Carlo Radiative Transfer code built upon the heterogeneous computing framework of Kratos, designed for self-consistent and efficient polarization calculations. It utilizes a comprehensive treatment of the Stokes parameters throughout photon propagation, featuring grain-lab frame transformations using quaternion algebra and a consistent analytical integration of polarized extinction and emission within each cell, which are useful in modeling radiative transfer processes with scatterings by aligned dust grains. The code implements two-step polarimetry imaging that decouples Monte Carlo sampling of scattering physics from imaging geometry, enabling efficient synthesis maximizing the utilization of photon packets. Extensive validation against analytical solutions and established codes demonstrates accurate treatment of diverse polarization phenomena, including self-scattering polarization, dichroic extinction in aligned dust grains, and complex polarization patterns in twisted magnetic field configurations. By leveraging massive GPU parallelism, optimized memory access patterns, and analytical approaches for optically thick cells, Kratos_polrad achieves performance improvements of ~10^2 times compared to CPU-based methods, enabling previously prohibitive studies in polarimetric astrophysics.
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High Energy Astrophysical Phenomena

Non-detection of FAST and Parkes follow-up observation for 27 Parkes discovered FRBs

Xuan Yang, Songbo Zhang and Xuefeng Wu

To investigate whether apparently non-repeating Fast Radio Bursts (FRBs) are truly one-off transients, we conducted systematic follow-up observations of 27 out of 81 non-repeating FRBs identified in the Parkes Transient Database. Using 59.0 hours of data from the Parkes Ultra-Wideband Low (UWL) receiver and 6.3 hours from the Five-hundred-meter Aperture Spherical Telescope (FAST) 19-beam receiver, we searched for repeated bursts from these sources. No additional bursts were detected from any of the 27 FRBs. Combining these non-detections with prior archival observations, we derived stringent upper limits on their repetition rates above 1 Jy under two statistical models: Poisson process constraints range from $\sim10^{-3.5}$ to $10^{-1.9}\,\mathrm{h^{-1}}$, while Weibull process constraints range from $\sim10^{-3.4}$ to $10^{-1.5}\,\mathrm{h^{-1}}$. These limits are approximately an order of magnitude stricter than those reported in previous studies. By applying consistent observational setups and analytical methodologies across all sources, the derived rate limits converge to a narrow, well-defined range. This suggests that these FRBs form a relatively homogeneous population with extremely low intrinsic activity rates.
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Instrumentation and Methods for Astrophysics

Egent: An Autonomous Agent for Equivalent Width Measurement

Yuan-Sen Ting, Serat Mahmud Saad, Fan Liu et al. (+1 more)

We present Egent, an autonomous agent that combines classical multi-Voigt profile fitting with large language model (LLM) visual inspection and iterative refinement. The fitting engine is built from scratch with minimal dependencies, creating an ecosystem where the LLM can reason about fits through function calls–adjusting wavelength windows, adding blend components, modifying continuum treatment, and flagging problematic cases. Egent operates directly on raw flux spectra without requiring pre-normalized continua. We validate against manual measurements from human experts using 18,615 lines from the C3PO program across 84 Magellan/MIKE spectra at SNR~50-250. The raw agreement between Egent and expert measurements is MAD=5-7mA, without any post-hoc per-spectrum correction. Per-spectrum slopes of ~0.85-1.19 around unity reflect differences in global continuum methodology rather than fitting failures. The LLM's primary role is quality control: it confirms good fits (~60-65% of lines are LLM-refined and accepted), flags problematic cases (~10-20%), and occasionally rescues edge cases where tool use improves fits. Agreement between GPT-5 and GPT-5-mini confirms reproducibility, with GPT-5-mini enabling low-cost analysis at ~200 lines per US dollar. Every fit stores complete Voigt parameters, continuum coefficients, and LLM reasoning chains, enabling exact reconstruction without re-running. Egent compresses what traditionally requires months of expert effort into days of automated analysis, enabling survey-scale EW measurement. We provide open-source code at https://github.com/tingyuansen/Egent, including a web interface for drag-and-drop analysis and a local LLM backend for fully offline operation on consumer hardware.
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All authors Yuan-Sen Ting, Serat Mahmud Saad, Fan Liu, Yuting Shen

Astrophysics of Galaxies

OzDES Reverberation Mapping of Active Galactic Nuclei: Final Data Release, Black-Hole Mass Results, & Scaling Relations

H. McDougall, T. M. Davis, Z. Yu et al. (+53 more)

Over the last decade, the Australian Dark Energy (OzDES) collaboration has used Reverberation Mapping to measure the masses of high redshift supermassive black holes. Here we present the final review and analysis of this OzDES reverberation mapping campaign. These observations use 6-7 years of photometric and spectroscopic observations of 735 Active Galactic Nuclei (AGN) in the redshift range 0.13-3.85 and bolometric luminosity range 44.3 - 47.5 erg/s. Both photometry and spectra are observed in visible wavelengths, allowing for the physical scale of the AGN broad line region to be estimated from reverberations of the He̱ta}, MgII and CIV emission lines. We successfully use reverberation mapping to constrain the masses of 62 super-massive black holes, and combine with existing data to fit a power law to the lag-luminosity relation for the He̱ta} and MgII lines with a scatter of ~0.25 dex, the tightest yet identified, fit specifically for consistency with high redshift AGN. We fit a similarly constrained relation for CIV, resolving a tension with the low luminosity literature AGN by accounting for selection effects arising from finite survey length. We also examine the impact of emission line width and luminosity (related to accretion rate) in reducing the scatter of these scaling relationships and find no significant improvement over the lag-only approach for any of the three lines. Using these relations, we further estimate the masses and accretion rates of 246 AGN with single epoch methods. We also use these relations to estimate the relative sizes of the He̱ta}, MgII and CIV emitting regions. In short, we provide a comprehensive benchmark of high redshift AGN reverberation mapping at the close of this most recent generation of surveys, including light curves, time-delays, and a set of significantly improved radius-luminosity relations for use with high-redshift populations.
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All authors H. McDougall, T. M. Davis, Z. Yu, P. Martini, C. Lidman, U. Malik, A. Penton, G. F. Lewis, B. E. Tucker, B. J. S. Pope, S. Allam, F. Andrade-Oliveira, J. Asorey, D. Bacon, S. Bocquet, D. Brooks, A. Carnero Rosell, D. Carollo, A. Carr, J. Carretero, T. Y. Cheng, L. N. da Costa, M. E. da Silva Pereira, J. De Vicente, H. T. Diehl, P. Doel, S. Everett, J. García-Bellido, K. Glazebrook, D. Gruen, G. Gutierrez, K. Herner, S. R. Hinton, D. L. Hollowood, D. J. James, A. G. Kim, K. Kuehn, S. Lee, M. March, J. L. Marshall, J. Mena-Fernández, F. Menanteau, R. Miquel, J. Myles, R. L. C. Ogando, A. Porredon, E. Sanchez, D. Sanchez Cid, R. Sharp, M. Smith, E. Suchyta, M. E. C. Swanson, C. To, D. L. Tucker, A. R. Walker, N. Weaverdyck

Astrophysics of Galaxies

OzDES Reverberation Mapping Program: CIV lags from six years of data

A. Penton, H. McDougall, T. M. Davis et al. (+52 more)

We present 29 successfully recovered CIV time lags in Active Galactic Nuclei from the complete Dark Energy Survey Reverberation Mapping campaign. The AGN in this sample span a redshift range of 1.9<z<3.5. We successfully measure the velocity dispersion from the CIV spectral linewidth for 25 of these 29 sources, and use these to calculate new high-redshift black hole mass estimates, finding masses between 0.8 and 1.3 billion solar masses. We also identify a selection effect due to the duration of the survey that can impact the radius-luminosity relation derived from this and other (high-redshift) data. This paper represents the culmination of the OzDES CIV campaign.
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All authors A. Penton, H. McDougall, T. M. Davis, Z. Yu, U. Malik, P. Martini, B. E. Tucker, C. Lidman, G. F. Lewis, R. Sharp, M. Aguena, S. Allam, F. Andrade-Oliveira, J. Asorey, D. Bacon, S. Bocquet, D. Brooks, R. Camilleri, A. Carnero Rosell, D. Carollo, A. Carr, J. Carretero, T. Y. Cheng, L. N. da Costa, M. E. da Silva Pereira, J. De Vicente, S. Desai, S. Everett, J. García-Bellido, K. Glazebrook, D. Gruen, G. Gutierrez, S. R. Hinton, D. L. Hollowood, K. Honscheid, K. Kuehn, O. Lahav, S. Lee, M. March, J. L. Marshall, J. Mena-Fernández, R. Miquel, J. Myles, R. L. C. Ogando, A. A. Plazas Malagón, A. Porredon, M. Rodriguez-Monroy, A. K. Romer, E. Sanchez, D. Sanchez Cid, M. Smith, E. Suchyta, M. E. C. Swanson, V. Vikram, N. Weaverdyck

High Energy Astrophysical Phenomena

Multi-frequency radio-continuum study of the LMC SNR N206 (Goat's Eye) and its "zig-zag" PWN

M. Ghavam, Z. J. Smeaton, M. D. Filipovic et al. (+17 more)

We present new radio-continuum observations of the Large Magellanic Cloud (LMC) supernova remnant (SNR) N206, which we give the name "Goat's Eye". Goat's Eye contains an interior radio structure that is likely a pulsar wind nebula (PWN), which we analyse in further detail. We use new radio observations from the Australia Telescope Compact Array (ATCA) telescope, as well as several archival radio observations, to calculate spectral indices, and find a steep spectral index for the whole SNR ($\alpha = -0.60\pm0.02$), and a flatter spectral index for the PWN ($\alpha = -0.16\pm0.03$). We also measure the polarisation and magnetic field properties of the PWN. Previously reported as a linear structure, the new observations show an unusual "zig-zag"-like structure, visible in radio-continuum total intensity, linear polarisation, and magnetic field orientations. The origin of this zig-zag structure is unclear, but we propose some origin scenarios that will require further observations to differentiate between.
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All authors M. Ghavam, Z. J. Smeaton, M. D. Filipovic, R. Z. E. Alsaberi, C. Bordiu, W. D. Cotton, E. J. Crawford, A. M. Hopkins, R. Kothes, S. Lazarevic, D. Leahy, N. Rajabpour, S. Ranasinghe, G. P. Rowell, H. Sano, M. Sasaki, D. Shobhana, K. Tsuge, D. Urosevic, N. F. H. Tothill

Solar and Stellar Astrophysics

Resolving Interchange Reconnection Dynamics in a Fan-Spine-like Topology Observed by Solar Orbiter

Yadan Duan, Xiaoli Yan, Junchao Hong et al. (+5 more)

Interchange reconnection is believed to play a significant role in the production of solar jets and solar wind. However, the dynamics of interchange reconnection in the low corona might be more complex than recognized before in higher temporal and spatial resolutions. Using unprecedentedly high-resolution observations from the Extreme Ultraviolet Imager (EUI) onboard the Solar Orbiter, we analyze the dynamics of interchange reconnection in a small-scale fan-spine-like topology. Interchange reconnection that continuously occurs around the multi-null points of the fan-spine-like system exhibits a quasi-periodicity of ~200 s, nearly covering the entire evolution of this system. Continuous evolution and reversal of multiple current sheets are observed over time near the null point. These results reveal that the dynamics of interchange reconnection are likely modulated by the emerging magnetic structures, such as mini-filaments and emerging arcades. Moreover, a curtain-like feature with a width of 1.7 Mm is also observed near the interchange reconnection region and persistently generates outflows, which is similar to the separatrix curtain reported in the pseudo-streamer structure. This study not only demonstrates the complex and variable reconnection dynamics of interchange reconnection within small-scale fan-spine topology but also provides insights into the self-similarity of magnetic field configurations across multiple temporal and spatial scales.
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All authors Yadan Duan, Xiaoli Yan, Junchao Hong, Hechao Chen, Yuhang Gao, Zheng Sun, Zhenyong Hou, Jincheng Wang

Solar and Stellar Astrophysics

Data-driven Radiative Magnetohydrodynamics Simulations with the MURaM Code: the Emergence of Active Region 11158 and the X2.2 Flare

Feng Chen

We present the application of the data-driven branch of the MURaM code to the extensively studied flare-productive active region 11158. We refine the hybrid model strategy, which was described in the earlier paper of this series, to model the emergence of the active region during 4 solar days starting shortly before 2011 February 11 and the eruption of an X2.2 flare on February 15. After 4 days of evolution, a major eruption of a magnetic flux rope occurs in the simulation at approximately 3 hours (3% difference) before the real flare. The eruption leads to magnetic reconnection that contributes to bulk heating in the chromosphere and corona. The deposition of flare energy in the chromosphere causes strong condensations and evaporations, which fill hot post-flare loops and bright flare ribbons that exhibit separation and extension similar to the observed ribbon evolution. The synthesized soft X-ray flux corresponds to X class, which is close to the real event. The upward eruption of the flux rope leads to a piston-driven shock and horizontal expansion that exerts a strong downward impact on the lower atmosphere and generate an apparently fast-propagating chromospheric Moreton wave. We conclude that the data-driven radiative simulation of this active region can reproduce the key observational results of the real flare and demonstrate the great potential of this method for studying solar eruptions in a realistic corona environment.
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High Energy Astrophysical Phenomena

Revisiting the Supernova Engines in the 3C 397 and W49B Supernova Remnants

Cole Treyturik, Chelsea Braun, Samar Safi-Harb et al. (+2 more)

The nature of the supernova remnants (SNRs) 3C 397 and W49B has long been a subject of debate, with prior studies offering conflicting interpretations between thermonuclear and core-collapse scenarios. To help settle this debate, we present a systematic, spatially resolved, spectroscopic analysis of both remnants using XMM-Newton. By applying multi-component thermal models, we derive key physical properties including elemental abundances, ejecta temperatures, ambient densities, and explosion energetics. We compare the inferred metal abundance ratios to a wide range of core-collapse and thermonuclear nucleosynthesis models, including new models whose explosion energies differ from the canonical value of $10^{51}$ ergs. We find that the observed Fe/Si and Ca/Si ratios in both SNRs are best matched by certain thermonuclear models. However, no model fully reproduces the complete set of observed abundance patterns. In 3C 397, high Fe enrichment and spatial abundance variations suggest interaction with a dense progenitor environment, and W49B's composition is overall consistent with a thermonuclear origin; however both require a low energy ($\sim 10^{50}$ erg) supernova explosion. We additionally map the Fe K$\alpha$ line centroid energies and find a spread, with W49B falling within the core-collapse region – highlighting both environmental complexity and the limitations of this diagnostic for supernova classification. Our results highlight the need for caution in relying on any single diagnostic or nucleosynthesis model for supernova typing, underscore the need for improved nucleosynthesis models, and motivate future high-resolution, high-throughput observations.
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All authors Cole Treyturik, Chelsea Braun, Samar Safi-Harb, Christopher L. Fryer, Gilles Ferrand

Earth and Planetary Astrophysics

Disintegration of Long-period Comet C/2019 Y4 (ATLAS). II. Post-Perihelion Remnant Recovery

Salvatore A. Cordova Quijano, Quanzhi Ye and Michael S. P. Kelley

We present an investigation into the fate of disrupting near-Sun comet C/2019 Y4 (ATLAS). Imaging observations with the Lowell Discovery Telescope (LDT), obtained 3–5 months after the reported disruption and the last sighting, constrained the primary component C/2019 Y4-B to an absolute magnitude of $H>20.5$ or a diameter of $D<0.5$~km (assuming a geometric albedo of 0.04) at an outbound heliocentric distance of 2.71~au. A search of shallower data obtained from the Zwicky Transient Facility (ZTF) survey, conducted when components A and B receded from 2.5 to 2.9~au from the Sun, yielded no detections, suggesting that the fragments had either ceased to exist or were not substantially active during this period. The uncertain fate of C/2019 Y4 highlights the challenge in understanding the state of presumably disrupted comets. Our review of six other presumably disrupted long-period comets reveals that negative confirmations were not reported for half of them, leaving their disruption presumptions inconclusive.
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Sunday 30 November

Solar and Stellar Astrophysics

A sudden fine-scale bright kernel captured by Hi-C Flare in 11 MK emission during an M1.6-class solar flare's post-maximum phase

Sanjiv K. Tiwari, Navdeep K. Panesar, Ronald L. Moore et al. (+17 more)

On April 17, 2024, the third successful Hi-C sounding rocket flight, Hi-C Flare, recorded coronal images in Fe XXI 129 A emission from 11 MK plasma during the post-maximum phase of an M1.6-class solar flare, achieving unprecedented spatial (~300 km) and temporal (1.3 s) resolutions. The flare started at 21:55 UT, peaked at 22:08 UT, and lasted ~40 minutes. Hi-C observed for over five minutes (22:15:45 to 22:21:25), starting roughly eight minutes after flare maximum. A sudden compact bright burst - 875 +/- 25 km wide, lasting 90 +/- 1.3 s, exhibiting a proper motion of ~50 km/s, and splitting into two toward the end - occurs near the foot of some post-flare loops. Its size and brightness are reminiscent of flare-ribbon kernels during a flare's rapid rise phase, kernels marking sites of sudden heating and hot plasma upflow, making its occurrence during the late phase surprising. Such isolated brightenings in a flare's post-maximum phase are rare, and have not been previously reported. The kernel was detected in all SDO/AIA channels. Its 1600 A light curve peaked ~50 s earlier than its 131 A light curve, similar to that of flare-ribbon kernels, albeit with a smaller delay of ~25 s, during the impulsive phase of the flare. In SDO/HMI magnetograms, the kernel sits in unipolar positive magnetic flux near an embedded clump of negative flux. Although localized magnetic reconnection within the kernel (a microflare) cannot be ruled out for its cause, the observations favor the localized brightening being an isolated, exceptionally late flare-ribbon kernel, resulting from an exceptionally late burst of the flare's coronal reconnection.
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All authors Sanjiv K. Tiwari, Navdeep K. Panesar, Ronald L. Moore, Sabrina L. Savage, Amy R. Winebarger, Genevieve D. Vigil, Juraj Lorincik, Vanessa Polito, Bart De Pontieu, Leon Golub, Ken Kobayashi, Patrick Champey, Jenna Samra, Anna Rankin, Robert W. Walsh, Crisel Suarez, Christopher S. Moore, Adam R. Kobelski, Jeffery W. Reep, Charles Kankelborg

Solar and Stellar Astrophysics

Generalization of Elliptical-Cylindrical Flux Rope Models for ICME Reconstruction

Marti Masso Moreno, Carlos Arturo Perez-Alanis and P. K. Manoharan

We present a generalized elliptical cylindrical flux rope model for interplanetary coronal mass ejections (ICMEs) that allows for a non zero poloidal component in the internal magnetic field. We introduce a two step reconstruction algorithm that decouples the geometric configuration from the magnetic field fitting in order to improve numerical stability and physical consistency. Applied to Parker Solar Probe data, the new radial poloidal model preserves the global flux rope geometry while achieving a substantially better fit to the internal magnetic field than the traditional radial model, offering a more accurate and realistic description of ICME structures.
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Solar and Stellar Astrophysics

Relationship Between Major Stellar Physical Parameters and Normal Mode Frequencies in Accreting White Dwarf Stars

Praphull Kumar, Dean M. Townsley and Hunter Anz

White dwarfs (WDs) are the final fate of about 97% of the stars in our galaxy, making them vital tracers of stellar history. A fraction of WDs exist in cataclysmic variable (CV) systems, accreting matter from a nearby companion star. A subset of CVs undergo episodic rapid mass transfer, termed dwarf novae (DNe) outbursts. Some accreting WDs exhibit near sinusoidal photometric variations, interpreted as $g$ mode pulsations. However, identifying pulsation modes in accreting WDs remains challenging due to the paucity of available observed modes. In this work, we present a comprehensive computation of the observable $g$ mode frequencies across a range of WD parameters, varying the WD mass, size of the newly accreted layer and core temperature. We also introduce a novel method for mode identification based on the time evolution of pulsation periods following an accretion episode. Our mode identification method does not rely on the direct detection of the consecutive radial mode orders, frequently required in isolated WDs. Moreover, this work improves upon our previous WD modeling efforts. We use a more realistic core temperature in addition to thermohaline mixing and element diffusion enabled during the accretion phase.
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Instrumentation and Methods for Astrophysics

Euclid Structural-Thermal-Optical Performance

Euclid Collaboration: A. Anselmi, R. Laureijs, G. D. Racca et al. (+289 more)

The Euclid system performance is defined in terms of image quality metrics tuned to the weak gravitational lensing (WL) cosmological probe. WL induces stringent requirements on the shape and stability of the VIS instrument system point spread function (PSF). The PSF is affected by error contributions from the telescope, the focal plane and image motion, and is controlled by a global error budget with error allocations to each contributor. Aims. During spacecraft development, we verified through a structural-thermal-optical performance (STOP) analysis that the built and verified telescope with its spacecraft interface meets the in-orbit steady-state and transient image quality requirements. Methods. For the purposes of the STOP analysis, a detailed finite-element mathematical model was set up and a standard set of test cases, both steady-state and transient, was defined, comprising combinations of worst-case boundary conditions. Results. The STOP analysis addressed the interaction of all spacecraft components in transmitting temperature-induced loads that lead to optical train deformation. The results of the prelaunch analysis demonstrated that temperature-induced optical perturbations will be well below the allowable limits for all permitted observing conditions. During the first year in orbit, we used the STOP analysis predictions to help interpret the measured performance as a function of environmental variables. Unpredicted disturbances were discovered and unexpected sensitivities were revealed. In-orbit temperature variations are small (<300 mK) and so are their effects on the telescope structure, but they are detected in the time histories of the image quality metrics and are a non-negligible factor in the PSF stability budget demanded by the WL science. Taking everything into account, our analysis confirms the excellent overall performance of the telescope.
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All authors Euclid Collaboration: A. Anselmi, R. Laureijs, G. D. Racca, G. Costa, L. Courcould Mifsud, J.-C. Cuillandre, M. Gottero, H. Hoekstra, K. Kuijken, V. Mareschi, L. Miller, S. Mottini, D. Stramaccioni, B. Altieri, A. Amara, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, R. Bender, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Canas-Herrera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, A. Da Silva, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, F. Ducret, C. A. J. Duncan, X. Dupac, S. Dusini, S. Escoffier, M. Fabricius M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, J. Hoar, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, E. Keihanen, S. Kermiche, A. Kiessling, R. Kohley, B. Kubik, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, R. Nakajima, C. Neissner, R. C. Nichol, S.-M. Niemi C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, R. Rebolo, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, C. Rosset, E. Rossetti, R. Saglia, Z. Sakr, J.-C. Salvignol, A. G. Sanchez, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, S. Serrano, C. Sirignano, G. Sirri, J. Skottfelt, L. Stanco, J. Steinwagner, P. Tallada-Cresp, D. Tavagnacco, A. N. Taylor, H. I. Teplitz, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, E. A. Valentijn, L. Valenziano, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, A. Veropalumbo, Y. Wang, J. Weller, A. Zacchei, G. Zamorani, E. Zucca, M. Ballardini, M. Bolzonella, E. Bozzo, C. Burigana, R. Cabanac, A. Cappi, J. A. Escartin Vigo, L. Gabarra W. G. Hartley, J. Martin Fleitas, S. Matthew, N. Mauri, R. B. Metcalf, A. Pezzotta, M. Pontinen, I. Risso, V. Scottez, M. Sereno, M. Tenti, M. Viel, M. Wiesmann, Y. Akrami, I. T. Andika, S. Anselmi, M. Archidiacono, F. Atrio-Barandela, D. Bertacca, M. Bethermin, A. Blanchard, L. Blot, M. Bonici, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, B. Camacho Quevedo, F. Caro, C. S. Carvalho, T. Castro, F. Cogato, S. Conseil, A. R. Cooray, O. Cucciati, S. Davini, G. Desprez, A. Diaz-Sanchez, J. J. Diaz, S. Di Domizio, J. M. Diego M. Y. Elkhashab, A. Enia, Y. Fang, A. G. Ferrari, A. Finoguenov, A. Franco, K. Ganga, J. Garcia-Bellido, T. Gasparetto, E. Gaztanaga, F. Giacomini, F. Gianotti, G. Gozaliasl, M. Guidi, C. M. Gutierrez, A. Hall, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, S. Kruk, J. Le Graet, L. Legrand, M. Lembo, F. Lepori, G. Leroy, G. F. Lesci, J. Lesgourgues, L. Leuzzi, T. I. Liaudat, S. J. Liu, A. Loureiro, J. Macias-Perez, M. Magliocchetti, F. Mannucci, R. Maoli, C. J. A. P. Martins, L. Maurin, M. Miluzio, P. Monaco, A. Montoro, C. Moretti, G. Morgante, S. Nadathur, K. Naidoo, A. Navarro-Alsina, S. Nesseris, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, A. Pisani, D. Potter, S. Quai, M. Radovich, S. Sacquegna, M. Sahlen, D. B. Sanders, E. Sarpa, A. Schneider, D. Sciotti, E. Sellentin, L. C. Smith, K. Tanidis, G. Testera, R. Teyssier, S. Tosi, A. Troja, M. Tucci, C. Valieri, A. Venhola, D. Vergani, G. Verza, P. Vielzeuf, N. A. Walton

Solar and Stellar Astrophysics

The 2023 Australian Total Solar Eclipse: Line Emission of Fe XIV, Fe X and Fe XI out to 6 solar radii

Benjamin Boe, Shadia Habbal, Miloslav Druckmüller et al. (+6 more)

We present narrowband observations of the Fe XIV (530.3 nm), Fe X (637.4 nm), and Fe XI (789.2 nm) coronal emission lines from the 2023 April 20 Total Solar Eclipse in Australia. We deployed pairs of telescopes for each emission line that were equipped with narrowband filters centered on, and several nanometers away from, the center wavelengths of the lines. The secondary continuum telescopes were used to measure and remove the combined continuum K- (electron) and F- (dust) corona, which dominate coronal emission at optical and infrared wavelengths. Significant emission was detected from all three lines from 1.03 solar radii (Rs) continuously outward to at least 6 Rs. The brightness of the lines and continuum are absolutely calibrated to the solar disk, and are validated by a comparison with LASCO-C2 observations made at the same time. Using these observations, we inferred the line emission ratios resolved throughout the middle-corona (defined as 1.5 to 6 Rs) for the first time. These line ratios are a probe of the electron temperature, which have important implications for constraining models of coronal heating and the characterization of solar wind formation, yet these emission lines have scarcely been quantified beyond 3 Rs in the corona. This study demonstrates the enduring potential of eclipse observations for coronal physics and suggests that future spacecraft missions could observe these lines farther out than has been attempted previously.
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All authors Benjamin Boe, Shadia Habbal, Miloslav Druckmüller, Pavel Štarha, Matěj Štarha, Jana Hoderová, Sage Constantinou, Eric Ayars, Daniell Casillas

High Energy Astrophysical Phenomena

The jetted NLS1 1H 0323+342: the Rosetta stone for accretion/ejection in AGN

Luigi Foschini

1H 0323+342 is the nearest gamma-ray narrow-line Seyfert 1 galaxy (z=0.063). Its X-ray spectrum (0.3-10 keV) is characterised by significant spectral variability observed by many authors, with a backbone with photon index ~2 occasionally superimposed by a hard tail. This spectral variability has been interpreted as the interplay between the X-ray corona and the relativistic jet. The X-ray fluxes in the 0.3-10 keV energy band are generally around ~10^-11 erg cm^-2 s^-1, making it easier to get sufficient statistics even with short exposures. Here I present a reanalysis of all the available X-ray observations with Swift (181 obs), XMM-Newton (7 obs), Chandra (1 obs), and Suzaku (2 obs) performed between 2006 and 2025. Possible interpretations are proposed and discussed.
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Solar and Stellar Astrophysics

Starspots and Flares are Generally Not Correlated

Andy B. Zhang, Jason R. Reeves, David V. Martin et al. (+4 more)

Sunspots and solar flares are two different manifestations of magnetic activity on the surface of the Sun. On the Sun, flares typically occur close to spots. In this paper we test this the connection between spots and flares on other stars. We detect 218,386 stellar flares on 14,163 spotted stars using a new algorithm called toffee. Inhomogeneous spot distributions mean that as stars rotate they become brighter when less spots are facing the observer, and dimmer when more spots are facing the observer. We determine that flares occur when the star is brighter $49.97\pm 0.21\%$ of the time, i.e. there is an equal preference for the flares to occur when the star is relatively bright or dim. We therefore find no evidence for a correlation between flare rate and spot occurrence, contrary to what is seen on the Sun.
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All authors Andy B. Zhang, Jason R. Reeves, David V. Martin, Veronica Pratt, Wata Tubthong, Arielle Weinstein, Isabella E. Ward

High Energy Astrophysical Phenomena

Impact of positrons on electrical conductivity of hot and dense astrophysical plasma

Tigran Petrosyan, Arus Harutyunyan and Armen Sedrakian

We study the influence of positrons on the outer crusts of neutron stars and the interiors of white dwarfs, introducing them as a novel component in both the composition of matter and in transport processes. We solve a system of coupled Boltzmann kinetic equations for the electron and positron distribution functions in the relaxation-time approximation, taking into account electron-ion, positron-ion, and electron-positron collisions. The relevant scattering matrix elements are calculated from one-plasmon exchange diagrams, with in-medium polarization tensors derived within hard-thermal-loop effective theory. Numerical results are obtained for matter composed of carbon nuclei. We find that the conductivity rises with temperature, following a power law sigma proportional to the 4th power of T in the semi-degenerate regime and sigma proportional to T in the nondegenerate regime, due to the intense creation of thermal electron-positron pairs and the resulting collisions among them. These results highlight the importance of including positrons in the transport properties of heated, dense astrophysical plasmas.
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Solar and Stellar Astrophysics · Cross-listed from physics.space-ph

A robust empirical relationship between speed and turbulence energy in the near-Earth solar wind

Rohit Chhiber, Yanwen Wang, Manuel E. Cuesta et al. (+2 more)

The connection between turbulence and solar-wind acceleration, long known in space physics, is further developed in this Letter by establishing a robust empirical law that relates the bulk-flow speed to the magnetohydrodynamic-scale fluctuation energy in the plasma. The model is based on analysis of twenty-five years of near-Earth observations by NASA's Advanced Composition Explorer. It provides a simple way to estimate turbulence energy from low-resolution speed data – a practical approach that may be of utility when high-resolution measurements or advanced turbulence models are unavailable. Potential heliospheric applications include space-weather forecasting operations, remote imaging datasets, and energetic-particle transport models that require turbulence amplitudes to specify diffusion parameters.
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All authors Rohit Chhiber, Yanwen Wang, Manuel E. Cuesta, Jiaming Wang, Sohom Roy

Earth and Planetary Astrophysics

Machine Learning for Exoplanet Discovery: Validating TESS Candidates and Identifying Planets in the Habitable Zone

Sarah Huang and Chen Jiang

The high-precision photometry from NASA's Kepler and TESS missions has revolutionized exoplanet detection, enabling the discovery of over 5500 confirmed exoplanets via the transit method and around 10000 additional candidates awaiting validation. However, confirming these candidates as true planets demands meticulous vetting and follow-up observations, which hampers the discovery of exoplanets in large-scale datasets. To address this challenge, we developed a machine learning framework trained on Kepler's catalog of confirmed exoplanets and false positives to accurately identify true planetary candidates. Our model uses transit properties, planetary characteristics, and host stellar parameters as training features. The optimized model achieved 83.9% accuracy in cross-validation. When applied to 3987 TESS candidates with complete observational data, the model identified 1595 new high-confidence planets and correctly recovered 86% (358/418) of all previously confirmed TESS exoplanets in a blinded validation test. Our analysis revealed 100 previously unrecognized multi-planet systems, including five systems–that host habitable-zone exoplanets. Additionally, we identified 15 more planets within the habitable zone of a single system, suggesting strong potential for liquid water stability under conservative planetary albedo assumptions. This work demonstrates that machine learning can accelerate exoplanet validation while maintaining scientific rigor. Our modular design enables direct adaptation to future photometric missions like PLATO or Earth 2.0.
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High Energy Astrophysical Phenomena

Measuring the Neutron-Star Moment of Inertia using Nonlinear Orbital Variations from Lense-Thirring Precession

Emmanuel Fonseca

A future measurement of Lense-Thirring (LT) precession using a binary radio pulsar is expected to yield the pulsar's moment of inertia ($I_{\rm p}$). However, most of the known pulsar-binary systems expected to provide this opportunity will exhibit linear variations in the orbital elements, due to LT precession, that are difficult to separate from distance-dependent variations induced by other mechanisms. In this work, we demonstrate that the pulsar-timing signature of LT precession for an arbitrary orbital orientation produces nonlinear orbital variations after a sufficient amount of time; if detected, these nonlinear variations provide a means to constrain $I_{\rm p}$ without the need for independent measurements of orbital geometry or distance. We show through simulations that these nonlinear signatures are indeed detectable in pulsar-binary systems with an appropriate combination of timing precision and orbital geometry. Our simulations also show that nonlinear orbital variations from LT precession are expected to be detectable in PSR J1757$-$1854 and that its $I_{\rm p}$ can be constrained to precision as high as 10% by 2040 even without knowledge of distance.
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Instrumentation and Methods for Astrophysics

Quiet Skies Report: A Primer on Protecting Radio Astronomy in the Age of Satellite Mega-Constellations

Gregory Hellbourg

The rapid expansion of satellite constellations is transforming the radio-frequency environment around the Earth. At the same time, radio astronomy is entering a new era of sensitivity and survey capability, requiring unprecedented control of interference. This primer introduces satellite operators, engineers, spectrum managers and policy makers to the basic concepts of radio astronomy, explains why the discipline is uniquely vulnerable to interference, and outlines the regulatory and practical tools available to manage coexistence.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Probing the Scalar Hair of Rotating Horndeski Black Holes through Thick Disk Images

Qian Wan, Yehui Hou and Minyong Guo

Horizon-scale images of black holes provide a potential probe of fundamental physics, including tests of gravity and black hole hair. To assess the impact of scalar hair on accretion-flow imaging self-consistently, we construct an analytical model of a geometrically thick, magnetized disk around a rotating hairy black hole in Horndeski theory and analyze its 230 GHz image morphology. We find that scalar hair modestly alters the inflow and magnetic-field structure but strengthens gravitational redshift, markedly reducing the total flux and lensed ring brightness through relativistic transfer and spectral-shift effects. Moreover, we highlight a previously unexplored channel: the maximum interferometric diameter of the first photon ring responds strongly to the hair parameter but shows little dependence on accretion-flow details, making it a promising observable for constraining black-hole hair with future space-based interferometry.
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Earth and Planetary Astrophysics

A First Order Filter for the Detection of Potentially Habitable Exoplanets

Raka Dabhade, Jebraan Mudholkar, Siddhesh Durgude et al. (+1 more)

The search for potentially habitable exoplanets is a primary objective in modern astrophysics, yet the vast number of candidates discovered by missions like Kepler and TESS presents a significant challenge for detailed follow-up characterization. An efficient and reliable method for prioritizing the most promising targets is therefore essential. In this paper, we propose a novel first-order filter for identifying potentially habitable worlds based on a simple geometric ratio: the orbital semi-major axis to the stellar diameter ($d/D_s$). Using data from the NASA Exoplanet Archive, we demonstrate that the ideal value for this ratio is not constant, but is dependent on the host star's spectral class. We establish a tiered framework of ideal ratios, beginning with $\approx 108$ for G-type stars (anchored by the Earth-Sun system), and decreasing by a factor of two for K-type ($\approx 54$) and M-type ($\approx 27$) stars, respectively. Our analysis reveals a strong correlation, showing that exoplanets whose $d/D_s$ ratios are close to these empirically derived values consistently exhibit high Earth Similarity Index (ESI) scores. We propose that these tiered ratios represent "Habitability Main Sequences," analogous to the Hertzsprung-Russell diagram for stars, providing a valuable and straightforward tool for the astronomical community to rapidly screen large datasets and efficiently shortlist high-priority candidates for further investigation with next-generation observatories.
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All authors Raka Dabhade, Jebraan Mudholkar, Siddhesh Durgude, Arpit Kottur

High Energy Astrophysical Phenomena

Thermal conduction and thermopower of a warm neutron star crust in magnetic fields

Henrik Danielyan, Arus Harutyunyan and Armen Sedrakian

We compute the thermal conductivity and thermopower of the inner crust of compact stars over a broad temperature-density domain relevant to proto-neutron stars, binary neutron-star mergers, and accreting neutron stars, spanning the transition from a semi-degenerate to a highly degenerate electron gas above the lattice melting temperature, where nuclei form a liquid. Nuclear composition is fixed by selected zero-temperature inner-crust models as temperature varies. Transport coefficients follow from the Boltzmann equation in the relaxation-time approximation, including anisotropies from non-quantizing magnetic fields. Electron scattering rates incorporate (i) dynamical screening of electron-ion interactions via the hard-thermal-loop QED approximation, (ii) ion-ion correlations in a one-component plasma, and (iii) finite nuclear-size effects. We also evaluate electron-neutron scattering from coupling to the neutron anomalous magnetic moment, finding it subdominant throughout. To test sensitivity to microphysics, we compare several inner-crust compositions from different nuclear interactions and many-body methods. Across most of the crust, relaxation times and the anisotropic thermal-conductivity and thermopower tensor components vary by factors of 3 to 4 and 1.5 to 2, respectively, except near the pasta-phase region. Within this single-component, fixed-composition approximation, these results offer composition-dependent microphysical inputs for dissipative magneto-hydrodynamic simulations of warm neutron stars and post-merger remnants, where anisotropic heat and charge transport are critical.
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Astrophysics of Galaxies

Possible quasi-periodic optical oscillations of ZTF blazars

Na Wang, Guowei Ren, Shun Zhang et al. (+3 more)

Based on the Zwicky Transient Facility (ZTF), we selected 10 blazars as our sample sources. Among these, we found four blazars (J 0923.5+4125, J 1221.3+3010, J 1503.5+4759, and J 1652.7+4024) showing possible indications of quasi periodic oscillations (QPOs) modulation. We conducted a detailed analysis of their optical light curves (g- and r-bands) over the past five years using the root mean square (RMS)-Flux relation, flux distribution, and QPO detection methods to investigate their variability characteristics. A linear RMS-Flux relation is present in both bands, and their flux distributions follow a log-normal form. This suggests that optical variability may arise from multiplicative, nonlinear processes across different timescales and flux states. Further QPO analysis using the weighted wavelet Z-transform (WWZ), Lomb-Scargle periodogram (LSP), and autoregressive integrated moving average (ARIMA) methods identified candidate periodic signals in four blazars. J 0923.5+4125 (period $\sim$ 205 days) and J 1221.3+3010 ($\sim$ 630 days) show local significances of $\sim 3 \sigma$, whereas J 1503.5+4759 ($\sim$ 38.5 days) and J 1652.7+4024 ($\sim$ 48 days) reach $\sim 4 \sigma$. After accounting for the look-elsewhere effect, the global significances for J 1503.5+4759 in the g- and r-bands are $\sim 2.7 \sigma$, while for J 1652.7+4024 they are approximately $\sim 2.5 \sigma$ in both bands. These two blazars warrant further monitoring and investigation.
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All authors Na Wang, Guowei Ren, Shun Zhang, Tingfeng Yi, Tong Liu, Mouyuan Sun

High Energy Astrophysical Phenomena

Images of shadow and thin accretion disk around Bardeen black hole surrounded by perfect fluid dark matter

Haiyuan Feng, Ziqiang Cai, Hao-Peng Yan et al. (+2 more)

We investigate the shadow and optical appearance of Bardeen black hole (BH) immersed in perfect fluid dark matter (PFDM). Using EHT observations of M87* and Sgr A*, we constrain the DM parameter to a narrow range $b/M \sim \mathcal{O}(10^{-1}-10^{-2})$ for M87* and to $\mathcal{O}(10^{-2}-10^{-3})$ for Sgr A*. From these constraints we derive a rough prediction for the PFDM density near the shadow scale ($R_{\mathrm{sh}}\sim5M$): $\rho_{\mathrm{PFDM}} \sim 0.27$-$2.67\,\mathrm{g/cm^3}$ for Sgr A*, dropping to $\sim10^{-24}$-$10^{-25}\,\mathrm{g/cm^3}$ at 100 pc. Moreover, increasing $b$ substantially enlarges the photon sphere, impact parameter, shadow radius, and suppresses the observed disk brightness, while the magnetic charge $g$ produces only negligible corrections completely masked by PFDM on macroscopic scales. Subsequently, we investigate the primary/secondary images, flux, and redshift profiles for the PFDM-Bardeen BH using the Novikov-Thorne disk model, and compare these quantities with those of NFW, Dehnen-type and Moore DM BHs. The four BH types exhibit distinct densities at the shadow radius and at 100 pc, offering a potential distinguishing signature. Furthermore, for all DM BH models, blueshift appears in the primary image as inclination increases, while the secondary image remains redshift dominated even at high inclinations. Hence, if significant blueshifted emission were detected at low inclination, the predictions of these four DM models would be seriously challenged.
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All authors Haiyuan Feng, Ziqiang Cai, Hao-Peng Yan, Rong-Jia Yang, Jinjun Zhang

Astrophysics of Galaxies

Investigating the Correlation between Dark Matter Content, Ages and Mass-to-Light Ratios in Spiral Galaxies

Arpit Kottur, Meet Mehta and Raka Dabhade

We present an empirical investigation into the relationship between galactic age and dark matter content across a sample of 16 nearby, well-resolved spiral galaxies. Using raw rotation curve data from IOA Tokyo's publicly available repository, we model each galaxy's mass distribution via a three-component decomposition (Hernquist bulge, exponential disk, and a Navarro-Frenk-White (NFW) dark matter halo) fit using Monte Carlo simulations. The onset of dark matter dominance was identified using the NFW scale radius, beyond which we computed the total enclosed mass via Keplerian dynamics. I-band luminosities for these regions were estimated using a calibrated Tully-Fisher relation, yielding precise mass-to-light (M/L) ratios. We further calculated dark matter mass and density using NFW profile equations, and galaxy ages were retrieved through an extensive literature survey of stellar population studies. Our analysis reveals strong positive correlations between galactic age and both dark matter mass (Pearson $r \approx 0.91$; Spearman $\rho \approx 0.93$) and density (Pearson $r \approx 0.91$; Spearman $\rho \approx 0.91$), as well as M/L ratios, suggesting a robust link between evolutionary history and dark matter build-up. These findings are in quantitative agreement with predictions from large-scale cosmological simulations that incorporate assembly bias and smooth accretion-dominated growth, reinforcing the view that older galaxies, having formed earlier in high-density peaks, have accumulated significantly more dark matter over cosmic time. Our results offer observational evidence for time-dependent dark matter assembly and establish galactic age as a meaningful tracer of halo evolution.
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Astrophysics of Galaxies

On the multiplicity of red-Herschel sources and its implications for extreme star formation

Marianela Quirós-Rojas, Alfredo Montaña, Jorge A. Zavala et al. (+3 more)

We study the multiplicity of galaxies in the largest sample of red-Herschel sources ($S_{250 \mu \mathrm{m}} < S_{350 \mu \mathrm{m}} < S_{500 \mu \mathrm{m}}$) using archival ALMA observations. Out of 2416 fields with ALMA detections (from a total of 3,089 analyzed maps), we identify 474 multiple systems within a radius of 16 arcsec (equivalent to the 500 $\mu$m Herschel beam-size): 420 doubles, 51 triples, and 3 quadruples. In each case the brightest source contributes, on average, 64, 48, and 42 per cent of the total flux in double, triple, and quadruple systems. The average combined ALMA flux density of the sources in double systems is comparable to that of the two brightest components within triple and quadruple systems. Non-parametric tests suggest that only a small fraction of the double systems ($\lesssim13$ per cent) are comprised of sources with compatible redshifts, while 47-67 per cent of triple and quadruple fields contain at least one potentially associated pair. Simulations using a mock catalogue of dusty star-forming galaxies suggest that 32 per cent of the double systems are likely physically associated ($\Delta z < 0.01$, i.e. $\lesssim$10 comoving Mpc at $z = 3$) and, while only 8 per cent of the triple and none of the quadruple systems meet this criterion, $\sim$ 70 per cent of them include at least one likely associated pair. Our results suggest that enhanced star formation rates in submillimetre galaxies are primarily driven by internal processes rather than large-scale interactions. This study also provides a catalog of potential overdensities for follow-up observations, offering insights into proto-cluster formation and evolution.
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All authors Marianela Quirós-Rojas, Alfredo Montaña, Jorge A. Zavala, Itziar Aretxaga, Norma Araceli Nava-Moreno, David H. Hughes