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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 27 February

Astrophysics of Galaxies

Predicting Resolved Dust Attenuation from Local Galaxy Properties Using MaNGA

Anilkumar Mailvaganam, Tayyaba Zafar, Pablo Corcho-Caballero et al. (+4 more)

Accurate spatially resolved dust corrections are critical for interpreting the structure and evolution of star-forming galaxies (SFGs). We present an empirical model for predicting spatially resolved dust attenuation ($A_V$) in SFGs using integral field spectroscopy from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey. Using a sample of 5,155 galaxies over $7.20<M_\ast<11.14$ and $0.0002 < z < 0.1444$, we derive $A_V$ maps from the Balmer decrement across more than 1,898,954 star-forming spaxels. Using local star formation rate surface density ($\Sigma_{\text{SFR}}$) as a predictor, the model achieves $R^2 = 0.69$ and RMSE $=0.22$ mag, with residuals that are approximately Gaussian and centred near zero. It predicts $A_V$ within a factor of $\sim$1.3 on kpc scales. We also demonstrate that the relation can be applied iteratively to recover dust-corrected $\Sigma_{\mathrm{SFR}}$ from uncorrected values, converging by the fourth iteration with minimal residual bias ($-0.01$ mag) and low RMSE ($0.42$ mag). The model accurately reproduces $A_V$ maps across diverse morphologies and orientations, including edge-on systems. It also recovers the observed radial $A_V$ profiles, capturing their dependence on stellar mass and relative star formation activity, with more massive and more strongly star-forming galaxies showing steeper gradients.
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All authors Anilkumar Mailvaganam, Tayyaba Zafar, Pablo Corcho-Caballero, Tamal Mukherjee, Jahang Prathap, Kyle B. Westfall, Kevin Bundy

Astrophysics of Galaxies

Constraining the mass of the M31 ionized baryon Halo using CHIME/FRB Catalog 2

Lordrick A. Kahinga, J. Xavier Prochaska, Sunil Simha et al. (+21 more)

The circumgalactic medium (CGM) surrounding galaxies is believed to be a significant reservoir of baryons, yet its total mass remains poorly constrained. We present a novel approach to probe the CGM of the Andromeda galaxy (M31) using fast radio bursts (FRBs) from the CHIME/FRB Catalog 2. By comparing the dispersion measures (DMs) of 171 FRBs whose sightlines intersect M31's halo (within $r_{\rm vir}= 302\,\mathrm{kpc}$) to a control sample of 684 FRBs, we estimate the DM contribution from M31's CGM. We find evidence for an excess DM of $\delta\mathrm{DM} = 5.9$–$59.6\,\mathrm{pc\,cm^{-3}}$ in the inner halo ($\approx 0$–$151\,\mathrm{kpc}$) and $\delta\mathrm{DM} = 25.7$–$64.6\,\mathrm{pc\,cm^{-3}}$ in the outer halo ($\approx 151$–$302\,\mathrm{kpc}$). Using a generalized halo model parameterized by a closure radius $r_{\mathrm{close}}$, we constrain the baryon distribution and infer a best-fit value for $r_{\mathrm{close}}$ to be $9.2^{+9.9}_{-4.9}\,r_{\rm vir}$ ($1\sigma$), corresponding to a total CGM mass of $M_{b,\mathrm{halo}} = 18.6^{+7.9}_{-8.4} \times 10^{10}\,M_\odot$. Our results suggest that M31 may harbor a substantial fraction of its cosmic baryon budget in diffuse, ionized gas. This work demonstrates the potential of FRBs as a powerful tool for studying the CGM of nearby galaxies, with future larger samples expected to provide tighter constraints on the baryon content of galactic halos.
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All authors Lordrick A. Kahinga, J. Xavier Prochaska, Sunil Simha, Calvin Leung, Amanda C. Cook, Radu V. Craiu, Gwendolyn Eadie, Emmanuel Fonseca, B. M. Gaensler, Victoria M. Kaspi, Afrokk Khan, Bikash Kharel, Adam E. Lanman, Robert A. Main, Lluis Mas-Ribas, Kiyoshi W. Masui, Paul Scholz, Ayush Pandhi, Swarali Shivraj Patil, Aaron B. Pearlman, K. Shin, Seth R. Siegel, Kendrick Smith, Michele Woodland

High Energy Astrophysical Phenomena

A NICER View of PSR J0030+0451: Updated Constraints from Six Years of NICER Observations

Yves Kini, Lucien Mauviard, Tuomo Salmi et al. (+13 more)

Pulse-profile modeling of rotation-powered millisecond pulsars targeted by NICER has enabled mass–radius constraints of several neutron star sources, with implications for the dense-matter equation of state. For the bright isolated pulsar PSR J0030+0451, the inferred mass–radius was previously found to depend strongly on the assumed hot spot model. These hot-spot models yielded different mass–radius constraints, with the statistically preferred model exhibiting some mild tension with results inferred for PSR J0437$-$4715, PSR~J0614$-$3329, and GW170817. We present an updated pulse-profile analysis of PSR J0030+0451 using new NICER observations obtained between 2017 July to 2023 January, increasing the number of X-ray counts by about 50% compared to previous analyses. We jointly analyze the NICER data with archival XMM-Newton observations to better constrain the source spectrum and background. The new analysis significantly reduces the discrepancy between the hot spot models. The inferred mass and radius are $M = 1.43^{+0.20}_{-0.17}\,M_\odot$ and $R_{\rm eq} = 12.68^{+1.31}_{-1.04}$ km (68% credible intervals), reducing the tension with the results from other sources. In addition, the inferred hot spot configurations suggest the presence of intra-spot temperature gradients.
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All authors Yves Kini, Lucien Mauviard, Tuomo Salmi, Anna L. Watts, Sebastien Guillot, Bas Dorsman, Devarshi Choudhury, Denis González-Caniulef, Mariska Hoogkamer, Daniela Huppenkothen, Christine Kazantsev, Matthew Kerr, Samaya Nissanke, Paul S. Ray, Pierre Stammler, Serena Vinciguerra

High Energy Astrophysical Phenomena

An investigation on the FWHM of absorption features of type Ia supernovae

Xulin Zhao, Keiichi Maeda and Xiaofeng Wang

We present an investigation of the full width at half maximum (FWHM, or {\gamma}) of absorption features of Type Ia supernova (SNe Ia). We found that, the average value of FWHM can be well predicted with the rest wavelength ({\lambda}). The velocity also plays an important role, as objects with a higher velocity tend to have a larger FWHM. Temperature may be the third factor, as we found that, at the same velocity (but different phases), a normal-velocity (NV) object tends to have a larger FWHM than high-velocity (HV) object. Also, 1991T/1999aa-like objects that are believed to have relatively high temperatures show the largest FWHMs if compared at the same velocity. Generally speaking, FWHM evolves very slowly with time and shows no correlation with {\Delta}m15, but 1991T/1999aa-like objects are characterized by relatively fast decreasing FWHM. On the other hand, we found that, objects with relatively small FWHMs shows a tighter correlation between absorption depth (A) and {\Delta}m15, possibly a sign of higher degree of homogeneity. We also found that A/{\gamma} of Si II {\lambda}5972 has a strong correlation with {\Delta}m15, and more importantly, a relatively slow time evolution, making it a useful luminosity estimator even in the absence of phase information.
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High Energy Astrophysical Phenomena

X-ray Quasi-Periodic Oscillations in Active Galactic Nuclei and Their Implications for the Changing Look Phenomenon

Mouyuan Sun, Shuying Zhou, Jihong Liu et al. (+12 more)

X-ray timing of active galactic nuclei (AGN) provides a unique probe of gas accretion onto supermassive black holes (SMBHs). Quasi-periodic oscillations (QPOs), which trace gas dynamics in the strongly curved spacetime around SMBHs, are rare in AGN. These signals often are analogs of high-frequency QPOs occasionally seen in some black-hole X-ray binaries, and their scarcity in AGN can partly be attributed to the low frequencies expected for typical SMBH masses. Intriguingly, robust X-ray QPO detections in SMBH systems have so far been reported only in narrow-line Seyfert 1 galaxies (NLS1s) and tidal disruption events (TDEs). Here we report the discovery of a QPO candidate during the 2018 outburst of the changing-look AGN (CL-AGN) NGC 1566. Numerical simulations indicate that the disk epicyclic oscillations responsible for high-frequency QPOs are damped by magnetohydrodynamic turbulence unless the accretion flow is misaligned and/or eccentric. In TDEs, the stellar debris stream is naturally misaligned with the SMBH spin, while NLS1s may host misaligned disks due to their youth. Motivated by the QPO candidate in NGC 1566, we propose that CL-AGN accretion is also misaligned – potentially fueled by captured, free-falling broad-line region clouds. This model naturally explains why CL-AGN transition timescales are much shorter than the standard disk viscous timescale. This picture can be tested by searching for QPOs or quasi-periodic eruptions in other CL-AGN.
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All authors Mouyuan Sun, Shuying Zhou, Jihong Liu, Ning Jiang, Zhen-Yi Cai, Hai-Cheng Feng, Hengxiao Guo, Zhi-Xiang Zhang, Qinbo Han, Juan Li, Linyue Jiang, Yu-Jing Xu, Junfeng Wang, Jun-Xian Wang, Yongquan Xue

Solar and Stellar Astrophysics

Acceleration of relativistic protons in a solar wind perturbed by a coronal mass ejection

Ahmed Houeibib, Filippo Pantellini and Lea Griton

We investigated the impact of a coronal mass ejection (CME) on the transport and acceleration of relativistic protons in the solar wind using a coupled 3D magnetohydrodynamics (MHD) simulation and a test-particle approach. The CME is driven by a spheromak injected into a Parker solar wind at a heliocentric distance of 0.139 AU. We integrated the trajectories of 5 GeV protons, injected toward the CME from 3 AU, in the guiding-center approximation and scattered the particles in velocity space with a mean free path $\lambda_{\|}$. Our results show that the CME can increase the protons' energy by several gigaelectronvolts. The acceleration occurs while particles stream along the portion of a magnetic field line downstream of the quasi-perpendicular portion of the CME-driven shock. In our configuration, the maximum energy gain, which is on the order of a few percent per passage through the acceleration region, occurs when the shock approaches 0.3 AU. Large energy gains require multiple passes through the acceleration region, made possible by the combined action of the mirror force and pitch-angle scattering. The efficiency of the acceleration on timescales on the order of hours scales as $\lambda_{\|}^{-3/2}$. Energy spectra harden with decreasing parallel mean free path $\lambda_{\|}$.
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Instrumentation and Methods for Astrophysics

Tri-coupler geometries for achromatic nulling interferometry in the near-infrared

Harry-Dean Kenchington Goldsmith, Nemanja Jovanovic, Anusha Pai Asnodkar et al. (+4 more)

Astrophotonics is central to the next generation of astronomical instrumentation, enabling compact photonic integrated circuits for both ground-based observatories and future space missions. Beam combination for nulling interferometry suppresses starlight, revealing exoplanets and companions. Two-waveguide photonic combiners rely on symmetric evanescent, inherently chromatic, coupling to interfere light. A three-waveguide configuration, or tri-coupler, offers the potential for deeper, broader, and more stable achromatic nulls compared with two-waveguide approaches. This work compares the simulated performance of evanescent tri-couplers and a multimode interference coupler across the 1.5-1.8 micron band, evaluating exoplanet throughput, starlight attenuation, sensing characteristics, and estimations on fabrication tolerance. All three tri-couplers achieved >40dB attenuation over a 270nm bandwidth. Including component loss, the tapered tri-coupler has the highest total throughput, averaging 97%, whereas the standard tri-coupler began with an equivalent exoplanet throughput and fell to 50% at the band edges. The tapered tri-coupler was further redesigned to achieve a non-degenerate sensing state. The MMI, while limited to a starlight attenuation of 40dB by uncoupled light, showed the greatest tolerance to fabrication errors. Future designs aim to combine high exoplanet throughput, deep starlight attenuation, and non-degenerate sensing within a single integrated architecture. This work provides a simulation suite for three tri-couplers.
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All authors Harry-Dean Kenchington Goldsmith, Nemanja Jovanovic, Anusha Pai Asnodkar, Yoo Jung Kim, Ahmed Sanny, Pradip Gatkine, Michael P. Fitzgerald

High Energy Astrophysical Phenomena

Search for Gamma-ray emission from Abell 119 galaxy cluster using INTEGRAL/ISGRI, COMPTEL, and DAMPE data

Siddhant Manna and Shantanu Desai

We present a comprehensive search for non-thermal high-energy $\gamma$-ray emission from the nearby merging galaxy cluster Abell~119 ($z=0.044$) using archival observations spanning over seven decades in photon energy. Our analysis combines hard X-ray data from INTEGRAL/ISGRI (30–100~keV), MeV $\gamma$-ray observations from COMPTEL (0.75–30~MeV), and GeV–TeV data from the DArk Matter Particle Explorer (DAMPE; 3~GeV–1~TeV). No statistically significant emission is detected at the cluster position in any energy band. In the hard X-ray regime, we derive a $3\sigma$ upper limit of $F_{30-100\,\mathrm{keV}} \lesssim 8.5 \times 10^{-11}$~erg~cm$^{-2}$~s$^{-1}$ from ISGRI mosaic imaging. Reanalysis of archival COMPTEL data yields 95% confidence-level upper limits ranging from $\sim 9 \times 10^{-11}$ to $\sim 8 \times 10^{-10}$~erg~cm$^{-2}$~s$^{-1}$ across 0.75–30~MeV. In the GeV–TeV range, DAMPE \rthis{places upper limits on the} differential energy flux to $\sim 10^{-12}$–$10^{-10}$~erg~cm$^{-2}$~s$^{-1}$ (95% confidence level). These results provide independent multi-band constraints on the reported GeV excess from recent Fermi-LAT studies. While our DAMPE limits do not exclude the flux levels claimed in those analyses, the absence of confirmation across keV–MeV–GeV bands indicates that any non-thermal emission from Abell~119 remains tentative.
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Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

Transition of Magnetic Reconnection Regimes in Partially Ionized Plasmas

Liang Wang, Chuanfei Dong, Yi-Min Huang et al. (+3 more)

Magnetic reconnection in partially ionized plasmas plays a crucial role in a wide range of solar, astrophysical, and laboratory environments. While reconnection in such plasmas is commonly characterized by the ion-neutral coupling strength and the ionization fraction $\chi=n_{i}/(n_{i}+n_{n})$, most previous studies have focused primarily on the former. A systematic exploration of the ionization fraction, particularly in combination with ion-neutral coupling, is still lacking. This study presents the first systematic scan of the two-dimensional parameter space defined by ion-neutral collisionality and ionization fraction, enabling investigation of the transition from strongly coupled reconnection to faster, decoupled reconnection. To achieve this, we employ a new three-fluid, five-moment numerical model that treats electrons, ions, and neutrals as separate species on an equal footing. We find that in the strongly coupled regime, the reconnection rate is consistent with a $\chi^{1/4}$ scaling. As collisionality decreases, the system transitions to a fast, ionization-independent regime. On the other hand, in the weakly coupled and fast-reconnection regimes, the current sheet approaches an ion-inertial-scale thickness rather than the expanded hybrid scale $d_{i}\chi^{-1/2}$ predicted by fully coupled analytic fluid theories. The identified critical thickness and the resulting onset of fast reconnection agree reasonably well with recent fully kinetic simulations and laboratory experiments. In addition, we show that, over a wide range of coupling strengths, the ion outflow velocities remain Alfvénic, scaling with the appropriate ion or hybrid Alfvén speed, while the hybrid outflow velocity scales as $\chi^{1/2}$ when normalized by ion Alfvén speed.
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All authors Liang Wang, Chuanfei Dong, Yi-Min Huang, Yue Yuan, Xinmin Li, Yang Zhang

High Energy Astrophysical Phenomena

The environmental dependence of mid-IR luminous dusty Supernovae

Lin Xiao, Zeyue Peng, Lluis Galbany et al. (+10 more)

Using the Spitzer and WISE images, we discovered 42 mid-IR luminous dusty supernovae with local integral-field spectroscopy data. The observed mid-IR emission indicates the presence of newly formed dust, or pre-existing dust heated by the radiation from the supernovae or circumstellar medium interactions. We carried out a systematic analysis of the supernova host environments and their dust properties, for understanding the dust-veiled exploding stars, and whether such an intense dust production process is associated with their local environments. We find that dusty supernovae prefer the locations with higher EW(H{\alpha}), lower metallicity, and heavier host extinctions compared to typical SN types, and they show the same increasing sequence in the values of EW(H{\alpha}) and oxygen abundance from hydrogen-rich, type IIn and hydrogen-poor dusty supernovae. These differences in environmental properties of different dusty SN types indicate the diversity of their progenitors. We also found that one marginal correlation is a negative correlation between the SN dust mass and star formation rate. This means that SNe would be more mid-IR luminous and more dust-rich at the region with lower star formation rate. However, the SN dust mass show no correlation with the metallicity and the host extinction, which were thought to be key factors affecting the mass-loss history of progenitors and the CSM environment of SNe. Therefore, the dust formation process in SNe might be insensitive to metallicity and the dust condition of their host environments.
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All authors Lin Xiao, Zeyue Peng, Lluis Galbany, Tamas Szalai, Ori D. Fox, Lei Hu, Maokai Hu, Thallis Pessi, Yi Yang, Takashi J. Moriya, Zhanwen Han, Xiaofeng Wang, Shengyu Yan

Earth and Planetary Astrophysics

Active Learning for Planet Habitability Classification under Extreme Class Imbalance

R. I. El-Kholy and Z. M. Hayman

The increasing size and heterogeneity of exoplanet catalogs have made systematic habitability assessment challenging, particularly given the extreme scarcity of potentially habitable planets and the evolving nature of their labels. In this study, we explore the use of pool-based active learning to improve the efficiency of habitability classification under realistic observational constraints. We construct a unified dataset from the Habitable World Catalog and the NASA Exoplanet Archive and formulate habitability assessment as a binary classification problem. A supervised baseline based on gradient-boosted decision trees is established and optimized for recall in order to prioritize the identification of rare potentially habitable planets. This model is then embedded within an active learning framework, where uncertainty-based margin sampling is compared against random querying across multiple runs and labeling budgets. We find that active learning substantially reduces the number of labeled instances required to approach supervised performance, demonstrating clear gains in label efficiency. To connect these results to a practical astronomical use case, we aggregate predictions from independently trained active-learning models into an ensemble and use the resulting mean probabilities and uncertainties to rank planets originally labeled as non-habitable. This procedure identifies a single robust candidate for further study, illustrating how active learning can support conservative, uncertainty-aware prioritization of follow-up targets rather than speculative reclassification. Our results indicate that active learning provides a principled framework for guiding habitability studies in data regimes characterized by label imbalance, incomplete information, and limited observational resources.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Light rings, gravitational lensing, and ISCOs of exotic compact objects in Einstein-scalar-Maxwell theories

Antonio De Felice and Shinji Tsujikawa

In Einstein-scalar-Maxwell theories with a coupling between the scalar field $\phi$ and the electromagnetic field strength $F$ of the form $\mu(\phi) F$, we investigate the existence of exotic compact objects (ECOs) and their observational signatures in photon and massive-particle dynamics. For $\mu(\phi)$ diverging at the origin while all physical quantities remain finite, we demonstrate the existence of electrically charged ECOs with a shell-like structure whose density peaks at an intermediate radius. We compute their mass and radius, together with the scalar and vector field profiles, on a static and spherically symmetric background. We then examine the existence of light rings and place bounds on a model parameter by requiring the absence of a linearly stable light ring. Under this condition, photon echoes from ECOs are absent. We also compute the gravitational-lensing deflection angle and show that it attains a maximum for an impact parameter of the same order as the ECO radius. Finally, we study the parameter space in which innermost stable circular orbits of massive particles exist.
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High Energy Astrophysical Phenomena

Realistic Equations of State Informing Neutron Star Post-Merger Gravitational-Wave Frequencies

Spencer J. Magnall, Nilaksha Barman, Debarati Chatterjee et al. (+2 more)

Binary neutron star mergers are thought to produce hot, rapidly rotating neutron stars with masses that can far exceed their Tolman-Oppenheimer-Volkoff mass. The gravitational-wave emission from such remnants provides a unique opportunity to measure the nuclear equation of state at densities and temperatures not available to terrestrial experiments. Current detector design is informed by gravitational-wave signals from general relativistic hydrodynamics simulations of neutron star mergers, typically with hybrid thermal treatments for the equation of state, where a cold equation of state is modified by adding a thermal component. We use realistic equations of state based on the relativistic mean field model with consistent treatment of thermal effects to compute the distribution of expected peak gravitational-wave frequencies. Marginalising over equation of state and progenitor neutron star masses, we show the peak frequency of emission ranges from $\sim2.5$ to 4 kHz. The width of this distribution suggests the need for broadband observatories with kHz sensitivity, and calls into question some of the so-called post-merger optimised configurations. We show the proposed KAGRA high-frequency design is well-suited to measuring post-merger remnants when compared to the KAGRA broadband design.
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All authors Spencer J. Magnall, Nilaksha Barman, Debarati Chatterjee, Paul D. Lasky, Simon Goode

Solar and Stellar Astrophysics

The Split Janus-faced Sun: Magnetic Rhythm and Duality in the Solar Cycle

Weiqi Chen, Kejun Li and Jingchen Xu

The solar cycle - most notably characterized by its sunspot activity patterns - serves as a cornerstone of heliospheric physics. This research uncovers a fundamental magnetic dichotomy in the Sun's full-disk field, identifying two functionally separate populations: the Strong-Field Group (SG) and Weak-Field Group (WG). The solar cycle exhibits a dual nature, much like Janus, with the SG and WG operating in opposing phases regardless of low or high latitudes. The SG-dominated cycle represents one facet of this duality and is visually prominent at the solar surface. It is well-established that this component synchronizes with the sunspot cycle at low latitudes but operates in anti-phase at high latitudes. In contrast, the WG-driven cycle acts as its hidden counterpart, functioning in opposition to the SG at both high and low latitudes – a behavior that had not been identified until now. Influenced by these magnetic field groups, this dual nature permeates the entire solar atmosphere, revealing that the full-disk solar activity is globally modulated by the Janus cycle.
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High Energy Astrophysical Phenomena

Superposition model for energy reconstruction and mass identification in cosmic ray spectra

Hu Liu, Fanping Li, J. Zhao et al. (+3 more)

The "knee" of cosmic ray spectra may reflect the maximum energy accelerated by galactic cosmic ray sources or the limit of the galaxy's ability to bind cosmic rays. Measurements of individual energy spectra are a crucial tool to understand the origin of the knee. Energy reconstruction and composition identification are foundations of the individual energy spectra measurements. One of the main scientific goals of Large High Altitude Air Shower Observatory (LHAASO) is measuring the cosmic ray energy spectra and composition from ~10 TeV to ~EeV. In this work, a novel method for reconstructing energy and logarithm mass (lnA) based on a superposition model is introduced. Energy and lnA are reconstructed using two universal, composition- and energy-independent calibration lines. For zenith angle below 40 degree, the energy and lnA biases are within +-5% and +-0.3, respectively, across all compositions. The method uses particle densities-measured by LHAASO's electromagnetic and muon detectors at a fixed distance from the shower axis-rather than integrated particle counts in annular bands. The density-based approach improves resolution for both energy and lnA, especially for heavy nuclei. The resulting energy resolution ranges from below 5% to ~15% above 1 PeV, the best mass resolution for iron achieved is below 25% above 10 PeV. The hadronic model dependencies of energy and lnA are also reported. These dependencies scale with lg(E/A) and are nearly independent of primary composition.
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All authors Hu Liu, Fanping Li, J. Zhao, L. Y. Wang, Zhe Li, S. Z. Chen

Solar and Stellar Astrophysics

Can the dust eclipses in WR 104 provide constraints on the system's inclination?

Noel D. Richardson, Ryan M. T. White, Anthony J. Fabrega et al. (+8 more)

When two massive stars orbit each other, their winds create a shock cone. In some cases, an evolved, carbon-rich Wolf-Rayet (WR) star's wind collides with that of an orbiting OB star, condensing into dust downstream. This dust is then seen as large spiral structures that eventually move into the interstellar medium. Among these colliding wind binaries, the archetype system WR104 has become an enigma. Aperture masking interferometry with Keck revealed an evolving face-on dust spiral with multiple rungs of dust visible from years of observations. In contrast to direct imagery, recent spectroscopic results implied that the orbit must have an inclination quite different from the face-on geometry. We examined the ASAS and ASAS-SN photometry to put further constraints on the geometry of the orbit. Through a phase-binning of the light curve, we find that the recent g-band light curve is brightest at a time when the OB star is in front of the WR star in our line of sight, with the lowest flux happening at the opposite conjunction. We fit the light curve with an illustrative model for scattering eclipses, which then allows us to infer an inclination of the system of $(41.8^{+13.0}_{-14.9})^\circ$. This inclination agrees with the recent spectroscopic orbit and presents challenges to previous interpretations of high-angular resolution images of the dust plume. We provide a qualitative geometric model for the dust plume to reconcile these results and show how WR104 can provide a means to study the properties of WR dust in detail.
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All authors Noel D. Richardson, Ryan M. T. White, Anthony J. Fabrega, Emma P. Lieb, André-Nicolas Chené, Peter G. Tuthill, John D. Monnier, Grant M. Hill, Peredur M. Williams, Anthony F. J. Moffat, Gerd Weigelt

Earth and Planetary Astrophysics

Contemporaneous Optical and Near-Infrared Observations of the Interstellar Comet 3I/ATLAS Pre- and Post-Perihelion

Kyle Medler, Willem B. Hoogendam, Christopher Ashall et al. (+12 more)

Interstellar objects provide a unique view into the formation of other star systems. Here we present spectroscopic observations of the recently discovered interstellar object 3I/ATLAS between a heliocentric distance of $3.7$ to $1.8$~au on either side of its travels through perihelion. We obtained several observations with the Keck-I/LRIS, Keck-II/NIRES, Gemini/GMOS, and UH88/SNIFS spectrographs, covering a wavelength range of $0.3 - 2.5~\mathrm{\mu m}$. We report the continued emission of both Ni and CN, along with post-perihelion detections of Fe and a weak detection of $\mathrm{C_3}$. We determine the spectral slope across optical and NIR wavelengths and find a positive spectral slope in the optical, with values ranging from $\sim 21 - 27\%$ in the blue regions ($0.4 - 0.55~\mathrm{\mu m}$) to $\sim 6 - 10\%$ in the red ($0.65 - 0.9~\mathrm{\mu m}$) regions. In contrast, the NIR showed a negative spectral slope of $\sim -0.9 \%$ between $0.9 - 1.5~\mathrm{\mu m}$ and $\sim -2.3\%$ between $1.9 - 2.5~\mathrm{\mu m}$. 3I/ATLAS shows a clear turnover in its spectral shape at $\sim 1.1~\mathrm{\mu m}$, corresponding to scattered light from the dusty coma. Finally, in the NIR, we do not find an increase in the depth of the water features identified in an earlier NIR observation of 3I/ATLAS. Our observations of 3I/ATLAS in the NIR show a similar shape to the NIR spectrum of 2I/Borisov as it approached perihelion.
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All authors Kyle Medler, Willem B. Hoogendam, Christopher Ashall, Bin Yang, James J. Wray, Benjamin J. Shappee, Karen J. Meech, Michael A. Tucker, Katie Auchettl, Dhvanil D. Desai, Jason T. Hinkle, Andrew M. Hoffman, Mark E. Huber, David O. Jones, Ruining Zhao

Thursday 26 February

Instrumentation and Methods for Astrophysics

Updates to the SBC Dark Rate Monitor

Alyssa M. Guzman and Roberto J. Avila

The Solar Blind Channel (SBC) typically exhibits elevated dark rate levels at temperatures exceeding 25.5{\deg}C. However, instances of rapid dark rate increases have been observed before the detector reaches this threshold. To more closely monitor these anomalies, the existing calibration program was expanded, scheduling 24 total orbits per year distributed across eight visits for Cycle 31 and beyond. With enhanced data availability, we provide further updates and analysis of the dark rate in this report. We investigated the influence of the South Atlantic Anomaly (SAA) passage on dark rates. Using orbital parameters from SPT products, we plotted the Hubble Space Telescope's (HST) locations during dark exposures relative to the SAA. Comparison of HST paths during elevated and stable dark rate visits revealed no significant correlation between proximity to the SAA boundary and dark rate increases. Furthermore, we examined the stability of dark rates in the vicinity of the SBC-LODARK aperture within the detector. Our findings confirm that this region maintains consistently low dark rates across visits, unaffected by the elevated dark current observed elsewhere in the detector. The SBC-LODARK aperture therefore continues to be recommended for small sources.
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Earth and Planetary Astrophysics · Cross-listed from physics.ao-ph

Monte Carlo Simulations of Secondary Cosmic-Ray Variations in Atmospheric Electric Fields : Implications for Long Duration Electron and Gamma-ray Emissions from Thunderclouds

Harufumi Tsuchiya

Monte Carlo simulations were conducted using the Particle and Heavy Ion Transport code System (PHITS) to investigate the role of secondary cosmic rays in the generation of long-duration bursts from thunderclouds and to clarify the conditions of the electric field region responsible for particle acceleration. The simulations utilized realistic secondary cosmic-ray spectra, including gamma rays, electrons, positrons, and muons, as input. The simulation results indicate that gamma rays provide the dominant supply of seed electrons for long-duration bursts, regardless of the geometry or strength of the electric field region. They also reveal the structure and strength of the electric field region required to produce gamma rays exceeding several tens of MeV, which have so far been detected only by high-altitude observations. Furthermore, the fluxes of long-duration bursts estimated from the simulation results were compared with observational data to constrain the properties of the electric field region. In particular, the comparison with measurements at Yangbajing, located at an altitude of 4.3~km, helps narrow down the possible range of electric field strengths and configurations.
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Instrumentation and Methods for Astrophysics

Evolution of Sink Pixels in ACS/WFC and Connection to Charge Transfer Efficiency

Alyssa M. Guzman and Jenna E. Ryon

In our study spanning 2015-2021, we examined sink pixels (SPs) in the Advanced Camera for Surveys Wide Field Channel (ACS/WFC) using dark and SP reference files. SPs are pixels with values $\le$ $-10$ electrons below the local background of LED-flashed short (0.5 sec) darks, that collect and trap significant charge during readout. Analyzing seven years of short dark data, we assessed SP creation and persistence. In this time frame, 5,430 SPs were created in WFC1 and 5,649 SPs in WFC2, with creation rates of about 2.15 pixels/day and 2.23 pixels/day, respectively. These calculations allowed us to detect 44,068 SPs, not including SP trails, in the detector by the end of 2021, constituting approximately 0.25% of the science frame. We found it is rare for SPs to return to a typical, non-negative pixel value. We observed more flagged SPs near the serial register than the chip gap. Skewed histograms for the $y$-position distribution, exhibiting a local peak in the distribution of SPs very near the chip gap described as the “bounce-back" effect, were evident for both WFC1 and WFC2, while the $x$-position distribution remained uniform. Examining CTE-corrected images from 2015, 2018, and 2021 revealed consistent trends, with the gradient getting steeper over time due to CTE losses, which is also worse for pixels further from the serial register. We simulated the CTE-impacted readout of a short dark exposure with uniformly distributed SPs, to assess how CTE influences SP detectability. While the gradient effect was reproduced, the local peak near the chip gap was not. Filling in of SPs by CTE charge-release during readout appears to explain most of the gradient in the $y$-position density of SPs.
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Instrumentation and Methods for Astrophysics

Extending Ground-Based Gravitational-Wave Sensitivity to 5 Hz

Amit Singh Ubhi, Lari Koponen, Jiri Smetana et al. (+11 more)

Extending the sensitivity of terrestrial gravitational-wave detectors below 20 Hz is a long-standing challenge, limited by ground motion and inertial sensing noise. In this letter, we demonstrate ultra-high-vacuum compatible inertial isolation and position sensing technologies that achieve active platform stabilization down to 10 mHz. Our laser position sensors reach a sub-pm/$\sqrt{\rm Hz}$ sensitivity above 10 mHz, independent of the input light polarization, representing a 100-fold improvement over the current LIGO position sensors. In addition, our inertial sensors provide at least a factor of 5 improvement in low-frequency sensitivity compared to state-of-the-art commercial seismometers. We integrate these technologies into a LIGO-like interferometer model and predict a low-frequency sensitivity improvement of up to an order of magnitude at 10 Hz, with enhanced linearity and calibration stability. This extension increases the detection horizon for intermediate-mass black hole binaries of mass $10^3 M_\odot$ by a factor of 3. Our results provide the first experimental demonstration of a practical pathway to sub-10 Hz operation of terrestrial gravitational-wave detectors and establish key technologies for next-generation observatories such as Cosmic Explorer and Einstein Telescope.
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All authors Amit Singh Ubhi, Lari Koponen, Jiri Smetana, Yulin Xia, Haixing Miao, Emilia Chick, John Bryant, Geraint Pratten, Teng Zhang, Richard Mittleman, Peter Fritschel, Alan V. Cumming, Giles Hammond, Denis Martynov

Astrophysics of Galaxies

ALMA High-J CO Spectroscopy of High-Redshift Galaxies. I. An Archive-based Catalog of CO Spectral Line Energy Distributions

Ken-ichi Tadaki

High-J CO emission in high-redshift galaxies has been studied primarily on an individual-source basis, limiting our ability to draw population-level conclusions about molecular-gas excitation. To address this limitation, we present a catalog of CO spectroscopy based on archival data from the Atacama Large Millimeter/submillimeter Array (ALMA) for a sample of galaxies at z > 3, focusing on high-J transitions (Jup = 9-17). Combining ALMA archival data with published measurements, we compile CO spectral line energy distributions (SLEDs) for 38 well-studied systems spanning z = 3.1-6.9, including 5 hot dust-obscured galaxies (Hot DOGs), 17 submillimeter-bright galaxies (SMGs), and 16 optically selected quasars. The class-median SLEDs rise steeply to Jup = 9 and remain approximately flat through Jup ~ 11-12. SMGs show relatively stronger low- to mid-J emission relative to CO J=9-8, while Hot DOGs exhibit tentative evidence for higher excitation. Comparison with simple excitation models suggests that X-ray dominated region (XDR) heating or dense, shock-heated gas can account for the extended high-J CO SLEDs. A tentative anti-correlation between the CO(9-8)-to-infrared luminosity ratio and excitation among the dusty galaxy populations suggests that the enhanced excitation in Hot DOGs may be driven by XDR heating from obscured AGN activity rather than by shocks. Because the sample is restricted to sources with detected high-J CO lines, it is biased toward highly excited systems. It nonetheless provides a reference for designing future systematic surveys of high-J CO emission with a statistically complete or flux-limited sample.
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High Energy Astrophysical Phenomena

Transient X-ray Sources as Extremely Eccentric Mass-Transfer Binaries with Compact Companions

Jonathan I. Katz and Michael A. Nowak

It has long been suggested that X-ray transients are produced at periastron of stellar-compact object binaries with eccentric orbits. Recoil of matter evaporated from the star by X-rays from matter transferred at periastron increases the orbital semi-major axis and eccentricity. After periastrons the object would be a transient X-ray source, a Galactic analogue of a tidal disruption event (TDE), but recurrent with a gradually increasing period rather than catastrophic.
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Cosmology and Nongalactic Astrophysics

nanoCMB: A minimal CMB power spectrum calculator in Python

Adam Moss

We present nanoCMB, a minimal but accurate calculator for the unlensed CMB temperature and polarisation angular power spectra ($C_\ell^{TT}$, $C_\ell^{EE}$, $C_\ell^{TE}$) of flat $\Lambda$CDM cosmologies. Written in $\sim$1400 lines of readable Python, the code implements the full line-of-sight integration method: RECFAST recombination, coupled Einstein–Boltzmann perturbation equations in synchronous gauge with a tight-coupling approximation, precomputed spherical Bessel function tables, and optimally constructed non-uniform grids in wavenumber and conformal time. Despite its brevity, nanoCMB achieves sub-percent agreement with CAMB across the multipole range $2 \le \ell \le 2500$, running in $\sim$10 seconds on a modern laptop. The entire calculation lives in a single, easily modifiable Python script, designed as a pedagogical bridge between textbook treatments and research-level Boltzmann solvers, with every approximation and numerical choice made explicit. We describe the physics, equations, and computational methods in detail, with code snippets illustrating each stage of the calculation. The code is publicly available at https://github.com/adammoss/nanoCMB.
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Instrumentation and Methods for Astrophysics

OmegaNeuron: Applying GravitySpy Similarity Methods to the Search for LIGO Glitch Witnesses

Bri Aleman and Derek Davis

Gravitational-wave (GW) astronomy has advanced our understanding of compact mergers through instruments like the Laser Interferometer Gravitational-Wave Observatory (LIGO). However, the extreme sensitivity required for these detections makes the instruments susceptible to short-duration transient noise, or glitches, which obscure GW data. Current tools such as Omega Scan and GravitySpy assist in identifying and classifying such noise, but are limited by manual inspection or dependence on large training sets. To address these challenges, we present OmegaNeuron, a machine-learning tool that integrates GravitySpy's image similarity methods with Omega Scan's transient analysis to automate the identification of auxiliary channels that witness glitches. Applied to multiple glitch examples, OmegaNeuron consistently highlighted plausible witness channels and showed strong agreement with existing correlation tools, while providing clearer ranking through a quantitative similarity metric. Integrated into the gwdetchar package, OmegaNeuron enables faster analysis that improves glitch witness identification, enhancing both detector sensitivity and the reliability of gravitational-wave observations.
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High Energy Astrophysical Phenomena

Modeling individual nearby radio galaxies as ultra-high-energy cosmic-ray accelerators

Andressa Colaço, Gabriel Azeredo, Isadora Parillo et al. (+2 more)

Nearby radio galaxies are among the most promising candidates for the acceleration of ultra-high-energy cosmic rays (UHECRs). In this work, we develop a physically motivated, source-resolved framework to quantify the contribution of the three nearest FR-I radio galaxies$-$Centaurus A, Virgo A, and Fornax A to the UHECR flux measured by the Pierre Auger Observatory. Acceleration spectra derived from detailed jet-acceleration models are combined with numerical simulations of extragalactic propagation, while the more distant radio-galaxy population is treated as a continuous background. By fitting exclusively the measured UHECR energy spectrum, we determine the relative contribution of each source and constrain the fraction of jet power converted into UHECR luminosity. We find that a small number of nearby radio galaxies can account for the highest-energy UHECR flux with acceleration efficiencies of order $10^{-3}-10^{-2}$, while the background contribution remains subdominant. The resulting scenarios yield mass-composition trends broadly consistent with observations and predict distinct levels of secondary neutrino fluxes. These results demonstrate that physically grounded, source-specific modeling of nearby radio galaxies provides a viable and predictive explanation for the origin of the highest-energy cosmic rays.
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All authors Andressa Colaço, Gabriel Azeredo, Isadora Parillo, Cainã de Oliveira, Vitor de Souza

Astrophysics of Galaxies

Starbursts hiding in the main sequence: a pathway toward quenching?

Florent Renaud, Katarina Kraljic, Jonathan Freundlich et al. (+10 more)

Star-forming galaxies spend most of their lifetimes on the star-forming main sequence, which establishes a tight empirical and statistical relation between stellar mass and star-formation rate. Occasional episodes of rapid star formation can push them temporarily above this sequence, turning them into starbursts. Yet some galaxies display starburst-like traits – rapid, dense, and compact star formation – while still remaining within the scatter of the main sequence. These "starbursts in the main sequence" (SBMSs) reveal the complexity and diversity of star formation modes, making them crucial for understanding how galaxies evolve and transition between different regimes. In this paper, we identify SBMSs in the cosmological simulation NewHorizon and follow their evolution across time to uncover their physical origins and the role of this special regime in shaping galaxy evolution. We explain the existence of SBMSs by a comparatively earlier assembly of their stellar mass, driven in particular by more frequent and repeated mergers as the other galaxies, as well as exceptionally productive starburst events triggered by these interactions. As a result, this regime appears preferentially – though not exclusively – in the most massive galaxies. The SBMS behavior is not continuous within individual galaxies but instead arises intermittently as a short-lived (~ 30 Myr) evolutionary mode. Nevertheless, such SBMS episodes exist throughout cosmic time across the galaxy population... [abridged]
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All authors Florent Renaud, Katarina Kraljic, Jonathan Freundlich, Benjamin Magnelli, Matthieu Béthermin, Cédric Accard, Diana Ismail, Emanuele Daddi, David Elbaz, Laure Ciesla, Gareth Martin, Yohan Dubois, Sébastien Peirani

High Energy Astrophysical Phenomena

The role of Bethe-Heitler pair production in reconnection-driven flares in M87*

Maria Petropoulou, Despina Karavola and Lorenzo Sironi

Rapid TeV flares have been observed from the core of the active galaxy M87. These have been attributed to inverse Compton scattering of disk photons by electrons and positrons accelerated in transient reconnection layers formed in baryon-poor regions of the magnetosphere of the central black hole, M87*. It was previously shown that even a small number of protons accelerated in the same layers can lead to bright GeV proton-synchrotron flares, if protons receive $\gtrsim20\%$ of the dissipated power for reconnecting fields of $\sim$100 G. We aim to investigate the role of Bethe-Heitler pair production in the emission of reconnection-driven flares from M87* in this physical regime. We perform numerical calculations that incorporate inelastic collisions between relativistic protons and photons, as well as photon-photon pair production, and compute the non-thermal radiation from the layer. The numerical calculations are also supported by analytical estimates. We find that disk photons act as targets for Bethe-Heitler pair production. The resulting pairs emit very high-energy synchrotron photons ($\gtrsim$0.1 TeV), which are subsequently attenuated by the disk photon field, leading to further pair production. The synchrotron emission of these secondary pairs produces soft photons, as part of an electromagnetic cascade, enhancing pion production and photon-photon attenuation down to tens-of-GeV energies.
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High Energy Astrophysical Phenomena

The PLUTO Code on GPUs: Offloading Lagrangian Particle Methods

Alessio Suriano, Stefano Truzzi, Agnese Costa et al. (+5 more)

The Lagrangian Particles (LP) module of the PLUTO code offers a powerful simulation tool to predict the non-thermal emission produced by shock accelerated particles in large-scale relativistic magnetized astrophysics flows. The LPs represent ensembles of relativistic particles with a given energy distribution which is updated by solving the relativistic cosmic ray transport equation. The approach consistently includes the effects of adiabatic expansion, synchrotron and inverse Compton emission. The large scale nature of such systems creates boundless computational demand which can only be satisfied by targeting modern computing hardware such as Graphic Processing Units (GPUs). In this work we presents the GPU-compatible C++ re-design of the LP module, that, by means of the programming model OpenACC and the Message Passing Interface library, is capable of targeting both single commercial GPUs as well as multi-node (pre-)exascale computing facilities. The code has been benchmarked up to 28672 parallel CPUs cores and 1024 parallel GPUs demonstrating $\sim(80-90)\%$ weak scaling parallel efficiency and good strong scaling capabilities. Our results demonstrated a speedup of $6$ times when solving that same benchmark test with 128 full GPU nodes (4GPUs per node) against the same amount of full high-end CPU nodes (112 cores per node). Furthermore, we conducted a code verification by comparing its prediction to corresponding analytical solutions for two test cases. We note that this work is part of broader project that aims at developing gPLUTO, the novel and revised GPU-ready implementation of its legacy.
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All authors Alessio Suriano, Stefano Truzzi, Agnese Costa, Marco Rossazza, Nitin Shukla, Andrea Mignone, Vittoria Berta, Claudio Zanni

High Energy Astrophysical Phenomena

Survival Analysis of Intermediate-Mass Black Holes in Dense Star Clusters

Miguel A.S. Martinez, Elena González Prieto and Frederic A. Rasio

Recently, an intermediate-mass black hole (IMBH) candidate was announced in the Galactic globular cluster Omega Centauri. IMBHs at the lower end of the traditional mass range have also been detected through gravitational-wave transients, though their formation and subsequent growth linking the two mass scales remains a mystery. One way IMBHs may be produced is through the collapse of very massive stars produced by stellar collisions in dense stellar environments. However, IMBHs may be ejected from such environments by either dynamical recoil from binary-single scattering or gravitational-wave recoil following the merger of two black holes. We conduct Newtonian and post-Newtonian binary-single scattering experiments to study dynamical ejection in greater detail. We obtain fits to the probabilities for dynamical ejection, gravitational wave capture, and per-encounter hardening as a function of the binary mass ratio and hardness with respect to its environment. We borrow techniques from survival analysis (commonly used in studies of medicine, epidemiology, engineering, etc.) to develop a model to calculate the probability of IMBH binary ejection vs in-cluster merger. We confirm that the dynamical ejection probability strongly depends on both the mass ratio of the IMBH compared to other BHs in its environment and on the environment's velocity dispersion. We estimate that for a typical Milky Way globular cluster, IMBHs with mass $\lesssim10^3\,\mathrm{M}_\odot$ are unlikely to be retained until the present. Our results also suggest that IMBH mergers with $q\lesssim0.2$ may be detectable at higher redshifts with future gravitational wave instruments such as the Einstein Telescope and Cosmic Explorer.
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