Astrophysics of Galaxies
A study of the Physical Properties and Star Formation Activity of a Large Sample of Molecular Clouds: I Distances
Juan Mei, Min Fang, Miaomiao Zhang et al. (+8 more)
Accurate distances to molecular clouds are crucial for determining their physical properties, understanding
star formation, and tracing
Galactic spiral structure. A number of 103,517 molecular clouds has been identified by the DBSCAN
algorithm in the MWISP Phase I CO survey (l = 9.75-229.75 deg, |b| <= 5.25 deg), most of which lack reliable distances. In this work, we propose three independent methods, all of which match the molecular cloud's velocity-integrated intensity maps of 12CO lines from the MWISP with the three-dimensional
dust extinction maps derived from
Gaia, Pan-STARRS 1, and 2MASS, to determine molecular cloud distances. We present a catalog of 1,573 molecular clouds with robust distances ranging from approximately 150 pc to 3000 pc, 90 percent of which are measured for the first time, with typical statistical and systematic uncertainties of approximately 20% and 10%, respectively. We also derive their physical properties, such as their mass and sizes. This publicly available catalog of molecular clouds with distances provides a foundation for testing molecular cloud scaling relations and probing how cloud conditions influence
star formation across diverse
Galactic environments.
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All authors Juan Mei, Min Fang, Miaomiao Zhang, Qing-Zeng Yan, Lixia Yuan, Xuepeng Chen, Zhiwei Chen, Yang Su, Shiyu Zhang, Zhibo Jiang, Ji Yang
High Energy Astrophysical Phenomena
Locating the Production Sites of High-Energy Neutrinos in Blazar Jets
Rui Xue, Yoshiyuki Inoue, Ze-Rui Wang et al. (+2 more)
The production sites of high-energy
neutrinos in blazar jets remain poorly constrained. In this work, we investigate the physical conditions required for efficient
neutrino production by using
radio-constrained jet properties to evaluate the radial
evolution of the external-to-
magnetic energy density ratio (Compton dominance $Y$). We identify $Y \gg 1$ as the key physical condition for efficient
neutrino production, as it simultaneously enhances photohadronic interactions and suppresses synchrotron radiation from secondary pairs, thereby avoiding an excess of hard X-ray emission. We find that such large values of $Y$ are most readily achieved near or within the broad-line region. This large-$Y$ condition is generally incompatible with reproducing the observed broadband spectral energy distribution within a single emission region, naturally indicating that the
neutrino-emitting region is physically distinct from the dominant electromagnetic emission zone. We further show that such a scenario can be realized either if the jet completes its acceleration within sub-parsec scales or if the bulk Lorentz factor is intrinsically large, both of which appear uncommon based on current observations. These results offer a physically motivated framework for identifying
neutrino production sites, provide a natural explanation for the rarity of blazar–
neutrino associations, and underscore the importance of constraining jet property at sub-parsec scales in the search for
neutrino-emitting blazars.
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All authors Rui Xue, Yoshiyuki Inoue, Ze-Rui Wang, Neng-Hui Liao, Dingrong Xiong
Instrumentation and Methods for Astrophysics
Polarized lines of the second solar spectrum (SrI, SrII, CaI, BaII) observed at the Pic du Midi Turret Dome spectropolarimeter with the slit orthogonal to the limb
Jean-Marie Malherbe
The second
solar spectrum is the spectrum of the Stokes parameter Q (linear polarization) close to the
solar limb. It differs significantly of the usual intensity spectrum (Stokes parameter I). The second
solar spectrum contains in the blue just a few polarized lines with Q/I of about 1% (such as CaI, SrI, SrII, BaII, most lines exhibit much weaker polarization. This paper presents new processing of observations made in 2004-2006 with the Pic du Midi Turret Dome spectropolarimeter, which are of strong interest for weak and turbulent unresolved
magnetic field measurements in the quiet Sun, through the interpretation of the Hanle effect. As the slit was orthogonal to the limb, the polarization rate Q/I is determined precisely and continuously up to 80” distance of the limb.
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Astrophysics of Galaxies
Radio Continuum Emission from Evolving Star-Forming Galaxies – I. Correlations Involving the Total Synchrotron Luminosity
Sukanta Ghosh, Luke Chamandy, Charles Jose et al. (+3 more)
Synchrotron radiation dominates the continuum emission of
star-forming
galaxies in the frequency range from a few $\rm MHz$ to about $30\,\rm{GHz}$. We model the total synchrotron emission of a large population of evolving
star-forming
galaxies using the semi-analytic
galaxy formation model GALFORM combined with the dynamo simulation code MAGNETIZER. Assuming local energy equipartition between
cosmic rays and
magnetic fields, we calculate the specific synchrotron luminosity $L_{\nu}$ for each simulated
galaxy at various frequencies and find strong positive correlations between $L_{\nu}$ and both the
star formation rate ($\rm SFR$) and characteristic
galaxy rotation speed $V_{\rm rot}$ for
redshifts up to $z\simeq 3$. At low
redshifts, the turbulent
magnetic field is found to dominate in the synchrotron luminosity, but the contribution of the large-scale
magnetic field increases with
redshift and becomes important for $z\gtrsim 1$. The correlation between $L_{\nu}$ and $\rm SFR$ arises from the tight correlation between the disc gas mass $M_{\rm gas}$ and $\rm SFR$, and the correlation between $L_{\nu}$ and $V_{\rm rot}$ is additionally a consequence of the
stellar mass Tully–Fisher relation for main-sequence
galaxies. At low
redshifts, the model predictions and observational data compiled for this work show remarkable agreement, but a discrepancy arises at higher
redshifts, where modelled $\rm SFR$ values are systematically smaller than those previously inferred from observations. These theoretical models will aid the interpretation of next-generation
radio surveys with the Square Kilometre Array and other
telescopes.
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All authors Sukanta Ghosh, Luke Chamandy, Charles Jose, Anvar Shukurov, Luiz Felippe S. Rodrigues, Fatemeh Tabatabaei
Astrophysics of Galaxies
Accurate inner stellar density slopes from projected surface densities in galaxies
Jorge Sanchez Almeida
The inner slope of the three-dimensional
stellar density in
dwarf galaxies (rho'[0]) is a sensitive probe of possible departures from the collisionless cold dark matter (CDM) paradigm, since cored
stellar distributions (rho'[0]=0) cannot easily reside within the cuspy potentials CDM predicts for low-mass systems. Photometry alone offers an observationally inexpensive way to constrain rho'(0), making this approach particularly attractive for the faint
galaxies most relevant to dark matter (DM) studies. Inferring volume densities, however, requires deprojecting the observed
stellar surface density, Sigma(R), a procedure that is notoriously ambiguous in the presence of noise. To avoid explicit deprojection, we derive an expression (Eq.~[9]]) to obtain rho'(0) directly from the radial derivatives of Sigma(R), assuming spherical
symmetry and smooth finite density profiles. All projected profiles are shown to have the same central functional form, independent of the underlying volume density (Eq.~[20]). As a result, the derivatives of Sigma(R) can be extrapolated to the center using constraints from larger radii, which in turn yields rho'(0). As an illustration, we apply the method to six ultra-faint
dwarf (UFD)
galaxies, finding that all of them have a surface density with the same shape, from which the presence of
stellar cores is inferred (rho'[0] simeq 0). The technique also has the ability to diagnose rho'[0]>0, corresponding to
galaxies with a central
stellar mass deficit potentially linked to black-hole scouring, MONDian dynamics, or deviations from CDM.
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Cosmology and Nongalactic Astrophysics
CSST large-scale structure analysis pipeline: IV. Cosmic Voids Identified from Galaxy Group Samples as Probes of the Large-scale Structure
Yingxiao Song, Xiaohu Yang, Yan Gong et al. (+16 more)
Because groups are directly associated with
halos, they allow for considerably simpler theoretical modeling than approaches based on individual
galaxies. We therefore propose to use voids identified in
galaxy group catalogs, referred to as group-voids, to investigate the
cosmic large-scale structure (LSS). Using the reference mock
galaxy redshift survey (MGRS) designed for the Chinese Space-station Survey
Telescope (CSST), we build two
galaxy group catalogs representing ideal and realistic scenarios, derived from
galaxy samples with 100% and roughly 30% spectroscopic
redshift completeness, respectively. We then identify voids in these two mock group catalogs, as well as in the underlying
halo catalog, and measure two void statistics, the void size function (VSF) and the void density profile, within five
redshift intervals spanning $z=0$ to $1.0$. We compare the statistics obtained from two kinds of voids: those defined by
galaxy groups (group-voids) and those defined by dark matter
halos (
halo-voids). In the void-finding process, we adopt the brightest central
galaxy (BCG) as the group center to improve the accuracy of the inferred void centers. Our analysis shows that void statistics derived from group-voids with spectroscopic
redshift completeness of at least 40% can faithfully reproduce the corresponding statistics from
halo-voids. Even when the
redshift completeness of
galaxies falls to as low as 30%, we can still reliably describe group-voids via
halo-voids by incorporating a
redshift error term. This indicates that group-voids are a promising tool for probing LSS and offer a valuable complement to standard void studies, which is especially advantageous for emulator-based methods.
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All authors Yingxiao Song, Xiaohu Yang, Yan Gong, Yizhou Gu, Qingyang Li, Hong Guo, Yunkun Han, Yipeng Jing, Cheng Li, Feng Shi, Jipeng Sui, Run Wen, Hu Zhan, Pengjie Zhang, Youcai Zhang, Gong-Bo Zhao, Xian Zhong Zheng, Xingchen Zhou, Hu Zou
Solar and Stellar Astrophysics
Visualizing the Magnetic Structure in Interplanetary Coronal Mass Ejections with ATHARV
Vivek Menon, Jyoti Sheoran, Vaibhav Pant et al. (+1 more)
Interplanetary coronal mass ejections (ICMEs) are major drivers of space weather, and their geoeffectiveness is strongly governed by the structure and orientation of their internal
magnetic field. However, in-situ observations provide only 1D sampling along a spacecraft trajectory, limiting direct inference of the ICME 3D
magnetic structure. We introduce the Analysis Tool for Heliospheric Arrangement of Remapped Vectors (ATHARV), which remaps in-situ time-series measurements into spatial coordinates while accounting for ICME expansion and spacecraft motion. ATHARV assumes self-similar expansion with different expansion rates along three orthogonal directions, while more general cases use measured velocities as proxies for
plasma motion. The framework also incorporates complementary diagnostics, including hodograms and
magnetic-field orientation angles, to assess
magnetic coherence and field rotation within ICMEs. We demonstrate ATHARV using multipoint observations of an ICME detected near 1 au by STEREO-A and Wind on 2023 April 23–24. The reconstructed sheath exhibits disordered and variable
magnetic fields, whereas the
magnetic ejecta (ME) shows a coherent rotation consistent with a right-handed SWN flux-rope configuration at both spacecraft. However, differences in
magnetic-field magnitude profiles, rotation signatures, and inferred ME sizes indicate mesoscale inhomogeneity within the ICME
magnetic structure, possibly associated with a writhed or distorted flux rope. This event highlights the limitations of interpreting ICME
magnetic configurations from single-point measurements and demonstrates the importance of multipoint observations for investigating their 3D structure and
evolution. ATHARV provides a consistent framework for interpreting in-situ ICME observations and investigating their spatial structure and
evolution, and is publicly available to the heliophysics community.
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All authors Vivek Menon, Jyoti Sheoran, Vaibhav Pant, Dipankar Banerjee
Earth and Planetary Astrophysics
Distribution and Evolution of the Debris Cloud from the Fragmentation of Intelsat 33E
Peng Shu, Meng Zhao, Yu-Yan Zhao et al. (+2 more)
The breakup of Intelsat 33E on 19 October 2024 posed a potential risk to satellites in the Geostationary Earth Orbit (GEO). This study analyzes the
evolution and distribution of these fragments using a probabilistic approach. The initial distribution of the fragments, derived from the NASA Standard Breakup Model, indicates the generation of 4,393 fragments larger than 1 centimeter. The spatial propagation of these fragments is modeled analytically in the Earth-Centered Earth-Fixed reference frame, showing the formation of high-density ring structures in the equatorial plane from 24 hours to 28 days after the breakup. The orbits of 36 cataloged fragments are retrieved and compared with the probability density. Furthermore, Monte Carlo simulations validate the probabilistic model and highlight its efficiency in capturing low-probability events. Collision risks to other GEO satellites are assessed, showing that the top 10% of satellites encounter a collision probability of up to $10^{-8}$ after 28 days. Satellites near the equatorial plane are at higher risk, whereas those with higher inclinations are less affected. These findings underscore the need for enhanced monitoring and mitigation strategies for GEO breakup events, given the challenges in detecting small fragments.
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All authors Peng Shu, Meng Zhao, Yu-Yan Zhao, Zhen Yang, Yu-Qiang Li
High Energy Astrophysical Phenomena
Mass and Spin Growth of Very Massive Stars in Star Clusters Potentially Associated with Little Red Dots
Ataru Tanikawa, Masaru Shibata and Kunihito Ioka
Using gravitational $N$-body simulations, we investigate the
evolution of mass and
spin for very massive
stars (VMSs) in dense
star clusters, which could subsequently evolve into Little Red Dots (LRDs). Our results show that VMS masses can reach $10^3$–$10^4\,M_\odot$, depending on the initial conditions of the host clusters. Notably, the VMS mass increases by up to a factor of three when accounting for the bloated state at the Hayashi track induced by
stellar collisions, provided that this state is maintained at
accretion rates exceeding $3 \times 10^{-2}\,M_\odot\,{\rm yr}^{-1}$. In all cases, the
spin of the VMS, when normalized to the dimensionless black hole (BH)
spin parameter, exceeds $10$, although the mass and
spin of VMSs after the post-main sequence phase could be decreased by the
stellar evolution process. We nonetheless demonstrate that VMSs formed in dense
star clusters can be highly spinning. Such a rapidly spinning VMS is expected to collapse into an intermediate-mass BH surrounded by a massive
accretion disk. This BH-disk system could trigger powerful explosions and emit burst gravitational waves, similar to those observed in GW190521 and GW231123, for which the remnant BH masses are estimated to be $\gtrsim 100\,M_\odot$.
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Solar and Stellar Astrophysics
LAMOST J010103.13+275449.6: A New Binary Exhibiting a Switch in Photometric Period from 1.7216\,d to 0.8444\,d
Y. H. Chen
LAMOST J010103.13+275449.6 is bright with an apparent magnitude of 10.764 in the SDSS $g$ band. We searched for two low resolution spectra from LAMOST, apparent magnitudes from GALEX, Pan-STARRS, 2MASS, and WISE, X-ray data from XMM-Newton, and light curve from TESS. It is very interesting that the photometric period of light curve switch from 1.7216\,d to 0.8444\,d. In previous large sample statistical studies, it was identified as an eclipsing binary, a rotational variable
star, or an emission line
star. The ultraviolet excess in 2006 from GALEX, the hard X-ray emission in 2016 from XMM-Netwon, the high amplitude photometric variability in 2019 from TESS, together with the nearly featureless photospheric spectra in 2011 and 2015 from LAMOST, collectively reduce the likelihood of the rapidly rotating single
star magnetic activity scenario. The spectral fitting for the two main-sequence components shows that the system is a main-sequence binary consisting of F and G type
stars. Mathematical modeling suggests that, with a 1.7216\,d orbital period and
tidal locking of the companion, the period switching of the light curve can be semi-quantitatively explained by orbital motion, involving a large spot at the substellar point in the early phase and small spots at both the substellar and antipodal points in the later phase. The binary parameters are preliminary with large uncertainties and more in-depth studies can be carried out in the future based on more spectra that may be released by LAMOST.
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High Energy Astrophysical Phenomena
Fast radio bursts, magnetars and earthquakes: their "family feud"?
Si-Lu Xu, Yong-Kun Zhang, Pei Wang et al. (+24 more)
Fast
radio bursts (FRBs) are millisecond-duration
cosmic transients whose origin remains elusive. Competing models invoke either earthquake-like processes or
flare-like mechanisms. To discriminate between these scenarios, we develop a novel diagnostic, the Pincus-Lyapunov diagram (PLD), to characterize the energetic transients in the stochasticity-chaos phase space. We compile burst sequences from five representative FRBs (FRB 20121102A, FRB 20190520B, FRB 20201124A, FRB 20220912A, and FRB 20240114A), together with those from magnetar
flares (SGR J1550$-$5418, SGR J0501+4516, SGR 1806$-$20, SGR 1900+14, and SGR J1935+2154),
pulsar glitches,
solar flares, and earthquakes, and map them onto the PLD for comparative analysis. The resulting diagram shows that FRBs occupy a distinct region of the phase space. Specifically, a permutation test reveals a statistically significant difference in the distributions of magnetar
flares and
pulsar glitches compared to those of repeating FRBs ($p$-value $\simeq 0.05$). To examine whether temporal variations in source activity can shift a repeater's position in this phase space, we analyze the time
evolution of the most prolific repeater, FRB~20240114A. For this repeating FRB, both Pincus Index and Lyapunov Exponent demonstrate statistically stable behaviour over the eight-month observation session, with Augmented Dickey–Fuller tests yielding $p \simeq 1.78\times10^{-3}$ and $9.91\times10^{-3}$, respectively. By assembling the most comprehensive
dataset to date, our work indicates that the trigger mechanisms of repeating FRBs are likely to be distinct from those driving magnetar
flares,
pulsar glitches,
solar flares, and earthquakes.
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All authors Si-Lu Xu, Yong-Kun Zhang, Pei Wang, Di Li, Jun-Shuo Zhang, Tian-Cheng Lv, Yong-Feng Huang, Tian-Cong Wang, Long-Xuan Zhang, Pei-Xin Zhu, Jin-Huang Cao, Yi Feng, He Gao, Jian Li, Wan-Jin Lu, Chen-Chen Miao, Chen-Hui Niu, Qing-Yue Qu, Chao-Wei Tsai, Yi-Dan Wang, Wen-Ting Wang, Su-Ming Weng, Jia-Fu Wu, Ru-Shuang Zhao, Yuan-Chuan Zou, Yu-Hao Zhu, Ya-Biao Wang
High Energy Astrophysical Phenomena
Possible High-Energy Neutrino Emission from Dark Matter Annihilation in the Disrupting Dwarf Galaxy Boötes~III
Shunhao Ji and Zhongxiang Wang
We report the first search for high-energy
neutrino emissions from dark matter (DM) annihilation in
stellar-stream cores. Motivated by a recent gamma-ray study that proposed these cores as a new class of indirect DM targets, we analyze three stream cores in the Northern Hemisphere using the public ten-year track-like
neutrino data released by IceCube. Under the $\chi\chi\to\nu\bar{\nu}$ annihilation hypothesis, the most significant excess among the three targets is found at the position of the nearby
dwarf galaxy Boötes~III, the core of the Styx stream, with the DM mass of $m_\chi\simeq10$–$31~{\rm TeV}$. The excess has a post-trial significance of $3.1\sigma$. Considering the existing IceCube
dwarf-
galaxy limit for the same channel, we obtain a limit on the J-factor $J_{\rm ann}$, $\log_{10}(J_{\rm ann}/{\rm GeV^2\,cm^{-5}})\gtrsim 19.1^{+0.3}_{-0.5}$. This limit is broadly consistent with empirical estimates of $J_{\rm ann}$ for Boötes~III. The results provide the first candidate target with a possible HE
neutrino signal associated with DM annihilation. This
neutrino excess and the general existence of DM-induced
neutrino signals from other similar sources will be confirmed with the near-future large high-energy
neutrino detectors, thus enabling us to probe the nature of DM particles.
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High Energy Astrophysical Phenomena
A 0.03 Hz Radio Quasi-periodic Oscillation During the 2025 Flare of GRS 1915+105
Ya Xing Li, Lei Liu, Wu Jiang et al. (+3 more)
Our weekly-cadence
radio monitoring campaign captured a bright
flare in 2025 from the microquasar GRS 1915+105, observed simultaneously in the S- and X-bands (2.25 GHz and 8.42 GHz) with a short single baseline of two
radio telescopes in Shanghai. Through high time resolution analysis, we detected a significant and short-lived quasi-periodic oscillation (QPO) at $\sim$0.03 Hz and its harmonic ($\sim$0.06 Hz) in both
radio bands of two consecutive observations on MJD 60765 ($>5.9 \sigma$) and MJD 60772 (2.8$\sigma$). Crucially, the QPO frequency is identical in both
radio bands and matches oscillations detected in previous years. The recurrence and wavelength independence of the QPO frequency suggest an intrinsic characteristic timescale of the
accretion-jet system.
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All authors Ya Xing Li, Lei Liu, Wu Jiang, Zhen Yan, Bo Xia, Zhi Qiang Shen
High Energy Astrophysical Phenomena
A new Chandra look at the globular cluster NGC 6540 and its peculiar X-ray flaring source
A. Sacchi, S. Mereghetti, R. Di Stefano et al. (+4 more)
We report the results of a deep ($\approx65$ ks) Chandra exposure of the globular cluster NGC 6540, obtained by combining three observations carried out in 2023-2024 to investigate the nature of the peculiar X-ray source 3XMM J180608.9-274553. This source was previously observed with XMM-Newton to exhibit a short ($\approx300$ s) and intense X-ray
flare whose luminosity and duration are inconsistent with both typical type I X-ray bursts from low-mass X-ray binaries and
stellar flares. Our new data indicate three faint X-ray sources near the position of the
flare seen by XMM-Newton, only one of which was detected in a previous, much shorter Chandra observation. Based on the properties of these sources, localized at sub-arc-second precision, and of their optical counterparts, we discuss their possible nature and association with 3XMM J180608.9-274553: only one of these newly detected sources is compatible with the position of the
flare. We also discuss a few scenarios, such as microlensing-induced amplification and black hole flaring activity analogous to that observed in Sgr A$^\ast$, to explain the X-ray
flare. Although these scenarios are intriguing, current observational evidence makes them both unlikely to be the origin of the XMM-Newton
flare.
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All authors A. Sacchi, S. Mereghetti, R. Di Stefano, J. A. Irwin, M. Rigoselli, A. De Luca, N. Sims
High Energy Astrophysical Phenomena
Reconnection-Driven Injection and Stochastic Reacceleration during Cosmological Magnetogenesis
Ji-Hoon Ha
We investigate whether
magnetic reconnection can provide suprathermal
proton seed particles during cosmological magnetogenesis prior to nonlinear structure formation. Previous work showed that pressure-anisotropy-driven
stochastic acceleration alone is strongly limited by cosmological expansion and Coulomb cooling. Here, we extend this framework by adding a phenomenological reconnection-driven source term to the Fokker–Planck equation for the isotropic ion distribution, with the injection power tied to the
magnetic-energy growth rate during magnetogenesis. We find that reconnection can act as a fast injection channel and can produce a visible suprathermal tail. However, the resulting nonthermal energy fraction remains very small, of order $10^{-7}$ in the fiducial model, implying a negligible nonthermal pressure contribution to the pre-structure intergalactic medium. This limitation arises because the extremely high-beta
plasma contains only a small
magnetic-energy reservoir, even when reconnection itself is locally fast. Using a test-particle shock reacceleration estimate, we further show that the reconnection-produced tail can enhance the suprathermal
proton population available for later structure-formation shocks by about an order of magnitude. Nevertheless, the associated hadronic gamma-ray emission from low-density cluster outskirts is expected to remain far below current detectability. We therefore conclude that reconnection during cosmological magnetogenesis is unlikely to dominate the
cosmic-ray energy budget directly, but may provide a low-level seed population for subsequent shock acceleration.
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Instrumentation and Methods for Astrophysics
Design and development of Fabry-Perot based wavelength calibration system for PARAS-2 spectrograph
Shubhendra Nath Das, Kapil Kumar Bharadwaj, Abhijit Chakraborty et al. (+5 more)
Precise wavelength calibration is essential for high-precision radial velocity (RV) spectrographs, necessitating a stable calibrator that provides a dense grid of uniformly spaced lines to accurately determine
stellar line positions and monitor instrumental drifts. In this work, we present the development of a cost-effective Fabry-Perot (FP) etalon-based wavelength calibrator designed to overcome the limitations of conventional sources such as hollow cathode lamps (HCLs) and iodine
cells. This FP calibrator, combined with a Xenon (Xe) arc lamp assembly, has been integrated with the PARAS-2 spectrograph on the PRL 2.5m
telescope at Mount Abu Observatory. Operated under controlled temperature and pressure conditions, the system generates a dense, comb-like spectrum covering 62 echelle orders with more than 10,000 well-defined and stable spectral lines, enabling precise measurement of instrumental drift. Initial results show that the free spectral range (FSR) varies from 0.16 Å~near 4000 Å~to 0.49 Å~ near 7000 Å, with a value of 0.3 Å~around the central wavelength of 5500 Å~. The estimated finesse ranges from 9 near 4000 Å~to 19 near 6900 Å, with an approximate value of 17 at 5500 Å. The temperature and pressure stability tests demonstrate RMS variations of $0.002 ^\circ\mathrm{C}$ and $5\times10^{-4}$ mbar, respectively. Based on these values, the theoretical stability of the FP wavelength calibrator is estimated to be within 10 cm/s, establishing it as a reliable alternative to
Laser Frequency Combs (LFCs) for high-resolution spectroscopic calibration. We present an initial assessment of the RV stability of the FP calibrator, yielding 40-70 cm/s of relative drifts, which are up for further investigations. The observed excess over the theoretically estimated limit is likely attributable to instabilities arising from arc wandering in the xenon arc lamp.
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All authors Shubhendra Nath Das, Kapil Kumar Bharadwaj, Abhijit Chakraborty, Kevikumar A. Lad, Jajaendra Siva Seshu Vera Prasad Neelam, Rishikesh Sharma, Nikitha Jithendran, Vishal Joshi
Solar and Stellar Astrophysics
Large ephemeral regions and their tilt angles
Rambahadur Gupta, Anu Sreedevi, Bibhuti Kumar Jha et al. (+1 more)
The ephemeral regions (ERs), which are short-lived bipolar
magnetic regions that emerge across the
solar cycle but do not appear as sunspots, play a crucial role in the Sun's
magnetic flux budget. However, their properties, particularly the tilt distribution, are poorly constrained by observations. In this study, we isolate ERs from the Automatic Tracking
Algorithm for Bipolar
Magnetic Regions (AutoTAB) catalog during
Solar Cycles 24 and 25 by applying flux and footpoint-separation thresholds. Although AutoTAB was designed to track high-flux regions, it also records ephemeral regions with fluxes of 10^19 to 10^20 Mx, placing them at the upper end of the ER spectrum. The isolated ERs have an average lifetime of 1.2 days. Footpoint separation begins at supergranular scales (about 20 Mm), grows during the first half of the lifetime, and then saturates. ERs occur most frequently near
solar minima, consistent with earlier studies and likely reflecting AutoTAB's greater sensitivity to weaker regions when strong BMRs are scarce. Tilt properties reveal a more complex picture. For lifetimes shorter than two days, ERs show a broad, noisy distribution with no systematic latitude dependence. Including longer-lived ERs produces a weak, though statistically insignificant, increasing trend with latitude, suggesting that short-lived ERs are shaped by turbulent convection, while stronger, longer-lived ERs may retain Coriolis-imparted tilts. Overall, these results support the view that ERs occupy the low-flux end of the BMR spectrum and contribute meaningfully to the
solar dynamo.
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All authors Rambahadur Gupta, Anu Sreedevi, Bibhuti Kumar Jha, Bidya Binay Karak
Astrophysics of Galaxies
Magneto-Gravitational Regulated Streamer Accretion onto a Class 0 Protostellar System
Bo Huang, Josep M. Girart, Ian W. Stephens et al. (+17 more)
How do
magnetic fields shape the way young
stars gather gas from their birth clouds? Using high-resolution Atacama Large Millimeter/submillimeter Array observations of a young triple protostellar system HOPS-182, we identify an elongated stream of gas, or
accretion streamer, that extends over several thousand astronomical units (1 astronomical unit is the Earth-Sun distance) and carries a substantial flow of material toward the system. The gas speeds along this filament increase toward the
star in a way consistent with gravitational free-fall, while the streamer's shape closely follows the
magnetic field threading the region. By comparing the strengths of
gravity and
magnetic tension and measuring how the gas rotates compared with the local
magnetic field, we show that the field is strong enough to help confine and guide the infalling gas and efficiently remove angular momentum. These results suggest that a substantial fraction of the material falling onto young protostellar systems can be funneled through elongated, magnetically structured
accretion streamers.
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All authors Bo Huang, Josep M. Girart, Ian W. Stephens, Tom Megeath, Valentin J. M. Le Gouellec, Nadia M. Murillo, Paulo Cortés, Manuel Fernández-López, Zhi-Yun Li, Leslie W. Looney, J. A. López-Vázquez, Jaime E. Pineda, Álvaro Sánchez-Monge, Patricio Sanhueza, Sarah Sadavoy, Qizhou Zhang, Charles L. H. Hull, Nicole Karnath, Enwei Liang, Philip C. Myers
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Ellis-Bronnikov Wormhole Shadows with Spherically Symmetric Accretion Flow
Mikiya M. Takahashi and Keisuke Nakashi
We investigate the observational differences between the Ellis–Bronnikov (EB) wormhole and the Schwarzschild black hole (BH) by performing general relativistic radiative transfer (GRRT) simulations. We consider a spherically symmetric steady-state
accretion flow and perform GRRT simulations incorporating synchrotron emission. For both the EB wormhole and the Schwarzschild BH, the simulated images consist of a central shadow region and a bright
photon ring. We find that both the shadow region and the
photon ring of the EB wormhole are brighter than those of the Schwarzschild BH. These differences arise from the absence of an event horizon in the EB wormhole, allowing the emission from the accreting matter around and beyond the throat to contribute to the intensity. We also compare the simulated images with the Event Horizon
Telescope (EHT) observations of M87*. Although the total flux and the ring diameter are comparable with the EHT results, our models with the spherically symmetric
accretion flow cannot reproduce the deep central brightness depression observed by the EHT, for both the EB wormhole and the Schwarzschild BH. This indicates that a non-spherical
accretion flow is required for a detailed comparison with the EHT image.
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Instrumentation and Methods for Astrophysics
The Murchison Widefield Array Phase III upgrade: Sensitivity Doubled, Number of Baselines Quadrupled, Flexibility Enhanced, and EoR Observations Optimised
S.J. Tingay, M. Johnston-Hollitt, R.B. Wayth et al. (+32 more)
We describe the latest iteration of upgrades (designated Phase III) to the Murchison Widefield Array (MWA), in the fourth paper in a series that covers the
evolution of the
telescope from design concept to initial operational facility, and through two major upgrades. As part of the Phase III upgrade of the MWA, we report the completion of work to design, build, and deploy a new fleet of digital receivers that further optimise the MWA for Epoch of Reionisation observations. These receivers complement existing receivers, such that the MWA now supports the full correlation of all 256
antenna tiles currently in the array. This step releases the MWA from the prior constraint of having to correlate only 128 of the 256 tiles at any given time, which means that the maximum instantaneous sensitivity of the MWA is doubled and the maximum number of interferometric baselines is approximately quadrupled. The upgrade is fundamentally enabled by the new MWAX correlator and various other improvements to the MWA sub-systems. In this paper we describe the new digital receivers and the other improvements that result in the Phase III system. A range of operational benefits arise from the upgrade and scientific flexibility is increased. We also comment on the transition from the MWA to the SKA-Low facility near the end of the decade, including a description of some unique science opportunities utilising joint MWA/SKA-Low data during the Science Verification phase of the SKA-Low Array Assembly 2 (AA2) period.
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All authors S.J. Tingay, M. Johnston-Hollitt, R.B. Wayth, T.A. Booler, J. Jones, Y. Wu, J. Gan, G. Sleap, A. McPhail, C. Wintle, A. Williams, C.J. Phillips, L. Verduyn, D. Emrich, P. Giersch, C.J. Riseley, S. Duchesne, C.M. Trott, D. Null, B.W. Myers, C.D. Nunhokee, N. Barry, L. Dressler, J. Ducharme, B. Hazelton, M. Lee, E. Lilleskov, M. Morales, J. Pober, Zhiqiang Shen, Xiang-ping Wu, Xiaoyu Hong, M.D. Filipović, S.E. Tremblay, M. Walker
High Energy Astrophysical Phenomena
Rapid quasi-periodic reconfiguration of the accretion column in pulsar 1A 0535+262
Lingda Kong, Xiaohang Dai, Andrea Santangelo et al. (+12 more)
Accretion onto strongly magnetized
neutron stars is commonly interpreted using quasi-steady models, in which the
accretion-column structure adjusts smoothly to the mass inflow rate. The cyclotron line in the X-ray spectrum, whose centroid energy traces the
magnetic field strength and thus the height of the line-forming region, provides a key diagnostic of this structure. Whether this simple quasi-steady description remains valid on short dynamical timescales has remained uncertain. Here we show that, during a
giant outburst of the X-ray
pulsar 1A~0535+262, quasi-periodic hard X-ray flux variations are accompanied by synchronized oscillations of the cyclotron line energy, with amplitudes exceeding those expected from simple
accretion-rate fluctuations. The anti-correlation between cyclotron energy and apparent flux provides direct spectral-timing evidence for rapid changes in the line-forming region, which we interpret as
geometric reconfiguration of the
accretion column. The variability emerges in the luminosity regime where radiation pressure becomes dynamically important. These results reveal limitations of a simple quasi-steady interpretation for this source and suggest that radiation-supported columns can enter intrinsically dynamical states in high-luminosity accreting
pulsars.
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All authors Lingda Kong, Xiaohang Dai, Andrea Santangelo, Long Ji, Valery F. Suleimanov, Alexander A. Mushtukov, Lorenzo Ducci, Shu Zhang, Qingcang Shui, Shuang-Nan Zhang, Hua Feng, Sergey S. Tsygankov, Honghui Liu, Pengju Wang, Qi Liu
Astrophysics of Galaxies
Signatures of Accreting Black Holes in Line Intensity Mapping
Erika Ogata, Kana Moriwaki, Adam Lidz et al. (+2 more)
Line-intensity mapping (LIM) has attracted growing
attention as a powerful technique for probing the large-scale distribution of
galaxies and the
cosmic history of
star formation through unresolved line emission. Existing LIM models for
galaxy-associated lines, such as H$\alpha$, often assume that the dominant contribution to observed emission arises from
star-forming activity, while the role of accreting black holes (BHs) remains largely unexplored. In this study, we use the IllustrisTNG cosmological hydrodynamical simulation to construct mock intensity maps of H$\alpha$ and He II, including contributions from both
star formation and BH
accretion. We show that the BH contribution to the mean intensity is significant, reaching $\sim$40–60 per cent for H$\alpha$ and $\sim$60–80 per cent for He II around
cosmic noon. Owing to the large luminosity weight of rare, bright sources, BH-powered emission dominates the shot-noise component of the power spectrum and significantly boosts the small-scale clustering amplitude, particularly for He II. We assess the implications for forthcoming LIM surveys and show that SPHEREx can probe the BH-influenced bright end of the H$\alpha$ voxel intensity distribution (VID) at $z\lesssim4$, and a CDIM-like experiment can further access the BH-dominated regime of He II. Our results demonstrate that accreting BHs represent an essential component of LIM signals, which was previously underappreciated. We thus conclude that accurately modeling the BH contribution is crucial for a physically complete interpretation of future LIM observations.
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All authors Erika Ogata, Kana Moriwaki, Adam Lidz, Rui Lan Jun, Naoki Yoshida
Solar and Stellar Astrophysics
Study of Massive OBA Stars with X-ray Emission
E. A. Nikolaeva, I. F. Bikmaev, E. N. Irtuganov et al. (+3 more)
A study of the physical parameters of a sample of 15 OBA-type
stars with detected X-ray emission from the Spektr-RG/eROSITA
telescope is presented. While X-ray emission from cool
stars (spectral types F-G-K-M) originates in their near-surface regions, namely in the chromosphere and corona, the origin of X-ray emission in OBA
stars requires case-by-case analysis since isolated OBA
stars are not intrinsic X-ray emitters. In this work, we derive the fundamental parameters of the
stars in our sample, including the effective temperature $T_{\mathrm{eff}}$ and surface
gravity $\log g$, based on spectral energy distribution fitting and optical spectroscopy obtained with the 1.5-m Russian-Turkish
telescope RTT-150. An additional analysis of the $\mathrm{H}\alpha$ line profiles allows us to identify possible mechanisms responsible for the observed X-ray emission, including non-stationary
stellar winds, interactions in circumstellar material, and coronal emission from hidden cool companions. We find that the X-ray emission in eight
stars, with typical luminosities in the range $\log L_{\mathrm{X}} = 28.5$-$30.0$, is most likely associated with hidden late-type companions.
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All authors E. A. Nikolaeva, I. F. Bikmaev, E. N. Irtuganov, M. R. Gilfanov, R. A. Sunyaev, P. S. Medvedev
Cosmology and Nongalactic Astrophysics
Primordial black holes spin from cosmological first-order phase transitions
Yu-Shi Hao
The
stochastic bubble nucleation during cosmological first-order phase transitions leads to variations in the phase transition initiation times across different Hubble volumes, thereby generating non-Gaussian density perturbations in regions with delayed transitions. Based on the accumulation mechanism and the false
vacuum island model . This paper investigates the
spin angular momentum of
primordial black holes formed from nonspherical collapse. By introducing the nucleation history integration method, without assuming a Gaussian distribution, we calculate the expectation values and variances of the semi-axis lengths of overdense ellipsoidal regions, combined with the statistical properties of the velocity shear tensor, we derive the quantitative relationship between the Kerr parameter $a_*$ describing black hole
spin and the phase transition parameters , latent heat strength $\alpha$ and phase transition rate $\beta$. The study finds that the Kerr parameter increases with $\alpha$ and decreases with $\beta$; estimate the typical the magnitude of $a_*$ can reach $10^{-3}$, which is significantly higher than that of
primordial black holes formed in the radiation-dominated era under peak theory, but still lower than that in a matter-dominated era.
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Astrophysics of Galaxies
Morphology of Optical Changing-Look AGN-host Galaxies: Evidence for an Important Role of Mergers
Jie Tian, Yinghe Zhao, Jin-Ming Bai et al. (+1 more)
Optical changing-look active
galactic nuclei (CL-AGNs) are characterized by the (dis)appearance of broad emission lines on unexpectedly short timescales. However, the underlying mechanisms and their potential connection to host-
galaxy properties are still unclear. In this work, we present an analysis of the morphology for 63 low-
redshift CL-AGNs (z < 0.15) selected from the largest CL-AGN catalog (Guo et al. 2025) to date, using images from DESI DR10 and employing both non-parametric methods and visual inspection. We find that CL-AGN hosts exhibit a concentration like late-type spirals, asymmetry like early-type spirals, and smoothness like ellipticals. This is confirmed by their Gini-M20 coefficients, suggesting weak/modest disturbances. Based upon our visual inspection, we further identify that 18 (29%) out of 63 sources are mergers, among which ~56% (10/18) show shell features. Compared to different non-CL-AGN samples, CL-AGN hosts have a higher (~2\times) possibility of being merging systems. Our results indicate that mergers/interactions may play an important role in driving the changing-look behavior.
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All authors Jie Tian, Yinghe Zhao, Jin-Ming Bai, Wei-Jian Guo
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Pitching Cosmic Curveballs: Environmental Effects on Extreme-Mass-Ratio Inspirals with Spinning Secondaries
Leif Lui, Lisa V. Drummond and Alejandro Torres-Orjuela
Much like the aerodynamic deflection of a spinning curveball, a rotating secondary in an extreme-mass-ratio inspiral (EMRI) experiences Magnus and lift forces, in addition to the standard drag force, when traversing a gaseous environment. We present the first framework that incorporates these specific
spin-coupled environmental effects (EEs) into the
evolution of EMRI. Over the multi-year observation windows of space-based gravitational-wave (GW) detectors, these interactions imprint a unique, distinguishable dephasing signature on the signal. Crucially, a Fisher
matrix analysis reveals that gas drag breaks the fundamental
vacuum-projection degeneracy between the secondary's
spin magnitude and inclination, thereby tightening parameter constraints. Thus, accounting for EEs is not merely a modeling necessity, but could potentially be a powerful tool for enhancing the detectability of the secondary's intrinsic
spin, and could serve as a novel probe of
accretion flows harboring massive black holes.
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Instrumentation and Methods for Astrophysics
JAXtronomy: A JAX port of lenstronomy
Alan Huang, Simon Birrer, Daniel Gilman et al. (+4 more)
Gravitational
lensing is a phenomenon where light bends around massive objects, resulting in distorted images seen by an observer. Studying gravitationally lensed systems provides insights into cosmology and astrophysics, including constraints of the expansion rate of the Universe and the distribution of dark matter. Thus, we introduce JAXtronomy, a re-implementation of the gravitational
lensing software package lenstronomy (Birrer, 2021; Birrer & Amara, 2018) using JAX (Bradbury et al., 2018). JAX is a Python library that uses an accelerated linear
algebra (XLA) compiler to improve the performance of computing software. Our core design principle of JAXtronomy is to maintain an identical API to that of lenstronomy. The main JAX features utilized in JAXtronomy are just-in-time compilation, which can lead to significant reductions in execution time, and automatic differentiation, which allows for the implementation of gradient-based
algorithms that were previously impossible. Additionally, JAX allows code to be run on GPUs or parallelized across CPU cores, further boosting the performance of JAXtronomy.
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All authors Alan Huang, Simon Birrer, Daniel Gilman, Natalie B. Hogg, Anowar J. Shajib, Aymeric Galan, Nan Zhang
Cosmology and Nongalactic Astrophysics
Optimal Transport Reconstruction of Biased Tracers in Primordial Non-Gaussian Fields
Farnik Nikakhtar, Ravi K. Sheth, Nikhil Padmanabhan et al. (+2 more)
Optimal transport provides an efficient method to infer the displacement of objects by mapping their initial positions to their present-day locations over
cosmic time; equivalently, it enables the reconstruction of initial positions from measurements taken at later times. The method has been shown to be accurate even if positions for only a biased subset of the particles are measured, provided that the initial displacement field was Gaussian. The method does not rely on the assumption of a Gaussian displacement field, and thus may be extended to the reconstruction of non-Gaussian initial conditions. Here, we demonstrate how this is achieved for a class of "local"
primordial non-Gaussian fields of current interest in cosmology. For these models, there is a distinctive signature in the large scale clustering of biased tracers which depends on the product of the
primordial amplitude $f_{\rm NL}$ and the nature of the tracers $b_\phi$. Our method exploits the fact that this signature is not present in the full field; it is only present in biased fields. Therefore, the mass that is not in the biased subset, what we call the "
dust", also has a characteristic scale-dependence, albeit of a different amplitude. We show that the quality of the optimal transport reconstruction improves as the model for this
dust becomes more realistic.
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All authors Farnik Nikakhtar, Ravi K. Sheth, Nikhil Padmanabhan, Bruno Lévy, Roya Mohayaee
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Gravitational-wave astronomy with a space-based optical clock network
Dhruva Ganapathy, Divya Singh, Sammith Singamsetty et al. (+1 more)
Since the first detection of a merging binary black hole system a decade ago, gravitational-wave astronomy has emerged as a powerful tool for astrophysics. Future space-based observatories, such as the
Laser Interferometer Space
Antenna (LISA), will unlock the millihertz (mHz) band, which remains entirely inaccessible to ground-based detectors due to terrestrial noise. In parallel, proposed atom-based gravitational-wave detectors, specifically those based on space-based optical clocks and atom interferometers, offer capabilities that are unique and complementary to traditional optical interferometers. Their highly tunable character enables sensitive measurements across a broad frequency band extending from the mHz up to and possibly even above the Hz regime. In this work, we investigate the use of one-way Doppler tracking in space-based atomic clock networks operating in concert with detectors like LISA. We analyze the dominant noise sources and develop dedicated measurement protocols, which operate in a targeted mode, using an externally supplied signal model to track the response coherently as the source chirps. Performing preliminary parameter estimation on simulated signals, we demonstrate how these detectors could be used to extract critical astrophysical information about binary gravitational-wave sources. We further show that the same instrument retains sensitivity in a search mode, where no prior on the source is assumed.
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All authors Dhruva Ganapathy, Divya Singh, Sammith Singamsetty, Shimon Kolkowitz
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
He-CF4-CH4 ternary mixtures as target gas for the CYGNO directional dark matter experiment
F.D. Amaro, R. Antonietti, E. Baracchini et al. (+41 more)
The CYGNO collaboration is advancing a high-resolution optical Time Projection Chamber (TPC) for directional dark matter searches and
solar neutrino spectroscopy at LNGS. The detector uses a He-40%CF4 gas mixture at atmospheric pressure and a triple-GEM cascade for ionization signal amplification. Scintillation light from GEM electron avalanches is read out using sCMOS cameras, enabling high sensitivity to interactions in the few keV range, alongside precise ionization event tracking and particle identification. This study investigates the effects of adding 3-10% methane to the He-40%CF4 mixture. Methane improves the electrical stability of the TPC, allowing for higher GEM voltages before discharge onset, which compensates for its scintillation quenching and leads to enhanced overall scintillation yield. Compared to prior studies performed with isobutane, methane demonstrates a lower quenching effect on visible and UV
photons while maintaining good energy resolution. Importantly, the inclusion of methane lowers the dark matter detection threshold by providing a lighter target and extending track lengths of light
nuclear recoils, thus enhancing directional discrimination. These results establish methane as a promising additive for optimizing CYGNO's performance in detecting low-mass dark matter candidates.
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All authors F.D. Amaro, R. Antonietti, E. Baracchini, L. Benussi, C. Capoccia, M. Caponero, L.G.M de Carvalho, G. Cavoto, I.A. Costa, A. Croce, M. D'Astolfo, G. D'Imperio, G. Dho, E. Di Marco, J.M.F. dos Santos, D. Fiorina, F. Iacoangeli, Z. Islam, H. P. Lima Jr, G. Maccarrone, R.D.P. Mano, D. J. G. Marques, L.G.M. de Carvalho, G. Mazzitelli, P. Meloni, A. Messina, C.M.B. Monteiro, R.A. Nobrega, I.F. Pains, E. Paoletti, F. Petrucci, S. Piacentini, D. Pierluigi, D. Pinci, F.Renga, R.J. da C. Roque, A. Russo, G.Saviano, P.A.O.C. Silva, R.C. Sousa, N.J.C. Spooner, R. Tesauro, S. Tomassini, D. Tozzi