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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 8 July

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

Massive Graviton Dark Matter from a Gapped Continuum

Eugenio Megias, Miguel Prieto and Mariano Quiros

We consider the possibility of dark matter in a warped extra-dimensional theory in the presence of a linear dilaton background, with a gapped continuum spectrum, in a brane-world cosmological scenario. Firstly, triggered by self-energy radiative corrections, we study the existence of an isolated resonance of massive gravitons, and its realization as a long-lived feebly interacting dark matter candidate, produced by the freeze-in mechanism. This massive graviton is proved to satisfy all theoretical and experimental constraints, in the sub-MeV mass range. We further consider the close relationship between the existence of this component of dark matter and the presence of an inflaton localized on the brane, with a mass around $10^{11}$ GeV and a sub-TeV reheating temperature, in a brane inflationary scenario that allows one to reproduce the most recent cosmological observables. Secondly, the gapped continuum of gravitons, a particular five-dimensional realization of the physics of unparticles, is identified as a holographic fluid which can play the role of holographic dark matter. The production of the holographic fluid goes by an ultraviolet freeze-in mechanism, with an abundance mainly depending on the reheating temperature. Depending on the values of the mass gap and the reheating temperature, one or both components of dark matter can be present.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Combining gravitational wave search pipelines to find subthreshold signals in GWTC-5.0

Ann-Kristin Malz, Samuel Russell, Gregory Ashton et al. (+1 more)

The detection of transient gravitational wave signals relies on independent search algorithms that analyse detector data and assign significance measures to candidate events. However, varying performance complicates their interpretation. We use supervised machine learning combined with conformal prediction, a framework to quantify uncertainties, to merge multi-pipeline information into well-calibrated confidence scores. We demonstrate that this approach is robust across different classifier architectures and remains stable when trained on different simulated datasets. When applied to events across the GWTC catalogue up to and including the second part of the fourth observing run, the framework identifies several subthreshold candidates with elevated confidence, including the binary neutron star candidate GW200311_103121. We examine the reliability of these up-rankings, finding evidence that high-confidence predictions correspond to signal-like events. This framework enables simplified systematic candidate assessment for gravitational wave catalogues and real-time alerts by providing a single, well-calibrated confidence measure per candidate.
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All authors Ann-Kristin Malz, Samuel Russell, Gregory Ashton, Nicolo Colombo

Astrophysics of Galaxies

Quantifying Environmental Effects on Galaxy Properties using Non-spherical Voids Identified from SDSS DR7

Yingxiao Song, Xiaohu Yang, Yan Gong et al. (+4 more)

Cosmic voids provide a distinct low-density region for studying the environmental effects of galaxy properties. Using the SDSS DR7 catalog, we identify non-spherical voids via Voronoi tessellation and the watershed algorithm, and classify void galaxies based on their local volume. We compare and find that void galaxies classified by this method are systematically less massive, fainter, bluer, and have higher specific star formation rate (sSFR) than non-void galaxies and all galaxy samples. We then divide void and non-void galaxies into stellar mass bins to focus on the environmental dependence of $g-r$ color and sSFR. By further classifying galaxies into blue/red and star-forming/quiescent populations, we calculate the ratio of blue to red and star-forming to quiescent for void and non-void galaxies separately. Comparing the ratio of the void value to the non-void value for both metrics presents an overall decreasing trend with stellar mass $M_*$ over the $9.4-10.4$ range in $\log[M_*/\mathrm{M}_\odot]$, indicating a stronger environmental effect in lower-mass systems. These results show that our classification of void galaxies in non-spherical voids based on local volume offers a robust approach for quantifying the influence of underdense environments on galaxy evolution.
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All authors Yingxiao Song, Xiaohu Yang, Yan Gong, Haitao Miao, Xingchen Zhou, Yizhou Gu, Yingjie Peng

Astrophysics of Galaxies

Hubble Space Telescope survey of Magellanic Cloud star clusters. Binaries, mass functions, blue stragglers, and structural parameters

F. Muratore, M. V. Legnardi, A. P. Milone et al. (+7 more)

Binary stars are key tracers of the dynamical evolution of star clusters and provide important constraints on stellar populations and mass functions. The Magellanic Clouds host clusters spanning a wide range of ages and masses, offering an ideal laboratory to investigate these properties in regimes poorly sampled in the Milky Way. We aim to characterize the binary populations, mass functions, blue straggler content, and structural parameters of intermediate-age Magellanic Cloud clusters, and to explore their dependence on global cluster properties. We analyze HST photometry for 16 clusters obtained with ACS/WFC and WFC3/UVIS. Structural parameters are derived from stellar density profiles. Binary fractions are measured using the binary map technique, focusing on systems with mass ratios q > 0.7. We derive MFs accounting for unresolved binaries and identify candidate BS populations from color-magnitude diagrams. The fraction of binaries with q > 0.7 ranges from 5% in NGC 2121 up to 13% in NGC 2173, with a mass-ratio distribution that is consistent with being flat on average. By combining our results with literature data, we confirm a clear anti-correlation between the core binary fraction and cluster mass, while no significant dependence on cluster age is found. The clusters follow the established relation between age and core radius, although with substantial scatter at fixed age. Within the narrow age range explored here, clusters exhibiting steeper MFs are found to have smaller core radii. We find no evidence for a correlation between the fractions of binaries and BS fractions. These findings are consistent with a scenario in which dynamical evolution plays a primary role in the formation of binary populations. The connection between MF slope and structural parameters provides new constraints on cluster evolution and suggests a link between MF slope and structural evolution.
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All authors F. Muratore, M. V. Legnardi, A. P. Milone, G. Cordoni, A. Mastrobuono-Battisti, A. F. Marino, T. Ziliotto, E. Dondoglio, E. Bortolan, E. P. Lagioia

Instrumentation and Methods for Astrophysics

The Deep Learning Cosmic Ray Energy Reconstruction Pipeline for the GRAPES-3 Experiment

Sambit Sarkar, Mansi Talwar and Pravata K. Mohanty

The mass independent energy reconstruction of cosmic rays is crucial for understanding their origin, acceleration, and propagation. Precise measurement of the primary energy can also lead to better mass classification and could enable energy dependent anisotropy maps for individual elements. The GRAPES-3 experiment located in Ooty consisting of 400 scintillator detector array placed 8 m apart covering an area of 25000 m$^2$ with a dedicated muon detector made of 3712 proportional counters, is designed to do these kinds of measurements. Previously electron size calibration curves have been used to find primary energy in the GRAPES-3 data analysis framework however significantly better precision can be established using graph neural network. Thus, in this work we have implemented a modular and dynamic GNN based reconstruction algorithm that automates feature mapping. We demonstrate how the model is learning by studying its latent space and show that scaling the metric in the latent space can lead to further improvements in response resolution. Fine-tuned strategies are presented and a thorough comparison of the reconstructed energy and bias is done for different fine-tuned models along with studying the resolution variation for different mass groups and shower age.
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Instrumentation and Methods for Astrophysics

Machine learning pipeline for identifying tracks of muons and hadrons at GRAPES-3 muon telescope

Mansi Talwar, Sambit Sarkar and Pravata K. Mohanty

The GRAPES-3 experiment is a ground-based extensive air shower array which consists of approximately $400$ closely packed plastic scintillator detectors and a large area muon telescope. Estimating the number of associated muons created in an air shower is crucial to understand the properties of primary cosmic rays. The GRAPES-3 muon telescope (G3MT) records these secondary muons, however, the punch-through hadrons can introduce background noise. This study aims to develop a machine learning pipeline to distinguish the tracks of secondary muons and hadrons at G3MT. We have used CORSIKA-simulated proton showers having energy in the range 100-158 TeV as an input for a Geant4-based detector simulation to analyze the signatures of both type of particles. Initially, single-particle classification was performed using decision trees, random forests, neural networks, and XGBoost, with XGBoost achieving the highest accuracy of 88.7%. For multiparticle classification, we modelled Graph Neural Networks (GNNs) where each event was represented as a graph with detector hits as nodes. A GNN with edge convolution layers was developed to classify each node as a muon or hadron hit. Following this, a deep learning regression model using Dynamic Reduction Network was developed to estimate the number of particles and muons striking G3MT simultaneously. Details of the analysis and results of the multiparticle classification task will be presented.
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Astrophysics of Galaxies

GalPort: Investigation of the bar in action-angle space

Viktor D. Zozulia

GalPort is a Python package for analysing the orbital dynamics of evolving disc galaxy numerical models in action-angle space. The package implements novel numerical methods for efficiently estimating actions, angles, and frequencies across different, particle-specific timescales: on the scale of radial or vertical oscillation and on the resonant libration/circulation timescale. The algorithm allows calculation of these dynamic quantities simultaneously at all time steps of the simulated galactic evolution. With this tool, one can trace orbital behaviour within time-varying galactic potentials and classify orbits (resonantly trapped, circulating, or passing through a resonance) based on their angle evolution. GalPort also includes specialised options for analysing the phase-space structure of a galactic bar in the disc plane and along its major axis. We demonstrate the package's performance on a typical N-body model of a barred galaxy, obtaining the global distributions of actions and frequencies and performing a detailed orbital decomposition. The code is publicly available under the MIT license at: https://github.com/vdzozulia/galport
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Astrophysics of Galaxies

From 2D to 3D: Recovering Turbulent Density Dispersions from Noisy Data

Luz L. Jimenez Vela, Christoph Federrath, David C. Collins et al. (+1 more)

Turbulence plays a central role in shaping the structure and dynamics of the interstellar medium (ISM), governing the star formation rate (SFR) and the initial mass function (IMF). A key consequence of turbulence is the generation of density fluctuations, which regulate the amount of dense gas available for star formation. Accurate measurements of the three-dimensional (3D) turbulent density dispersion are therefore essential for understanding molecular-cloud structure and star formation. However, observations typically provide only two-dimensional (2D) column densities and are often affected by measurement/detector noise. The Brunt method estimates the 3D density dispersion from 2D column-density maps, but it does not account for finite signal-to-noise ratio (SNR). Here, we extend the method to recover the 3D turbulent density dispersion from noise-contaminated observations. Using numerical simulations spanning a range of density perturbation amplitudes and noise types, we identify a characteristic noise wavenumber, k_noise, corresponding to the intersection of the signal and noise spectra. Restricting the Brunt reconstruction to wavenumbers below k_noise yields a denoised density-dispersion estimate that closely reproduces the noise-free result. We provide a practical prescription to determine k_noise directly from the measurement SNR and image resolution. Alternatively, if the noise spectrum is known, it can be subtracted directly from the observed spectrum, eliminating the need to estimate k_noise. The proposed correction recovers the noise-free density dispersion with errors of <~5% for SNR>=3 and <~15% for SNR>=1, enabling substantially more reliable estimates of turbulent density fluctuations from noisy column-density data.
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All authors Luz L. Jimenez Vela, Christoph Federrath, David C. Collins, Seth Davidovits

High Energy Astrophysical Phenomena

X-ray Spectral Properties of Four Classical TeV Blazars using Simultaneous Observations from NICER and NuSTAR

Riya Bhowmick and Alok C. Gupta

We present a detailed study of X-ray spectral properties observed in 4 classical TeV (tera-electron volt) photon-emitting high synchrotron-peaked BL Lacertae objects using the simultaneous data of NICER and NuSTAR satellites. We analyzed 13 spectra in total from four BL Lacertae objects: Mrk 421, Mrk 501, PG 1553+113, and PKS 2155-304. We fitted all the spectra using the absorbed Log-Parabolic (LP) model first. While 7 spectra were fitted well using the absorbed LP model, we observed that 4 spectra of Mrk 421 and 2 spectra of Mrk 501 were not fitted satisfactorily using the absorbed LP model. The investigation of the flux states of the sources revealed that Mrk 421 was in a moderate to low-flux state during the 4 epochs and Mrk 501 was in a low-flux state during the 2 epochs. We concluded that there was a contribution from the disk in these 6 spectra. The moderate to low-flux state can justify the contribution of disk emission in the X-ray spectra. In the case of 4 spectra of Mrk 421, we observed a Gaussian feature between 1.42 and 1.70 keV.
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High Energy Astrophysical Phenomena

Multi-band optical photometric variability of the blazar OJ 287 from 2015 to 2025

Alok C. Gupta, Karan Dogra, Mark Kidger et al. (+101 more)

We present the most densely sampled multi-band optical photometric observations of the peculiar BL Lacertae object OJ 287 from 2015 to 2025 with a focus on its optical activity on diverse timescales. We present a total of 2296, 10927, 11484, and 2982 data points in B, V, R, and I bands, respectively. The densely sampled observations allow us to keep track of the source evolution that it has exhibited since the start of the predicted major optical flaring activity at the end of 2015. The study reveals clear and persistent bluer when brighter trends in both the long-term and short-term variations. Different bands were cross-correlated with discrete correlation functions, which peak at zero lag, implying co-spatial emission. Using eight optical spectra in the low flux states of OJ 287 taken from 2017 October 21 to 2017 November 22, from Steward Observatory, we estimate the central black hole mass to be at least 3.89 $\times \ \rm{10}^{9} \ \rm{M}_{\odot}$ from the [O III] line width. The emission mechanism of the binary black hole blazar, and its possible implication in various aspects of multi-messenger astronomy are briefly discussed.
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All authors Alok C. Gupta, Karan Dogra, Mark Kidger, Mauri J. Valtonen, Paul J. Wiita, Pankaj Kushwaha, Sergey S. Savchenko, Sofia O. Kurtanidze, Svetlana G. Jorstad, Alan P. Marscher, Katsura Matsumoto, Lang Cui, Shao Ming Hu, Goran Damljanovic, Rumen Bachev, O. Vince, Mai Liao, Zhongxiang Wang, A. Darriba, S. Haque, F. S. Alfaro, J. B. Amatller, J. M. F. Andujar, S. Arnold, T. Arranz, M. Bachini, C. L. Barcelo, S. Boeva, G. A. Borman, D. Boyd, D. Buczinski, J. D. Casal, X. Chen, J. M. Cores, F. C. Cucarella, P. U. Devanand, V. Dhiman, L. T. Espasa, J. H. Fan, R. G. Farfan, J. R. Fernandez, F. Garcia, R. C. Garcia, H. Gaur, J. C. Gomez, J. L. S. Gonzalez, J. L. Gonzalez-Carballo, T. S. Grishina, F. H. Grondona, M. F. Gu, H. Guo, V. A. Hagen-Thorn, G. Hurst, S. Ibryamov, R. Z. Ivanidze, N. James, B. Jardine, S. Johnstone, M. D. Jovanovic, N. Kalita, S. Karge, S. Kishore, E. N. Kopatskaya, O. M. Kurtanidze, A. Kurtenkov, E. G. Larionova, E. R. Lorenz, J. Lozano, E. F. Mananes, F. L. Martinez, M. Mobberley, M. Morales-Aimar, D. A. Morozova, M. G. Nikolashvili, Y. Nikolov, R. N. Nogues, P. A. Novikova, L. M. Penas, A. E. Perez, C. Perello, R. Pickard, F. G. Pinilla, G. Poyner, F. Rahmatullaeva, B. Rajkumar, N. G. Ribes, E. Semkov, E. V. Shishkina, M. Stojanovic, A. Strigachev, T. Tripathi, Yu. V. Troitskaya, I. S. Troitskiy, J. Valero, A. A. Vasilyev, B. Villarroel, A. E. Volvach, L. N. Volvach, S. J. Wagner, Z. R. Weaver, Wen-Xin Yang, Z. Zhang, A. V. Zhovtan, W. Zuo

High Energy Astrophysical Phenomena

Detection of Quasiperiodic Oscillations in the Blazar PKS 0735+178 with TESS

Shubham Kishore, Alok C. Gupta, Paul J. Wiita et al. (+2 more)

We report here the detection of signatures of a quasiperiodic oscillation (QPO) and a short flare in the optical light curve of the blazar PKS 0735+178, observed in two sectors, 71 and 72, spanning around 49 days with the Transiting Exoplanet Survey Satellite. The modest flare in sector 71 lasted ~4.3 days and appears as a combination of two sub-flares. In sector 72, a transient QPO with a period ~11.2 hours is detected at local and global significance levels of 4.11$\sigma$ and 3.06$\sigma$, respectively. We used weighted wavelet z transform, Lomb-Scargle periodogram, and phase dispersion minimization analysis techniques to look for and confirm the QPO feature. We also performed a segment-wise statistical inspection of these light curves and discuss here possible mechanisms that could explain the observed flux behavior.
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All authors Shubham Kishore, Alok C. Gupta, Paul J. Wiita, Sandeep K. Mondal, M. Vivek

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

Higgs boson mass and thermal wino dark matter from Starobinsky supergravity with the MSSM

Daniel Frolovsky, Alexander Belyaev and Sergei V. Ketov

We propose a framework connecting cosmic microwave background (CMB) observables with high-energy particle phenomenology, based on Starobinsky supergravity coupled to the Minimal Supersymmetric Standard Model (MSSM). Cosmic inflation and supersymmetry (SUSY) breaking occur within the hidden sector emerging from Starobinsky supergravity. The inflationary scale sets the hidden-sector mass scale and, via gravitational mediation of SUSY breaking, the MSSM soft terms. The same hidden sector can also dynamically generate a high-scale $\mu$ term. The resulting MSSM spectrum fixes the high-scale threshold corrections and the boundary conditions for the renormalisation-group (RG) evolution of the Higgs quartic coupling. Three-loop RG evolution of the Higgs quartic coupling gives a Higgs boson mass consistent with the measured value within the theoretical and experimental uncertainties, thereby linking the amplitude of primordial scalar perturbations to the Higgs boson mass. With conserved R-parity, the lightest supersymmetric particle is stable, and the minimal framework developed here points to a nearly pure neutral wino as the dark-matter (DM) candidate. In the thermal-relic scenario, the observed abundance selects a wino mass of about $3$ TeV. Recent gamma-ray analyses exclude it as the sole DM component, even for conservative cored Galactic profiles. Alternatives include a subdominant wino fraction or late entropy dilution. Its loop-induced spin-independent wino-nucleon scattering cross section lies below current LUX-ZEPLIN sensitivity but within reach of next-generation liquid-xenon detectors. Electroweak corrections generate a small charged-neutral wino mass splitting, producing a long-lived charged wino and disappearing-track signature. A future $100$ TeV proton collider can discover the corresponding pure-wino signal or exclude the scenario independently of its cosmological abundance.
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Instrumentation and Methods for Astrophysics

A search for narrowband technosignatures from LTT 3780 with the Allen Telescope Array and the Karl G. Jansky Very Large Array

Chenoa D. Tremblay, Sofia Z. Sheikh, Vishal Gajjar et al. (+9 more)

The LTT3780 system hosts two known exoplanets-LTT3780b, a rocky super-Earth, and LTT3780c, a temperate sub-Neptune-orbiting a nearby M dwarf on opposite sides of the radius valley. LTT3780c has been proposed as a candidate Hycean world, making the system an important target for astrobiological investigation, particularly in light of recent JWST atmospheric observations. Although biosignature and technosignature searches both seek evidence of life beyond Earth, these approaches have historically been pursued independently. Well-characterized exoplanet systems provide an opportunity to combine these complementary search strategies. In this work, we conducted radio technosignature observations of the LTT3780 system using both the Allen Telescope Array (ATA) and the Karl G. Jansky Very Large Array (VLA). The two facilities provide complementary observational capabilities, with the ATA optimized for wide-band multi-beam post-processing analyses and the VLA enabling high-sensitivity real-time interferometric searches. Across approx 30 hr of total observing time, we searched for narrowband Doppler-drifting signals in the frequency range approx 1–10 GHz. After applying comprehensive radio-frequency interference mitigation and multi-beam consistency tests, no candidate signals consistent with astrophysical or technosignature origins were identified. We place minimum detectable effective isotropic radiated power limits of 4.7 X 10^12–3.6 X 10^13W across the observed bands and facilities. Although no technosignatures were detected, this work demonstrates how complementary observation and analysis strategies can be applied to exoplanets of astrobiological interest and serves as a pathfinder for future combined biosignature and technosignature investigations.
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All authors Chenoa D. Tremblay, Sofia Z. Sheikh, Vishal Gajjar, Nikku Madhusudhan, Isabel Gerrard, Daniel Czech, Talon Myburgh, David E. MacMahon, Ross A. Donnachie, Andrew P.V. Siemion, Matthew Lebofsky, Alex W. Pollak

High Energy Astrophysical Phenomena

Weakly supervised machine learning for model-agnostic searches of new phenomena in the $\gamma$-ray sky

Michael Krämer, Silvia Manconi and Kathrin Nippel

The $\gamma$-ray sky, as observed by the Fermi Large Area Telescope, contains a significant number of unassociated sources that may point to new astrophysical populations or more exotic phenomena. Machine-learning methods are widely used for source classification and searches for new physics, but most existing approaches rely on fully supervised training and therefore on explicit signal models. We explore weakly supervised classification as a less model-dependent strategy for analysing $\gamma$-ray source spectra. In a background-versus-mixture setup, classifiers are trained on samples with different signal admixtures rather than on fully labelled signal and background events. We study three representative scenarios: pulsar-active galactic nuclei separation as a controlled benchmark, the identification of dark-matter subhalos, and spectral irregularities induced by axion-photon oscillations. In each case we investigate the impact of signal fraction and sample composition on classification performance. Our results show that weak supervision can identify anomalous or signal-like subsets of data while reducing the reliance on detailed signal templates during training. In favourable cases, the method approaches the performance of fully supervised classifiers, while remaining applicable in situations where the signal model is uncertain or only partially specified. Weakly supervised learning therefore provides a complementary candidate-selection and anomaly-ranking strategy for $\gamma$-ray data analysis and searches for new phenomena.
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Astrophysics of Galaxies

The MAGPI Survey: Evidence for Non-Universal Resolved Dust Attenuation Relations Beyond the Local Universe

A. Mailvaganam, T. Zafar, P. Corcho-Caballero et al. (+39 more)

We study the spatially resolved relation between dust attenuation ($A_V$) and star formation rate surface density ($\Sigma_{\mathrm{SFR}}$) in galaxies from the MAGPI survey ($0.25 < z < 0.42$). Using Balmer-decrement-based attenuation maps for 178 galaxies, we investigate whether the locally calibrated resolved $A_V$–$\Sigma_{\mathrm{SFR}}$ relation remains valid at intermediate redshift by comparing MAGPI with the local relation measured from MaNGA. We find a clear positive correlation between $A_V$ and $\Sigma_{\mathrm{SFR}}$ in MAGPI, with systematically higher attenuation than in MaNGA at fixed $\Sigma_{\mathrm{SFR}}$. After matching galaxies in stellar mass ($M_{*}$) and offset from the star-forming main sequence ($\Delta$SFMS), MAGPI galaxies remain more attenuated than MaNGA galaxies at fixed $\Sigma_{\mathrm{SFR}}$. The attenuation excess is strongest for galaxies below the SFMS ($\Delta A_V \sim 0.40$ mag), weaker for galaxies on the SFMS ($\Delta A_V \sim 0.28$ mag), and minimal for galaxies above the SFMS ($\Delta A_V \sim 0.07$ mag). The dependence of the offset on $\Delta$SFMS suggests that nebular attenuation on kpc scales is regulated not only by local star formation activity, but also by the global evolutionary state of the host galaxy. Together, these results indicate that the resolved $A_V$–$\Sigma_{\mathrm{SFR}}$ relation is not universal, and that locally calibrated attenuation relations may not fully describe galaxies at intermediate redshift. This highlights the need for attenuation calibrations that account for galaxy population and redshift when interpreting spatially resolved galaxy properties.
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All authors A. Mailvaganam, T. Zafar, P. Corcho-Caballero, S. Salim, Y. Koyama, K. E. Harborne, C. D. P. Lagos, J. T. Mendel, E. Wisnioski, I. U. Aalia, S. Ayyappan, S. Barsanti, A. J. Battisti, J. Bland-Hawthorn, I. Breda, S. Carlson, Q.-H. Chen, B. Courtney-Barrer, S. M. Croom, S. Ellis, C. Foster, E. Gjergo, K. Grasha, S. Gurung-Lopez, S. Mobina Hosseini, S. Jeon, X. Lyu, T. Mukherjee, M. Mun, Hye-Jin Park, Y. Peng, L. A. Porta, J. Prathap, A. Raidani, R. S. Remus, B. S. Salmasi, G. Sharma, Sarah M. Sweet, Dian P. Triani, L. M. Valenzuela, G. van de Ven, Bodo L. Ziegler

Astrophysics of Galaxies

Vortex-reconnection energy bounds in Bose-Einstein-condensed and superfluid dark matter halos

Kaz{\i}m Yavuz Ekşi

Bose-Einstein-condensed (BEC) and superfluid dark-matter (SFDM) halos can contain coherent, wave-supported cores whose angular momentum is carried by quantized vortices. When vortices form a tangle, reconnections convert part of the vortex kinetic energy into dark phonons, density waves, Kelvin waves, and vortex loops, providing a microscopic channel by which vortex structure can affect halo-core evolution. We estimate the dynamical importance of this channel by combining the local Gross-Pitaevskii (GP) reconnection law with a halo-scale vortex-line density calibrated against Schrödinger-Poisson (SP) simulations. Vortex reconnections cannot appreciably restructure a standard SP halo core under the fiducial assumptions: for a $m=10^{-22}$ eV, $r_c=1$ kpc soliton and a one-percent energy-transfer efficiency per event, an unforced network transfers at most $1.3\%$ of the core virial energy in 10 Gyr. Reconnection converts ordered vortex energy into sound and smaller-scale excitations; we bound the cumulative transfer using a spectral scale measured in published SP halo simulations. To connect the result with measured systems, we match the standard soliton profile to half-light masses derived with a single mass estimator for eight classical Milky Way dwarf spheroidals. Assigning the measured aperture mass to the soliton gives ceilings of $0.98-4.52\%$ at the Mocz line-density reference and $0.061-3.19\%$ for a modest-rotation normalization. The largest value is a factor of 22 below the core virial-energy scale and limits the fixed-structure velocity change to $2.3\%$. The spectral reference represents fewer than one projected vortex crossing, so these are continuum upper limits; a vortex-free core has no reconnection heating. Reconnections remain worth testing because they are unavoidable when a tangle exists.
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High Energy Astrophysical Phenomena

Prospect for Detection of Strongly Lensed Multi-messenger Signals of Binary Neutron Star Mergers

Zhiwei Chen, Youjun Lu and Changwen Zeng

The gravitational lensing of multi-messenger signals from binary neutron star mergers (BNSs), including gravitational waves (GWs), short Gamma-Ray bursts (sGRBs), kilonovae, and afterglows, can serve as a unique probe to constrain the mass of the graviton and cosmological parameters. In this paper, we estimate the detection rates of lensed electromagnetic counterparts associated with lensed BNS GW events detected by Cosmic Explorer and Einstein Telescope. For kilonovae and afterglows, we further consider a complementary pointed follow-up strategy targeting pre-identified galaxy-scale lens candidates within the GW localization region. By utilizing both numerical and observational constraints on BNS mergers, we find that: (1) Future $\gamma$-ray telescopes, even with a sensitivity more than ten times better than that of Fermi-GBM, may only detect lensed sGRB prompt emission at a rate $\sim 0.1$ yr$^{-1}$, corresponding to $\sim 2\times 10^{-3}$ of detectable lensed BNS GW events. (2) For the known-lens pointed strategy, the identifiable lensed-host fraction is approximately $0.15-0.30$ for the fiducial deep lens-catalog case considered, suggesting a possible gain in per-lens sensitivity for faint kilonovae and afterglows. (3) An RST-like near-infrared facility could detect lensed kilonovae at rates of approximately $\sim 0.45^{+0.81}_{-0.34}$, $0.55^{+0.98}_{-0.41}$, and $0.078^{+0.139}_{-0.059}$ yr$^{-1}$ in the F106, F158, and F213 bands, respectively. (4) Lensed afterglows remain difficult to detect in the optical and radio bands, while ATHENA-like X-ray observations may detect $0.5-5$ events over ten years.
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High Energy Astrophysical Phenomena

Microquasar Cygnus X-3 as the PeVatron powering the Cygnus Bubble

Zhaodong Shi, Guangwei Wang, Ruizhi Yang et al. (+1 more)

The recent discovery by the LHAASO collaboration of a variable ultra-high-energy (UHE; $E_\gamma \ge$ 100 TeV) $\gamma$-ray source associated with the microquasar Cygnus X-3, with a spectrum extending to several PeV, provides compelling evidence for a hadronic super-PeVatron operating within the binary system. Inside the binary, the accelerated protons lose only a small fraction of their energy; upon escaping into the interstellar medium, they propagate diffusively to form a vast gamma-ray “halo" structure extended to hundreds of parsecs. We argue that this halo has already been detected and corresponds to the Cygnus Bubble, an extended UHE $\gamma$-ray source reported by the LHAASO collaboration – which possesses an angular extension of $\approx 6^{\circ}$ and an energy spectrum reaching 1 PeV. While the Cygnus Bubble is generally attributed to the star-forming region Cygnus X (specifically the Cygnus OB2 association at 1.4 kpc), we demonstrate that an association with Cygnus X-3 is physically more natural at energies above 400 TeV. This is supported by the cosmic-ray radial distribution, derived from the $\gamma$-ray and gas distributions, which points to continuous injection from a point-like source. The energetic requirements of the central accelerator are reasonably affordable and feasible. This reassignment identifies the Cygnus Bubble as a member of the recently discovered population of microquasar UHE $\gamma$-ray halos.
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All authors Zhaodong Shi, Guangwei Wang, Ruizhi Yang, Felix Aharonian

Astrophysics of Galaxies · Cross-listed from hep-ex

The Dark Photon in the PHELEX Experiment

A.V.Kopylov, I.V.Orekhov, V.V.Petukhov et al. (+1 more)

This paper presents diurnal measurements of the single-electron count rate in the PHELEX experiment using multi-cathode counters over the period from 2023 to 2026. The results obtained are interpreted as an indication of a possible effect from dark photons with masses ranging from 10 to 40 eV. The correlation of the measured rates in counters with Fe and Al cathodes suggests that the effect does not depend on the magnetic properties of the cathode material. This can be interpreted as an argument against many dark matter models related to magnetic moments. The result, if confirmed in an independent experiment, could narrow the range of possible candidates to those that interact primarily through an electric (or longitudinal) field, insensitive to spin. A dark photon with kinetic mixing fits this description ideally.
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All authors A.V.Kopylov, I.V.Orekhov, V.V.Petukhov, A.E.Solomatin

Astrophysics of Galaxies

Unveiling the Milky Way with a Gaia DR3 census of OB-type stars within 2 kpc. I. Tracing local Galactic structure, massive star-forming regions and core-collapse supernova progenitors

Alexis L. Quintana, Kiril Maltsev, Eloisa Poggio et al. (+10 more)

O- and B-type stars are young and hot, thereby serving as vital tracers of the star formation and spiral arm structure of the Milky Way. At the dusk of the Gaia DR3 era, a high-confidence and accurate catalogue appears timely. We have characterized 105,971 OB-type stars (T$_{\rm eff} >$ 10,000 K) within 2 kpc from the Sun, using an astro-photometric Bayesian inference tool. Our map unveils a complex view of the young stellar populations across the thin disk, with prominent large-scale features such as the Cepheus Spur, the Giant Oval Cavity, and a segment the Sagittarius-Carina arm all visible. Their inhomogeneous spatial distribution implies that massive star formation has taken place clustered across a few highly concentrated regions. We find a correlation between the overdensities of OB-type stars and young open clusters, and attribute departure from it to extinction effects. We identify 4200 stars as model-dependent core-collapse supernova (ccSN) or direct-collapse black hole (BH) progenitor candidates, including 6 ccSN progenitor candidates within 125 pc – the maximum radius within which a ccSN explosion could be harmful to Earth's biosphere – but our analysis suggests none of them exploding within the next 5 Myrs. Finally, we anticipate more evolved OB-type stars to collapse to form BHs within the next 1 Myr than ccSN progenitors will explode, despite the former's much scarcer number. A possible interpretation is a recent star formation burst in the local Milky Way, consistent with overdensities of ccSN progenitor candidates in Cyg OB2 and the Sagittarius-Carina arm.
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All authors Alexis L. Quintana, Kiril Maltsev, Eloisa Poggio, Emily L. Hunt, Nicholas J. Wright, Sara R. Berlanas, Laia Casamiquela, Abel de Burgos, Hanna Parul, Misha Haywood, Paola Di Matteo, Chervin Laporte, Juan Martínez García

Astrophysics of Galaxies

Fast Dynamical Modelling of Milky Way Globular Clusters – I. Implications for Initial Cluster Densities

Nolan Dickson, Vincent Hénault-Brunet, Fotios Fronimos Pouliasis et al. (+2 more)

We infer the initial conditions of Milky Way (MW) globular clusters (GCs) from present-day observations, through the coupling of recently updated rapid cluster evolution models with multimass equilibrium models. This novel method is validated by fitting to simulated observations of a large grid of star-by-star Monte Carlo models, demonstrating that we are able to recover cluster properties like the total mass, half-mass radius/density and black hole (BH) mass fraction, both initially and at the present day, across a large region of parameter space. We apply this framework to a sample of 40 MW GCs, fitting to a suite of observed radial profiles of number densities, proper motions, line-of-sight velocities and stellar mass functions. From these fits we infer a distribution of initial half-mass densities with a median and $1\sigma$ width, across our sample, of $\rho_{h,0} = 10^{6.4\pm0.9}\,{M_\odot pc^{-3}}$, higher than what is found for young massive clusters in the Local Universe and in line with young clusters at high redshift. We also find stellar initial mass functions that are bottom-light in comparison to canonical prescriptions, and relatively small present-day BH mass fractions ($\lesssim 1.5\%$). We discuss the implications of these initial cluster densities for observations of high-redshift proto-GCs, binary BH merger rates and intermediate-mass BHs (IMBHs) in GCs. Finally, we quantify how these densities may depend on assumptions typically made surrounding BH formation and natal kicks.
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All authors Nolan Dickson, Vincent Hénault-Brunet, Fotios Fronimos Pouliasis, Mark Gieles, Peter J. Smith

Astrophysics of Galaxies

The dynamical origin of the magnetic field distributions in compressible turbulence

Evangelia Ntormousi and Fabio Del Sordo

Magnetohydrodynamical (MHD) simulations of isothermal compressible turbulence report that the density distribution is well described by a lognormal with a variance proportional to the flow's Mach number. The distribution of magnetic field strength also has a lognormal component, but includes long, power-law-like tails. In this work, we use semi-analytical arguments to predict the distributions of density and magnetic field strength in compressible turbulent flows. Specifically, in the Lagrangian description of the continuity and the induction equations, we model the velocity gradients of the turbulent flow as a simple random process, essentially turning these equations into stochastic differential equations. Integrating them leads to a lognormal distribution for the density field and the strength of the magnetic field. The power-law tails in the magnetic field PDF appear when we introduce intermittent shocks due to sampling rare events. Gradually increasing the frequency of these events, essentially going closer to a continuous process, leads to lognormal-like distributions again. The asymmetry is connected to the relative abundance of slow and fast shocks. An overabundance of fast MHD shocks produces a high-value tail, while the contrary produces low-value tails. We propose that the appearance of power-law tails along lognormals in turbulent flows is the signature of the co-existence of continuous, diffusion-like propagation combined with localized, intermittent events.
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Solar and Stellar Astrophysics

Kinetic Processes to Radio Burst: First Observational-driven Study in Coronal Loops

Mehdi Yousefzadeh, Marian Karlicky, Artem Koval et al. (+3 more)

Understanding the origin of coherent solar radio bursts requires linking macroscopic coronal structures with the kinetic processes responsible for wave generation. We investigate emissions from slowly positively drifting bursts (SPDBs), a specific type of solar radio emission. SPDBs provide observational constraints for modeling beam-plasma interactions in coronal loops, serving as a basis for a multiscale description. We employ a three–stage numerical framework that combines nonlinear force–free field (NLFFF) magnetic extrapolation, guiding–center simulations, and fully kinetic particle–in–cell (PIC) modeling. The background plasma density is described using a hydrostatic model consistent with active–region conditions, producing a plasma–frequency gradient comparable to that inferred from the observed SPDBs spectrum. Energetic electrons injected near the loop top evolve through magnetic mirroring, pitch–angle scattering, turbulence development, and partial precipitation. Evolved velocity distribution functions (EVDFs) are sampled after approximately one bounce period and used in PIC simulations to evaluate emission properties. The results show that the evolved beam distribution of energetic electrons predominantly excites beam–Langmuir waves and fundamental plasma emission along the loop, with the emission intensity gradually decreasing from the loop top toward the footpoint. The modest initial beam velocity of energetic electrons explains the inefficient generation of harmonic plasma emission. The temporal evolution of the modeled emission reproduces key SPDB characteristics, including the ~ 4s duration and frequency drift behavior. These results suggest plasma emission explains the mechanisms behind SPDB generation and demonstrate the feasibility of a unified model connecting coronal magnetic topology, particle transport, and radio emission.
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All authors Mehdi Yousefzadeh, Marian Karlicky, Artem Koval, Alena Zemanova, Yao Chen, Jun Lin

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

From inflation to hot big bang – a tutorial on cosmological perturbations

Mikko Laine and Simona Procacci

These lecture notes are meant as a pedagogic guide to cosmological inflation and the early epochs thereafter. Inflation explains how the seeds for density perturbations, which evolved into the largest structures in our universe, could have formed during a period of exponential expansion. Apart from density perturbations, also tensor perturbations are generated, which may be observed as gravitational waves. The formalism is developed through explicit computations, paying attention to general-relativistic gauge invariance, and to thermalization (the mechanism that converts part of the energy density driving exponential expansion into the conventional hot big bang). For the steps best handled numerically or computer-algebraically, simple python scripts are provided. We aim at an unassuming style, hopefully accessible to students of theoretical high-energy physics.
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Astrophysics of Galaxies

XRISM Reveals a Kinematically Coherent Core System of the Nearby Cool-Core Cluster Abell 2199

Kazunori Suda, Kyoko Matsushita, Kosuke Sato et al. (+14 more)

We present the results of a deep 251 ks XRISM/Resolve observation of the cool core of the galaxy cluster Abell 2199. From the integrated spectrum of the central $3' \times 3'$ Resolve field of view ($104 \times 104 \mathrm{~kpc}^2$), we find that the intracluster medium (ICM) redshift is consistent with that of the brightest cluster galaxy, within the optical-redshift uncertainty. This indicates that they form a kinematically coherent core system, which offset from the mean cluster redshift by $\sim200~\mathrm{km~s^{-1}}$. The observed velocity dispersion of $\sim100~\mathrm{km~s^{-1}}$ corresponds to a three-dimensional Mach number of $M_{\mathrm{3D}}=0.16$ and a non-thermal pressure fraction of $P_{\mathrm{NT}}/P_{\mathrm{tot}}=1.4\pm0.2$%. Abell 2199 is one of the most dynamically quiescent relaxed clusters observed with XRISM, despite the presence of radio jets and a plume-like structure possibly associated with sloshing motions. Order-of-magnitude estimates suggest that turbulent dissipation could offset a non-negligible fraction of the radiative cooling losses, with $Q_{\mathrm{turb}}/Q_{\mathrm{cool}}\approx0.2$ for a large-scale driver such as sloshing and larger values for smaller AGN-feedback scales. Finally, we detect a localized enhancement of the Fe XXV He$\alpha$ $y$ line in the southeast region, which spatially coincides with a Chandra surface brightness discontinuity.
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All authors Kazunori Suda, Kyoko Matsushita, Kosuke Sato, Kotaro Fukushima, Ming Sun, Caroline Kilbourne, John A. ZuHone, Edmund Hodges-Kluck, Shogo B. Kobayashi, Simon Dupourque, Daniel R. Wik, Priyanka Chakraborty, Arnab Sarkar, Marie Kondo, Itsuki Aihara, Eric D. Miller, Francois Mernier

Cosmology and Nongalactic Astrophysics

KAN-LSTM-Transformer Neural Networks, MFV and Cosmological Parameters

Jiang Zhang and Yan-dong Chen

Reconstructing the cosmic distance ladder directly from observations is a crucial issue in cosmology. In this paper, we present a novel method for modeling the cosmic distance ladder and estimating cosmological parameters through the use of Kolmogorov-Arnold networks (KAN), Long Short-Term Memory (LSTM), and Transformer networks (collectively referred to as KLT-Net), based on the apparent magnitude data from the Pantheon SN Ia compilation. As a data-driven, non-parametric method for reconstructing the distance modulus $\mu(z)$, KLT-Net is shown to be highly effective in capturing the intricate, nonlinear measurement distributions. After validating against various statistical and machine learning models, we have identified it as the most effective choice among the considered alternatives and ablation experiments. Subsequently, the statistical inference of $H_0$ and $\Omega_{\rm m}$ adopts the flat $\Lambda$CDM framework. Moreover, we introduce the Most Frequent Value (MFV) approach to evaluate the absolute magnitude, $M_B$, from existing literature data. In addition, we employ the Hessian matrix to validate the Bayesian method, demonstrating that the Hubble constant can be precisely constrained from the KLT-Net predictions within the flat $\Lambda$CDM framework. The integration of KLT-Net, the MFV approach, and Bayesian statistics establishes a robust framework for inferring cosmological parameters. This methodology facilitates future cosmological research, particularly in the analysis of complex datasets and the exploration of high-dimensional parameter spaces.
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High Energy Astrophysical Phenomena · Cross-listed from stat.ME

Compensator-based inference for signal detection under unknown background: the binned data case

Aritra Banerjee and Sara Algeri

The problem of signal detection under an unknown background can be framed as one of inferring the weight of a mixture model with one misspecified component. Banerjee and Algeri (2026) show that, for this problem, the conservativeness of the inference is entirely determined by one single parameter, called the compensator. They demonstrate that, when the data are independent and identically distributed, an inferential approach based on the compensator circumvents the need to estimate the density of the misspecified component and the associated challenges. The main purpose of this manuscript is to broaden the scope of such an approach and extend it to the case in which, as is often encountered in modern experiments in physics and astronomy, the data consist of Poisson counts observed over a large number of bins.
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Cosmology and Nongalactic Astrophysics

Constructing a Mock Galaxy Catalog for the All-sky SPECtroscopic Survey of Nearby Galaxies (A-SPEC) Using the Machine-assisted Semi-Simulation Model

Dongkok Kim, Yongseok Jo, Ho Seong Hwang et al. (+26 more)

We present a methodology for constructing a mock galaxy catalog for the All-sky SPECtroscopic survey of nearby galaxies (A-SPEC) using the Machine-assisted Semi-Simulation Model. The model is trained on the cosmological magnetohydrodynamical simulation IllustrisTNG to predict baryonic properties of subhalos from dark-matter-only features and is applied to our own N-body simulation tailored to satisfy the requirements of A-SPEC. We have improved the model's accuracy by introducing additional features such as subhalo anisotropy parameters and modified definitions of the subhalo environment, which result in the coefficient of determination R^2=0.96, 0.90, 0.70, 0.79 for stellar mass, gas mass, star formation rate, and gas metallicity, respectively. The resulting mock galaxies reproduce the luminosity-dependent clustering of the target galaxies when tuned to match the number density. We discuss avenues for further improvement, including the role of environment in the predictions. We release the mock galaxy catalog with the baryonic properties predicted from the model.
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All authors Dongkok Kim, Yongseok Jo, Ho Seong Hwang, Ji-hoon Kim, Juhan Kim, Jaehyun Lee, Hyeonguk Bahk, Young-Man Choi, Moo-Young Chun, Sang-Hyun Chun, Haeun Chung, Kim Dachan, Sungwook E. Hong, Minhee Hyun, Donghui Jeong, Jae-Woo Kim, Kang-Min Kim, Yunjong Kim, Jongwan Ko, Minseong Kwon, Ho-Gyu Lee, Jong Chul Lee, Yongseok Lee, Hyunho Lim, Heeyoung Oh, Changbom Park, Hyunmi Song, Mingyeong Yang, Yongmin Yoon

Earth and Planetary Astrophysics · Cross-listed from physics.optics

Exoplanet Detection Using Adaptive Quantum-Optimal Measurement

Hyunsoo Choi, Hyoung Won Baac, Zubin Jacob et al. (+1 more)

Detecting terrestrial exoplanets in the habitable zones of nearby stars remains a critical challenge. Such planets can be \(10^8\) to \(10^{10}\) times fainter than their host stars and lie at diffraction-limited angular separations, where starlight strongly obscures the companion signal. Here we present an adaptive quantum measurement method for estimating the number, positions, and brightnesses of mutually incoherent point sources in the sub-Rayleigh, ultra-high-contrast regime, operating at contrasts down to \(10^{-8}\) – five orders of magnitude beyond previous quantum imaging approaches to exoplanet detection. The method adopts a spatial-mode basis that is updated to maximize the quantum Fisher information per detected photon. Estimation is performed by maximum likelihood in log-brightness coordinates, and the source count is determined by Bayesian-information-criterion (BIC) model selection directly from photon-count statistics, without a tunable detection threshold. For point sources within sub-Rayleigh separations and with brightness ratios spanning eight orders of magnitude, the method reconstructs complete scenes with a mean success rate of \(72.5\%\). Furthermore, it is robust to misalignment, maintaining a \(71.3\%\) success rate under offsets of up to six pixels. These results demonstrate that terrestrial exoplanets can be detected below the Rayleigh limit, a regime previously inaccessible to direct imaging.
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All authors Hyunsoo Choi, Hyoung Won Baac, Zubin Jacob, Haejun Chung

Astrophysics of Galaxies

A CO detection in the off-plane region of the edge-on galaxy NGC 4565 with the Nobeyama 45-m telescope

Ren Matsusaka, Fumi Egusa, Fumiya Maeda et al. (+1 more)

Understanding the cycling of interstellar medium (ISM) between the galactic plane and off-plane regions is crucial for tracing the evolution of disk galaxies. We present $^{12}$CO($J=1-0$) multi-pointing observations of the edge-on, Milky Way-like galaxy NGC 4565 obtained with the Nobeyama 45-m telescope, with an angular resolution of 14 arcsec, corresponding to about 0.8 kpc. Along a prominent dust filament, we detect significant CO emission at three off-plane positions above the galactic plane. After evaluating possible beam-pattern contamination, the detections remain robust. The derived per-beam molecular masses are $M_{\rm mol} \simeq (2.1-4.3) \times 10^7 M_\odot$. While the off-plane spectra show broader effective line widths, $\sigma_{\rm eff}=83-115$ km s$^{-1}$, than the disk spectra, they contain CO components consistent with the local disk rotation. The mean observed off-plane CO intensity fraction is about 0.34. Comparison with geometrically thin-disk models suggests that this large fraction is best explained by gas above the disk. The large $\sigma_{\rm eff}$ values are partly attributable to a high-velocity component with molecular gas mass $M_{\rm mol}^{\rm HV} \sim 10^7 M_\odot$ that is offset by about 100 km s$^{-1}$ from the local disk velocity. The kinetic energy of this component is estimated to be $E_{\rm kin} \sim 10^{54}$ erg. Such a large energy requirement is difficult to explain by disk-driven feedback in NGC 4565, which has a Milky Way-like star formation rate. External inflow is therefore one possibility.
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All authors Ren Matsusaka, Fumi Egusa, Fumiya Maeda, Toshihiro Handa