Astrophysics of Galaxies
The variability angular diameter distance and the intrinsic brightness temperature of active galactic nuclei
Whee Yeon Cheong, Sang-Sung Lee, Chanwoo Song et al. (+5 more)
Context. It has recently been suggested that angular diameter distances derived from comparing the variability timescales of blazars to angular size measurements with very long baseline interferometry (VLBI) may provide an alternative method to study the cosmological
evolution of the Universe. Once the intrinsic brightness temperature ($T_{\rm int}$) is known, the angular diameter distance may be found without knowledge of the relativistic Doppler factor, opening up the possibility of a single rung distance measurement method from low $(z_{\rm cos}\ll1)$ to high $(z_{\rm cos}>4)$
redshifts. Aims. We aim to verify whether the variability-based estimates of the intrinsic brightness temperature of multiple active
galactic nuclei (AGNs) converges to a common value. We also investigate whether the intrinsic brightness temperature changes as a function of frequency. Methods. We estimated the $T_{\rm int}$ of AGNs based on the flux variability of the
radio cores of their jets. We utilized
radio core light curves and size measurements of 75 sources at 15 GHz and of 37 sources at 43 GHz. We also derived $T_{\rm int}$ from a population study of the brightness temperatures of VLBI cores using VLBI survey data of more than $100$ sources at 24, 43, and 86 GHz. Results.
Radio core variability-based estimates of $T_{\rm int}$ constrain upper limits of $\log_{10}T_{\rm int}$ [K]$<11.56$ at 15~GHz and $\log_{10}T_{\rm int}$ [K]$<11.65$ at 43 GHz under a certain set of
geometric assumptions. The population analysis suggests lower limits of $\log_{10}T_{\rm int}$ [K]$>9.7$, $9.1$, and $9.3$ respectively at 24, 43, and 86 GHz. Even with monthly observations, variability-based estimates of $T_{\rm int}$ appear to be cadence-limited. Conclusions. Methods used to constrain $T_{\rm int}$ are more uncertain than previously thought. However, with improved
datasets, the estimates should converge.
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All authors Whee Yeon Cheong, Sang-Sung Lee, Chanwoo Song, Jeffrey Hodgson, Sanghyun Kim, Hyeon-Woo Jeong, Young-Bin Shin, Sincheol Kang
Solar and Stellar Astrophysics
Quasi-Biennial Oscillations and Rieger-type Periodicities in a Babcock-Leighton Solar Dynamo
Pawan Kumar, Belur Ravindra, Partha Chowdhury et al. (+1 more)
The Sun's
magnetic field shows the 11-year
solar cycle and shorter periodicities, popularly known as the quasi-biennial oscillations (QBOs) and Rieger-type periods, or “season of the Sun." Although several theories have been proposed to explain the origin of QBOs and Rieger-type periods, no single theory has widespread acceptance. We explore whether the \bl\ dynamo can produce Rieger-type periodicity and QBOs and investigate their underlying physical mechanisms. We use the observationally guided three-dimensional kinematic \bl\ dynamo model, which has emerged as a successful model for reproducing many characteristic features of the
solar cycle. We use Morlet wavelet and global wavelet power spectrum techniques to analyze the data obtained from the model. In our model, we report QBOs and Rieger-type periods for the first time. Further, we investigate the individual \bl\ parameters (fluctuations in flux, latitude, time delay and tilt scatter) role in the occurrence of QBOs and Rieger-type periods. We find that while fluctuations in the individual parameters of the \bl\ process can produce QBOs and Rieger-type periodicity, their occurrence probability is enhanced when we consider combined fluctuations of all parameters in the \bl\ process. Finally, we find that with the increase of dynamo supercriticality, the model tends to suppress the generation of Rieger-type periodicity. Thus, this result supports earlier studies that suggest the
solar dynamo is not highly supercritical.
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All authors Pawan Kumar, Belur Ravindra, Partha Chowdhury, Bidya Binay Karak
Astrophysics of Galaxies
Tracing The Start and End of Cosmic Reionization – Exploring The Role of Ionizing Sources as drivers
Arghyadeep Basu
This thesis investigates the Epoch of
Cosmic Reionization (EoR), a key period in the early Universe when the first luminous sources formed and their radiation transformed the intergalactic medium (IGM) from neutral to ionized. Understanding this process reveals how the first
stars and
galaxies formed, influenced their surroundings, and shaped large-scale structures. The work traces both hydrogen and helium reionization by identifying the sources that produced ionizing radiation and examining how this radiation affected the thermal and ionization history of the IGM. Using the SPICE cosmological radiation-hydrodynamics simulations, the first part analyzes the ultraviolet luminosity function (UVLF) of high-
redshift galaxies. It shows that different
supernova feedback models drive distinct UVLF variability across mass and
redshift, potentially alleviating the bright-
galaxy tension seen by JWST. The second part explores how spectra from ionizing sources i.e. single and binary
stars, X-ray binaries, emission from the interstellar medium, and active
galactic nuclei impact the timing,
topology, and thermal history of hydrogen reionization and the Lyman-alpha forest. At lower
redshifts, radiative-transfer simulations reveal how helium reionization driven by
quasars progressed and how the timing and temperature of the IGM relate to
quasar luminosity functions and He II Ly-alpha observations. Finally, predictions for the 3.5 cm hyperfine transition of singly ionized helium-3 offer a novel probe of the post-reionization IGM. Together, these studies combine
galaxy formation, radiative processes, and IGM
evolution to provide a coherent picture of
cosmic reionization and its observable signatures.
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High Energy Astrophysical Phenomena
On the acceleration of cosmic rays at the post-adiabatic shocks of supernova remnants
O. Petruk, R. Bandiera, T. Kuzyo et al. (+2 more)
When a
supernova remnant (SNR) interacts with the dense material of an interstellar cloud, its shock wave decelerates rapidly, and the post-shock temperature drops to levels that permit efficient cooling of the shocked
plasma. At this stage, the shock enters the post-adiabatic phase of its
evolution. During this phase, the internal structure of the SNR undergoes significant changes, particularly in the immediate post-shock region, at spatial scales relevant to
cosmic ray acceleration. Once the shock enters the post-adiabatic regime, the efficiency of diffusive shock acceleration increases due to a higher
plasma compression, to a change in the direction of the advection velocity, and to an increased rate of momentum gain. As a result, the momentum spectrum of relativistic particles hardens, deviating from a pure power law at high energies. Particles could reach higher maximum values compared to classical predictions. We highlight the dynamics of post-adiabatic flows in SNRs, study their impact on particle acceleration, and present supporting observational evidence in the
radio band.
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All authors O. Petruk, R. Bandiera, T. Kuzyo, R. Brose, A. Ingallinera
Instrumentation and Methods for Astrophysics · Cross-listed from physics.optics
Zernike Mode Sorting with Vortex Phase Filters: Perfect Coronagraphs and Ideal Wavefront Sensors
Jacob Trzaska and Amit Ashok
Spatial mode sorting has come to prominence as an optical processing modality capable of saturating fundamental limits to numerous sensing tasks including wavefront sensing, coronagraphy, and superresolution imaging. But despite their promising theoretical advantages, contemporary mode sorters often feature large crosstalk, high loss, or sort modes that are poorly adapted to conventional imaging systems (e.g., Hermite- and Laguerre-Gauss). Here, we introduce an alternative architecture that sorts spatial modes natural to circularly symmetric apertures: Zernike
polynomials. Using conventional optics hardware and even-order
vortex phase plates, we show how to assemble a series of
vortex phase filters that can in principle separate the various Zernike
polynomials losslessly and without crosstalk. This idea is demonstrated via application to wavefront sensing and coronagraphy, where we propose an optical system that saturates the
quantum sensitivity limits to both tasks. We expect our work to prove useful for high-contrast imaging of extrasolar
planets, improving both wavefront control and coronagraph performance.
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Cosmology and Nongalactic Astrophysics
Evidence of dynamical dark energy found via the DESI DR2 Lyman$\alpha$ forest
Salvatore Capozziello, Himanshu Chaudhary, G. Mustafa et al. (+1 more)
We present a comprehensive analysis of the cosmological implications of the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) Lyman-$\alpha$ forest
baryon acoustic oscillation (BAO) measurements, combined with DESI DR2
galaxy BAO, Type Ia
supernova samples (Pantheon$^+$, DES-Dovekie, and Union3), and the
cosmic microwave background CamSpec likelihood. We consider several dark-energy parameterizations, including Chevallier-Polarski-Linder, logarithmic, exponential, Jassal-Bagla-Padmanabhan, Barboza-Alcaniz, and generalized emergent dark energy, as well as the $w$CDM model and non-flat extensions of $\Lambda$CDM and $w$CDM. Using the Metropolis-Hastings MCMC
algorithm, we constrain cosmological parameters and compute
Bayesian evidence with MCEvidence. We find that non-flat extensions remain consistent with spatial flatness, with $\Omega_k \approx 0$. All parameterizations favor a dynamical dark-energy scenario with $w_0 > -1$, $w_a < 0$, and $w_0 + w_a < -1$, consistent with a Quintom-B behavior. A moderate preference for dynamical dark-energy models is found relative to $\Lambda$CDM, reaching up to $\sim3.10\sigma$ for Ly$\alpha$ + CMB +
galaxy BAO. When combined with SNe~Ia
datasets, the deviations decrease to $\lesssim2\sigma$, corresponding to inconclusive preference. The Bayes factor ($\ln B_{ij}$) shows that model preference depends strongly on the
dataset combination: $w$CDM and o$w$CDM exhibit moderate evidence for Ly$\alpha$ + CMB +
galaxy BAO, while most other models show weak or inconclusive evidence. With Pantheon$^{+}$ or DES-Dovekie, o$w$CDM shows strong evidence, whereas other models remain moderately favored.
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All authors Salvatore Capozziello, Himanshu Chaudhary, G. Mustafa, S. K. J. Pacif
Earth and Planetary Astrophysics
Earth Analogs in Reflected Light: Insights from Early Spectral Characterization in Unconstrained Orbits
Arnaud Salvador and Tyler D. Robinson
A next generation of space-based observatories aims to detect and characterize potentially Earth-like
exoplanets around Sun-like
stars using reflected light spectroscopy. However, it remains unclear how such direct imaging observations$-$limited in spectral coverage and signal-to-noise ratio (S/N)$-$translate into constraints on atmospheric composition and habitability. Coronagraphs used for high-contrast imaging typically operate over narrow bandpasses, and exposure time limits can restrict data quality. To optimize observing strategies and instrument design, we use our atmospheric
retrieval tool, $\texttt{rfast}$, to assess the performance of a $\mathit{Habitable\ Worlds\ Observatory}$-type mission across different spectral bandpasses ("Red", "Blue", "Visible", "NIR", and their combination) and S/N levels (10, 15, and 20; from moderate to moderate-high observation quality) in retrieving a wide range of 17 atmospheric, surface, bulk, and orbital parameters of a habitable Earth analog. We outline the observation requirements for each parameter and the detection capabilities of each case, within a novel scenario where spectral data are taken "early", prior to achieving orbit constraints (which may require repeat visits to a system). For coronagraph-restricted and NIR-only bandpasses, most of the limited retrievable information is already captured at S/N = 10, with little improvement at higher S/N. For broader spectral coverage, the quality and quantity of retrieved information improve with increasing S/N, but combining visible and NIR ranges provides the most comprehensive characterization, even at moderate S/N. To maximize returns, wider spectral coverage should be prioritized over improving S/N when spectral access is limited.
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Astrophysics of Galaxies
Under Pressure: Decoding the Effect of High Densities on Derived Nebular Properties
Z. Martinez, D. A. Berg, B. L. James et al. (+6 more)
Recent JWST observations have uncovered a population of compact, high-
redshift ($z>6$)
galaxies exhibiting extreme nebular conditions and enhanced nitrogen abundances that challenge standard chemical
evolution paradigms. We present a joint UV and optical abundance analysis using a new suite of $\texttt{Cloudy}$ photoionization models covering a wide density range ($n_e=10^2-10^9$ cm$^{-3}$), combined with HST and JWST spectroscopy for a sample of
star-forming
galaxies across $0.0\lesssim z \lesssim10.6$. We find that assuming uniform, low-density conditions ($n_e\sim10^2$ cm$^{-3}$) in high-density environments ($n_e\sim10^5$ cm$^{-3}$) can bias nebular diagnostics by overestimating $T_e$ (up to 1800 K), overpredicting $\log U$ (by $>1$ dex), and underestimating O/H (up to 0.67 dex), while only modestly inflating N/O. Therefore, robust abundance determinations at high-$z$ require a multi-phase density model. Using this model, we recalculate O/H and N/O abundances for our sample and present the first $\log U$ diagnostics and ICFs for high-ionization UV N lines. We find that the UV tracers systematically overestimate N/O by $\sim0.3-0.4$ dex relative to the optical
benchmark. We find that N/O increases with
redshift, correlating with both $n_e$ and
star formation rate surface density ($\rm\Sigma_{SFR}$), suggesting that N/O is temporarily enhanced in compact, high-pressure environments. However, the $n_e$
evolution with $z$ is more gradual than the $(1+z)^3$ scaling of virial
halo densities, suggesting that $n_e$
evolution is shaped by both cosmological structure growth and baryonic processes. These trends point to
prompt N/O enrichment potentially driven by very massive
stars, with key implications for interpreting UV emission and determining reliable chemical abundances from JWST observations of the early universe.
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All authors Z. Martinez, D. A. Berg, B. L. James, K. Z. Arellano-Córdova, D. P. Stark, P. Senchyna, E. D. Skillman, N. S. J. Rogers, J. Chisholm
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Bubble wall velocity with out-of-equilibrium corrections
Carlo Branchina, Angela Conaci, Stefania De Curtis et al. (+1 more)
We study how out-of-
equilibrium effects modify the steady-state propagation of bubble walls during a cosmological first-order electroweak phase transition. Going beyond the local thermal
equilibrium approximation, we numerically solve the coupled system of scalar field, hydrodynamic and Boltzmann equations using a spectral
algorithm that allows a first-principle treatment of the collision integral. This approach enables a quantitative assessment of non-
equilibrium perturbations in the
plasma and their backreaction on the wall motion. Focusing on the singlet extension of the Standard Model as a minimal
benchmark scenario, we find that out-of-
equilibrium corrections substantially enhance the effective friction on the expanding front, leading to slower wall velocities and broader wall profiles compared to the
equilibrium case. These modifications have significant implications for cosmological observables. For instance, they enhance the efficiency of electroweak baryogenesis, thus improving the viability of
baryon asymmetry generation within realistic parameter regions that can also be probed by future gravitational wave interferometers.
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All authors Carlo Branchina, Angela Conaci, Stefania De Curtis, Luigi Delle Rose
Solar and Stellar Astrophysics
SPYGLASS. VII-A. The Demographics and Ages of Small Nearby Young Associations
Ronan Kerr, Facundo Peŕez Paolino, Jonathan C. Tan et al. (+5 more)
Recent
Gaia-based young
stellar association surveys have revealed dozens of low-mass populations that have, until recently, been too small or sparse to detect. These populations represent a largely unstudied demographic with unknown origins, and their relative isolation may minimize gravitational disruptions that impact traceback, making them compelling targets for dynamical studies. In this paper, we survey 15 of these isolated young associations for the first time: Andromeda South (SCYA-97), Aquila East, Aries South (SCYA-104), Cassiopeia East (SCYA-43), Canis Major North, Leo Central (SCYA-2), Leo East (SCYA-3), Theia 72, Ophiuchus Southeast, Scutum North (SCYA-70), Taurus-Orion 1 (TOR1), Theia 78, Vulpecula East (UPK 88), SCYA-54, and SCYA-79. By combining
Gaia astrometry and photometry with new ground-based spectroscopic measurements, we assess the membership of each population, search for substructure, analyze their demographics, and compute ages. We find that the smallest populations in our sample contain $<20$ $M_{\odot}$ of
stellar mass, making them the smallest associations ever detected. Four host substantial substructure, including TOR1, where we discover TOR1B, a new 16 $M_{\odot}$ association with radial velocities inconsistent with an origin in the parent complex. Using PARSEC isochrones, we produce self-consistent ages for all populations supported by dynamical and lithium depletion ages, which range from 6.9 $\pm$ 0.5 Myr in TOR1A to 42.8 $\pm$ 2.4 in AndS. Our results provide the first detailed overview of the properties of these populations, characterizing a largely unknown category of young associations that may have an important role in tracing the processes that guide local
star formation.
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All authors Ronan Kerr, Facundo Peŕez Paolino, Jonathan C. Tan, Joshua S. Speagle, Adam L. Kraus, José G. Fernández-Trincado, Keivan G. Stassun, Julio Chanamé
Cosmology and Nongalactic Astrophysics
Dynamical Dark Energy Meets Varying Electron Mass: Implications for Phantom Crossing and the Hubble Constant
Adam Smith, Emre Özülker, Eleonora Di Valentino et al. (+1 more)
We investigate the interplay between varying electron mass ($m_e$) and dynamical dark energy by analysing the Chevallier-Polarski-Linder (CPL) parametrization and its non-crossing variants, both with and without a varying-$m_e$ component. Our aim is to assess whether the preference for late-time dynamics and phantom divide line (PDL) crossing persists when early-time physics is introduced, and whether these combined models improve the alleviation of the Hubble tension compared to the varying-$m_e$ extension alone. Using the latest CMB, BAO, and
supernova datasets, we derive updated constraints on $\Lambda$CDM, CPL, and their extensions, and examine their impact on $H_0$ and the preference for late-time dynamics. We find that $\Lambda$CDM+$m_e$ yields the largest upward shift in $H_0$, while replacing $\Lambda$ with the CPL parametrization or its non-crossing variants provides modest improvements in the overall fit. The data consistently favour dynamical dark energy and a phantom divide line crossing at scale factors $a_{\rm c}\simeq0.6-0.9$, and these preferences remain robust, though somewhat weaker ($\gtrsim2\sigma$), when the electron mass is also allowed to vary. Among the late-time models, CPL performs better than its non-crossing variants, further reinforcing the evidence for a genuine phantom divide crossing. The alleviation of the $H_0$ tension in the varying-$m_e$ case arises from late-time data breaking the strong $\Omega_m$-$m_e$ degeneracy in the CMB, while the additional degrees of freedom in CPL models allow the late-time dynamics to absorb this impact, thereby weakening the degeneracy breaking and further lowering $H_0$ through their ability to yield a decreasing dark energy contribution.
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All authors Adam Smith, Emre Özülker, Eleonora Di Valentino, Carsten van de Bruck
High Energy Astrophysical Phenomena
Characterizing Low-Latency Sky Localization in Multi-Detector Gravitational-Wave Networks
Amazigh Ouzriat, Viola Sordini and Francesco Di Renzo
Low-latency analyses of gravitational-wave (GW) data from LIGO, Virgo, and KAGRA enable rapid detection of compact binary coalescences (CBC) and
prompt sky localization, essential for electromagnetic follow-up in multi-messenger astronomy. We evaluate the performance and limitations of low-latency sky localization using BAYESTAR
algorithm, and investigate the impact of low-significance Virgo triggers. We inject simulated CBC signals into Gaussian-stationary noise and into Virgo data from the second part of the third LIGO-Virgo observing run (O3b), then reconstruct skymaps across multiple detector network configurations. Localization accuracy is assessed using Percentile-Percentile plots, the Jaccard index, and the Kullback-Leibler divergence. Binary
neutron star mergers are statistically consistent with ideal calibration, showing deviations below 3$\sigma$, particularly when Virgo is included in the network, whereas skymaps for
neutron star–black hole and binary black hole mergers tend to be overconfident. Adding a third detector generally improves accuracy, but the searched area can degrade when Virgo's signal-to-noise ratio is low (SNR $\leq$ 5). For high-SNR events, relying on two detectors can mislocalize the source. Excluding Virgo can therefore cause the HL skymap to miss the true location when Virgo has strong
antenna response, in such cases a three-detector configuration is required to recover the correct position and avoid misleading multi-messenger follow-up. We introduce diagnostics to flag problematic skymaps and apply them to O3 public alerts, recovering simulation-predicted trends and flagging a few anomalous morphologies. The results are relevant for improving rapid vetting of GW alerts and guiding observational strategies in multi-messenger astronomy.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Seafloor Topography Enhances KM3NeT Sensitivity to ANITA-like Events
Carlos A. Argüelles, Toni Bertólez-Martínez, Alba Burgos-Mondéjar et al. (+3 more)
In this article, we introduce the concept of topographic enhancement in the context of ultra-high-energy
neutrino detection by
underwater neutrino telescopes. We demonstrate that the local topography around KM3NeT/ARCA can increase the detection efficiency in scenarios involving long-lived particles by up to a factor of $\sim 3$ due to the presence of an
underwater mountain range in the direction of Malta. We consider a simplified model-independent approach that parametrizes the new physics able to generate both track-like and cascade-like signals in
neutrino telescopes. When explaining the KM3-230213A event with a diffuse dark flux hypothesis, including its azimuthal direction–in addition to the zenith angle–provides additional constraints on the parameter space. In this effective model, the observations by KM3NeT and ANITA-IV can be simultaneously explained, but a global tension with the lack of a corresponding detection in IceCube remains at 2.7 sigma. This work underscores the importance of incorporating topographic effects in the design and optimization of next-generation
neutrino telescopes, as is done in the context of mountain-based detectors such as TAMBO. We present a numerical code which can be used to easily extend this topographical analysis to other experiments.
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All authors Carlos A. Argüelles, Toni Bertólez-Martínez, Alba Burgos-Mondéjar, Anne-Katherine Burns, Jacobo Lopez-Pavon, Jordi Salvado
Cosmology and Nongalactic Astrophysics
Illuminating the Diffuse Radio Emission in Low-Mass Cluster: Abell 13
Nasmi S Anand, Swarna Chatterjee, Ramij Raja et al. (+2 more)
Recent advances in high-sensitivity
radio observations have uncovered a population of faint, ultra-steep-spectrum sources in
galaxy clusters, commonly known as
radio phoenixes. However, their observational classification remains poorly constrained due to the limited number of confirmed detections. This study presents a detailed multi-frequency, high-sensitivity, and high-resolution analysis of diffuse
radio emission in the merging
galaxy cluster Abell 13. Using GMRT (147.5 MHz), uGMRT (400 MHz), ASKAP-low (887.5 MHz), and MGCLS (1284 MHz) images, we detect complex, filamentary diffuse emission with a largest linear extent of 521 kpc. This emission originates from the cluster center and extends westward, confined within the X-ray-emitting intra-cluster medium (ICM). Chandra X-ray data confirm that Abell 13 is undergoing a merger, and the
radio morphology reflects signatures of this ongoing dynamical activity. We observed filamentary structures extending towards east-northeast and southwest directions. The spectral index across the emission appears irregular and lacks a coherent spatial gradient. The integrated spectrum reveals a steep spectral index of -1.85 +/- 0.05 and a spectral
curvature of -0.93 +/- 0.21. These spectral properties, along with the observed morphology and brightness distribution, are consistent with a re-energization of a fossil
radio plasma driven by adiabatic compression, supporting the classification of the emission as a
radio phoenix.
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All authors Nasmi S Anand, Swarna Chatterjee, Ramij Raja, Majidul Rahaman, Abhirup Datta
Instrumentation and Methods for Astrophysics
Likelihood Reconstruction for Radio Detectors of Neutrinos and Cosmic Rays
Martin Ravn, Christian Glaser, Thorsten Glüsenkamp et al. (+2 more)
Ultra-high-energy
neutrinos and
cosmic rays are excellent probes of astroparticle physics phenomena. For astroparticle physics analyses, robust and accurate reconstruction of signal parameters such as arrival direction and energy is essential.
Radio detection is an established detector concept explored by many observatories; however, current reconstruction methods ignore bin-to-bin noise correlations, which limits reconstruction resolution and, so far, has prevented calculations of event-by-event uncertainties. In this work, we present a likelihood description of
neutrino or
cosmic-ray signals in
radio detectors with correlated noise, as present in all
neutrino and
cosmic-ray
radio detectors. We demonstrate, with simulation studies of both
neutrinos and
cosmic-ray
radio signals, that signal parameters such as energy and direction, including event-by-event uncertainties with correct coverage, can be obtained. This method reduces reconstruction uncertainties and biases compared to previous approaches. Additionally, the Likelihood can be used for event selection and enables differentiable end-to-end detector optimization. The reconstruction code is available through the open-source software NuRadioReco.
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All authors Martin Ravn, Christian Glaser, Thorsten Glüsenkamp, Ayca Özcelikkale, Alan Coleman
Astrophysics of Galaxies
The velocity dispersion profile of nine open clusters in the solar neighborhood
Bingqian Ma, XiaoYing Pang, Sambaran Banerjee et al. (+2 more)
We analyze the velocity dispersion profiles of nine open clusters in the
solar neighborhood using kinematic data from
Gaia DR 3, aiming to identify potential dynamical signatures of
stellar-mass black holes through a comparison of theoretical and observed dispersion profiles. The selected clusters include LP2373 gp4, NGC 1980, NGC 2451A, NGC 2516, NGC 3532, NGC 6475, UBC 7, Praesepe, and Pleiades. We refine the center positions of the clusters with the Meanshift
algorithm. Using the Markov Chain Monte Carlo method, we calculate the velocity dispersion for each cluster and construct one-dimensional velocity dispersion profiles. NGC 2516, NGC 3532, and NGC 6475 show potential central cusps in their radial velocity dispersion profiles, which may indicate the presence of
stellar-mass black holes. LP2373 gp4, NGC 6475, and Praesepe all display a negative correlation between velocity dispersion and
stellar mass, indicating these clusters are approaching energy equipartition or expanding. NGC 2516 and NGC 3532 exhibit a positive dependence between velocity dispersion and
stellar mass, which may be attributed to the preferential ejection of massive
stars following dynamical interactions involving binaries or black holes. These two clusters are the only two that are dynamical not relaxed and are closest to virial
equilibrium. We compare the observations with N-body simulations of
star clusters. A comparison of observed and simulated velocity dispersion profiles reveals that NGC 2516 and NGC 3532 exhibit lower proper motion dispersions than model clusters. Better agreement with the observed profiles is achieved for model clusters with larger ages. This suggests that the observed clusters may have undergone rapid dynamical
evolution. Our results suggest that NGC 2516 and NGC 3532 may host at least two
stellar-mass black holes each.
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All authors Bingqian Ma, XiaoYing Pang, Sambaran Banerjee, Pengfei Ren, M.B.N. Kouwenhoven
High Energy Astrophysical Phenomena
Suppressed "lump" EM signature in radiation pressure dominated accreting massive black hole binaries
Fabiola Cocchiararo, Alessia Franchini, Alessandro Lupi et al. (+1 more)
We investigate the impact of radiation pressure on electromagnetic signatures of accreting massive black hole binaries (MBHBs) at milli-parsec separations, using 3D hyper-Lagrangian resolution hydrodynamical simulations. We model binaries embedded in a self-gravitating circumbinary disc that evolves following an adiabatic equation of state, including viscous heating and black-body cooling. Focusing on binaries with a total mass of $10^6 \, M_{\odot}$, eccentricities $e=0,0.45,0.9$ and mass ratios $q=1, 0.7$, we find that radiation pressure significantly affects both the spectral energy distributions (SEDs) and the light curves (LCs). The emission from the mini-discs shifts from the optical towards UV frequencies and with a peak luminosity orders of magnitude higher, while the circumbinary disc becomes colder and dimmer as a result of its geometrically thinner configuration. Temporal variability is affected as well: near UV and soft-X ray fluxes are higher and more variable. Crucially, radiation pressure suppresses the characteristic "lump" formation in equal-mass circular systems, while a lump is formed for higher eccentricities without imprinting any modulation on the flux. In the circular case we still find a modulation on the cavity edge timescale at a frequency $0.36 \, f_{\rm K}$, while in eccentric binaries, only robust orbital period modulations ($f=1,2 \, f_{\rm K}$) are observed, with no modulation associated with the cavity orbital motion. Moreover, the enhanced emission from the mini-discs and streams due to radiation pressure, one redshifted, results in brighter flux in the optical G band, proving detectability of MBHBs signatures even at higher
redshift ($z=0.6-1.0$). Our results reveal that radiation pressure plays a crucial role in shaping MBHBs spectral and time-domain features, with implications for their identification in time-domain surveys.
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All authors Fabiola Cocchiararo, Alessia Franchini, Alessandro Lupi, Alberto Sesana
Cosmology and Nongalactic Astrophysics
XRISM constraints on the velocity power spectrum in the Coma cluster
D. Eckert, M. Markevitch, J. A. ZuHone et al. (+6 more)
The velocity field of intracluster gas in
galaxy clusters contains key information on the virialization of infalling material, the dissipation of AGN energy into the surrounding medium, and the validity of the hydrostatic hypothesis. The statistical properties of the velocity field are characterized by its fluctuation power spectrum, which is usually expected to be well described by an injection scale and a turbulent cascade. Here we propose a simulation-based inference technique to retrieve the properties of the velocity power spectrum from X-ray micro-calorimeter data by generating simulations of Gaussian random fields from a parametric power spectrum model. We forward model the measured bulk velocities and velocity dispersions by including the most relevant observational effects (projection, emissivity weighting, PSF smearing). We then train a neural network to learn the mapping between the power spectrum parameters and the generated data vectors. Considering a three-parameter model describing turbulent energy injection on large scales and a power-law cascade, we found that two XRISM/Resolve pointings are sufficient to accurately determine the turbulent Mach number and set interesting constraints on the injection scale. Applying our method to the Coma cluster data, we obtain a model that is characterized by a large injection scale that rivals the size of the cluster ($\ell_{inj}=2.2_{-1.0}^{+2.0}$ Mpc). When this power spectrum model is integrated over the cluster scales ($0<\ell<R_{500}=1.4 $Mpc), the Mach number of the gas motions is $\mathcal{M}_{3D,500}=0.45_{-0.13}^{+0.18}$, which exceeds the value derived from the velocity dispersions only. Further observations covering a wider area are required to decrease the
cosmic variance and constrain the slope of the turbulent cascade.
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All authors D. Eckert, M. Markevitch, J. A. ZuHone, M. Regamey, I. Zhuravleva, Y. Ichinohe, N. Truong, N. Okabe, D. R. Wik
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Superhorizon Isocurvature as a Window into Dark Matter Production
Christopher Gerlach, Wolfram Ratzinger and Pedro Schwaller
In the presence of
primordial isocurvature perturbations, for example in a separate dark radiation sector, the superhorizon
evolution of
curvature perturbations becomes nontrivial. If the dark sector is radiation-like and constitutes a significant fraction of the energy density, its isocurvature can imply isocurvature in the inflaton sector even without direct interactions between the sectors. In this article, we revisit superhorizon
curvature and isocurvature
evolution in the long-wavelength limit systematically, drawing a simple picture of how to understand the nature of these fluctuations from first principles and without brute-force
cosmic perturbation theory. We show how the described setup is able to source isocurvature in simple models of dark matter such as freeze-in and freeze-out and demonstrate that future measurements of matter and
neutrino isocurvature can potentially discriminate between these two mechanisms.
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Astrophysics of Galaxies
Shadows of the Colossus: Hierarchical Black Hole Mergers in a 10-million-body Globular Cluster Simulation
Aidan Mai, Kyle Kremer and Fulya K{\i}roğlu
The LIGO/Virgo/Kagra (LVK) Collaboration has detected numerous binary black hole mergers with properties that challenge standard binary
evolution scenarios, such as component masses above the pair-instability gap and high
spin magnitudes. Dense
stellar environments such as globular clusters provide a natural channel for producing such systems through hierarchical mergers, where black hole remnants formed in earlier mergers are retained in the cluster and undergo successive mergers. However, gravitational-wave
recoil kicks often eject merger remnants from typical globular clusters, which limits hierarchical growth. Massive clusters with deeper potential wells, such as those found in
giant elliptical
galaxies like M87, may overcome this barrier, but direct simulations of such massive globular clusters remains computationally challenging. In this study, we present a 10-million-body cluster simulation performed with the $\texttt{Cluster Monte Carlo}$ ($\texttt{CMC}$) code, referred to as $\texttt{colossus}$, which serves as a proxy for the most massive low-
metallicity globular clusters observed in the local Universe. This simulation demonstrates that extended chains of hierarchical mergers can occur in massive globular clusters, producing black holes up to fifth generation with masses approaching $250\,M_\odot$, comparable to the most massive LVK events observed to date (e.g., GW231123). Combining the $\texttt{colossus}$ simulation with the previous $\texttt{CMC Cluster Catalog}$, we develop a framework to extrapolate binary black hole merger predictions for the thousands of globular clusters seen in the Virgo Supercluster.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Electroweak Baryogenesis with BARYONET: a self-contained review of the WKB approach
Giulio Barni
We present a comprehensive, self-contained pedagogical computation of the
baryon asymmetry of the Universe within electroweak baryogenesis (EWBG), from the derivation of the semiclassical, CP-dependent force to the formulation and solution of the transport equations obtained from the Boltzmann equations$-$all implemented in the open-source code BARYONET. Our analysis follows the semiclassical WKB approach, where spatially varying complex masses across expanding bubble walls feel CP-violating forces that bias
plasma transport. Starting from the stationary Boltzmann equation in the wall frame and projecting onto a hierarchy of velocity moments, we derive a compact, fluid-like system of coupled differential equations for chemical potentials and velocity perturbations. After obtaining the solutions, one can define the left-handed
baryon chemical potential, which acts as the source term for the weak sphalerons. These processes generate the
baryon asymmetry in front of the wall, which is subsequently frozen once it passes through it. We validate the framework against established formalisms and provide
benchmarks in representative scenarios, including singlet extensions of the Standard Model, two-
Higgs-doublet models, and
Higgs$-\phi^6$ constructions. The resulting BARYONET implementation delivers an automated, reproducible pipeline for WKB-based baryogenesis studies, connecting formal derivations with phenomenological applications. In parallel, we revisit standard EWBG ingredients$-$
diffusion constants, Yukawa/helicity-flip rates, and strong/weak sphaleron rates$-$to clarify conventions, update numerical inputs, and present a pedagogical derivation, ensuring transparent reproducibility.
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