Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
The integral and correlation scales of solar wind turbulence
Jean C. Perez, Sofiane Bourouaine and Mason Dorseth
Many works have attempted to estimate the correlation and integral timescales associated with turbulent fluctuations in the
solar wind, which are interpreted as length scales based on Taylor's~Hypothesis. However, accurate estimates of these timescales from spacecraft observations heavily rely on the accurate estimation of autocorrelation functions (ACF), which have been recently shown to depend strongly on the interval length used to estimate them. In this Letter, we show that this dependence on interval length may be artificial because common ACF
estimators do not correctly capture the long-lag behavior of the true ACF of the underlying
turbulence. We introduce a new ergodicity-based methodology to unambiguously estimate the integral timescale, and a new ACF
estimator with better ergodic convergence than current ones. Due to its ergodic properties, the new ACF
estimator properly captures the long-lag behavior, and is independent of the interval length. We use this approach to estimate the integral and correlation scales of
magnetic fluctuations in the
solar wind near $1~{\rm au}$.
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Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph
A Numerical Experiment on Oscillatory Magnetic Reconnection in a Laboratory Plasma System Driven by Alternating Currents
Sripan Mondal, Abhishekh Kumar Srivastava and Eric R. Priest
Using the open source MPI-AMRVAC framework, we study oscillatory reconnection in a laboratory
plasma, which occurs when a
magnetic null is perturbed by incoming fast magnetoacoustic waves driven by an alternating current. The
magnetic null region collapses to first form a $y$-directed current sheet that later changes its orientation to the $x$-direction. The $x$-directed current sheet has smaller enhanced thermal pressure and out-of-plane current than the $y$-directed current sheet. The
Hall effect produces an out-of-plane
plasma flow that evolves with a time lag with respect to the enhanced thermal pressure and out-of-plane current density. Increasing the amplitude of the alternating current produces higher thermal pressure, out-of-plane current density, and out-of-plane
plasma flow, while the first peaks of thermal pressure and out-of-plane current density occur earlier.
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Astrophysics of Galaxies
ATLAS. I. A Scaling Relation of LRDs between Broad H$\alpha$ and Bolometric Luminosities: Enhanced Broad H$\alpha$ Emission Relative to Low-$z$ Type 1 AGN
Hiroto Yanagisawa, Masami Ouchi, Tomokazu Kiyota et al. (+6 more)
We investigate the demography of little red dots (LRDs) using 37 objects at $z\sim3$-$7$ with JWST/NIRSpec PRISM and grating spectra compiled from various JWST programs. We focus on spectroscopic quantities of the broad H$\alpha$ luminosity $L_\mathrm{H\alpha,broad}$ (and the broad H$\beta$ luminosity $L_\mathrm{H\beta,broad}$ where available) and the bolometric luminosity $L_\mathrm{bol}$ represented by modified blackbody emission, avoiding quantities contaminated by host-
galaxy emission (e.g., total H$\alpha$ luminosity). We identifiy a tight scaling relation between $L_\mathrm{H\alpha,broad}$ and $L_\mathrm{bol}$, supporting the interpretation that these emissions are primarily powered by the central engine. Interestingly, the $L_\mathrm{H\alpha,broad}$-$L_\mathrm{bol}$ scaling relation of LRDs is enhanced by a factor of $\sim40$ in $L_\mathrm{H\alpha,broad}$ relative to that of low-$z$ Type 1 AGN. A similar trend is found in the $L_\mathrm{H\beta,broad}$-$L_\mathrm{bol}$ relation, although the enhancement in $L_\mathrm{H\beta,broad}$ is smaller, only by a factor of $\sim10$. We explore the physical origin of these enhancements and find that Cloudy photoionization modeling within the classic locally optimally-emitting cloud (LOC) framework can explain them through an increase in the covering factor from $\sim20$% (Type 1 AGN) to $\sim100$% (LRDs), together with an increase in the hydrogen column density from $N_\mathrm{H}\sim10^{23}\,\mathrm{cm}^{-2}$ to $\gtrsim10^{24}\,\mathrm{cm}^{-2}$, with a preferred gas density of $\sim10^{10}\,\mathrm{cm}^{-3}$, successfully reproducing the modified blackbody emission. Such a nearly unity covering factor without requiring a gas density increase may result from a significant increase in the BLR filling factor or size, corresponding to a “stuffed BLR" or “
giant BLR," respectively.
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All authors Hiroto Yanagisawa, Masami Ouchi, Tomokazu Kiyota, Yuta Kageura, Makoto Ando, Yuichi Harikane, Minami Nakane, Yoshiaki Ono, Yui Takeda
Astrophysics of Galaxies
NEXUS: Abundance, Environments, and Spectral Diversity of Little Red Dots from the NIRSpec MSA Sample
Zhiwei Pan, Ming-Yang Zhuang, Yue Shen et al. (+6 more)
We present a comprehensive study of Little Red Dots (LRDs) at 2.3 < z < 7.4 using NIRCam photometry and NIRSpec MSA/PRISM spectra from the ongoing NEXUS program. Photometric selection combining several commonly adopted methods yields a high completeness of about 85% for LRD selection over this
redshift range and for a flux limit of F444W < 26. The overall purity is about 60%, with contamination from emission-line
galaxies and normal active
galactic nuclei (AGNs), as well as
dwarf stars. Most (>90%) of the spectroscopically confirmed LRDs have robust broad-line detection. Our spectroscopic sample of 36 LRDs displays the full range of spectral diversity of LRDs. It includes objects with extreme Balmer breaks similar to the LRD "Cliff", as well as objects with moderately reddened rest-optical continua that can be fit with low-temperature blackbody components in the recent BH* model framework. The broad H$\alpha$ emission is correlated with the continuum emission at 5100 Angstrom, suggesting common origins for these emission components; the narrow [O III] emission, however, is poorly correlated with the optical continuum. We do not find evidence of
redshift evolution in these spectral properties. The space density of LRDs declines toward z about 2, opposite to the trend for normal AGNs, although low-luminosity LRDs at z about 2-4 may be more abundant than currently probed by ground-based searches. The clustering of LRDs suggests that they live in dark matter
halos of several times $10^{11}\ h^{-1}$
solar masses, albeit with large uncertainties. Overall, these results are consistent with recent observations of LRDs and with the emerging picture of accreting SMBHs enshrouded in dense gas envelopes as the origin of LRDs.
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All authors Zhiwei Pan, Ming-Yang Zhuang, Yue Shen, Feige Wang, Jenny E. Greene, Adam J. Burgasser, Junyao Li, Zachary Stone, Padmavathi Venkatraman
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
PTA-Compatible Domain Walls at LISA and Taiji: Bayesian Reconstruction and Multiband Inference
Satyabrata Datta and Rome Samanta
Domain walls provide an excellent fit to
Pulsar Timing Array (PTA) data. A distinctive feature of the associated gravitational-wave (GW) spectrum is its ultraviolet (UV) tail, which can extend into the mHz band and thereby make cross-detection with space-based interferometers such as LISA and Taiji possible. In this work, we explore the PTA-compatible parameter space of domain-wall models and study both the reconstruction prospects at LISA and Taiji and the information gain achievable through joint PTA–LISA and PTA–Taiji analyses. We find that LISA and Taiji can probe an extended region of parameter space yielding an ultraviolet tail in the milli-Hz band, even in the presence of astrophysical foregrounds. Within the PTA-supported region, however, the genuinely informative regime is more restricted and concentrated toward the high-signal edge. In the space-based-detector-only analysis, the posterior is strongly degenerate in the underlying model parameters, although one principal parameter combination can be reconstructed with high precision where the signal is sufficiently strong. When PTA-informed priors are incorporated, the additional information gain is localized to the same high-signal region: there the space-based data produce a non-negligible posterior update and strongly suppress the catastrophic LISA(Taiji)-only degeneracy, while the final posterior often retains an axis ratio comparable to that of PTA alone. Our analysis is based on a 10-dimensional
Bayesian inference with two domain-wall signal parameters and eight nuisance parameters describing instrumental noise and astrophysical foregrounds. We use 49 grid injections for the LISA-only and Taiji-only analyses and 65 injections from the PTA-supported region for the joint analyses, with Clough–Tocher interpolation used to construct posterior heat maps.
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Cosmology and Nongalactic Astrophysics
Stochastic constant-roll inflation beyond the hilltop with the spectral method
Eemeli Tomberg
Stochastic inflation can be used to study large inflationary perturbations. This paper presents such a study for a quadratic hilltop potential, corresponding to constant-roll inflation. I solve the perturbation distribution using the spectral method, with detailed solutions of the
eigenvalues and eigenfunctions of the Fokker-Planck operator. Contrary to previous studies of
stochastic constant-roll inflation, the solution allows trajectories that cross the hilltop and get stuck near a reflecting boundary on the other side, tunneling out slowly in a way dictated by the lowest eigensolution. Despite their rarity, these trajectories turn out to dominate the mean first-passage time. For this reason, I argue the mean does not properly describe the inflationary background. Using the median instead, I compute the distribution of the coarse-grained $\Delta N$ distribution and show that its well-known exponential tail first flattens out and then forms a peak near a maximal $\Delta N$ value. I argue similar intricacies arise in
primordial black hole models.
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Astrophysics of Galaxies
A Meta-Learning Framework for Multitask Reverberation Mapping in Active Galactic Nuclei
Aman N. Raju, Andjelka B. Kovačević, Dragana Ilić et al. (+8 more)
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) is expected to observe active
galactic nuclei (AGN) at sky densities of approximately 1000-4000 per sq. deg, enabling photometric reverberation mapping on an unprecedented scale. We present a meta-learning framework for AGN photometric reverberation mapping based on Attentive Latent Neural Processes (ALNP), developed by the SER-SAG-S1 directable software in-kind team for LSST. The framework clusters AGN light curves with similar
topologies using Self-Organizing Maps and combines ALNPs with Mixture Density Models to learn light-curve structure, supermassive black hole (SMBH) properties, and
accretion-disk transfer functions in an unsupervised manner. We evaluate the framework on simulated AGN light curves spanning a range of cadences and transfer functions, as well as on real data from the Zwicky Transient Facility. The learned latent representations encode information on both transfer functions and SMBH parameters. Relative to ensemble-trained baseline regressors, including Gaussian-process models, the framework improves light-curve reconstruction by 60-70%. The transfer function recovery improves by approximately 35% relative to the training prior in a low-variability cluster, while recovery of intrinsic SMBH and red-noise parameters improves by approximately 34%. We further demonstrate that models trained on simulated data can be applied to real AGN light curves. These results indicate that ALNP-based representations provide a flexible and scalable approach to photometric reverberation mapping and are well suited to the diverse AGN population expected from LSST and future time-domain surveys.
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All authors Aman N. Raju, Andjelka B. Kovačević, Dragana Ilić, Francesco Tombesi, Luka Č. Popović, Eric Slezak, Paula Sanchez-Saez, Marina Pavlović, Iva Čvorović-Hajdinjak, Saša Simić, {\DJ}or{\dj}e Savić
Astrophysics of Galaxies
Star Formation Drives Production of Low Energy Cosmic Rays
Ningyu Tang, Jiahao Liu, Di Li et al. (+18 more)
For over a century, the origin of low-energy
cosmic rays (LECRs), the dominant heaters and ionizers of dense interstellar gas, remains elusive owing to
solar modulation and uncertain transport processes. In this study, we introduce a new astrophysical approach based on HI Narrow Self-Absorption (HINSA) to obtain spatially resolved measurements of LECR ionization rates using high-fidelity HI observations toward the Orion region from the FAST
telescope. The LECR ionization rate is found to scale with local
star formation rate (SFR) as $log_{10}\zeta = (1.4\pm 0.70)log_{10}\mathrm{SFR} + (-10.5\pm 2.9)$. Moreover, it increases with visual extinction, and is found to exceed, toward active
star-forming regions, the value predicted for diffuse regions based on Voyager measurements and an external propagation model. These findings demonstrate that LECRs are generated in situ by
star-forming activities rather than penetrating from the broader
Galactic cosmic-ray population. This is further supported by
Fermi-LAT gamma-ray observations toward the Orion region. Together, these results resolve a key uncertainty in
cosmic-ray origin and establish a new avenue for quantifying the energetic feedback that regulates the interstellar medium.
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All authors Ningyu Tang, Jiahao Liu, Di Li, Ruizhi Yang, Thomas G. Bisbas, Bing Liu, Marko Krco, Paul Goldsmith, Paola Caselli, Sihan Jiao, Yan Gong, Gan Luo, Xinwen Shu, Liangchong Zhu, Xiaohui Sun, Chen Wang, Tao-Chung Ching, Donghui Quan, Junzhi Wang, Xuejian Jiang, Pei Zuo
Cosmology and Nongalactic Astrophysics
Pantheon+ supernovae corrected for progenitor age indicate the universe is decelerating
Animesh Sah, Mohamed Rameez and Subir Sarkar
We examine the impact of progenitor age-dependent luminosity
evolution of Type Ia
supernovae on a cosmographic measurement of the deceleration parameter $q_0$. Our recent
redshift tomographic analysis showed that locally $q_0$ has a strong dipole anisotropy aligned approximately with the bulk flow, and only a small monopole component remains at distances exceeding a few hundred Mpc. Applying
redshift-dependent corrections for progenitor age to the Pantheon+ catalogue, we find that this shifts the monopole component of $q_0$ to positive values (i.e. deceleration), while leaving the local dipole component essentially unchanged.
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Astrophysics of Galaxies
A differentiable forward model for weakly perturbed stellar streams: substructure forecasts from density and kinematics spectra
Noemi Anau Montel and Fabian Schmidt
Stellar streams are a promising way to gravitationally detect low-mass substructure, since their low dynamical temperature makes them retain the imprint of weak gravitational perturbations. We develop a fast, differentiable forward model for perturbed
stellar streams in the
diffusion regime, where the stream is heated by many small velocity kicks rather than by a few strong encounters. The substructure population enters only through its power spectrum, so the computational cost is insensitive to the number of perturbers, and alternative dark matter models and/or baryonic perturbers can be explored by changing this single input. We validate the simulations against analytical predictions, then forecast the sensitivity of a GD-1-like stream to the substructure power spectrum, adding to the stream density the full kinematics, both proper motions and the radial velocity. Kinematic information tightens the constraints by a factor of $\sim 3$-$5$ relative to density alone, improving the precision on the dark matter free-streaming cutoff scale from $\sim 1.2$ dex to $\sim 0.25$ dex at a fiducial value of $M_{\rm hm} = 10^6 M_\odot$ for a $5$ Gyr stream. A single well-measured stream could thus constrain dark matter competitively with current limits from strong
lensing and satellite counts.
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Solar and Stellar Astrophysics
Balmer decrements as a new diagnostic for period-bounce Cataclysmic Variable stars
Santiago Hernández-Díaz, Beate Stelzer and Daniela Muñoz-Giraldo
Cataclysmic variable
stars (CVs) evolve toward shorter orbital periods ($P_{\rm orb}$) until they reach a minimum $P_{\rm orb}$ near $P_{\rm orb}\sim80$ min. Beyond this point, the donor
star becomes out of thermal
equilibrium or increasingly degenerate, causing the system to "bounce back" to longer $P_{\rm orb}$ values. Such highly evolved systems are known as period-bouncers. Although 40-80% of all CVs are expected to have reached this stage, period-bouncers come up for only 3-25% of the observed CV population. This is likely a consequence of their intrinsic faintness associated with lower mass-transfer rates. Establishing new diagnostics to unveil this missing population is therefore crucial. Two samples of non-
magnetic CVs with public SDSS optical spectra were constructed: one of short-period pre-bounce CVs and another of period-bounce CVs. For systems showing Balmer absorption from the white
dwarf (WD), hydrogen-dominated atmosphere models were fitted and subtracted to correct for the WD component. H$\alpha$, H$\beta$, and H$\gamma$ fluxes were measured. We then investigated statistical relations between the Balmer decrements, the H$\beta$ line luminosity, and $P_{\rm orb}$, and compared the measured Balmer decrements with theoretical predictions from
accretion disc models. Short-period pre-bounce CVs show flat Balmer decrements, that is Balmer line ratios close to unity. In contrast, systems near and beyond the period minimum exhibit progressively steeper decrements (H$\alpha$/H$\beta$>1 and H$\gamma$/H$\beta$<1). This behaviour is attributed to their lower mass
accretion rates, as inferred from the H$\beta$ line luminosity. We fitted a linear logistic regression model to the diagram of H$\gamma$/H$\beta$ versus H$\alpha$/H$\beta$. We establish that this diagnostic diagram effectively separates period-bouncers from pre-bounce CVs.
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Solar and Stellar Astrophysics
Peristaltic Flow in Compressible, Ideal Magnetohydrodynamics: A Mechanism For Solar Spicules
D. Tsiklauri
We present analytical model for peristaltic transport within compressible, ideal magnetohydrodynamics (MHD). By employing small-amplitude perturbation expansion, under thin-tube long-wavelength approximation with a uniform axial background
magnetic field, we study non-linear coupling between thermodynamic pressure variations and Maxwell's
magnetic tension stresses. The resulting net time-averaged volumetric flow rate $\langle Q \rangle$ is calculated. When applied to
solar chromospheric spicules under equipartition constraints ($\beta \sim 1$), where sound speed matches the Alfvén speed, we find $\langle Q \rangle = 4\epsilon^2/(M^2-1)$. Because the denominator remains positive across all operational supersonic Mach numbers ($M \approx 2\text{--}10$), upward-propagating mechanical disturbances drive a highly directional, collimated upward flow which we interpret as a spicule. Estimates show that for observationally realistic magnetosonic waves with amplitudes of $\approx 10\%$, the peristaltic mechanism generates a localized mass flux $\approx 100$ times that of
solar wind. We propose an explicit observational signature of this mechanism, wherein the launch of individual spicular jets is directly preceded by magnetosonic wave trains detectable as localized intensity modulations. Beyond
solar chromospheric application, the model may be applicable to traveling
magnetic field pinches in laboratory
plasma devices and astrophysical mass-loading processes in
stellar winds and inner regions of magnetized
accretion disks.
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High Energy Astrophysical Phenomena
Measuring radii of merging neutron stars with interface-mode asteroseismology informed by nuclear theory and experiment
Duncan Neill, William G. Newton, Jeremy W. Holt et al. (+3 more)
The structure and dynamics of
neutron stars can be used to probe the physics of extreme matter at
nuclear densities and beyond. Nucleonic matter up to ~2-3 times
nuclear saturation density is well-studied by
nuclear experiments and theoretical modelling. Matter beyond these densities may contain non-nucleonic degrees of freedom that determine the structure of the
neutron star inner core and influence bulk observables like
stellar radius.
Neutron star radius is a key parameter for constraining the core equation of state, but is not a direct gravitational-wave observable during
neutron star mergers. Here we show that, if nucleonic physics is well constrained at low densities, the frequency of the asteroseismic crust-core interface mode in a
neutron star can be used to infer its radius to within 5-10%, in a way which is notably insensitive to the details of the inner core. This frequency can be measured through multimessenger coincident timing of resonant shattering
flares, or direct observation of dynamical
tidal resonance with next-generation gravitational-wave detectors. We show that improved constraints on low-density nucleonic physics by
nuclear experimental and theoretical efforts will substantially improve such a radius measurement, leveraging low-density efforts for an improved understanding of physics at higher densities.
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All authors Duncan Neill, William G. Newton, Jeremy W. Holt, Christian Drischler, Jérôme Margueron, David Tsang
Astrophysics of Galaxies
Blowing star formation away in AGN hosts (BAH) – V: The Feeding-Feedback Cycle in local AGNs as revealed by their stellar populations
Rogério Riffel, Rogemar A. Riffel, Gabriel L. Souza-Oliveira et al. (+9 more)
We present a spatially resolved analysis of the
stellar populations in the inner kiloparsec of NGC 3884, 3C 293, and CGCG 012-070. Using near-infrared spectroscopy, we reconstruct their
star formation histories (SFHs) by comparing the M13, XSL, and FSPS
stellar population synthesis models. The
stellar light is dominated by intermediate-age to old populations (t >= 1 Gyr) with super-
solar metallicities (Z >= 1 Z_sun). All models clearly indicate recent
star formation (rejuvenation) in these AGN hosts, with young to intermediate-age populations contributing significantly in the
nuclear regions. The SFHs from M13 and XSL broadly agree in showing coexisting old and young components, whereas FSPS favours a larger fraction of very young (t < 50 Myr)
stars. Moreover, XSL- and FSPS-based SFHs are generally more irregular and "bumpy," while M13 yields smoother, more continuous SFHs. In NGC 3884 and 3C 293,
stars with 0.2 < t <= 0.7 Gyr form a ring-like structure around the
nucleus. The
nuclear spectra further require non-
stellar components: a featureless power-law continuum (FC) and hot
dust emission (HD). In 3C 293, the FC component appears in two spatially separated regions, possibly indicating a dual active
galactic nucleus, though a heavily reddened starburst origin for the secondary component cannot be excluded. Nearly all fits show a central drop in
stellar metallicity, consistent with inflow of metal-poor gas that fuels recent
accretion and AGN activity. Radial profiles show that HD and FC contributions decrease with radius, while younger
stellar populations become more prominent outward. Together, these results support a feeding-feedback scenario in which gas inflows trigger circumnuclear
star formation and, via
stellar mass loss, help sustain ongoing AGN activity. .
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All authors Rogério Riffel, Rogemar A. Riffel, Gabriel L. Souza-Oliveira, Nadia L. Zakamska, Thaisa Storchi-Bergmann, Marina Bianchin, Lais Nery Marinho, Sandra Jaison, Suresh Parekh, Maitê S. Z. de Mellos, José Henrique Costa-Souza, Rafael S. de Souza
High Energy Astrophysical Phenomena
Modelling Galactic neutrino emission: contributions from massive star clusters and interstellar cosmic rays
Stefano Menchiari, Silvia Celli, Vittoria Vecchiotti et al. (+3 more)
The recent detection of
Galactic neutrinos by the IceCube Observatory constitutes a remarkable achievement for
neutrino astrophysics. By means of model dependent analyses based on spatial and spectral templates, a purely diffuse
neutrino flux was measured in which no individual source was resolved. We present here a novel theoretical computation about the expected
neutrino emission from the
Galactic Plane that, differently from previous models, includes both the contributions from
cosmic-ray (CR) sea and hadronic sources, represented by
star clusters and
supernova remnants therein, which are to date believed to be the dominant sources of
Galactic CR
protons. For the modelling of sources, diffusive particle acceleration is considered at both the collective wind termination shock blown by member
stars and at the
supernova shocks. The predicted flux of very-high energy
neutrinos from individual
star clusters is found to be marginally detectable even by cubic kilometer scale detectors, such that their cumulative contribution is expected to appear as an unresolved diffuse component, on top of that guaranteed by the CR sea interacting with the gas along the Plane. The overall
neutrino production of the Milky Way
star cluster population is computed, based on multiple synthetic realizations of the cluster population reproducing local
stellar observations. As a result, we obtain novel
neutrino template maps and provide them to the community, to be tested in future
neutrino analyses in order to constrain the role of
star clusters for extreme CR acceleration and
neutrino production. The normalization of our models is consistent with the IceCube best-fit of existing
Galactic templates, suggesting that the unresolved contribution from cluster emission may be non-negligible.
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All authors Stefano Menchiari, Silvia Celli, Vittoria Vecchiotti, Giovanni Morlino, Giada Peron, Rubén López-Coto
High Energy Astrophysical Phenomena
A thousand looks at X Persei: X-ray spectroscopy at high time resolution
G. Sanjurjo-Ferrín, J. M. Torrejón, J. J. Rodes-Roca et al. (+3 more)
X Persei is a classical Be/X-ray binary composed of an O9.5III-B0V Be-type
star and a
neutron star (NS). The NS exhibits coherent pulsations with a
spin period of ~837 s, orbiting the Be
star with a ~250 d period. X Persei is notable for its exceptionally hard X-ray emission extending beyond 100 keV. Due to the mild eccentricity of the orbit, ~0.11, the orbital separation varies between roughly 35 R_
star at periastron and 44 R_
star at apastron. In this work, we analyze five targeted observations obtained with the XMM-Newton and Chandra observatories taken over a 10-year time span, with the aim of investigating the structure and variability of the circumstellar disk surrounding the Be
star, in particular the presence of over-dense areas known as clumps. We performed spectral and timing analyses, including average and NS
spin-resolved spectroscopy for three of the observations, producing individual spectra at intervals as short as 210 s, corresponding to different epochs of the NS
spin, resulting in approximately 1200 spectra. This detailed analysis aimed at resolving emission-line features otherwise diluted in averaged spectra and the
evolution of continuum components along the NS
spin. The observed spectra are accurately modeled by a two-component continuum comprising a high-temperature blackbody and a power-law component. Phase-resolved spectroscopy reveals transient Fe K alpha emission linked to clumps in the circumstellar disk during high-density epochs, with an 8-9% prevalence. Dips in the X-ray light curve are tied to clump passages. The disk-density modeling, based solely on X-ray data, suggests a compact and dense disk, with a radial density exponent alpha of 2.4-3.3, and a high inner disk density, rho_0 ~ (6-20) x 10^-10 g cm^-3, in agreement with previous studies conducted in the optical and infrared bands.
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All authors G. Sanjurjo-Ferrín, J. M. Torrejón, J. J. Rodes-Roca, K. Postnov, J. Planelles-Villalva, L. Oskinova
Astrophysics of Galaxies
Characterizing Stellar Streams with Error-Aware Machine Learning
Alexandros Pratsos, Biprateep Dey and Ting S. Li
Stellar streams are thin, elongated collections of
stars formed by gravitational disruption of orbiting
star clusters or
dwarf galaxies and are highly sensitive probes of the Milky Way's dark matter distribution and formation history. We present $\texttt{SCREAM}$ ($\textbf{S}$tream $\textbf{C}$ha$\textbf{R}$acterization with $\textbf{E}$rror $\textbf{A}$ware $\textbf{M}$achine Learning), a weakly-supervised framework to identify member
stars of
stellar streams. Building on the $\texttt{CATHODE}$ method originally developed for particle physics, $\texttt{SCREAM}$ identifies streams as localized feature-space over-densities, avoiding rigid physical priors like assumed gravitational potentials or strict isochrone filtering. Crucially, $\texttt{SCREAM}$ is the first machine learning (ML) framework in this domain to directly incorporate observational uncertainties into the neural network training objective. Using astrometric and photometric data from
Gaia Data Release 3 and the Dark Energy Spectroscopic Instrument (DESI) Legacy imaging survey, we demonstrate our
algorithm's performance on the prominent GD-1 stream. Validated against independent labels, $\texttt{SCREAM}$ achieves an F1 score of 0.745, substantially outperforming existing ML methods in both precision and recall. Furthermore, $\texttt{SCREAM}$ recovers the physically expected diffuse "cocoon" of GD-1 and faint main-sequence members that classical physics-based
algorithms (e.g., $\texttt{STREAMFINDER}$) miss. Our results highlight the transformative potential of uncertainty-aware, weakly-supervised ML to uncover complex
galactic structures.
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Solar and Stellar Astrophysics
Apparent Transverse Motion of Light Bridges Coupled to Coronal Loop Dynamics
Atul Bhat, Sreejith Padinhatteeri, J.M. Borrero et al. (+1 more)
Light bridges are commonly observed in active regions and are interpreted as signatures of magnetoconvective processes in sunspots. Several studies have attempted to classify them in the past based on their morphological characteristics. Recent observations have revealed new dynamical properties of light bridges, including their signatures in the upper
solar atmosphere, particularly in the chromosphere, and their coupling with coronal features. In this study, we observed two cases of rare and unusual dynamics as light bridges evolve. Using data from the
Solar Dynamics Observatory, the
evolution of the light bridges is analysed, and the results are reported here. Based on our findings, we propose that the unique movements of the light bridges in the observed sunspot and earlier studies could be an apparent view of the umbral core dynamics. Investigation into these dynamics through signatures in the higher atmosphere reveals a clear coupling to coronal loops and their dynamics.
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All authors Atul Bhat, Sreejith Padinhatteeri, J.M. Borrero, Jayant Joshi
Instrumentation and Methods for Astrophysics
Control problem in millimeter-wave adaptive optics
Ichiro Jikuya and Yoichi Tamura
Millimeter-wave Adaptive Optics (MAO) is essential for high-precision large-aperture submillimeter
telescopes, requiring real-time compensation of wavefront errors by capturing them as spatially-discrete excess path length (EPL) fluctuations. This paper presents a unified control-theoretic framework for the EPL compensation problem. We first model the optical drive system as a plant where input commands relate to measured EPL through a first-order system representing mechanical response delay and a measurement
matrix characterizing the actuator-to-sensor coupling. We mathematically formulate the control task as an asymptotic disturbance suppression problem, specifically targeting low-frequency disturbances such as thermal and wind-induced deformations. Second, we propose an Anti-Windup Proportional-Integral (AWPI) control law. By employing a decoupling strategy, the design is reduced to a loop-shaping problem for decoupled scalar sensitivity functions, ensuring both stability margins and asymptotic disturbance suppression of constant-valued disturbances. The anti-windup mechanism is integrated to maintain control continuity during the recovery from saturation, preventing undesirable discontinuities in the drive command. Third, we introduce practical operational tools: a manual focus adjustment scheme that allows observer intervention without interfering with the feedback loop, and the cosine similarity index to quantify the suppressibility of specific Zernike modes. Numerical simulations, incorporating a three-axis secondary reflector drive and five-point EPL measurements, demonstrate direction-dependent disturbance rejection and the suppression of von Karman-modeled wind
turbulence, validating the effectiveness of the proposed framework for real-world
telescope applications.
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Cosmology and Nongalactic Astrophysics
Spectral distortion anisotropies from photon to dark photon conversions
Sara Evangelista, Jens Chluba and Bryce Cyr
Dark
photons are a gauge
boson of a hypothetical dark sector, representing one of the most-studied minimal extensions of the Standard Model, with wide-ranging theoretical and observational implications. Here, we consider scenarios in which an initially unpopulated dark
photon sector is populated via resonant
photon to dark
photon conversions. This process leads to observable spectral distortions in the
cosmic microwave background (CMB), that can be used to constrain these models. We extend previous spectral distortion studies of the monopole spectrum to anisotropic spectral distortions, using the newly developed Frequency Hierarchy (FH) framework of CosmoTherm. We illustrate the physics by presenting detailed computations of the
photon transfer functions and distortion cross power spectra throughout the dark
photon parameter space. We find that the dark
photon mass explicitly controls the shape (i.e., multipole-dependence) of the signal power spectra, while the overall amplitude of the signal is determined by the kinetic mixing parameter of the model. Using these results, we place complementary limits on the minimal dark
photon model using data from Planck, finding that the constraints are only marginally weaker than those obtained with COBE/FIRAS data for the average (monopole) distortion. In addition, we compute the corrections to the standard temperature field, arguing that conversions at
redshifts larger than $2\times 10^6$ may add iso-
curvature type perturbations, which could lead to novel constraints in regimes where distortion anisotropies thermalize.
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Solar and Stellar Astrophysics
Quantifying isochrone-based age uncertainties for rapidly rotating A-type stars
Simon J. Murphy, Anuj Gautam and Zachary R. Claytor
Accurate
stellar ages and masses are essential for interpreting the demographics and physical properties of
exoplanets, particularly for intermediate-mass, early-type
stars where conventional age indicators are ineffective. Isochrone fitting remains the primary tool for characterising such
stars, yet its uncertainties are often underestimated, especially in the presence of rapid rotation and unresolved binarity. We present a population-synthesis framework designed to quantify realistic mass and age uncertainties for intermediate-mass
stars (1.4-2.5 M$_{\odot}$), incorporating distributions in rotation rate, mass,
metallicity, binarity, inclination, and observational error. Rotational and
geometric effects are applied a posteriori to
stellar evolutionary models, enabling a continuous treatment of rotation and its impact on effective temperature and luminosity. By comparing synthetic populations against commonly used isochrone grids, we demonstrate that rotation and unresolved companions systematically bias inferred masses and ages, particularly for young
stars, and introduce random uncertainties at the $\sim$0.1-M$_{\odot}$ and $\sim$180-Myr level, often exceeding formal fitting errors. The effect is strongest near the zero-age main sequence, where ages are underestimated by a factor of $\geq2$, while for older A
stars ($>$10% of their main-sequence lifetime), ages are overestimated by 31% with 27% scatter. Our findings carry important consequences for
planet detectability, characterisation, and population studies. We provide a publicly available tool, RAPID, for probabilistic inference of
stellar parameters from these synthetic populations, and we demonstrate its application to known
exoplanet hosts.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Primordial Black Holes from Slow Phase Transitions with Delayed Reheating: A Peak-Theory Approach
Indra Kumar Banerjee
We study the possibility of significant PBH production from a slow first-order phase transition with delayed reheating. Since delayed reheating results in an early matter-dominated phase between percolation and reheating, we developed a peak-theoretic approach to PBH formation during this phase based on the non-Gaussian distribution of overdensity arising from the transition. To obtain the collapse probability, we performed large-scale Monte Carlo simulations and employed the hoop-
conjecture criterion. We include
tidal-torque terms to investigate the initial
spin of the PBHs and find that the average
spin parameter is $\mathcal{O}(10^{-3})$. Furthermore, we obtain an emergent overdensity threshold for collapse that depends on the phase transition properties and reheating efficiency. We find that the resulting PBH abundance is extremely sensitive to the reheating efficiency, with order-unity changes in efficiency leading to variations of many orders of magnitude in the collapse fraction. We identify regions of parameter space where the resulting PBHs can account for the entirety of the dark matter abundance. Finally, we also constrain the phase transition and reheating properties from current data on (non-)observations of PBHs.
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Earth and Planetary Astrophysics
MRI-triggered instability at the inner dead zone edge: disc evolution and burst modes tied to magnetic field strengths
Michael Cecil, Mario Flock and Daniel Steiner
The inner edge of the dead zone (DZIE) in protoplanetary discs is prone to episodic instability caused by the activation of the magneto-rotational instability (MRI) in the weakly turbulent regions. We show how different
magnetic field configurations set the inner disc structure and regulate the morphologies of instability cycles. We performed 2D and 3D radiation hydrodynamic simulations of the regions around the DZIE of a Class II disc over a thousand-year timescale. We implemented MRI activation criteria based on ambipolar and Ohmic
diffusion coupled to
magnetic field strength profiles comprising
stellar and disc components. The properties and consequences of the episodic
accretion events are highly sensitive to the
magnetic field strength. We recover previously reported behaviour by considering relatively strongly magnetised discs. A new burst mode is revealed, in which the midplane MRI activity is restricted to small radii in the presence of weak
magnetic fields. In this narrow mode, the pressure bump at the DZIE does not remain static even during quiescence. A distinct dichotomy between the wide and narrow modes is established by the hydrodynamic (in)stability of the ionisation front. Both modes are additionally separated into a reflaring and a non-reflaring version. Our setup does not lead to the classical thermal instability by hydrogen ionisation. In quiescence, the MRI active region shows a layered structure that converges towards the midplane near the
star. Our 3D model reveals the breaking of density features produced in the narrow mode, leading to
vortices at radii smaller than 0.5 AU. Coupling MRI activity directly to different
magnetic field strengths, rather than using simple temperature thresholds, enables a variety of burst modes. Each mode exhibits characteristic
accretion burst signatures and has different consequences for
planet formation and migration conditions.
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Solar and Stellar Astrophysics
Reframing the Wide Eccentric Binary Problem: Eccentricity as a Probe of Mass-transfer Physics
A. Parkosidis, S. Toonen, E. Laplace et al. (+1 more)
Observations of wide post-interaction binaries show an unexpected feature; orbital eccentricity, which is not understood theoretically. A promising resolution to this long-standing puzzle is eccentric mass transfer (MT). Here the first complete framework for MT in orbits with arbitrary eccentricity, the general mass-transfer (GeMT) model, is confronted with the latest observations of hot subdwarfs of spectral type B (sdB) with main-sequence (MS) companions in wide orbits. SdBs are excellent
benchmarks for binary
evolution models, since their progenitors provide unique constraints on their formation histories. We isolate the effects of eccentric MT from other physical process and we show that it explains the observed orbital-parameter distributions and their correlations seen in wide sdB+MS binaries. To quantitatively constrain their orbital parameters,
stellar evolution and tides should be included in future studies, yet it is encouraging that the GeMT model provides the first mechanism that qualitatively reproduces the observed distributions. We further demonstrate that post-MT eccentricities depend directly on key MT parameters, including transferred mass,
accretion efficiency, and angular momentum loss. Given the multitude of eccentric post-MT binaries with components ranging from low- to high-mass
stars to compact objects, we propose that post-MT eccentricities offer a new window onto binary
evolution, presenting a powerful tool to constrain highly uncertain binary-
evolution parameters and mass-transfer formation histories across diverse populations. Post-MT eccentricity should therefore be embraced as a key observable, rather than treated as a problem to be corrected.
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All authors A. Parkosidis, S. Toonen, E. Laplace, V. Schaffenroth
Cosmology and Nongalactic Astrophysics
Modifying $\Lambda$CDM dynamics via out-of-equilibrium axions: reconciling SH0ES and DESI $H_0$ values
Giovanni Montani, Luis A. Escamilla, Nakia Carlevaro et al. (+1 more)
We investigate late-Universe dynamics in which the dark matter component is described by
axion particles. The proposed framework departs from the standard $\Lambda$CDM paradigm due to a small fraction of
axions driving the system away from thermal
equilibrium. We analyze the
evolution of the
axion energy density using both a kinetic and a classical field approach, yielding an identical macroscopic
evolution equation for the dark matter density. We emphasize that the BGK parameter is introduced phenomenologically at the kinetic level and this does not supply an independent microscopic derivation. The present work therefore explores the phenomenological consequences of late-time, out-of-
equilibrium axion production rather than claiming a completed microphysical model. The resulting scenario modifies $\Lambda$CDM dynamics in the late Universe (specifically at $z \lesssim 1$), while asymptotically recovering the standard baseline at earlier
cosmic epochs. We compare the theoretical predictions of our formulation against a comprehensive suite of late-Universe
datasets. Our statistical analysis reveals that when the SH0ES local calibration is included, the collisional
axion model becomes significantly favored over $\Lambda$CDM, yielding a best-fit Hubble constant of $H_0 \simeq 73~{\rm km\,s^{-1}\,Mpc^{-1}}$. Ultimately, this cosmological scenario successfully accommodates local distance-ladder measurements while maintaining excellent agreement with
Baryon Acoustic Oscillation data from the DESI Collaboration.
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All authors Giovanni Montani, Luis A. Escamilla, Nakia Carlevaro, Francesco Cianfrani
Astrophysics of Galaxies
Class I CH3OH Maser Emission from Bar-Driven Inflow Colliding with the Central Molecular Zone
V. S. Veena, W.-J. Kim, P. Schilke et al. (+9 more)
The Central Molecular Zone of the Milky Way is shaped by the interplay of bar-driven inflows, shocks, and
star formation. At
Galactic longitude l=1.3, gas inflowing along the near-side
dust lane has been proposed to interact with the CMZ boundary and overshoot above the
Galactic plane, making this a key site to investigate how large-scale gas dynamics regulates
star formation. We aim to investigate the presence of Class I methanol maser emission in this transitional region, testing whether large-scale gas interactions in the CMZ can trigger widespread maser activity via
star formation or shocks. We conducted a dedicated search for the 36.2 and 44.1 GHz Class I CH3OH maser lines, along with the 48.4 GHz thermal transition, using the Yebes 40m
telescope. We complemented these data with archival data from the Herschel-HiGAL survey and the CHIMPS2 survey to explore links between masers, shocks, and
star formation. We detect widespread 36.2 GHz maser emission and two candidate 44.1 GHz masers in a region extending several parsecs. The brightest maser has an isotropic luminosity 0.9x10^-3 L_Sun, placing it among the most luminous
Galactic Class I masers. Thermal CH3OH and SiO emission extend over mapped area of 24 pc, with both species showing enhanced fractional abundances. CO position-velocity analysis further shows that the masers are associated with an extended velocity feature at VLSR~100 km/s. We conclude that the observed masers are primarily associated with shock-processed gas in a kinematically complex bar-CMZ interface region. Large-scale gas interactions are likely to play an important role in producing the maser emission, although a subset of the masers may also be linked to shocks driven by local
star-formation activity. This region therefore provides a promising
Galactic analogue of shock-dominated Class I CH3OH maser environments observed in
nuclear regions of barred
galaxies.
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All authors V. S. Veena, W.-J. Kim, P. Schilke, A. Sanchez-Monge, C. Henkel, S. Viti, G. Esplugues, F. Wyrowski, W. E. Banda-Barragan, M. C. Sormani, D. Riquelme, G. A. Fuller
High Energy Astrophysical Phenomena
Fast Radio Bursts produced during collapse of macroscopic X-mode in magnetized pair plasma
Maxim Lyutikov
We demonstrate that in highly magnetized pair
plasma nonlinear long-wavelength X-modes experience wave collapse/breaking, whereby the wave undergoes severe spatial steepening, driven by nonlinear modifications of the refractive index and strong ponderomotive forces. The collapse/wave breaking occurs in a narrow parameter regime, when the fluctuating part of the
magnetic field exceed the guide field, and
plasma magnetization is close to the current starvation regime. This regime is naturally achieved in highly magnetized
neutron stars, magnetars. Breaking during a fraction of the dynamic timescale, and quickly generates high-k modes. The initial EM energy, spread over large spatial scales, is squeezed into these highly localized, short-wavelength (yet macroscopic) singular pulses. The corresponding electromagnetic “foam” spectrum is red, $E_k \propto k^{-2}$, while the particles' spectrum is exceptionally hard, $f(\gamma) \propto \gamma^0$ The wave collapse produces short bright EM pulses - astrophysical Fast
Radio Bursts. The highest energy particles may produce short contemporaneous high energy bursts.
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Astrophysics of Galaxies
Towards a consistent framework of determining active galactic nucleus contribution fraction and host galaxy properties
Mi Chen, Lingyu Wang, Berta Margalef-Bentabol et al. (+3 more)
Decomposing active
galactic nucleus (AGN) emission from host-
galaxy light is essential for identifying AGN-dominated systems and accurately deriving host-
galaxy physical properties. However, estimating AGN contributions from multi-wavelength photometry remains challenging due to inherent parameter degeneracies in spectral energy distribution (SED) fitting. In this work, we establish a unified framework for estimating AGN contribution fractions and host-
galaxy properties by combining complementary diagnostics: SED decomposition with two independent fitting codes, CIGALE and GRAHSP, and deep-learning-based imaging decomposition. We apply this framework to
galaxies in the COSMOS-Web field using multi-wavelength photometry from the ultraviolet to the far-infrared. We calculate the AGN contribution fraction in the JWST/NIRCam F150W filter and compare the SED-derived estimates with independent AGN fractions obtained from deep-learning image decomposition. Our results reveal significant degeneracies in current SED-fitting approaches based on empirical or theoretical AGN templates and demonstrate that incorporating independent morphological information can help break these degeneracies and improve the reliability of AGN and host-
galaxy property estimates.
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All authors Mi Chen, Lingyu Wang, Berta Margalef-Bentabol, Katarzyna Małek, Brivael Laloux, Antonio La Marca
Astrophysics of Galaxies
TYC 170-1218-1: A new r-process-enhanced extremely metal-poor star, rich in Th
E. Caffau, P. Bonifacio, L. Sbordone et al. (+5 more)
Context . Extremely metal-poor (EMP)
stars are formed from gas clouds enriched by one or a few
supernova explosions belonging to the first
stellar generation and this very limited number of sources of metal enrichment is suitable to produce peculiar chemical patterns that give birth to
stars with anomalous chemical composition. Among the EMP
stars, r-II
stars are characterised by an over-abundance of the heavy elements with respect to iron. Aims . In the search for apparently young, metal-poor
stars, we serendipitously selected TYC 170-1218-1, which turned out to be an EMP
star, enhanced in
neutron capture elements over iron. Our aim is to obtain a detailed chemical inventory for this exceptional object. Methods . We investigated high-resolution spectra observed with UVES at the VLT
telescope and Mike at the Magellan Clay
telescope. We derived the abundance of 33 elements using the MyGIsFOS code and an ATLAS 9 model atmosphere. Results . The
star is an EMP with [Fe/H] = -3.52. It is enhanced in the $\alpha$ elements, as EMP
stars usually are. It is an r-II
star with [Eu/Fe] = +1.84 and [Th/Fe] = +1.85. The
star is also poor in carbon with respect to iron. The quality of the spectra was insufficient for us to detect uranium. Kinematically the
star belongs now to the
Galactic halo, but it joined the Milky Way during the Sequoia
accretion event.
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All authors E. Caffau, P. Bonifacio, L. Sbordone, L. Monaco, J. Alazzawi, M. Spite, P. François, A. Mucciarelli
Astrophysics of Galaxies
A Unified Ionization Framework for the Spectroscopic Diversity of Tidal Disruption Events
Lars L. Thomsen, Lixin Dai, Daniel Kasen et al. (+4 more)
Optical
tidal disruption events (TDEs) exhibit extremely broad emission lines ($\approx 10^3$-$10^4~{\rm km~s^{-1}}$) and are observationally classified into four spectroscopic types: H-dominated, He-dominated, H+He, and featureless. The prevalent H+He class often displays Bowen fluorescence lines (notably \niii~and \oiii), features that are rarely observed in active
galactic nuclei and whose origin has remained poorly understood. We present the first unified radiative transfer framework that reproduces all four TDE spectroscopic classes using simulations of optically thick, outflowing envelopes with
solar composition. Our models successfully capture both the continuum properties and key spectral features, including strong \ha, \heii~and Bowen emissions. We demonstrate that the spectroscopic diversity of TDEs is primarily governed by the gas ionization state, controlled by the ratio of injected luminosity to envelope mass. As the ionization level decreases, the observed sequence of spectroscopic classes emerges naturally, transitioning from featureless to He-dominated, to Bowen-dominated, and finally to H-dominated spectra. We further show that electron scattering in the optically thick
outflow is the dominant mechanism responsible for the extreme line widths, linking line profiles directly to the physical properties of the wind. The model also explains the observed correlations with luminosity, black hole mass, and the relative stability of spectral classifications during TDE
evolution. This work establishes a unified physical framework for TDE spectroscopy, providing new insight into the emission mechanisms, energetics, and
outflow structure of these transient events, and offering a practical pathway for interpreting and fitting observed spectra.
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All authors Lars L. Thomsen, Lixin Dai, Daniel Kasen, Enrico Ramirez-Ruiz, Panos Charalampopoulos, Giorgos Leloudas, Brenna Mockler