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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 20 November

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

k-inflation: Non-separable case meets ACT measurements

Tahere Fallahi Serish, Seyed Ali Hosseini Mansoori, Fereshteh Felegary et al. (+2 more)

We investigate a non-separable subset of $k$-essence in which the kinetic and potential sectors interact through an $X^{\rho}V(\phi)$ coupling, implemented via a potential-dependent prefactor $f(\phi)=1+2\mathcal{K}V$. In slow roll, this structure preserves a constant sound speed $c_s^2=1/(2\rho-1)$ while modifying the Hubble flow in a controlled way, thereby shifting the inflationary observables relative to the separable template. For monomial potentials $V=A\phi^n$ (with $n=2$ and $n=2/3$ as representative cases) we derive closed analytic expressions for $n_s(N_\ast)$ and $r(N_\ast)$ to $\mathcal{O}(\epsilon_{\rm mix}^2)$, where $\epsilon_{\rm mix}\propto\mathcal{K}$ encodes the non-separable $X^\rho V$ mixing, and we validate them against exact background integrations. The analytic and numerical predictions agree at the sub-per-mille level for $n_s$ and at the percent level for $r$, confirming the accuracy of the small-mixing expansion. For $\mathcal{K}<0$ the mixing systematically lowers both $n_s$ and $r$ at fixed $N_\ast$, allowing otherwise marginal monomials to fall within the region favored by recent ACT+Planck+BAO constraints (P–ACT–LB). All solutions shown satisfy the health conditions $f(\phi)>0$, $\rho>\tfrac12$, and the positivity bound $V<1/(2|\mathcal K|)$ (from $f>0$). We also discuss parameter dependence and the expected equilateral-type non-Gaussianity, which remains comfortably within current bounds for the benchmarks considered.
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All authors Tahere Fallahi Serish, Seyed Ali Hosseini Mansoori, Fereshteh Felegary, Özgür Akarsu, Mohamad Sami

Astrophysics of Galaxies

The ensemble broad-frequency power spectrum of Stripe-82 quasars from multiple surveys

Vincenzo Petrecca, Iossif E. Papadakis, Maurizio Paolillo et al. (+5 more)

Variability is a striking features of quasars, observed at all timescales wavelengths. Studying its properties and the correlations with the physical parameters (e.g. black hole mass and accretion rate) provides significant insights into accretion physics. However, the detailed picture and the exact interplay between different emitting regions are not yet clear. We combine data from Sloan Digital Sky Survey (SDSS), the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1, PS1), the Zwicky Transient Facility (ZTF), and the Gaia space telescope to constrain the power spectrum of quasars in the Stripe-82 region over a broad frequency range, 10^{-1} to 10^{-3} day^{-1}(rest frame). Light curves are matched and cross-calibrated to reach \sim 20 years in the r-band for 4037 quasars. We split the sample into bins of the same black hole mass, accretion rate, and redshift, and measure the ensemble power spectral density (PSD) in each bin. The power spectra of SDSS, ZTF, and Gaia are measured independently. We do not measure it on PS1 data due to more erratic cadence, but we discuss the use of interpolation techniques, eventually allowing us to use the data together. We find significant evidence that the long-term UV/optical variability of quasars is stationary, as the ensemble PSD estimates from SDSS, Gaia and ZTF are consistent within the errors despite coming from different surveys and years. The PSD shape is consistent with a bending power law with spectral indices of -2.7 and -1 at high and low frequencies. A fit with the PSD associated with a damped random walk is significantly worse. The PSD amplitude below the break does not depend on black hole mass, but there is some evidence for anti-correlation with the accretion rate. The bending frequency, instead, scales with the black hole mass as $\nu_b$ \propto M_{\mathrm{BH}}^{-0.6\pm0.1} and does not depend on the accretion rate.
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All authors Vincenzo Petrecca, Iossif E. Papadakis, Maurizio Paolillo, Demetra De Cicco, Franz E. Bauer, Maria Isabel Carnerero, Claudia Maria Raiteri, Marta Fatovic

Instrumentation and Methods for Astrophysics · Cross-listed from physics.comp-ph

Deep Learning Framework for Enhanced Neutrino Reconstruction of Single-line Events in the ANTARES Telescope

A. Albert, S. Alves, M. André et al. (+137 more)

We present the $N$-fit algorithm designed to improve the reconstruction of neutrino events detected by a single line of the ANTARES underwater telescope, usually associated with low energy neutrino events ($\sim$ 100 GeV). $N$-Fit is a neural network model that relies on deep learning and combines several advanced techniques in machine learning –deep convolutional layers, mixture density output layers, and transfer learning. This framework divides the reconstruction process into two dedicated branches for each neutrino event topology –tracks and showers– composed of sub-models for spatial estimation –direction and position– and energy inference, which later on are combined for event classification. Regarding the direction of single-line events, the $N$-Fit algorithm significantly refines the estimation of the zenithal angle, and delivers reliable azimuthal angle predictions that were previously unattainable with traditional $\chi^2$-fit methods. Improving on energy estimation of single-line events is a tall order; $N$-Fit benefits from transfer learning to efficiently integrate key characteristics, such as the estimation of the closest distance from the event to the detector. $N$-Fit also takes advantage from transfer learning in event topology classification by freezing convolutional layers of the pretrained branches. Tests on Monte Carlo simulations and data demonstrate a significant reduction in mean and median absolute errors across all reconstructed parameters. The improvements achieved by $N$-Fit highlight its potential for advancing multimessenger astrophysics and enhancing our ability to probe fundamental physics beyond the Standard Model using single-line events from ANTARES data.
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All authors A. Albert, S. Alves, M. André, M. Ardid, S. Ardid, J.-J. Aubert, J. Aublin, B. Baret, S. Basa, Y. Becherini, B. Belhorma, F. Benfenati, V. Bertin, S. Biagi, J. Boumaaza, M. Bouta, M.C. Bouwhuis, H. Brânzaş, R. Bruijn, J. Brunner, J. Busto, B. Caiffi, D. Calvo, S. Campion, A. Capone, F. Carenini, J. Carr, V. Carretero, T. Cartraud, S. Celli, L. Cerisy, M. Chabab, R. Cherkaoui El Moursli, T. Chiarusi, M. Circella, J.A.B. Coelho, A. Coleiro, R. Coniglione, P. Coyle, A. Creusot, A.F. Díaz, B. De Martino, C. Distefano, I. Di Palma, C. Donzaud, D. Dornic, D. Drouhin, T. Eberl, A. Eddymaoui, T. van Eeden, D. van Eijk, S. El Hedri, N. El Khayati, A. Enzenhöfer, P. Fermani, G. Ferrara, F. Filippini, L. Fusco, S. Gagliardini, J. García-Méndez, C. Gatius Oliver, P. Gay, N. Geißelbrecht, H. Glotin, R. Gozzini, R. Gracia Ruiz, K. Graf, C. Guidi, L. Haegel, H. van Haren, A.J. Heijboer, Y. Hello, L. Hennig, J.J. Hernández-Rey, J. Hößl, F. Huang, G. Illuminati, B. Jisse-Jung, M. de Jong, P. de Jong, M. Kadler, O. Kalekin, U. Katz, A. Kouchner, I. Kreykenbohm, V. Kulikovskiy, R. Lahmann, M. Lamoureux, A. Lazo, D. Lefèvre, E. Leonora, G. Levi, S. Le Stum, S. Loucatos, J. Manczak, M. Marcelin, A. Margiotta, A. Marinelli, J.A. Martínez-Mora, P. Migliozzi, A. Moussa, R. Muller, S. Navas, E. Nezri, B. Ó Fearraigh, E. Oukacha, A.M. Păun, G.E. Păvălaş, S. Peña-Martínez, M. Perrin-Terrin, P. Piattelli, C. Poiré, V. Popa, T. Pradier, N. Randazzo, D. Real, G. Riccobene, A. Romanov, A. Sánchez Losa, A. Saina, F. Salesa Greus, D.F.E. Samtleben, M. Sanguineti, P. Sapienza, F. Schüssler, J. Seneca, M. Spurio, Th. Stolarczyk, M. Taiuti, Y. Tayalati, B. Vallage, G. Vannoye, V. Van Elewyck, S. Viola, D. Vivolo, J. Wilms, S. Zavatarelli, A. Zegarelli, J.D. Zornoza, J. Zúñiga

Solar and Stellar Astrophysics

Searching for close-in planets around TWA 7 with SPIRou

J.-F. Donati, P.I. Cristofari, C. Moutou et al. (+7 more)

We outline in this paper observations of the young pre-main-sequence low-mass star TWA 7, hosting a debris disk and a distant planet. Using data collected with the near-infrared SPIRou spectropolarimeter / precision velocimeter at the Canada-France-Hawaii Telescope from early 2019 to mid 2021, we detected the magnetic field of TWA 7 from the circularly polarized Zeeman signatures and Zeeman broadening of atomic spectral lines, and the rotational modulation of its longitudinal component at the known stellar rotation period (of 5.012+-0.007 d). We then modeled the large-scale and small-scale magnetic properties of TWA 7 using Zeeman-Doppler imaging. We found that TWA 7 hosted a mainly poloidal field that significantly evolved from 2019 to 2021, the dipole component getting stronger (increasing from 0.5 kG in 2019 to 0.7 kG in 2021) and less inclined to the stellar rotation axis (from 22{\deg} in 2019 to 15{\deg} in 2021). We also analyzed the radial velocities of TWA 7 derived from the SPIRou data, and found a tentative planet signature at a period of 15.2 d (with aliases at 20.8 and 30.4 d), very close to the detection limit of our data and that would correspond to a 0.17 Mjup planet at a distance of 0.09 au if confirmed. We finally report modulation of the 1083 nm He I and 1282 nm Pa-beta lines of TWA 7 with a period of 6.6 d, different from the rotation period and potentially hinting at the presence of a close-in planet triggering star-planet interactions.
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All authors J.-F. Donati, P.I. Cristofari, C. Moutou, A. Lavail, J. Bouvier, S.H.P. Alencar, P. Petit, A. Carmona, X. Delfosse, the SPIRou science team

Cosmology and Nongalactic Astrophysics

Dark energy after pre-recombination early dark energy in light of DESI DR2 and the latest ACT and SPT data

Hao Wang and Yun-Song Piao

It has been noted that with the pre-recombination early dark energy (EDE) resolution of Hubble tension, the preference of recent datasets for the evolving dark energy (DE) can be suppressed significantly. In this work, we clarify and reconfirm this result with DESI DR2 and the latest ACT DR6 and SPT-3G D1, the tightest small-scale CMB constraints up to date. In the $w_0w_a$CDM model with EDE, a quintessence-like component ($w_0+w_a\geq-1$) can be 1$\sigma$ consistent with Planck+ACT+SPT+DESI+Pantheon+SH0ES datasets, and $\Delta\chi^2\lesssim -14$ compared with $w_0w_a$CDM model without EDE. This reveals the possibility that when the potential resolutions of Hubble tension are considered, current accelerated expansion can attribute to a canonical evolving scalar field or cosmological constant, and again highlights the importance of re-examining the nature of DE within the broader context of cosmological tensions.
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Solar and Stellar Astrophysics

FQ Circini: An Ordinary Nova with a High-mass B1 V(n)(e) Companion Whose Decretion Disk Transfers Mass to the White Dwarf via Roche-Lobe Overflow

Bradley E. Schaefer, Andrew Pearce, Tom Love et al. (+4 more)

FQ Cir was an ordinary fast He/N classical nova, peaking at $V$=10.9. The pre-eruption and post-eruption counterpart was at $V$=14.0, making the smallest known classical nova amplitude of 3.1 mag. The nova light and the counterpart coincide to 0.034 arc-seconds, and the counterpart is a rare hot/blue emission-line star with flickering, so the identification of the quiescent nova is certain. The counterpart is a weak Be main sequence star, B1 V(n)(e). A coherent photometric period appears in all four TESS Sectors and in the AAVSO post-eruption light curve, as ellipsoidal modulation with orbital period 2.041738 days. The companion must have been spun-up to a fast rotation, and like all Be stars, a decretion disk is exuded. With the constraints of the blackbody radius and the main sequence, the companion mass is 13.0$^{+0.2}_{-0.5}$ $M_{\odot}$, with radius 6.2$\pm$0.2 $R_{\odot}$. This is the discovery of a cataclysmic variable with a high-mass companion, a new class that we call `High Mass Cataclysmic Variables'. The white dwarf mass is 1.25$\pm$0.10 $M_{\odot}$ and must have an accretion disk that supplies fuel for the nova eruption. FQ Cir represents a new mode of accretion in interacting binaries, with Roche lobe overflow from the decretion disk feeding mass into the usual accretion disk around the white dwarf, for disk-to-disk accretion. From the mass budget of the binary, the primary star must have its initial mass $>$7.6 $M_{\odot}$, forming an ONe white dwarf, so FQ Cir can never become a Type Ia supernova.
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All authors Bradley E. Schaefer, Andrew Pearce, Tom Love, Michael M. Shara, Lee Townsend, Simon J. Murphy, Christopher J. Corbally

Instrumentation and Methods for Astrophysics

Bayesian polarization calibration and imaging in very long baseline interferometry

Jong-Seo Kim, Jakob Roth, Jongho Park et al. (+6 more)

Extracting polarimetric information from very long baseline interferometry (VLBI) data is demanding but vital for understanding the synchrotron radiation process and the magnetic fields of celestial objects, such as active galactic nuclei (AGNs). However, conventional CLEAN-based calibration and imaging methods provide suboptimal resolution without uncertainty estimation of calibration solutions, while requiring manual steering from an experienced user. We present a Bayesian polarization calibration and imaging method using Bayesian imaging software resolve for VLBI data sets, that explores the posterior distribution of antenna-based gains, polarization leakages, and polarimetric images jointly from pre-calibrated data. We demonstrate our calibration and imaging method with observations of the quasar 3C273 with the VLBA at 15 GHz and the blazar OJ287 with the GMVA+ALMA at 86 GHz. Compared to the CLEAN method, our approach provides physically realistic images that satisfy positivity of flux and polarization constraints and can reconstruct complex source structures composed of various spatial scales. Our method systematically accounts for calibration uncertainties in the final images and provides uncertainties of Stokes images and calibration solutions. The automated Bayesian approach for calibration and imaging will be able to obtain high-fidelity polarimetric images using high-quality data from next-generation radio arrays. The pipeline developed for this work is publicly available.
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All authors Jong-Seo Kim, Jakob Roth, Jongho Park, Jack D. Livingston, Philipp Arras, Torsten A. Enßlin, Michael Janssen, J. Anton Zensus, Andrei P. Lobanov

Cosmology and Nongalactic Astrophysics

Dark Matter-Dark Radiation Interactions and the Hubble Tension

Manuel A. Buen-Abad, Zackaria Chacko, Ina Flood et al. (+3 more)

Models in which a subcomponent of dark matter interacts with dark radiation have been proposed as a solution to the Hubble tension. In this framework, the interacting subcomponent of dark matter is in thermal equilibrium with the dark radiation in the early universe, but decouples from it around the time of matter-radiation equality. We study this general class of models and evaluate the quality of fit to recent cosmological data on the cosmic microwave background (from Planck 2018 and ACT DR6), baryon acoustic oscillations, large-scale structure, supernovae type Ia, and Cepheid variables. We focus on three benchmark scenarios that differ in the rate at which the dark matter decouples from the dark radiation, resulting in different patterns of dark acoustic oscillations. Fitting without ACT DR6 data, we find that all three scenarios significantly reduce the Hubble tension relative to $\Lambda$CDM, with an exponentially fast decoupling being the most preferred. The tension is reduced to less than $2 \, \sigma$ in fits that don't include the SH0ES collaboration results as part of the data and to less than $1 \, \sigma$ when these are included. When ACT DR6 data is included, the fit is significantly worsened. We find that the largest $H_0$ value at the $95 \%$ confidence region is $70.1$ km/s/Mpc without the SH0ES data, leading to only a mild reduction in the tension. This increases to $72.5$ km/s/Mpc, corresponding to a reduction in the tension to less than $3 \, \sigma$, if the SH0ES results are included in the fit.
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All authors Manuel A. Buen-Abad, Zackaria Chacko, Ina Flood, Can Kilic, Gustavo Marques-Tavares, Taewook Youn

Solar and Stellar Astrophysics

Fundamental effective temperature measurements for eclipsing binary stars - VII. The solar twin in LL Aquarii

N. J. Miller, P. F. L. Maxted, A. Hahlin et al. (+1 more)

The eclipsing binary LL Aqr is a bright V = 9.32, detached system consisting of two solar-type stars in an eccentric orbit (P = 20.2 d). The secondary component, LL Aqr B, was previously found to have physical and atmospheric parameters very similar to the Sun. Using high-precision photometry from TESS along with previously published orbital solutions, we obtain updated model-independent stellar radii and masses: $R_A = 1.3180 \pm 0.0013~R_{\odot}$, $R_B = 0.9927 \pm 0.0008~R_{\odot}$, $M_A = 1.1947 \pm 0.0009~M_{\odot}$, and $M_B = 1.0334 \pm 0.0006~M_{\odot}$. We derive the bolometric flux and fundamental effective temperature for each component using observed magnitudes, flux ratios from light curves in multiple bands and angular diameters derived from the radii and parallax from long baseline interferometry, measuring the following values: $T_{\rm eff,A} = 6242 \pm 50$ K, $T_{\rm eff,B} = 5839 \pm 44$ K, with an additional 9 K systematic error from the flux scale zero-point. We confirm that LL Aqr displays low stellar activity by obtaining $2\sigma$ upper limits on the mean surface magnetic field strengths of 78 G and 96 G. Our results suggest an age of 2.67 - 3.01 Gyr, which is consistent with previous studies. LL Aqr now joins an ever-growing sample of well-characterised benchmark stars that can be used to test and calibrate a wide variety of methods and techniques in stellar astrophysics.
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All authors N. J. Miller, P. F. L. Maxted, A. Hahlin, D. Graczyk

Earth and Planetary Astrophysics

Disc fragmentation. I. Ejection of Jupiter-mass Free Floating Planets from growing binary systems

Aleksandra Ćalović, Sergei Nayakshin, Sarah Casewell et al. (+1 more)

Over the past 25 years, observations have uncovered a large population of free-floating planets (FFPs), whose origins remain debated. Massive FFPs (several Jupiter masses or more) may form via gravitational collapse of molecular clouds, similar to stars. Lower-mass FFPs likely originate in planetary systems and are later ejected through dynamical interactions. We show that disc fragmentation in very young stellar binaries may be an abundant source of Jupiter-like FFPs (JFFPs), with masses above 0.3 Jupiter masses. In our model, disc fragmentation at tens to 100 au from the primary star produces gas giants, while fragmentation further out forms a more massive object that will eventually evolve into the secondary star. We present 3D simulations of massive, self-gravitating discs with embedded Jupiter-mass planets and a secondary seed ($5-50 M_J$). Chaotic migration leads to frequent planet-secondary interactions, imparting velocity kicks via gravitational slingshot that usually end in planet ejection. The ejection fraction increases steeply with the secondary-to-primary mass ratio, $q_s$, reaching 0.6 for $q_s > 0.05$. Compared to Core Accretion JFFPs, disc fragmentation JFFPs: (i) form earlier, and may be more abundant in young clusters; (ii) are ejected at much lower velocities; (iii) may retain compact circum-planetary discs. To reproduce the observed abundance of JFFPs, disc fragmentation planets must be in the post-collapse configuration. They must also either form more frequently in binary systems than around single stars, or be frequently disrupted in inner disc regions, as previously suggested in certain versions of the theory.
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All authors Aleksandra Ćalović, Sergei Nayakshin, Sarah Casewell, Núria Miret-Roig

High Energy Astrophysical Phenomena

Neutron star heating vs. HST observations

Luis E. Rodríguez, Andreas Reisenegger, Denis González-Caniulef et al. (+5 more)

Passively cooling neutron stars (NSs) should reach undetectably low surface temperatures $T_s<10^4$ K in less than $10^7$ yr. However, HST observations have revealed likely thermal UV emission from the Gyr-old millisecond pulsars PSR~J0437$-$4715 and PSR~J2124$-$3358, and from the $\sim10^{7-8}$ yr-old classical pulsars PSR~B0950$+$08 and PSR~J0108$-$1431, implying $T_s\sim10^5$ K and the need for heating mechanisms. We compute the thermal evolution of these NSs including rotochemical heating (RH) in the core with normal or Cooper-paired matter, vortex creep (VC) in the inner crust, and crustal heating through nuclear reactions, and compare the results with observations and with the upper limit for PSR~2144$-$3933. No single mechanism explains all sources. The high temperature of PSR~J0437$-$4715 can be reproduced by RH with a large Cooper pairing gap $\Delta_i\sim1.5$ MeV for either neutrons or protons, but this requires an unrealistically short initial period $P_0\lesssim1.8$ ms to activate the same mechanism in PSR~B0950$+$08. Conversely, the latter can be explained by RH with modified Urca reactions in normal matter or by VC with an excess angular momentum $J\sim3\times10^{43}$ erg,s, but these models underpredict PSR~J0437$-$4715. A model combining RH with a large pairing gap and VC matches both pulsars and is consistent with the upper limits for the remaining three. It further predicts that their temperatures should lie close to these limits, suggesting that deeper or broader-wavelength observations would provide a strong test of this scenario.
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All authors Luis E. Rodríguez, Andreas Reisenegger, Denis González-Caniulef, Cristóbal Petrovich, George Pavlov, Sébastien Guillot, Oleg Kargaltsev, Blagoy Rangelov

High Energy Astrophysical Phenomena

Two-beam Multiparticle Many-body simulations of Inhomogeneous FFI

Zoha Laraib and Sherwood Richers

Neutrino flavor evolution in dense astrophysical environments is inherently nonlinear and sensitive to many-body (MB) quantum effects beyond the mean-field (MF) approximation. Existing MB studies are constrained by small system sizes, closed boundaries, and highly idealized symmetry assumptions. We present a unified tensor-network framework that enables simulations of inhomogeneous and anisotropic flavor evolution under conditions relevant to core-collapse supernovae and neutron-star mergers. Within this framework, we examine the effects of inhomogeneity, boundary conditions, and convergence with resolution for multiple neutrino distributions, allowing direct comparison of these setups under one consistent formulation. In our simulations, many-body systems equilibrate earlier than their mean-field counterparts while approaching similar final flavor states. Enlarging the interaction region allows open boundaries to reproduce closed-system behavior, but only when the beams begin superimposed and interact continuously. By contrast, initially separated configurations develop entanglement more slowly, interact over longer times, and equilibrate to a flavor content that differs from that obtained from initially superimposed calculations.
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Instrumentation and Methods for Astrophysics

A Butterfly's Eye Camera for Intensity Interferometry with Cherenkov Telescopes

Juan Cortina, Alejo Cifuentes-Santos, Tarek Hassan et al. (+1 more)

In recent years, imaging atmospheric Cherenkov telescopes (IACTs) have emerged as promising platforms for optical interferometry through the use of intensity interferometry. IACTs combine large segmented mirrors, photodetectors with nanosecond-scale time response capable of detecting signals from just a few photo-electrons, and array configurations with baselines of hundreds of meters. As a result, all major IACT facilities have now been upgraded to function also as optical intensity interferometers, achieving sensitivities an order of magnitude better than their predecessor, the Narrabri Stellar Intensity Interferometer. However, further improvements in sensitivity are currently limited by key IACT design constraints, namely the combination of poor optical quality and small focal ratios. Here we present three practical implementations of the "I3T concept", in which segments of the IACT primary mirror are focused onto different pixels of its camera. This approach yields several unexpected but significant advantages. Optics with larger focal ratios allow to integrate narrow-band optical filters, while lower photon fluxes enable to deploy next-generation photodetectors operating in photon-counting mode. We demonstrate that this so-called "Butterfly's Eye" configuration enhances the sensitivity of IACT-based intensity interferometers by a factor between 4 and 6. Moreover, as originally envisioned, the I3T design introduces imaging capabilities on angular scales from 2 to 40 milliarcseconds, unlocking new scientific opportunities such as direct surface imaging of nearby red giants. Besides, realistic simulations show that it can have a transformative impact on at least two key science cases: imaging the earliest stages of nova ejecta, and measuring the oblateness and circumstellar disks of fast-rotating stars.
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All authors Juan Cortina, Alejo Cifuentes-Santos, Tarek Hassan, Fernando Frias

Earth and Planetary Astrophysics

A homogeneous TTV investigation of all TESS systems with a confirmed single transiting planet

Luca Naponiello

Transit Timing Variations (TTVs) are a powerful tool for detecting unseen companions in systems with known transiting exoplanets and for characterizing their masses and orbital properties. Large-scale and homogeneous TTV analyses are a valuable method to complement the demographics of planetary systems and understand the role of dynamical interactions. We present the results of a systematic TTV analysis of 423 systems covering 16000 transits, each with a single transiting planet first discovered by the TESS mission and afterwards confirmed or validated. The primary aim of this survey is to identify the most promising candidates for dynamically active systems that warrant further investigation. In the first stage of our analysis, precise measurements of the transit times are extracted for each system in an homogeneous way. In the second stage, we apply a decision framework to classify candidates by analyzing the resulting variations. Based on excess timing scatter and the difference in Bayesian Information Criterion of periodic models over linear ones, the TTVs are classified as significant, marginal, or non-detections. We find 11 systems with significant TTVs, 5 of which were announced in previous works, and 10 more systems with marginal evidence in our sample. We present 3-panel diagnostic plots for all the candidates, showing phase-folded light curves, the transit variations over time, and the variations folded on the recovered TTV period. A comprehensive summary table detailing the fitted parameters and TTV significance for the entire survey is also provided. This survey constitutes the largest homogeneous TTV analysis of TESS systems to date. We provide the community with updated ephemerides and a catalogue of high-quality TTV candidates, enabling targeted follow-up observations and dynamical modelling to uncover the nature of unseen companions and study system architectures.
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Earth and Planetary Astrophysics

Searching for primitive, dark, spectrally red asteroid families in the main belt with Gaia

Ullas Bhat, Chrysa Avdellidou, Marco Delbo et al. (+1 more)

Dark asteroids with featureless neutral to red spectra are of particular interest due to their ability to potentially harbour primitive, hydrated, and possibly organic-rich material. These asteroids belong to the spectroscopic C-complex, to the X-types with low geometric visible albedo values as well as to the T- and D-type end members of the Bus-DeMeo spectroscopic taxonomy. Here we used Gaia Data Release 3 visible reflectance spectra to study the average spectral profiles of the C- and X-complex asteroid families in the central and outer main belt (orbital semi-major axis between 2.5 - 3.7~au). We found that eight of these families, namely 96 Aegle, 627 Charis, 1484 Postrema and 5438 Lorre, previously classified as C-complex families, and 322 Phaeo, 1303 Luthera, 5567 Durisen and 53546 2000BY6 previously classified as X-complex families, have redder slopes than implied by their previous classification and could be better classified as T-/D-type families. Some of these families may also feed the near-Earth asteroid population, being responsible for the observed T-/D-type excess. However, the analysis of their principal components of Gaia Data Release 3 spectra suggest that further near-infrared observations are needed in order to verify this identification.
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All authors Ullas Bhat, Chrysa Avdellidou, Marco Delbo, Thomas Dyer

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

WIMP Freeze-out dynamics under Tsallis statistics

Matias P. Gonzalez and Roberto A. Lineros

We generalize thermal WIMP (Weakly Interacting Massive Particle) freeze-out within Tsallis nonextensive statistics. Using Curado-Tsallis $q$-distributions $f_q(E;\mu,T)$ we compute $q$-deformed number and energy densities, pressure, entropy density and Hubble rate, $\{n_q,\rho_q,P_q,s_q,H_q\}$. The Boltzmann equation is generalized accordingly to obtain the comoving abundance $Y_{\chi,q}(x)$ and relic density $\Omega_{\chi,q}h^2$ for a dark-matter candidate $\chi$ in a model-independent setup. The thermally averaged cross section is expanded as $\langle\sigma v\rangle_q \approx a + b\,\langle v_{\rm rel}^2\rangle_q$ up to $p$-wave. The freeze-out parameter $x_f(q)$ is determined from $\Gamma_{{\rm ann},q}(T_f)\simeq H_q(T_f)$ using a $q$-logarithmic inversion, with the expansion rate modified through ultra-relativistic rescalings $R_\rho(q)$ of the effective relativistic degrees of freedom $g_*$ and $g_{*s}$. We show that $x_f$ increases with $q$ and that QCD-threshold features propagate into $Y_{\chi,q}(x)$ and $\Omega_{\chi,q}h^2$. We then perform two $q$-grid scans: fixing $\langle\sigma v\rangle_q$ while varying the dark-matter mass $m_\chi$, and fixing $m_\chi$ while varying the $s$-wave coefficient $a$. For an $s$-wave dominated scenario we construct $\chi^2$ profiles in these planes by comparing $\Omega_{\chi,q}h^2$ with the Planck benchmark $\Omega_c h^2 = 0.120\pm 0.001$. In both cases we find a clear degeneracy in the preferred nonextensive parameter $q_{\rm best}$ along valleys in parameter space. However, fixed-mass scans (varying $\langle\sigma v\rangle_q$) are significantly more constraining than fixed-cross-section scans, reflecting that $\Omega_{\chi,q}h^2$ is mainly controlled by $\langle\sigma v\rangle_q$, so that for realistic cross sections the best-fit $q_{\rm best}$ remains close to the extensive limit $q\to 1$.
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Astrophysics of Galaxies

Collision frequency between dark matter subhaloes within Milky Way-like galaxies

Koki Otaki, Yudai Kazuno and Masao Mori

In the standard cold dark matter (CDM) model, sub-galactic structures hierarchically collide and merge to build up larger structures. Mergers and collisions between dwarf galaxies and dark matter subhaloes (DMSHs) play an important role in the evolution and formation of structures within a massive galaxy. We investigate the collision frequency between DMSHs associated with a massive host galaxy such as the Milky Way. We analytically estimate the density distribution of DMSH pairs for the relative distance and relative velocity ($r_\mathrm{rel}$-$v_\mathrm{rel}$) and the distance from the centre of the host halo and relative velocity ($r$-$v_\mathrm{rel}$) planes, based on the distribution function of the host halo in the phase space. Then, we evaluate the collision frequencies of DMSHs by integrating the orbital evolution of DMSHs in Milky-Way-like host haloes selected from cosmological $N$-body simulations. The frequency of violent encounters, in which the relative distance of DMSHs is shorter than the sum of scale radii, is averaged as $2.1\times 10^2\,\mathrm{Gyr}^{-1}$. Since the time scale of violent encounters, $4.7\,\mathrm{Myr}$, is shorter than the dynamical time of the host halo, collisions between DMSHs occur frequently within the host halo. Although interactions between DMSHs produce pairs with higher relative velocities, the density distributions of all and colliding pairs between DMSHs provided by numerical results are approximately similar to those of the analytical model neglecting the interactions of DMSHs on $r_\mathrm{rel}$-$v_\mathrm{rel}$ plane for all pairs and $r$-$v_\mathrm{rel}$ plane for colliding pairs. We compare our results with observed colliding dwarf galaxies and provide insight into the abundance of DMSHs.
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High Energy Astrophysical Phenomena

Tracing Early Cosmic Chemical Enrichment: A Uniform XMM-Newton Survey of Metallicity in Galaxy Groups and Clusters

Anne E Blackwell, Joel N Bregman and Sophia Chan Davis

Observed metal abundances in the intracluster medium (ICM) of galaxy groups and clusters, $Z_{ICM}$, exceed what is expected from present-day stellar populations alone. Galaxy clusters are presumed to be near closed-box systems, allowing constraints to be placed on the origins of metals and stellar populations responsible for $Z_{ICM}$. We present a uniform XMM-Newton survey of 26 galaxy groups and clusters, measuring radial metallicity profiles and relating $Z_{ICM}$ with the stellar fraction $M_*/M_{gas}$. We determine $Z_{ICM}$ via spectral fitting across multiple annuli finding a best fit of $Z_{ICM} = -0.08^{+0.07}_{-0.07}\, log\left(\frac{M_*}{M_{gas}}\right) + 0.30^{+0.06}_{-0.06}$ with intrinsic scatter $\sigma_p = 0.09^{+0.02}_{-0.01}$. We use closed-box chemical evolution models to estimate the metallicity yield from observable stellar populations, incorporating updated supernova yields and corrections for metals locked in remnants, $Z_* = (1.14 \pm 0.52) \, log\left(1 + \frac{M_*}{M_{gas}}\right)$. Our results demonstrate that present-day stellar populations systematically underpredict $Z_{ICM}$, with an inferred excess component increasing in systems with low $M_*/M_{gas}$. This trend supports the need for an early enrichment population (EEP) distinct from visible stars, $Z_{EEP}$. We find this necessity holds when reconsidering the closed-box assumption by removing all galaxy groups, potential leaky systems, deriving $Z_{EEP}$ within $1\sigma$ when including and excluding groups. Three systems (NGC1132, NGC5098, and NGC4325) deviate from the survey trend, exhibiting steep negative radial metallicity gradients and unusually low $Z_{ICM}$. We posit these systems to be late-forming whose ICM enrichment reflects only recent stellar populations. Our analysis quantifies the necessity of an EEP and provides trends for testing cluster chemical evolution models.
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High Energy Astrophysical Phenomena

Aql X-1 from dawn 'til dusk: the early rise, fast state transition and decay of its 2024 outburst

A. Marino, F. Coti Zelati, K. Alabarta et al. (+36 more)

Transient Low-Mass X-ray Binaries (LMXBs) are usually first detected by all-sky X-ray monitors when they enter new outbursts, typically at X-ray luminosities above $\sim$10$^{36}$ erg/s. Observations of these sources during the early rise of the outbursts have so far been very limited. However, the launch of the Einstein Probe (EP) has greatly improved our ability to detect fainter X-ray activity, unlocking access to the outburst early rise. In September 2024, EP detected the early onset of a new outburst from the neutron star LMXB Aql X-1, catching the source at a luminosity below 10$^{35}$ erg/s. In this paper we present results from a comprehensive, multi-wavelength campaign of this event, combining data from EP, NICER, NuSTAR, Swift and Las Cumbres Observatory covering the full outburst from its early rise through its decay. By comparing X-ray and optical light curves obtained with Las Cumbres Observatory during the initial rise, we show that the start of the X-ray emission lagged the optical rise by, at most, 13 days. Time-resolved X-ray spectroscopy revealed how the geometry and the physical properties of the accretion flow evolve during this early stage of the outburst, as well as at higher luminosities as the source transitioned through the canonical X-ray spectral states - hard, intermediate and soft. These data show that the source underwent a very rapid, about 12-h long, transition from the hard to the soft state about two weeks after the optical onset of the outburst. The evolution of the temperature and physical sizes of both the inner region of the disk and a black body near the NS surface suggest that at the state transition, a boundary and spreading layer likely formed. We discuss these results in the context of time-scales for outburst evolution and state transitions in accreting neutron stars and black holes.
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All authors A. Marino, F. Coti Zelati, K. Alabarta, D.M. Russell, Y. Cavecchi, N. Rea, S.K. Rout, T. Di Salvo, J. Homan, Á. Jurado-López, L. Ji, R. Soria, T.D. Russell, Y.L. Wang, A. Anitra, M.C. Baglio, H. Feng, S. Fijma, S. Guillot, Y.F. Huang, G. Illiano, M. Imbrogno, C. Jin, F. Lewis, Y.F. Liang, M.J. Liu, R. Ma, G. Mastroserio, S.E. Motta, J.U. Ness, E. Parent, A. Patruno, P. Saikia, L. Tao, M. Veresvarska, X.P. Xu, W. Yuan, G.B. Zhang, Z.J. Zhang

Cosmology and Nongalactic Astrophysics

Denoising weak lensing mass maps with diffusion model and generative adversarial network

Shohei D. Aoyama, Ken Osato and Masato Shirasaki

The matter distribution of the Universe can be mapped through the weak gravitational lensing (WL) effect: small distortions of the shapes of distant galaxies, which reflects the inhomogeneity of the cosmic density field. The most dominant contaminant in the WL effect is the shape noise; the signal is diluted due to the finite number of source galaxies. In order to explore the full potential of WL measurements, sharpening the signal by removing the shape noise from the observational data, i.e., WL denoising, is a pressing issue. Machine learning approaches, in particular, deep generative models, have proven effective at the WL denoising task. We implement a denoising model based on the diffusion model (DM) and conduct systematic in-depth comparisons with generative adversarial networks (GANs), which have been applied in previous works for WL denoising. Utilizing the large suite of mock simulations of WL observations, we demonstrate that DM surpasses GAN in the WL denosing task in multiple aspects: (1) the training process is more stable, (2) taking the average of multiple samples from DM can robustly reproduce the true signal, and (3) DM can recover various statistics with higher accuracy.
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Instrumentation and Methods for Astrophysics

How Single-Star Guiding affects HST's Pointing Stability

Jay Anderson and Sylvia Baggett

HST is designed to use two guide stars (GSs) in the fine-guidance sensors (FGSs) to maintain its pointing and tracking during exposures. The primary GS holds the boresight fixed and the secondary GS keeps the orientation fixed. However, HST is also able to track using only a single GS by fixing the boresite on one star and maintaining the orientation using the available gyro(s). We evaluate the pointing quality achieved in this latter case, when one GS and one gyro (RGM, a.k.a., reduced gyro mode) are used. We find that in 1GS-RGM, there is indeed more drift during the course of an orbit than when two guide stars are used, but the drift is much smaller than was seen in previous times of sub-optimal gyro performance. We quantify the 1GS-RGM drift seen in recent archival GO data and in images from a test calibration program and find that (a) for exposures < 500 sec, the PSF quality in 1GS is indistinguishable from that of 2GS and (b) over the course of full orbits (~2500 sec), the drift in four of five cases was less than 0.2 pixel and ~0.4 pix in the other case. Such a drift is marginally detectable in observations, but it should have a marginal impact on most science programs, since the variation in the PSF caused by drift is smaller than the PSF variations with focus and with location on the detector. For observers who wish to correct drift effects, we show that the use of a perturbed PSF during post-acquisition data analysis removes essentially all astrometric residuals, even for drift levels up to ~0.5 pix, as well as most of the photometric residuals.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Development & Characterization of Electrodes for large-scale Xenon Time Projection Chambers

A. Elykov, S. Vetter, V. H. S. Wu et al. (+16 more)

Dual-phase liquid xenon time projection chambers are the core detector elements of many experiments that conduct searches for Dark Matter and rare events, as well as in neutrino and high-energy physics. As part of this detector technology, high-voltage electrodes are instrumental for the generation of observable signals and their physical interpretation. Thus, electrode design and manufacturing has to fulfill stringent requirements, and their production is associated with significant engineering challenges. In this work we describe the successful development of electrodes on the 1.5 m-scale, from their design and simulation to subsequent assembly and high-voltage testing in a gaseous argon environment. The produced electrodes were recently installed as an anode and a cathode during an upgrade to the XENONnT experiment.
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All authors A. Elykov, S. Vetter, V. H. S. Wu, A. Deisting, K. Eitel, R. Gumbsheimer, M. Kara, S. Lichter, S. Lindemann, T. Luce, Y. Ma, J. Müller, K. Müller, K. Ni, U. Oberlack, M. Schumann, P. Shagin, K. Valerius, M. Zhong

Earth and Planetary Astrophysics

Grain growth in protoplanetary disks in the Upper Scorpius revealed by millimeter-wave spectral indices

Tau Bito, Akimasa Kataoka, Takahiro Ueda et al. (+3 more)

The measurement of dust size from millimeter-wavelength spectra provides direct constraints on grain growth in protoplanetary disks. The spectral indices between 0.88 mm and 2.9 mm have been measured in multiple young star-forming regions, such as Taurus, Ophiuchus, and Lupus, which have ages of 1-3 Myr. These spectral indices are as low as 2-3, suggesting that grains in disks are much larger than those in the interstellar medium. In this study, we analyze the ALMA archival data of 23 disks in the Upper Scorpius region. The observed wavelength is 2.9 mm in Band 3, the angular resolution is 3.3 arcsec x 2.1 arcsec, which is not high enough to resolve the targets, and the rms noise is below 0.075 mJy beam$^{-1}$ for almost all sources. Together with the literature values of the Band 7 fluxes of the same targets, we find that the average spectral index of the disks in the Upper Scorpius region is $\alpha_\mathrm{mm}=2.09 \pm 0.10$, which is equal to or slightly smaller than those at the other younger regions. To explain the relationship between the fluxes and spectral indices of the disks in the Taurus, Ophiuchus, Lupus, and Upper Scorpius regions, we construct simple disk evolution models. The observations are best reproduced by models in which the inner radius of the disk increases. This suggests that a substantial amount of dust mass must persist in the outer disk regions where the dust temperature is lower than 20 K even at late evolutionary stages. These findings offer key insights into the grain growth and the temporal evolution of protoplanetary disks.
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All authors Tau Bito, Akimasa Kataoka, Takahiro Ueda, Luca Ricci, Tilman Birnstiel, John Carpenter

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

High-frequency Gravitational Waves from Superstring Phases in the Early Universe

Joseph P. Conlon, Edmund J. Copeland, Edward Hardy et al. (+1 more)

When moduli roll in the early universe, all physical scales - including string tensions - simultaneously evolve. The dynamics of cosmic string loops with time-varying tension can produce cosmic string loop trackers in which most of the energy density of the universe lies in the form of string loops. This solution can exist as an attractor until the rolling modulus reaches its minimum, when the loops ultimately decay through gravitational wave emission. We explore the spectrum of gravitational waves produced by such string loop trackers. The resulting spectrum is high-frequency and peaks in the GHz regime today. The amplitude of the signal is diluted by any subsequent matter-dominated epochs, and thus the potential observability of the signal crucially depends on the duration of the moduli-dominated epoch that follows once the moduli settle down and oscillate about their minimum.
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All authors Joseph P. Conlon, Edmund J. Copeland, Edward Hardy, Noelia Sánchez González

Instrumentation and Methods for Astrophysics

WFC3/IR Geometric Distortion - Time Evolution of Linear Terms w.r.t. Gaia DR3

Anne O'Connor and Varun Bajaj

We examine the relative offsets of the linear terms in the geometric distortion between WFC3/IR and the Gaia DR3 catalog using the Mikulski Archive for Space Telescopes (MAST) pipeline WFC3/IR to Gaia DR3 alignment solutions to assess temporal stability over the lifetime of the WFC3 instrument (2009-2024). We find a period of increased uncertainty and offsets in the rotation term between 2018 and 2021, as seen in a previous analysis of WFC3/UVIS linear geometric distortion (O'Connor et al., 2024), corresponding with a period of increased jitter. We find a similar pattern of increased uncertainty between 2018 and 2021 in the skew offsets to Gaia DR3, as well. We find no significant linear temporal evolution in the rotation, skew, or scale offsets between the WFC3/IR IDCTAB distortion solution and Gaia DR3 over the 16-year lifetime of the WFC3 instrument; however, we do see temporal evolution in the shift offsets (the difference -in pixels- between the IDCTAB and Gaia WCS positions), which are dominated by telescope pointing inaccuracy external to the WFC3/IR geometric distortion solution. For observers requiring high-precision astrometry, we continue to recommend that observers verify or improve image alignment using the tweakreg routine.
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Instrumentation and Methods for Astrophysics

WFC3/UVIS EPER CTE 2009-2025

Anne O'Connor and Harish Khandrika

In this report, we examine the behavior of Charge Transfer Efficiency (CTE) on the WFC3/UVIS detector over time as computed by the Extended Pixel Edge Response (EPER) technique, using internal calibration data acquired from 2009 through 2025. We find that the CTE has continued to decline as expected, with a steeper loss rate for lower signal levels. The lowest signal level (160e-) has continued to decline at a rate of 0.0001 per year, with a total overall decline of 0.0015. Analyses from 2016 and 2020 found that the rate of decline was not well fit by a linear function. This report verifies the rate of decline is instead better fit by a quadratic function (which results in the smallest min. and max. residuals, on average) or a cubic function (which has the best "goodness of fit" $\chi^2$ and $R^2$ values). We continue to see periodic oscillations of the residuals around all three fit lines (linear, quadratic, and cubic) on which we perform a Lomb-Scargle periodogram analysis of the residuals. We find a periodicity of about 8 years for the residuals around the linear fit lines and about 9 years for the quadratic and cubic fit lines.
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Earth and Planetary Astrophysics

An observationally based wind model contemporaneous with the radio detections in $\tau$ Boötis

Dag Evensberget, Aline A. Vidotto, Filip Elekes et al. (+2 more)

Recent low-frequency array (LOFAR) radio signal detections bearing from the $\tau$ Boötis system have been cautiously attributed to auroral emissions from the hot Jupiter $\tau$ Boötis Ab. The auroral emissions are believed to be excited by interaction between the exoplanet and the winds of its host star. Since stellar winds respond to stellar surface magnetism, three-dimensional stellar wind modelling, able to account for the star's contemporaneous magnetic field geometry, can aid the interpretation of radio detections. For the first time, we present spectropolarimetric observations of $\tau$ Boötis A from the same epoch as the LOFAR detections. We derive a contemporaneous large-scale magnetic map of $\tau$ Boötis A, which shows a poloidally dominated field with mean strength 1.6 G. From our magnetic map, we create a three-dimensional numerical wind model and characterise the wind properties around $\tau$ Boötis Ab. To compute the wind power dissipated in $\tau$ Boötis Ab's magnetosphere, we apply two approaches: A) the solar system-based empirical relation called Bode's law; and B) a resolved numerical model of the planetary magnetosphere. When consistently applying best-case assumptions, we redict radio flux densities around 50 mJy and 0.68 mJy respectively. Our values are much too small to be consistent with the reported observation of $890_{-500}^{+690}$ mJy; a stellar surface magnetic field scaling $\gtrsim 10$ is required to reproduce the observed signal strength. As $\tau$ Boötis A has a rapid magnetic cycle, we speculate that wind variations cased by variation in stellar magnetism may explain the lack of detections from follow-up observations. Our work emphasises the importance of contemporaneous observations of stellar magnetism and observational signatures of star-planet interaction.
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All authors Dag Evensberget, Aline A. Vidotto, Filip Elekes, Sandra V. Jeffers, Rik T. Luisman

Astrophysics of Galaxies

Environmental Invariance of the Galaxy Size-Mass Relation

Li-Wen Liao and Andrew Cooper

The galaxy size-luminosity and size-stellar mass relations are important constraints on the galactic baryon cycle of gas accretion, star formation, and feedback. There are conflicting claims in the literature regarding how environment influences size: both direct transformative effects and `assembly bias' may contribute to observed variations with environment. We construct a large homogeneous sample of size measurements to M*~10^7 Msun. Our sample fills a gap in field galaxy size measurements around 10^7-10^8 Msun; the literature at these masses is biased towards satellites of L* galaxies and members of galaxy clusters. We use sizes from the DESI-LS, together with a published catalog that contains stellar masses and cluster positions derived from DESI-LS photometry. Our sample extends to z<0.3 and comprises 540,228 galaxies with spectroscopic redshifts and 9,513,732 galaxies with photometric redshifts. We explore the environmental dependence of size for a mass-limited subset of our sample at z<0.05, based on distance to the nearest cluster center. We obtain size-luminosity and size-mass relations in good agreement with previous studies. By separating galaxies according to color and morphology, we show that the environmental variation of the overall size-mass relation on Mpc scales can be understood as the consequence of a changing mixture of subpopulations, rather than direct size transformation. For example, at fixed mass, quiescent (red) late-type galaxies within 2Mpc of a cluster have the same size as quiescent late-type galaxies 30Mpc from the nearest cluster. Our results support individual galaxy assembly histories as the primary determinant of galaxy size. The existence of significantly different, environment-insensitive size mass relations for subpopulations separated by color and Sersic index provides a clear target for calibration of the baryon cycle in cosmological simulations.
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Astrophysics of Galaxies

Can Wolf-Rayet stars be the missing ingredient to explain high-z He II ionizing radiation?

G. González-Torà, A. A. C. Sander, E. Egorova et al. (+7 more)

Classical Wolf-Rayet (WR) stars are hot, massive stars with depleted hydrogen. At low metallicities (Z), WN3-type WR stars have relatively thin winds and are major sources of ionizing flux. The detection of high-ionization emission lines in high-redshift ($z$) galaxies as well as nearby low-Z dwarf galaxies raises questions about the origin of He II ionizing radiation and its role in galaxy evolution, as stellar population models fail to reproduce the required fluxes. Low-Z WN3 stars may provide the missing contribution but are easily hidden in integrated light. Using the Local Volume Mapper, we compare resolved optical spectra of SMC WN3 stars with integrated regions, focusing on the broad He II $\lambda4686\,\AA$ line. We find stellar emission diluted within nebular regions, becoming undetectable when integrating over areas larger than 24 pc. Nonetheless, these stars emit enough ionizing photons to explain observed He II nebular emission, being strong candidates for the He II ionizing sources in low-Z and high-$z$ galaxies.
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All authors G. González-Torà, A. A. C. Sander, E. Egorova, O. Egorov, M. Bernini-Peron, J. Josiek, K. Kreckel, R. R. Lefever, V. Ramachandran, E. C. Schösser

High Energy Astrophysical Phenomena

Thermal equilibrium curves of accretion disks driven by magnetorotational instability

Shigenobu Hirose

Analogous to the HR diagram for stars, the thermal equilibrium curve encodes the thermodynamics of accretion disks by expressing the local balance between heating – primarily via viscous dissipation – and cooling – typically through radiative transfer. These curves are commonly plotted as surface density versus effective temperature. When an S-shaped locus appears, local annuli become bistable, and limit-cycle oscillations arise when the external mass-transfer rate falls within an unstable band. This behavior underpins the disk instability model for recurring outbursts in cataclysmic variables. This paper reviews first-principles thermal equilibrium curves for accretion disks driven by magnetorotational instability (MRI), with emphasis on dwarf novae. Unlike the parameterized $\alpha$-viscosity approach, the curves are obtained by solving the governing equations with radiation magnetohydrodynamics simulations, thereby reproducing S-shaped loci without prescribing $\alpha$. The disk instability in dwarf-nova systems and the physical origin of angular-momentum transport (shear stresses) are also briefly reviewed. Notes on the stability of radiation-dominated accretion flows are included in the Appendix.
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2511.16314 · 20 Nov · This paper is based on an invited talk presented at the 87th Fujihara Seminar: The 50th Anniversary Workshop of the Disk Instability Model in Compact Binary Stars (DIM50TH2025), held on 22–26 September 2025 in Tomakomai, Japan. It has been accepted for publication in PoS (Proceedings of Science), and is scheduled to appear in February 2026 at https://pos.sissa.it/493/

Abstract PDF $ACCR ×4$EQLB ×3$DWRF ×2$STAR ×1