High Energy Astrophysical Phenomena
Fingerprints of Individual Supermassive Black Hole Binaries in Pulsar Timing Arrays
Chiara M. F. Mingarelli, Bjorn Larsen, Ellis Eisenberg et al. (+2 more)
With evidence for a nanoHertz gravitational-wave background now established by
Pulsar Timing Arrays, the search focuses on identifying individual supermassive black hole binaries. We show that these binaries produce a distinct spatial correlation pattern across the array, acting as a deterministic analogue to the
stochastic Hellings & Downs curve. We derive a closed analytic expression for this single-source overlap reduction function, $\Upsilon_{ab}$, factorizing the signal into a source-dependent amplitude and a purely
geometric fingerprint. Using simulated
datasets, we demonstrate that this fingerprint breaks the degeneracy between an individual binary and a
stochastic background. Including these cross-correlations yields Bayes factors of $1611$ favoring the continuous-wave model over a Hellings & Downs correlated background model and $159$ favoring the continuous-wave model over an uncorrelated red-noise model. Furthermore, these new cross-correlations improve sky localization by a factor of $11\times$ over an uncorrelated search. Finally, while coherent matched filtering offers higher theoretical sensitivity, we argue that a cross-correlation-based search for individual binaries provides a robust alternative that hedges against the possibility of overfitting to noise fluctuations by focusing on the evidence for the correlations. Indeed, the
geometric fingerprints we present here show that spatial correlations can also be used to identify the first nanoHertz gravitational-wave sources.
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All authors Chiara M. F. Mingarelli, Bjorn Larsen, Ellis Eisenberg, Qinyuan Zheng, Forrest Hutchison
Earth and Planetary Astrophysics
Photodynamical modeling of TOI-4504 reveals its deeply resonant state and similarity to GJ 876
J.M. Almenara, R. Mardling, A. Leleu et al. (+15 more)
The K-
dwarf TOI-4504 hosts two
giant planets in 2:1 mean-motion resonance, with orbital periods of 41.3 days (
planet d) and 82.8 days (
planet c). They exhibit among the largest known absolute transit-timing variations, with respective peak-to-node amplitudes up to 5 and 3 days. Newer TESS data show that the previously non-transiting
planet d has now precessed into transiting, and we derive updated system parameters with significant discrepancies with the discovery paper. The revised parameters place
planets d and c deep in the resonance and close to or in the fully-relaxed limit-cycle state, with the resonant and secular modes interfering nonlinearly to induce non-zero relaxed free eccentricities which precess at the same rate as the forced eccentricities and the longitude of conjunctions, in turn enabling precise measurement of the full eccentricities and apsidal angles. We discuss the predictions of linear theory and how it can be used to understand the true state of the system revealed by N-body integrations, and more generally why it is that the posteriors of systems more compact than 2:1 tend to suffer from significant eccentricity degeneracy. We show that the extraordinary dynamical states of the
giant pairs orbiting TOI-4504 and the M-
dwarf GJ 876 are remarkably similar, in spite of the significant difference in their host-
star masses, and discuss the implications for damping timescales during the relatively gentle formation process of Type II migration.
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All authors J.M. Almenara, R. Mardling, A. Leleu, S. Udry, T. Forveille, X. Bonfils, F. Bouchy, C. Cadieux, J. Couturier, R.F. Díaz, Y. Eyholzer, E. Fontanet, T. Guillot, G. Hébrard, R.M. Hoogenboom, J. Korth, M. Lendl, A. Nigioni
Solar and Stellar Astrophysics
Determination of the Height-Temperature Profile Above a Solar Active Region from Multi-Frequency Radio Observations
T. I. Kaltman, A. G. Stupishin and G. A. Makoev
An iterative method is presented for reconstructing the height-temperature profile of the
solar atmosphere above a sunspot using multi-frequency spectro-polarimetric microwave observations. It is assumed that the emission is formed predominantly under gyroresonance conditions at harmonics of the electron gyrofrequency, and that the contribution at each frequency is associated with a layer of optical depth of order unity. The frequency-height correspondence is determined from extrapolation of the photospheric
magnetic field into the corona. The reconstruction of the profile is reduced to solving an overdetermined system of linear equations with regularization, ensuring noise stability and physical smoothness of the solution. The method is tested on synthetic data for a dipole sunspot model and applied to observations of active region NOAA 11312 obtained with the RATAN-600
radio telescope. The derived temperature profiles are consistent with contemporary models of active regions and reproduce the observed spectra in the 3-18~GHz range with an accuracy of a few percent.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th
Pathologies of dimension-zero scalar fields
James M. Cline and Anamaria Hell
It has been claimed in a series of papers that scalar fields with a fourth-order Lagrangian $\sim(\Box\varphi)^2$ can solve the cosmological constant problem by canceling the loop contributions from standard model fields, and that their fluctuations can be the source of the
primordial density perturbations of the Universe, without the need for inflation. We dispute these claims. The spectrum of the theory includes a ghost, which leads to classical instabilities and
quantum violation of unitarity. We show that the new scalar particles cannot cancel the standard model contributions to the cosmological constant, unless they include a unitarity-violating ghost at the
quantum level. Further, the coupling of such scalars to the particles of the standard model induces a confining fifth force which rules it out as a source of density perturbations in the early Universe.
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High Energy Astrophysical Phenomena
SuperSNEC: Fast and Accurate Light Curve Production for Large Hydrodynamic Model Grids Using Adaptive Gridding
Christoffer Fremling and K-Ryan Hinds
We present SuperSNEC, an accelerated version of the
SuperNova Explosion Code (SNEC) designed for rapid production of large radiation-hydrodynamic model grids using low-zone-count simulations ($\sim100$ zones). The main advance is adaptive gridding of the computational grid, which preserves light-curve fidelity relative to a high-resolution SNEC baseline ($\sim1000$ zones) while delivering a runtime improvement of ${\sim}420\times$. SuperSNEC also includes solver optimizations, optimized radioactive-energy deposition and ray-tracing, improved $^{56}$Ni mixing controls, and a smooth photosphere luminosity correction that suppresses low-resolution artifacts. We quantify the speed-accuracy trade-off for a 100-zone configuration against a 1000-zone reference and define baseline settings for efficient large-grid inference of stripped-envelope
supernovae. Our optimized 100-zone setup achieves an RMS light-curve residual of $0.022$ mag relative to the 1000-zone reference, at a runtime of $<2$ seconds per model. Applied to SN 2011dh (Type IIb), SN~1993J (Type IIb), and SN 2020oi (Type Ic), SuperSNEC recovers light-curve parameters consistent with the literature; in particular, SN 2020oi is well reproduced by a purely radioactive model, with no clear evidence that an additional power source is required.
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High Energy Astrophysical Phenomena
A search for optical counterparts in quiescent black hole X-ray transients
I.V. Yanes-Rizo, J. Casares, M.A.P. Torres et al. (+7 more)
Dynamical mass measurements of compact
stars in X-ray transients demand the detection of optical/near infrared counterparts in quiescence. Out of the 73 black-hole candidates in X-ray transients, optical and near-infrared quiescent counterparts have only been identified for 34 objects. We present ULTRACAM photometric observations of nine candidate black hole X-ray transients with no reported counterparts in quiescence, complemented with data from the public surveys DECaPS and Pan-STARRS. In addition, we analyze photometry of three sources (SWIFT J1539.2-6227, XTE J1817-330 and XTE J1818-245) obtained during their discovery outburst. The data provide the first optical identifications and precise astrometry of four targets (MAXI J1348-630, SWIFT J1539.2-6227, XTE J1726-476 and XTE J1817-330) plus $3\sigma$ lower limits to the quiescent optical magnitudes for an additional five (MAXI J0637-430, 4U 1755-338, MAXI J1803-298, XTE J1818-245 and MAXI J1828-249). Of these five, 4U 1755-338 was found to be active during our ULTRACAM observations and we use our images to derive refined astrometric coordinates. We use the photometric magnitudes and colors to place preliminary constraints on the orbital periods and spectral types of the companion
stars. Finding charts of all the targets are also provided to facilitate future follow-up studies. Finally, we present updated astrometry for XTE J1650-500 using archival FORS2 images.
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All authors I.V. Yanes-Rizo, J. Casares, M.A.P. Torres, V. S. Dhillon, T. R. Marsh, M. Armas Padilla, P. G. Jonker, T. Muñoz-Darias, S. Navarro Umpiérrez, D. Steeghs
Solar and Stellar Astrophysics
Active regions and the large-scale magnetic field of solar cycle 24
Ismo Tähtinen, Timo Asikainen and Kalevi Mursula
Most of the intracyclic variability in the large-scale
solar magnetic field comes from the equatorial dipole component of the
solar magnetic field. The equatorial dipole component is highly sensitive to the longitude distribution of the active regions. We quantify the effect of individual active regions on the large-scale
solar magnetic field of the
solar cycle 24. We study the effect of the longitude distribution of active regions on the strength of the large-scale dipole component. We used a surface flux transport (SFT) model to simulate the
evolution of individual active regions and quantified their effect on the large-scale
magnetic field using the recently developed vector sum method. We took advantage of the longitudinal translational invariance of the SFT model and compared the observed
solar cycle 24 to the 10 000 simulations of the
solar cycle 24 using randomized longitudinal source locations, but otherwise identical flux emergence. We find that taking into account both the axial and equatorial components of the vector sum characterizing the global
solar magnetic field sets better constraints on the parameter space of the SFT model than, for example, using the axial dipole moment alone as an optimization metric. We studied the maximum of cycle 24 and identified the recurrent and localized flux emergence in the southern hemisphere as the main culprit behind the rapid strengthening of the large-scale
magnetic field in late 2014. We find that during the declining phase of the
solar cycle, the strength of the large-scale
magnetic field stayed above the median level of randomized simulations (p < 0.027) for 42 subsequent. This indicates that the longitudinal distribution of active regions is not random and, rather, that it demonstrates a tendency for some regions to emerge at longitudes where their equatorial components reinforce the large-scale equatorial field.
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Astrophysics of Galaxies
A cationic carrier for diffuse interstellar band at 862.1 nm: Evidence from the skin effect in nearby diffuse-to-translucent clouds
He Zhao and Lu Li
The tendency of some diffuse interstellar band (DIB) carriers to concentrate in the outer, UV-illuminated layers of molecular clouds (MCs)–the “skin effect”–makes their spatial distribution a powerful probe of their physical nature. We leverage
Gaia DR3 measurements of the DIB at 862.1 nm to investigate its behavior across 12 nearby MCs, spanning diffuse to translucent regimes ($A_{\rm V}\,{\sim}\,0.2{-}3.5$ mag). We find significant diversity in the DIB behavior, both between different clouds and within individual clouds from their outer to inner regions. To quantify these trends, we employed a piecewise linear model (PLM) to fit the average slope ($\alpha$) between the normalized DIB strength, ${\rm log_{10}}(W_{8621}/A_{\rm V})$, and
dust extinction, ${\rm log_{10}}(A_{\rm V})$. In general, ${\rm log_{10}}(W_{8621}/A_{\rm V})$ declines with ${\rm log_{10}}(A_{\rm V})$ with $\alpha$ between 0 and –1, becoming progressively steeper at higher $A_{\rm V}$. These observed slopes and their variations are consistent with the photoionization
equilibrium models, where the carrier abundance is governed by local conditions, particularly the UV radiation field and cloud structure (e.g., density profiles, clumpiness). Particularly, the Taurus cloud region uniquely displays an initial increase in ${\rm log_{10}}(W_{8621}/A_{\rm V})$ at low extinction, a signature predicted for a cationic carrier. By fitting the slope of this rising trend, we estimate an ionization potential of $E_{\rm IP}\,{=}\,12.40^{+1.90}_{-2.29}$ eV for the DIB$\lambda$8621 carrier, which aligns well with the secondary ionization energies of large carbonaceous molecules like polycyclic aromatic hydrocarbons (PAHs) or fullerenes.
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High Energy Astrophysical Phenomena
Thermal Electrons in an Ultra-Relativistic Shock Shape the Optical Afterglow of GRB 250702F
Martin Jelínek, Annarita Ierardi, Filip Novotný et al. (+8 more)
Observing early optical emission from gamma-ray bursts (GRBs) contemporaneous with the MeV
prompt emission phase remains rare, requiring rapid-response robotic facilities. The Ondřejov D50
telescope detected the optical counterpart of GRB 250702F at z = 1.520 only 27.8 s after trigger, enabling high-cadence monitoring during the brightest
prompt emission pulses. The optical light curve reveals two distinct
flares. The first (30 - 100 s) is spectrally consistent with the MeV
prompt emission. The second
flare (100 - 1400 s) exhibits an unusual morphology (F_nu ~ t^-alpha): a rapid rise to a plateau, followed by a steep decay (alpha ~ 1.6) before transitioning to a standard power-law afterglow (alpha = 0.79). This steep decay phase cannot be explained by nonthermal electrons accelerated at the forward shock, and reverse-shock scenario is disfavored due to the long duration of the
flare and the temporal offset from the underlying deceleration time. We interpret the steep decay as the synchrotron frequency of a thermal (Maxwellian) electron population sweeping through the optical band. Modeling yields a non-thermal energy fraction delta ~ 0.8 with the remaining energy heating electrons at characteristic Lorentz factor gamma_th ~ 900. These observations provide evidence for thermal electron signatures in GRB afterglows, consistent with predictions from particle-in-
cell simulations of ultra-relativistic collisionless shocks.
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All authors Martin Jelínek, Annarita Ierardi, Filip Novotný, Gor Oganesyan, Biswajit Banerjee, Dimitrios Giannios, Sergey Karpov, Martin Topinka, Elias Kammoun, Jan Štrobl, Alberto J. Castro-Tirado
Astrophysics of Galaxies
The case of NGC 5824, a cluster possibly embedded in a dark matter halo
Paula B. Díaz, Berenice Muruaga, Ricardo R. Muñoz et al. (+3 more)
The globular cluster NGC 5824 exhibits a diffuse
stellar envelope that extends beyond its nominal King
tidal radius and symmetrically surrounds the cluster. The origin of these
stars and whether they remain gravitationally bound to the cluster center is unclear. A possible explanation is that such clusters are embedded within dark matter
halos, which influences their kinematic and photometric properties. Specifically, their outer volume density profile would be characterized by a power law with an index $\gamma > -3$. In this study we assessed this photometric prediction by comparing it to the cluster's observed profile through an analysis of deep $g$-band photometry from MegaCam and DECam, combined with
Gaia DR3 proper motions and photometry. We determined
star membership using color-magnitude diagrams and proper motion constraints in order to fit King and power-law profiles to the observed profile. Additionally, we analyzed NGC 5824's luminosity function to assess its spatial
symmetry and extent. Our results show that NGC 5824 is symmetrically extended to at least $\sim20'$ with an outer surface density profile characterized by a power-law index of $\gamma \sim - 2.6\pm0.1$, which is consistent with the predicted values for a cluster embedded within a dark matter
halo. Spectroscopic observations carried out to study the velocity dispersion profile will provide a more definitive answer regarding the dark matter content of NGC 5824.
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All authors Paula B. Díaz, Berenice Muruaga, Ricardo R. Muñoz, Julio A. Carballo-Bello, Pete B. Kuzma, Valentina Suárez
Instrumentation and Methods for Astrophysics
Long-Integration Magnetar Burst Observatory (LIMBO): Instrument Summary and Early FRB Rate Constraints
Darby McCauley, Aaron Parsons, Wei Liu et al. (+3 more)
The Long-Integration Magnetar Burst Observatory (LIMBO) is a real-time
radio transient detection pipeline designed to search for dispersed fast
radio bursts (FRBs) from
Galactic magnetars. Deployed at the University of California, Berkeley's Leuschner
Radio Observatory, LIMBO employs a $4.3~\mathrm{m}$ dish with a dual-polarization feed to continuously monitor a $125~\mathrm{MHz}$ band centred at $1460~\mathrm{MHz}$. A real-time processing pipeline performs a search for dispersed transients on the summed polarizations, with detections triggering dumps of buffered voltage data to disk. Based on calibrated sensitivity measurements, synthetic signal-injection and recovery tests, and successful detection of pulses from the Crab
Pulsar, we determine that LIMBO is sensitive to
radio transients with fluences $\geq 43~\mathrm{Jy \cdot ms}$. Between May and August 2023, LIMBO conducted 833 hours of follow-up observations of the
Galactic magnetar SGR 1935+2154, yielding 12 candidate FRB detections. If these events are true, we measure FRB-like event rates from SGR 1935+2154 of $R(\geq 65~\mathrm{Jy \cdot ms}) = 112.3^{+81.3}_{-54.5}~\mathrm{yr}^{-1}$ and $R(\geq 130~\mathrm{Jy \cdot ms}) = 17.7^{+40.8}_{-15.1}~\mathrm{yr}^{-1}$. Combining these results with previously reported FRBs from SGR 1935+2154, we infer a cumulative rate-fluence power-law slope of $\alpha=-0.60^{+0.24}_{-0.28}$ in the fluence range between $10$ and $10^6\rm\, Jy \cdot ms$. These observations demonstrate the capability of continuous, real-time monitoring of
Galactic magnetars and establish LIMBO as an effective instrument for detecting
Galactic FRBs.
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All authors Darby McCauley, Aaron Parsons, Wei Liu, Wenbin Lu, Dirk Wright, Dan Werthimer
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
The continuum spectrum of nonrelativistic multi-frequency Proca stars
Galo Diaz-Andrade, Alberto Diez-Tejedor, Jose Luis Medina-Garcia et al. (+1 more)
Multi-frequency Proca
stars are excited selfgravitating solutions of the $s=1$ Schrödinger-Poisson system that generalize the conventional stationary states of a massive vector field. Unlike stationary states, which are characterized by a single oscillation frequency, multi-frequency configurations exhibit a quasi-periodic dynamics involving two or three distinct frequencies. In this paper, we present a systematic study of the spectrum of spherical multi-frequency Proca
stars and show that, at fixed particle number, they form continuous families interpolating between discrete stationary states of constant linear polarization. Furthermore, we analyze their stability and demonstrate that a subset of these multi-frequency configurations are linearly stable against general perturbations. In particular, we show that a necessary, although not sufficient, condition for stability is the presence of a non-negligible nodeless component, and that radial stability alone is not sufficient to guarantee full linear stability. Finally, we briefly discuss the potential implications of multi-frequency states for proving the particle
spin in ultralight dark matter models.
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All authors Galo Diaz-Andrade, Alberto Diez-Tejedor, Jose Luis Medina-Garcia, Armando A. Roque
Earth and Planetary Astrophysics
Exocomets of $\beta$ Pictoris II: Two dynamical families of exocomets simulated with REBOUND
K.P. Jaworska and H.J. Hoeijmakers
We investigate the dynamical
evolution of particles in the $\beta$ Pic system to determine likely formation pathways to the present-day observed exocomet populations. We aim to relate these results to similar studies recently carried out since the discovery of the inner
planet $\beta$ Pic c. We simulate the $\beta$ Pic system using the non-
symplectic adaptive N-body integrator IAS15 in REBOUND. We seed the system with over 100,000 mass-less test particles that evolve for 25 Myr, and adopt initial conditions and a particle distribution that closely matches similar simulations in recent literature. Using IAS15, REBOUND resolves close-encounters between test particles and the two gas
giants in the system, which is crucial for understanding aspects of the dynamical
evolution.
Planet-disk interactions rapidly clear most of the system within 35 AU apart from a region within the orbit of $\beta$ Pic c, and a region between 20 and 25 AU. After 10 Myr, exocomets can be sourced continuously from these regions, as well as from the inner edge of the region beyond ~35 AU where particles are stable on longer timescales. From the region interior to $\beta$ Pic c, the exocomets are formed by excitation via mean-motion resonance with $\beta$ Pic c, obtaining a narrow distribution of radial velocities, consistent with spectroscopic observations. Particles initialized in the outer system may enter onto stargrazing orbits due to disruption by the two gas
giants, causing a wider radial velocity distribution, and we propose that this population corresponds to a second dynamical family previously observed via spectroscopy. These particles typically undergo chaotic dynamical
evolution for $10^2$ to $10^3$ years after passing the water sublimation limit at ~8 AU until reaching the sublimation distance of calcium near 0.4 AU, implying that the two families of exocomets may have different volatile contents.
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Earth and Planetary Astrophysics
Vertical Structure of Protoplanetary Disks in Scattered Light: A large sample analysis
J. Byrne, C. Ginski, R. F. van Capelleveen et al. (+5 more)
High-resolution scattered-light imaging has revealed complex morphologies in protoplanetary and circumstellar disks. Measuring the vertical height of the scattering surface is key to understanding disk structure,
evolution, and the properties of embedded
dust. We develop a methodology for fitting elliptical shapes to scattered-light images of protoplanetary disks in order to extract vertical height profiles of the
dust scattering surface across a large and morphologically diverse disk sample. The
dataset consists of 92 near-infrared polarimetric images obtained with VLT/SPHERE. The aim is to identify trends in vertical structure across different disk morphologies and test for correlations with
stellar mass, age, and disk
dust mass, as well as to investigate the implications of the derived height profiles for the masses of potential embedded
planets. We implement a structure extraction and ellipse fitting (SEEF)
algorithm that uses edge detection and Gaussian fitting to locate disk structures. Ellipse fitting reveals spatial offsets between the ellipse centre and the
stellar position, which are interpreted as vertical height assuming circular ring geometry. Disk inclination, position angle, and the aspect ratio h/r are also derived. The method yields vertical height measurements for 92 disks, showing profiles consistent with flared disk geometries. However, the full sample cannot be described by a single power-law relation. Subdivision by morphology shows no strong correlations for most disk classes, except for extended disks with outer radii larger than about 150 au, which exhibit a clear power-law flaring trend. The lack of strong correlations with other system properties suggests that either different morphologies exhibit distinct vertical structures or that additional physical factors influence disk flaring.
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All authors J. Byrne, C. Ginski, R. F. van Capelleveen, N. Fitzgerald, A. Garufi, C. Coyne, C. Lawlor, D. McLachlan
Instrumentation and Methods for Astrophysics · Cross-listed from cs.LG
On the Value of Tokeniser Pretraining in Physics Foundation Models
Hadi Sotoudeh, Payel Mukhopadhyay, Ruben Ohana et al. (+4 more)
We investigate the impact of tokeniser pretraining on the accuracy and efficiency of physics emulation. Modern high-resolution simulations produce vast volumes of data spanning diverse physical regimes and scales. Training foundation models to learn the dynamics underlying such data enables the modelling of complex multiphysics phenomena, especially in data-limited settings. The emerging class of physics foundation models typically aims to learn two tasks jointly: (i) extracting compact representations of high-resolution spatiotemporal data, and (ii) capturing governing physical dynamics. However, learning both tasks from scratch simultaneously can impede the effectiveness of either process. We show that pretraining the tokeniser with an autoencoding objective prior to training the dynamics model enhances computational efficiency for physics emulation. Notably, the magnitude of this benefit depends on domain
alignment: pretraining on the same physical system as the emulation task yields the largest improvements, while pretraining on other systems provides moderate gains. In-domain pretraining reduces VRMSE by 64% after 10,500 training steps compared to training from scratch. To our knowledge, this is the first systematic investigation of tokeniser pretraining for physics foundation models. We further introduce flexible spatiotemporal compression operations that extend causal convolutions to support runtime-adjustable compression ratios, enabling efficient adaptation to diverse downstream tasks. Our findings provide practical guidance for training efficient physics emulators and highlight the importance of strategic pretraining data selection.
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All authors Hadi Sotoudeh, Payel Mukhopadhyay, Ruben Ohana, Michael McCabe, Neil D. Lawrence, Shirley Ho, Miles Cranmer
Astrophysics of Galaxies
Weighing gas-rich starless halos: Dark matter parameter inference based on gas distributions
Francesco Turini and Alejandro Benitez-Llambay
Reionization-Limited $H_I$ Clouds (RELHICs) are starless dark matter
halos retaining a significant neutral hydrogen($H_I$ ) reservoir. The gas resides in near hydrostatic
equilibrium within the dark matter potential and in thermal
equilibrium with the
cosmic ultraviolet background. This simplicity allows analytic frameworks to link observable $H_I$ column densities directly to fundamental dark matter
halo structural parameters. We systematically assess the accuracy of inferring host
halo parameters from RELHIC gas distributions on an object-by-object basis, quantifying biases, intrinsic degeneracies, and the limits of parameter recovery. Using RELHICs from a
redshift z = 0 high-resolution cosmological hydrodynamical simulation, we employ
Bayesian nested sampling to infer dark matter
halo mass and concentration. We evaluate this against 3D spherically averaged total gas and $H_I$ density profiles, alongside 2D $H_I$ column density profiles. We found that while the ensemble inference yields a robust, unbiased recovery of
halo virial mass from 3D profiles, individual systems exhibit a mass-concentration degeneracy driven by local environmental density. Overdense environments yield slightly overestimated masses and underestimated concentrations; underdense regions show the inverse. We demonstrate that treating environmental density as a free parameter breaks this degeneracy and completely neutralizes the systematic mass bias. Although concentration recovery remains limited by simulation resolution, the virial mass is exceptionally well constrained, establishing a highly reliable framework for weighing starless
halos in upcoming surveys.
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Cosmology and Nongalactic Astrophysics
X-SORTER (X-ray Survey Of meRging clusTErs in Redmapper): X-ray and Spectroscopic Characterization of 12 Optically Selected Galaxy Cluster Merger Candidates
Christopher Hopp, David Wittman, Rodrigo Stancioli et al. (+3 more)
Merging
galaxy clusters offer a unique probe of dark matter (DM) interactions through the spatial offsets between
galaxies, the intracluster medium, and the DM
halo. Systems that are binary, near the plane of the sky, and observed shortly after first pericenter provide the cleanest constraints on the DM self-interaction cross-section. The X-SORTER (X-ray Survey Of meRging clusTErs in redMaPPer) program aims to systematically identify such mergers using optical indicators of binarity in the redMaPPer cluster catalog and to follow up promising candidates with X-ray and spectroscopic observations. We select massive clusters where the top redMaPPer brightest cluster
galaxy (BCG) probability is below 0.98, the top two BCGs are separated by at least 0.95 arcmin, and the optical richness exceeds $\lambda = 120$. We present XMM and Keck/DEIMOS observations of twelve clusters with no previous XMM-Newton or Chandra archival data meeting these criteria. The X-ray data reveal that most targets are morphologically disturbed, with several clear post-pericenter, dissociative systems exhibiting X-ray peaks between the BCGs. Spectroscopy confirms cluster membership and rules out foreground or background contamination. Together, these results demonstrate that optical BCG properties provide an efficient means of identifying dynamically active clusters, including clean dissociative mergers suitable for detailed, multi-wavelength studies of dark matter and cluster
evolution.
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All authors Christopher Hopp, David Wittman, Rodrigo Stancioli, Zhuoran Gao, Faik Bouhrik, Scott Adler
Astrophysics of Galaxies
Consistent Gas-Phase Temperatures and Metallicities from UV and Optical Nebular Emission: A Reliable Foundation from z=0 to Cosmic Dawn
Erin Huntzinger, Yuguang Chen, Tucker Jones et al. (+6 more)
The rest-frame UV spectra of
star-forming
galaxies are increasingly important as they become one of the primary windows to probe the physical properties of
cosmic dawn (z>8)
galaxies with the James Webb Space
Telescope. However, the systematic discrepancies between UV and optical gas-phase
metallicity measurements remain poorly understood in the local universe, partly due to challenges in achieving precise comparisons between UV and optical spectra for the same objects. In this work, we introduce a novel method that leverages the HeII 1640 and HeII 4686 nebular emission lines to achieve accurate aperture and reddening corrections between UV and optical spectra. Here we apply this method to three nearby Blue Compact
Dwarf (BCD)
galaxies. Our results demonstrate that this approach enables precise measurements, with electron temperatures ($T_e$) derived from UV and optical spectra exhibiting closer agreement compared to previous studies, and O/H abundance agreeing within 0.1 dex. However, two BCDs appear to have lower UV-based electron temperatures $T_{e~1666} < T_{e~4363}$, in contrast to expectations from the temperature fluctuation model. We consider a variety of possible explanations for these unphysical temperatures - differential
dust attenuation, aperture differences, and spatial extent of emission lines - but no suitable cause is identified. These findings suggest a complex gaseous environment associated with
star formation, and underscore the need for additional observations to further investigate the nature of HeII nebular emission and address the systematic issues between UV and optical nebular properties. Nonetheless, the close empirical agreement of these results indicates that UV- and optical-based nebular temperature and abundance measurements can be reliably compared within 0.1 dex, providing a solid foundation for evolutionary studies from the local Universe to
cosmic dawn.
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All authors Erin Huntzinger, Yuguang Chen, Tucker Jones, Ryan Sanders, Peter Senchyna, Daniel P. Stark, Fabio Bresolin, Stephane Charlot, Jacopo Chevallard
Solar and Stellar Astrophysics
Solar Irradiance Reconstruction over the Telescopic Era Using a Revised Photospheric Magnetic Field Model
D. Temaj, N.A. Krivova, T. Chatzistergos et al. (+2 more)
The Sun is the primary source of energy for Earth and one of the main external drivers of its
climate.
Solar irradiance – the radiative power emitted by the Sun and received at 1-AU – varies on all observable timescales. It is measured as total
solar irradiance (TSI), the spectrally integrated flux, or as spectral
solar irradiance (SSI), its wavelength-dependent distribution. However, direct space-based irradiance measurements span only about five decades and are too short to capture long-term trends, making reconstructions crucial for studying
solar influence on
climate. On
climate-relevant timescales, irradiance variations are driven by changes in the
solar surface
magnetic field, which form the basis of reconstructions guided by physics. Here we present revised reconstructions of TSI and SSI over the past four centuries using the physics-based SATIRE-T (Spectral And Total Irradiance REconstruction, for the Telescopic era) model. SATIRE-T relates irradiance variability to the
evolution of the
solar surface
magnetic field inferred from sunspot number records. In this work, we implement a recently revised description of
magnetic field
evolution that more realistically links the emergence of small-scale
magnetic features to sunspot activity, constrained by modern observations. Using two independent sunspot number series as input, we obtain consistent reconstructions of
magnetic flux and
solar irradiance. The model reproduces the observed or independently reconstructed total and open
magnetic flux, and agrees closely with satellite measurements of TSI and Lyman-$\alpha$ irradiance, with correlation coefficients of 0.81-0.98 for 81-day-smoothed space-based TSI records, 0.69-0.85 for TSI at daily cadence, and 0.92 for daily Lyman-$\alpha$ irradiance. On secular timescales, the reconstructed TSI increases by 0.67-0.75$\,\mathrm{W/m^2}$ between the 50-year means over 1650-1700 and 1967-2017.
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All authors D. Temaj, N.A. Krivova, T. Chatzistergos, S.K. Solanki, B. Hofer
Instrumentation and Methods for Astrophysics
The Extremely Large Telescope Interferometer
Francisco Prada, Enrique Perez, Sergio Fernandez-Acosta et al. (+2 more)
The ELTI concept capitalizes on recent breakthroughs in large-format SPAD (Single-
Photon Avalanche Diode) imaging sensors, combining them with the unprecedented collecting area and segmented architecture of the ELT to deliver a fundamentally new observational capability for the 2040s: visible-light intensity interferometry with ELT-scale angular resolution and
quantum-limited temporal sampling. By uniting three transformative innovations - segmented sub-pupil beam combination, megapixel SPAD arrays with picosecond time resolution, and high-dispersion spectroscopy - ELTI opens an entirely new region of observational parameter space in angular resolution, spectral bandwidth, and temporal precision. This capability enables true milliarcsecond imaging of
stellar surfaces, direct probes of extreme-
gravity and strong electromagnetic-field environments around compact objects, precision studies of
accretion physics, and even the potential detection of Earth-sized
exoplanets through minute visibility modulations. ELTI thus positions the ELT as the world-leading facility for ultra-high-resolution optical astronomy in the coming decades.
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All authors Francisco Prada, Enrique Perez, Sergio Fernandez-Acosta, Km Nitu Rai, Joel Sanchez-Bermudez
High Energy Astrophysical Phenomena
Radiation GRMHD Models of Accretion onto Stellar-Mass Black Holes: III. Near-Eddington Accretion
Lizhong Zhang, James M. Stone, Shane W. Davis et al. (+3 more)
We present a comprehensive analysis of four near-Eddington black hole
accretion models from GRMHD simulations with full radiation transport. This study investigates the dynamical effects of
magnetic field
topology and black hole
spin using two representative choices of each. Two stable near-Eddington solutions emerge in these models: a thin thermal disk embedded within a
magnetic envelope when sufficient net vertical
magnetic flux is present (e.g., vertical field $\gtrsim 5\times10^5$ G at $20r_g$), and a magnetically elevated disk when the net vertical flux is weak or absent. One model initialized without net vertical flux evolves into the thin disk solution, as strong, anisotropic radiation feedback at high
accretion rates promotes the accumulation of vertical
magnetic flux in the inner disk. In the thin thermal disk,
accretion is driven primarily by mean-field Maxwell stress and proceeds largely within the
magnetic envelope, while heat dissipation is spatially decoupled and concentrated near the midplane. However, in the magnetically elevated disk,
accretion occurs throughout the disk body and is comparably driven by mean-field and turbulent stresses; heat dissipation therefore occurs locally through
turbulence. Radiation transport is
diffusion-dominated, enabling efficient radiative cooling ($\sim$4-10%). An optically thin wind is launched from the disk surface by combined radiative and
magnetic forces, with stronger winds found in models with larger vertical
magnetic flux and higher
spin. Both strong and weak jets are produced: strong jets are persistent, highly relativistic, and magnetically driven, while weak jets are intermittent, mildly relativistic, and powered by a combination of
magnetic and radiative forces.
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All authors Lizhong Zhang, James M. Stone, Shane W. Davis, Yan-Fei Jiang, Patrick D. Mullen, Christopher J. White
Earth and Planetary Astrophysics
Predictions of Imminent Earth Impactors Discovered by LSST
Ian Chow, Mario Jurić, R. Lynne Jones et al. (+5 more)
Imminent impactors are natural bodies discovered in space before impacting the Earth. They provide a rare opportunity to characterize individual near-Earth objects (NEOs) in great detail as asteroids in space, meteors in Earth's atmosphere and meteorites on the ground. The Vera C. Rubin Observatory's upcoming Legacy Survey of Space and Time (LSST) is expected to transform our understanding of the NEO population. In this work, we evaluate LSST's expected discovery performance for imminent impactors using $343$ meter-size objects previously recorded in NASA's CNEOS database as fireballs impacting Earth's atmosphere. We simulate pre-impact observations of these CNEOS impactors with the Sorcha survey simulator under LSST's default three-night discovery strategy and a one-night strategy for fast-moving objects that relies on matching aligned streaks in two exposures on the same night. We estimate that LSST will discover $\sim1-2$ meter-size and larger imminent impactors per year, representing $\sim4\%$ of all Earth impactors $\gtrsim1$ m in diameter and almost doubling the current discovery rate of imminent impactors. The median time of discovery and median time of first observation for impactors discovered in our simulations are $\sim1.57$ and $\sim3.06$ days before impact, respectively. The spatial distribution of the 11 previously discovered imminent impactors is biased towards the Northern Hemisphere, where the observatories that discovered them are located. We find a similar trend towards Southern Hemisphere impacts in our simulated LSST detections of the CNEOS impactors, suggesting Rubin will provide a powerful counterpart to existing asteroid surveys primarily located in the Northern Hemisphere.
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All authors Ian Chow, Mario Jurić, R. Lynne Jones, Kathleen Kiker, Joachim Moeyens, Peter G. Brown, Aren N. Heinze, Jacob A. Kurlander
Solar and Stellar Astrophysics
The TESS All-Sky Rotation Survey: Periods for 1,046,317 Stars Within 500 pc
Andrew W. Boyle, Luke G. Bouma and Andrew W. Mann
Stellar rotation is a fundamental tracer of
stellar magnetic evolution, age, and activity, with broad implications for
Galactic archaeology and
exoplanet characterization. The Transiting
Exoplanet Survey Satellite (TESS) provides high-precision time-series photometry across the sky, enabling rotation measurements for an unprecedented number of
stars. We present the TESS All-Sky Rotation Survey (TARS), an all-sky catalog of
stellar variability periods for 1,046,317
stars with T < 16 and distances within 500 pc. We estimate that 93% of these periods are rotation periods. This catalog increases the number of rotation period measurements for
stars with T < 16 within 100 pc by a factor of 2.3 and within 500 pc by 4.0. We also present a method to correct half-period aliases in TESS data and show that it reliably recovers periods as long as 25 days from a single TESS sector. TARS represents the largest homogeneous catalog of
stellar rotation periods to date, providing a foundation for studies of
stellar ages, young associations, and
Galactic structure. We make the light curves used in our analysis available as a HLSP through MAST. Beyond the default TARS catalog, we provide code that allows users to generate rotation period catalogs with adjustable completeness and reliability thresholds. This code and all rotation period measurements are available through Zenodo.
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Astrophysics of Galaxies
ENhanced Galactic Atmospheres With Arepo: Resolving the CGM at 200 pc with the ENGAWA Simulations
Scott Lucchini, Cecilia Abramson, Cameron Hummels et al. (+3 more)
Simulating the small-scale features and dynamics of the circumgalactic medium (CGM) is computationally challenging due to its large volume, low densities, multiphase structure, and chaotic environmental effects. Traditional mass-based refinement schemes focus computational power on the high-density regions, thus alternative techniques are required to study the details of the CGM. In this paper, we introduce a new suite of four cosmological zoom-in simulations of Milky Way-like
galaxies in which we include fixed-volume refinement throughout the CGM combined with the IllustrisTNG
stellar and AGN feedback model down to
redshift zero. Reaching spatial resolutions of 200 pc, we see enhancements in low ion column densities (H I and Mg II) and the number of cold clouds around
galaxies, relieving some of the longstanding tensions between simulations and observations of the CGM. We additionally apply the COLT radiative transfer code in post-processing to account for
stellar radiation, providing a more realistic gauge of ion populations. We find a reduction in the H I with minimal impact to the Mg II and O VI, tempering the impact of resolution while still providing results consistent with observations. In addition to the increase in the number of cold clouds in the CGM, we find that their intermediate temperature boundary regions are reduced in size as the resolution is increased, leading to smoother transitions to the ambient CGM temperature. This paper outlines initial results from this fixed-volume simulation suite which will serve as a basis for future explorations of CGM dynamics, gas
accretion, and
galaxy evolution.
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All authors Scott Lucchini, Cecilia Abramson, Cameron Hummels, Charlie Conroy, Lars Hernquist, Aaron Smith
Instrumentation and Methods for Astrophysics
UK White Paper on Magnetohydrodynamic (MHD) seismology of solar and heliospheric plasmas
Valery M. Nakariakov, David B. Jess, Andrew N. Wright et al. (+6 more)
Magnetohydrodynamic (MHD) seismology uses naturally occurring MHD waves to infer
plasma properties that are otherwise hard to measure, especially
magnetic field strength and
topology, electric currents, fine structuring, transport coefficients, and energy release. Across the
solar atmosphere, heliosphere, and planetary magnetospheres, multi-wavelength remote sensing and in-situ observations of waves provide powerful diagnostics that can address major open problems including chromospheric and coronal heating,
flare and eruption physics,
solar wind acceleration, and space weather impacts. This White Paper sets out the case for a coordinated UK programme that couples high precision observations with advanced theory and numerical modelling, modern time-frequency methods for non-stationary signals, and machine learning approaches for detection, classification, and parameter inference from rapidly growing multi-instrument
datasets. It outlines priority needs such as robust mode identification, reliable density and temperature constraints, multi line-of-sight capability, and models that include partial ionisation and non-adiabatic/collisionless effects, alongside enabling instrumentation such as next-generation spectropolarimetry, integral field units, and
radio facilities including the Square Kilometre Array. The paper highlights the UK's strong track record and infrastructure, and argues that sustained investment will amplify UK scientific return through international partnerships and mission involvement, delivering transformative
plasma diagnostics and downstream benefits for space weather
forecasting and related applications.
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All authors Valery M. Nakariakov, David B. Jess, Andrew N. Wright, Timothy K. Yeoman, Thomas Elsden, James A. McLaughlin, Dmitrii Y. Kolotkov, Viktor Fedun, Robertus Erdélyi
Instrumentation and Methods for Astrophysics · Cross-listed from physics.atom-ph
Environmental Measurements in the Sedrun Access Shaft to the Gotthard Base Tunnel – a Promising Site for a Long-Baseline Atom Interferometer
M. Guinchard, O. Buchmüller, S. Calatroni et al. (+7 more)
Atom interferometer (AI) experiments offer interesting prospects for searches for the interactions of ultralight bosonic dark matter with Standard Model particles as well as detection of gravitational waves in a frequency band inaccessible to experiments that are operating or under construction. Ideal locations for the next generation of such experiments are provided by long vertical shafts, such as that providing access to the Gotthard base railway tunnel from the Sedrun locality in the Canton Grisons of Switzerland. We present the results of an exploratory environmental measurement campaign at this location to evaluate the ground motion activity and the background electromagnetic field quality. We find that the backgrounds due to both ground motion and electromagnetic fields, including those due to passing trains, are low enough for successful operation of a 800-m AI experiment.
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All authors M. Guinchard, O. Buchmüller, S. Calatroni, J. Ellis, S. Hoell, M. Jaussi, L. Lombriser, M. Pentella, D. Thuliez, D. Valuch
Astrophysics of Galaxies
A FAST Survey of H I Absorption in Low-power Radio Sources
Yang Su, Qingzheng Yu, Taotao Fang et al. (+3 more)
We conducted a HI 21cm absorption study of a sample of 147 nearby (z < 0.1) low-power
radio sources with $10\,\mathrm{mJy} < S_{1.4\,\mathrm{GHz}} < 30\,\mathrm{mJy}$ and $\log(P_{1.4\,\mathrm{GHz}}/\mathrm{W\,Hz^{-1}}) = 20.5-23.7$, using the Five-hundred-meter Aperture Spherical
radio Telescope. By investigating the origin and kinematics of HI absorbing gas, we aim to study the interplay between the active
galactic nucleus (AGN) and its surrounding interstellar medium. Our observations detect 12 new absorbers, combining results from the pilot survey (three absorbers out of 26 sources), yielding a detection rate of $\sim10.2^{+3.1}_{-2.0}\%$. The detection rate in our sample is lower than in higher-power samples, which is likely due to emission dilution and the dominance of extended sources, indicating a gas-rich and
star-forming-dominated population in low-power sources. Among new detections, most line profiles are narrow and show velocities close to systemic ones, consistent with rotating disks, while four show disturbed kinematics indicative of inflows or
outflows. The fraction of
outflow candidates rises with
radio power, while the fraction of inflow ones remains constant, suggesting the effect of
radio emission on driving HI
outflows. In our sample, compact sources show a higher HI detection rate than extended sources. Contrary to expectations from higher-power samples, MIR-bright sources at low-power
radio do not exhibit a higher HI detection rate or more disturbed kinematics. In low-power
radio sources, blueshifted absorption occurs only in Seyferts and low-ionization
nuclear emitting regions, indicating the connection between atomic
outflows and the ionization state of AGN.
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All authors Yang Su, Qingzheng Yu, Taotao Fang, Junfeng Wang, Jianfeng Wu, Bo Zhang
Cosmology and Nongalactic Astrophysics
The Bayesian view of DESI DR2 with unimpeded: Evidence and tension in a combined analysis with CMB and supernovae across cosmological models
Dily Duan Yi Ong, David Yallup and Will Handley
We apply the $\texttt{unimpeded}$ framework to perform a fully
Bayesian reanalysis of the DESI DR2 data, using nested sampling with $\texttt{PolyChord}$ to compute evidences for $\Lambda$CDM and seven extensions across combinations of DESI DR1/DR2, Planck CMB,
supernovae (Pantheon+, Union3, DES-SN5YR, DES-Dovekie), and DES-Y1 weak
lensing. The
Bayesian Ockham's razor penalises extended models, yielding weaker or opposite preferences compared to $\Delta\chi^2$-based analyses. For DESI DR2 BAO combined with Planck CMB alone, the DESI collaboration's $3.1\sigma$ frequentist preference for $w_0w_a$CDM is eliminated entirely: we obtain ${\ln B = -0.57{\scriptstyle\pm0.26}}$, modestly favouring $\Lambda$CDM. Adding DES-Dovekie, the recalibration of DES-SN5YR, maintains this concordance (${\ln B = -0.30{\scriptstyle\pm0.19}}$). However, when the earlier DES-SN5YR calibration is included instead, the DESI collaboration's $4.2\sigma$ result survives the
Bayesian Ockham penalty as a $3.07{\scriptstyle\pm0.10},\sigma$ preference (${\ln B = +3.32{\scriptstyle\pm0.27}}$). That this signal persists despite the Ockham penalty makes the role of tension quantification essential: our analysis traced the preference to the earlier DES-SN5YR calibration, which introduced a $2.95{\scriptstyle\pm 0.04},\sigma$ conflict with DESI DR2 within $\Lambda$CDM – a tension that stands out from the grid – reduced to $1.96{\scriptstyle\pm 0.04},\sigma$ with the DES-Dovekie recalibration. With DES-Dovekie, the
Bayesian evidence for dynamical dark energy vanishes.
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High Energy Astrophysical Phenomena
A likelihood analysis for gamma-ray background models
Chance Hoskinson, Jason Kumar and Pearl Sandick
Indirect searches for dark matter using
dwarf spheroidal
galaxies are limited by systematic uncertainties in modeling diffuse gamma-ray backgrounds. We present a likelihood-based comparison of locally constructed empirical background models and theoretically-motivated models that incorporate the
Fermi-LAT diffuse background. The empirical models we study include both an independent-binning approach and a covariance-based approach that captures cross-energy correlations. Using ensembles of blank-sky regions and information criteria which account for model complexity, we find that empirical background descriptions provide a statistically competitive fit to gamma-ray data on degree scales in high-latitude regions.
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Solar and Stellar Astrophysics
TILARA: Template-Independent Line-by-line Algorithm for Radial velocity Analysis. I. Description of the code and application on a Sun-like star
C. San Nicolas Martinez, N. C. Santos, V. Adibekyan et al. (+3 more)
Precise radial velocities (RVs) are commonly derived through cross-correlation or template-matching methods, both of which rely on a reference spectrum that can introduce biases when the data are variable, contaminated, or sparsely sampled. Line-by-line methods offer an alternative way to compute RVs but generally still rely on template creation and therefore share its inherent limitations. We introduce TILARA, a template-independent, line-by-line RV extraction code designed to allow us to derive line-by-line RVs and to operate effectively even when spectral template construction is not recommended. While originally motivated by future PoET disk-resolved
solar observations, TILARA has been built with the flexibility to work with different
stellar spectral types and instruments. A curated list of individual absorption lines is used as a reference to automatically measure line centers with via Gaussian fitting with ARES. Then, using the reference lines list, and the lines measured with ARES on the spectra of the target
star, TILARA computes the RVs and applies configurable outlier rejection through sigma-clipping or down-weighting methods. We tested different configurations of the code, RV uncertainty estimation methods, and line selection criteria. The code was applied to 520 ESPRESSO observations of the Sun-like
star HD 102365 to evaluate its performance. TILARA was then tested against other RV extraction methods. Both in its sigma-clipping and its down-weighting mode, TILARA provided resulting RV time-series with similar standard deviation and error bars as the ones derived using existing methods that follow different approaches.
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All authors C. San Nicolas Martinez, N. C. Santos, V. Adibekyan, K. Al Moulla, A. M. Silva, S. G. Sousa