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Physics Astrophysics

astro-ph Watch Astrophysics

Friday 18 September

Cosmology and Nongalactic Astrophysics

A note on oscillons: non-negligible metric fluctuations during preheating

Daniel del-Corral, Paolo Gondolo, K. Sravan Kumar et al. (+1 more)

The dominant lattice approach to post-inflationary preheating and oscillon formation evolves an inhomogeneous inflaton field on a spatially homogeneous Friedmann-Lemaître-Robertson-Walker background, whose expansion is sourced by a volume-averaged energy density, while metric perturbations are neglected. We examine the consistency of this approximation with General Relativity. Using the linearized Einstein constraints, we show that the suppression of the Bardeen potential, characteristic of slow-roll inflation, disappears during preheating: once the first slow-roll parameter becomes of order unity, the metric and inflaton fluctuations enter at the same perturbative order. We further show that the scalar-field equation evolved in the fixed-FLRW prescription omits leading-order contributions generated by metric fluctuations. We then derive the proper-volume average of the ADM Hamiltonian constraint and show that it does not reduce to the Friedmann equation used in lattice simulations: the exact averaged constraint contains additional contributions from the spatial curvature, the variance of the local expansion, the shear, and metric corrections to the local energy density. Finally, we illustrate numerically, for Starobinsky and $\alpha$-attractor models, that the metric contribution becomes comparable to the scalar-field contribution during the amplification stage. These results directly affect the standard lattice description of oscillon formation and motivate numerical relativity as a consistent framework for the nonlinear preheating problem.
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All authors Daniel del-Corral, Paolo Gondolo, K. Sravan Kumar, João Marto

Instrumentation and Methods for Astrophysics

Status and performance of the Asgard/NOTT cold nulling camera

P. Chingaipe, G. Medgyesi, A. Mazzoli et al. (+25 more)

Long-baseline nulling interferometry suppresses the on-axis light of a star, enabling high-contrast observations of faint circumstellar emission and exoplanets at high angular resolution. The Nulling Observations of dusT and PlaneTs (NOTT) instrument is the L'-band nulling interferometer of the Asgard instrument suite and will be the first nuller installed at the Very Large Telescope Interferometer (VLTI). Its main scientific goals are to characterise hot/warm exozodiacal dust and young Jupiter-like exoplanets at close (<10 AU) orbital separations, where indirect detection methods are most sensitive. NOTT uses a four-telescope integrated-optics photonic beam combiner operating over 3.5-4.0 micrometres. The photonic chip produces photometric, bright, and nulled outputs that are polarization-split, spectrally dispersed, and imaged onto a 5-micrometre-cutoff HAWAII-2RG detector by the NOTT cold nulling camera. The cold optical assembly includes the photonic-chip interface, injection optics, collimator, Wollaston prism, dispersive element, imager, and cryogenic detector stage. The mechanical implementation is designed for operation near 90 K using aluminium support structures, spring-loaded optical mounts, and cryogenic-compatible mechanisms to preserve alignment during cooldown. We present the current status and performance of the NOTT cold nulling camera and cryostat assembly. The system is undergoing assembly, integration, and verification to validate thermal stability, detector operation, vacuum performance, and opto-mechanical repeatability. Initial cryogenic tests have demonstrated operation near 100 K for the cold optics and 30 K for the detector, cryogenic validation of the filter wheel, and a vacuum pressure of 8 x 10^-8 mbar. These activities represent a key step toward deploying NOTT as the first nulling interferometer at the VLTI.
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All authors P. Chingaipe, G. Medgyesi, A. Mazzoli, E. Bouzerand, R. Laugier, P. Abraham, C. Dandumont, D. Defrère, A. Glauser, G. Garreau, M. Ireland, A.P. Joo, J. Loicq, M-A. Martinod, K. Missiaen, M. Montoya, J. Morren, G. Raskin, M. Salman, W. Schofield, W. Verstraeten, S. Ertel, T. A. Stuber, J. P. Scott, S. Kraus, F. Martinache, X. Haubois, N. Schuhler

Solar and Stellar Astrophysics

The independence of the mid-infrared RR Lyrae Period-Luminosity relation from metallicity from a study of three globular clusters in the Large Magellanic Cloud

Steve Ardern, Vicky Scowcroft and Stijn Wuyts

RR Lyrae are pulsating variable stars tracing old ($>10$ Gyr) stellar populations, and exhibit a strong mid-infrared Period-Luminosity (PL) relation that can be calibrated with known parallaxes to infer distances. Here we present Period-Luminosity relations and distance moduli for three isolated globular clusters in the Large Magellanic Cloud: Reticulum, NGC 1841, and NGC 1466. Our analysis uses legacy Spitzer Space Telescope images obtained by the Carnegie RR Lyrae Program, and an internally self-consistent sample restricted to RRab stars, with cluster membership confirmed using Gaia DR3 proper motions and photometry. In the Spitzer 3.6~$\mu$m band, we simultaneously fit a PL for these clusters using a slope derived from Galactic Globular Clusters, yielding extinction-corrected distance moduli of $18.47\pm0.09$ mag for Reticulum, $18.29\pm0.09$ mag for NGC 1841, and $18.61\pm0.09$ mag for NGC 1466. The latter two are the first RR Lyrae PL-based distance moduli for these clusters, and all three are consistent with literature values from other techniques. Additionally we fit a PL with slope as a free parameter, and find that this LMC-derived PL is consistent with that derived from Galactic GCs. Simultaneously fitting a PLZ for the three clusters yields a metallicity coefficient $c= -0.03\pm0.05~\mathrm{mag}~\mathrm{dex}^{-1}$ which can be considered a negligible dependence of the PL on metallicity ($|c| <0.1$ mag dex$^{-1}$). Modelling an intrinsic width, $W$, to the PL/ PLZ yields a consistent value $W\approx0.1\pm0.02~\mathrm{mag}$, suggesting intrinsic width is not driven by metallicity.
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Astrophysics of Galaxies

An Orbital Interpretation of Decreasing Galaxy Velocity Distance Relations in Systems Dominated by Giant Elliptical Galaxies

Rabia Melati, Takia Larbaoui, Mohammed Ridha Benzidane et al. (+1 more)

The persistence of approximately flat rotation curves observed in many galaxies, is commonly interpreted as evidence for extended dark matter halos or as an indication of modified gravitational laws at low accelerations. In this work, we investigate an alternative orbital framework for the large scale kinematics of galaxy systems dominated by giant elliptical galaxies. We propose that selected non active companion galaxies form gravitationally bound orbital systems around a dominant central elliptical galaxy, conceptually analogous to the Solar System Using galaxy group catalogs together with data from the NASA IPAC Extragalactic Database, we analyze three independent systems centered on M87, M60, and NGC 1399. Candidate companions are selected according to common observational and dynamical criteria, including their location within the adopted search volume, approximate spatial coplanarity, and consistency of the effective gravitational parameter (Geff). For the three systems, the resulting velocity distance relations exhibit clear decreasing trends with increasing distance from the central elliptical galaxy, qualitatively consistent with Keplerian like orbital dynamics.
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All authors Rabia Melati, Takia Larbaoui, Mohammed Ridha Benzidane, Mourad Lounis

Cosmology and Nongalactic Astrophysics

21-cm Constraints on S-wave Dark Matter Annihilation with Subhalo-enhanced Effects

Zixuan Xu and Sibo Zheng

Observations of the 21-cm signal can probe energy injection into the intergalactic medium arising from dark matter annihilation during cosmic dawn and reionization. For s-wave annihilation, the annihilation rate depends on the squared dark matter density, making the 21-cm signal sensitive to dark matter halo substructure. In this work, we extend the numerical method of DM21cm to address spatially inhomogeneous s-wave annihilation including subhalo effects, using semi-analytical treatment of SASHIMI-C. Our numerical results show that the projected HERA limit for the $\gamma\gamma$ annihilation channel is stronger than the Leo~T bound within the dark matter mass range of $m_{\chi}\leq 3\,{\rm keV}$, whereas the projected HERA limit for the $e^+e^-$ annihilation channel is the strongest among the existing bounds for $m_\chi\sim 0.1$–$1\,{\rm GeV}$.
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Instrumentation and Methods for Astrophysics

Development of a Temperature-Variable Cold Blackbody Calibrator for Millimeter and Submillimeter Wave Detectors

Kazuki Watanabe, Taiki Sato, Shuhei Inoue et al. (+3 more)

We report the design, fabrication, and characterization of a cryogenic blackbody calibrator intended for laboratory-based detector characterization, providing multi-temperature calibration of millimeter- and submillimeter-wave detectors over a temperature range of 4 K to ~10 K. The device employs a Stycast/SiC absorber shaped for uniform array illumination and mounted on a phosphor-bronze substrate with optimized thermal links. Measured thermal conductance and heat capacity show the expected temperature dependence, although the conductance was lower than estimated, yielding a thermal time constant of 8.5 s at 10 K versus the 3.7 s design estimate. The response remains practical, demonstrating the calibrator's effectiveness as a stable reference source for precise calibration of detector arrays.
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All authors Kazuki Watanabe, Taiki Sato, Shuhei Inoue, Shinsuke Uno, Tatsuya Takekoshi, Tai Oshima

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

The high-velocity dark matter halo of the Milky Way in light of the LZ 248 keV event

Ciaran A. J. O'Hare

The interpretation of high-energy nuclear recoil events in direct-detection experiments can depend sensitively on the poorly understood high-speed tail of the Galactic dark matter velocity distribution. This fact has been brought into sharper focus recently by an anomalous nuclear-recoil event at $E_R\approx248~\mathrm{keV}$ observed by the LZ experiment. If interpreted as caused by a dark-matter-induced recoil, kinematic constraints on many models imply this particle would have to emerge from the high-speed tail. Here, we re-assess this astrophysical uncertainty using Milky Way analogues from the IllustrisTNG and FIRE simulations. We find that the maximum laboratory-frame DM speed on June 16, when the event was observed, is $792.7^{+82.9}_{-95.6}\, \mathrm{km/s}$ (median and 95% containment across simulations), with a median very close to the fiducial SHM value. Modelling the tail of the velocity distribution in three dimensions is complicated by the fact that these simulated dark matter halos are anisotropic and are generically seen to spin in the same direction as the baryonic disk. However, we find that this does not reduce the maximum laboratory-frame DM speed because the approximately Gaussian azimuthal velocity distribution is negatively skewed by this co-rotation, rather than shifted by it. We illustrate these results in the context of an inelastic dark matter interpretation of the LZ event.
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High Energy Astrophysical Phenomena

Gamma-ray Quasi-periodic Oscillations in the Changing Look Blazar B2 1420+326 (OQ 334)

Sunanda, Shubham Kishore and Alok C. Gupta

In the Fermi-LAT gamma-ray light curve from January 1 to August 25, 2026, of the changing look blazar B2 1420+326, we report here the detection of transient quasi-periodic oscillations (QPOs) of period ranging around 10-13 d. The source entered the flare state around May 7, 2026, and lasted till around mid-August, 2026 during which it depicted strong QPO signatures. We utilized standard techniques, including weighted wavelet Z-transform analysis, generalized Lomb-Scargle periodogram, and phase dispersion minimization, to search for and confirm these findings. Prior to the flare, the source displayed a mild damped oscillatory feature of similar periodicity with a damping timescale of around 20 d. Based on the period timescale and nature of the QPOs detected, we discuss possible physical mechanisms for the observed salient features.
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Astrophysics of Galaxies

Fountain pattern of baryon cycle revealed in galaxy ecosystems

Chengyu Ma, Yangyao Chen, Enci Wang et al. (+11 more)

Baryons in galaxy ecosystems are believed to undergo continuous cycles of inflow and outflow, forming fountain-like patterns that encode key information about how galaxies acquire matter from their environments and respond through feedback. The presence of such baryon cycles has been inferred from pieces of observational evidence, but a concrete understanding remains elusive because individual galaxy ecosystems are diverse and dynamic. Here we introduce a stacking method that combines baryonic fields across ensembles of individual galaxy ecosystems to suppress irregularities and reveal the underlying pattern. Applied to a cosmological hydrodynamic simulation, this approach unveils strikingly regular patterns in gas properties across the full spatial extent of galaxy ecosystems, in close agreement with those inferred from observations. This method is straightforward to implement, allowing the processes shaping the gas-cycling pattern to be fully understood within the structure-formation paradigm, and a solid framework to be constructed for linking simulated galaxy ecosystems with observations.
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All authors Chengyu Ma, Yangyao Chen, Enci Wang, Houjun Mo, Huiyuan Wang, Tao Wang, Qirong Yuan, Min Du, Zhaozhou Li, Kai Wang, Cheqiu Lyu, Haoran Yu, Zeyu Chen, Xiaoxuan Chen

Astrophysics of Galaxies

From Observation to Ground Truth: Reconstruction Losses of Galaxy Imaging Under Heteroscedastic Noise

Renhao Ye, Shiyin Shen and Quanfeng Xu

Deep learning is widely used to analyze galaxy images, and the reconstruction loss determines which image features a model prioritizes during training. Mean squared error (MSE) and mean absolute error (MAE) correspond to homoscedastic Gaussian and Laplace likelihoods, respectively, whereas the inverse-variance-weighted $\chi^2$ loss accounts for the spatially varying uncertainties of heteroscedastic astronomical noise. Comparing how closely these objectives recover the underlying signal requires a ground truth (GT), which real observations cannot provide. We therefore generate noise-free galaxy images with IllustrisTNG, SKIRT, and GalaxyGenius, convolve them with a point-spread function (PSF) to define the GT, and construct noisy simulated observations. We train otherwise identical variational autoencoders (VAEs) with the three reconstruction losses and evaluate their outputs against the GT. Over most of the evaluated signal-to-noise ratio (SNR) range, the $\chi^2$-trained model yields lower relative reconstruction errors than the MSE- and MAE-trained models, indicating that inverse-variance weighting improves galaxy-image reconstruction under the heteroscedastic noise considered here.
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High Energy Astrophysical Phenomena

A Gamma-ray Emitting Head-Tail Radio Galaxy Swimming Through the Hot Medium of the Merging Cluster Abell 3627

Vaidehi S. Paliya, M. Böttcher, Swayamtrupta Panda et al. (+4 more)

Head-tail radio sources are jetted active galactic nuclei (AGN) moving through the dense intracluster medium of galaxy clusters. They are extremely rare in the gamma-ray sky, likely because they are usually observed at large viewing angles. Therefore, every new gamma-ray detection of head-tail radio galaxies allows us to probe the origin of the high-energy emission in this unique class of AGN. Here we report, for the first time, the association of ESO~0137-G007 (z=0.016), a head-tail radio galaxy located at the outskirts of the merging cluster Abell 3627, with the gamma-ray source FL16Y~J1615.5$-$6034. The motion of the galaxy through the dense cluster environment and subsequent ram pressure and/or intracluster medium turbulence have led to the formation of a $>$500 kpc-long jet exhibiting a twisted, wiggly radio morphology. Its optical spectrum, obtained with the 4.1 m SOAR telescope, is devoid of emission lines, indicating that the underlying accretion activity is radiatively inefficient. From the measured line-of-sight stellar velocity dispersion, we estimate the mass of the central supermassive black hole to be $(3.36\pm1.32)\times10^9$ \Msun. We briefly discuss several radiative models to explain the observed broadband spectral energy distribution of ESO~0137$-$G007. We conclude that deeper multi-wavelength observations of this unique gamma-ray emitting head-tail radio galaxy will enable us to better understand the interaction of the jet with the hot cluster environment, thus setting the stage for the research of this class of AGN with the upcoming Square Kilometer Array.
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All authors Vaidehi S. Paliya, M. Böttcher, Swayamtrupta Panda, Kiran Wani, D. J. Saikia, Mahadev Pandge, C. S. Stalin

Astrophysics of Galaxies

A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30

Scott C. Chapman, Kedar A. Phadke, Nikolaus Sulzenauer et al. (+20 more)

We present 11 newly identified ultra-red galaxies selected with JWST/NIRCam in the core of the z=4.3 protocluster SPT2349-56. Although these sources are not yet spectroscopically confirmed, their extremely red colours (m200-m444 > 2.0 mag), strong spatial concentration, and number density - at least 2000 times that of comparable field populations - make a chance projected association unlikely. Their colours overlap those used to select the widely studied “little red dot” (LRD) population, although most of the sources are spatially resolved and are therefore better described as extended red dots (ERDs). The resolved morphologies disfavour continuum emission dominated by an unresolved active nucleus and imply a substantial stellar contribution. Deep ALMA observations put strong limits on obscured star formation, and the ERD population mostly lies significantly below the star-forming main sequence. One object, ERD1/Q1, is substantially brighter and more massive, lying far below the main sequence, making it a strong candidate for a massive quiescent galaxy. These JWST-selected red galaxies reveal a previously inaccessible population extending to lower luminosities and stellar masses than the Dusty Star Forming Galaxy (DSFG) population which characterizes the dense protocluster core. SPT2349-56 may therefore capture an early phase of cluster assembly in which extreme starbursts coexist with galaxies already transitioning toward the passive galaxies characteristic of mature cluster cores.
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All authors Scott C. Chapman, Kedar A. Phadke, Nikolaus Sulzenauer, Dazhi Zhou, Hollis Akins, Manuel Aravena, James R. Burgoyne, Caitlin M. Casey, Erin Foley, Leah Fryer, Ryley Hill, Nicholas LeVar, Monica Natalia Isla Llave, Matt Malkan, Vismaya Pillai, William Rasakanya, Manuel Solimano, Justin S. Spilker, Aurelie Torti, Joaquin D. Vieira, Fabio Vito, David Vizgan, George Wang

Astrophysics of Galaxies

Patchy Reionization Delays Quenching in Isolated Ultra-faint Dwarf Galaxies

Juyoung Kim, Myoungwon Jeon, Yumi Choi et al. (+1 more)

The spatially inhomogeneous nature of cosmic reionization is directly encoded in the quenching timescales of ultra-faint dwarf galaxies (UFDs). While most cosmological simulations employ a spatially uniform UV background (UVB) for computational efficiency, such homogeneous treatment may oversimplify the physical impact of reionization on UFDs, whose star formation histories (SFHs) are highly sensitive to local environments. Under these idealized, instantaneous UVB frameworks, star formation in UFDs is typically truncated abruptly at the onset of reionization, creating a tension with the extended and diverse SFHs observed in Local Group UFDs. To address this discrepancy, we perform high-resolution cosmological zoom-in simulations to contrast two distinct reionization models: a conventional uniform UVB and an on-the-fly radiative transfer (RT)-based patchy reionization model. We find that RT-based reionization delays star-formation quenching by ~440 Myr on average, a result consistent with recent observational constraints. However, this extended star formation does not necessarily leave a discernible imprint on the stellar metallicity distribution, indicating that the delay–while physically significant for gas dynamics–is still insufficient to drive substantial chemical enrichment. Our results emphasize the necessity of more realistic, patchy reionization modeling to explain the observed diversity of the Local Group population.
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All authors Juyoung Kim, Myoungwon Jeon, Yumi Choi, Sangmo Tony Sohn

High Energy Astrophysical Phenomena

Why most neutron star low-mass X-ray binaries accrete transiently: an evolutionary study of transient and persistent phases

Divyansh Tripathi, Sudip Bhattacharyya and Pulkit Ojha

A neutron star (NS) low-mass X-ray binary (LMXB), in which an NS accretes matter from a low-mass donor star, is an ideal source for probing some fundamental aspects of physics and astronomy, such as strong gravity, superdense matter, and the accretion-ejection processes. However, to reliably achieve these goals, one must adequately understand NS LMXBs, including why some accrete persistently and others transiently. Focused models, such as those based on a thermal-viscous instability in the accretion disk, are considered to explain transient accretion. However, broader perspectives, including which LMXB parameter values and phases cause transients and why there are more transients than persistents, remain poorly understood. Here, our computation of the long-term evolution of NS LMXBs addresses these questions, providing insight into LMXB parameters and phases, naturally producing more transients than persistents, and being partially consistent with the known properties of observed sources. For example, we typically find a greater fraction of persistent phase at lower orbital periods from the LMXB evolution computation, which is somewhat consistent with observations. However, a lack of full consistency calls for improving the aforementioned focused models, and our computations provide a new way to discriminate among these models.
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High Energy Astrophysical Phenomena

Neutrino Emission from Proton Photon Jet Interactions in Microquasars

Theodoros Smponias

Microquasars are candidate sites for high energy particle production within our galaxy. Because their distances and compact emission regions limit direct observational constraints, numerical simulations are useful for connecting jet dynamics with possible multi messenger signatures. This work models neutrino production from relativistic magnetohydrodynamic microquasar jets, focusing on the proton photon channel associated with interactions between accelerated protons and ambient photon fields. Proton proton interactions are acknowledged as a possible process in dense environments, but they are not modeled in the present calculation. A ray tracing procedure is applied to the hydrodynamic simulation output to produce synthetic neutrino images from the perspective of a stationary observer. Synthetic spectra and intensity maps are presented and compared with representative sensitivities of current and future neutrino detectors.
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Instrumentation and Methods for Astrophysics

A report on the First Technology Demonstration mission of the Little UV Camera (LUVCam1)

Coby Silayan, Suresh Sivanandam, Aaron Tohuvavohu et al. (+13 more)

Here we report on the status of the first on-orbit technology demonstration of the Little UV Camera (LUVCam1). LUVCam1 is a 0.4U payload aboard the 2U cubesat GRBBeta that was launched in July 2024. The primary objective of the mission was to qualify the GSENSE4040 CMOS sensor and its readout electronics in preparation for the Quick UltraVIolet Kilonova Surveyor (QUVIK; Werner et al. \cite{Werner22, Werner24}) satellite. LUVCam will serve as the primary scientific camera for this mission. We report on the performance of the GSENSE4040FSI sensor used on LUVCam1, beginning with its in-lab characterization followed by an assessment of its on-orbit performance using astronomical observations made by LUVCam1. The camera remains operational two years later and has taken pictures of the Moon and stars that we show here. Through LUVCam1, we demonstrated an approach leveraging new-space to qualify the latest COTS CMOS sensors for astronomy missions.
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All authors Coby Silayan, Suresh Sivanandam, Aaron Tohuvavohu, Albert Lau, Marianna Dafčíková, Mark Barnet, Patrick Nkwari, Shaojie Chen, Gavin Hay, J.C. Fronteddu, Norbert Werner, Andras Pal, Filip Münz, Jakub Řípa, Emily Hu, Andy Gong

High Energy Astrophysical Phenomena

CRAFT HTR2: Polarimetry of 64 non-repeating fast radio bursts from the updated CRAFT catalogue

T. Dial, A. T. Deller, Marcin Glowacki et al. (+6 more)

We present high-time resolution spectro-polarimetric data for 34 new fast radio bursts (FRBs) discovered by the Commensal Real-time Fast Transients (CRAFT) survey on the Australian Square Kilometer Array Pathfinder (ASKAP) during the period May 2024 to June 2026. Most of these were detected by the higher-sensitivity CRAFT COherent (CRACO) detection system that was commissioned on the telescope during this period. This new sample doubles the size of the CRAFT HTR catalogue and probes a fainter population of FRBs thanks to the improved sensitivity of CRACO. We compare the distribution of extragalactic rotation measure (RM) and polarisation fraction to the CHIME and DSA catalogues. While no significant differences were seen between CRAFT and DSA, the extragalactic RM distribution seen in CHIME FRBs (which are detected at lower frequency) was substantially lower. Surprisingly, we find no significant differences in the linear polarisation fraction distribution between the three FRB catalogues, suggesting an indifference to the different telescope observing frequencies. We show tentative evidence for wider and fainter bursts possessing lower polarisation fractions; this is predominantly driven by the growing sample of unpolarised bursts that are, in almost all cases, wider ($\gg$10 ms) and fainter ($\ll$10$^{34}$ ergs s$^{-1}$ Hz$^{-1}$) than the median ASKAP detection.
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All authors T. Dial, A. T. Deller, Marcin Glowacki, A. Bera, R. M. Shannon, Clancy W. James, Joscha N. Jahns-Schindler, Ziteng Wang, Akhil Jaini

Thursday 17 September

Solar and Stellar Astrophysics

COPAS: Compact Objects and the Physics of Accretion Survey I. Accreting Binaries with P < 83 Minutes

Wendy Mendoza, Liliana Rivera Sandoval, Jan Kára et al. (+9 more)

We present the first results from the Compact Objects and the Physics of Accretion Survey (COPAS), a high-cadence photometric survey focused on the detection of accreting white dwarf binaries mainly through their outbursts using TESS. From an initial sample of 2,054 cataclysmic variable (CV) candidates observed during TESS Cycle 6 and 7, we identify 11 systems with periods below 83 minutes. This includes 7 AM CVns and 4 CVs. Our Gemini spectroscopic data confirm ZTF18aaxuusk and ASASSN-21eo as AM CVns, while Gaia21akb is confirmed as a CV. We provide the first period measurements for 6 out of the 11 systems. Complementing our TESS data with ground-based observations, we measured superoutburst recurrence times of approximately one year for the AM CVn systems ASASSN-21in and ZTF18aaxuusk, and 1.8-2.0 years for the short-period CVs ASASSN-18rd and ASASSN-15ev. Using TESS, we also estimate the mass-ratio for ASASSN-19ct (q = 0.05 +/- 0.02), which is consistent with a highly evolved low-mass donor star. Though the number of ultracompact systems detected among the total sample is low (0.54%), and likely the result of observational biases and intrinsic population rareness, the reclassification of 5 systems as AM CVns highlights the importance of continuous monitoring to identify more systems through their outbursts and short periods.
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All authors Wendy Mendoza, Liliana Rivera Sandoval, Jan Kára, Ryan J. Oelkers, Yuri Cavecchi, Thomas J. Maccarone, Manuel Pichardo Marcano, Meryem K. Dağ, Simone Scaringi, Kieran O'Brien, Martina Veresvarska, Christian Knigge

High Energy Astrophysical Phenomena

Effects of Physical Cooling on the Structure of Circumbinary Disks

Minjae V. Kim, Julian H. Krolik and Scott C. Noble

Radiation pressure and radiative cooling often play an important role in deciding the structure and dynamics of astrophysical objects. In this paper, we present a radiative MHD simulation of a circumbinary disk (CBD) around an equal-mass SMBBH. It employs an approximate thermodynamic model based on local thermodynamic equilibrium and diffusion cooling which captures how the internal energy evolves in an optically thick region. The disk reaches a quasi-steady state within $r=5a$ whose mass distribution differs substantially from the one obtained from simulations without physical thermodynamics: the local maximum in the azimuthally-averaged surface density and the lump are completely erased; the time-averaged inner edge becomes more eccentric; and the vertical density distribution depends strongly on the radius. These changes are attributable to the enhancement of the magnetic fields caused by the cooling-driven vertical compression of the disk. Our result emphasizes that the basic properties of the inner CBD are sensitive to both radiation and magnetic physics.
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Astrophysics of Galaxies · Cross-listed from gr-qc

Granular Structure and Local de Broglie Wavelength in Fuzzy Dark Matter Halos

Flavio Rosales-Infante, Alejandro Quiñonez-Guerrero, Iván Álvarez-Rios et al. (+1 more)

We study the granular structure that emerges in a Fuzzy Dark Matter (FDM) halo formed through kinetic relaxation. After the system reaches a virialized core-halo structure, we separate the density field into a smooth spherical component and a residual density that contains the interference pattern characteristic of FDM halos. The power spectrum of this residual field shows a well defined dominant scale, different from the characteristic scale of the total density and of the smooth core-halo model. We compare this granular scale with a local de Broglie wave-lenght calculated from the velocity field obtained from the density current of the system. We find that both scales remain of the same order of magnitude, with the granular scale systematically smaller than the de Broglie wavelength. The radial behavior of the de Broglie wavelength also reveals a non-uniform internal structure, it decreases from the core and reaches its minimum near the transition between the solitonic core and the outer halo. These results provide a quantitative connection between density fluctuations, the local velocity field, and the core-halo morphology of FDM halos.
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All authors Flavio Rosales-Infante, Alejandro Quiñonez-Guerrero, Iván Álvarez-Rios, Francisco S. Guzmán

Instrumentation and Methods for Astrophysics

Calibration electronics for the 30 and 40 GHz instrument (TFGI) of the QUIJOTE experiment

Jorge Luis Díaz-Acosta, Roger John Hoyland, Francisco Javier Casas et al. (+1 more)

The 30 and 40 GHz instruments of the QUIJOTE radio astronomy experiment use very sensitive receivers which need to be characterized both to ensure their proper functioning and for their calibration. Given the age of the PXI-1031DC device used up until now for this purpose, the design of a new device, the Calibrator TFGI QUIJOTE, has been proposed. This new device has been designed with the idea of being simple and modular, easy to use and upgrade. It is built on a Raspberry Pi 5 system, using an MCC 118 as analog reading module. This system, widely known among both makers and professionals, not only meets the requirements of modularity and ease of use, but also ensures that the device is much more economically competitive than the PXI. A first version of the device has been built and tested, obtaining good results in accuracy and ease of use.
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All authors Jorge Luis Díaz-Acosta, Roger John Hoyland, Francisco Javier Casas, Enrique Martinez-González

Earth and Planetary Astrophysics

The Birth of Minor-Body Populations in the $\beta$ Pictoris System I: The First 25 Myr

S. Torres, J.L. Gragera-Más, A.J. Mustill et al. (+1 more)

The discovery of the third known giant planet, $\beta$ Pic d, offers a new opportunity to investigate how planet-disk interactions build the minor-body architecture of the young Beta Pictoris system. We study the formation and redistribution of scattered-disk objects, falling evaporating bodies, a proto-Oort-cloud population, transitional interstellar objects, and interstellar objects. Using $N$-body simulations, we evolve a primordial planetesimal disk extending from 0.5 to 1000 au for 25 Myr under the perturbations of $\beta$ Pic b, c, and d, together with reconstructed stellar encounters from Gaia DR3. The resulting evolution is strongly radius-dependent. The planets efficiently restructure the inner disk, while the outermost primordial population remains largely unchanged beyond $325$ au. $\beta$ Pic c remains the main driver of the star-grazing population, showing that the falling-evaporating-body pathway persists after the inclusion of $\beta$ Pic d. At larger radii, $\beta$ Pic b and d dominate planetary scattering and produce a surviving disk edge near 50 au, consistent with the observed debris-disk truncation. Over 25 Myr, $8.74\%$ of the initial disk enters the scattered-disk population, $2.04\%$ reaches the proto-Oort-cloud region, and $6.44\%$ becomes unbound. Planetary stirring also generates a transient one-armed spiral among particles originating at $\sim60$-150 au, overlapping part of the observed "Cat's Tail" and the radial location of the prominent CO clump near 85 au. The reconstructed stellar encounters included here produce only weak perturbations, although the encounter catalog is complete only over the first ~2.5 Myr of the present epoch. The early evolution of the Beta Pictoris minor-body system is therefore dominated by its planetary architecture, offering a view of distinct minor-body populations while they are still being formed and redistributed.
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All authors S. Torres, J.L. Gragera-Más, A.J. Mustill, E. Villaver

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Non-Conservative Mechanics in the Compact-Body Mass-Shell Model and its Waveform Structuring

Noah M. MacKay

A novel reinterpretation on the effective one-body (EOB) mapping of compact-body binary (CBB) coalescence was previously considered. Instead of the conventional “marble in a funnel" description of EOB, CBB coalescence is modeled as the concurrent rotation and contraction of a hollow shell with a constant reduced mass measure. Merger is achieved, therefore, when the shell radius reaches the total mass radius. While past works analyzed the energetics sector of the model and the radiated gravitational waves (GWs), this work considers the geometric waveform modeling aspect. More specifically, we mature the mass-shell waveform analysis initially discussed with toy-model conditions by imposing necessary non-conservative mechanics, leading to the analytical expression of usable mass-shell modeled GW-forms. This is to set the foundation for eventual computational endeavors with the analytical waveforms presented here, enabling a comparison against current and state-of-the-art models.
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High Energy Astrophysical Phenomena

Energy Partition in Relativistic Electron-Positron-Ion Reconnection

Nilay Mancini, Luca Comisso and Lorenzo Sironi

Relativistic magnetic reconnection, a prime mechanism for particle acceleration, has been extensively studied in electron–ion and pair plasmas, but how the dissipated energy is shared among species in electron–positron–ion plasmas, and in particular how ions are energized within a pair-dominated layer, remains poorly understood. We develop an analytic theory that couples single-particle orbit dynamics to the collective plasma response, and we validate it with particle-in-cell simulations spanning pair-dominated to electron–ion compositions. Particles are directly energized in electric-dominated regions until the reconnected magnetic field deflects them into the outflow; the characteristic escape length is in turn set by the relativistic skin depth of the reconnection-heated mixture, including the ion contribution. Writing $\sigma_e^*$ for the magnetic energy available per particle in units of $m_ec^2$ and $\mu=m_i/m_e$, the mean lepton energy scales as $\sigma_e^*$, whereas the mean ion energy scales as $\mu^{1/3}(\sigma_e^*)^{2/3}$ when ions escape non-relativistically from the electric-dominated regions and approaches the lepton energy when their escape is ultrarelativistic. The predicted energy fractions agree with simulations across composition, mass ratio, and magnetization. The ion share of the dissipated energy can fall far below the commonly assumed ion–lepton equipartition, reducing the energy available for hadronic and neutrino emission in reconnection-powered astrophysical sources.
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High Energy Astrophysical Phenomena

The Auger Radio Infill SKALA Extension (ARISE): First Air-Shower Measurements

Carmen Merx for the Pierre Auger Collaboration

The Auger Radio Infill SKALA Extension (ARISE) was installed at the Pierre Auger Observatory in 2025 to detect the radio emission in the band of $50-350\,$MHz of near-vertical cosmic-ray air showers of energies around and above $100\,$PeV. The array comprises 18 SKALA~v2 antennas deployed around one of the surface-detector stations of the $433\,$m array (SD-433), which provides the trigger for ARISE. We present first measurements with ARISE and show the detection of radio pulses associated with extensive air showers. Radio signals are found in coincidence with SD-433 events, and a comparison of the arrival directions reconstructed from the radio and surface detector signals confirms the measurement of air showers with ARISE. These observations provide a first assessment of the detector setup and demonstrate the potential of ARISE for radio detection of near-vertical air showers.
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Solar and Stellar Astrophysics

Tidal Dissipation from Circularization in Kepler Binaries

Joshua Schussler, Torsha Majumder and Kaloyan Penev

Understanding tidal dissipation is a requisite step for explaining the evolution of systems such as short-period binaries. This understanding has not yet been achieved, and in fact there are many different approaches to modelling tides. By using Bayesian analysis on a system-by-system basis, we provide additional constraints on dissipation for 105 short-period Sun-like Kepler binaries. We account for period-dependent $Q$ and stellar evolution, and propagate observational uncertainties to uncertainties in our constraints. We find a group constraint of $\log Q_*' \approx 6.75$, with no apparent dependence on tidal period. We also do not detect mass dependence for $Q$. Our inferred prescription for the tidal dissipation successfully reproduces the unexpected overlap between almost perfectly circular and significantly non-circular orbits in binaries of Sun-like stars reported by arXiv:2112.05868.
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High Energy Astrophysical Phenomena

A mechanism for fast radio bursts and their narrow spectra

Andrei M. Beloborodov and Ivan Demidov

We find an emission mechanism for fast radio bursts (FRBs) capable of producing broad and narrow spectra. It operates in magnetar explosions, which launch an electromagnetic pulse from the inner magnetosphere at radii $r_0\sim 10^{7}$ cm. Plasma inside the pulse accelerates outward with Lorentz factor $\Gamma(r)\approx r/r_0$. Before exiting the magnetosphere at radius $r\sim 10^{10}$ cm, the pulse passes through ambient kHz waves that populate the magnetospheres of active magnetars. We show that the waves experience stimulated scattering inside the pulse, with the boost factor $\Gamma^2$ converting them into radial GHz radiation. This process exponentially amplifies tiny GHz seeds to extreme luminosities consistent with observed FRBs. The produced GHz burst rides inside the explosion pulse, which helps it escape to distant observers. The FRB duration and energy are controlled by the pulse duration and energy. In a saturated emission regime, the predicted burst contains an ultrastrong microsecond component.
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Instrumentation and Methods for Astrophysics

Flux Density Calibration of Radio Bursts Detected in the Sidelobes of the Canadian Hydrogen Intensity Mapping Experiment

Fengqiu Adam Dong, Meena Seth, Paul Scholz et al. (+6 more)

The Canadian Hydrogen Intensity Mapping Experiment/Fast Radio Burst (CHIME/FRB) instrument is a transient astrophysical burst survey that is discovering FRBs, pulsars, and long-period transients. As a transit telescope, the survey is most sensitive within 2 degrees of the meridian; however, CHIME/FRB can detect bright astrophysical bursts out to its horizon, at 10^-2 to 10^-3 of its peak sensitivity. In this study, we detail the flux density calibration procedure for these bursts detected in the CHIME sidelobes for both channelized voltage (baseband) and intensity data. We validate and estimate the calibration uncertainties by beamforming baseband data towards bright, steady sources in the sidelobes, comparing baseband and intensity flux density calibrations of the same astrophysical transients, and calibrating intensity flux densities for transiting steady sources. We are able to calibrate flux densities for declinations spanning -12 degrees to +59 degrees out to hour angles of 30 degrees, and out to 90 degrees in hour angle for declinations near that of Taurus A (Crab Nebula, declination of about +22 degrees). We conclude that uncertainties in the flux density calibration for transients in the CHIME sidelobes range from 20% to 42%, depending on the data used and the hour angle of the burst.
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All authors Fengqiu Adam Dong, Meena Seth, Paul Scholz, Nina V. Gusinskaia, Kiyoshi W. Masui, Juan Mena-Parra, Daniele Michilli, Ari Polterovich, Ingrid Stairs

Astrophysics of Galaxies

ALMA Chemical Evolution (ACE) Survey: Molecular gas properties of low-mass, low-metallicity galaxies at cosmic noon

Gergő Popping, Ivanna Langan, Nikki N. Geesink et al. (+13 more)

Molecular gas plays a central role in regulating star formation and galaxy evolution, yet observational constraints at cosmic noon remain biased toward massive, metal-rich systems. We present ALMA Band 3 observations of the CO J=3-2 transition in 26 unlensed star-forming galaxies from the ALMA Chemical Evolution (ACE) Large Program at z~2-2.5, probing stellar masses of $10^{9} < M_\star < 10^{10.5}\,\mathrm{M}_{\odot}$ and sub-solar metallicities (8.2 < 12 + log(O/H) < 8.6). We derived molecular gas masses using a metallicity-dependent CO-to-H$_2$ conversion factor and alongside analysed stacking measurements and a homogenized literature compilation spanning both local and high-redshift galaxies. We find that the ACE galaxies extend established molecular-gas scaling relations to an order of magnitude lower stellar masses than previously explored at cosmic noon. The molecular gas mass ($M_{\rm mol}$) correlates tightly with star formation rate (SFR), while molecular gas fractions show a strong dependence on specific star formation rate (sSFR) and offset from the star-forming main sequence. In contrast, molecular gas fractions show only weak trends with stellar mass and no significant dependence on metallicity. Molecular gas depletion times are ~1 Gyr and vary little with stellar mass or metallicity, and weakly with sSFR and offset from the star-forming main sequence. Together this further reinforces that the availability of molecular gas is the primary driver of the SFR in galaxies, with changes in star-formation efficiency playing a secondary role. Leveraging the expanded parameter space probed by the ACE and literature samples, we derive a new empirical prescription for predicting $M_{\rm mol}$ as a function of SFR and sSFR. The persistence of the observed scaling relations suggests a largely universal framework governing the molecular gas-star formation cycle across cosmic time.
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All authors Gergő Popping, Ivanna Langan, Nikki N. Geesink, Melanie Kaasinen, Irene Shivaei, Leindert A. Boogaard, Daizhong Liu, Max Parente, Alexandra Pope, Roxana Popescu, Manuel Solimano, Bahram Mobasher, Bianca Moreschini, Desika Narayanan, Naveen Reddy, Ryan L. Sanders

Astrophysics of Galaxies

ALMA Chemical Evolution (ACE) survey: the dust content of subsolar metallicity galaxies at cosmic noon

M. Solimano, I. Shivaei, G. Popping et al. (+11 more)

Dust plays a key role in galaxy evolution by influencing star formation and shaping the observed spectrum of galaxies. However, at z~2 (cosmic noon) our knowledge of the dust mass budget is currently limited to the most massive, metal-rich systems, which are not representative of the bulk galaxy population. Here, we probe the lower mass, subsolar metallicity regime by measuring the dust mass of 25 galaxies at z~2.3 from the ALMA Chemical Evolution (ACE) Large Program. The sample contains star-forming galaxies in the COSMOS field with robust strong-line metallicities down to ~0.3 $Z_\odot$. Using the dust continuum emission detected at 873micron or 1.3mm we constrain the dust mass by assuming an optically thin single-temperature modified blackbody. The resulting dust masses average $10^{8}\,\mathrm{M}_\odot$, and they are three to nine times larger than those of z=0 galaxies at a matched metallicity and stellar mass. We also find positive correlations between dust mass and stellar mass, metallicity, and star formation rate (SFR). In contrast, we find that the $M_\mathrm{dust}/M_\mathrm{stars}$ (DtS) ratio scatters around $10^{-2.2}$ but shows no evidence of correlation with metallicity. This result is consistent with dust evolution models that predict a constant DtS once the ISM reaches the critical metallicity, at which metal accretion onto grains becomes the main mode of dust buildup. The correlation between $M_\mathrm{dust}/\mathrm{SFR}$ and metallicity also suggest that ACE galaxies have already surpassed the critical metallicity. Finally, we find that the DtS ratio is correlated to the specific SFR (sSFR). Since the sSFR are high ($> 10^{-8}\,\mathrm{yr}^{-1}$) this explains the DtS excess over z~0 galaxies. In turn, both sSFR and DtS are likely driven by the molecular gas fraction, as supported by CO(3-2) measurements taken as part of ACE.
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All authors M. Solimano, I. Shivaei, G. Popping, L. A. Boogaard, I. Langan, R. Popescu, N. N. Geesink, A. Pope, L. Arriscado, B. Mobasher, D. Narayanan, M. Parente, N. Reddy, R. Sanders