High Energy Astrophysical Phenomena
The influence of free-free absorption on the radio spectrum of Particle-Accelerating Colliding-Wind Binaries
Michaël De Becker, Agustina Belen Blanco, Mathilde Tasseroul et al. (+4 more)
The study of massive
stars in binary and higher-multiplicity systems that participate in particle acceleration is a key topic at the crossroads of massive
star physics, shock physics, and galactic
cosmic ray astrophysics. From an observational perspective,
radio measurements are our pri- mary tool for identifying these systems through their synchrotron
radio emission. Out of the 54 such systems known to date, all but two have been discovered via their non-thermal
radio emission. However, identifying these systems is not straightforward. The main challenge lies in free-free absorption, which can obscure the synchrotron signature and hinder detection. This paper summarizes recent developments in our understanding of these systems, with a particular focus on the strong observational bias introduced by free-free absorption. This bias significantly limits our ability to determine the true fraction of particle accelerators among colliding-wind binaries.
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All authors Michaël De Becker, Agustina Belen Blanco, Mathilde Tasseroul, Anandmayee Tej, Anindya Saha, Paula Benaglia, Santiago del Palacio
Cosmology and Nongalactic Astrophysics
Probing Inflationary Origins of Primordial Black Holes with LIGO–Virgo–KAGRA O1–O4a data
Haipeng An, Huai-Ke Guo, Mai Qiao et al. (+3 more)
Large primordial
curvature perturbations not only produce primordial black holes (PBHs) but also inevitably source a scalar-induced
stochastic gravitational-wave background upon horizon reentry. We analyze the combined LIGO–Virgo–KAGRA O1–O4a data to constrain two representative inflationary mechanisms for generating such perturbations: ultra-slow-roll inflation and an inflationary phase transition. Detecting no evidence for either scenario, we place 95% credible upper limits on the
curvature-spectrum amplitude across the frequency range accessible to ground-based interferometers. Translated into the PBH context, these limits already exceed conventional constraints, probing abundance fractions far below unity. Our results remain robust even when the PBHs themselves are too rare to be directly detected or have evaporated. This work demonstrates that
stochastic gravitational-wave observations offer a powerful and complementary probe of small-scale inflationary physics and PBH formation, with upcoming interferometers promising to extend sensitivity to a wider range of inflationary epochs and PBH masses.
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All authors Haipeng An, Huai-Ke Guo, Mai Qiao, Lian-Tao Wang, Chen Yang, Yue Zhao
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
Reconstructing the Dark Matter Equation of State with Compact Object Inspirals
Boris Betancourt Kamenetskaia, Qianhang Ding and Hui-Yu Zhu
We investigate the gravitational wave (GW) signatures of compact binaries embedded in extended dark matter (DM) configurations in hydrostatic
equilibrium. If a
neutron star is surrounded by a sufficiently massive and extended envelope, an inspiraling companion experiences dynamical friction (DF) in addition to the standard GW energy loss. We show that this environmental effect can be isolated through a GW observable, the $D$-function, which directly characterizes the additional dissipative power induced by the surrounding medium. Since the density of the envelope is directly determined by the DM equation of state together with the stellar boundary conditions, the frequency dependence of the $D$-function provides direct information about the macroscopic properties of the dark sector. We develop a regression-based framework to reconstruct both the density profile and the DM equation of state over the density range probed by observations of the GW inspiral. Using representative DM models as
benchmarks, we demonstrate that the method accurately recovers the input equation of state while remaining largely independent of the microscopic realization of DM. Our results show that future GW observations of compact binaries can provide a probe of the equation of state of DM.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
The Wavelet Detection Filter: a real time unmodeled pipeline for gravitational wave transients, ranking coincidences with a graph neural network
Elena Cuoco
Accurate waveform models are unavailable for many potential sources of gravitational wave transients, motivating searches that do not assume a predefined template family. The Wavelet Detection Filter (WDF) is an unmodeled pipeline that identifies excess energy in the wavelet coefficients of whitened detector data. Here, we develop WDF into a low latency pipeline for both detection and reconstruction and this paper describes and validates that pipeline. We use a zero phase streaming autoregressive whitening filter that preserves transient morphology with a fixed latency and we use the retained wavelet coefficients to provide both a detection statistic and a sparse representation of the signal. By combining coefficients across consecutive analysis windows, the pipeline reconstructs transients longer than a single window. We represent candidate coincidences between detectors with a trigger graph and rank them with supervised and unsupervised graph neural networks (GNNs). We estimate the significance of the ranked coincidences from time shifted data. We validate the pipeline on Gaussian noise colored according to the Advanced LIGO sensitivity curve and on real O4 strain containing compact binary and core collapse
supernova injections. Applied to GW250114, WDF identifies the event as the loudest zero lag candidate in the analyzed segment without using waveform templates. We measure the computational cost of the pipeline and the latency it introduces. Both are compatible with a low latency search,so WDF can run on a stream in real time.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ex
The DALI Haloscope: A Magnetized Phased Array Coupled to a Semi-Open Fabry–Pérot Resonator
Javier De Miguel, Antonios Gardikiotis, Eduardo David González-Carretero et al. (+10 more)
DALI is an
axion haloscope consisting of a magnetized phased array backed by a conducting mirror and coupled in the near field to a semi-open Fabry–Pérot resonator. The applied static
magnetic field makes both the dielectric interfaces and the conducting mirror sensitive to
axion-induced electromagnetic conversion. Each interface acts as a radiating surface, and the resulting fields are projected onto the mode collected by the resonator and delivered to the receiver. We derive the detected power in terms of the power available from the magnetized mirror, the coherent contribution of the dielectric interfaces, the transverse mode overlap, the loaded quality factor, and the receiver-coupling coefficient. This formulation separates two distinct enhancement mechanisms. The dielectric-interface emissions may add coherently, producing a dielectric boost, while the semi-open Fabry–Pérot resonator provides enhancement through resonant storage of the coupled electromagnetic field. These contributions depend differently on the dielectric thicknesses, spacings, and resonant mode, and should therefore be evaluated independently. The same assembly can operate between the limits of a coherently boosted dielectric haloscope and a mirror-sourced, resonantly enhanced Fabry–Pérot haloscope. This combined architecture offers a flexible approach to resonant
axion searches at frequencies for which conventional closed microwave cavities become increasingly limited in conversion volume.
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All authors Javier De Miguel, Antonios Gardikiotis, Eduardo David González-Carretero, Elvio Hernández-Suárez, Roger J. Hoyland, Enrique Joven, Abaz Kryemadhi, Marios Maroudas, Chiko Otani, J. Alberto Rubiño-Martín, Yannis K. Semertzidis, Michael E. Tobar, Konstantin Zioutas
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ex
Constraints on Galactic Dark Photons from a DALI Prototype
Javier De Miguel, Antonios Gardikiotis, Elvio Hernández-Suárez et al. (+10 more)
An analysis of 36 hours of data from a DALI haloscope reveals no statistically significant excess attributable to dark-
photon dark matter. We therefore set new constraints in the 6.88691–6.91792 GHz band, reaching a dark-
photon-to-
photon kinetic mixing strength of $\chi\lesssim 6.8\times10^{-14}$ at $28.54 \, \mu\mathrm{eV}$. To our knowledge, this result established the strongest laboratory-based exclusion limit in this frequency range.
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All authors Javier De Miguel, Antonios Gardikiotis, Elvio Hernández-Suárez, Roger J. Hoyland, Enrique Joven, Abaz Kryemadhi, Haroldo Lorenzo-Hernández, Marios Maroudas, Chiko Otani, J. Alberto Rubiño-Martín, Yannis K. Semertzidis, Michael E. Tobar, Konstantin Zioutas
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Intrinsic pressure anisotropy in spherical Proca stars
Ilídio Lopes
Pressure anisotropy in relativistic
stars is commonly prescribed through a phenomenological closure, obscuring its microscopic origin and relation to stress-energy conservation. Here it is derived directly from the minimally coupled Einstein-complex-Proca theory. For spherical Proca
stars, the principal-pressure difference admits an exact on-shell form whose sign is controlled solely by the local mass-shell threshold. The stress is radially dominated in the core, reverses on a surface of fixed gravitational
redshift, and becomes tangentially dominated in the envelope. At the first mass maximum, the fractional anisotropy reaches about 21% near the density maximum, whilst the region beyond the reversal contains about 9% of the mass. Its exact atmospheric limit is approximately 24%, equal in magnitude and opposite in sign to the scalar-
boson-
star limit. Because the usual local fluid variables remain non-zero at the crossing, no sign-definite closure constructed from them can reproduce the profile. These results identify an intrinsically vectorial stress reversal, generated without additional interactions, and provide a first-principles
benchmark for anisotropic bosonic compact objects.
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Earth and Planetary Astrophysics
Limits on a Host Star around a Saturn-mass Free-floating Planet Candidate KMT-2024-BLG-0792/OGLE-2024-BLG-0516
Przemek Mróz, Klara Piotrowska, Antoine Mérand et al. (+2 more)
Recent studies found a number of short-timescale microlensing events that are thought to be produced by free-floating or wide-orbit
planets. The microlensing event KMT-2024-BLG-0792/OGLE-2024-BLG-0516 is currently the only free-floating
planet candidate with a directly measured mass ($0.73^{+0.25}_{-0.15}$ Saturn masses), derived from joint ground-based and Gaia satellite observations. However, it remains unclear whether the lens is truly isolated or bound to a widely separated host
star. Here, we report high-angular-resolution interferometric observations of the event obtained with the Very Large
Telescope Interferometer/
GRAVITY instrument two years after peak magnification. We detect no luminous host
star up to a projected separation of 90 au, supporting the hypothesis that the lens is indeed a free-floating
planet. We derive a 5 sigma upper limit on the mass of a putative host
star of approximately 0.5-0.6 M_solar. This work demonstrates that interferometry provides a powerful method for directly searching for or constraining host
stars in short-duration and planetary microlensing events.
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All authors Przemek Mróz, Klara Piotrowska, Antoine Mérand, Subo Dong, Zexuan Wu
Solar and Stellar Astrophysics · Cross-listed from physics.atom-ph
Experimental Ni II Oscillator Strengths for Transitions from $3d^84d$ to $3d^84p$ Levels Measured Using High-resolution Fourier Transform Spectroscopy
Ruijie Chen, Christian P. Clear, Gillian Nave et al. (+1 more)
We present the first experimentally measured oscillator strengths for Ni II 3d$^8$4d - 3d$^8$4p transitions. High-resolution
Fourier transform spectra were recorded of Ni-He hollow cathode lamps, and intensity calibrated using deuterium standard lamps to determine relative intensities of Ni II emission lines between 200 and 395 nm. Branching fractions were determined for observed lines from 35 3d$^8$4d upper levels in total, and account for at least 95% of the predicted transition probability for 31 of these levels, with sufficient completeness to give reliable branching fractions. Combining our measured branching fractions with four experimental and 27 theoretically calculated energy level lifetimes provided absolute oscillator strengths for 174 lines, for which no previous experimental values exist. We compare the results with three sets of previously published theoretical calculations, illustrating the improvement of laboratory measurements for these atomic data. Please note: The transition probability
datasets are withheld from this pre-print to ensure that only the peer-reviewed, definitive versions are released. This approach prevents the propagation of duplicate or inconsistent data across widely used atomic databases and modelling frameworks.
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All authors Ruijie Chen, Christian P. Clear, Gillian Nave, Juliet C. Pickering
Astrophysics of Galaxies
Identification of Cosmic Chronometers in the GAMA Survey
Laura J. Hunt, Kevin A. Pimbblet and David M. Benoit
We present a pure sample of 231 massive, passively evolving elliptical
galaxies as
cosmic chronometer candidates selected from the
Galaxy and Mass Assembly (GAMA) survey between $0.03<z<0.4$. The goal of this work is to increase the pool of high-purity
cosmic chronometer candidates available in the literature and assess the effect of purity on statistical uncertainty to make $H(z)$ and $H_0$ calculations more robust in future studies. We use traditional selection criteria to identify
cosmic chronometers using photometry and spectroscopy in conjunction with modelled parameters such as stellar mass and velocity dispersion. We use an NUVrJ photometric selection to identify quiescent
galaxies and identify a number of spectral features, including H$\alpha$, [OII] and H$\delta$ to use as tracers for ongoing or recently halted
star formation. Additionally, as part of the selection, we calculate the ratio between the Ca II H and K lines to determine whether a
galaxy's stellar population is dominated by older or younger
stars. We confirm CC candidacy by selecting only the most massive
galaxies and perform a visual inspection of the spectra and images of CC candidates. We provide an analysis of the parent sample in comparison to the CC sample and confirm CCs have much lower sSFR, with a median sSFR of $10^{-12}~\text{Myr}^{-1}$. Additionally, we find their median ages are $\sim2~\text{Gyr}$ older than the parent sample.
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Solar and Stellar Astrophysics
Plasmoid-Trapped Condensation Associated with a Transient Thermal-Instability-Like Process in Chromospheric Magnetic Reconnection
Abdullah Zafar, Lei Ni, Samrat Sen et al. (+4 more)
We perform high-resolution 2.5D single-fluid magnetohydrodynamic (MHD) simulations to explore the development of cool-dense structures within plasmoids during chromospheric
magnetic reconnection. The model incorporates temperature-dependent ionization degrees of hydrogen and helium, resulting in improved diffusivities and viscosity, as well as adequate radiative cooling. The numerical results show that
plasma is significantly hot with temperatures reaching several tens of thousands of Kelvin in newly developed plasmoids in the low initial
plasma-$\beta$ cases, $\beta_0$ = 0.05. Later, the localized accumulation of
plasma and decreasing temperature result in an explosive much stronger radiative cooling process. Radiative cooling peaks over the temperature range 8000 K$-$20,000 K. The co-spatial density enhancement, substantial radiative cooling, shorter radiative cooling timescales, and a significant temperature decrease support the existence of thermal-instability-like condensation within the plasmoids. Similar cool-dense structures are identified in all low-$\beta_0$ cases at different chromospheric altitudes, suggesting that this occurrence is not limited to a single chromospheric layer. In contrast, in the high initial
plasma-$\beta$, $\beta_0$ = 0.5 case, the maximum temperature inside the dense plasmoids is only about 8000 K. Therefore, the radiative cooling has never entered into the explosive increasing stage and the thermal-instability-like condensation does not happen. These findings reveal that plasmoid-trapped condensation may develop in chromospheric reconnection once radiative losses become self-amplifying under low-$\beta_0$ conditions.
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All authors Abdullah Zafar, Lei Ni, Samrat Sen, Yuhao Chen, Mohamed Sedik, Mehdi Yousefzadeh, Jun Lin
Solar and Stellar Astrophysics
Large-Scale Latitude-time Relationships Between the Green-Line Corona and Sunspot Activity During Solar Cycles 18-24
Jouni J. Takalo
We investigate the latitude-time relationship between the solar green-line corona and sunspot activity during Solar Cycles 18-24 using homogeneous coronal observations and a Gaussian representation of sunspot activity fields. The activity-field model is constructed from individual sunspot areas and latitudes in order to describe the large-scale spatial organization of solar
magnetic activity more realistically than traditional sunspot number or sunspot area indices. The analysis reveals a stable double-peaked latitude-dependent correlation structure centered on the active-region belts, where the strongest corona-sunspot correlations are observed. The latitude profiles remain remarkably similar from cycle to cycle, indicating that the large-scale relationship between coronal emission and photospheric activity is largely independent of cycle amplitude and parity. The lag-correlation profiles exhibit broad positive lag plateaus in most cycles. Although formal lag-correlation maxima occur at positive lags, surrogate-data tests indicate that these maxima are generally not statistically distinguishable from neighboring lag values. The results therefore suggest temporal persistence and
memory of large-scale coronal
magnetic structures rather than a precisely defined physical delay. The Gaussian activity-field representation produces substantially stronger and more coherent correlations with the green-line corona than conventional sunspot measures, supporting the interpretation that the large-scale distribution of
magnetic activity, rather than individual sunspots alone, governs the
evolution of the large-scale corona.
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Astrophysics of Galaxies
Heavy Seed Black Hole Growth in Metal-Enriched Halos through Disk-Induced Stellar Disruptions: A Semi-Analytical Modelling
Zijian Wang, Zhili Wang, Yiqiu Ma et al. (+4 more)
Recent simulations suggest that heavy seed black holes may form in weakly metal-enriched atomic cooling
halos, where the supermassive-
star progenitor and small-scale stellar fragments emerge nearly coevally. In this picture, the newly born heavy seed is naturally embedded in a metal-enriched Pop~I/II nuclear
star cluster rather than in an isolated pristine environment. We investigate whether disk-induced tidal disruption events (TDEs) from these Pop~I/II
stars can provide an efficient and sustained growth channel for heavy seed black holes. We construct a semi-analytical model for stellar orbital damping, disk capture, migration, and tidal disruption around a heavy seed black hole, and incorporate the resulting disk-induced TDE contribution into cosmological merger trees with baryonic and
metallicity evolution. Heavy seed host
halos are selected from atomic cooling
halos with $Z\lesssim10^{-3}Z_\odot$ that satisfy either a rapid gas-inflow criterion or a strong Lyman–Werner radiation criterion. We find that disk-induced Pop~I/II TDEs can dominate the early growth of heavy seeds: the median black hole mass grows from $\sim10^4\,M_\odot$ to $\sim10^5\,M_\odot$ within the first $\sim0.1$ Gyr after seed formation, and reaches several $10^5\,M_\odot$ by $\sim0.2$ Gyr. The cumulative mass supplied by TDEs initially exceeds that from gas
accretion and remains comparable over the first $\sim200$ Myr. Including disk-induced TDEs shifts the black hole population toward higher masses, increases the abundance of massive black holes at $z\sim9$–10, and produces larger black hole-to-stellar mass ratios. This channel helps alleviate, but does not fully remove, the tension between heavy-seed models and the most extreme high-
redshift black hole candidates, suggesting that additional growth mechanisms may still be required.
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All authors Zijian Wang, Zhili Wang, Yiqiu Ma, Boyuan Liu, Zheng Cai, Mengye Wang, Qingwen Wu
High Energy Astrophysical Phenomena
Optical Follow-Up of Two Spider Pulsar Candidates: An Irradiated Redback and a Possible Double Giant Impostor
Bettina Due, Jundile Bridziute, Manuel Linares et al. (+2 more)
Compact binary millisecond
pulsars (nicknamed "spiders") are a growing class of
neutron stars: more than 100 systems are known in the Galactic field, including more than 30 candidates where pulsations have not been detected. Here we report the results of an optical follow-up of two spider
pulsar candidates: 2FGL J0846.0+2820 (J0846, a huntsman candidate in an 8.1 d orbit) and 4FGL J0935.3+0901 (J0935, with a 2.4 h orbital period and proposed as a spider of either the transitional, black widow or redback sub-class). We also analyzed their multi-wavelength properties (infrared, X-ray and $\gamma$-ray bands), in order to assess their nature and current state. The optical orbital light curves of J0846 change from double-peaked in 2023 to single-peaked in 2024, but we argue they are not consistent with either irradiation-driven or ellipsoidal orbital modulation. Its spectral energy distribution shows evidence for two blackbody-like components with similar temperatures ($T$) and radii ($R$), which dominate the optical ($T_2\simeq6000$ K, $R_2\simeq1.8$ R$_\odot$) and infrared ($T_1\simeq3400$ K, $R_1\simeq5.2$ R$_\odot$) bands. Based on this, we argue that J0846 is not a bona fide
pulsar candidate and propose an alternative identification: a detached double red giant. In J0935, we find a light curve with one flux maximum around superior conjunction of the companion, where the colors and inferred temperature increase, suggesting prominent irradiation from the
pulsar. We place constraints on its companion base temperature ($4000\!-\!4600$ K), which support one of the three classifications proposed for J0935: a redback spider in the
pulsar state.
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All authors Bettina Due, Jundile Bridziute, Manuel Linares, Marco Turchetta, Maksat Satybaldiev
Astrophysics of Galaxies
E-INSPIRE - II. Finding relics from wide-sky multi-band surveys: A proof-of-concept machine learning regression algorithm
Charles Rosen, Chiara Spiniello, John Mills et al. (+7 more)
In this second paper of the E-INSPIRE series, we train a machine-learning-based regression on $\sim430$ nearby ($z<0.5$) ultra-compact massive
galaxies (UCMGs) with spectroscopically inferred kinematics, stellar population parameters and a measured “degree of relicness” (DoR). Our goal is to investigate how robustly the spectroscopically inferred DoR can be statistically reconstructed from observable
galaxy properties, and to explore the potential applicability of this framework to future wide-area surveys. We test several regression
algorithms finding that Support Vector Regression (SVR) provides the best performance. We explore multiple input feature configurations, from a minimal set including only age and
metallicity to more comprehensive ones incorporating stellar population parameters, kinematics, structural properties, and the associated uncertainties. All tested models achieve similarly high performance on the training set ($R^2\ge0.81$), except for the minimal configuration ($R^2\sim0.78$). When evaluated on an independent INSPIRE sample of 52 UCMGs, the predictive power remains robust, although with increased model-to-model variation. The DoR distribution shows three regimes, with low (DoR$<0.3$) and high (DoR$>0.6$) values sparsely populated, leading to mild regression shrinkage toward intermediate values. However, this behaviour enables a conservative selection strategy:
galaxies with predicted DoR$\ge0.6$ are strongly biased toward genuine extreme relics, making them
prime targets for follow-up observations. This proof-of-concept confirms that the spectroscopically inferred DoR is robustly connected to observable stellar population and kinematical properties, and provides a first step toward future relic-candidate selection strategies in large photometric and spectroscopic surveys.
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All authors Charles Rosen, Chiara Spiniello, John Mills, Alexey Sergeyev, Vladyslav Khramtsov, Anna Ferré-Mateu, Johanna Hartke, Michalina Maksymowicz-Maciata, Malgorzata Siudek, Crescenzo Tortora
High Energy Astrophysical Phenomena
Spin-polarization of the neutron ocean in magnetar crusts
Juliette Servais and Nicolas Chamel
Magnetars,
neutron stars harboring the strongest
magnetic fields known in the Universe, are associated with a broad range of observational phenomena, from giant
flares to fast
radio bursts, and have also been proposed as potential sites of heavy-element nucleosynthesis. These phenomena are thought to be closely linked to the structure and composition of magnetar crusts. The outer crust consists of fully ionized
nuclei embedded in a degenerate electron gas, while the inner crust additionally contains free
neutrons. We investigate how strong
magnetic fields modify magnetar crusts, accounting for the
spin polarization of free
neutrons. Arising from the coupling between the
magnetic field and the
neutron magnetic moment,
neutron spin polarization lowers both the pressure and matter density marking the boundary between the outer and inner crusts for
magnetic field strengths $B \gtrsim 10^{17}~\mathrm{G}$. As a consequence, the outer crust becomes thinner, the formation of the superheavy
nuclei predicted in previous studies is suppressed, and the
neutron ocean permeating the inner crust becomes
spin-polarized. These effects may have important implications for the diverse manifestations of magnetars and for $r$-process nucleosynthesis in the ejecta of magnetar giant
flares.
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Earth and Planetary Astrophysics
Terminal instability of the Solar System triggered by stochastic solar mass loss
Konstantin Batygin, Jim Fuller and Fred C. Adams
From its birth, celestial mechanics has been deeply intertwined with the question of the Solar System's dynamical stability. For the inner
planets, this question is now statistically settled: Mercury's orbit carries a $\sim$1% chance of destabilization before the Sun leaves the main sequence. The outer Solar System has seemed more secure, with its intrinsic dynamical lifetime estimated at $\sim10^{18}$ years. Even accounting for the Sun's mass loss and stellar flybys, the orbital architecture of the giant
planets had been expected to persist for $\sim$100 Gyr. Here we show that these estimates rest on the assumption that solar mass loss is smooth. The recently measured white dwarf recoil demands asymmetric mass loss that is most readily attributed to discrete, independently directed ejections that impulsively perturb stellar motion. As the Sun sheds its envelope in such parcels, the
planets' orbits random-walk with amplitude set by the mass-loss granularity. At a coarseness corresponding to observationally permitted kicks, this
stochastic forcing restructures the outer Solar System concurrently with the Sun's death. In particular, our numerical experiments reveal that orbit crossings can commence on the red giant branch, with $\sim$40% of realizations undergoing disruption or violent scattering before the white dwarf forms and $\sim$90% self-destructing within 3 Gyr. The outer Solar System's dynamical lifetime thus collapses from $10^{18}$ years to approximately a gigayear after white dwarf formation.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
A semicoherent resampling method for long-transient gravitational wave searches with applications to subsolar-mass primordial black-hole binaries
Neil Lu, Cristiano Palomba, Ornella J. Piccinni et al. (+1 more)
Resampling removes the modeled phase
evolution of a frequency-evolving signal, transforming it into a monochromatic one. We introduce a novel implementation for long-transient gravitational-wave searches that evaluates the
Fourier spectrum of the resampled data using a type-I non-uniform fast
Fourier transform (NUFFT). This implementation can be up to two orders of magnitude faster than some previous implementations, depending on coherent length, sampling rate, and desired accuracy. To demonstrate its application, we
benchmark the method with a semicoherent search for long-duration inspiral signals from subsolar-mass primordial black hole binaries. For a search over $40$–$60\,\mathrm{Hz}$ and chirp masses of $5\times10^{-4}$–$10^{-1}\,M_\odot$, with a coherent duration of $30\,\mathrm{s}$ and a realistic computing cost, the estimated horizon distance exceeds the Galactic Center for all of the parameter space considered and exceeds Andromeda for chirp masses above approximately $2\times10^{-2}M_\odot$. These results establish NUFFT-based resampling as a computationally efficient and broadly applicable approach for searches for modeled, frequency-evolving gravitational-wave signals.
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All authors Neil Lu, Cristiano Palomba, Ornella J. Piccinni, Ling Sun
Solar and Stellar Astrophysics
Magnetic Fields and Asymmetric Accretion in the Class 0 Protostellar System L1527 IRS
Hanju Nam, Woojin Kwon, Youngwoo Choi et al. (+2 more)
Magnetic fields play a crucial role in regulating the collapse of dense molecular clouds, shaping the early stages of protostellar
evolution. We present polarization observations in submillimeter wavelengths with the SCUBA-2/POL-2 instrument on James Clerk Maxwell
Telescope toward the Class 0 protostellar system L1527 IRS (IRAS 04368+2557). The
magnetic field morphology varies across the core of L1527 IRS.
Magnetic fields in the eastern region are perpendicular to the outflow axis, while those in the western region show a pinched morphology, overall aligned with the outflow cavity. These distinct bipolar outflow regions also have a clear color difference in near infrared observed by James Webb Space
Telescope. In addition, the spectral index derived from 450 {\mu}m and 850 {\mu}m observations reveals that the northwestern region of the protostellar system is colder and denser compared to the southeastern region. Furthermore, in the large-scale structures and
magnetic fields revealed by Herschel and Planck, we find a ~0.1 pc scale filamentary structure parallel to the large-scale
magnetic fields in the eastern region and a relatively isotropic mass distribution in the western region. Based on these results, we propose an
accretion scenario of the protostellar system in which an asymmetric mass distribution causes the distinct features observed in near-infrared and submillimeter wavelengths.
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All authors Hanju Nam, Woojin Kwon, Youngwoo Choi, Ian W. Stephens, Leslie W. Looney
Astrophysics of Galaxies
The constrainability of galaxy positions in the $M_*$ – SFR plane from SED fitting
Sabine Bellstedt, Aaron S. G. Robotham, Luke J. M. Davies et al. (+2 more)
Using a sample of 6,029 $z<0.06$
galaxies from the GAMA survey, we characterise the spread of
galaxy property inferences on the M$_*$ – SFR plane via Spectral Energy Distribution (SED) fitting. We analyse 24 different model configurations using the stellar population library code ProGeny, and the SED-fitting code ProSpect, and quantify how modelling assumptions affect inferred stellar masses,
star formation rates, and the resulting classification of
galaxies. We find that the reproducibility of inferred
galaxy positions depends strongly on location within the $M_*$ – SFR plane, with uncertainties increasing dramatically below $\log_{10}(\rm{sSFR}/\rm{yr}^{-1}) \sim -11$. This boundary closely tracks the transition between robustly and poorly constrained SFR estimates, regardless of whether SFRs are derived from SED fitting or H$_{\alpha}$ measurements. We find that
star-bursting
galaxies cannot be robustly isolated from SED fitting alone, while the separation of
star-forming and passive
galaxies is most consistently conducted by a cut in sSFR, rather than a dex cut relative to either a curved or linear SFS (
Star Forming Sequence). We further show that transitioning (or Green Valley) selections using SED fitting are highly unstable, with only $\sim$25% of the sample being repeatedly selected, on average.
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All authors Sabine Bellstedt, Aaron S. G. Robotham, Luke J. M. Davies, Luca Cortese, Simon P. Driver
Solar and Stellar Astrophysics
Superoutbursts and Superhumps of Cataclysmic Variables observed with TESS
Qi-Bin Sun, Sheng-Bang Qian, Li-Ying Zhu et al. (+10 more)
Superoutbursts and superhumps are characteristic signatures of SU UMa-type cataclysmic variables, yet the full diversity of superhump evolutionary behaviour remains poorly constrained owing to the limitations of ground-based photometric monitoring. Here we report a systematic analysis of 30 SU UMa-type dwarf novae observed with the Transiting
Exoplanet Survey Satellite, covering 37 superoutburst events. We detect coherent superhump signals in 29 systems-including five first-time detections-and determine or refine orbital periods for 13 objects. The high-cadence light curves clearly resolve the canonical three-stage (A-B-C) superhump period
evolution. Using Stage A periods, we derive dynamical mass ratios for 18 systems, consistent with established cataclysmic variable evolutionary tracks. The measured Stage B period derivatives match the range of values from ground-based campaigns, with prominent positive drifts concentrated in short-period, low-mass-ratio systems. Repeated superoutbursts yield consistent evolutionary patterns, demonstrating that superhump morphology is an intrinsic, repeatable property. Two systems break the standard template: RZ LMi shows an inverted stage sequence inconsistent with classical precession theory, while ASASSN-14kj exhibits no stage
evolution but a coherent long-period modulation. Persistent superhumps during normal outbursts in three systems provide direct evidence that eccentric disk structures can survive beyond their parent superoutbursts, revealing a decoupling between thermal
accretion and tidal eccentricity cycles. These results demonstrate the power of space-borne photometry for probing
accretion disk dynamics and testing precession models across the cataclysmic variable parameter space.
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All authors Qi-Bin Sun, Sheng-Bang Qian, Li-Ying Zhu, Qin-Mei Li, Wen-Ping Liao, Fu-Xing Li, Wen-Xu Lin, Min-Yu Li, Ping Li, Fang-Zhou Yan, Zi-Mo Li, Tao Wang, Mao-Han Zhang
Earth and Planetary Astrophysics
KMT-2026-BLG-0083L: A Two-Jovian-Planet System Orbiting an M Dwarf Discovered by Microlensing
Cheongho Han, Chung-Uk Lee, Zhixing Li et al. (+65 more)
We present the analysis of the microlensing event KMT-2026-BLG-0083, which was independently detected by the KMTNet, OGLE, and
PRIME surveys and also monitored by the DREAMS survey. The combined data provide dense coverage of two distinct short-duration anomalies in the light curve that cannot be reproduced by a standard binary-lens model. Independent analyses of the two anomalies indicate that each is produced by a planetary companion to the lens, motivating a triple-lens interpretation. The modeling yields two pairs of degenerate solutions arising from the well-known inner–outer degeneracy, with each pair exhibiting two local solutions depending on whether the source passes above or below the distant planetary companion. The preferred model indicates two giant
planets with mass ratios $q_2=(5.25\pm 0.08)\times 10^{-3}$ and $q_3=(3.04\pm 0.24)\times10^{-3}$ orbiting a common host.
Bayesian analysis indicates that the host is an M-dwarf
star with a mass of $0.48^{+0.36}_{-0.28}~M_\odot$, hosting two giant
planets with masses of $2.65^{+1.96}_{-1.55}~M_{\rm J}$ and $1.54^{+1.14}_{-0.90}~M_{\rm J}$. The projected
planet–host separations are $10.6^{+1.7}_{-2.2}$~au and $1.7^{+0.3}_{-0.3}$~au, placing the inner
planet near the host's snow line and the outer
planet at a substantially larger separation. Thus, KMT-2026-BLG-0083L becomes the seventh confirmed multiple-
planet system discovered through gravitational microlensing, providing another example of a cold giant planetary system orbiting a subsolar-mass
star.
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All authors Cheongho Han, Chung-Uk Lee, Zhixing Li, Weicheng Zang, Andrzej Udalski, Ian A. Bond, Yoon-Hyun Ryu, Steve Heathcote, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Youn Kil Jung, Kyu-Ha Hwang, Hongjing Yang, Yossi Shvartzvald, In-Gu Shin, Doeon Kim, Dong-Jin Kim, Byeong-Gon Park, Richard W. Pogge, Qiyue Qian, Yaosong Yu, Yuchen Tang, Yuxin Shang, Tomas Ahumada, imothy Abbott, Guillermo Damke, Konstantina Boutsia, Alfredo Zenteno, Shude Mao, Andong Xu, Przemek Mróz, Michał K. Szymański, Jan Skowron, Radosław Poleski, Igor Soszyński, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof A. Rybicki, Patryk Iwanek, Krzysztof Ulaczyk, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mróz, David P. Bennett, Aparna Bhattacharya, Kotaro Daimon, Ryusei Hamada, Yuki Hirao, Shuma Makida, Stela Ishitani Silva, Shota Miyazaki, Tutumi Nagai, Seiya Nakayama, Kansuke Nunota, Ryo Ogawa, Ryunosuke Oishi, Hideaki Ose, Nicholas J. Rattenbury, Yuki K. Satoh, Takahiro Sumi, Daisuke Suzuki, Motohide Tamura, Takuto Tamaoki, Sean K. Terry, Chihiro Ueda, Aikaterini Vandorou, Hibiki Yama
Astrophysics of Galaxies
A systematic study of the long-term mid-infrared color variations of Seyfert 1 galaxies
Jiahua Wu, Liming Dou, Zhining Chen et al. (+7 more)
We present a comparative analysis of long-term mid-infrared (MIR) color variations (MCVs) for 1,977 narrow-line Seyfert 1 (NLSy1) and 4,113 broad-line Seyfert 1 (BLSy1)
galaxies at $z < 0.3$. Using 14 years of WISE and NEOWISE data, we quantify the correlation between $W1-W2$ color and $W1$ magnitude. We categorize sources into bluer-when-brighter (BWB), redder-when-brighter (RWB), and weak/no MCV populations. Our results show that the MCV properties of BLSy1s are consistent with those of NLSy1s. This suggests that host-contaminated dust reprocessing is a universal mechanism across Seyfert 1s. Bolometric luminosity ($\Lbol$) is the primary driver of MCV behavior. However, at fixed $\Lbol$, the fraction of RWB sources decreases with increasing Eddington ratio ($\REdd$). This reveals a secondary dependence on the
accretion state. Ensemble structure function analysis further shows that higher-$\REdd$ sources exhibit flatter structure functions at a given $\Lbol$, indicating smaller dust
torus radii. These findings suggest that the central engine's radiation and
accretion state shape the circumnuclear dust geometry.
Radio-loud sources follow the same trends as
radio-quiet counterparts, implying that jet emission does not significantly impact long-term MIR variability. Finally, modified blackbody modeling indicates that grains with sizes $a \gtrsim 0.1~\mu$m are responsible for the observed MCVs. Our results establish a unified framework for MCVs in Seyfert~1s, where the Eddington ratio modulates both variability patterns and the physical scale of the dust
torus. Furthermore, given the similarity between the MCV distributions of CLAGNs and RWB sources, we estimate that $\lesssim 6\%$ of Seyfert~1s may be CLAGN candidates, offering a potential MIR-based pre-selection.
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All authors Jiahua Wu, Liming Dou, Zhining Chen, Fupeng Zhang, Luis C. Ho, Yanli Ai, Tinggui Wang, Xinwen Shu, Ning Jiang, Junfeng Wang
High Energy Astrophysical Phenomena
Evolution of first-interaction second-harmonic anisotropy in cosmic-ray air showers
Hao Sun and Cunfeng Feng
The longitudinal
evolution of second-harmonic anisotropy inherited from the first interaction in extensive air showers is investigated with CORSIKA simulations. Events with large initial anisotropy are selected. Second-harmonic observables are evaluated separately using the coordinate and momentum azimuths at several atmospheric depths and compared with their corresponding initial harmonic orientations. More than 84% of the initial second-harmonic signal is attenuated within the first 20 g cm$^{-2}$ of shower development. In coordinate space, the second-harmonic correlation with the initial orientation persists to ground level at approximately 0.09% of its initial magnitude. This residual is evaluated against a matched source-isotropized reference, constructed for each selected event by independently randomizing the azimuths of the first-interaction final-state particles and simulating the shower under identical atmospheric conditions. The positive coordinate-space ensemble-mean difference at ground level is statistically resolved, and the two samples show little event-level separation. In momentum space, a weak ensemble-level residual remains at 200 g cm$^{-2}$, and the original and source-isotropized signals become statistically indistinguishable by 300 g cm$^{-2}$ and remain so at ground level.
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High Energy Astrophysical Phenomena
A Localized Current-Sheet Magnetic-Diffusion and Heating Prescription for Ideal-GRMHD Simulations of M87*-like Accretion Flows
Songyan Dai and Renyue Cen
Ideal-GRMHD calculations provide the bulk
accretion flows used in black-hole emission models. A localized dissipation prescription can add a resolved map of current-sheet activity while retaining that dynamical reference. We implement such a prescription in Athena++, using a smooth threshold on the dimensionless current proxy $\alpha_J$ to select the
magnetic-
diffusion coefficient. The constrained-transport update is coupled to a conservative energy-flux correction. Gas heating follows from primitive recovery; $q_{Ohm}=\eta J^2$ is recorded as a diagnostic, without a second energy source. Static
Fourier and traveling Alfvén tests measure the evolved thermal gain, and an open-boundary Schwarzschild test closes the Killing-energy ledger. The relative total-energy residual is below $2\times10^{-15}$ in these tests. A two-resolution Harris
matrix gives localized rate exponents $0.510\pm0.027$ and $0.488\pm0.028$, consistent with $1/2$ over the specified early interval. The $\eta=10^{-3}$ rate exceeds the same-resolution ideal control by a factor of 5.96. In matched axisymmetric M87*-like runs, localized
diffusion changes the early mean
magnetic flux,
accretion rate, and normalized flux by less than $0.02\%$, with a radial-density distance of $0.005\%$. During the late active phase, a common-restart on/off comparison keeps these mean shifts below $1.6\%$, within the intrinsic temporal variability, and gives a density distance of $0.29\%$. Uniform
diffusion at the tested coefficient reduces the raw flux and
accretion rate by $85\%$ and $99.8\%$. These comparisons establish a spatially selective
diffusion prescription with explicit energy accounting and a quantified, small bulk-flow response.
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Earth and Planetary Astrophysics
High water D/H ratio of the interstellar object 3I/ATLAS is consistent with a low-metallicity origin
Kenji Furuya, Martin Cordiner, Dominique Bockelée-Morvan et al. (+5 more)
Recent JWST observations have revealed unusually high $^{12}$C/$^{13}$C ratios in carbon-bearing molecules of the interstellar object 3I/ATLAS, consistent with formation in a lower-
metallicity environment than the present-day local interstellar medium (ISM). 3I/ATLAS also exhibits an exceptionally high water D/H ratio, exceeding those in Solar System comets and nearby low-mass
star-forming regions. Here we investigate whether this high water D/H ratio can be reproduced in a low-
metallicity formation scenario, using gas-ice astrochemical models. Assuming that the water observed in 3I/ATLAS was inherited from the parent molecular cloud and core, we perform a grid of astrochemical models covering the cloud to core stages, varying the gas density, ultraviolet radiation field ($\chi$),
cosmic-ray ionization rate ($\zeta$), and
metallicity, while solving thermal balance for the gas temperature. We find that lower
metallicity enhances H$_3^+$ deuteration and, more importantly, its transfer to water ice. In contrast, water D/H ratio depends non-monotonically on $\chi$ and $\zeta$, because of competing chemical and thermal effects. In our models, the observed water D/H ratio is most readily reproduced at subsolar
metallicities, $\lesssim0.5Z_\odot$, and relatively high cloud densities of $\sim$10$^4$ cm$^{-3}$ without strong constraints on either $\chi$ or $\zeta$, as long as $\zeta<10^{-15}$ s$^{-1}$. The D/H ratio of methane normalized by that of water is not sensitive to the
metallicity, being consistent with the similar values observed in 67P/Churyumov-Gerasimenko and 3I/ATLAS. These results suggest that water deuteration may provide a complementary probe of the
metallicity and physical condition of the parent molecular cloud and dense core of interstellar objects.
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All authors Kenji Furuya, Martin Cordiner, Dominique Bockelée-Morvan, Dennis Bodewits, Colin Orion Chandler, Maria N. Drozdovskaya, Nathan X. Roth, Geronimo Villanueva
Astrophysics of Galaxies
Stellar bar occurrence in TNG50 and TNG100: disentangling environmental effects and assembly history at z = 0
Karol Chim-Ramirez, Bernardo Cervantes-Sodi and Yetli Rosas-Guevara
In this work, we investigate the dependence of bar presence on environment using TNG50 and TNG100 simulations at z=0. We select disc
galaxies within $2 R_{200}$, with stellar mass M$_{\star} \geq 10^{10}$ M$_{\odot}$ (TNG100) and M$_{\star} \geq 10^{9}$ M$_{\odot}$ (TNG50). With these criteria, our final samples consist of 1719 and 859 satellite
galaxies in TNG100 and TNG50, respectively. The environment is characterised by host
halo mass: massive (M$_{\rm h} \geq 10^{14}$ M$_{\odot}$), intermediate ($10^{13} < \rm M_{\rm h} < 10^{14}$ M$_{\odot}$), and low-mass
haloes (M$_{\rm h} \leq 10^{13}$ M$_{\odot}$). We find that our samples recover the morphology-density relation, with thin disc fractions increasing with cluster-centric distance and decreasing
halo mass. The bar fraction and the bar length normalized by the effective radius decrease mildly with cluster-centric distance, while absolute bar lengths remain constant. At fixed distance, the bar fraction increases with
halo mass, partly because more massive
galaxies reside in more massive
haloes. In addition, we find that
galaxies with earlier assembly times show a higher bar fraction, especially within $0.5 R_{200}$, suggesting a connection between earlier assembly and a higher probability of hosting a bar. Overall, we find a mild environmental dependence, with a stronger connection to stellar mass and assembly history.
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Astrophysics of Galaxies
Mapping the Quasar Main Sequence in the UV range: A Connection with the UV Fe III Emission
D. Martínez Collipal, M. L. Martínez-Aldama, A. Pandey et al. (+3 more)
The
quasar main sequence (MS) provides a consistent unification scheme for type I AGNs. This framework, constructed from the relative flux between the optical emissions $\mathrm{H}\beta$ and $\mathrm{Fe\,II\,(\lambda4570)}$, and the $\mathrm{FWHM(H\beta)}$, organizes
quasars into two populations (B, A) and the subpopulation xA, which typically consists of highly accreting sources. We explored the use of the UV 1900 blend emissions ($\mathrm{Al\,III}\,\mathrm{\lambda}1860$, $\mathrm{Si\,III]}\,\mathrm{\lambda}1892$, $\mathrm{C\,III]}\,\mathrm{\lambda}1909$) and the $\mathrm{Fe\,III}$ and $\mathrm{Fe\,II}$ transitions between 1700 and 2200 Angstrom as tracers of this main sequence. We fitted these emissions for a sample of 69 low-$z$ ($z\lesssim0.8$)
quasars observed with the Hubble Space
Telescope (HST) that had available optical measurements, enabling a direct comparison with the optical
quasar main sequence. We found a UV plane defined by $\mathrm{FWHM}(\mathrm{Al\,III})$ and the equivalent width of the combined emissions of $\mathrm{Fe\,III}$ and $\mathrm{Fe\,II}$. The plane defined by these parameters mirrors the
quasar main sequence in the optical regime and shows a clear distinction between the different populations. The plane also enables the identification of xA sources with high completeness but a non-negligible rate of false positives. Our results suggest that the UV iron emission around the 1900 blend could be used to trace the
quasar main sequence trend, offering an alternative way to study this scheme at high
redshift.
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All authors D. Martínez Collipal, M. L. Martínez-Aldama, A. Pandey, M. Cardenas, P. Marziani, S. Panda
High Energy Astrophysical Phenomena
Electromagnetic Probes of the Supernova Engine
Chris L. Fryer
Explosions from stellar collapse are important in nearly all aspects of astronomy: formation of compact remnants (including the potential seeds of supermassive black holes), the production of compact binaries the produce X-ray binaries and
radio pulsars, the origin of many of the heavy elements (a critical aspect of galactic chemical
evolution), and as standard candles to probe the early universe (including the nature of
star formation). Because these explosions occur in extreme conditions, if we can understand them, they can be used to probe fundamental physics: matter at extreme densities (exceeding nuclear densities,
quark formation),
neutrino physics (including
neutrino oscillations) and, in black-hole forming systems, the nature of relativity. Gravitational waves and
neutrinos provide the most direct probe of stellar collapse, but these diagnostics require nearby events. Electromagnetic probes, from shock breakout to observations of
supernova remnants, can be much more common and provide complementary diagnostics of the explosive engines behind stellar collapse. In this review, we review these electromagnetic diagnostics, the physics behind them and the theory and modeling work we require to take advantage of these probes.
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