Cosmology and Nongalactic Astrophysics
Constraining Spatial Curvature with Priors from Swampland Conjectures
Simran Arora, Hun Jang and Shinji Mukohyama
We study a string-motivated theoretical prior on the quintessential dark energy model with exponential potential, \( V(\phi) = V_0 e^{-\lambda \phi} \), allowing for non-zero spatial
curvature. First, we formulate the corresponding dynamical system and investigate its cosmological
evolution numerically, illustrating the phase-space behaviour and the influence of
curvature on the background dynamics. In open universes (\( \Omega_k > 0 \)), it has been suggested that a
curvature-related fixed point may support accelerated expansion even for relatively steep potentials compatible with swampland considerations. Next, we explicitly impose swampland-motivated priors on the slope parameter $\lambda$, restricting it to values consistent with the de Sitter
conjecture that excludes the (curved) $\Lambda$CDM limit. Furthermore, we restrict our considerations to the range of field excursion that is consistent with the swampland distance
conjecture. Our primary interest is the possibility that such theoretically-motivated priors may shift values of cosmological parameters inferred by observational data, compared with the standard analysis based on theory-agnostic priors such as a sufficiently wide flat prior. We examine this possibility using a combination of Planck CMB data, DESI BAO measurements, and recent Type Ia
supernova samples, performing a
Bayesian inference of the model parameters. Our analysis indicates that the swampland-motivated prior mildly shifts the values of $\Omega_k$.
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Earth and Planetary Astrophysics
Prospects for detecting surface color heterogeneity on asteroid surfaces from sparse multiband photometric survey data
Oriel Humes and Jessica Agarwal
Automated sky surveys frequently report sparse-in-time multiband photometric observations of asteroids passing through their fields of view. Photometric data are currently available for tens of thousands of asteroids, and new data collection is ongoing. We aim to describe and characterize the performance of a statistical test for identifying asteroids that display surface color heterogeneity based on sparse-in-time multiband photometric survey data. Using simulated photometry for a set of synthetic asteroids with predetermined physical properties, we estimated the sensitivity of the statistical test for surface color heterogeneity to errors in assumed model properties using a Monte Carlo approach. We evaluated the detection and false positive rates as a function of the number of observations, measurement noise, error in assumed period, pole orientation, shape, and phase function. We examined the required accuracy in various parameters of the photometric model needed to obtain reliable results to evaluate the feasibility of applying the test to realistic
datasets. Regional-scale surface color heterogeneity can be detected by examining differences in the shape of an asteroid's light curve as a function of viewing geometry across multiple bandpasses. Differences in light curve shapes as a function of wavelength are highlighted in this work through comparison of the observed photometric measurements to the predictions of a well-fitting, uniformly colored photometric model. Statistically significant deviations from the prediction of the uniformly colored model are taken as evidence of surface color heterogeneity. The performance of this test depends on the accuracy of model assumptions, with the detection rate being most sensitive to errors in the assumed rotational period, while the false positive rate is most sensitive to errors in the assumed band-dependent phase functions.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Dark Energy in Ghost-free non-local Gravity
S.D. Odintsov, V.K. Oikonomou and G.S. Sharov
Ghost-free non-local
gravity is investigated with regards to its late-time dynamics. Viable solutions in this model are confronted with the observational data including the Pantheon+ catalogue of Type Ia
supernovae, the Dark Energy Spectroscopic Instrument, the measurements of
baryon acoustic oscillations and the Hubble parameter estimations $H(z)$. The ghost-free non-local
gravity is found to be successful in these tests in comparison to the $\Lambda$CDM model and can be also comparable with the generalized exponential $F(R)$
gravity scenario. However the model encounters difficulties when the data from the above observations and the
cosmic microwave background radiation data are combined. In tests with the whole set of Pantheon+, DESI, $H(z)$ and CMB data, the generalized exponential $F(R)$ model is essentially more successful. This success is related with the dynamical behavior of its effective dark energy equation of state evolving from a phantom to a quintessence phase during the late-time epoch, whereas the ghost-free non-local model demonstrates only a quintessence behavior. Hence the ghost-free non-local
gravity scenario is successful only when the Pantheon+, DESI and $H(z)$ data are considered. The generalized exponential $F(R)$ model satisfies the viability conditions and in tests with all observational data including CMB surpasses the $\Lambda$CDM model in $\chi^2$ statistics and also with information criteria.
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High Energy Astrophysical Phenomena
A.Neronov, D.Savchenko and M.Poleshchuk
Neutrino signal from a population of Seyfert
galaxies has been detected by IceCube
neutrino telescope in the
muon neutrino channel that has sensitivity mostly to the Northern Hemisphere sources. This detection can be verified by KM3NeT
telescope that has sensitivity also in the Southern Hemisphere. We define a catalog of Seyfert
galaxies that are expected to be detectable with KM3NeT, assuming that the
neutrino luminosity scales with the intrinsic hard X-ray luminosity of the sources. We find that four sources: NGC 1068, NGC 4151, NGC 4945 and Circinus
galaxy, are detectable by KM3NeT, if their spectra follow either NGC 1068 or NGC 4151 spectral template based on IceCube data. We discuss uncertainties of the
neutrino flux estimate, considering the Compton-thick nature of three of the four detectable sources: NGC 1068, NGC 4945 and Circinus. The limited catalog of the four sources can be used in KM3NeT source search to reduce the trial factor of analysis aimed at independent verification of the
neutrino signal from Seyfert
galaxies.
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High Energy Astrophysical Phenomena
Magnetar Fireballs and Short Bursts: Curved Spacetime Lensing, QED Effects, Spectra, Polarization, and Impulse Responses
Zorawar Wadiasingh, Hoa Dinh Thi, Constantinos Kalapotharakos et al. (+12 more)
Magnetar short bursts (SBs) are hard X-ray transients of durations $0.01-1$ s peaking at $\sim 10-100$ keV, and are
prime targets for new high-energy missions and polarimeters. The recent association of SBs with bright
radio bursts in SGR 1935+2154 has broadened interest in SB physics. We present new advanced fireball models combining general relativistic light bending, polarized transport in magnetized photospheres,
magnetic photon splitting attenuation, and magnetospheric
vacuum birefringence. These models also have relevance to trapped fireballs in magnetar
giant flare pulsating tails. We adopt confined flux tube geometries consistent with adiabatic fireballs, and anisotropic/polarized emergent intensities to produce spectra and polarizations, and energy-time Stokes impulse responses. We predict that most fireballs are highly linearly polarized, especially when
vacuum birefringence is important. There is rich potential for diagnostics: coexisting direct and lensed delayed images, gaps by occultation of the
neutron star surface, and Shapiro+Rømer delay with temporal caustics. These effects can imprint
spin phase dependence of the spectral and polarization character of bursts. Predicted signatures depend strongly on viewing geometry, fireball configuration, and
photon splitting assumptions, yielding large variance in model high-energy spectral shapes and cutoffs, and energy-dependent polarization. The models can reproduce established double-blackbody SB spectral phenomenology, and we find that the unusual April 2020
radio-associated SB from SGR 1935+2154 is broadly consistent with a footpoint close to the
magnetic pole, and possibly near pole-on viewing geometry. Our models motivate reverberation-style analyses for SBs and suggest that high-quality data might constrain source geometry, burst crustal footpoints, and, potentially,
neutron star masses and radii.
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All authors Zorawar Wadiasingh, Hoa Dinh Thi, Constantinos Kalapotharakos, Kun Hu, Matthew G. Baring, Alice K. Harding, George Younes, Sebastien Guillot, Andrea Sanna, Michela Negro, Jeremy D. Schnittman, Oliver J. Roberts, Eric Burns, Chin-Ping Hu, Ersin Göğüş
Cosmology and Nongalactic Astrophysics
Signatures of Modified Gravity on Linear Scales in a Dynamical Dark Energy Background
Yo Toda and Adrià Gómez-Valent
Cosmological data from the
cosmic microwave background (CMB),
baryon acoustic oscillations, and Type Ia
supernovae suggest that the component driving the accelerated expansion of the Universe may be dynamical at the $\sim 2.5$-$3\sigma$ CL. The best-fit CPL model produces a level of
cosmic structure similar to that of $\Lambda$CDM, with both models exhibiting mild tension with
redshift-space distortion data. In this Letter, we parametrize possible departures of the effective gravitational coupling from Newton's constant in the late Universe, below a comoving scale $\lambda_c$, using two
redshift bins, $0 \leq z < 1$ and $1 \leq z \leq 3$. We then determine the optimal values of $\lambda_c$ and the amplitude of these deviations from General Relativity, assuming a background with dynamical dark energy in CPL form. We find that, in order to achieve the required suppression of structure growth at low
redshifts while remaining consistent with CMB constraints – primarily from the late-time ISW effect at low $\ell$ and
lensing at high $\ell$ – we must require modified
gravity effects to have a characteristic scale of $\lambda_c \lesssim 150\,\mathrm{Mpc}$ (95% CL). This places the relevant scales squarely within the range probed by
galaxy surveys. The best-fit value is $\lambda_c \simeq 40\,\mathrm{Mpc}$, well below the 95% CL upper limit. Using Planck PR4, DESI DR2, Pantheon+ (or DES-Dovekie) and
redshift-space distortions data we confirm that a CPL background with standard
gravity is moderately preferred over $\Lambda$CDM; this preference strengthens to a mildly strong level when modified
gravity effects are included. This enhancement leaves the CPL parameters largely unchanged, but shifts them slightly further into the quintom region.
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Earth and Planetary Astrophysics
Probing close-in satellites of Trans-Neptunian Objects through thermal and direct size measurements
J. M. Gómez-Limón, R. Leiva, J. L. Ortiz et al. (+6 more)
Context: Trans-Neptunian objects are distant bodies that retain valuable information about the origin and
evolution of the
Solar System. Many of these objects constitute binary systems. Studying binaries allows us to further characterise this primitive population and is critical for determining mass densities, a key but elusive physical property. Nevertheless, satellite detection can be challenging. Aims: This study aims to constrain the presence of close-in satellites around a selection of ten trans-Neptunian objects, including four known binary systems used for methodology validation. Methods: We developed a methodology independent of primary-secondary separation. We exploit the combination of occultation-derived sizes and thermal emission data from the "TNOs are Cool" Herschel Space Observatory key project. We model the thermal emission from a binary system to explain the thermal excess that cannot be reproduced by a single body of the occultation-derived size. Results: We obtain satisfactory constraints for the validation targets (208996) Achlys, (229762) G!kún{"hòmdímà, (38628) Huya and (174567) Varda. We find that (84522) 2002 TC302, (119951) 2002 KX14, and (307261) Máni are likely binary systems, which was previously unknown. We report size estimates for their putative satellites. For (84922) 2003 VS2, (28978) Ixion, and (470316) 2007 OC10 we find that no sizable satellite is needed to reconcile thermal and occultation data.
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All authors J. M. Gómez-Limón, R. Leiva, J. L. Ortiz, P. Santos-Sanz, M. Kretlow, Y. Kilic, J. L. Rizos, A. Álvarez-Candal, T. G. Müller
High Energy Astrophysical Phenomena
Nature of 4FGL J2249.4+6229: Evidence for a redback system with a cool companion and low X-ray and $\gamma$-ray luminosities
A. V. Karpova, D. A. Zyuzin, S. V. Zharikov et al. (+1 more)
We report the identification of the likely X-ray and optical counterpart to the unassociated
Fermi source 4FGL J2249.4+6229. To clarify its nature, we investigate the X-ray data from Swift/XRT and SRG/eROSITA as well as photometric data from optical catalogues and archival spectroscopic data from the Gemini-North
telescope. Using Zwicky Transient Facility data spanning over 6.6 yr, we confirmed a period of $\approx$5.6 h likely associated with the orbital motion in a binary system. The folded light curves have a smooth sinusoidal shape with two peaks per period and the amplitude of $\approx$0.2 mag. The X-ray spectra of the source are well fitted by an absorbed power law with the
photon index of $\approx$2.0 and unabsorbed flux of $\approx$1.4$\times10^{-13}$ erg s$^{-1}$ cm$^{-2}$. All these together with the X-ray to optical flux ratio of $\sim$0.2 implies that 4FGL J2249.4+6229 is a promising redback candidate. Fitting the optical light curves with the direct heating model, we obtained the companion mass of $\approx$0.5 M$_\odot$ and temperature of $\approx$3600 K implying an M-type
star. This places it among the coldest and most massive companions known in redback systems.Optical spectra confirms the M-type
star and shows the broad asymmetric H$\alpha$ emission line. For the distance of 500–550 pc derived from the optical data, the source can be the redback with the lowest X-ray and $\gamma$-ray luminosities.
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All authors A. V. Karpova, D. A. Zyuzin, S. V. Zharikov, M. R. Gilfanov
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Probing freeze-in dark matter using Bose-Einstein condensate in neutron star
Deep Ghosh and Anirban Das
Neutron star (NS) is one of the most promising astrophysical targets to probe non-gravitational interaction of dark matter (DM) with visible matter. Their compactness makes them an ideal object which can capture particle DM efficiently over its lifetime using the DM-nucleon scattering cross-section. If DM particles are bosonic, then the captured DM population may form a Bose-Einstein condensate at the center of the NS, increasing the DM density significantly. In this work, we study the phenomenology of such scenario with enhanced DM annihilation rate due to the increased density in a condensate. The enhanced DM annihilation makes the NS surface `hotter' than in the standard cooling scenario. We show that the annihilation rate is enhanced by a factor of $\mathcal{O}(10^{15}-10^{20})$ if DM forms a condensate without large self-interaction, and DM with freeze-in value annihilation cross-section can heat up the NS to higher temperatures, bringing it within the reach of James Webb Space
Telescope. It also allows us to probe DM-nucleon scattering cross section within the
neutrino fog regime which will complement the terrestrial direct detection searches. Moreover, the enhanced annihilation from the condensate changes the lower limits on s-wave DM annihilation cross-section for capture-annihilation
equilibrium and the formation of a black hole inside the NS. Finally, we show an example of a scalar DM model where such small annihilation and DM-nucleon scattering cross sections can generically arise.
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Solar and Stellar Astrophysics
A Robust Deep Learning Framework for Prominence Detection through Composite Feature Representations
Harry Birch, Stéphane Régnier and Richard Morton
Solar prominences are dynamic structures suspended within the
solar corona and are manifestation of
solar activity. Their
evolution includes eruptions linked to coronal mass ejections, making their detection critical for space weather monitoring and
forecasting. The vast amounts of high-cadence data provided by missions such as SDO/AIA motivate the application of deep learning frameworks capable of assimilating large-scale
datasets. However, previous studies have reported poor model performance caused by contamination from hot coronal emission from the EUV HeII 304 Å channel. Using an existing labeled prominence
dataset, we find that trained YOLOv5 object detection models exhibit a strong bias towards the 304 Å colormap, rather than physically meaningful prominence features. We develop a further two models comprising three-channel images constructed through an original
dataset preprocessing pipeline: (i) full-disk grayscale, full-disk enhanced corona, and disk-removed, (ii) same as (i) with all disk-removed images. Our pipeline corrects instrument degradation to maintain more consistent feature representations across the
solar cycle. The composite model (i) achieves a mAP@50 of 0.749 and a recall of $78\%$ on the test set, outperforming previous bounding box methods. Visual analysis of the composite models reveals that many apparent false positives are valid unlabeled prominences. We additionally demonstrate cross-instrument generalization by testing the composite model on SUVI image data. By examining
dataset biases that propagate into model predictions, we provide recommendations for robust
dataset construction. We present a reliable, physically-motivated, and versatile deep learning model to automatically detect prominences in EUV images, providing a framework beneficial for space weather applications.
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Astrophysics of Galaxies
Silicate cosmic dust grain collisions in the interstellar medium: A molecular dynamics study
C.J. Esmerian, S.R. Hashemi, W.M.C. Sameera et al. (+7 more)
(abridged) We aim to predict the most important parameters for grain-grain collision outcomes in models of interstellar grain population
evolution: the threshold velocities for shattering and vaporization, and the resulting distributions of grain sizes. We use molecular dynamics simulations which evolve the dynamics of each atom in a
dust grain to explore the outcomes of collisions between silicate grains of radii $a \in [5,50]~\AA$ at velocities 0.1-20 km/s. We run simulations of grains with two materials: amorphous SiO$_2$ and an amorphous silicate of composition suggested by Draine & Hensley (2021). With these simulations, we quantify the collision velocity dependence of shattered and vaporized mass fractions, and the resulting size distributions of shattering products. We find grain shattering thresholds are $\sim$6 km/s for both materials, a factor of $\sim$2 higher than the canonical value for silicates of 2.7 km/s from Tielens et al. (1994) and Jones et al. (1996). The size distributions of shattered products are generally not consistent with the power law distributions predicted by Jones et al. (1996), but the physical reasons for these discrepancies remain uncertain. The Tielens et al. (1994) expressions fail to predict the fraction of shattered or vaporized material observed in our numerical simulations, over-predicting the shattered fraction and under-predicting the vaporized fraction, except for the most massive grains we simulate, where the predicted vaporized fraction agrees reasonably well. The model of Hirashita & Kobayashi (2013) similarly fails to match the simulations. We provide updated shattering velocity thresholds for nanoscale silicate grains, which suggest that the smallest astrophysical
dust grains composed of silicate materials may be more robust to shattering in the interstellar medium than previously assumed.
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All authors C.J. Esmerian, S.R. Hashemi, W.M.C. Sameera, B. Lankhaar, W. Vlemmings, S. Andersson, T. J. L. C. Bakx, K. K. Knudsen, S. Aalto, G. Nyman
High Energy Astrophysical Phenomena
Quasi-Simultaneous Broadband Spectral Energy Distributions of a Sample of Fermi Blazars – I. Correlation Results
Yi Zhong, Zhujian Wan, Rui Xue et al. (+3 more)
Blazars' non-thermal emission shows rapid variability across all wavelengths, so spectral energy distributions (SEDs) built from quasi-simultaneous data are crucial for revealing the jets physical properties. In this work, we construct quasi-simultaneous broadband SEDs for 93
Fermi blazars (56 FSRQs, 35 BL Lacs, and 2 blazar candidates of uncertain type), fit both peaks with cubic functions to allow for potential asymmetries, and examine correlations among key parameters. Our main results are summarized as follows: (1) We find that synchrotron peak frequency and
curvature are only weakly related, suggesting that charged particles are accelerated by mixed acceleration mechanism. (2) The blazar sequence is confirmed in the observer's frame through negative correlations of both the bolometic luminosity $\log L_{\rm bol}$ and the Compton dominance $\log Y$ with the synchrotron peak frequency $\log \nu_{\rm syn}^{\rm peak}$. After correcting for Doppler boosting, a weak positive correlation emerges between $\log L_{\rm bol}$ and $\log \nu_{\rm syn}^{\rm peak}$. FSRQs and BL Lacs exhibit distinct correlation patterns within the blazar sequence, indicating differences in cooling mechanisms. (3) Using variability time lags between 0.1-1 GeV and 1-300 GeV light curves, we estimate lower limits of Doppler factors for 4 sources, providing a jet-speed diagnostic anchored directly to the $\gamma$-ray emission zone.
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All authors Yi Zhong, Zhujian Wan, Rui Xue, Hubing Xiao, Dingrong Xiong, Ze-Rui Wang
Cosmology and Nongalactic Astrophysics
Debottam Nandi and Debajyoti Choudhury
Magnetic fields observed across
cosmic scales are difficult to explain within conventional physics. A
primordial origin is, thus, often assumed. While a nonminimal coupling of the inflaton with the electromagnetic field could theoretically generate
magnetic fields of about $10^{-13}$ G, this approach faces significant issues, including strong-coupling and backreaction problems. “Dark
photons", arising naturally in hidden-sector extensions of the Standard Model, provide a well-motivated framework for addressing various
cosmic as well as particle physics issues. We demonstrate that coupling dark
photons with standard ones can result in adequate magnetogenesis without the limitations of existing models. This minimal mechanism may also provide insights into unresolved
cosmic mysteries.
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Astrophysics of Galaxies
A Unified HI Rotation Curve Database for 122 Dwarf and Irregular Galaxies
David C. Flynn
We present a unified HI rotation curve database for 122
dwarf and irregular
galaxies drawn from three Local Volume surveys, the Local Volume HI Survey (LVHIS; 32
galaxies), VLA-ANGST (29) and LITTLE THINGS (26), and from the WALLABY DR2 kinematic catalogue (35). The database provides standardised kinematic parameters, distance estimates, morphological classifications, and rotation curve data in machine-readable JSON, JSONL, and CSV formats with a documented schema, supporting
retrieval-augmented generation (RAG) applications and cross-survey kinematic analysis. Quality tiers distinguish 26
galaxies with published tilted-ring rotation curves and per-point uncertainties from 96 automated-pipeline, single-ring or profile-width entries. Three worked examples demonstrate corpus queries, including evaluation of the $\omega$
estimator for DDO 154 (LITTLE THINGS). This work is presented as a data resource; no new dynamical model is proposed. This version describes corpus v1.3, which corrects the LITTLE THINGS curves (v1.1), the WALLABY entries (v1.2) and the LVHIS entries and reference (v1.3) of v1.0. The database and all computation scripts are available at Zenodo (https://doi.org/10.5281/zenodo.23503221).
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Instrumentation and Methods for Astrophysics
Spectra as Language: Large Language Models for Scalable Stellar Parameter and Abundance Inference
Hai-Ling Lu, Yu-Yang Li, Yin-Bi Li et al. (+4 more)
Stellar spectra encode key information on the physical properties and chemical compositions of
stars. Accurate
stellar parameter determination is essential for addressing major questions such as
galaxy and
stellar evolution. Large-scale spectroscopic surveys have accumulated unprecedented spectral data. Traditional feature extraction or model-fitting approaches struggle with high-dimensional, massive
datasets, limited generalization, and computational inefficiency. Recent advances in large
language models demonstrate strong generalization and feature-learning in tasks like natural
language processing, DNA/RNA sequence analysis, and
protein/chemical parsing.
Stellar spectra are continuous sequential signals, enabling the transfer of
language models to
stellar spectroscopy. Here, we propose a two-stage large
language model framework for
stellar parameter inference, achieving accurate estimation of effective temperature, surface
gravity,
metallicity, and abundances of ~20 chemical elements. Scaling-law analyses show systematic performance improvements with increasing data, providing a scalable framework for forthcoming large-scale surveys.
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All authors Hai-Ling Lu, Yu-Yang Li, Yin-Bi Li, Cun-Shi Wang, A-Li Luo, Jun-Chao Liang, Shuo Li
Cosmology and Nongalactic Astrophysics
Blue-tilted spectral running and the JWST early galaxy tension
Mikage U. Kobayashi, Gen Chiaki, Kazutaka Kimura et al. (+4 more)
Recently, the James Webb Space
Telescope (JWST) collaboration has found the unexpectedly large abundance of massive
galaxies with
stellar masses of $\sim 10^{10}~M_{\odot}$ at high
redshifts $z \simeq 6.5 - 9$ compared with the prediction of the standard $\Lambda$CDM model. As a possible solution to the tension, we consider a blue-tilted spectrum of density perturbations with a positive running. We find that, for $\alpha_s \simeq 0.02$ and $\beta_s \simeq 0.02$, a joint analysis with CMB observations shows that the tension can be resolved at the 1$\sigma$ confidence level. Such a blue-tilted spectrum is also plausible from the perspective for formations of
primordial black holes on much smaller scales in the early Universe.
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All authors Mikage U. Kobayashi, Gen Chiaki, Kazutaka Kimura, Kazuyuki Akitsu, Kazunori Kohri, Tomo Takahashi, Kazuyuki Omukai
High Energy Astrophysical Phenomena
There and back again: Mysterious optical pulse profile behavior of the transitional millisecond pulsar PSR J1023+0038
S.V. Karpov, Artyom S. Tanashkin, G.M. Beskin et al. (+3 more)
Neutron stars in close binary systems have the potential to
spin up to millisecond periods due to the
accretion of matter and angular momentum from their low-mass companions. In later stages of this process, they sometimes start to swing between the
accretion-powered and rotation-powered regimes, manifesting themselves as low-mass X-ray binaries and millisecond
radio pulsars, respectively. Such systems are known as transitional millisecond
pulsars. PSR J1023+0038 was the first one of this kind to be discovered and the first to show optical pulsations at the rotation frequency of the
neutron star during a peculiar low
accretion state. The optical pulse profile is characterized by a smooth double-peaked shape resembling thermal light curves of X-ray
pulsars, but more likely emerging from re-emission of the
pulsar wind energy by charged particles in the surrounding medium. Although the amplitudes of the peaks show strong variability, the overall structure of the pulse profile was observed to be fixed, with the optical pulsed fraction less than 1 percent. Here, we report time-resolved observation of a dramatic violation of this permanence during our high temporal resolution observations of PSR J1023+0038 with the 6-m BTA
telescope of the Special Astrophysical Observatory. On a timescale of a few seconds the pulse profile took a single-peaked, nearly sinusoidal shape, with synchronous magnification of the pulsed fraction up to about 5 percent. After spending about 220 seconds in this new regime, accompanied by flaring activity, the system returned to its normal state. We discuss a number of possible explanations of this peculiar behavior in the context of the physics and geometry of interactions between the
pulsar wind and surrounding matter. However, a complete picture is yet to be revealed.
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All authors S.V. Karpov, Artyom S. Tanashkin, G.M. Beskin, V.L. Plokhotnichenko, Y.A. Shibanov, D.A. Zyuzin
High Energy Astrophysical Phenomena
Self-Supervised ConvLSTM for Fermi Large Area Telescope Transient Detection
Alberto Garinei, Stefano Speziali, Alessandro Vispa et al. (+11 more)
We present a framework for detecting transient gamma-ray phenomena in a controlled environment by combining end-to-end simulations of the
Fermi-LAT sky with self-supervised spatio-temporal deep learning. We generate a ten-year synthetic Universe with gtobssim and process the simulated events into daily all-sky maps of counts and exposure, obtaining a time-ordered sequence that mirrors the structure of
Fermi-LAT observations. To model the nominal
evolution of the sky, we employ a Convolutional Long Short-Term
Memory (ConvLSTM) network that operates directly on map sequences, preserving spatial locality while learning temporal dependencies. The model is trained to reconstruct expected emission, and departures from the learned baseline are quantified through pixel-wise mean-squared residual maps. We then define statistically motivated anomaly criteria by estimating per-pixel thresholds from the residual distribution on the training set, and we enforce spatial coherence via local filtering to suppress isolated fluctuations. The ConvLSTM is then deployed as trained predictor on
Fermi-LAT daily maps, where the sky can depart from the nominal behavior because of genuine astrophysical variability and instrumental non-stationarities. The resulting pipeline flags localized, time-dependent excesses consistent with high-variable sources or transient events (e.g.,
flares or GRBs) and provides a
benchmark for evaluating anomaly-detection strategies on long-duration,
Fermi-LAT-like
datasets.
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All authors Alberto Garinei, Stefano Speziali, Alessandro Vispa, Andrea Marini, Sara Cutini, Emanuele Piccioni, Marcello Marconi, Francesco Longo, Matteo Martini, Francesca Fallucchi, Romeo Giuliano, Ernesto William De Luca, Umberto Di Matteo, Sabino Meola
Cosmology and Nongalactic Astrophysics
Machine Learning applications to Galaxy Clusters
Gustavo Yepes and Daniel de Andrés
This chapter reviews the application of Artificial Intelligence (AI) techniques to the study of
galaxy clusters, covering both theoretical developments and their use as tools to infer cluster properties from a variety of observational tracers. We discuss recent advances in mass estimation from SZ, X-ray, optical, and dynamical data, highlighting the ability of AI methods to capture non-linear features, projection effects, and complex cluster morphologies beyond more classical approaches. In addition, we present other emerging applications, including the emulation of baryonic physics from N-body simulations, the characterization of dynamical states and mergers, and the analysis of the diffuse components such as the intracluster light. Particular emphasis is placed on the role of simulations in training these models, the impact of baryonic modelling, and the need for a robust uncertainty quantification and interpretability. Finally, we outline current limitations and future prospects, stressing the importance of combining flexible simulation strategies with AI techniques to fully exploit next-generation surveys for precision cosmology.
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High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph
PIC simulations of nonrelativistic high-Mach-number oblique shocks propagating in a turbulent medium
Karol Fulat, Eloise Moore, Mahmoud Alawashra et al. (+4 more)
Collisionless shocks are common in astrophysical systems and stand as sites of particle acceleration. While particles at perpendicular shocks may not return to the upstream region, at oblique shocks a fraction of energetic electrons manage to escape the shock and travel upstream. An extended region known as the electron foreshock is formed, where these reflected particles drive various instabilities that may promote electron acceleration. Here we present the first 2D3V particle-in-
cell (PIC) simulations of electron-ion non-relativistic oblique shocks that explore the interaction of the foreshock with pre-existing compressive
turbulence with relative amplitude of 15% based on interstellar medium estimates. We find that pre-existing
turbulence influences the emergence and behavior of the whistler-wave instability, as it enhances the amplitudes of the
magnetic-field fluctuations and leads to larger nonlinear structures. This impacts the dynamics of the reflected electrons, resulting in a shorter and hotter electron foreshock. At the end of our simulations, with pre-existing upstream
turbulence we observe non-thermal electrons that are more numerous, reach higher energies, and carry a larger portion of the total energy.
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All authors Karol Fulat, Eloise Moore, Mahmoud Alawashra, Michelle Tsirou, Artem Bohdan, Takanobu Amano, Martin Pohl
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
On the Presence of a Tertiary Compact Object in GW190814
Lalit Pathak, Hemantakumar Phurailatpam and Achamveedu Gopakumar
Gravitational waves from merging compact binaries are sensitive to line-of-sight acceleration (LOSA) induced by a massive companion in their vicinity. Interestingly, the leading-order contributions of LOSA and residual orbital eccentricity to the
Fourier phase of the inspiral waveform exhibit similar frequency dependence, raising the possibility that a small eccentricity could mimic LOSA effects in transient GW events such as GW190814. We perform
Bayesian inference using the IMRPhenomXPHM waveform family as the baseline LIGO-Virgo-KAGRA waveform model, augmented with leading-order LOSA and residual eccentricity corrections while using 32 seconds of data associated with GW190814. For a LOSA-only analysis, we find no evidence for a non-zero LOSA effect in GW190814, with a Bayes factor relative to the baseline model of approximately 0.22, consistent with the findings of Hendriks et al. and in tension with the claim by Yang et al., who employed only 4 seconds of GW190814 data. In a joint analysis that includes both leading-order LOSA and eccentricity effects, we obtain informative posteriors for both parameters, with representative values a/c approximately -2.8 x 10^{-3} s^{-1} and e_0 approximately 0.11. However, the corresponding Bayes factor relative to the baseline model is approximately 0.64, suggesting that the 32-second data do not provide significant evidence for either LOSA or residual eccentricity in GW190814. Further, our
Bayesian runs reveal a strong correlation between the LOSA and eccentricity parameters, indicating a significant degeneracy in their imprint on the inspiral phase. This finding is consistent with our theoretical arguments and most likely explains the non-zero parameter estimates obtained in the joint analysis.
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High Energy Astrophysical Phenomena
Discovery of a Featureless Tidal Disruption Event at z~1 with the Wide Field Survey Telescope
Jiazheng Zhu, Zelin Xu, Ning Jiang et al. (+31 more)
We report the discovery of
tidal disruption event (TDE) WFST250820mmsw/AT2025wet by the 2.5-meter Wide Field Survey
Telescope (WFST). It exhibits a blue
nuclear flare throughout the observed
evolution with a g-band peak magnitude ~22, which is about 3 magnitudes brighter than its host
galaxy. A Keck/LRIS spectrum taken near the optical peak reveals a featureless blue continuum, with no discernible emission lines. However, its
redshift can be accurately determined to be 1.037 by its host
galaxy absorption lines. Blackbody fits to the multiband spectral energy distribution (SED) of AT2025wet yield a constant temperature of ~19,000K and a peak luminosity of (8.27 +0.92 -0.71)*10^44 erg s^-1 while actually the SED likely peaks at a much shorter wavelength than a 19,000K blackbody. The SED modeling of the host
galaxy implies a
stellar mass of ~10^11.2 M_odot and an estimated central black hole mass of ~10^8 M_odot, with no evidence of significant active
galactic nucleus activity prior to the
flare. All of these observations are well consistent with a featureless TDE scenario, making it the highest-
redshift non-jetted TDE known to date. TDEs at such high
redshift provide us a unique opportunity to explore the intrinsic SEDs of TDEs, particularly to test whether they peak in the extreme-UV regime, thereby addressing the missing energy puzzle and the origin of optical emission in TDEs. Ongoing surveys represented by WFST and the Legacy Survey of Space and Time (LSST) are expected to discover an increasing number of TDEs at higher
redshifts, which will extend our census of SMBHs across
redshift space and help unravel the mysteries of optical TDEs through direct probes of their UV emission.
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All authors Jiazheng Zhu, Zelin Xu, Ning Jiang, Ji-an Jiang, Tinggui Wang, Yuhan Yao, Ryan Chornock, Erica Hammerstein, Yibo Wang, Min-Xuan Cai, Shifeng Huang, Wenkai Li, Mingxin Wu, Chichuan Jin, Jie Lin, Jianwei Lyu, Dezheng Meng, Weiyu Wu, Zhengyan Liu, Junhan Zhao, Ziqing Jia, Chengyi Wang, Lulu Fan, Xu Kong, Feng Li, Ming Liang, Jinling Tang, Hairen Wang, Jian Wang, Yongquan Xue, Ji Yang, Hongfei Zhang, Wen Zhao, Qingfeng Zhu
Solar and Stellar Astrophysics
Photospheric abundances of the rapidly-rotating A-type star Altair
Yoichi Takeda
Altair is an A-type
star known to have an appreciably oblate shape owing to its very fast rotation (~300 km/s). Despite of numerous publications on this
star, its chemical abundances have been scarcely investigated so far, presumably because of the practical difficulty that spectral lines are considerably broadened by rapid rotation and badly blended with each other. Motivated by this situation, a spectroscopic analysis was conducted to study the photospheric abundances of Altair by using the synthetic spectrum-fitting technique, in order to clarify whether or not any chemical peculiarities exist. The microturbulent velocity was determined to be 2.9 (+/-0.9) km/s by requiring that the
metallicity does not show any systematic region-dependence. Then, the abundances of 17 elements (C, N, O, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Sr, Ba) were derived, where the non-LTE effect was taken into consideration as much as possible. The results revealed considerable region-by-region dispersion (several tenths dex or even more), reflecting the difficulty of reliable abundance determination for such a very rapid rotator. Nevertheless, the differential mean abundances relative to the Sun turned out to fall within -0.5 < [X/H] < +0.3 for all elements without any dependence upon the atomic number. Accordingly, we may conclude that (1) no appreciable anomalies of chemical abundance patterns exist in the atmosphere of Altair, (2) but its global
metallicity is likely to be slightly subsolar (~-0.2 dex on the average).
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Astrophysics of Galaxies
Shinya Komugi, Toshiki Saito, Tomonari Michiyama et al. (+5 more)
Time variability is a strong probe of energetic phenomena which occur at small spatial scales, like Active
Galactic Nuclei (AGN). We use ALMA observations at 100 GHz executed over a period of 2.5 months to look for time variability in the
Antennae galaxies, a prototypical early stage merger
galaxy pair, for which there are no previous signatures of an AGN in the optical, infrared or X-ray. Most 100 GHz detections in the
Antennae are spatially extended and associated with
star forming regions, but two sources in the southern
galaxy NGC 4039 are compact. One of these compact sources, S3, is offset by 1 arcsecond in the northeast direction from the
stellar peak of NGC 4039, and marginally resolved at 10 parsec resolution. The other source, S4, is co-spatial with the
stellar peak of NGC 4039 and unresolved even at a resolution of 4 parsec. We examine the time variability of these two sources using their power spectrum. We find that S4 varies with a characteristic timescale of 13+/-3 days, indicating that the phenomena responsible for the 100 GHz emission is smaller than 0.01 parsecs. By comparing the observed flux of the two sources with various candidate origins, we show that while S3 can be explained either by a young massive
stellar cluster or an AGN, S4 is likely to be an AGN that is possibly Compton-thick.
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All authors Shinya Komugi, Toshiki Saito, Tomonari Michiyama, Yoshiyuki Inoue, Kouichiro Nakanishi, Kazuki Tokuda, Fumiya Maeda, Yuzuki Nagashima
Astrophysics of Galaxies
Powerful Radio Sources in the Southern Sky. IV. Observations of the G4Jy-3CRE Catalog with the Australian Square Kilometre Array Pathfinder
Siegfried A. Gawenda, Juan P. Madrid, Francesco Massaro et al. (+19 more)
A recent 2023 paper by Massaro et al. introduced the G4Jy-3CRE, a new catalog of the brightest
radio sources in the southern hemisphere that serve as a southern equivalent to the Third Cambridge Catalog Revised (3CR). The G4Jy-3CRE catalog selected 264 sources from the GLEAM-4Jy survey based on the same criteria used to select the sources in the 3CR. In this paper, we present new Australian Square Kilometre Array Pathfinder (ASKAP) continuuum imaging of the G4Jy-3CRE catalog. We use the three most recent data releases from the Rapid ASKAP Continuum Survey (RACS), covering the sky south of +30{\deg}decl.: RACS-low1, RACS-mid, and RACS-high. Together, these data releases cover a range of frequencies from 600 to 1800 MHz. The RACS surveys have improved spatial resolution and sensitivity over archival surveys at the same frequency, enabling us to classify 173 sources (66% of the sample) with morphologies indicative of the presence of jets, 37 of which did not show jet activity on archival
radio maps. We were able to effectively classify FRI/FRII
galaxies up to a
redshift of z = 1.35. Moreover, we identified six optical counterparts for sources that were either previously unidentified or ambiguous.
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All authors Siegfried A. Gawenda, Juan P. Madrid, Francesco Massaro, Sara V. White, C.C. Cheung, Chiara Mazzucchelli, Abigail García-Pérez, I. Andruchow, Vahram Chavushyan, Ralph Kraft, Victoria Reynaldi, Ana Jimenez-Gallardo, Alessandro Capetti, Barbara Balmaverde, William R. Forman, H. A. Peña-Herazo, Nicole Nesvadba, Sergio A. Cellone, Romana Grossová, Alessandro Paggi, Eleonara Sani, C. Leto
High Energy Astrophysical Phenomena
The powerful shocks in RS Oph: NuSTAR X-ray data and a complete review
Marina Orio, Gerardo Juan M. Luna, Ehud Behar et al. (+4 more)
In the 2021 outburst of RS Ophiuchi, the gamma- and the X-ray flux were measured quasi-simultaneously from day 1 after the optical peak, offering the first comprehensive view of shocks in a nova occurring in a symbiotic system. We present a previously unpublished observation done with NuSTAR in the 3-79 keV range, 9 days after maximum, and we review the complex history of the evidence of shocks in the previous outbursts of this nova in the light of the intensive X-ray monitoring of 2021. We find evidence that the shock causing the particle acceleration measured with the Cherenkov
telescopes produced also the thermal flux detected in the 0.2-30 keV X-ray range, while the large gamma-ray flux observed with
Fermi after about a day, is not consistent with the X-ray observations. We conclude that an initial, strong shock, with particle-particle loss timescale shorter than the timescale of particle acceleration at energy higher than a few GeV, occurred close to the red
giant atmosphere,where either the X-rays' emitting volume was reduced by
turbulence, or - perhaps less likely - the X-rays were completely absorbed by large column density near the
giant and by the
accretion wake along the line of sight. We compare RS Oph with other novae in long period systems with evolved companions,discussing how the shocks' phenomenology is a powerful tool to derive other physical parameters. Finally, we discuss predictions that in T CrB, expected to have a new outburst within the next few years, the shocks may not be as energetic as in RS Oph.
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All authors Marina Orio, Gerardo Juan M. Luna, Ehud Behar, Rebecca Diesing, Jay Gallagher, Joanna Mikolajewska, Jan-Uwe Ness