Cosmology and Nongalactic Astrophysics · Cross-listed from physics.ins-det
Advances in the Fabrication of On-chip Superconducting Integral Field Units for CMB and Line-Intensity Astronomy
L. G. G. Olde Scholtenhuis, D. Perez Capelo, K. Karatsu et al. (+7 more)
Studying the polarization and spectral distortion of the
Cosmic Microwave Background (CMB) in tandem with intensity fluctuations of the
Cosmic Infrared Background (CIB) allows us to verify our assumptions on
cosmic inflation and investigate the dynamics and
evolution of
galaxy clusters in the last 10 billion years. Because of its broadband emission and being an all-sky extended source, observing the entire CMB in detail is a very time-consuming and expensive exercise. Fortunately, in the last few years, the on-chip superconducting spectrometer technology has moved out of the lab and into the
telescope. With its compact size and background-limited sensitivity, this family of instruments is particularly well-suited for fast and large area observations in a relatively unexplored range of the electromagnetic spectrum. However, recent examples of this technology do not yet reach the requirements needed for large spectroscopic and polarimetric surveys of the CMB. We formulate several of these requirements and introduce novel on-chip components and fabrication techniques. We introduce a cross-over to enable distinguishing signal polarization, minimize signal loss by locally optimized lithography of a coplanar-waveguide (CPW), lower the spectral resolution of microstrip filters by deposition of a dielectric layer, and increase the yield of the spectrometer array by removing individual line shorts. These together have culminated in the successful fabrication of a fourteen-spaxel IFU.
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All authors L. G. G. Olde Scholtenhuis, D. Perez Capelo, K. Karatsu, D. J. Thoen, A. J. van der Linden, S. O. Dabironezare, L. H. Marting, J. J. A. Baselmans, S. Vollebregt, A. Endo
Solar and Stellar Astrophysics
The sensitivity and behaviour of the curvature in the échelle diagram of red-giant stars
S. Hekker, Y. Elsworth, S. Basu et al. (+5 more)
In the convective envelopes of relatively cool
stars, oscillations are excited by turbulent convection. In these so-called
solar-like oscillators, radial oscillation modes appear at nearly equally spaced frequencies. This spacing is referred to as the `large frequency separation'. Deviations from equally-spaced frequencies are a result of the internal structure of a
star being different from a sphere of ideal gas at constant temperature. Hence, these deviations provide information on the internal structure of the
star. In this work, we investigate the second-order deviation from uniform spacing, referred to as
curvature. We aim to provide homegeneous values for observed red-
giant stars, understand differences between the results from observations and predictions from
stellar models, and reveal the connection between
curvature and
stellar structure. We used Kepler data of red-
giant stars and computed the
curvature for several thousand
stars. We compared these to the
curvature derived from MESA models. We subsequently investigated the trends and differences between results from observations and models. Finally, we computed sensitivity kernels to identify the
stellar region to which the
curvature is most sensitive and performed a glitch analysis. We found that the
curvature is sensitive to evolutionary phase and mass. The observed values and values from models show discrepancies. The glitch analysis shows that in theory this provides information on the location and strength of the HeI and HI ionisation layers. The
curvature provides a probe into the near-surface structure of the
star. The deviations between the
curvature derived from observations and models call henceforth for improvements in the near-surface layers of
stellar models.
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All authors S. Hekker, Y. Elsworth, S. Basu, F. Ahlborn, W.H. Ball, E.P. Bellinger, L. Buchele, F. Espinoza-Rojas
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Energy Conditions in Gauss-Bonnet Gravity
Francesco Bajardi
We study the Energy Conditions in modified $f(G)$
gravity, with $G$ being the topological Gauss-Bonnet term. Then we use the cosmographic parameters to constrain the functional form of the gravitational action and investigate the possibility to have standard inflation in the early time. Specifically, we select models containing
symmetries within the modified $f(\G)$ theory and obtain conditions for which i) the energy conditions can be violated and ii) the magnitude of the slow-roll parameters is small, thus suggesting that under given limits the analyzed theory can potentially trace the
cosmic history both at early and at the late times.
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Earth and Planetary Astrophysics
A Search for the Lost Comet P/2010 H2 (Vales)
Quanzhi Ye, Tony L. Farnham, Perry Cai et al. (+1 more)
Short-period comet P/2010 H2 (Vales) underwent a significant outburst of $>7.5$~mag in 2010 and has not been detected since that apparition. Here we report our recovery attempt of P/Vales using the 4.3-m Lowell Discovery
Telescope (LDT) during its 2015 and 2025 apparitions, as well as the data from the Transiting
Exoplanet Survey Satellite (TESS) taken in 2023. With the LDT data, we did not detect the comet within the $3\sigma$ positional uncertainty ellipse to a $3\sigma$ limiting magnitude of $r\sim25$, corresponding to an absolute
nuclear magnitude of $20.6$, or a diameter of $0.5$~km assuming a
geometric albedo of 0.04. Similarly, the TESS data reveals no comet or debris trail, providing no direct evidence for a disruption event although not precluding one. The new constraint on the
nucleus size tightens the range of viable activity mechanisms for P/Vales and is most consistent with a recently implanted, weakly processed
nucleus. Our non-detection of P/Vales down to $m_r=25$ shows that objects like this are difficult to detect in their inactive state with Rubin Observatory, but shift-and-stack techniques and targeted observations on 10-m-class
telescopes can provide more useful constraints on these objects.
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All authors Quanzhi Ye, Tony L. Farnham, Perry Cai, Lori Feaga
High Energy Astrophysical Phenomena
Observational Constraints on WIMP Mini-Spikes Around Stellar-Mass Primordial Black Holes with 17 Years of Fermi-LAT Data
Ana Vitória de Almeida Martinheira Braga, Murillo Gregorio Grefener da Silva and Aion Viana
The quest to identify the true nature of dark matter remains one of the most pressing challenges in modern physics. We present a novel approach to probe the Weakly Interacting Massive Particle (WIMP) paradigm by analyzing density enhancements, or “mini-spikes,” around
stellar-mass black holes (sBHs) using 17 years of data from the
Fermi Large Area
Telescope. Motivated by the anomalous orbital decay observed in the black hole low-mass X-ray binaries A0620–00 and XTE J1118+480, we model these systems under the hypothesis of adiabatic spike formation around
primordial black holes, incorporating the effects of
tidal disruption in the
Galactic disk. Finding no statistically significant gamma-ray excess at either location ($TS < 1$), we derive 95% C.L. upper limits on the WIMP annihilation cross section. Our results exclude the canonical thermal relic cross section ($3 \times 10^{-26} \, \text{cm}^3\text{s}^{-1}$) across the 10~GeV to 10~TeV mass range for $b\bar{b}$ and $W^+W^-$ channels, and up to $\sim$6~TeV for the $\tau^+\tau^-$ channel. Recasting these results into a
Galactic discovery reach, we demonstrate that
Fermi-LAT is sensitive to $10\,M_\odot$ mini-spikes even at distances surpassing the
Galactic Center, provided the WIMP mass is below 1~TeV. These findings establish a significant tension between the dynamical friction interpretation of orbital decay in these systems and the WIMP hypothesis, providing robust observational constraints on the coexistence of
primordial black holes and annihilating dark matter.
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Cosmology and Nongalactic Astrophysics
Testing the Coexistence of Dark Energy and Dark Matter with Late-time Observational Data
Shambel Sahlu, Andronikos Paliathanasis, Genly Leon et al. (+1 more)
We investigate the viability of a cosmological scenario with interacting dark sector, which can describe the coexistence between dark energy and dark matter. The model possesses an analytical solution for the Hubble function and we constrain the free parameters by applying the newly released
cosmic chronometers data (31 old data and 3 new data from DESI), the Baryonic Acoustic Oscillators from the Dark Energy Spectroscopic Instrument Survey (DESI DR2 BAO), along with Gamma-ray bursts (GRBs) and
Supernova catalogues (Pantheon Plus, Union3, and DES-Dovekie). We find that the coexistence model fits the data sets in a better way than the reference models - the $\Lambda$CDM and $w$CDM models. The analysis shows that the coexistence scenario can provide a cosmologically viable model for the description of the late-time acceleration of the universe. Nevertheless, for large
redshifts, the model has a similar behaviour to that of the $w$CDM model, as the introduction of the GRB data indicates in the statistical parameters. Finally, it is worth mentioning that the coexistence model provides a statistically smaller value for the $H_{0}$ parameter.
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All authors Shambel Sahlu, Andronikos Paliathanasis, Genly Leon, Amare Abebe
Earth and Planetary Astrophysics
Laplace-Legendre expansion of the planar planetary Hamiltonian
Aya Alnajjarine, Jacques Laskar and Federico Mogavero
We explore a hybrid expansion of the disturbing function in planetary dynamics that combines elements of the classical Laplace and Legendre developments. This formulation retains the structure of the Laplace expansion, but expresses the inverse of the mutual distance as a series whose terms keep an exact dependence on both the eccentricity and the semi-major axis ratio. We use it to construct the first-order secular
Hamiltonian of the planar 3-body problem, relevant for modeling the long-term
evolution of planetary systems. We assess the convergence of the new expansion numerically and compare it with that of the Laplace and Legendre series across a range of orbital configurations. The results show that the new expansion provides consistent performance across diverse dynamical regimes, bridging the domains of applicability of the two classical approaches.
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High Energy Astrophysical Phenomena
Singular Templates of Imaging Cherenkov Shower distribution (STOICS): A background estimation method for Very-High-Energy $\gamma$-ray observations
Ruo-Yu Shang, Karl Kosack and Brian Humensky
Analyses of Imaging Atmospheric Cherenkov
Telescope (IACT) data for extended $\gamma$-ray sources face the issue that the field of view does not offer sufficient regions for background estimations. In cases where the source angular size exceeds or occupies a significant part of the field of view, an independent background estimation method is necessary to carry out IACT analyses and to have a better understanding of the systematic uncertainties. The proposed new method utilizes Singular Value Decomposition to extract the low-dimension representations of the distribution of
cosmic-ray events in OFF runs and uses
cosmic-ray-like events in the ON runs to estimate the background of $\gamma$-like events. Using VERITAS archival data, we demonstrate that the new method is capable of providing reliable background modeling for observations across a wide range of observing conditions.
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Solar and Stellar Astrophysics
Stellar Wind of Components of Detached Binary Systems
A. V. Tutukov and A. V. Sobolev
The paper is devoted to the consideration of the role of the donor
stellar wind in the matter exchange between the components of detached binary systems. A classification of close binary systems with interacting components is proposed. A list of potential donors and accretors of such systems, including X-ray binary and symbiotic
stars, is given. Analytical tasks have been completed to evaluate the conditions and efficiency of interaction through the
stellar wind, a criterion was found for maintaining the self-induced
stellar wind of X-ray binaries, and a condition for the formation of an
accretion disk during
accretion of
stellar wind matter by a compact accretor. Three-dimensional gas dynamic models of component interaction are constructed for the five initial velocities of the
stellar wind using the example of Sco X-1 type systems. The simulation results are illustrated by pictures of streamlines, temperature distribution, and wind gas densities in the orbital and frontal planes. Model focusing of the donor wind flow by the accretor is confirmed by the observed phase X-ray light curve of Vela X-1.
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Instrumentation and Methods for Astrophysics
Geometric Search for Hawking Radiation from Nearby Primordial Black Holes
Shuo Xiao and Shuang-Nan Zhang
A nearby
primordial-black-hole (PBH) evaporation burst would produce a curved gamma-ray wavefront, leading to detectable departures from plane-wave inter-satellite delays. We introduce a purely
geometric method that combines imaging localizations with multi-spacecraft timing to determine the distance of a gamma-ray transient. Applied to Swift-localized short GRBs, the current sample shows no significant deviation from the plane-wave expectation, with the most constraining event reaching $1.2$ AU and already probing a meaningful
Solar-System-scale regime. Our analysis shows that direct distance measurements are achievable to $10^3$ AU scales with the current and near-future technical capabilities. Once a finite source distance is measured, the corresponding PBH mass and lifetime can be directly inferred. Future wide-field localization and long-baseline deep-space gamma-ray detectors could extend such searches to $10^5$ AU and beyond.
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Earth and Planetary Astrophysics
Color and Size Distributions of Small Jupiter Trojans
Fumi Yoshida, Tsuyoshi Terai and Keiji Ohtsuki
We conducted a two-band imaging survey observation using the Subaru
Telescope and its wide-field camera, Suprime-Cam, to study the visible colors and size distribution of Jupiter's Trojan asteroids. The survey covered an area around Jupiter's L4 Lagrange point totaling 9.2 square degrees. We detected 120 Trojan asteroids in this survey. From these Trojan asteroids, we extracted 44 unbiased samples with absolute magnitudes in the $g^\prime$ band ranging from 12.9 to 16.9 mag (corresponding to diameter ranges of approximately $\sim$3 - 16 km assuming an albedo of 0.05) and analyzed their $g^\prime - i^\prime$ color and size distributions. Large Jupiter Trojan asteroids are known to be classified into two color groups, ”red” and ”less red”. We found that such bimodality in the color distribution is absent for small Jupiter Trojan asteroids, which is consistent with previous studies. Previous studies have also shown that these two groups have different slopes in the magnitude distributions from each other, which was explained by conversion of red objects to less-red fragments through catastrophic disruptions. In contrast, we found that the size frequency distributions of our two sample groups divided by the color of $g^\prime - i^\prime$ = 0.7 (in AB magnitude) are quite similar. Our results can provide new insights into collisional
evolution of color and size distribution of small Jupiter Trojans.
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High Energy Astrophysical Phenomena
Diversity of Type Ia supernova optical light curves among different spectroscopic subclasses
R. B. Koshi, M. Doi, S. Sako et al. (+3 more)
Attempts to reveal the spectroscopic diversity of Type Ia
supernovae (SNe Ia) have led to subclassification schemes such as the Branch system, which classifies SNe Ia into four categories: core normal (CN), broad line (BL), cool (CL), and shallow silicon (SS). The physical origin of these spectroscopic differences, including progenitor channels, explosion mechanisms, or other parameters, however, remains unclear. Moreover, previous work has concentrated primarily on properties near peak luminosity, yielding limited insight into their behavior at later epochs. In this study, we compile $UBVRI$ photometry for 109 SNe Ia and construct the first set of average light curves for each Branch subgroup, spanning from pre-maximum through the late tail. We find pronounced diversity in the $I$-band, especially in the timing of the secondary maximum across subgroups and in the late-time decline of CL events. After correcting for light curve stretch, which reflects the combined influence of ${}^{56}$Ni and ejecta masses, we show that the secondary maximum is powered by Fe II recombination, and its timing is particularly sensitive to the amount of stable iron-group elements (IGEs) synthesized in the explosion. This implies an anti-correlation between the mass of stable IGEs and ${}^{56}$Ni: CL (and possibly BL) events have a larger mass ratio of IGEs/$^{56}$Ni resulting in earlier secondary maxima, while SS events have a smaller ratio and thus later secondary maxima. This trend is naturally explained within the near-$M_{\rm Ch}$ delayed-detonation scenario, whereas it is inconsistent with the positive correlation predicted by the sub-$M_{\rm Ch}$ double-detonation scenario. Finally, we show that stretch-corrected late-time slopes provide a practical diagnostic for CL events, likely linked to an emission feature around $7,200$ Angstroms.
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All authors R. B. Koshi, M. Doi, S. Sako, K. Maeda, M. Tanaka, N. Takanashi
Earth and Planetary Astrophysics
GEMS JWST: A sub-Solar metallicity atmosphere for giant planet TOI-5293Ab orbiting a rapidly changing M-dwarf
Shubham Kanodia, Caleb I. Cañas, Jacob Lustig-Yaeger et al. (+13 more)
The growing sample of
Giant Exoplanets around M-
dwarf Stars (GEMS) helps probe the extremes of
giant planet formation. Comparing the properties of this sample with their FGK counterparts can help us understand how
planet formation and migration depend on
stellar mass. We initiated a large Cycle 2 JWST transmission spectroscopy survey of seven GEMS. Here we present the atmospheric characterization using two JWST transits of TOI-5293Ab, a 0.5 $M_J$
planet orbiting an early M-
dwarf with a period of $\sim$ 3 days. The two NIRSpec/PRISM transits indicate the
planet is eclipsing a rapidly changing (heterogeneous)
stellar photosphere. We see that Visit 1 had heterogeneity crossings across the entire transit chord, rendering inferences from it to be unreliable. The Visit 1 spectrum exhibits a downward slope ${<1}$ $\mu$m suggestive of
stellar contamination from faculae. In contrast, for Visit 2 we are able to model the heterogeneity crossings and obtain a transmission spectrum free from
stellar contamination. We therefore limit our conclusions to a detailed analysis of Visit 2, and using
Bayesian free chemistry
retrievals, we find a low atmospheric
metallicity ($\log [\mathrm{M/H}] = -1.03^{+0.53}_{-0.44}$ $\times$
Solar) and slightly super-
solar C/O ratio ($1.23^{+2.94}_{-0.75}$). The
retrievals yield Bayes factors that indicate strong evidence for \ce{CH4} as well as low significance detections of \ce{CO2}, \ce{H2O}, \ce{NH3}. Finally, using thermal
evolution models we find that the radius of TOI-5293Ab is inflated above theoretical expectations ($\sim$ 1.07 $R_J$), despite it having an temperature of $\sim$ 700 K, and hence we were unable to constrain its bulk composition.
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All authors Shubham Kanodia, Caleb I. Cañas, Jacob Lustig-Yaeger, Giannina Guzmán Caloca, Nicole L. Wallack, Simon Müller, Ravit Helled, Knicole D. Colón, Ian Czekala, Megan Delamer, Te Han, Jessica Libby-Roberts, Anjali A. A. Piette, Kevin B. Stevenson, Gudmundur Stefansson, Johanna Teske
Instrumentation and Methods for Astrophysics
LenghuSky-8: An 8-Year All-Sky Cloud Dataset with Star-Aware Masks and Alt-Az Calibration for Segmentation and Nowcasting
Yicheng Rui, Xiao-Wei Duan, Licai Deng et al. (+9 more)
Ground-based time-domain observatories require minute-by-minute, site-scale awareness of cloud cover, yet existing all-sky
datasets are short, daylight-biased, or lack astrometric calibration. We present LenghuSky-8, an eight-year (2018-2025) all-sky imaging
dataset from a premier astronomical site, comprising 429,620 $512 \times 512$ frames with 81.2% night-time coverage,
star-aware cloud masks, background masks, and per-pixel altitude-azimuth (Alt-Az) calibration. For robust cloud
segmentation across day, night, and lunar phases, we train a linear probe on DINOv3 local features and obtain 93.3% $\pm$ 1.1% overall accuracy on a balanced, manually labeled set of 1,111 images. Using
stellar astrometry, we map each pixel to local alt-az coordinates and measure calibration uncertainties of approximately 0.37 deg at zenith and approximately 1.34 deg at 30 deg altitude, sufficient for integration with
telescope schedulers. Beyond
segmentation, we introduce a short-horizon nowcasting
benchmark over per-pixel three-class logits (sky/cloud/contamination) with four baselines: persistence (copying the last frame), optical flow, ConvLSTM, and VideoGPT. ConvLSTM performs best but yields only limited gains over persistence, underscoring the difficulty of near-term cloud
evolution. We release the
dataset, calibrations, and an open-source toolkit for loading, evaluation, and scheduler-ready alt-az maps to boost research in
segmentation, nowcasting, and autonomous observatory operations.
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All authors Yicheng Rui, Xiao-Wei Duan, Licai Deng, Fan Yang, Zhengming Dang, Zhengjun Du, Junhao Peng, Wenhao Chu, Umut Mahmut, Kexin Li, Yiyun Wu, Fabo Feng
Astrophysics of Galaxies
Unveiling an Hourglass-Shaped Magnetic Field toward IRDC G351.77-0.53
O. R. Jadhav, L. K. Dewangan, I. I. Zinchenko et al. (+5 more)
We present the SOFIA/HAWC+ 214 $\mu$m polarimetric observations toward the infrared dark cloud G351.77-0.53 (hereafter G351), complemented by existing multi-wavelength data sets. Infrared excess from the embedded sources indicate ongoing
star formation activity in the cloud. The G351 cloud hosts two prominent
star-forming clumps, i.e., c1 and c2. The plane-of-the-sky
magnetic field lines from Planck observations are predominantly oriented perpendicular to the filament's major axis.
Magnetic field orientations from SOFIA/HAWC+ 214 $\mu$m observations reveal distinct hourglass-shaped field configuration toward c1, while the field lines remain perpendicular to the rest of the filament. Using the Davis-Chandrasekhar-
Fermi method, we estimate a mean plane-of-the-sky
magnetic field strength of $\sim$147 $\pm$ 60 $\mu$G in the G351 filament, with values reaching $\sim$0.8 mG toward c1. The mass-to-flux ratio analysis indicates that the filament is magnetically transcritical, where the gravitational and
magnetic field energies are comparable. The hourglass-shaped
magnetic field observed toward c1 could result from magnetically regulated gravitational collapse, the
alignment of converging sub-filaments with the
magnetic field, or a combination of both processes. The energy budget analysis further indicates that
magnetic fields play an important role in governing the cloud's gas dynamics, followed by contributions from
turbulence and
gravity.
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All authors O. R. Jadhav, L. K. Dewangan, I. I. Zinchenko, Thushara G. S. Pillai, Patricio Sanhueza, A. K. Maity, Ram K. Yadav, Saurabh Sharma
Cosmology and Nongalactic Astrophysics
Perturbative Effects of Dark Matter Environments on Black Hole Shadows
Gabriel Gomez
Constructing spacetime solutions that describe black holes embedded in dark matter environments is a crucial step toward probing the properties of dark matter in the strong-field regime of
gravity. At present, however, there is no unique or systematic framework to model such configurations, and several commonly adopted approaches raise methodological ambiguities. Motivated by these challenges, we build upon a perturbative framework to describe deformations of static, spherically symmetric black holes induced by a surrounding dark matter distribution. Within this framework, we compute the leading-order corrections to both the
photon-sphere radius and the radius of the black hole shadow, assuming a generic dark matter
halo profile. We then apply the formalism to physically motivated density profiles, including the Hernquist and Navarro-Frenk-White models, obtaining closed-form analytical expressions for the perturbed metric functions and for the critical impact parameter in the Schwarzschild background. Using these results, we obtain quantitative estimates for the corresponding shadow deviations and find that they lie well beyond the current observational bounds set by Keck and VLTI measurements. As a consistency check, we further estimate the total dark matter mass enclosed within the orbital radius of the S2
star and show that it remains well below the $0.1\%$ upper limit reported by the
GRAVITY collaboration. Overall, this approach offers a systematic avenue to investigate perturbative effects of dark matter on black hole phenomenology, including potential implications for gravitational wave observations.
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High Energy Astrophysical Phenomena
Correlations Between kHz QPOs and Spectral Parameters from Time-Resolved Spectro-Temporal Analysis of 4U 1728-34
Kewal Anand, Ranjeev Misra, J. S. Yadav et al. (+1 more)
We present a time-resolved analysis of the persistent emission in 4U 1728–34 using AstroSat observations from 2016 to 2019. We detect kilohertz quasi-periodic oscillations (kHz QPOs) during all epochs, with centroid frequencies ranging from $\sim 350$ to $1180~\mathrm{Hz}$, although some detections are of lower significance ($< 3\sigma$). We model the simultaneous spectra from the Soft X-ray
Telescope and the Large Area X-ray Proportional Counter using a combination of an absorbed disk component (diskbb), a blackbody component (bbodyrad), a thermal Comptonization model (thcomp), and a broad Gaussian line. From the diskbb parameters, we estimate the
accretion rate and find that all observations fall into two
accretion regimes, namely AR1 and AR2, with
accretion rates of $\sim 3 \times 10^{16}~\mathrm{g\,s^{-1}}$ and $\sim 7 \times 10^{16}~\mathrm{g\,s^{-1}}$, respectively. Interestingly, we find that for AR1, the lower kHz QPO frequency ($\nu_{\mathrm{L}}$) is always $< 500~\mathrm{Hz}$, while for AR2 it is $\gtrsim 500~\mathrm{Hz}$. We found that the spectral index showed no clear correlation with $\nu_{\mathrm{L}}$. For AR1, the coronal electron temperature ($kT_{\mathrm{e}}$) and optical depth ($\tau$) are $\sim 10~\mathrm{keV}$ and $\sim 5$, respectively. In contrast, for AR2, $kT_{\mathrm{e}}$ decreases to $\sim 3~\mathrm{keV}$ and $\tau$ increases to $\sim 12$, showing correlations with $\nu_{\mathrm{L}}$, with Spearman's rank correlation coefficients of $-0.78$ and $0.71$, respectively. The transition of the spectral parameters at $\nu_{\mathrm{L}} \sim 500~\mathrm{Hz}$ indicates the existence of a critical QPO frequency governed or influenced by the
accretion state of the source.
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All authors Kewal Anand, Ranjeev Misra, J. S. Yadav, Pankaj Jain
Solar and Stellar Astrophysics
The role of ambipolar heating in the energy balance of solar prominences
Llorenç Melis and Roberto Soler
Solar prominence threads are typically located around
magnetic dips, where cold and dense
plasma is suspended against
gravity in the hot corona thanks to the upward
magnetic force. Because prominences are partially ionized, ambipolar
diffusion can deposit part of the energy of their non-force-free
magnetic field into the
plasma. This ambipolar heating may therefore play a role in the energy balance of prominences. In this proof-of-concept work, we explore the effect of ambipolar
diffusion in one-dimensional models that satisfy both mechanical
equilibrium and energy balance. The
magnetic configuration is based on the classic Kippenhahn-Schlüter model, incorporating a sheared
magnetic field. The temperature profile along the
magnetic field is computed numerically by balancing radiative losses, thermal conduction, and ambipolar heating. The resulting models consistently consist of a cold, dense, partially ionized thread with prominence core conditions, a very thin prominence-corona transition region, and an extended, hot, fully ionized region with coronal conditions. In addition to providing heating that partly compensates for radiative losses, ambipolar
diffusion also gives rise to stationary flows associated with the gravitational drainage of neutrals in the partially ionized region. We investigate how the length of the cold threads depends on the central temperature, central pressure,
magnetic field strength, and shear angle, and show that thread lengths compatible with observations are obtained for realistic values of these parameters. Therefore, we demonstrate that ambipolar
diffusion plays a relevant role in this simple configuration, indicating that this effect should be incorporated into more elaborate multi-dimensional models and simulations.
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High Energy Astrophysical Phenomena
Detectability of Nearby Binary Neutron Stars with Future sub-mHz Gravitational Wave Missions
Zhiwei Chen, Youjun Lu, Yuchao Luo et al. (+4 more)
Binary
neutron stars (BNSs) are one of the most important gravitational wave (GW) sources, which provide key insights to
evolution of massive binary
stars and
nuclear physics. Beyond
Laser Interferometer Space
Antenna (LISA), Taiji, and Tianqin missions, proposed concepts for next generation space-based GW observatories, including LISAmax, Folkner, and eASTROD, aim to explore the sub-millihertz (mHz) to microhertz ($\mu$ Hz) frequency band. Because the proposed designs substantially suppress low-frequency noise, these detectors are expected to outperform LISA, Taiji, and Tianqin in detecting eccentric
Galactic BNS systems. In this paper, we estimate the detectability of nearby inspiraling BNSs using future sub-mHz GW detectors. By utilizing compact binary population synthesis simulations to generate mock BNS samples and estimate their signal-to-noise ratios (SNRs) correspondingly for each GW detector over an observation period of $5-10$\,years, we find that LISAmax may detect $\sim 520-900$
Galactic BNSs, whereas Folkner and eASTROD may detect $\sim 780-1370$
Galactic BNSs. Notably, LISAmax excels in detecting highly eccentric systems $(e>0.90)$ owing to its higher sensitivity at relatively higher sub-mHz frequencies. We further identify seven observed
radio BNSs as viable candidates for validation, in particular J0737-3039, which reaches an SNR of $\sim 100$. The expected detection number of LMC inspiraling BNSs is about $\sim 4-18$ for these sub-mHz detectors over an observation period of $5-10$\,years, while detecting inspiraling BNSs in SMC is challenging. This study highlights the significant potential of future sub-mHz GW missions in unraveling BNS formation and
evolution physics.
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All authors Zhiwei Chen, Youjun Lu, Yuchao Luo, Jihui Zhang, Xiao Guo, Jifeng Liu, Wei-Tou Ni
Instrumentation and Methods for Astrophysics
High-Precision Photometry with a scientific CMOS Camera: II On-Sky Testing of the Marana camera at the NGTS facility
Ioannis Apergis, Daniel Bayliss, Paul Chote et al. (+24 more)
Modern scientific CMOS cameras offer very fast readout speeds and low read noise. In this study, we evaluate the performance of the Andor Marana CMOS camera through on-sky testing carried out at the NGTS facility at the ESO Paranal Observatory in Chile. We mount the Marana camera to an NGTS
telescope, and conduct photometric observations of bright
stars. In particular, we target transit events around eight known bright
exoplanet host
stars. Simultaneous observations are carried out using an existing Andor iKon-L CCD camera on a neighbouring NGTS
telescope. This allows for a direct comparison of the photometric precision between the CMOS and CCD cameras. We find that the Marana CMOS exhibits a similar level of photometric performance to the CCD camera, achieving 500\,ppm at a 30-minute timescale for a T $=10$\,mag
star. Although the CCD has a slightly better
quantum efficiency over the NGTS filter range (520-890\,nm), we find that the faster readout speed of the CMOS compared to the CCD means that the CMOS camera detects 20\,% more
photons per unit time for a
solar-type
star in our standard 10\,s exposure time operation mode. This results in the CMOS performing slightly better photometry in the
photon-limited regime. We conclude that modern CMOS cameras, such as the Marana, are very well-suited for astronomical time-series photometry applications.
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All authors Ioannis Apergis, Daniel Bayliss, Paul Chote, James McCormac, Peter J. Wheatley, Morgan A. Mitchell, Jorge Fernández Fernández, Sam Gill, Edward M. Bryant, Toby Rodel, Leonidas Asimakoulas, David R. Anderson, James A. Blake, Sara L. Casewell, Fintan Eeles-Nolle, Faith Hawthorn, James S. Jenkins, Monika Lendl, Isobel S. Lockley, Maximiliano Moyano, Sean M. O'Brien, Suman Saha, Alexis M. S. Smith, Philip G. Steen, Jose I. Vines, Richard G. West, Tafadzwa Zivave
Instrumentation and Methods for Astrophysics
Explainable machine learning workflows for radio astronomical data processing
S. Yatawatta, A. Ahmadi, B. Asabere et al. (+3 more)
Radio astronomy relies heavily on efficient and accurate processing pipelines to deliver science ready data. With the increasing data flow of modern
radio telescopes, manual configuration of such data processing pipelines is infeasible. Machine learning (ML) is already emerging as a viable solution for automating data processing pipelines. However, almost all existing ML enabled pipelines are of black-box type, where the decisions made by the automating
agents are not easily deciphered by astronomers. In order to improve the explainability of the ML aided data processing pipelines in
radio astronomy, we propose the joint use of fuzzy rule based inference and deep learning. We consider one application in
radio astronomy, i.e., calibration, to showcase the proposed approach of ML aided decision making using a Takagi-Sugeno-Kang (TSK) fuzzy system. We provide results based on simulations to illustrate the increased explainability of the proposed approach, not compromising on the quality or accuracy.
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All authors S. Yatawatta, A. Ahmadi, B. Asabere, M. Iacobelli, N. Peters, M. Veldhuis
Instrumentation and Methods for Astrophysics
Optimising the FRB Search Pipeline for the Northern Cross Radio Telescope
Hayley Camilleri, Alessio Magro, Andrea Geminardi et al. (+8 more)
FRB search pipelines are being developed to operate under strict real-time constraints while maintaining sensitivity to short-duration transient signals. In incoherent dedispersion based pipelines such as Heimdall, apart from observation bandwidth and number of beams, detection performance and computational throughput are strongly dependent on the choice of processing parameters, which are often selected heuristically. In this work, we present a systematic evaluation of key dedispersion and matched filtering parameters and quantify their impact on both detection accuracy and runtime performance. A controlled synthetic injection framework is developed in which artificial FRB pulses with known DMs, SNRs, and pulse widths are embedded into realistic filterbank data containing instrumental noise representative of observations from the Northern Cross
radio telescope. Using this framework, a grid of Heimdall configurations is explored, spanning DM tolerance, boxcar filter width, and processing gulp size. Detection performance is assessed by comparing recovered and injected signal properties, while computational performance is evaluated through end-to-end processing time measurements. The results reveal clear trade-offs between sensitivity and throughput across parameter choices. We identify an empirically optimal configuration that provides burst recovery while maintaining processing speeds exceeding real-time requirements. While the specific optimal parameters are derived for the Northern Cross, the methodology and findings are broadly applicable to any real-time transient detection pipeline employing matched-filtering and dedispersion, and are particularly relevant for low-frequency
radio telescopes with similar observing configurations. These findings demonstrate the value of data-driven parameter evaluation for improving the performance of real-time transient detection pipelines.
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All authors Hayley Camilleri, Alessio Magro, Andrea Geminardi, Giovanni Naldi, Gianni Bernardi, Luca Bruno, Valentina Cesare, Francesco Fiori, Davide Pelliciari, Maura Pilia, Matteo Trudu
High Energy Astrophysical Phenomena
Time-Lag properties associated with LFQPO in X-ray variability classes of GRS 1915+105: Findings from AstroSat
Prajjwal Majumder, Broja G. Dutta and Anuj Nandi
We present a comprehensive analysis of Low Frequency Quasi-periodic Oscillation (LFQPO) associated time-lags in the persistently variable black hole binary GRS 1915+105 using 441 ks of AstroSat observations from March 2016 to March 2019. LFQPO frequency ($1.38-7.38$ Hz) are detected across the $\theta$, $\beta$, $\rho$, and $\chi$ classes, with the $\chi$ class further subdivided into $\chi_1$, $\chi_2$, $\chi_3$, and $\chi_4$ based on spectro-temporal characteristics. Class transitions occur on timescales of a few hours, appearing either as a simultaneous increase in X-ray count rate and QPO frequency, or vice versa, indicating rapid changes in the
accretion flow geometry. The $\text{rms}_{\rm QPO}$ increases with QPO frequency up to $\sim 3.4$ Hz and declines at higher frequencies, a trend similar to RXTE observations, where peak occurred at $\sim 2$ Hz. Spectro-temporal correlations reveal that increasing $F_{\rm Comp}$ drives higher $\text{rms}_{\rm QPO}$ and decreases the soft-lag magnitude, while $\nu_{\rm QPO}$ and $\Gamma$ also decline, suggesting that the observed time lag may result from the combined effects of multiple physical mechanisms. The consistent increase of $\text{rms}_{\rm QPO}$ with $F_{\rm Comp}$ provides clear evidence that modulated Comptonized
photons enhance the rms power ($\text{rms}_{\rm QPO}$). Moreover, the soft-lag ($1.59-13.49$ ms) observed across all QPO frequencies, without the sign reversal at $\sim$ 2 Hz observed in RXTE observations, is interpreted within the framework of a dynamical
accretion disk model around the black hole.
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High Energy Astrophysical Phenomena
Resonant scattering at the center of the galaxy cluster PKS 0745-191 with XRISM
Keita Tanaka, Megan Eckart, Kotaro Fukushima et al. (+11 more)
We report evidence for the resonant scattering effect at the center of the
galaxy cluster PKS 0745-191 with XRISM. We analyzed XRISM/Resolve commissioning-phase observations of the distant cluster PKS 0745-191 (z = 0.103) with a 54 ks exposure. The gain drift was corrected using the onboard modulated X-ray source (MXS), and spectra were extracted from all pixels well illuminated by MXS, the core region (four central pixels, about 100 kpc), and the surrounding region. A single-temperature collisional ionization
equilibrium (CIE) model fits the full field-of-view spectrum with kT about 6 keV and a turbulent velocity of about 120 km/s. From the core (r < 50 kpc) spectrum, we detect about 22 percent suppression of the Fe XXV He-alpha resonance (w) line relative to the CIE prediction. We performed Monte Carlo simulations to calculate the resonant scattering (RS) effect using radial profiles from Chandra data. The RS-inferred
turbulence agrees with that inferred from Resolve line broadening, demonstrating that RS provides an independent and consistent constraint on ICM
turbulence. These results highlight the potential of XRISM/Resolve for
turbulence studies in
galaxy clusters.
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All authors Keita Tanaka, Megan Eckart, Kotaro Fukushima, Liyi Gu, Kyoko Matsushita, Brian McNamara, François Mernier, Ikuyuki Mitsuishi, Frederick S. Porter, Kosuke Sato, Makoto Sawada, Kazunori Suda, Irina Zhuravleva, Noriko Y. Yamasaki
Cosmology and Nongalactic Astrophysics
Cosmological hydrodynamical simulations of clustering dark energy with Nefertiti
Linda Blot, Théo Gayoux, Fabian Schmidt et al. (+2 more)
We present the first cosmological simulations that consistently include nonlinear clustering dark energy evolved as a fluid with the numerical hydrodynamics code Nefertiti. Dark energy perturbations become fully nonlinear on small scales, developing significant density fluctuations without exhibiting the catastrophic instabilities previously reported. We show results for the density distribution, power spectrum, and
halo profiles of dark energy. Clustering dark energy contributes to the total density perturbation at the $\sim 10\%$ level inside and around massive
halos in our simulations with constant $w=-0.9$, a significant potential signal for
lensing and dynamical probes. These simulations pave the way to robust constraints on the speed of sound of dark energy perturbations from large-scale structure data.
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All authors Linda Blot, Théo Gayoux, Fabian Schmidt, Pier Stefano Corasaniti, Bastien de Ligondes
High Energy Astrophysical Phenomena · Cross-listed from nucl-th
Jian Zhou, Junbo Pang, Hong Shen et al. (+1 more)
We investigate
nuclear pasta phases appearing in hot
neutron-
star matter based on the compressible
liquid-drop model, where the matter consists of a dense
liquid phase and a dilute gas phase separated by a sharp interface. The surface tension is calculated self-consistently from the Thomas-
Fermi approximation, and it depends on temperature and isospin asymmetry. We employ relativistic mean-field models with different
symmetry energy slopes to describe
nuclear interactions. It is found that the TM1e model with a small
symmetry energy slope of $L=40$ MeV predicts various pasta shapes at low temperatures, while the TM1 model with $L=110.8$ MeV yields only the droplet configuration up to the crust-core transition density. We examine the occurrence and influence of pasta phases in proto-
neutron stars with a constant
entropy per
baryon. These pasta phases may occur in the inner crust with a thickness of about $1.2$ km, playing an important role in the thermal
evolution of the
star.
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All authors Jian Zhou, Junbo Pang, Hong Shen, Jinniu Hu
Astrophysics of Galaxies
Evolution of fractality in centrally concentrated young clusters
Almat Akhmetali, Adilkhan Assilkhan, Mordecai-Mark Mac Low et al. (+6 more)
We investigate the structural
evolution of young
star clusters forming within centrally concentrated molecular clouds. Our simulations use the Torch framework, which integrates the FLASH magnetohydrodynamics code with the AMUSE environment, enabling a self-consistent treatment of gas dynamics,
star formation,
stellar evolution, radiative transfer, and gravitational interactions. We quantify cluster structure using the $Q$ parameter for fractality and compute fractal dimensions via two methods: box-counting and correlation dimension. Our results show that clusters generally inherit fractal substructure from their parental clouds, which is typically erased within $\sim 2.5\,t_\mathrm{ff}$ through dynamical relaxation. Massive
stars can induce the formation of secondary subclusters via feedback, with outcomes strongly dependent on
stellar mass and formation timing. Interactions among subclusters, including mergers and dispersal, can extend fractal structure beyond $4\,t_\mathrm{ff}$. We also find systematic correlations between the fractality parameter $Q$ and the fractal dimension: fractality is positively correlated with both the correlation and box-counting dimensions, with the correlation dimension exhibiting a stronger correlation. These results demonstrate how
stellar feedback and internal dynamics jointly shape the measurable fractal properties of embedded
star clusters.
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All authors Almat Akhmetali, Adilkhan Assilkhan, Mordecai-Mark Mac Low, Nurzhan Ussipov, Marat Zaidyn, Ernazar Abdikamalov, Alison Sills, Xiaoying Pang, Bekdaulet Shukirgaliyev
High Energy Astrophysical Phenomena
HESS J1832-085: evidence for a new gamma-ray binary candidate
Agnibha De Sarkar and Tanuman Ghosh
The
Galactic plane survey conducted by the High Energy Stereoscopic System (H.E.S.S.) has revealed numerous teraelectronvolt (TeV) sources, many of which remain unidentified. HESS J1832-085 is a point-like TeV source lacking a confirmed multiwavelength (MWL) counterpart. In this paper, we present evidence supporting a gamma-ray binary interpretation of HESS J1832-085. Archival X-ray observations were examined to search for a counterpart and to characterize its spectrum and potential variability. We further analyzed $\sim$17.3 yrs of
Fermi-LAT data between 1 and 300 GeV to establish a possible gigaelectronvolt (GeV) counterpart of HESS J1832-085. We also examined archival NIR images from the UKIRT Infrared Deep Sky Survey (UKIDSS) and the Two Micron All Sky Survey (2MASS), together with 2MASS catalog photometry. The broadband emission was interpreted using models commonly applied to gamma-ray binaries. A potential X-ray counterpart is identified in archival X-ray data, exhibiting a hard, absorbed spectrum and moderate variability. We also identify a tentative GeV gamma-ray excess spatially consistent with HESS J1832-085 and the proposed X-ray counterpart. We further identified a candidate
stellar counterpart in both the UKIDSS and 2MASS images, located in close spatial proximity to the X-ray counterpart. The adopted illustrative binary radiative model broadly reproduces the X-ray and TeV emission, but fails to explain the emission from the tentative GeV excess. Our results support HESS J1832-085 as a promising gamma-ray binary candidate, motivating dedicated MWL follow-up observations to confirm the source nature.
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High Energy Astrophysical Phenomena
A Candidate Open Cluster Pulsar: Timing Analysis of PSR J1922+3745 in NGC 6791
Xiao-Jin Liu, Ralph P. Eatough, Zhichen Pan et al. (+15 more)
PSR J1922+3745 was recently identified as a
radio pulsar toward the old open cluster NGC 6791, raising the prospect of the first
pulsar associated with an open cluster. We report FAST follow-up observations that yield a phase-coherent timing solution, a precise position, a measurement of the
spin-down rate and the
pulsar's polarization properties. PSR J1922+3745 is consistent with an isolated slow
pulsar with a characteristic age of 7.8 Myr, comparable to the small population of long-period
pulsars found in globular clusters. Motivated by the potential cluster association, we re-process deeper searches of the NGC 6791 field at higher sensitivity but detect no additional
pulsars. We also assess whether HI absorption spectroscopy can provide a useful distance constraint and find that such measurements are unlikely to be constraining with currently available sensitivity. Consequently, existing evidence does not yet establish membership in NGC 6791. Further deep searches for additional
pulsars with similar dispersion measures in the cluster field will likely be the most direct path to confirming a physical association.
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All authors Xiao-Jin Liu, Ralph P. Eatough, Zhichen Pan, Matthew Bailes, Wei-Cong Jing, Yong-Sheng Wang, Xujia Ouyang, Yong Zhang, Rahul Sengar, Jianping Yuan, Na Wang, Weiwei Zhu, Peng Jiang, Lei Qian, Lu Zhou, He Gao, Zong-Hong Zhu, Xing-Jiang Zhu