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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 17 November

Instrumentation and Methods for Astrophysics

Thermal infrared characterization of spatially unresolved resident space objects: Prospects from analytical two-component modeling

Stephen Catsamas, Sarah Caddy, Michele Trenti et al. (+5 more)

In this work we investigate the potential of a thermal infrared (IR) space telescope to remotely characterize the component temperatures of a satellite. With the rapid increase in the number of objects launched in recent years, the ability to detect, track, identify and determine the intent of satellites has become of increasing importance. Spectral modeling of satellites from multi-wavelength photometry in the thermal IR is a technique that has the potential to derive information about the temperature and operational status of a satellite in orbit, without the requirement to spatially resolve the target. Previous work has focused on determination of a single/effective temperature for a Resident Space Objects (RSOs) - such as satellites, asteroids, debris and rocket bodies - from remote observations, obtaining mixed results in terms of ability to classify objects. To progress, we explore a two-greybody component spectral model. Using this analytical model, we investigate which temperature characteristics may be identified from unresolved multi-wavelength photometric observations as a function of the signal-to-noise ratio, under the assumption of Poisson noise-dominated data. With this instrument-agnostic framework, we then quantify the potential of this model to discriminate between RSOs with a single temperature (e.g. natural rocks) versus human-made satellites with a chassis and deployed solar panels where significant component temperature differences exist under typical orbital configurations. Last, we comment on promising prospects of this model for applications to existing and future space telescope observations to characterize RSOs from spatially unresolved photometry
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All authors Stephen Catsamas, Sarah Caddy, Michele Trenti, Benjamin Metha, Simon Barraclough, Robert Mearns, Airlie Chapman, Rachel Webster

Astrophysics of Galaxies

AGN feedback in merging galaxies with a SMUGGLE multiphase ISM

Aneesh Sivasankaran, Laura Blecha, Paul Torrey et al. (+6 more)

We study fast nuclear winds driven by Active Galactic Nucleus (AGN) feedback in merging galaxies using high-resolution hydrodynamics simulations. We use Stars and MUltiphase Gas in GaLaxiEs (SMUGGLE) to explicitly model the multiphase interstellar medium (ISM) and employ sub-grid dynamical friction for massive black holes (BHs). Furthermore, we use a super-Lagrangian refinement scheme to resolve AGN feedback coupling to the ISM at $\sim10-100\,$pc scales. By comparison between merging and isolated galaxies, with and without AGN feedback, we identify trends in the complex interplay between dynamics, BH fueling and feedback, and star formation and feedback. We consider three galaxy types: Milky Way analogs, Sbc-type galaxies, and Small Magellanic Cloud (SMC) analogs. The synergy between AGN feedback and merger dynamics is strongest in the Milky Way-like mergers, where the AGN winds are energetically dominant and entrain more gas when the initially thin disks become thick and amorphous during the merger. In contrast, the merger of thicker, vigorously star-forming Sbc galaxies is not strongly impacted by AGN feedback until star formation declines in the post-merger phase. Finally, while the sub-grid dynamical friction prescription effectively retains BHs in galactic nuclei during more massive mergers, the clumpy multiphase ISM induces significant wandering of low-mass BHs $\mathrm{(<10^5M_\odot)}$ in the shallow potentials of the SMC-like galaxies. These low-mass BHs wander at distances $\gtrsim 2$ kpc from the galactic center, yielding negligible BH accretion and feedback. This has implications for LISA event rates and present a further challenge to understanding the rapid growth of $z\sim7-10$ quasars discovered by JWST.
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All authors Aneesh Sivasankaran, Laura Blecha, Paul Torrey, Luke Zoltan Kelley, Aklant Bhowmick, Mark Vogelsberger, Lars Hernquist, Federico Marinacci, Laura V. Sales

High Energy Astrophysical Phenomena

Helical Magnetic Field in the Acceleration–Collimation Zone of the M87 Jet

Jongho Park, Kazuya Takahashi, Kenji Toma et al. (+10 more)

Relativistic jets from supermassive black holes are expected to be magnetically launched and guided, with magnetic energy systematically converted to bulk kinetic energy throughout an extended acceleration-collimation zone (ACZ). A key prediction of magnetohydrodynamic (MHD) models is a transition from poloidally dominated fields near the engine to toroidally dominated fields downstream, yet direct tests within the ACZ are hampered by weak polarization and strong Faraday rotation. We report quasi-simultaneous, high-sensitivity, multifrequency very long baseline interferometric polarimetry of M87 spanning 1.4-24.4GHz. We present high-fidelity, Faraday rotation-corrected maps of intrinsic linear polarization that continuously resolve the ACZ in the de-projected distance range of ~9e3 to ~3.6e5 gravitational radii from the black hole. The maps reveal pronounced north-south asymmetries in fractional linear polarization and electric vector position angle (EVPA), peaking in the inner ACZ at a projected distance of ~20mas along the jet and remaining prominent out to ~100mas. These signatures are best reproduced by models with a large-scale, ordered helical field that retains a substantial poloidal component-contrary to the rapid toroidal dominance expected under steady, ideal MHD. This tension implies ongoing magnetic dissipation that limits toroidal buildup over the ACZ. The handedness of the helix provides an independent constraint on the black hole's spin direction, supporting a spin vector oriented away from the observer, consistent with the orientation inferred from horizon-scale imaging. Farther downstream, the asymmetries diminish, and the EVPA and fractional polarization distributions become more symmetric; we tentatively interpret this as evolution toward a more poloidally dominated configuration, while noting current sensitivity and dynamic-range limits.
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All authors Jongho Park, Kazuya Takahashi, Kenji Toma, Kazuhiro Hada, Masanori Nakamura, Hung-Yi Pu, Keiichi Asada, Paul T. P. Ho, Motoki Kino, Tomohisa Kawashima, Minchul Kam, Kunwoo Yi, Ilje Cho

Earth and Planetary Astrophysics

Orbit Elements from Kepler Solutions in Projective Coordinates

Joseph T.A. Peterson, Manoranjan Majji and John L. Junkins

Closed-Form Kepler solutions in projective coordinates are used to define a corresponding set of eight orbit elements and obtain their governing equations for arbitrarily-perturbed two-body dynamics. The elements and their dynamics are singularity-free in all cases besides rectilinear motion (when angular momentum vanishes). The classic J2-perturbed two-body problem is developed and used for numerical verification.
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Solar and Stellar Astrophysics

SN 2016iog: A fast declining Type II-L supernova with an ultra-faint tail, persistently interacting with circumstellar material

Z.-H. Peng, S. Benetti, Y.-Z. Cai et al. (+26 more)

We present optical photometric and spectroscopic observations of the rapidly declining Type IIL supernova (SN) 2016iog. SN 2016iog reached its peak $\sim$ 14 days after explosion, with an absolute magnitude in the $V$ band of $-18.64 \pm 0.15$ mag, followed by a steep decline of $8.85 \pm 0.15$~mag~(100\,d)$^{-1}$ post-peak. Such a high decline rate makes SN~2016iog one of the fastest declining Type~IIL SNe observed to date. The rapid rise in the light curve, combined with the nearly featureless continuum observed in the spectrum at +9.3 days, suggests the presence of interaction. In the recombination phase, we observed broad H$\alpha$ lines that persist at all epochs. In addition, the prominent double-peaked H$\alpha$ feature observed in the late-time spectrum (+190.8 days) is likely attributable either to significant dust formation within a cool dense shell or to asymmetric circumstellar material. These features suggest the presence of sustained interaction around SN~2016iog. We propose that the observed characteristics of SN~2016iog can be qualitatively explained by assuming a low-mass H-rich envelope surrounding a red supergiant progenitor star with low-density circumstellar material.
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All authors Z.-H. Peng, S. Benetti, Y.-Z. Cai, A. Pastorello, G. Valerin, A. Reguitti, A. Fiore, Q.-L. Fang, Z.-Y. Wang, M. Berton, L. Borsato, E. Cappellaro, E. Congiu, N. Elias-Rosa, V. Granata, J. Isern, G. La Mura, P. Ochner, R. Raddi, G. Terreran, L. Tomasella, M. Turatto, S.-Y. Yan, S.-P. Pei, C.-Y. Wu, S. Zha, X.-F. Wang, B. Wang, Y. Pan

Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Efficient Reconstruction of Matched-Filter Signal-to-Noise Ratio Time Series from Nearby Templates for Compact Binary Coalescences Searches

Yasuhiro Murakami, Tathagata Ghosh and Soichiro Morisaki

We present a method for efficiently searching long-duration gravitational wave signals from compact binary coalescences (CBCs). The approach exploits the smooth frequency-domain behavior of ratios between neighboring waveform templates. The matched-filter signal-to-noise ratio (SNR) time series of a data segment is first computed for a reference template, and the SNRs of nearby templates are then reconstructed by convolving this reference SNR time series with the ratio waveforms, defined as the frequency-domain ratios between the reference and neighboring templates. The computational speedup arises because the ratio waveforms can be safely truncated: they are significant only over a short interval approximately equal to the duration difference between the templates. Storing these truncated ratio waveforms is practical and enables additional efficiency gains, in contrast to storing full templates, which is generally infeasible for long-duration, low-mass signals. We demonstrate the efficacy of the method with mock non-spinning CBC injections in the $1-3~M_\odot$ range. The reconstructed SNR time series agrees with that obtained from standard matched filtering to an accuracy of $O(10^{-4})$, while the relative computational cost is reduced by $\gtrsim 25\%$. With a truncation threshold of $10^{-3}$ applied to the ratio waveform amplitudes, the storage requirement is reduced by a factor of $\sim 60$ relative to storing the full template bank.
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Astrophysics of Galaxies

Near-infrared [P II] and [Fe II] line mapping of Galactic supernova remnants

Takuma Kokusho, Yuki Katsurada, Yong-Hyun Lee et al. (+7 more)

Phosphorus (P) is one of the key ingredients for life, yet its origins in galaxies remain poorly understood. In order to investigate the production of P by supernovae, we performed near-infrared (IR) [P II] and [Fe II] line mapping of 26 Galactic supernova remnants (SNRs) with the Infrared Survey Facility and Kanata telescopes, using the narrow-band filters tuned to these lines. By combining our data with archival [Fe II] maps from UKIRT, we detected both the [P II] and [Fe II] emissions in five SNRs, only the [Fe II] emission in 15 SNRs, and no line emissions in the remaining six. Using the observed [P II]/[Fe II] ratios and upper limits for non-detections, we derived the P/Fe abundance ratios, which vary by up to two orders of magnitude among our sample SNRs. This suggests that the production rate of P and/or the degree of dust destruction may differ from remnant to remnant, the latter being due to the fact that P is volatile while Fe is mostly locked in dust grains. We used the mid- and far-IR maps to examine the dust content for the five SNRs where both the line emissions are detected. As a result, we find that high P/Fe abundance ratios in the northern and southeastern regions of Cassiopeia A and the Crab Nebula, respectively, are not likely due to dust destruction but may reflect an asymmetric ejection of P during supernova explosions. In the Crab Nebula, it is also possible that near-IR [Ni II] emission contaminates the observed flux in the southeastern region, suggesting that the Ni/Fe abundance ratio, rather than the P/Fe abundance ratio, is relatively high in this part of the remnant.
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All authors Takuma Kokusho, Yuki Katsurada, Yong-Hyun Lee, Bon-Chul Koo, Takahiro Nagayama, Hidehiro Kaneda, Koji S. Kawabata, Tatsuya Nakaoka, Ho-Gyu Lee, Rommy L.S.E. Aliste Castillo

Sunday 16 November

High Energy Astrophysical Phenomena

The Cosmic Star Formation History: Insights from Kilonova-Associated Gamma-Ray Bursts

Qin-Mei Li, Qi-Bin Sun, Sheng-Bang Qian et al. (+2 more)

The origin of the Universe and its material content remains one of the most fundamental questions in science. Gamma-ray bursts (GRBs), with their extreme luminosities and high-redshift detectability, provide a unique window into the history of cosmic formation and chemical evolution. Consequently, the GRB formation rate (FR) has been employed to trace the star formation rate (SFR) across cosmic time. GRBs are conventionally classified into long and short categories (lGRBs and sGRBs) based on their $ T_{90} $ duration. sGRBs are widely employed as tracers of the delayed SFR, owing to their origin linked to the inspiral timescales of compact binary systems. However, some studies suggest that the detection of supernova-associated sGRBs may indicate potential contamination by core-collapse events. In this work, we move beyond the $ T_{90} $ classification and focus exclusively on GRBs with confirmed kilonova signatures, which provide unambiguous evidence of binary compact star mergers, to reassess their connection with the delayed SFR. Through analysis of a kilonova-associated GRB (KN/GRBs) sample, we find that even within this robust subset, the KN/GRB FR displays a trend contrary to that of the delayed SFR at low redshifts ($ z < 1 $). This result challenges the conventional theory by indicating that low-redshift KN/GRBs may not accurately trace the delayed SFR, independent of core-collapse contamination, while further validation with larger KN/GRB samples is essential to determine the reliability of compact binary mergers as probes of delayed SFR.
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All authors Qin-Mei Li, Qi-Bin Sun, Sheng-Bang Qian, Si-Yuan Zhu, Fu-Xing Li

Earth and Planetary Astrophysics · Cross-listed from physics.hist-ph

The Great January Comet of 1910 (C/1910 A1): A Key Opportunity Missed by New Zealand Astronomers

John Drummond, Wayne Orchiston, Carolyn Brown et al. (+1 more)

C/1910 A1 was one of the Great Comets of the twentieth century. Although it was widely observed from the Northern Hemisphere, it was first discovered by observers south of the Equator. The comet arrived just months before the widely anticipated apparition of Comet 1P/Halley and was significantly more spectacular. As a result, the two comets were confused, and many who, in later years, talked about how prominent Comet 1P/Halley was in 1910 were often remembering C/1910 A1. In this paper, we present the results of a detailed search through historical records and media publications in Aotearoa / New Zealand, to investigate how extensively C/1910 A1 was observed from New Zealand. We compare our results with observations reported for Comet 1P/Halley later in 1910, finding that surprisingly few observations of C/1910 A1 were made by New Zealand observers. We discuss cases where the comet was misidentified as being an early sighting of 1P/Halley and compare the observations made in New Zealand with international observations/records/accounts. We find that, although the Great January Comet of 1910 was observed from New Zealand, it was witnessed by few compared to other parts of the world, meaning that the apparition of C/1910 A1 was something of a missed opportunity for New Zealand astronomers.
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All authors John Drummond, Wayne Orchiston, Carolyn Brown, Jonathan Horner

Solar and Stellar Astrophysics

Modeling stellar convective transport with plumes : II. Transport Properties of Locally and Non-locally driven Convection

Youhei Masada, Tomoya Takiwaki and Nobumitsu Yoko

We perform three-dimensional hydrodynamic simulations of two idealized regimes of stellar convection: a cooling-driven model (Model C) and an entropy-gradient-driven model (Model S). The two regimes exhibit striking contrasts: while Model S develops large, relatively stationary eddies excited at depth, Model C is dominated near the surface by intermittent plume-like downflows that produce broad non-Gaussian velocity distributions and a turbulent energy flux that exceeds Model S by nearly an order of magnitude in the upper convection zone. Conventional gradient-diffusion (GD) closures reproduce the transport in Model S but significantly underestimate it in Model C, demonstrating that plume-driven convection lies beyond the scope of local, gradient-based models. To address this, we introduce a Time-Space Double Averaging (TSDA) method that extracts coherent fluctuations, yielding a diagnostic variable $\tilde{\boldsymbol{u}}$ that peaks where the flux is largest. Building on this insight, we propose a modified GD closure in which the turbulent diffusivity is corrected by a plume-mediated term, achieving quantitative agreement with simulation results. Although the closure requires a calibrated model parameter and a careful choice of the averaging window, it provides a physically transparent framework that links coherent plume dynamics to mean-field transport, and offers a pathway toward improved subgrid models for non-equilibrium stellar convection zones.
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Earth and Planetary Astrophysics

Orbital Eccentricities Suggest a Gradual Transition from Giant Planets to Brown Dwarfs

Gregory J. Gilbert, Judah Van Zandt, Erik A. Petigura et al. (+3 more)

To date, hundreds of sub-stellar objects with masses between $1-80\ M_{\rm Jup}$ have been detected orbiting main-sequence stars. The current convention uses the deuterium-burning limit, $M_c \approx 13 M_{\rm Jup}$ to divide this population between giant planets and brown dwarfs. However, this classification heuristic is largely divorced from any formation physics and may not accurately reflect the astrophysical nature of these objects. Previous work has suggested that a transition from “planet-like” to “brown-dwarf-like” characteristics occurs somewhere in the range $1-10 M_{\rm Jup}$, but precise the crossover mass and whether the transition is gradual or abrupt remains unknown. Here, we explore how the occurrence rate, host star metallicity, and orbital eccentricities vary as a function of mass in a sample of 70 Doppler-detected sub-stellar objects ($0.8 < M_c/M_{\rm Jup} < 80$) from the California Legacy Survey. Our population consists of objects near and beyond the water ice line ($1 < a / \text{AU} < 10$), providing valuable clues to the details of giant planet formation physics at a location in the proto-stellar disk where planet formation efficiency is thought to be enhanced. We find that occurrence rate, host star metallicity, and orbital eccentricity all change gradually across the mass range under consideration, suggesting that “bottom-up” core accretion mechanisms and “top-down” gravitational instability mechanisms produce objects that overlap in mass. The observed eccentricity distributions could arise either from different formation channels or from post-formation dynamical interactions between massive sub-stellar objects.
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All authors Gregory J. Gilbert, Judah Van Zandt, Erik A. Petigura, Steven Giacalone, Andrew W. Howard, Luke B. Handley

Solar and Stellar Astrophysics

On the Temporal Variability in the Magnetic Dichotomy of Late M Dwarf Stars

Giuseppina Nigro, Francesco Berrilli, Giuseppe Bono et al. (+4 more)

Rapidly rotating late M dwarfs are observed in two different branches of magnetic activity, although they operate in the same stellar parameter range. Current empirical evidence indicates that M dwarfs with spectral types ranging from M3 / M4 to late-type M dwarfs, stellar masses smaller than 0.15 M$_\odot$, and rotational period shorter than four days display either a stable dipolar magnetic field or magnetic structures with significant time variability. The magnetic activity of fully convective M dwarfs is known to be regulated by a mechanism named the ${\alpha}^2$ dynamo. To further constrain the physics of this mechanism, we use a low-dimensional model for thermally driven magnetoconvection producing an ${\alpha}^2$ dynamo, specifically a modified magnetohydrodynamic (MHD) shell model. Although the model neglects density stratification, it captures the essential nonlinear dynamics of an $\alpha^2$ dynamo. Therefore, the results should be interpreted in a qualitative sense, highlighting possible trends rather than providing direct quantitative predictions for fully convective stars. The model is validated by comparing the statistical properties of magnetic polarity reversals with paleomagnetic data, since the geodynamo provides the only natural ${\alpha}^2$ dynamo with sufficiently rich reversal statistics. Our findings reveal that increased convective heat transport correlates with more frequent magnetic-polarity reversals, resulting in enhanced magnetic variability. This suggests that the observed magnetic dichotomy in late M dwarfs could be interpreted in terms of differences in global heat transport efficiency. However, additional models and observations of M dwarfs are needed to further constrain this interpretation.
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All authors Giuseppina Nigro, Francesco Berrilli, Giuseppe Bono, Dario Del Moro, Luca Giovannelli, Valentina Penza, Raffaele Reda

Solar and Stellar Astrophysics

Observations of Five Southern-Hemisphere Cataclysmic Binary Stars

John R. Thorstensen, Annabelle E. Niblett, Shreya Gandhi et al. (+7 more)

We present observations and analyses of five little-studied cataclysmic binary stars in the southern celestial hemisphere. Our new observations are from the South African Astronomical Observatory. The objects and salient results are as follows: (i) 6dF0752-54 is a dwarf nova with an orbital period Porb = 5.05 hr that shows a contribution from a mid-M type secondary in its mean spectrum. (ii) J0916-26 had been suspected of being a magnetic CV with an eclipse period of 3.37 hr. Our spectrum corroborates this classification. (iii) GSC 08944 is a novalike variable with Porb = 3.80 hr. Archival photometry also shows a persistent photometric period near 4.03 hr, apparently from a positive super- hump. Its emission line behavior is consistent with an SW Sextantis-type novalike. (iv) MGAB-V253, also Gaia20eys, had been identified as a short-period eclipsing novalike with Porb = 1.44 hr. Our spectrum shows shows broad emission lines consistent with this, and the extensive TESS data show a persistent modulation near 1.35 hr, evidently a negative superhump. It is less luminous than most novalikes, but significantly brighter than quiescent dwarf novae with comparably short periods. (v) Finally, DDE 45 shows a complicated variability history, cycling rapidly between high and low states for a time and more recently showing outbursts resembling a U Gem-type dwarf nova. We find a 2.07 hr radial velocity period, which also appears in archival TESS photometry. The emission lines are double-peaked, with an orbital S-wave similar to low-inclination dwarf novae. To be published in Astronomical Journal.
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All authors John R. Thorstensen, Annabelle E. Niblett, Shreya Gandhi, Lauren P. Zanarini, Gavin D. Goss, Arnav Singh, Divik Verma, Ryan C. Hickox, Emmanuel A. Durodola, Jiaqi Martin Ying

Astrophysics of Galaxies

From Images to Physics: Probabilistic Inference of Galaxy Parameters and Emission Lines via VAE & Normalizing Flows

Adiba Amira Siddiqa, Sayed Shafaat Mahmud and Rafael Martinez-Galarza

We introduce a Variational Autoencoder (VAE)–Normalizing Flow (NF) framework for rapid probabilistic inference of galaxy properties and emission line fluxes at $z \leq 0.3$ from SDSS gri imaging and photometry. Our model probabilistically infers stellar mass, star formation rate (SFR), redshift, gas-phase metallicity, and central black hole mass for a given galaxy. The model accruacy matches current non-spectroscopic methods for stellar mass and redshift, surpasses them for SFR and metallicity, and introduces the first probabilistic central black hole mass estimates from imaging + photometry. It also delivers probabilistic estimates of H$\alpha$, H$\beta$, [N~ii], and [O~iii] emission line fluxes directly from imaging, enabling SFR, metallicity, dust, and AGN/shock diagnostics without spectroscopy. This approach opens new pathways for scalable, physics-informed inference in upcoming surveys such as Roman and Rubin LSST.
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High Energy Astrophysical Phenomena

Pulsar B1237+25 Aberration/Retardation Analysis from Decimeter to Decameter Wavelength: Challenge to "Radius-to-Frequency Mapping"

Joanna M. Rankin, Vyacheslav Zakharenko, Oleg Ulyanov et al. (+9 more)

PSR B1237+25 is perhaps the canonical example of a pulsar with a core/double cone profile. Moreover, it is bright with little spectral turnover, and its profile perhaps uniquely remains undistorted by scattering far into the decametric band. Here we assemble more than a dozen of the highest quality profiles (30 MHz to 5 GHz) from half a dozen observatories, where possible polarimetric. The pulsar's 2.6$^{\circ}$ core component marks the magnetic axis longitude, and we confirm that this point coincides both with the linear polarization angle inflection point and the zero-crossing of its antisymmetric circular signature – thus providing the possibility to estimate emission heights over a very broad band using aberration/retardation (A/R). We then carefully fit the profile components with Gaussians to identify and study the subtle asymmetries produced by A/R. We find a consistent A/R in the pulsar's profiles of some 0.5$^{\circ}$ longitude or 2 ms – corresponding to a putative conal emission height of 200-400 km – with a formal error of about 100 km. Our analysis finds no evidence whatsoever for an emission height increase with wavelength, the so-called “radius-to-frequency mapping”. Nor do we find any significant difference in A/R effect between the outer and inner cones.
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All authors Joanna M. Rankin, Vyacheslav Zakharenko, Oleg Ulyanov, Ihor Kravtsov, Pratik Kumar, Jean-Mathias Griessmeier, N. D. Ramesh Bhat, Geoff Wright, Patrick Weltevrede, Fabian Jankowski, Jerome Petri, Gilles Theureau

Cosmology and Nongalactic Astrophysics

The Chandra Strong Lens Sample: Measuring the Dynamical States and Relaxation Fraction of a Sample of 28 Strong Lensing Selected Galaxy Clusters

Raven Gassis, Matthew B. Bayliss, Michael McDonald et al. (+10 more)

We present the results of our dynamical state proxy measurements performed on 28 strong lensing galaxy clusters from the Sloan Giant Arcs Survey (SGAS). Using Chandra ACIS-I/S X-ray data supplemented with HST WFC3 imaging, we measure four morphological parameters: the concentration parameter (c), asymmetry parameter (A), centroid shift (log(w)), and the X-ray-BCG centroid separation (D [kpc]). Our goals are to (A) provide a robust classification of the dynamical state of the clusters in this strong lensing selected sample to enable studies that test various problems in cluster astrophysics and observational cosmology; (B) identify correlations, biases, or disagreements between different measurement proxies and cluster properties; and (C) measure the relaxation fraction (the fraction of clusters classified as relaxed based on X-ray morphology) and compare it to relaxation fractions from cluster samples selected using other methods. We combine the four morphological parameters into a single metric, the combined parameter M, which effectively separates the cluster sample into four dynamical state categories: relaxed; moderately relaxed; moderately disturbed; and disturbed. We find no significant trend in a cluster's dynamical state with its size, and only a weak, statistically limited dependence on mass and redshift. Based on our classification system, we find that $43\%^{+9}_{-9}$ of the clusters are relaxed, which is consistent with relaxation fractions measured for other cluster samples selected on mass-observables. This implies a strong lensing selected sample of clusters is on average dynamically similar to clusters selected via different methods.
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All authors Raven Gassis, Matthew B. Bayliss, Michael McDonald, Keren Sharon, Guillaume Mahler, Michael D. Gladders, Hakon Dahle, Michael K. Florian, Jane R. Rigby, Lauren A. Elicker, M. Riley Owens, Prasanna Adhikari, Gourav Khullar

Solar and Stellar Astrophysics

IdentYS: A Python-Based Tool for Identifying Young Stars in Star-Forming Regions

E. Nikoghosyan, D. Baghdasaryan, D. Andreasyan et al. (+3 more)

Research on young stellar populations is essential to understand the properties of embedded clusters and advance theories of their formation. This has driven advancements in methodologies for star detection, leading to the development of valuable databases and software. We present the scientific justification and operating principles of the IdentYS tool, which is designed to identify young stellar objects (YSOs) in star-forming regions. The tool facilitates the identification of young stars with infrared (IR) excess in remote and embedded star-forming regions, focusing primarily on Class I and II YSOs. For this purpose, near- and mid-IR photometric data and five colour-colour diagrams (J - H) vs. (H - K), K - [3.6] vs. [3.6] - [4.5], [3.6] - [4.5] vs. [5.8] - [8.0], [3.6] - [4.5] vs. [8.0] - [24], and [3.4] - [4.6] vs. [4.6] - [12] are used. The purity of the YSOs sample is enhanced by excluding field contamination from stellar and extragalactic objects. As a result, we compile a list of YSO candidates displaying the source designation, astrometric, and photometric parameters, as well as information on the evolutionary stage determined by the presence of IR excess, as indicated by certain diagrams. The application of this program can greatly streamline the statistical analysis of young stellar populations across diverse star-forming regions, including distant and deeply embedded ones, which typically require processing large volumes of initial data.
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All authors E. Nikoghosyan, D. Baghdasaryan, D. Andreasyan, N. Azatyan, A. Samsonyan, A. Yeghikyan

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Thermal Quarkyonic Matter and Its Implications for Neutron Star Structure

K. Folias and Ch.C. Moustakidis

The structure and basic properties of dense nuclear matter still remain one of the open problems of Physics. In particular, the composition of the matter that composes neutron stars is under theoretical and experimental investigation. Among the theories that have been proposed, apart from the classical one where the composition is dominated by hadrons, the existence or coexistence of deconfined quark matter is a dominant guess. An approach towards this solution is the phenomenological view according to which the existence of quarkyonic matter plays a dominant role in the construction of the equation of state (EOS). According to it the structure of the EOS is based on the existence of the quarkyonic particle which is a hybrid state of a particle that combines properties of hadronic and quark matter with a corresponding representation in momentum space. In this paper we propose a phenomenological model for hot quarkyonic matter, borrowed from corresponding applications in hadronic models, where the interaction in the quarkyonic matter depends not only on the position but also on the momentum of the quarkyonic particles. This consideration, as we demonstrate, can have a remarkable consequence on the shape of the EOS and thus on the properties of neutron stars, especially in those for which the effect of temperature is significant, offering a sufficiently flexible model. Comparison with recent observational data can place constraints on the parameterization of the particular model and help improve its reliability.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

Auto-encoder model for faster generation of effective one-body gravitational waveform approximations

Suyog Garg, Feng-Li Lin and Kipp Cannon

Upgrades to current gravitational wave detectors for the next observation run and upcoming third-generation observatories, like the Einstein telescope, are expected to have enormous improvements in detection sensitivities and compact object merger event rates. Estimation of source parameters for a wider parameter space that these detectable signals will lie in, will be a computational challenge. Thus, it is imperative to have methods to speed-up the likelihood calculations with theoretical waveform predictions, which can ultimately make the parameter estimation faster and aid in rapid multi-messenger follow-ups. In this work we study auto-encoder models for gravitational waveform generation by adopting the best-performing architecture of Liao & Lin (2021) to approximate aligned-spin SEOBNRv4 inspiral-merger-ringdown waveforms. Our parameter space consists of four parameters, [$m_1$, $m_2$, $\chi_1(z)$, $\chi_2(z)$]. The masses are uniformly sampled in $[5,75]\,M_{\odot}$ with a mass ratio limit at $10\,M_{\odot}$, while the spins are uniform in $[-0.99,0.99]$. Our model is able to generate $10^3$ waveforms in $\sim 0.1$ second at an average speed of about 50 microsecond per waveform on a GPU. This is about 4 orders of magnitude faster than the native SEOBNRv4 implementation, and 2–3 orders of magnitude faster than existing non-machine-learning accelerated waveform variants. The median mismatch for the generated waveforms in the test dataset is $\sim10^{-2}$, with better performance in a restricted parameter space of $\chi_{\rm eff}\in[-0.80,0.80]$. The latent sampling error of our model can be quantified at a median mismatch standard deviation of $4\times10^{-3}$. Although the accuracy of our model does not enable full production-use yet, the model could be useful wherever high-volume of approximate theoretical waveforms are required, for instance, for rapid sky localization.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

From the Virgo interferometer calibration to the bias and uncertainty of the h(t) detector strain during the O4 run

Cervane Grimaud, Florian Aubin, Benoît Mours et al. (+6 more)

Since the first gravitational wave detection in 2015, ground-based interferometer sensitivities have significantly improved, requiring highly precise calibration to ensure accurate reconstruction of the h(t) strain signal. In this talk we will outline the Virgo interferometer calibration steps performed in preparation of the O4b run started in April 2024. We will first describe the Photon Calibrator power devices intercalibration allowing for a 0.48% precision on mirror displacement. Before explaining how the Photon Calibrator is used to calibrate every Virgo mirror actuators. We will also discuss the monitoring of the h(t) strain reconstruction during the run showing that, on the 10 Hz to 2 kHz band, the reconstructed strain achieves a precision of 2% in modulus and 30 mrad in phase. Special emphasis will be given on the newly developed frequency-dependent bias and uncertainty computation method and the resulting online unbiasing of the h(t) strain.
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All authors Cervane Grimaud, Florian Aubin, Benoît Mours, Thierry Pradier, Loïc Rolland, Monica Seglar-Arroyo, Hans Van Haevermaet, Pierre Van Hove, Didier Verkindt

Solar and Stellar Astrophysics

Simulations of structured upflows from plumes and their connection to the solar wind

Kamlesh Bora, Lakshmi Pradeep Chitta, Yajie Chen et al. (+3 more)

Small-scale transient jetlet activity and associated upflows from coronal hole plumes are potential sources of the solar wind. To elucidate the magnetic origins and driving mechanisms of such upflows, we perform three-dimensional radiative magnetohydrodynamic simulations using the MURaM code, spanning from the upper convection zone to the low corona. We synthesize Fe\,x 174\,Å emission to capture the plume evolution comparable to observations, examining underlying plasma flows, thermal structures, and magnetic topologies. We identify a pronounced transition from cool downflows in the lower atmosphere to hot upflows in the corona at the interface between plume-rooted like-polarity flux concentrations. These upflows are threaded by a complex, filamentary network of Quasi-Separatrix Layers (QSLs) – a topology distinct from standard interchange reconnection scenarios. The domain-averaged mass flux over a 38-minute interval ranges from $10^{-9}$ to $10^{-8}\,\mathrm{g\,cm^{-2}\,s^{-1}}$, substantially exceeding observed solar-wind loss rates. Our results demonstrate that highly structured plasma outflows are channeled along strong QSLs at open–open field boundaries, providing a pathway to sustain the solar wind from coronal-hole plumes without requiring interchange reconnection triggered by opposite-polarity flux emergence.
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All authors Kamlesh Bora, Lakshmi Pradeep Chitta, Yajie Chen, Damien Przybylski, David Pontin, Nikil Panyam

Astrophysics of Galaxies

Sub-millimeter galaxies in hierarchical models: revisiting the need for a top-heavy stellar initial mass function with Bayesian optimisation

Edward Elliott, C.M. Baugh and Cedric Lacey

The properties of high-redshift sub-millimetre galaxies (SMGs) remain controversial within hierarchical structure formation models. We revisit whether a top-heavy stellar initial mass function (IMF) in starbursts is required to reproduce both SMG observations and local galaxy properties. Using Bayesian optimisation, we perform an extensive search of the 15-dimensional parameter space of the GALFORM semi-analytical model. This efficient approach converges to optimal parameter values in fewer than 200 model evaluations, representing orders of magnitude fewer runs than traditional methods. We test whether GALFORM can simultaneously match three key observational constraints: the $z=0$ $K$-band luminosity function, the SMG number counts at 850~$\mu$m, and the SMG redshift distribution. We consider two model variants: one with a universal solar neighbourhood IMF for all star formation, and another allowing the IMF slope in starbursts to vary as a free parameter. When assuming a universal Chabrier IMF, we find no parameter combination that simultaneously reproduces all three datasets. The model either matches the SMG constraints while grossly overpredicting the local $K$-band luminosity function, or matches the local luminosity function while severely underpredicting SMG counts by factors of 3–100. In contrast, allowing a top-heavy IMF in starbursts enables excellent simultaneous fits to all constraints. The best-fitting model prefers an IMF slope parameter $x \approx 0.7$ (where d$n$/dlog$m \propto m^{-x}$), somewhat more top-heavy than recent models but less extreme than early proposals. Our comprehensive parameter space exploration definitively confirms that, within the GALFORM framework, a top-heavy IMF in starbursts is necessary to reconcile high-redshift dusty star-forming galaxies with local galaxy populations.
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Cosmology and Nongalactic Astrophysics

Homogeneity scale in the local Universe: Model-independent estimate from S-PLUS iDR6 blue galaxies

Camila Franco, Felipe Avila, Armando Bernui et al. (+8 more)

We present a model-independent estimate of the angular homogeneity scale in the local Universe by analysing data from the Southern Photometric Local Universe Survey (S-PLUS). Two complementary estimators are employed: (i) a parametric approach fitting the power-law of the two-point angular correlation function, which yields the homogeneity scale $\theta_H = 8.94_{-3.38}^{+1.20}\;{\rm deg}$; and (ii) a nonparametric fractal correlation dimension method, computing $\mathcal{D}_2(\theta)$ directly from the correlation function, which results in $\theta_H = 7.91_{-2.94}^{+5.50}\;{\rm deg}$. We apply both methodologies to a set of mock catalogs, generated with the Generator for Large Scale Structure algorithm, and find that both estimates are well within $1 \sigma$ of their respective median values. The transition scale to homogeneity, according to the $\Lambda$ cold dark matter (CDM) model, is defined for matter, i.e., $b = 1$. Measurements of this scale with observational data clearly depend on the cosmic tracer analyzed, and a calibration is necessary. Our study with blue galaxies, with bias $b \simeq 1$, provides a suitable estimate for comparison. Indeed, the results obtained in both approaches are compared with the value expected in the $\Lambda$CDM model, obtaining a good concordance.
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All authors Camila Franco, Felipe Avila, Armando Bernui, Ulisses Ribeiro, Clécio R. Bom, Arianna Cortesi, E. Telles, W. Schoenell, T. Ribeiro, A. Kanaan, C. Mendes de Oliveira

Solar and Stellar Astrophysics

Unraveling eMSTO in NGC 2355: Stellar Rotation and Binaries

Jayanand Maurya, Yu Zhang and Hubiao Niu

The extended Main Sequence Turn-off (eMSTO) in the open cluster NGC 2355 is investigated using precise astrometry and photometry from Gaia DR3 and spectroscopic data from the Gaia-ESO Survey. We find a clear positive correlation between the rotational velocity (v sin i) and color of eMSTO stars, supporting the role of stellar rotation and gravity darkening in causing the observed color spread. Contrary to predictions from binary tidal-locking scenarios, spatial distribution analysis reveals that fast-rotating stars are preferentially concentrated in the cluster's central regions. This finding provides the observational evidence favoring star-disk interactions during the pre-main-sequence phase, rather than tidal locking in binaries, as the primary mechanism responsible for the origin of rotational spread in eMSTO stars.
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Cosmology and Nongalactic Astrophysics

The first AKRA mass map reconstruction from HSC Y1 data

Yuan Shi, Pengjie Zhang, Zhao Chen et al. (+4 more)

Weak lensing mass-mapping from shear catalogs faces systematic challenges from survey masks and spatially varying noise. To overcome these issues and reconstruct unbiased convergence $\kappa$ maps, we have constructed the AKRA (Accurate Kappa Reconstruction Algorithm), a prior-free and maximum-likelihood based analytical method. It has been validated for mock shear catalogs with a variety of survey masks. In this work, we present the first real-data application of the AKRA on the Subaru Hyper Suprime-Cam Year 1 (HSC Y1) data. We first validate AKRA using mock shear catalogs from the Kun simulation suite, with masks corresponding to the six HSC Y1 regions (GAMA09H, GAMA15H, HECTOMAP, VVDS, WIDE12H, and XMMLSS). The investigated statistics, including the lensing power spectrum, $\langle \kappa^2\rangle$, $\langle \kappa^3\rangle$, and the one-point probability distribution function of $\kappa$, are all unbiased. We then apply AKRA to the HSC Y1 shear catalog and provide reconstructed $\kappa$ maps ready for subsequent scientific analyses.
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All authors Yuan Shi, Pengjie Zhang, Zhao Chen, Jian Qin, Li Cui, Furen Deng, Ji Yao

Instrumentation and Methods for Astrophysics

Mock Observations for the CSST Mission: Integral Field Spectrograph–Instrument Simulation

Zhao-Jun Yan, Jun Yin, Lei Hao et al. (+25 more)

The Chinese Space Station Survey Telescope (CSST) is a next-generation Stage-IV facility renowned for its wide field of view, high image quality, and multi-band observational capabilities. Among the five instruments onboard the CSST, the Integral Field Spectrograph (IFS) offers the unique ability to simultaneously capture spatial and spectral information across a field of view of no less than $6^{''}\times6^{''}$. Key advantages of the IFS include a high spatial resolution of $0.2^{''}$ and a broad spectral coverage from 350 to 1000 nm, making it an ideal instrument for studying physical processes in the vicinity of supermassive black holes within galaxies. To more accurately assess the technical and scientific performance of the CSST-IFS, it is essential to develop a simulation tool that incorporates realistic effects from all optical components. Such a simulation will form an integral part of the CSST-IFS data and pipeline system, enabling the development of the data reduction pipeline well ahead of actual observations. This paper presents an end-to-end simulation workflow for the CSST-IFS, incorporating a wide range of instrumental effects that may influence its spectral and imaging performance. The simulation accounts for optical diffraction effects introduced by all components, such as image slicers and slit array, as well as sub-pixel effects from gratings. It also includes various detector noises, frame-shifting effects, and charge-transfer inefficiency. Real observational conditions–such as target Doppler shift, cosmic rays, and other in-orbit operational effects–are also considered. We describe the technical implementation of the simulation and present results that quantitatively characterize key instrument parameters.
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All authors Zhao-Jun Yan, Jun Yin, Lei Hao, Shi-Yin Shen, Wei Chen, Shuai Feng, Yi-Fei Xiong, Chun Xu, Xin-Rong Wen, Lin Lin, Chao Liu, Lin Long, Zhen-Lei Chen, Mao-Chun Wu, Xiao-Bo Li, Zhang Ban, Xun Yang, Yu-Xi Jiang, Guo-Liang Li, Ke-Xin Li, Jian-Jun Chen, Nan Li, Cheng-Liang Wei, Lei Wang, Bai-Chuan Ren, Jun Wei, Jing Tang, Ran Li

Instrumentation and Methods for Astrophysics

Mock Observations for the CSST Mission: Multi-Channel Imager–Instrument Simulation

Zhao-Jun Yan, Huan-Yuan Shan, Zhen-Ya Zheng et al. (+40 more)

The Chinese Space Station Survey Telescope (CSST), a two-meter aperture astronomical space telescope under China's manned space program, is equipped with multiple back-end scientific instruments. As an astronomical precision measurement module of the CSST, the Multi-Channel Imager (MCI) can cover a wide wavelength range from ultraviolet to near-infrared with three-color simultaneous high-precision photometry and imaging, which meets the scientific requirements for various fields. The diverse scientific objectives of MCI require not only a robust airborne platform, advanced optical systems, and observing facilities but also comprehensive software support for scientific operations and research. To this end, it is essential to develop realistic observational simulation software to thoroughly evaluate the MCI data stream and provide calibration tools for future scientific investigations. The MCI instrument simulation software will serve as a foundation for the development of the MCI data processing pipeline and will facilitate improvements in both hardware and software, as well as in the observational operation strategy, in alignment with the mission's scientific goals. In conclusion, we present a comprehensive overview of the MCI instrument simulation and some corresponding performances of the MCI data processing pipeline.
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All authors Zhao-Jun Yan, Huan-Yuan Shan, Zhen-Ya Zheng, Xi-Yan Peng, Zhao-Xiang Qi, Chun Xu, Lin Lin, Xin-Rong Wen, Chun-Yan Jiang, Li-Xin Zheng, Jing Zhong, Fang-Ting Yuan, Zhen-Lei Chen, Wei Chen, Mao-Chun Wu, Zhen-Sen Fu, Ke-Xin Li, Lin Nie, Chao Liu, Nan Li, Qiao Wang, Zi-Huang Cao, Shuai Feng, Guo-Liang Li, Lei Wang, Cheng-Liang Wei, Xiao-Bo Li, Zhang Ban, Xun Yang, Yu-Xi Jiang, De-Zi Liu, Yong-He Chen, Xiao-Hua Liu, Fang Xu, Xue Cheng, Yue Su, Tong-Fang Duan, Chao Qi, Na Li, Geng Zheng, Chong Ma, Jing Tang, Ran Li

High Energy Astrophysical Phenomena

Detection of disk-jet co-precession in a tidal disruption event

Yanan Wang, Zikun Lin, Linhui Wu et al. (+46 more)

Theories and simulations predict that intense spacetime curvature near black holes bends the trajectories of light and matter, driving disk and jet precession under relativistic torques. However, direct observational evidence of disk-jet co-precession remains elusive. Here, we report the most compelling case to date: a tidal disruption event (TDE) exhibiting unprecedented 19.6-day quasi-periodic variations in both X-rays and radio, with X-ray amplitudes exceeding an order of magnitude. The nearly synchronized X-ray and radio variations suggest a shared mechanism regulating the emission regions. We demonstrate that a disk-jet Lense-Thirring precession model successfully reproduces these variations while requiring a low-spin black hole. This study uncovers previously uncharted short-term radio variability in TDEs, highlights the transformative potential of high-cadence radio monitoring, and offers profound insights into disk-jet physics.
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All authors Yanan Wang, Zikun Lin, Linhui Wu, Weihua Lei, Shuyuan Wei, Shuang-Nan Zhang, Long Ji, Santiago del Palacio, Ranieri D. Baldi, Yang Huang, Jifeng Liu, Bing Zhang, Aiyuan Yang, Rurong Chen, Yangwei Zhang, Ailing Wang, Lei Yang, Panos Charalampopoulos, David R. A. Williams-Baldwin, Zhu-Heng Yao, Fu-Guo Xie, Defu Bu, Hua Feng, Xinwu Cao, Hongzhou Wu, Wenxiong Li, Erlin Qiao, Giorgos Leloudas, Joseph P Anderson, Xinwen Shu, Dheeraj R. Pasham, Hu Zou, Matt Nicholl, Thomas Wevers, Tomas E. Muller-Bravo, Jing Wang, Jianyan Wei, Yu-Lei Qiu, Weijian Guo, Claudia P. Gutierrez, Mariusz Gromadzki, Cosimo Inserra, Lydia Makrygianni, Francesca Onori, Tanja Petrushevska, Diego Altamirano, Lluis Galbany, Miguel Perez-Torres, Ting-Wan Chen

High Energy Astrophysical Phenomena

Spectral-Timing Evolution of a Black hole X-ray binary Swift J1727.8-1613: Linking Disk Reflection and Type-C QPO Frequency During the 2023 Outburst

Manoj Ghising, Nirpat Subba, Mohammed Tobrej et al. (+2 more)

We present a comprehensive spectral-timing analysis of a BHXB Swift J1727.8$-$1613 during its 2023 outburst, using five pointed NuSTAR observations sampling the luminous hard-intermediate state. Broadband 3-79 keV spectroscopy employs a physically motivated model combining a cool truncated disk (diskbb), relativistic reflection (relxill in reflection-only mode), and Comptonized continuum (nthComp) to probe the inner accretion geometry around a rapidly spinning black hole ($a_\ast\!=\!0.98$) at moderate inclination. Simultaneous timing analysis reveals type-C quasi-periodic oscillations (QPOs) with novel coherence evolution: the quality factor ($Q$) exhibits a striking non-monotonic dependence on both QPO frequency and luminosity, peaking near $\nu_{\rm QPO}\!\sim\!1.2$~Hz and declining at both lower and higher frequencies. This turnover directly constrains Lense-Thirring precession geometry, implying optimal coherence at intermediate truncation radius. A tight photon-index-QPO-frequency correlation demonstrates that spectral softening and frequency rise are concurrent signatures of inward truncation-radius motion. The triadic luminosity evolution-rising disk and Compton, declining reflection-traces precession-driven geometry changes and corona beaming effects. Interpreting disk-normalization variability as apparent-area changes rather than physical radius swings provides new insight into disk-corona boundary layers. These quantitative results provide strong evidence for global Lense-Thirring precession regulation of both timing and spectral properties, establishing Swift J1727.8$-$1613 as a benchmark source for understanding accretion-geometry physics during black hole state transitions.
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All authors Manoj Ghising, Nirpat Subba, Mohammed Tobrej, Binay Rai, Bikash Chandra Paul

Astrophysics of Galaxies

The influence of AGN feedback on star formation in red spiral galaxies

Moreom Akter, Wayne A. Barkhouse, Sandanuwan P Kalawila Vithanage et al. (+2 more)

We investigated the influence of Active Galactic Nuclei (AGN) feedback on star formation in red spiral galaxies by analyzing a sample of 324 red and 273 blue face-on spirals selected from 115 low-redshift galaxy clusters. This multi-wavelength dataset combines optical emission line data from the Sloan Digital Sky Survey with X-ray fluxes from Chandra and XMM-Newton X-ray space telescopes. Using diagnostic emission line ratios, we constructed Baldwin-Phillips-Terlevich (BPT) diagrams, introduced in 1981 to classify galaxies based on nuclear activity. Our analysis reveals that most red spirals exhibit AGN or low-ionization nuclear emission-line region (LINER) signatures, based on optical data, as determined by their location in the BPT, Cid Fernandes, and Mazzolari diagrams. These results are consistent with the presence of negative feedback from AGNs quenching star formation. Conversely, X-ray analysis reveals that many blue spirals exhibit high X-ray luminosities and are situated in the AGN region of emission line ratio diagrams, suggesting that AGN-driven positive feedback may be enhancing star formation. Our findings support the hypothesis that AGN feedback plays a key role in the evolution of spiral galaxies, particularly in quenching star formation and driving the transition from blue to red spiral systems.
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All authors Moreom Akter, Wayne A. Barkhouse, Sandanuwan P Kalawila Vithanage, Gihan L. Gamage, Omar López-Cruz