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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 8 October

Instrumentation and Methods for Astrophysics

In-flight performance of the IXPE telescopes

Riccardo Ferrazzoli, Enrico Costa, Sergio Fabiani et al. (+15 more)

We present a comprehensive characterization of the on-orbit imaging performance of the three telescopes on board the Imaging X-ray Polarimetry Explorer (IXPE). Each telescope comprises a Wolter-I mirror module assembly and a Gas Pixel Detector focal-plane detector unit (DU). We analyze data from point-like X-ray sources and fit a composite point spread function (PSF) model that we compare with ground calibrations. We study the dependence of the PSF parameters and of the angular resolution, in terms of half-power diameter (HPD), on the time and source counting rate. We find no significant secular evolution of PSF parameters or HPD over 30 months on orbit, with average HPDs of $26.1 \pm 0.5$ arcsec (Telescope 1), $32.1 \pm 0.5$ arcsec (Telescope 2), and $30.9 \pm 0.6$ arcsec (Telescope 3), and rate trends consistent with zero up to source counting rates of $\sim60$ cts s$^{-1}$ in the 2-3 keV energy band for all three telescopes. We set a 99% C.L. upper limit of 4.4% on the optics-induced polarization in the PSF halo, and find no measurable degradation of the polarization modulation factor in the wings versus the core due to mis-reconstructed photoelectron tracks. IXPE's imaging performance thus is consistent with the $\leq30$ arcsec observatory requirement with high stability, ensuring robust spatially resolved polarization measurements for the mission's projected lifetime through 2030.
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All authors Riccardo Ferrazzoli, Enrico Costa, Sergio Fabiani, Philip Kaaret, Stephen L. O'Dell, Brian D. Ramsey, Paolo Soffitta, Luca Baldini, Ronaldo Bellazzini, Alessandro Di Marco, Fabio La Monaca, Luca Latronico, Alberto Manfreda, Fabio Muleri, John Rankin, Carmelo Sgrò, Stefano Silvestri, Martin C. Weisskopf

High Energy Astrophysical Phenomena

1FLAT: a Firmamento-based catalog of AGN in Fermi-LAT high Galactic latitude {\gamma}-ray sources

P. Giommi, M. Doro, M. Gouvêa et al. (+15 more)

We present a systematic reassessment of 5,062 high-Galactic latitude gamma-ray sources from the Fermi-LAT 4FGL-DR4 catalog using Firmamento, a web-based platform for multi-frequency source discovery and analysis. Our goal is to provide an independent evaluation of LAT gamma-ray source associations through alternative spectral and spatial methods that combine recent and legacy survey data, supplemented by human supervision of spectral energy distributions (SEDs), source morphology, flux variability, and template-based comparisons. Firmamento confirms the 4FGL-DR4 and 4LAC-DR3 counterparts or unassociated sources in 4,493 cases (88.8%), demonstrating the robustness of both approaches. Beyond this general agreement, we identify 421 new blazar counterparts among previously unassociated sources, thereby reducing the fraction of unidentified extragalactic Fermi-LAT sources from 25% to 17%. In addition, in 64 cases we find alternative blazar associations, while in 49 instances we do not confirm the 4FGL-DR4 association. For all confirmed blazar counterparts we provide homogeneous estimates of synchrotron peak frequency and peak flux using machine-learning and template-based methods; these agree with 4LAC-DR3 values in most cases, though significant discrepancies appear for a few dozen sources, often due to improved X-ray coverage. The primary outcome of this work is the 1st Firmamento LAT AGN table (1FLAT), made publicly available through the Firmamento platform (https://firmamento.nyuad.nyu.edu), where all related multi-wavelength data and images are available. The project involved extensive manual validation and benefited from the active participation of graduate and undergraduate students, highlighting the platform's value for both research and education.
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All authors P. Giommi, M. Doro, M. Gouvêa, L. Fronte, F. Metruccio, F. Arneodo, U. Barres de Almeida, S. Di Pippo, T. Kerscher, A. Macció, B. Mazzon, M. Morrone, E. Prandini, A. Rodríguez, A. Ruina, N. Sahakyan, L. Silveri, D. Tripathi

Astrophysics of Galaxies · Cross-listed from gr-qc

When vacuum breaks: a self-consistency test for astrophysical environments in extreme mass ratio inspirals

Lorenzo Copparoni, Rohit S. Chandramouli and Enrico Barausse

Gravitational-wave signals are typically interpreted under the vacuum hypothesis, i.e. assuming negligible influence from the astrophysical environment. This assumption is expected to break down for low-frequency sources such as extreme mass ratio inspirals (EMRIs), which are prime targets for the Laser Interferometer Space Antenna (LISA) and are expected to form, at least in part, in dense environments such as Active Galactic Nuclei or dark-matter spikes and cores. Modeling environmental effects parametrically is challenging due to the large uncertainties in their underlying physics. We propose a non-parametric test for environmental effects in EMRIs, based on assessing the self-consistency of vacuum parameter posteriors inferred from different portions of the signal. Our results demonstrate that this test can reveal statistically significant inconsistencies from vacuum signals – arising from e.g. incomplete modeling, environmental effects or deviations from General Relativity – without introducing additional parameters or assumptions about the underlying physics.
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Astrophysics of Galaxies

Simulations of Globular Cluster Evolution with Multiple Stellar Populations

Mirek Giersz, Abbas Askar, Arkadiusz Hypki et al. (+3 more)

The formation of stars with light-element abundance variations in globular clusters and the subsequent dynamical evolution of these multiple populations remains an open question. One of the most widely discussed is the AGB scenario, in which chemically processed material from the envelopes of AGB stars mixes with re-accreted primordial gas flowing into the center of the cluster. Based on this scenario, more than two hundred MOCCA simulations of cluster evolution have been carried out, incorporating additional physical processes related to the external environment of globular clusters and the initial properties of multiple stellar populations. Analysis of the simulations shows that most observed properties of multiple stellar populations and the global parameters of Milky Way clusters are well reproduced, with the exception of the correlation between cluster mass and the fraction of second-population stars. We present a speculative scenario of globular cluster evolution that may account for the observed properties of Milky Way clusters, including the correlation between cluster mass and the fraction of enriched stars. The scenario further predicts that, under certain conditions, the pristine first population can be more centrally concentrated than the enriched second population, as observed in some clusters. \end{abstract
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All authors Mirek Giersz, Abbas Askar, Arkadiusz Hypki, Jongsuk Hong, Grzegorz Wiktorowicz, Lucas Hellstrom

Earth and Planetary Astrophysics

Is the high-energy environment of K2-18b special?

S. Rukdee, M. Güdel, I. Vilović et al. (+7 more)

K2-18b lies near the radius valley that separates super-Earths and sub-Neptunes, marking a key transitional regime in planetary and atmospheric composition. The system offers a valuable opportunity to study how M-dwarf high-energy stellar radiation influences atmospheric stability and the potential for sustaining volatile species, especially important in the context of the upcoming ELT and its ANDES spectrograph. This study characterizes the high-energy environment of K2-18 with X-ray observations from eROSITA, the soft X-ray instrument on the Spectrum-Roentgen-Gamma (SRG) mission, Chandra, and XMM-Newton. We derive a representative 0.2-2 keV X-ray flux with an APEC thermal plasma model fitted with the Bayesian X-ray Analysis (BXA). With the observed X-ray flux from the exoplanet host star, we estimate the photoevaporative mass loss of exoplanet K2-18b using the energy-limited model. In addition, we examine the thermal structure of the system based on a hydrodynamic model. In 100 ks XMM-Newton observation we identified K2-18 as a very faint X-ray source with $\mathrm{F_X = 10^{-15}\ erg\,s^{-1}\,cm^{-2}}$, with an activity level of (Lx/Lbol) $\sim 10^{-5}$. A small flare has been detected during the observation. The planet is irradiated by an X-ray flux of $\mathrm{F_{pl,X} = 12\pm3\ erg\,s^{-1}\,cm^{-2}}$. The X-ray flux measurement of K2-18 gives important limitations for atmospheric escape and photochemical modeling of its exoplanets. Despite its near orbit around an M-dwarf star, K2-18b's low activity level environment suggests that it can retain an atmosphere, supporting recent tentative detections of atmospheres.
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All authors S. Rukdee, M. Güdel, I. Vilović, K. Poppenhäger, S. Boro Saikia, J. Buchner, B. Stelzer, G. Roccetti, J. V. Seidel, V. Burwitz

Instrumentation and Methods for Astrophysics

Textual interpretation of transient image classifications from large language models

Fiorenzo Stoppa, Turan Bulmus, Steven Bloemen et al. (+4 more)

Modern astronomical surveys deliver immense volumes of transient detections, yet distinguishing real astrophysical signals (for example, explosive events) from bogus imaging artefacts remains a challenge. Convolutional neural networks are effectively used for real versus bogus classification; however, their reliance on opaque latent representations hinders interpretability. Here we show that large language models (LLMs) can approach the performance level of a convolutional neural network on three optical transient survey datasets (Pan-STARRS, MeerLICHT and ATLAS) while simultaneously producing direct, human-readable descriptions for every candidate. Using only 15 examples and concise instructions, Google's LLM, Gemini, achieves a 93% average accuracy across datasets that span a range of resolution and pixel scales. We also show that a second LLM can assess the coherence of the output of the first model, enabling iterative refinement by identifying problematic cases. This framework allows users to define the desired classification behaviour through natural language and examples, bypassing traditional training pipelines. Furthermore, by generating textual descriptions of observed features, LLMs enable users to query classifications as if navigating an annotated catalogue, rather than deciphering abstract latent spaces. As next-generation telescopes and surveys further increase the amount of data available, LLM-based classification could help bridge the gap between automated detection and transparent, human-level understanding.
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All authors Fiorenzo Stoppa, Turan Bulmus, Steven Bloemen, Stephen J. Smartt, Paul J. Groot, Paul Vreeswijk, Ken W. Smith

High Energy Astrophysical Phenomena

Recasting the nature of INTEGRAL hard X-ray transients previously classified as active galactic nuclei

V. Sguera and L. Sidoli

We present new broad-band X-ray results aimed at the identification and characterization of four poorly studied hard X-ray transients discovered by INTEGRAL: IGR J16426+6536, IGR J09446-2636, IGR J21268+6203, and IGR J02447+7046. The key properties and X-ray behavior of these sources have remained largely unknown until now. We investigated the temporal, spectral, and energetic characteristics of their hard X-ray outbursts detected above 20 keV by INTEGRAL. In addition, we performed a systematic analysis of unpublished archival soft X-ray observations below 10 keV, enabling a full exploration of their large INTEGRAL error circles in search of the most likely soft X-ray counterparts. Within their arcsecond-sized X-ray error circles, we identified single optical/near-infrared counterparts for each source. We analyzed their photometric properties to constrain the nature of the systems. Our results show that the X-ray properties of these four transients are inconsistent with the previously proposed extragalactic AGN origin, and instead support a Galactic nature for all of them. Specifically, we propose a very faint X-ray transient classification for IGR J16426+6536, a nearby flaring star for IGR J09446-2636 and IGR J21268+6203, finally a gamma-ray binary nature for IGR J02447+7046.
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Astrophysics of Galaxies

The radial acceleration relation at the EDGE of galaxy formation: testing its universality in low-mass dwarf galaxies

Mariana P. Júlio, Justin I. Read, Marcel S. Pawlowski et al. (+6 more)

A tight correlation between the baryonic and observed acceleration of galaxies has been reported over a wide range of mass ($10^8 < M_{\rm bar}/{\rm M}_\odot < 10^{11}$) - the Radial Acceleration Relation (RAR). This has been interpreted as evidence that dark matter is actually a manifestation of some modified weak-field gravity theory. In this paper, we study the radially resolved RAR of 12 nearby dwarf galaxies, with baryonic masses in the range $10^4 < M_{\rm bar}/{\rm M}_\odot < 10^{7.5}$, using a combination of literature data and data from the MUSE-Faint survey. We use stellar line-of-sight velocities and the Jeans modelling code GravSphere to infer the mass distributions of these galaxies, allowing us to compute the RAR. We compare the results with the EDGE simulations of isolated dwarf galaxies with similar stellar masses in a $\Lambda$CDM cosmology. We find that most of the observed dwarf galaxies lie systematically above the low-mass extrapolation of the RAR. Each galaxy traces a locus in the RAR space that can have a multi-valued observed acceleration for a given baryonic acceleration, while there is significant scatter from galaxy to galaxy. Our results indicate that the RAR does not apply to low-mass dwarf galaxies and that the inferred baryonic acceleration of these dwarfs does not contain enough information, on its own, to derive the observed acceleration. The simulated EDGE dwarfs behave similarly to the real data, lying systematically above the extrapolated RAR. We show that, in the context of modified weak-field gravity theories, these results cannot be explained by differential tidal forces from the Milky Way, nor by the galaxies being far from dynamical equilibrium, since none of the galaxies in our sample seems to experience strong tides. As such, our results provide further evidence for the need for invisible dark matter in the smallest dwarf galaxies.
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All authors Mariana P. Júlio, Justin I. Read, Marcel S. Pawlowski, Pengfei Li, Daniel Vaz, Jarle Brinchmann, Martin P. Rey, Oscar Agertz, Tom Holmes

Astrophysics of Galaxies

Unlocking AGN Variability with Custom ZTF Photometry for High-Fidelity Light Curves and Robust Selection

P. Arévalo, P. Sánchez-Sáez, B. Sotomayor et al. (+2 more)

(Abridged)We explore the potential of optical variability selection methods to identify AGN, including those challenging to detect with conventional techniques. Using the unprecedented combination of depth, sky coverage, and cadence of the ZTF survey, we target even starlight-dominated AGN, known for their redder colours, weaker variability signals, and difficult nuclear photometry due to their resolved hosts. We perform aperture photometry on ZTF reference-subtracted images for 40 million sources across 8,000 deg^2, assemble light curves and classify objects employing an RF algorithm into 14 classes, including 341,938 candidate AGN. We compare variability metrics derived from our photometry to those obtained from ZTF Data Release light curves (DR11-psf), to assess the impact of our analysis. We find that the fraction of low-z quiescent galaxies exhibiting significant variability drops dramatically (from 98% of the sample to 7%) when replacing the DR11-psf light curves with our difference image, aperture photometry (DI-Ap) version. The overall number of variable low-z AGN remains high (99% when using DR11-psf lightcurves, 83% when using DI-Ap), however, implying that our photometry can detect the fainter variability in host dominated AGN. The classifier effectively distinguishes between AGN and other sources, demonstrating high recovery rates even for AGN in resolved nearby galaxies. AGN candidates in eROSITA's eFEDS field, detected in X-rays and bright enough for ZTF optical observations, were classified as AGN (79%) and non-variable galaxies (20%). These groups show a 2 dex difference in X-ray luminosity but not in X-ray flux. A significant fraction of X-ray AGN are optically too faint for ZTF, and conversely, a quarter of ZTF AGN in the eFEDS area lack X-ray detections, highlighting a wide range of X-ray-to-optical flux ratios in AGN.
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All authors P. Arévalo, P. Sánchez-Sáez, B. Sotomayor, P. Lira F. E. Bauer, S. Ríos

Solar and Stellar Astrophysics · Cross-listed from nucl-ex

Measurement of the $^{35}Cl(n, p)^{35}S$ cross-section at the CERN n\_TOF facility from subthermal energy to 120 keV

Marco Antonio Martínez-Cañadas, Pablo Torres-Sánchez, Javier Praena et al. (+130 more)

Background: The $^{35}Cl(n, p)^{35}S$ reaction is of special interest in three different applications. First, in Boron Neutron Capture Therapy due to the presence of $^{35}Cl$ in brain and skin tissue. Second, it is involved in the creation of $^{36}S$, whose astrophysical origin remains unresolved. Third, in the designing of fast nuclear reactors of new generation based on molten salts. Purpose: To measure the $^{35}Cl(n, p)^{35}S$ cross-section from thermal energy to 120 keV, determine the resonance parameters in this range and Maxwellian Averaged Cross-Section (MACS). Method: We made use of the Time-of-Flight technique with microMEGAS detectors at Experimental Area 2 (EAR-2) of n\_TOF facility at CERN. The $^{10}B(n, \alpha)^{7}Li$ and $^{235}U(n, f)$ reactions were used as references. Rutherford Back-scattering Spectrometry technique was performed at Centro Nacional de Aceleradores (CNA) in Sevilla, in order to accurately determine the masses of the irradiated samples. Results: We obtain a thermal cross-section of $0.470 \pm 0.009$ barns. The $1/v$ energy dependence of the cross-section is observed up to the first resonance at 0.398 keV, the resonances up to 120 keV are analyzed and MACS calculated for $k_{B} T$ from 1 to 100 keV. Conclusions: The $^{35}Cl(n, p)^{35}S$ cross-section has been obtained over a wide energy range for the first time, with high accuracy across the aforementioned range. The thermal cross-section and first two resonances are in agreement with latest evaluation in ENDF/B-VIII.1, while lower resonance strength was found for high energy resonances. These data are used to calculate the MACS for different $k_{B} T$.
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All authors Marco Antonio Martínez-Cañadas, Pablo Torres-Sánchez, Javier Praena, Ignacio Porras, Marta Sabaté-Gilarte, Oliver Aberle, Victor Alcayne, Simone Amaducci, Józef Andrzejewski, Laurent Audouin, Vicente Bécares, Victor Babiano-Suarez, Michael Bacak, Massimo Barbagallo, František Bečvář, Giorgio Bellia, Eric Berthoumieux, Jon Billowes, Damir Bosnar, Adam Brown, Maurizio Busso, Manuel Caamaño, Luis Caballero, Francisco Calviño, Marco Calviani, Daniel Cano-Ott, Adria Casanovas, Francesco Cerutti, Yonghao Chen, Enrico Chiaveri, Nicola Colonna, Guillem Cortés, Miguel Cortés-Giraldo, Luigi Cosentino, Sergio Cristallo, Lucia-Anna Damone, Maria Diakaki, Mirco Dietz, César Domingo-Pardo, Rugard Dressler, Emmeric Dupont, Ignacio Durán, Zinovia Eleme, Beatriz Fernández-Domínguez, Alfredo Ferrari, Francisco Javier Ferrer, Paolo Finocchiaro, Valter Furman, Kathrin Göbel, Ruchi Garg, Aleksandra Gawlik-Ramięga, Benoit Geslot, Simone Gilardoni, Tudor Glodariu, Isabel Gonçalves, Enrique González-Romero, Carlos Guerrero, Frank Gunsing, Hideo Harada, Stephan Heinitz, Jan Heyse, David Jenkins, Erwin Jericha, Franz Käppeler, Yacine Kadi, Atsushi Kimura, Niko Kivel, Michael Kokkoris, Yury Kopatch, Milan Krtička, Deniz Kurtulgil, Ion Ladarescu, Claudia Lederer-Woods, Helmut Leeb, Jorge Lerendegui-Marco, Sergio Lo Meo, Sarah-Jane Lonsdale, Daniela Macina, Alice Manna, Trinitario Martínez, Alessandro Masi, Cristian Massimi, Pierfrancesco Mastinu, Mario Mastromarco, Francesca Matteucci, Emilio-Andrea Maugeri, Annamaria Mazzone, Emilio Mendoza, Alberto Mengoni, Veatriki Michalopoulou, Paolo Maria Milazzo, Federica Mingrone, Agatino Musumarra, Alexandru Negret, Ralf Nolte, Francisco Ogállar, Andreea Oprea, Nikolas Patronis, Andreas Pavlik, Jarosław Perkowski, Luciano Persanti, José-Manuel Quesada, Désirée Radeck, Diego Ramos-Doval, Thomas Rauscher, René Reifarth, Dimitri Rochman, Carlo Rubbia, Alok Saxena, Peter Schillebeeckx, Dorothea Schumann, Gavin Smith, Nikolay Sosnin, Athanasios Stamatopoulos, Giuseppe Tagliente, José Tain, Zeynep Talip, Ariel Tarifeño-Saldivia, Laurent Tassan-Got, Andrea Tsinganis, Jiri Ulrich, Sebastian Urlass, Stanislav Valenta, Gianni Vannini, Vincenzo Variale, Pedro Vaz, Alberto Ventura, Vasilis Vlachoudis, Rosa Vlastou, Anton Wallner, Philip John Woods, Tobias Wright, Petar Žugec

Astrophysics of Galaxies

MEGATRON: The environments of Population III stars at Cosmic Dawn and their connection to present day galaxies

Anatole Storck, Harley Katz, Julien Devriendt et al. (+7 more)

We present results of Pop. III formation in the MEGATRON suite of simulations, which self-consistently follows radiation and non-equilibrium chemistry, and resolves gas at near-pc resolution of a Milky Way-mass halo at Cosmic Dawn. While the very first Pop. III stars form in halos with masses well below the atomic cooling limit, whose cooling is dominated by molecular hydrogen, the majority of Pop. III stars form in more massive systems above the $10^4$~K atomic cooling threshold. The shift in cooling regime of halos hosting new Pop. III stars occurs within $100$ Myr of the first Pop. III star as the Lyman-Werner (LW) background rapidly increases to $10^{-21}\,\rm erg\,s^{-1}\,cm^{-2}\,Hz^{-1}\,sr^{-1}$. We find that the global Pop. III star formation rate stabilizes to a value of $10^{-3}\,\rm M_\odot\,yr^{-1}$ at $z=20$. Among the three processes that quench Pop. III star formation in mini-halos, the LW background, gas starvation, and external chemical enrichment, the LW background is most important. A small fraction of haloes undergo multiple episodes of Pop. III star formation when the earlier forming stars all directly collapse to black holes. If the halos become massive enough, they can form up to $\sim100$ Pop. III stars in a single burst, which may be observable by JWST with moderate gravitational lensing. Pop. III stars form at a wide range of distances from UV-bright galaxies, with only $0.06\%$ of Pop. III stars forming within the virial radius of galaxies with $M_{\rm UV} < -17$. Finally, by tracking Pop. III star remnants down to $z=0$, we find that $75-80\,$% reside in the stellar halo of our simulated Milky Way analogue, while the remainder are gravitationally bound to lower-mass systems, including satellite halos.
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All authors Anatole Storck, Harley Katz, Julien Devriendt, Adrianne Slyz, Corentin Cadiou, Nicholas Choustikov, Martin P. Rey, Aayush Saxena, Oscar Agertz, Taysun Kimm

Astrophysics of Galaxies

JWST observations of photodissociation regions: II. Warm molecular Hydrogen spectroscopy in the Horsehead nebula

M. Zannese, P. Guillard, A. Abergel et al. (+16 more)

H2 is the most abundant molecule in the interstellar medium and is a useful tool to study photodissociation regions, where radiative feedback from massive stars on molecular clouds is dominant. The James Webb Space Telescope, with its high spatial resolution, sensitivity, and wavelength coverage provides unique access to the detection of most of H2 lines and the analysis of its spatial morphology. Our goal is to use H2 line emission detected with the JWST in the Horsehead nebula to constrain the physical parameters (e.g., extinction, gas temperature, thermal pressure) throughout the PDR and its geometry. The study of H2 morphology reveals that FUV-pumped lines peak closer to the edge of the PDR than thermalized lines. From H2 lines, we estimate the value of extinction throughout the PDR. We find that AV is increasing from the edge of the PDR to the second and third H2 filaments. Then, we study the H2 excitation in different regions across the PDR. The temperature profile shows that the observed gas temperature is quite constant throughout the PDR, with a slight decline in each of the dissociation fronts. This study also reveals that the OPR is far from equilibrium. We observe a spatial separation of para and ortho rovibrational levels, indicating that efficient ortho-para conversion and preferential ortho self-shielding are driving the spatial variations of the OPR. Finally, we derive a thermal pressure in the first filament around P > 6x10$^6$ K cm$^{-3}$, about ten times higher than that of the ionized gas. We highlight that template stationary 1D PDR models cannot account for the intrinsic 2D structure and the very high temperature observed in the Horsehead nebula. We argue the highly excited, over-pressurized H2 gas at the edge of the PDR interface could originate from the mixing between the cold and hot phase induced by the photo-evaporation of the cloud.
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All authors M. Zannese, P. Guillard, A. Abergel, E. Habart, P. Dell'Ova, B. Trahin, J. Le Bourlot, K. Misselt, D. Van De Putte, A. N. Witt, K. D. Gordon, A. Noriega-Crespo, M. Baes, P. Bouchet, B. R. Brandl, M. Elyajouri, O. Kannavou, P. Klassen, N. Ysard

High Energy Astrophysical Phenomena

Hard X-ray view of two $\gamma$-ray detected low-luminosity active galactic nuclei: NGC 315 and NGC 4261

Yuwei Yu and Jin Zhang

Aims. The accretion disk of low-luminosity active galactic nuclei (LLAGNs) is a radiatively inefficient accretion flow (RIAF). Our goal is to find evidence of RIAF radiation from LLAGNs with jets and analyze their radiation properties, which also adds samples to future research on LLAGNs. Methods. Weconducted an analysis of the X-ray data obtained from NuSTAR and XMM-Newton observations of NGC 315 and NGC 4261, encompassing both timing and spectral investigations. The joint X-ray spectra of the two LLAGNs were fitted using various functional forms and radiative models in XSPEC. Results. No significant variability on timescales of days is observed for both NGC 315 and NGC 4261. The X-ray continuum emission of NGC 315 is suitable for cutoff power-law (PL) fitting, yielding a cutoff energy of Ecut = 18.45 keV, which is the lowest value found in LLAGNssofar. In contrast, the X-ray continuum of NGC 4261 is composed of two PL components, with no signs of a cutoff energy. A prominent neutral Fe K{\alpha} line is observed in NGC 315, while an ionized Fe XXV line is seen in NGC 4261. The derived reflection fractions are R = 0.61 for NGC 315 and R = 0.18 for NGC 4579. Neither NGC 315 nor NGC 4261 shows evidence of a Compton reflection bump. Conclusions. The X-ray spectral characteristics support the RIAF emission as the dominant origin of the X-rays in both sources, although an additional soft PL component originating from the inner jet is observed in NGC 4261. The higher reflection fraction compared to other LLAGNs, along with the detection of a neutral Fe K{\alpha} line, suggests the existence of a truncated accretion disk with a relatively small radius in NGC 315. Bremsstrahlung radiation appears to be the dominant cooling mechanism for the plasma in NGC315, while Comptonization within the RIAF is more likely responsible for the X-ray emission in NGC 4261.
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High Energy Astrophysical Phenomena

A Giant Peanut-shaped Ultra-High-Energy Gamma-Ray Emitter Off the Galactic Plane

Zhen Cao, Felix Aharonian, Yunxiang Bai et al. (+313 more)

Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts), {\gamma}-rays manifests extreme particle acceleration in astrophysical sources. Recent observations by {\gamma}-ray telescopes, particularly by the Large High Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE sources, indicating numerous Galactic sources capable of accelerating particles to PeV (10^15 electronvolts) energies. However, discerning the dominant acceleration mechanisms (leptonic versus hadronic), the relative contributions of specific source classes, and the role of particle transport in shaping their observed emission are central goals of modern UHE astrophysics. Here we report the discovery of a giant UHE {\gamma}-ray emitter at -17.5{\deg} off the Galactic plane - a region where UHE {\gamma}-ray sources are rarely found. The emitter exhibits a distinctive asymmetric shape, resembling a giant "Peanut" spanning 0.45{\deg} \times 4.6{\deg}, indicative of anisotropic particle distribution over a large area. A highly aged millisecond pulsar (MSP) J0218+4232 is the sole candidate accelerator positionally coincident with the Peanut region. Its association with UHE {\gamma}-rays extending to 0.7 PeV, if confirmed, would provide the first evidence of a millisecond pulsar powering PeV particles. Such a finding challenges prevailing models, which posit that millisecond pulsars cannot sustain acceleration to PeV energies. The detection reveals fundamental gaps in understanding particle acceleration, cosmic-ray transport, and interstellar magnetic field effects, potentially revealing new PeV accelerator (PeVatron) classes.
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All authors Zhen Cao, Felix Aharonian, Yunxiang Bai, Yiwei Bao, Denis Bastieri, Xiaojun Bi, YuJiang Bi, Mr Bian WenYi, A. Butkevich, Chengmiao Cai, Wenyu Cao, Zhe Cao, Jin Chang, Jinfan Chang, Mr Aming Chen, Ensheng Chen, Mr Guo-Hai Chen, Mr Huaxi Chen, Liang Chen, Long Chen, Mingjun Chen, Mali Chen, Qihui Chen, Shi Chen, Suhong Chen, Songzhan Chen, Tianlu Chen, Xiaobin Chen, Xuejian Chen, Yang Chen, Ning Cheng, Yaodong Cheng, Ming Chung Chu, Mingyang Cui, Shuwang Cui, Xiaohong Cui, Yidong Cui, Benzhong Dai, Hongliang Dai, Z. G. Dai, Danzengluobu ., Yangxuan Diao, Xuqiang Dong, Kaikai Duan, Junhui Fan, Yi-Zhong Fan, Jun Fang, Jianhua Fang, Kun Fang, Cunfeng Feng, Hua Feng, Li Feng, Shaohui Feng, Xiaoting Feng, Yi Feng, Youliang Feng, Stefano Gabici, Bo Gao, Chuandong Gao, Qi Gao, Wei Gao, Weikang Gao, Maomao Ge, Ting-Ting Ge, Lisi Geng, Gwenael Giacinti, Guanghua Gong, Quanbu Gou, Minhao Gu, Fulai Guo, Jing Guo, Xiaolei Guo, Yiqing Guo, Yingying Guo, Yiang Han, Otto A. Hannuksela, Mariam Hasan, Huihai He, Hao-Ning He, Jiayin He, Xinyu He, Yu He, Sergio Hernández-Cadena, Bowen Hou, Chao Hou, Xian Hou, Hongbo Hu, Shicong Hu, Chen Huang, Daihui Huang, Jiajun Huang, Tian-Qi Huang, Wenjun Huang, Xingtao Huang, Xiaoyuan Huang, Yong Huang, Yi-Yun Huang, Xiaolu Ji, Huanyu Jia, Kang Jia, Houbing Jiang, Kun Jiang, Xiaowei Jiang, Zejun Jiang, Min Jin, Samy Kaci, Mingming Kang, Ivan Karpikov, Dmitry Khangulyan, Denis Kuleshov, Kirill Kurinov, Bingbing Li, Cheng Li, Mr Cong Li, Dan Li, Fei Li, Haibo Li, Huicai Li, Jian Li, Jie Li, Kai Li, Long Li, Rong-Lan Li, Sidai Li, Tianyang Li, Wenlian Li, Xiurong Li, Xin Li, Yizhuo Li, Yuan Li, Zhe Li, Zhuo Li, Enwei Liang, Yunfeng Liang, Su-Jie Lin, Bing Liu, Cheng Liu, Dong Liu, Dangbo Liu, Hu Liu, Haidong Liu, Jia Liu, Jiali Liu, Jiren Liu, Maoyuan Liu, Ruo-Yu Liu, Siming Liu, Wei Liu, Xi Liu, Mr Yi Liu, Yu Liu, Yinong Liu, Yu-Qing Lou, Qing Luo, Yu Luo, Hongkui Lv, Bo-Qiang Ma, Lingling Ma, Xinhua Ma, Jirong Mao, Zhen Min, Warit Mitthumsiri, Guobin Mou, Huijun Mu, Andrii Neronov, Kenny Chun Yu Ng, Mingyang Ni, Lin Nie, Mr Lejian Ou, Petchara Pattarakijw anich, Zhiyuan Pei, Jincan Qi, Mengyao Qi, Jiajun Qin, Ali Raza, Chongyang Ren, David Ruffolo, Alejandro Sáiz, Dmitri Semikoz, Lang Shao, Oleg Shchegolev, Yunzhi Shen, Xiangdong Sheng, Zhaodong Shi, Fuwen Shu, Huichao Song, Vladimir Stepanov Stepanov, Yang Su, Dongxu Sun, Hao Sun, Qinning Sun, Xiaona Sun, Zhibin Sun, Mr Nabeel Tabasam, Jumpei Takata, P. H. T. Tam, Honbin Tan, Qingwen Tang, Ruiyi Tang, Zebo Tang, Wenwu Tian, Chaonan Tong, Li-Hong Wan, Chao Wang, Guangwei Wang, Hongguang Wang, Jiancheng Wang, Ke Wang, Kai Wang, Kai Wang, Liping Wang, Lingyu Wang, Luyao Wang, Ran Wang, Wei Wang, Xianggao Wang, Xinjian Wang, Xiang-Yu Wang, Yang Wang, Yudong Wang, Zhonghai Wang, Zhongxiang Wang, Zheng Wang, Daming Wei, Jun-Jie Wei, Yongjian Wei, Tao Wen, Shan-Shan Weng, Chaoyong Wu, Hanrong Wu, Qingwen Wu, Sha Wu, Xue-Feng Wu, Yusheng Wu, Shaoqiang Xi, Jie Xia, Junji Xia, Guangman Xiang, Dixuan Xiao, Gang Xiao, Yuliang Xin, Yi Xing, Dingrong Xiong, Zheng Xiong, Donglian Xu, Renfeng Xu, Renxin Xu, Weili Xu, Liang Xue, Dahai Yan, Tian Yan, Chaowen Yang, Chuyuan Yang, Fengfan Yang, Lili Yang, Mingjie Yang, Ruizhi Yang, Ms Wen-xin Yang, Zihan Yang, Zhiguo Yao, Xuanang Ye, Liqiao Yin, Na Yin, Xiaohao You, Zhiyong You, Qiang Yuan, Hua Yue, Houdun Zeng, Tingxuan Zeng, Wei Zeng, Xiangtao Zeng, Min Zha, Binbin Zhang, Bing Zhang, Chao Zhang, Feng Zhang, Hongfei Zhang, Haiming Zhang, Hengying Zhang, Jianli Zhang, Li Zhang, Pengfei Zhang, Peipei Zhang, Rui Zhang, Shaoru Zhang, Shoushan Zhang, Weiyan Zhang, Xiao Zhang, Xiaopeng Zhang, Yi Zhang, Yong Zhang, Zhipeng Zhang, Jing Zhao, Lei Zhao, Lizhi Zhao, Shiping Zhao, Xiao-Hong Zhao, Zihao Zhao, Fu Zheng, Wenjuan Zhong, Bin Zhou, Hao Zhou, Jianeng Zhou, Meng Zhou, Ping Zhou, Rong Zhou, Xiaoxi Zhou, Xunxiu Zhou, Ben-Yang Zhu, Chengguang Zhu, Fengrong Zhu, Hui Zhu, Kejun Zhu, Yuan-chuan Zou, Xiong Zuo, Oscar Macias

Instrumentation and Methods for Astrophysics

Low-noise Fourier Transform Spectroscopy Enabled by Superconducting On-Chip Filterbank Spectrometers

Chris S. Benson, Peter S. Barry, Patrick Ashworth et al. (+4 more)

Historically employed spectroscopic architectures used for large field of view mapping spectroscopy in millimetere and sub-millimetre astronomy suffer from significant drawbacks. On-chip filterbank spectrometers are a promising technology in this respect; however, they must overcome an orders-of-magnitude increase in detector counts, efficiency loss due to dielectric properties, and stringent fabrication tolerances that currently limit scaling to resolutions of order 1000 over a large array. We propose coupling a medium-resolution Fourier transform spectrometer to a low-resolution filterbank spectrometer focal plane, which serves as a post-dispersion element. In this arrangement, medium resolution imaging spectroscopy is provided by the Fourier transform spectrometer, while the low resolution filterbank spectrometer serves to decrease the photon noise inherent in typical broadband Fourier transform spectrometer measurements by over an order of magnitude. This is achieved while maintaining the excellent imaging advantages of both architectures. We present predicted mapping speeds for a filterbank-dispersed Fourier transform spectrometer from a ground-based site and a balloon-borne platform. We also demonstrate the potential that an instrument of this type has for an R~1000 line intensity mapping experiment using the James Clerk Maxwell Telescope as an example platform. We demonstrate that a filterbank-dispersed Fourier transform spectrometer would be capable of R~1000 measurements of CO power spectra with a signal-to-noise ratio of 10–100 with surveys of $10^5$–$10^6$ spectrometer hours.
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All authors Chris S. Benson, Peter S. Barry, Patrick Ashworth, Harry Gordon-Moys, Kirit S. Karkare, Izaak Morris, Gethin Robson

Astrophysics of Galaxies

A Sample of HeII $\lambda$4686 "Changing-Look" Quasars

Wentao Lu and Jun-Xian Wang

We present the first systematic search for "changing-look" ("CL") behavior in the broad He ii $\lambda$4686 emission line in quasars, utilizing repeated spectroscopy from the Sloan Digital Sky Survey (SDSS). The He ii line, originating from high-ionization gas and powered by extreme ultraviolet photons, serves as a sensitive tracer of changes in the ionizing continuum. After applying strict spectral selection criteria and visual inspection to a parent sample of over 9,000 quasars with multi-epoch spectra, we identify a sample of 34 He ii "changing-look" quasars that show a significant appearance or disappearance of the broad He ii $\lambda$4686 line. Compared with previously known H$\beta$ "CL" quasars, the He ii "CL" sample exhibits similarly strong continuum variability and broad-line flux changes, yet shows a preference for higher Eddington ratios and lower host-galaxy contamination. These results highlight the value of He ii line in studying the central variable engines of AGNs and uncovering a more complete census of extreme quasar variability. A comparison with H$\beta$ "CL" further underscores the profound selection biases inherent in "changing-look" studies, especially those associated with line strength, host-galaxy contamination, and spectral signal-to-noise ratio.
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Astrophysics of Galaxies

Warm absorber outflows in radio-loud active galactic nucleus 3C~59

Yijun Wang, Tao Wang, Junjie Mao et al. (+8 more)

Both jets and ionized outflows in active galactic nuclei (AGNs) are thought to play important roles in affecting the star formation and evolution of host galaxies, but their relationship is still unclear. As a pilot study, we performed a detailed spectral analysis for a radio-loud (RL) AGN 3C~59 ($z=0.1096$) by systematically considering various factors that may affect the fitting results, and thereby establishing a general spectral fitting strategy for subsequent research with larger sample. 3C~59 is one rare target for simultaneously studying jets and warm absorbers (WAs) that is one type of ionized outflows. Based on the multi-wavelength data from near-infrared (NIR) to hard X-ray bands detected by DESI, GALEX, and XMM-Newton, we used SPEX code to build broadband continuum models and perform photoionization modeling with PION code to constrain the physical parameters of WAs in 3C~59. We found two WAs with ionization parameter of $\log [\xi/(\rm{erg\ cm\ s}^{-1})] = 2.65^{+0.10}_{-0.09}$ and $1.65\pm 0.11$, respectively, and their outflowing velocities are $v_{\rm out} = -528^{+163}_{-222}\ \rm{km\ s}^{-1}$ and $-228^{+121}_{-122}\ \rm{km\ s}^{-1}$, respectively. These WAs are located between outer torus and narrow (emission-)line region, and their positive $v_{\rm out}$-$\xi$ relation can be explained by the radiation-pressure-driven mechanism. We found that the estimations of these physical properties are affected by the different spectral fitting strategies, such as the inclusion of NIR to ultra-violet data, the choice of energy range of spectrum, or the composition of the spectral energy distribution. Based on the same fitting strategy, this work presents a comparative study of outflow driven mechanism between a RL AGN (3C 59) and a radio-quiet AGN (NGC 3227), which suggests a similar driven mechanism of their WA outflows and a negligible role of jets in this process.
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All authors Yijun Wang, Tao Wang, Junjie Mao, Yerong Xu, Zhicheng He, Zheng Zhou, Chen Li, Yongquan Xue, Jiayi Chen, Fangzheng Shi, Missagh Mehdipour

High Energy Astrophysical Phenomena

Identifying the secondary jet in the RadioAstron image of OJ~287

Mauri J. Valtonen, Lankeswar Dey, Staszek Zola et al. (+27 more)

The 136 year long optical light curve of OJ~287 is explained by a binary black hole model where the secondary is in a 12 year orbit around the primary. Impacts of the secondary on the accretion disk of the primary generate a series of optical flares which follow a quasi-Keplerian relativistic mathematical model. The orientation of the binary in space is determined from the behavior of the primary jet. Here we ask how the jet of the secondary black hole projects onto the sky plane. Assuming that the jet is initially perpendicular to the disk, and that it is ballistic, we follow its evolution after the Lorentz transformation to the observer's frame. Since the orbital speed of the secondary is of the order of one-tenth of the speed of light, the result is a change in the jet direction by more than a radian during an orbital cycle. We match the theoretical jet line with the recent 12 $\mu$as-resolution RadioAstron map of OJ~287, and determine the only free parameter of the problem, the apparent speed of the jet relative to speed of light. It turns out that the Doppler factor of the jet, $\delta\sim5$, is much lower than in the primary jet. Besides following a unique shape of the jet path, the secondary jet is also distinguished by a different spectral shape than in the primary jet. The present result on the spectral shape agrees with the huge optical flare of 2021 November 12, also arising from the secondary jet.
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All authors Mauri J. Valtonen, Lankeswar Dey, Staszek Zola, Alok C. Gupta, Shubham Kishore, Achamveedu Gopakumar, Paul J. Wiita, Minfeng Gu, Kari Nilsson, Zhongli Zhang, Rene Hudec, Katsura Matsumoto, Marek Drozdz, Waldemar Ogloza, Andrei V. Berdyugin, Daniel E. Reichart, Markus Mugrauer, Tapio Pursimo, Stefano Ciprini, Tatsuya Nakaoka, Makoto Uemura, Ryo Imazawa, Michal Zejmo, Vladimir V. Kouprianov, James W. Davidson, Jr., Alberto Sadun, Jan Strobl, Martin Jelinek, Abhimanyu Susobhanan

High Energy Astrophysical Phenomena

Diagnosing the Properties and Evolutionary Fates of Black Hole and Wolf-Rayet X-ray Binaries as Potential Gravitational Wave Sources for the LIGO-Virgo-KAGRA Network

Zi-Yuan Wang, Ying Qin, Georges Meynet et al. (+7 more)

IC 10 X-1, NGC 300 X-1, and Cyg X-3 constitute a unique class of X-ray binaries in which a stellar-mass black hole (BH) accretes material from a Wolf-Rayet (WR). These systems are particularly intriguing because of their short orbital periods, which make them promising progenitors of gravitational-wave (GW) sources detectable by the LIGO-Virgo-KAGRA (LVK) network. Adopting a revised accretion efficiency within the standard Bondi-Hoyle-Lyttleton framework, we perform detailed binary evolution calculations using MESA to characterize their properties at different evolutionary stages and to assess their ultimate fates as potential LVK-detectable GW sources. By applying additional constraints from the observed properties of IC 10 X-1 and NGC 300 X-1, we find that the upper limits on the BH masses in these systems ($M_{\rm BH} \lesssim 25\, M_\odot$ for IC 10 X-1 and $M_{\rm BH} \lesssim 15\, M_\odot$ for NGC 300 X-1) are significantly lower than previous estimates. Both systems are expected to form binary black holes (BBHs) that will merge within a Hubble time, except in the case where the BH in NGC 300 X-1 has a mass of $9\,M_\odot$, corresponding to the lower limit inferred in a previous study using the continuum-fitting method with a relativistic slim-disc model. For Cyg X-3, we find that the BH spin magnitude is constrained to be $\lesssim$ 0.6. Moreover, the WR star in Cyg X-3 is likely to form a lower-mass-gap BH, and the resulting BBH system is also expected to merge within a Hubble time.
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All authors Zi-Yuan Wang, Ying Qin, Georges Meynet, Qing-Zhong Liu, Xin-Wen Shu, Ya-Wen Xue, Liang Yuan, Jun-Qian Li, Kun Jia, Han-Feng Song

Cosmology and Nongalactic Astrophysics

Benchmarking AI-evolved cosmological structure formation

Xiaofeng Dong, Nesar Ramachandra, Salman Habib et al. (+1 more)

The potential of deep learning-based image-to-image translations has recently attracted significant attention. One possible application of such a framework is as a fast, approximate alternative to cosmological simulations, which would be particularly useful in various contexts, including covariance studies, investigations of systematics, and cosmological parameter inference. To investigate different aspects of learning-based cosmological mappings, we choose two approaches for generating suitable cosmological matter fields as datasets: a simple analytical prescription provided by the Zel'dovich approximation, and a numerical N-body method using the Particle-Mesh approach. The evolution of structure formation is modeled using U-Net, a widely employed convolutional image translation framework. Because of the lack of a controlled methodology, validation of these learned mappings requires multiple benchmarks beyond simple visual comparisons and summary statistics. A comprehensive list of metrics is considered, including higher-order correlation functions, conservation laws, topological indicators, and statistical independence of density fields. We find that the U-Net approach performs well only for some of these physical metrics, and accuracy is worse at increasingly smaller scales, where the dynamic range in density is large. By introducing a custom density-weighted loss function during training, we demonstrate a significant improvement in the U-Net results at smaller scales. This study provides an example of how a family of physically motivated benchmarks can, in turn, be used to fine-tune optimization schemes – such as the density-weighted loss used here – to significantly enhance the accuracy of scientific machine learning approaches by focusing attention on relevant features.
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All authors Xiaofeng Dong, Nesar Ramachandra, Salman Habib, Katrin Heitmann

Astrophysics of Galaxies

3D B-fieLds in the InterStellar medium and Star-forming regions (3D-BLISS): I. Using Starlight Polarization in the Massive IRDC Filament G11.11-0.12

Bao Truong, Thiem Hoang, Nguyen Bich Ngoc et al. (+3 more)

Measuring three-dimensional magnetic fields (3D B-fields) is essential to understand the formation and evolution of the interstellar medium and multi-scale star formation; however, the accurate measurement of 3D B-fields is still challenging. The dust polarization angles by magnetically aligned grains provide the projected B-fields onto the plane-of-sky, while the dust polarization degree provides the B-field's inclination angle with respect to the line-of-sight. Our previous theoretical studies proposed a new method of probing 3D B-fields using dust polarization combined with the Radiative Torque (RAT) alignment theory and demonstrated the accurate inference of B-field inclination angles using synthetic polarization data. In this paper, we report the first application of the new technique to study 3D B-fields and dust properties in the G11.11-0.12 filament (hereafter G11) from starlight polarization observations taken by ISRF/SIRPOL at $2.19\,\rm\mu m$. Using both observed starlight polarization and optical dust extinction curves from the Gaia mission, we constrained the maximum grain size of $0.25\,\rm\mu m$ and the grain elongation with an axial ratio of $s\gtrsim 1.4$ in the outer regions of G11. We calculated the alignment properties in G11 by using the DustPOL\_py code. The B-field's inclination angles in G11 are then inferred from the observed starlight polarization efficiency when the grain alignment is included, with a mean angle of $\sim 48$ degrees. From these inferred inclination angles, we found evidence of the local 3D arc-shaped B-field structure toward the sightline. These findings are important for understanding 3D B-field's roles in the formation and evolution of massive filamentary clouds.
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All authors Bao Truong, Thiem Hoang, Nguyen Bich Ngoc, Nguyen Chau Giang, Le Ngoc Tram, Ngan Le

Astrophysics of Galaxies

Spectropolarimetry of NGC 1275 reveals a narrow-line radio galaxy with polarization parallel to its radio jet axis

F. Marin, T. Pursimo, I. Liodakis et al. (+4 more)

Concomitant with the Imaging X-ray Polarimetry Explorer (IXPE) observation of the Perseus cluster, we obtained optical spectropolarimetry of its central active galactic nucleus, NGC 1275, using the Alhambra Faint Object Spectrograph and Camera (ALFOSC) on the Nordic Optical Telescope (NOT). While the total-light spectrum confirms its edge-on, core obscured (type-2) classification, the polarized spectrum shows a polarization angle aligned with the arcsecond radio jet axis – an exceptional behavior for type-2 objects. Our polarization analysis also reveals wavelength-dependent linear polarization at level 2-3% in the continuum, likely rising from a combination of variable syn
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All authors F. Marin, T. Pursimo, I. Liodakis, E. Lindfors, J. Biedermann, D. Hutsemékers, M. Turkki

Astrophysics of Galaxies

The Star-forming Main Sequence and Bursty Star-formation Histories at $z>1.4$ in JADES and AURORA

Leonardo Clarke, Alice E. Shapley, Natalie Lam et al. (+5 more)

We analyze JWST spectroscopic and HST+JWST photometric observations of 659 star-forming galaxies at $1.4<z<9$ from DR3 of the JADES survey and the AURORA Cycle 1 program. We measure the star-forming main sequence (SFMS) for galaxies above $10^{8.5}\rm\ M_\odot$ where the sample is largely representative, estimating star-formation rates (SFRs) using the H$\alpha$ line flux and rest-frame far UV (1600Å) continuum measurements, each independently corrected for dust attenuation. We find that the intrinsic, measurement-error-subtracted scatter in the SFMS ($\sigma_{\rm int}$) increases with decreasing stellar mass for the H$\alpha$-based SFMS, and we find no mass dependence of $\sigma_{\rm int}$ in the UV-based SFMS. Additionally, we find that $\sigma_{\rm int}$ decreases with increasing redshift, from $0.36^{+0.02}_{-0.02}$ dex to $0.22^{+0.08}_{-0.07}$ dex (H$\alpha$ SFMS), and from $0.28^{+0.02}_{-0.02}$ dex to $0.20^{+0.08}_{-0.07}$ dex (UV SFMS) between $z\sim2$ and $z\sim 6.5$. We also measure the redshift evolution of the specific SFR and find that, assuming $\rm sSFR\propto (1+z)^\gamma$, $\gamma=1.89^{+0.16}_{-0.15}$ for the H$\alpha$-based SFMS, and $\gamma=1.36^{+0.13}_{-0.13}$ for the UV-based SFMS. Analyzing the observed H$\alpha$/UV luminosity ratios and star-formation histories from the prospector fitting code, we find that 41–60% of the sample is inconsistent with having a constant star-formation history. Finally, we find tentative evidence for shorter SFR burst timescales with increasing redshift based on the distribution of $\rm L_{H\alpha}/\nu L_{\nu,1600}$ vs. $\Delta\rm \log(L_{H\alpha})$. Taken together, these results are consistent with recent theoretical predictions (e.g., the thesan-zoom simulations) of bursty star formation in the early Universe and provide valuable constraints for theoretical models of galaxy evolution.
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All authors Leonardo Clarke, Alice E. Shapley, Natalie Lam, Michael W. Topping, Gabriel B. Brammer, Ryan L. Sanders, Naveen A. Reddy, Shreya Karthikeyan

Astrophysics of Galaxies

Formation of A Nuclear Star Cluster Through A Merger Event In The Low Surface Brightness Galaxy AGC 223218

Tian-Wen Cao, Zi-Qi Chen, Zi-Jian Li et al. (+8 more)

We present the properties of the nuclear star cluster (NSC) in the low surface brightness galaxy AGC 223218. The disk of the galaxy can be modeled using two S$\acute{\rm e}$rsic components with distinct central positions: one representing the inner bright disk and the other corresponding to the extended outer disk. We estimate the stellar masses of the NSC and the host galaxy using two methods: spectral energy distribution (SED) fitting and mass-to-light versus color relations (MLCRs). The stellar mass ratio of the NSC to AGC 223218 is 0.094 based on the SED method and 0.072 using MLCRs. The NSC presents a younger stellar population and a lower [Fe/H] value than the host, as determined from SDSS and LAMOST spectra analysis using pPXF fitting. AGC 223218 is located at the boundary between the Seyfert and star-forming regions in the [SII]-BPT diagram, whereas in the [NII]-BPT diagram, it falls in the track of star-forming SDSS galaxies. This suggests the presence of strong shocks in AGC 223218. We propose that the NSC in AGC 223218 may have formed as a result of a merger event. Furthermore, the observed X-ray luminosity of AGC 223218 with eROSITA is two orders of magnitude higher than the expected X-ray luminosity from X-ray binaries, suggesting the presence of an intermediate-mass black hole (IMBH) in the NSC. To account for the observed X-ray luminosity, we estimate the IMBH accretion rate to be approximately 0.001.
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All authors Tian-Wen Cao, Zi-Qi Chen, Zi-Jian Li, Cheng Cheng, Gaspar Galaz, Venu M. Kalari, Jun-feng Wang, Chun-Yi Zhang, Pei-Bin Chen, Meng-Ting Shen, Hong Wu

Astrophysics of Galaxies

Ionized gas components in low surface brightness galaxy AGC 111629

Tian-Wen Cao, Pei-Bin Chen, Zi-Jian Li et al. (+8 more)

We present integral field spectroscopy of ionized gas components in AGC 111629, an edge-on low surface brightness galaxy (LSBG) with a stellar mass of 5.7$\times$10$^{8}$ M$_{\odot}$. AGC 111629 displays an irregular H$\alpha$ morphology and an arch-like structure in the extraplanar region, which is absent in continuous stellar image. The irregular H$\alpha$ morphology may be related to a past merger event with its satellite galaxy AGC 748815. A peanut-shaped structure at the center in the integrated [OIII]$\lambda$5007 map, with a position angle that differs from that of the main stellar disk. This structure exhibits a higher [OIII]$\lambda$5007/H$\beta$ flux ratio, a larger equivalent width (EW) of [OIII]$\lambda$5007, and a lower H$\alpha$/H$\beta$ flux radio ($<$ 2.86). Some spaxels associated with the peanut-shaped structure fall within the composite region of the BPT diagram based on [NII]$\lambda$6583. These features may be associated with the central AGN. Additionally, a sub-peak in the southern disk is clearly visible in the [OIII]$\lambda$5007 map. An extended region ($\sim$ 2 kpc) with an extremely low value of H$\alpha$/H$\beta$ flux ratio is observed near this sub-peak. We interpret the sub-peak as a superbubble likely driven by supernova explosions in the southern disk. We derive the gas-phase metallicity, 12+log(O/H), using the [NII]$\lambda$6583/H$\alpha$ diagnostic and find that AGC 111629 exhibits low central metallicity. This may result from feedback associated with AGN activity and supernova explosions.
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All authors Tian-Wen Cao, Pei-Bin Chen, Zi-Jian Li, Cheng Cheng, Venu M. Kalari, Meng-Ting Shen, Chun-Yi Zhang, Junfeng Wang, Gaspar Galaz, Hong Wu, Zi-Qi Chen

Solar and Stellar Astrophysics

A chemodynamical study of $r$-process-enhanced stars

Pallavi Saraf, Thirupathi Sivarani, Carlos Allende Prieto et al. (+2 more)

The $r$-process enrichment in the Galaxy still remains elusive with regard to its nucleosynthesis conditions and the astrophysical sites where it occurs. As part of ongoing efforts to pinpoint the origin of chemically peculiar $r$-process-enhanced (RPE) stars, we concentrate in this study on the kinematics of RPE stars to investigate possible variations in the $r$-process enrichment among the Galactic components. We calculate the orbital parameters of a sample of 472 metal-poor RPE stars and associate them to the Galactic bulge, disk and halo populations using a physically motivated classification based on apocenter distance and maximum absolute vertical height of the orbit. We show that the Toomre diagram does not properly separate stars in the disk and halo components when they are on highly eccentric and/or retrograde orbits. The Galactic disk and halo share a similar fraction of RPE stars, in contrast to the earlier perception that the majority of RPE stars belong to the halo. We find that the stars most likely to be accreted belong to the halo. However, 3/4 of the stars lie in a mixed-zone. The inner disk, inner halo and outer halo stars exhibit similar abundance trends for the n-capture elements.
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All authors Pallavi Saraf, Thirupathi Sivarani, Carlos Allende Prieto, Shashikiran Ganesh, Drisya Karinkuzhi

High Energy Astrophysical Phenomena

Dual perspectives on GX 17+2: a simultaneous NICER and NuSTAR study

Malu Sudha, Renee M. Ludlam, Jeroen Homan et al. (+3 more)

We performed the first simultaneous NICER & NuSTAR spectral and timing study of the Sco-like Z source GX 17+2. The source traced the full Z track during four observations. We detect signatures of relativistic reflection in the broadband spectra and report results using a reflection framework. The disk is relatively close to the innermost stable circular orbit ($\sim$ 1-4 R$_{ISCO}$), which agrees with previous studies of GX 17+2, but the location of the inner disk is farther out in the horizontal branch (HB) and moves inward toward the flaring branch (FB). We find the FB to be the point of closest approach of the disk to the neutron star. We qualitatively conclude that the evolution of the source along the HID is that of a relatively truncated disk in the HB ($\sim$ 4 R$_{ISCO}$) that approaches the neutron star as it goes along the HID towards the normal branch (NB), soft apex (SA), and finally the FB. We attribute the source evolution along the Z track to varying mass accretion rate and disk instabilities. Rms variability increases from the NB towards the SA and then drops to a constant along the FB indicating that the observed variability likely originates from the disk/boundary layer rather than the corona.
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All authors Malu Sudha, Renee M. Ludlam, Jeroen Homan, Dacheng Lin, Benjamin Coughenour, Edward M. Cackett

Instrumentation and Methods for Astrophysics · Cross-listed from cs.ET

A Review of 10 Years of ProtoSpace: Spacecraft CAD Visualization in Collaborative Augmented Reality

Benjamin Nuernberger, Samuel-Hunter Berndt, Robert Tapella et al. (+4 more)

ProtoSpace is a custom JPL-built platform to help scientists and engineers visualize their CAD models collaboratively in augmented reality (AR) and on the web in 3D. In addition to this main use case, ProtoSpace has been used throughout the entire spacecraft mission lifecycle and beyond: ventilator design and assembly; providing AR-based instructions to astronauts in-training; educating the next generation on the process of spacecraft design; etc. ProtoSpace has been used for a decade by NASA missions-including Mars Perseverance, Europa Clipper, NISAR, SPHEREx, CAL, and Mars Sample Return-to reduce cost and risk by helping engineers and scientists fix problems earlier through reducing miscommunication and helping people understand the spatial context of their spacecraft in the appropriate physical context more quickly. This paper will explore how ProtoSpace came to be, define the system architecture and overview-including HoloLens and 3D web clients, the ProtoSpace server, and the CAD model optimizer-and dive into the use cases, spin-offs, and lessons learned that led to 10 years of success at NASA's Jet Propulsion Laboratory.
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All authors Benjamin Nuernberger, Samuel-Hunter Berndt, Robert Tapella, Laura Mann, Aaron Plave, Sasha Samochina, Victor X. Luo

Earth and Planetary Astrophysics

Revisiting the Orbital Dynamics of the Hot Jupiter WASP-12 b with New Transit Times

Shraddha Biswas, Ing-Guey Jiang, Li-Chin Yeh et al. (+10 more)

In this study, we examine the transit timing deviations of the extensively studied hot Jupiter WASP-12 b using a comprehensive dataset of 391 transit light curves. The dataset includes 7 new photometric observations obtained with the 1.3 m Devasthal Fast Optical Telescope, the 0.61 m VASISTHA telescope, and the 0.3 m AG Optical IDK telescope, along with 119 light curves from the Transiting Exoplanet Survey Satellite (TESS), 97 from the Exoplanet Transit Database (ETD), 34 from the ExoClock Project, and 134 from previously published sources. To ensure homogeneity and precision, we modeled all 391 light curves and determined their mid-transit times. A detailed transit timing analysis revealed a significant orbital decay rate of $-31.97 \pm 0.80~\mathrm{ms~yr^{-1}}$, corresponding to a stellar tidal quality factor of $Q'_\star = (1.52 \pm 0.038) \times 10^{5}$, thereby confirming that the orbit of WASP-12 b is indeed decaying rapidly. Furthermore, the computation of model selection metrics ($\chi^2_r$, BIC, AIC) favors orbital decay as the most likely explanation. However, the presence of an eccentricity above the threshold value allows apsidal precession to remain a viable alternative. We also derived a planetary Love number of $k_p = 0.63 \pm 0.089$, consistent with Jupiter's value, suggesting a similar internal density distribution. In this study, orbital decay is strongly supported, as a plausible cause of the timing deviations observed in WASP-12 system. Continued high-precision monitoring will be essential to further constrain the system's orbital evolution.
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All authors Shraddha Biswas, Ing-Guey Jiang, Li-Chin Yeh, Hsin-Min Liu, Kaviya Parthasarathy, D. Bisht, Sandip K Chakrabarti, D Bhowmick, Mohit Singh Bisht, A. Raj, Bryan E. Martin, R. K. S. Yadav, Geeta Rangwal

Instrumentation and Methods for Astrophysics

RFSoC receiver calibration system for 21-cm global spectrum experiments from space: The CosmoCube case

Jiacong Zhu, Eloy de Lera Acedo, Kaan Artuc et al. (+1 more)

The CosmoCube project plans to deploy a global 21-cm spectrometer with 10-100 MHz observation band in a lunar orbit. The farside part of such an orbit, i.e. the part of orbit behind the Moon, offers an ideal site for accurately measuring the 21-cm signal from the Dark Ages, Cosmic Dawn and Epoch of Reionization, as the effects of the Earth's ionosphere, artificial radio frequency interference (RFI), and complex terrain and soil are all avoided. Given the limitations of a satellite platform, we propose a receiver calibration system design based on a Radio Frequency system-on-chip, consisting of a Vector Network Analyzer (VNA) sub-system, and a source switching sub-system. We introduce the measurement principle of the VNA, and discuss the effect of quantization error. The accuracy, stability and trajectory noise of the VNA are tested in laboratory experiments. We also present the design of the source-switching sub-system, generating mock datasets, showing that the imperfect return loss, insertion loss, and isolation of surface-mounted microwave switches have a minimal effect on the sky foreground fitting residuals, which are within $\pm10$ mK under optimal fitting condition. When all possible measurement errors in reflection coefficients and physical temperatures are taken into account, the foreground fitting residuals for the 50-90 MHz part of the spectrum remain around $\pm20$ mK.
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All authors Jiacong Zhu, Eloy de Lera Acedo, Kaan Artuc, Xuelei Chen