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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 3 August

High Energy Astrophysical Phenomena

The progenitors and circumstellar environments of stripped-envelope interacting supernovae from BPASS

B. Warwick, J. Lyman, D. L. Coppejans et al. (+4 more)

Understanding the progenitors of stripped-envelope interacting supernovae (SEISNe) is crucial for probing the final stages of massive star evolution. Despite this, their rarity means the nature of their progenitors remains poorly constrained. We investigate the progenitors of SEISNe, using the Binary Population and Spectral Synthesis stellar evolution models. The 30,153 stellar models that result in hydrogen-poor core-collapse supernovae (SN) includes both binary and single stars, spanning 13 metallicities ($Z=10^{-5}$ to $0.04$). Circumstellar material (CSM) formation during their last 100\,kyr is reconstructed from line-driven and Roche lobe overflow (RLOF) mass loss using three scenarios for the CSM, one looking at a wind only distribution for the CSM, and two involving the formation of a circum-binary disc (CBD). Light curve parameters from each scenario are calculated using an analytical model and fiducial SN explosion parameters. We find only the two CBD scenarios, and consequently no single star models, reproduce the luminosities and rise times of observed SEISNe. The inferred rates are comparable to observations. Expected progenitors were only found in models with ZAMS masses of $14-40\,$M$_{\odot}$ at $\geq Z_\odot$ and $30-40\,$M$_{\odot}$ at $< Z_\odot$. Modelling the radio emissions shows that early ($\leq8\,$days) and high frequency ($\geq70\,$GHz) observations are required to constrain the nature of CBDs in these systems. These results indicate that, without phenomena such as eruptive mass loss, SEISNe require massive stars in binary systems in order to produce sufficient masses of CSM and confine them close to the progenitor.
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All authors B. Warwick, J. Lyman, D. L. Coppejans, C. M. Byrne, J. J. Eldridge, M. Pursiainen, E. R. Stanway

High Energy Astrophysical Phenomena

Searching for core-collapse supernovae in binaries with ZTF

Sylvia J. Zhu, Jakob Nordin, Emma de Oña-Wilhelmi et al. (+1 more)

Context. Stripped envelope supernovae occur in massive stars that have lost their outer layers before exploding, possibly from binary interactions. Recently, SN 2022jli was detected with significant periodic oscillations in its lightcurve, likely due to accretion from a binary companion onto the newborn compact object. Aims. While evidence for periodic oscillations has been found in a few bright and noteworthy supernovae, the population properties are best understood with systematic searches of large data sets. We present prospects for running a search on data from ZTF and similar surveys that is flexible and computationally inexpensive, with the goal of setting up a search in realtime on data from ZTF, LSST, and similar surveys. Methods. We simulate core collapse supernova lightcurves with additional features from the binary interactions. We use spline fits to remove the underlying supernova behavior and isolate the periodicities, then apply a Lomb-Scargle periodogram to recover the simulated period. By varying the conditions, we can make recommendations for different kinds of data sets. Finally, we run the search on two sets of archival ZTF supernovae to illustrate the concept. Results. For a wide range of binary interaction parameters, we find that a long baseline (200 days) of observations with a three-day cadence effectively retrieve ~50% of the binary oscillations. However, this rate plummets with more typical observation durations; only a few percent are recoverable with a 30-day observation, and 10% with a 75-day observation. A substantial fraction of supernovae could therefore have binary companion interactions that have simply been undetected. Out of 212 moderately bright and well observed ZTF supernovae, we find suggestions of periodic oscillations in two candidates.
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All authors Sylvia J. Zhu, Jakob Nordin, Emma de Oña-Wilhelmi, Andrea Ercolino

Solar and Stellar Astrophysics

A new methodology for inferring the plasma conditions in solar flare energetic electron source regions from in situ electron energy spectra

Samuel Carter, Natasha L. S. Jeffrey, Robert T. Wicks et al. (+1 more)

The conditions within solar flares that lead to efficient electron acceleration are not well constrained. It is not clear whether the populations accelerated out into the heliosphere and inward into the chromosphere originate in the same regions. By analysing the energy distributions of heliospheric populations, modelling suggests that it should be possible to see evidence of their originating region(s), including the presence of hot, dense flare plasma. By creating and utilising a novel in situ spectral analysis package called INSPEX we have performed this analysis for flare electrons observed in situ on 09/10/2021, constructing both peak flux and fluence spectra from combined Solar Orbiter in situ electron measurements. We compare how differing methodologies for combining the datasets influence the spectral shapes and the retrieved parameters over an energy range of 0.5-80 keV. We fit different functions to the multi-component form of the energy spectra, testing combinations of thermal and/or power law components, comparing the fit statistics. We find that the spectra can be fitted with two distinct thermal curves at energies below 20 keV, corresponding to typical corona/active region and flaring material temperatures, varying between 1.4 - 4.1 MK and 12.5 - 23.1 MK depending on the rebinning window and peak flux extraction method. This study showcases how INSPEX can provide a novel and user-friendly methodology for studying electron spectra with different instrumentation, allowing investigation of multiple spectral types and signatures of acceleration and transport. This first application provides a benchmark case for the analysis of similar flares.
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All authors Samuel Carter, Natasha L. S. Jeffrey, Robert T. Wicks, Georgios Nicolaou

Solar and Stellar Astrophysics

A multi-epoch spectral and photometric study to understand the nature of the interesting Be star candidate HD 249179

Suman Bhattacharyya, Blesson Mathew, S Muneer et al. (+2 more)

HD 249179, a B5 star with unclear classification as either a classical Be star or a high-mass X-ray binary (HMXB) system, is investigated using the first multi-epoch spectral and photometric analysis over 5.5 years (2017-2023). Optical spectroscopy from LAMOST, BeSS, and the Himalayan Chandra Telescope show large H-alpha variability (-17.6 to -3.2 angstrom, in six days, returning to -31.3 angstrom, in 2022) and the presence of Paschen and O I lines, confirming active circumstellar disc dynamics. H-alpha double peak profiles show weak V/R ratio variations 0.92–1.28 indicating one-armed density waves. TESS observations presents hybrid beta Cephei/slowly pulsating B-type variability with primary frequencies of 3.5 c/d and 1.5-1.6 c/d, and an outburst-like brightening with phase-dependent frequency evolution. Simultaneous anti-correlation between optical brightness and H$\alpha$ equivalent width suggest moderate disc inclination. Gaia DR3 CMD analysis rules out HD 249179 as a BeXRB but instead places it in the classical Be-star region. The BeppoSAX survey, despite previous X-ray cataloging, found no emission above the sensitivity limits. Our analysis shows that HD 249179 is most likely a classical Be star with variable circumstellar disc activity and hybrid pulsations, and that there is no strong evidence for an HMXB classification.
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All authors Suman Bhattacharyya, Blesson Mathew, S Muneer, Sreeja S Kartha, Prakruthi Prasad

Astrophysics of Galaxies

Environmental dependence of galaxy properties in the DESI DR1 Bright Galaxy Survey: Star formation, morphology, and AGN activity at z < 0.55

Duho Kim

We present the environmental dependence of galaxy properties using $\sim$1.4 million BGS_BRIGHT galaxies in groups and clusters ($\log(M_h/M_\odot) \geq 12.5$) from the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 at $0.05 < z < 0.55$. Using the magnitude-limited BGS_BRIGHT sample ($r < 19.5$) and the extended halo-based group catalogue, we examine how specific star formation rate (sSFR), Sersic index, and active galactic nucleus (AGN) fraction depend on halo mass across stellar masses $\log(M_*/M_\odot) = 9.0$-$12.0$ and halo masses $\log(M_h/M_\odot) = 12.5$-$15.0$. The median sSFR decreases with increasing halo mass, but much of this trend is driven by the rising satellite fraction rather than stronger suppression of individual galaxies. Satellites show lower median sSFR than centrals at fixed stellar mass and halo mass, most clearly at intermediate stellar masses. The stellar mass threshold at which the environmental trend becomes apparent shifts from $\log(M_*/M_\odot) \sim 11$ at $z \sim 0.4$ to $\sim 10$ at $z \sim 0.1$, a shift that partly tracks the survey's rising stellar-mass completeness limit. The mean Sersic index increases only weakly with halo mass (median $\Delta\log(n) \approx 0.05$ from field to cluster at fixed stellar mass and redshift). Among emission-line-detected galaxies (S/N $> 3$ in all four BPT lines), the combined AGN fraction increases monotonically with stellar mass. At fixed stellar mass, the Seyfert fraction shows no significant environmental trend (consistent with flat; field-to-cluster differences $\lesssim 3\sigma$ in the only well-populated high-mass bin), and the LINER fraction likewise shows no clear environmental trend. The most robust outcome of this work is the relative environmental ordering of galaxy properties and its decomposition into intrinsic suppression and compositional (satellite fraction) effects.
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Astrophysics of Galaxies

Investigation of Calcium Dust in the Interstellar Medium

Ya-Yu Chu, Sascha Zeegers, Hsien Shang et al. (+7 more)

Calcium is a highly depleted element in the interstellar medium (ISM), however its composition in the solid phase remains elusive. The detection of Ca-bearing dust has been limited due to its lack of distinct spectral features in the cold phase of the diffuse ISM. X-rays provide a direct method for exploring the absorption and scattering properties of interstellar dust. In this study, we utilize high-resolution X-ray absorption spectroscopy to characterize Ca-bearing dust analogs at the Ca K-edge using X-ray Absorption Fine Structure (XAFS). We present new X-ray absorption spectra of seven calcium-bearing interstellar dust analogs measured at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan. The extinction cross sections, calculated from the laboratory measurements are incorporated in the dust absorption model AMOL of the X-ray spectral fitting tool SPEX. We select three Low Mass X-ray Binaries (LMXBs) with high column densities, GX 340+00, GX 5-1, and GX 13+1, as background sources to study the intervening ISM along their sightlines. The best-fit models are compared with Chandra archive data using SPEX. Additionally, we employ simulations with the XRISM and NewAthena telescopes to achieve enhanced resolution and more effective coverage at the energy range near the Ca K-edge. These simulations set the boundary conditions for the future X-ray observation of calcium in the interstellar medium.
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All authors Ya-Yu Chu, Sascha Zeegers, Hsien Shang, Chi-Liang Chen, Mau-Tsu Tang, Ming-Jye Wang, Yun-Liang Soo, Elisa Costantini, Ioanna Psaradaki, Daniele Rogantini

High Energy Astrophysical Phenomena

Abnormal Nitrogen Abundance in the X-ray Spectrum of Quasi-periodically Erupting Source AT2019wzc

Tao Wu, Xinwen Shu, Luming Sun et al. (+3 more)

Quasi-periodic eruptions (QPEs) are rapid, recurring soft X-ray bursts, whose nature is still in dispute. A compelling case of QPEs has emerged in the slowly evolving optical transient AT2019wzc, possibly associated with the tidal disruption of a post-main-sequence star by a supermassive black hole. Further evidence of a tidal disruption event (TDE) is crucial to understand the nature of AT2019wzc and establish the link between TDE and QPEs. Here we report the detection of a narrow, blueshifted N VI absorption line in its high-resolution X-ray spectra obtained by XMM-Newton, but weak or undetectable absorption lines from other elements of similar ionization states such as carbon and oxygen. The absorption line features can be reproduced by an ionized gas with ionization parameter $\log \xi \sim 0.3\ {\rm erg~cm~s^{-1}}$ and column density $N_{\rm H}\sim 10^{20}\ {\rm cm^{-2}}$, under the condition of a nitrogen abundance of $11.6_{-7.8}^{+19.6}$ times the solar value. This abnormal nitrogen abundance favors a TDE origin for AT2019wzc, and the absorbing gas may originate from the outflow induced by self-collision of the TDE's debris stream.
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All authors Tao Wu, Xinwen Shu, Luming Sun, Ning Jiang, Jiazheng Zhu, Wenjie Zhang

Solar and Stellar Astrophysics

The location and propagation of fine structures in type II solar radio bursts

S. Normo, K. Bhandari, A. Nadiger et al. (+1 more)

Solar eruptions such as coronal mass ejections can drive collisionless shocks that are good particle accelerators. Electrons accelerated by these shocks can be observed remotely via the electromagnetic emission they generate at low radio frequencies. The radio signatures of shock-accelerated electrons at the Sun are type II radio bursts that can be used to track the propagation of the shock wave in the solar corona and beyond. However, type II radio bursts can have complex morphologies in dynamic spectra, being composed of numerous fine time and frequency structures. Here, we aim to determine the location and propagation of the fine structures composing type II bursts using radio imaging from the Nançay Radioheliograph. We investigate the origin of a type II radio burst that was only co-temporal with a flare and a coronal wave, and it was not associated with a CME eruption. The type II burst still showed complex morphology. We find that emission lanes and fine structures composing the type II burst originate from multiple locations around the flare site. The source regions also move in peculiar non-uniform propagation directions following the shock expansion. Our findings are consistent with the idea that multiple radio emission source regions form as a shock propagates through the solar corona.
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All authors S. Normo, K. Bhandari, A. Nadiger, D. E. Morosan

Cosmology and Nongalactic Astrophysics

Boosting the optical depth to Thomson scattering with primordial black hole evaporation at high redshift

Isaac Sierra, Gabriel P. Lynch, Lloyd Knox et al. (+3 more)

BAO and CMB data are somewhat discrepant when interpreted in the context of $\Lambda$cdm, discrepancies that show up as a `matter density deficit' and as a `CMB lensing excess'. One possible resolution is an increased optical depth to scattering off of free electrons in the post-recombination universe, $\tau$, a possibility raised by Sailer et al. 2025 and Jhaveri et al. 2025. Since Planck measurements of the low-$\ell$ polarization `reionization bump' already constrain $\tau$ from standard stellar-driven reionization at $z<10$, we investigate additional optical depth sourced by transient or partial reionization at higher redshift from exotic processes. For specificity, we explore the impact of Hawking radiation from a monochromatic spectrum of primordial black holes, retaining the high-$\ell$ $TT/TE/EE$ data that constrain such histories and varying the reionization redshift jointly. We find that the CMB data do not significantly prefer these additional signals: the boost is at most $\Delta\tau \simeq 0.008$, well short of the $\Delta\tau \simeq 0.03$ that would completely eliminate the moderate discrepancy. The matter density deficit and the lensing excess are not significantly eased: we explain why, tracing it to compensation from the reionization redshift and the residual PBH signal at $\ell > 30$.
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All authors Isaac Sierra, Gabriel P. Lynch, Lloyd Knox, Vivian Poulin, Lennart Balkenhol, Ali Rida Khalife

Astrophysics of Galaxies

The TNG50-SKIRT Atlas: Spatially resolved synthetic galaxies from the ultraviolet to the submillimetre (DR2)

Maarten Baes, Paul Vauterin, Abdurro'uf et al. (+20 more)

We present the second data release (DR2) of the TNG50-SKIRT Atlas (TSA), a library of synthetic, spatially resolved galaxy observables. The atlas is constructed by post-processing a stellar-mass-complete ($10^{9.8}~{\text{M}}_\odot < M_\star < 10^{12}~{\text{M}}_\odot$) sample of 1154 $z=0$ galaxies from the TNG50 cosmological hydrodynamical simulation with the Monte Carlo radiative transfer code SKIRT. Compared to the first release, TSA DR2 extends the wavelength coverage from the ultraviolet to the submillimetre, including dust emission, and incorporates updated stellar population models together with an improved treatment of dust-enshrouded star-forming regions. The atlas provides spatially resolved spectral energy distributions, broadband images, and physical property maps for multiple viewing orientations, as well as a catalogue of integrated properties enabling direct comparison with unresolved observations. We validate the data products through extensive quality control, including an assessment of Monte Carlo noise, and demonstrate their internal consistency using diagnostic relations between luminosities and star formation rates. TSA DR2 provides a versatile resource for studies of dust attenuation and emission, star formation tracers, galaxy morphology, and multi-wavelength scaling relations across spatial scales. The atlas and associated data products are publicly released and are intended to support a wide range of observationally oriented studies of galaxy evolution.
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All authors Maarten Baes, Paul Vauterin, Abdurro'uf, Nick Andreadis, Thiago Bueno-Dalpiaz, Sena Bokona Tulu, Peter Camps, Abdissa Tassama Emana, Jacopo Fritz, Andrea Gebek, Anand Utsav Kapoor, Inja Kovačić, Arno Lauwers, Kosei Matsumoto, Karín Menéndez-Delmestre, Aleksandr V. Mosenkov, Angelos Nersesian, Lara Pantoni, Mariana Rivas Sánchez, Waad Saftly, Samir Salim, Marko Stalevski, Qi Zeng

Astrophysics of Galaxies

Projection Effects in Merger Dating for Illustris TNG Shell Galaxies

Tuğba Erol, Mustafa Kürşad Y{\i}ld{\i}z, Ivana Ebrová et al. (+1 more)

Stellar shells are low-surface-brightness structures that typically appear as concentric arcs. They are observed in many giant elliptical and lenticular galaxies, as well as in some spiral and dwarf galaxies. They presumably result from minor and intermediate close-to-radial mergers of galaxies. An essential factor in determining the merger time are the distances of shells from the centre of the galaxy. Consequently, estimates of the merger time can be significantly affected if some shells remain undetected due to projection effects. In this study, we present the first systematic investigation of how measured shell radii depend on the orientation of a galaxy relative to the observer. Using the Illustris TNG50 simulation, we examine shell galaxies from nine selected lines of sight and measure the shell radii. We model shell evolution and calculate the merger time accordingly for each viewing angle and quantify the impact of orientation on the inferred merger age. Our results indicate that the line of sight can have a substantial effect on merger-time estimates derived from shell radii.
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All authors Tuğba Erol, Mustafa Kürşad Y{\i}ld{\i}z, Ivana Ebrová, Michal Bílek

Cosmology and Nongalactic Astrophysics

Revisiting Metastable Dark Energy in Light of DESI DR2 BAO and DESI DR1 Full-Shape Measurements

Purba Mukherjee, Arman Shafieloo and Varun Sahni

We revisit metastable dark energy (DE) models described by a radioactive-like decay law. We consider three scenarios: an effective, exponentially decaying DE component; decay of DE into non-baryonic dark matter (DM); and decay of DE into dark radiation (DR). We constrain the metastable DE models using DESI DR2 baryon acoustic oscillation (BAO) data, Type Ia supernovae (SNIa), cosmic microwave background (CMB) observations, and, for the first time, the current available DESI DR1 full-shape (FS) clustering measurements. The BAO+SNIa combinations show a mild preference for positive $\Gamma/H_0$, with a deviation from the $\Lambda$CDM limit at the $\gtrsim 2\sigma$ level. This corresponds to a decaying DE density and an effective quintessence-like behaviour at low redshift. Once CMB information from either Planck or P-ACT is included, however, the constraints become statistically consistent with $\Gamma/H_0=0$. The FS measurements probe the growth sector and help distinguish the interacting DM-DE behaviour of Model 2 from the effective decaying-DE response of Model 1 and the weaker DR-induced response of Model 3. For CMB+FS+DES-Dovekie, Model 1 shows a slight deviation from $\Gamma/H_0=0$ at the $\gtrsim 2\sigma$ level, while Models 2 and 3 remain consistent with the $\Lambda$CDM limit within $2\sigma$. Overall, metastable DE remains phenomenologically viable: current data allow late-time dynamics but do not provide decisive evidence for a nonzero decay rate. These results motivate extending our analysis to the upcoming DESI DR2 FS data to obtain tighter constraints on metastable dynamics.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Spectroscopic study of argon electroluminescence light with a wavelength-sensitive particle detector

R. Santorelli, V. Pesudo Fortes, G. Vera Díaz et al. (+5 more)

We present a spectroscopic study of argon electroluminescence (EL) light in a gaseous time projection chamber (TPC). Using a compact detector equipped with photomultiplier tubes with different spectral sensitivities, we measure the light emission in two nominal wavelength regions, approximately [110, 160] nm and [160, 650] nm, at different gas pressures. In addition to the well-known 128 nm emission of the second continuum, significant emission is observed in the [160, 650] nm band, with a prompt, nanosecond-scale response indicating that photon production closely follows the transit of drifting electrons across the high-field EL region. In contrast, the [110, 160] nm emission displays a markedly slower time evolution, dominated by excimer formation and de-excitation dynamics, with the light output governed primarily by the long-lived triplet component of the argon second continuum emission. We demonstrate that the full VUV pulse shape can be reproduced by convolving the fast UV3 response with excimer formation and decay functions, providing a coherent phenomenological interpretation of the observed signals. Our results provide new insights into the spectral and temporal properties of argon electroluminescence and have direct implications for the design and optimization of next-generation rare-event detectors based on gaseous TPCs. Further studies are underway to characterize this emission more precisely and to investigate its potential for particle discrimination.
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All authors R. Santorelli, V. Pesudo Fortes, G. Vera Díaz, C. K. Guérard, R. López Manzano, L. Luzzi, J. Martínez Morales, L. Romero

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Primordial Correlators from a Kaluza-Klein Graviton Continuum

Shuntaro Aoki

Cosmological collider signals are usually discussed for isolated massive particles, whose exchange produces characteristic logarithmic oscillations in primordial correlators. In this work, we study how this signal is modified when the exchanged states form a continuous mass spectrum. We first develop a spectral representation for inflationary correlators mediated by a continuum field. In the soft limit, the non-analytic part of the seed function is expressed as a Fourier–Laplace transform of the spectral weight with respect to logarithmic momentum variables. This representation shows that a continuum superposes clock signals with different frequencies and can dephase the sharp oscillation associated with a single massive particle. We then realize this mechanism in an RS2-like inflationary braneworld, where the inflaton is localized on a de Sitter brane in a five-dimensional AdS bulk. The tensor sector contains a localized massless graviton and a continuum of Kaluza-Klein gravitons starting at \(m=3H/2\). We derive the KK wavefunctions and identify the brane spectral weight fixed by the continuum wavefunction on the brane. Applying this weight to the inflaton four-point function, we find a smooth seed function rather than a persistent logarithmic clock oscillation. This behavior follows from the fact that the continuum starts at zero clock frequency, while the KK spectral weight vanishes near threshold. Our results provide a concrete higher-dimensional example in which deviations from the standard cosmological collider signal encode the structure of a continuum high-energy spectrum.
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Solar and Stellar Astrophysics

Alfvénic Motions in a Stratified Open Flux Tube: Transition from Propagating to Locally Standing Motions and Implications for the Kelvin-Helmholtz Instability

Mingzhe Guo, Bo Li, Yuhang Gao et al. (+1 more)

Standing transverse waves in closed coronal structures have been widely studied as a possible route to energy dissipation, with resonant absorption transferring kink wave energy to localized Alfvénic motions and the Kelvin-Helmholtz instability (KHI) accelerating the formation of small dissipative scales. However, it remains unclear whether the same mechanism applies to the open corona, given the long-standing consensus that the KHI tends to be prohibited for propagating Alfvénic waves. Within the framework of magnetohydrodynamics (MHD), we perform three-dimensional MHD simulations of boundary-driven kink waves in a gravitationally stratified open flux tube extending from the chromosphere into the corona. We find that propagating waves in open magnetic structures can also drive the system toward a turbulent state, with KH vortices clearly identifiable across the flux tube. This occurs because resonant absorption transfers energy from the propagating kink waves to azimuthal Alfvénic motions near the tube boundary, and wave reflection off the gradient of the Alfvén speed subsequently enables these boundary motions to acquire a locally standing character. Our results provide a possible answer to the long-standing question of whether and how propagating waves in open magnetic structures can generate nonlinear turbulent fine structures despite their globally propagating nature.
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All authors Mingzhe Guo, Bo Li, Yuhang Gao, Yao Chen

Astrophysics of Galaxies

NEXUS: Spectral Variability of Little Red Dots and Blue Active Galactic Nuclei at $2 \lesssim z \lesssim 6$

Zachary Stone, Yue Shen, Ming-Yang Zhuang et al. (+4 more)

We present spectral measurements for 17 Little Red Dots (LRDs) and 14 blue broad-line active galactic nuclei (AGNs) at $2\lesssim z \lesssim 6$ using multi-epoch JWST NIRSpec MSA spectra from the NEXUS program, sampling rest-frame timescales of $\sim 1-3$ months. Overall, the LRD population shows significantly enhanced Balmer decrement compared with both blue JWST AGNs at similar redshifts and 56 low-redshift broad-line AGNs matched in H$\rm\alpha$ luminosity. The rest-optical continua of LRDs show little ensemble variability (rms $\lesssim 3\%$), and the total H$\rm\alpha$ emission also shows weaker ensemble variability compared with low-redshift AGNs matched in H$\rm\alpha$ luminosity and rest-frame timescales. Based on the flux uncertainties, we constrain the intrinsic H$\rm\alpha$ rms variability to be $\lesssim 4\%$ for the LRD population over these timescales. Combining our results with recent broad-line variability measurements of LRDs over yearly to decade timescales reveals a low-level white-noise pattern across all timescales, in stark contrast to the variability amplitude ($\sim 6\%$ over monthly timescales) and red-noise pattern observed in normal AGNs. These results add to the growing observational studies that suggest population-wise, LRDs have weak variability both in optical continuum and broad-line emission. Furthermore, the distinct white-noise broad-line variability pattern suggests different production mechanisms of broad-line emission in LRDs as opposed to normal AGNs, and/or different properties of the driving ionizing flux from the central engine.
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All authors Zachary Stone, Yue Shen, Ming-Yang Zhuang, Junyao Li, Zhiwei Pan, Jenny E. Greene, Feige Wang

High Energy Astrophysical Phenomena

Parameter Estimation Horizon of Core-Collapse Supernovae with a Network of Gravitational-Wave Detectors

Almat Akhmetali, Y. Sultan Abylkairov, Solange Nunes et al. (+3 more)

Core-collapse supernovae are among the most promising yet still undetected sources of gravitational waves. A future detection would provide a direct view of the physical processes occurring deep inside a collapsing star. In this work, we investigate how networks of current and future gravitational-wave detectors can constrain the properties of rapidly rotating core-collapse supernovae using their characteristic core-bounce and early post-bounce signals. Using deep-learning techniques, we estimate the peak frequency, rotation rate, and signal amplitude from noisy detector data and compare the performance of different detector-network configurations. We find that detector networks improve both parameter recovery and sky coverage. For current-generation networks, estimation of the peak frequency is possible out to about 30 kpc, while the rotation rate and signal amplitude remain recoverable out to distances exceeding 100 kpc. Third-generation observatories extend these distances by nearly an order of magnitude.
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All authors Almat Akhmetali, Y. Sultan Abylkairov, Solange Nunes, José Antonio Font, Michele Zanolin, Ernazar Abdikamalov

Astrophysics of Galaxies

Evolution of superthin galaxies under Milgromian dynamics

Zhe-Qi Huang, Hao Chen, Xin-Lei Ge et al. (+1 more)

This work investigates the long-term evolution of the vertical structure of superthin galaxies within the framework of Milgromian dynamics (MOND). By constructing an observationally constrained model of UGC 7321, a typical superthin galaxy, we test whether its disc can maintain an extremely flattened structure in a MOND gravitational field. We also construct models with different values of the MOND depth index D_M to study how the global MOND depth affects disc evolution. We perform three-dimensional hydrodynamical N-body simulations using the publicly available code Phantom of RAMSES. In the observationally constrained model of UGC 7321, the galaxy develops a strong bar and undergoes a buckling instability during the early stages of the simulation. The bar strength then decreases gradually, and the system eventually exhibits a weak bar structure. The vertical evolution reflects the combined effects of heating induced by non-axisymmetric structures and vertical confinement in the Milgromian potential. The stellar disc undergoes only limited vertical thickening, and the disc remains largely within the superthin regime, h_z/R_D<0.1, after 5.0 Gyr. The comparison of models with different D_M values suggests that models with lower D_M values, associated in our model suite with higher baryonic masses or more compact discs, exhibit stronger vertical heating and more significant disc thickening. By contrast, models with higher D_M values, corresponding to lower masses or more diffuse structures, tend to maintain a superthin structure. Overall, the simulation results indicate that superthin discs can remain vertically thin during long-term isolated evolution in MOND, and that the long-term maintenance of superthin structures is influenced, at least partly, by the degree to which a galaxy lies in the low-acceleration regime.
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All authors Zhe-Qi Huang, Hao Chen, Xin-Lei Ge, Cheng-Qun Pang

Solar and Stellar Astrophysics

Deformation of the CME and CME-driven shock due to interaction with the ambient solar wind: I. Modelling with Cone Model

A. Niemela, A. Valentino and J. Magdalenic

Context. The near-Earth environment is continuously impacted by the solar wind and the transients embedded in it. The largest eruptions of plasma and magnetic field at the Sun are Coronal Mass Ejections (CMEs), which, upon reaching Earth, can induce geomagnetic storms and disrupt our technologically advanced societies. Aims. We aim to improve our understanding of how CMEs and CME-driven shock waves interact with the ambient solar wind, and how the resulting deformations in time and space affect the accuracy of space weather forecasting. Methods. We studied two Earth-directed CMEs, observed on December 7, 2020 and October 28, 2021. To model the solar wind and CME propagation in the inner heliosphere, we used the state-of-the-art 3D MHD model EUHFORIA with the cone CME model, focusing on the regions along the main direction of propagation (MDP) and along the Sun-Earth line. Results. The deformations of the CME and the CME-driven shock can be significant. Both CMEs propagate in a variable background wind and are structured differently even at very close angular distances. The first, in a mildly structured wind, shows its stronger deformation predominantly away from the MDP; the second, in a more complex environment, develops a strongly structured shock at very different locations, including regions close to the MDP. Conclusions. These interactions also affect the characteristics of the CME-driven shock, such as the gas compression ratio across it. CMEs observed as flank encounters at Earth can be strongly affected by the ambient solar wind, with the expected differences in the arrival time at Earth reaching up to 16 hours.
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Astrophysics of Galaxies

Spatially resolved thermal dust emission in the L1157 outflow reveals grain-driven molecular enrichment

Siyi Feng, Hauyu Baobab Liu, Yang Lu et al. (+11 more)

Protostellar outflow shocks reshape local dust properties and molecular chemistry. The L1157 outflow is an archetypal chemically rich shocked region, but the thermal dust associated with its successive shocks has remained unresolved because molecular-line contamination obscures the broadband continuum. We obtained new James Clerk Maxwell Telescope (825–906 $\mu$m) spectral-line observations and Submillimeter Array (1.1–1.4 mm) continuum observations toward L1157 B0-B1-B2, probing spatial scales from 0.4 pc to 1200 au. After removing molecular-line contamination on a pixel-by-pixel basis, we derived the dust temperature, column density, and dust opacity index from continuum data spanning 70 $\mu$m to 1.3 mm. The line-corrected continuum maps reveal the dust distribution across successive shocks. The dust opacity index ($\beta\approx1.8$–2.3) indicates that grains have not grown to millimeter sizes throughout the shocked regions. Combined with previous $\rm NH_3$ observations, we find that the dust emission resolves into compact clumps along the precessing jet, whereas gaseous $\rm NH_3$ peaks at the shock fronts, reaching abundances of $\sim10^{-5}$ relative to $\rm H_2$, even where the 0.85 and 1.3 mm dust emission is detected at only 3–5$\sigma$. Our newly developed physicochemical shock model shows that $\rm NH_3$ forms predominantly on grain surfaces and is released by shock-induced sputtering, with the highest abundances occurring where post-shock re-adsorption remains inefficient. These results establish spatially resolved dust continuum imaging as a direct observational probe of grain evolution and provide new observational constraints on dust-gas interactions in protostellar shocks.
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All authors Siyi Feng, Hauyu Baobab Liu, Yang Lu, Qiancheng Yang, Sheng-Yuan Liu, Paola Caselli, Zhi-Yu Zhang, Shuting Lin, Xuejian Jiang, Sihan Jiao, Linjing Feng, Donghui Quan, Fujun Du, Yuanzhen Xiong

Sunday 2 August

Instrumentation and Methods for Astrophysics

Hard X-Ray Focal-Plane Compton Spectro-Polarimeter: Detector Development and Sensitivity Evaluation

Abhay Kumar, Tanmoy Chattopadhyay, Santosh V. Vadawale et al. (+1 more)

The scientific potential of X-ray polarimetry has long been recognized, yet the challenges of measuring polarization have left it largely unexplored, mainly in the hard X-ray regime. With the advent of hard X-ray focusing optics, sensitive focal-plane Compton polarimeters are now feasible. An early example is CXPOL (Compton X-ray Polarimeter), developed at Physical Research Laboratory (PRL), India, which demonstrated 20 - 80 keV polarimetric capabilities using a plastic scatterer and a CsI(Tl) absorber array. The CXPOL prototype demonstrated polarimetric capabilities in the 20 - 80 keV range, establishing a foundation for further development. Building on this concept, we evaluate a hard X-ray spectro-polarimeter employing a position-sensitive plastic scatterer surrounded by position-sensitive absorber detectors. This geometry enables efficient reconstruction of Compton events and allows combined polarimetric and spectroscopic measurements via interaction positions and deposited energies in the detectors. We evaluate key performance parameters of the revised configuration of the second version of the CXPOL. Using Geant4 simulations, we assess key performance parameters, including modulation factor, polarimetric efficiency, and expected sensitivity with modern hard X-ray optics. We also present the characterization results of first prototype of a 100x20x5 mm3 NaI(Tl) absorber read out on both ends by silicon photomultiplier (SiPM) array operating in coincidence, evaluating energy and position resolution and light-output variation along the detector. The coincidence readout also reduces SiPM background by an order of magnitude. The results demonstrate the strong potential of a position-sensitive Compton- based focal-plane instrument for next-generation hard X-ray spectro-polarimetry.
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All authors Abhay Kumar, Tanmoy Chattopadhyay, Santosh V. Vadawale, N. P. S. Mithun

Instrumentation and Methods for Astrophysics

In orbit background for hard X-ray CubeSat polarimeters: case study of the CUSP mission in low-earth orbit

Abhay Kumar, Giovanni Lombardi, Riccardo Campana et al. (+45 more)

The CUbesat Solar Polarimeter (CUSP) project aims to measure the linear polarization of solar flares in the 25 - 100 keV hard X-ray band using a Compton scattering polarimeter. CUSP is a project in the framework of the Alcor Program of the Italian Space Agency aimed to develop innovative CubeSat technologies and missions. As part of CUSPs Phase B study, initiated in December 2024 and closed on July 2nd, 2026, estimating the in orbit background to optimize the signal-to-background ratio was one of the key objectives. In low-Earth orbit, the instrument is exposed to cosmic and albedo X-ray backgrounds, charged particles, and secondary radiation from the spacecraft and atmosphere. Simulating these contributions enables optimization of detector geometry and shielding to maximize signal-to-noise performance. We present initial in orbit background estimates for CUSP using a Geant4-based simulator. A detailed mass model of the CUSP has been implemented to simulate background components and estimate the background count rate in the CUSP orbit.
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All authors Abhay Kumar, Giovanni Lombardi, Riccardo Campana, Giovanni De Cesare, Sergio Fabiani, Ettore Del Monte, Andrea Alimenti, Enrico Costa, Mauro Centrone, Nicolas De Angelis, Sergio Di Cosimo, Giuseppe Di Persio, Pasqualino Loffredo, Gabriele Minervini, Fabio Muleri, Paolo Romano, Alda Rubini, Emanuele Scalise, Enrico Silva, Paolo Soffitta, Giovanni Cucinella, Vito Di Bari, Simone Di Filippo, Andrea Negri, Massimo Perelli, Dario Modenini, Andrea Curatolo, Nicolas Gagliardi, Daniele Pecorella, Alice Ponti, Paolo Tortora, Andrea Del Re, Davide Albanesi, Valerio Campamaggiore, Giulia de Iulis, Adam Ebrahim, Paolo Leonetti, Marco Schepis, Alessandro Zambardi, Ilaria Baffo, Pierluigi Fanelli, Costantino Zazza, Valerio Vagelli, Daniele Brienza, Immacolata Donnarumma, Matteo Merge, Emanuele Zaccagnino, Alessandro Turchi

Astrophysics of Galaxies

Dust Seeding Molecules in a Massive Protostar – Detection of TiO in Orion Source I

Ziwei E. Zhang, Nami Sakai, Marcelino Agundez et al. (+16 more)

We report the first detection of TiO in star-forming regions based on Atacama Large Millimeter/submillimeter Array observations of Orion Source I, a well-characterized massive protostar. Multiple rotational transitions are identified, with emission spatially resolved within $\sim 50$ au, showing a compact distribution with a velocity structure consistent with the base of a rotating outflow. The spatial and velocity distributions of TiO are consistent with those of AlO, with both species being key dust seeding refractory molecules. The column density of TiO is derived to be $(3.0 \pm 0.4)\times10^{15}\ {\rm cm^{-2}}$, corresponding to $X_{\rm TiO/SiO} \sim 12.8 \pm 1.7 \times10^{-3}$, higher than CI chondrites and indicative of efficient dust-to-gas conversion near the protostar. The detection of TiO, a key dust seeding species, offers important constraints on refractory chemistry and the formation environments of primitive minerals, linking astrochemical processes in protostellar systems to the earliest stages of Solar System material formation.
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All authors Ziwei E. Zhang, Nami Sakai, Marcelino Agundez, Linda Podio, Claudio Codella, Tomoya Hirota, Adam Ginsburg, Brett McGuire, Nadia M. Murillo, Yuki Okoda, Yoko Oya, Giovanni Sabatini, Aki Takigawa, Kei E. I. Tanaka, Yichen Zhang, Qiuyi Luo, Yu Cheng, Izaskun Jimenez-Serra, Shogo Tachibana

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Search for active-sterile neutrino transitions using Pierre Auger Observatory data

The Pierre Auger Collaboration: A. Abdul Halim, P. Abreu, M. Aglietta et al. (+347 more)

We investigate the sensitivity of the Pierre Auger Observatory to physics beyond the Standard Model arising from magnetic-moment-induced transitions between active and heavy sterile neutrinos. Such dipole portal interactions can enhance neutrino-nucleon cross sections above a kinematic threshold set by the sterile neutrino mass, leading to observable modifications of neutrino detection rates at ultrahigh energies (UHE). We estimate the impact of these interactions on both down-going and Earth-skimming neutrino detection channels, the contrasting responses of which enable discrimination between an enhanced neutrino flux and a modified interaction cross section. Using the non-observation of UHE neutrino candidates, we derive neutrino-flux-dependent constraints with 90% confidence-level on the transition magnetic moment for sterile neutrino masses in the range 1 TeV-100 TeV. Under the assumed flux scenarios, the resulting flavor-independent limits extend existing bounds into previously unexplored parameter space.
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All authors The Pierre Auger Collaboration: A. Abdul Halim, P. Abreu, M. Aglietta, M. Ahmed, I. Allekotte, K. Almeida Cheminant, R. Aloisio, J. Alvarez-Muñiz, A. Ambrosone, J. Ammerman Yebra, L. Anchordoqui, B. Andrada, L. Andrade Dourado, L. Apollonio, C. Aramo, J.C. Arteaga Velázquez, P. Assis, G. Avila, E. Avocone, A. Bakalova, Y. Balibrea, A. Baluta, F. Barbato, A. Bartz Mocellin, O. Batalla Cruz, J.P. Behler, C. Berat, M.E. Bertaina, M. Bianciotto, P.L. Biermann, V. Binet, K. Bismark, T. Bister, J. Biteau, J. Blazek, J. Blümer, M. Boháčová, D. Boncioli, C. Bonifazi, N. Borodai, J. Brack, P.G. Brichetto Orquera, S. Buitink, A. Bwembya, T.R. Caba Pineda, K.S. Caballero-Mora, S. Cabana-Freire, L. Caccianiga, J. Caraça-Valente, R. Caruso, A. Castellina, F. Catalani, G. Cataldi, L. Cazon, M. Cerda, B. Čermáková, A. Cermenati, K. Cerny, J.A. Chinellato, J. Chudoba, L. Chytka, R.W. Clay, A.C. Cobos Cerutti, R. Colalillo, R. Conceição, A. Condorelli, G. Consolati, M. Conte, F. Convenga, D. Correia dos Santos, P.J. Costa, C.E. Covault, M. Cristinziani, C.S. Cruz Sanchez, S. Dasso, K. Daumiller, B.R. Dawson, R.M. de Almeida, E.-T. de Boone, B. de Errico, J. de Jesús, S.J. de Jong, J.R.T. de Mello Neto, I. De Mitri, D. de Oliveira Franco, F. de Palma, V. de Souza, E. De Vito, A. Del Popolo, O. Deligny, N. Denner, K. Denner Syrokvas, L. Deval, A. di Matteo, C. Dobrigkeit, J.C. D'Olivo, L.M. Domingues Mendes, T. Dominguez, Y. Dominguez Ballesteros, Q. Dorosti, R.C. dos Anjos, J. Ebr, F. Ellwanger, R. Engel, M. Erdmann, A. Etchegoyen, C. Evoli, H. Falcke, G. Farrar, A.C. Fauth, T. Fehler, F. Feldbusch, A. Fernandes, M. Fernández Alonso, B. Fick, J.M. Figueira, P. Filip, A. Filipčič, B. Flaggs, A. Franco, M. Freitas, T. Fujii, A. Fuster, C. Galea, B. García, C. Gaudu, P.L. Ghia, U. Giaccari, M. Giammarco, C. Glaser, F. Gobbi, F. Gollan, G. Golup, P.F. Gómez Vitale, J.P. Gongora, N. González, D. Góra, A. Gorgi, M. Gottowik, F. Guarino, G.P. Guedes, Y.C. Guerra, L. Gülzow, S. Hahn, P. Hamal, M.R. Hampel, P. Hansen, V.M. Harvey, A. Haungs, M. Havelka, T. Hebbeker, C. Hojvat, J.R. Hörandel, P. Horvath, M. Hrabovský, T. Huege, A. Insolia, P.G. Isar, M. Ismaiel, P. Janecek, V. Jilek, K.-H. Kampert, B. Keilhauer, V.V. Kizakke Covilakam, H.O. Klages, M. Kleifges, A. Klingel, J. Köhler, F. Krieger, M. Kubatova, N. Kunka, B.L. Lago, N. Langner, N. Leal, M.A. Leigui de Oliveira, Y. Lema-Capeans, A. Letessier-Selvon, I. Lhenry-Yvon, L. Lopes, M. Mallamaci, S. Mancuso, D. Mandat, P. Mantsch, A.G. Mariazzi, C. Marinelli, I.C. Mariş, G. Marsella, D. Martello, S. Martinelli, O. Martínez Bravo, A. Martínez-Mendez, M.A. Martins, H.-J. Mathes, J. Matthews, G. Matthiae, E. Mayotte, S. Mayotte, P.O. Mazur, G. Medina-Tanco, D. Melo, A. Menshikov, C. Merx, S. Michal, M.I. Micheletti, L. Miramonti, M. Mogarkar, S. Mollerach, F. Montanet, L. Morejon, K. Mulrey, R. Mussa, W.M. Namasaka, S. Negi, L. Nellen, K. Nguyen, G. Nicora, M. Niechciol, D. Nitz, D. Nosek, A. Novikov, V. Novotny, L. Nožka, A. Nucita, L.A. Núñez, S.E. Nuza, J. Ochoa, M. Olegario, C. Oliveira, L. Östman, M. Palatka, J. Pallotta, G. Parente, T. Paulsen, M. Pech, J. Pękala, R. Pelayo, C. Pérez Bertolli, L. Perrone, S. Petrera, T. Pierog, M. Pimenta, M. Platino, P. Privitera, C. Priyadarshi, M. Prouza, K. Pytel, S. Querchfeld, J. Rautenberg, D. Ravignani, J.V. Reginatto Akim, M.Z. Rennó, A. Reuzki, J. Ridky, F. Riehn, M. Risse, V. Rizi, B. Rocha Moldes, E. Rodriguez, G. Rodriguez Fernandez, J. Rodriguez Rojo, S. Rossoni, M. Roth, E. Roulet, A.C. Rovero, A. Saftoiu, M. Saharan, F. Salamida, H. Salazar, G. Salina, P. Sampathkumar, N. San Martin, J.D. Sanabria Gomez, F. Sánchez, F.M. Sánchez Rodriguez, E. Santos, F. Sarazin, R. Sarmento, R. Sato, P. Savina, V. Scherini, H. Schieler, M. Schimp, D. Schmidt, O. Scholten, H. Schoorlemmer, P. Schovánek, F.G. Schröder, J. Schulte, T. Schulz, S.J. Sciutto, M. Scornavacche, A. Sedoski, S. Sehgal, S.U. Shivashankara, G. Sigl, K. Simkova, F. Simon, R. Šmída, S. Soares Sippert, P. Sommers, S. Stanič, J. Stasielak, P. Stassi, S. Strähnz, M. Straub, T. Suomijärvi, A.D. Supanitsky, Z. Svozilikova, Z. Szadkowski, F. Tairli, A. Tapia, C. Taricco, C. Timmermans, O. Tkachenko, P. Tobiska, C.J. Todero Peixoto, B. Tomé, A. Travaini, P. Travnicek, C. Trimarelli, M. Tueros, M. Unger, R. Uzeiroska-Geyik, L. Vaclavek, M. Vacula, I. Vaiman, J.F. Valdés Galicia, L. Valore, P. van Dillen, E. Varela, V. Vašíčková, A. Vásquez-Ramírez, D. Veberič, I.D. Vergara Quispe, S. Verpoest, V. Verzi, J. Vicha, S. Vorobiov, J.B. Vuta, A.A. Watson, A. Weindl, M. Weitz, L. Wiencke, H. Wilczyński, B. Wundheiler, B. Yue, A. Yushkov, E. Zas, D. Zavrtanik, M. Zavrtanik

Instrumentation and Methods for Astrophysics

MiraSOL: a DMD-based spectrograph for resolved solar spectroscopy

Christian Robles, Suvrath Mahadevan and Lawrence Ramsey

We present the science motivation, preliminary design requirements, device laboratory testing and a prototype for an new experimental platform for solar observations, MiraSOL. MiraSOL will use digital micromirror technology to actively select regions on the solar disk for spectroscopic observation to determine the spatially dependent radial velocity signatures of stellar variability, and can create transits on the solar disk to probe the effects of stellar contamination on exoplanet transmission spectra. MiraSOL uses the Texas Instruments DLP801RE as a spatial light modulator to allow a mask, with 3 arcsecond spatial sampling per micromirror, capable of resolving features on the solar disk. This instrument will have a fiber output which can then be coupled with state-of-the-art extreme precision radial velocity (EPRV) spectrometers, such as HPF or NEID, for high resolving power, stable spectra of sunspots and plage, or a low resolution spectrometer for studies of stellar contamination in transit spectra. We discuss a 60 Hz flicker signal we discovered, likely due to the commercial off-the-shelf (COTS) evaluation board of the digital micromirror device electronics. We also build a proof-of-concept prototype and demonstrate imaging and pixel-level control of the full solar disk to demonstrate the feasibility of this technology.
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High Energy Astrophysical Phenomena

Spectral decoherence without depolarization in curvature radiation

A. G. Tevzadze and N. L. Shatashvili

Context: Fast radio bursts often exhibit strong linear polarization together with pronounced spectral structure. Yet in coherent curvature radiation, spectral decoherence and depolarization are not necessarily simultaneous. Aims: We investigate spectral and polarization coherence in curvature radiation from extended ultrarelativistic sources. Methods: Using the coherency matrix formalism together with an asymptotic phase expansion for a uniformly emitting extended source, we derive the spectral and polarization coherence properties of curvature radiation. Results: We show that spectral decoherence and depolarization are governed by distinct physical conditions and therefore develop on separate scales. Retardation phase variations suppress spectral coherence, whereas polarization remains largely preserved across the relativistic beaming cone, naturally producing a broad polarized but spectrally decoherent regime whose extent increases toward higher frequencies and larger Lorentz factors. Conclusions: Spectral decoherence without strong depolarization naturally arises in ultrarelativistic curvature radiation and may explain highly polarized fast radio bursts with strong spectral modulation or narrow band structure.
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High Energy Astrophysical Phenomena

Signatures of Lorentz violation in bright ring for Sgr A* images by radiation ineffective accretion flows

Cuiyu Zhao, Songbai Chen and Jiliang Jing

We have investigated effects of Lorentz violation (LV) on bright ring in Sgr A* images illuminated by the 230 GHz thermal synchrotron emission from radiation ineffective accretion flows around a rotating LV black hole within the low-energy Hořava gravity framework. Our results reveal that the LV parameter reduces the bright ring diameter yet increases its width, luminosity, azimuthal asymmetry and orientation angle. Higher spin parameter strengthens the LV-induced effects on bright ring properties.Increasing disk thickness reduces the ring diameter and enhances the LV parameter's effects on this diameter. The ring width shows no systematic dependence on the disk thickness. These quantities of bright ring display similar trends against black hole spin and the LV parameter for the rotating LV black hole. Using EHT observational data of Sgr A*, we find that, at fixed disk thickness, the allowed range of the LV parameter first broadens and then contracts with growing black hole spin, and shifts toward smaller LV parameter values. In addition, the LV parameter narrows the permitted range of black hole spin: negative LV parameter values shift this range to higher spin, while positive values shift it to lower spin. Finally, we probe effects of the LV parameter on the peak position value and the width of the primary image and the $n=1$ photon ring for the rotating LV black hole. The peak positions and their widths decrease with the LV parameter, except for a narrow range. The peak position differences for various LV parameter are more pronounced for pure Keplerian accretion flow. In additional, the primary image and the $n=1$ photon ring produced by pure radially free-falling flows are broader than their counterparts generated by pure Keplerian flows.
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Solar and Stellar Astrophysics

Cross-Calibration of Chandrayaan-2 XSM with INSPIRESat-1 DAXSS and GOES-16 XRS

N. P. S. Mithun, Santosh V. Vadawale, Asif M. Mandayapuram et al. (+9 more)

X-ray spectroscopic observations of the solar corona and flares provide crucial diagnostics of plasma properties and are essential for understanding the physical processes responsible for coronal heating and solar eruptive activity. The Chandrayaan-2 Solar X-ray Monitor (XSM) provides disk-integrated spectra of the Sun in the 1–15~keV soft X-ray band, enabling modeling of the thermal X-ray emission from the corona across quiet phases to intense solar flares. XSM has been operational for about seven years, starting from the last solar minimum and covering the maximum of the current Solar Cycle. The Dual-zone Aperture X-ray Solar Spectrometer (DAXSS) instrument on board INSPIRESat-1 covers the solar X-ray spectra in a similar energy range as XSM and was operational during 2022–2026. With multiple instruments simultaneously observing the Sun in X-rays, there is scope to compare measurements across instruments. Here, we present the cross-calibration of XSM with DAXSS and a broadband X-ray flux monitor, the GOES-16 X-ray Sensor (XRS). Comparisons of XSM and DAXSS spectra reveal an unaccounted attenuation in the XSM low-energy response. Supported by laboratory measurements, we attribute this difference to the effective detector beryllium window thickness being 25 microns rather than the previously assumed 8 microns. Incorporating this revision into the XSM calibration significantly improves the agreement between the two instruments, with flux measurements agreeing within ~10% in the 1–8 Angstrom band. Comparison with GOES-16 XRS measurements over a broad range of solar activity levels further demonstrates consistency, with a median flux difference of less than 10%.
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All authors N. P. S. Mithun, Santosh V. Vadawale, Asif M. Mandayapuram, M. Shanmugam, Soumya Kohli, Mehul R. Pandya, Anil Bhardwaj, Robert Sewell, Bennet Schwab, Amir Caspi, Thomas N. Woods, Janet L. Machol

High Energy Astrophysical Phenomena

Probing strange quark matter objects with future space-based gravitational wave detectors DECIGO and BBO

Abdusattar Kurban, Xia Zhou, Na Wang et al. (+9 more)

The Strange Quark Matter (SQM) hypothesis posits that objects composed of SQM could exist across a wide mass range, from strange planets (SPs) to strange stars (SSs). It has been proposed that gravitational waves (GWs) emitted by inspiraling SS-SP systems may be detectable by ground-based GW observatories such as advanced LIGO and the Einstein Telescope. Nevertheless, such a system may undergo an extended period of orbital evolution in a close configuration before entering the inspiraling phase. During this time, it can generate continuous GW signals at frequencies ranging from milli-hertz (mHz) to deci-hertz (dHz). The detailed characteristics of these GWs have not yet been thoroughly explored. In this study, we delve into the continuous GW features of SS-SP systems, with a focus on exploring the physically viable parameter space. We compared the GW signals emitted by these systems to the sensitivity curves of next-generation space-based GW detectors like the Deci-hertz Interferometer Gravitational wave Observatory (DECIGO) and the Big Bang Observer (BBO). Our analyses demonstrate that both the DECIGO and BBO detectors are capable of detecting continuous GWs from SS-SP systems across a broad parameter space. These GWs carry important information for testing the SQM hypothesis, as well as for advancing our understanding of supernovae and compact star merger processes.
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All authors Abdusattar Kurban, Xia Zhou, Na Wang, Yong-Feng Huang, Wenming Yan, Jianping Yuan, Ali Esamdin, Rai Yuen, Jin-Hong Chen, Xiao-Fei Dong, Zhigang Wen, Yu-Bin Wang

Instrumentation and Methods for Astrophysics

Design and modeling of an oblique incidence dichroic mirror for a high contrast imaging system

Joanna Rosenbluth, Ramya Anche, Kyle Van Gorkom et al. (+4 more)

The proposed Habitable Worlds Observatory (HWO) aims to detect and characterize Earth-like planets around Sun-like stars from the ultraviolet to the infrared using high-contrast imaging. A dichroic mirror is a natural choice for splitting light between multiple wavelength channels in such a system, but the coating must introduce minimal polarization aberrations and chromatic wavefront errors (WFE) to avoid limiting contrast. We present the design of a long-pass dichroic mirror operated at a $7^\circ$ angle of incidence that provides high reflection in the short-wavelength band, high transmission in the long-wavelength band, and a sharp cut-on near 550~nm. A multilayer thin-film design process was used to meet these spectral requirements while reducing polarization aberrations and chromatic WFE sensitivity. Reflected phase optimization was also incorporated to reduce sensitivity to manufacturing-induced layer-thickness variations, which can produce wavelength-dependent WFE and degrade coronagraph performance. The resulting coating-induced WFE was propagated through simulations of a vector vortex coronagraph to assess contrast performance. Simulations predict dark-hole contrast residuals at the $10^{-12}$ level, indicating that the optimized dichroic mirror does not limit coronagraph performance.
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All authors Joanna Rosenbluth, Ramya Anche, Kyle Van Gorkom, Nikoli Cooper, William Melby, Daewook Kim, Ewan Douglas