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Physics Astrophysics

astro-ph Watch Astrophysics

Wednesday 2 September

High Energy Astrophysical Phenomena

Searching for optical pulsations from spider millisecond pulsars with the fast photometer SiFAP2

Christian Malacaria, Alessandro Papitto, Filippo Ambrosino et al. (+18 more)

Optical pulsations from millisecond pulsars (MSPs) have recently been detected in a transitional MSP and an accreting MSP. Evidence for optical pulsations has also been found for a rotation-powered redback MSP. Observations suggest that optical pulsed emission is produced by different mechanisms depending on whether an accretion disk is present in the system. We explored a sample of rotation-powered MSPs in close binaries (P$_{orb}<1\,$day; redbacks and black widows), searching for optical periodic signals with the $SiFAP2$ photometer mounted on the $Telescopio\,Nazionale\, Galileo$ (TNG). We performed pulsation searches using the epoch-folding method with the most up-to-date (radio or gamma-ray) orbital solution for each system. These solutions were based either on previously published works or recent observations from Nançay, the Giant Metrewave Radio Telescope, the Parkes Observatory, and $Fermi$-LAT. We update or confirm radio and gamma-ray ephemerides for five of the presented systems. No optical pulsations were detected with a significance exceeding a $3\sigma$ confidence level in any of our searches, despite achieving sensitivities close to the instrument's limit. This places correspondingly stringent upper limits on the systems' optical pulsed magnitude and conversion efficiency. Our upper limits are consistent with the pulsed optical luminosity of optical pulsations from the redback PSR J2339-0533. Compared to accreting and transitional MSPs, redback and black widow systems show much lower efficiency in converting their spin-down power into pulsed optical emission. This supports the recent suggestion that the accretion disk around the neutron star plays a role in accelerating the particles responsible for producing bright optical pulsed emission.
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All authors Christian Malacaria, Alessandro Papitto, Filippo Ambrosino, Caterina Ballocco, Riccardo La Placa, Giulia Illiano, Arianna Miraval Zanon, Luigi Stella, Marco Turchetta, James D. Turner, Clara Blanchard, Ignacio Cognard, Lucas Guillemot, Marta Burgay, Aleksandr Burtovoi, Andrea Sanna, Sergio Campana, Massimo Cecconi, Adriano Ghedina, Andrea Possenti, Diego Torres

Astrophysics of Galaxies

Inside-out growth and the kiloparsec-scale star formation main sequence for low-surface-brightness disk galaxies in MaNGA

Bing-qing Zhang, Ze-hao Zhong, Yi-nan Zhu et al. (+1 more)

Low surface brightness galaxies (LSBGs) are very faint objects in the universe whose formation and evolution have long remained an unresolved problem. We selected a late-type, face-on, and disk-dominated galaxy sample from the MaNGA survey, composed of 38 LSBGs and 216 high surface brightness galaxies (HSBGs) by adopting a central surface brightness threshold $\mu_{0}(g) = {\rm 22.0\ mag\ arcsec^{-2}}$. Based on maps derived from pipe3D products of star-forming areas in galaxies, we investigated the global and resolved star formation main sequence (SFMS and rSFMS) and radial profiles of the stellar mass density ($\mathrm{\Sigma_{*}}$), star formation rate density ($\mathrm{\Sigma_{SFR}}$), and specific star formation rate ($\mathrm{\Sigma_{sSFR}}$). The radial profiles of $\mathrm{\Sigma_{*}}$ and $\mathrm{\Sigma_{SFR}}$ present negative gradients, while those of $\mathrm{\Sigma_{sSFR}}$ present positive gradients. Compared to HSBGs, the LSBGs show similar, flatter, and steeper slopes in $\mathrm{\Sigma_{*}}$, $\mathrm{\Sigma_{SFR}}$, and $\mathrm{\Sigma_{sSFR}}$ gradients, respectively. The very flat $\mathrm{\Sigma_{SFR}}$ gradients of LSBGs, whose slopes range from -0.1 to -0.2, indicates uniform star formation throughout the whole galaxy, and the positive $\mathrm{\Sigma_{sSFR}}$ gradients reflects their “inside-out” growth. Our LSBGs and HSBGs follow the same global and resolved SFMS as the full sample, and $\mu_{0}$ shows no influence on both SFMS and rSFMS. For our full sample and two subsamples (HSBGs and LSBGs), the slopes of global SFMS and rSFMS are consistent, which indicates that the SFMS still hold on a kiloparsec scale and the star formation activities are regulated by local events. The treatment of different excitation sources in galaxies affects the slope of the SFMS and rSFMS, and using star-forming areas only is more advisable.
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All authors Bing-qing Zhang, Ze-hao Zhong, Yi-nan Zhu, Hong Wu

Solar and Stellar Astrophysics

Surface brightness inhomogeneity on the helium-rich hot subdwarf in the X-ray binary HD 49798

C. Simon Jeffery and Gavin Ramsay

HD 49798 is an X-ray binary consisting of a hot helium-rich subdwarf primary and an accreting compact companion with an orbital period of 1.55 d. TESS observations of its optical light curve suggest short-period brightenings superimposed on a sinusoidal variation. The latter can be attributed to the tidal deformation of the primary, while frequency analysis of the additional variations shows up to eleven frequencies which form an harmonic series based on a period of 1.4 d, in excellent agreement with the stellar rotation period inferred independently from spectroscopy. These brightenings may be explained by a slowly changing and inhomogeneous temperature distribution across the surface of the hot subdwarf, such as might be associated with a magnetic field or with the presence of Rossby waves in the stellar envelope.
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Earth and Planetary Astrophysics

The NC-CC dichotomy in ruthenium isotopes: Implications for the origin of the late veneer

Jonas Pape, Emily A. Worsham and Thorsten Kleine

High-precision mass-independent Ru isotope data for iron meteorites reveal that in three-isotope diagrams including the p-process Ru nuclides 96Ru or 98Ru, non-carbonaceous (NC) meteorites plot along an s-process mixing line, while the carbonaceous (CC) type irons plot as a cluster off the NC-line. As previously observed for Mo, this offset can be accounted for by an r-process excess in CC over NC materials. As a highly siderophile element, Ru in the bulk silicate Earth (BSE) is thought to predominantly derive from the late veneer, making the Ru isotope dichotomy a powerful genetic tracer of Earth's late accretionary epoch. The BSE and the isotopically anomalous Itsaq Gneiss Complex as defined in prior studies plot on the NC-line defined in this study, suggesting a predominantly NC late veneer that may have evolved over time from more s-process-enriched to more s-process-depleted compositions. However, more precise 96Ru and 98Ru measurements of the BSE's composition are needed to more reliably determine the genetic heritage of the late veneer and to quantify as to whether it contains CC material.
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Instrumentation and Methods for Astrophysics

Searching for Gravitational Wave Events Counterparts in X-Rays by Tilting the Multiple Shells of Wolter-I Optics

John Rankin, Daniele Spiga, Paolo Conconi et al. (+5 more)

Current X-ray telescopes have a combination of field of view and angular resolution that makes it difficult to quickly localize the electromagnetic counterparts of gravitational wave events — which will become increasingly important when the LIGO and Virgo experiment will work at full sensitivity or when the Einstein Telescope and the Cosmic Explorer observatories will come online in the next decades. We investigate what X-ray optical designs could provide — in a small mission — a field of view wide enough to observe quickly the region of the sky constrained by gravitational wave detectors, and at the same time an angular resolution sufficiently good to localize these sources. We study, using ray tracing simulations, how we can optimize a Wolter-I telescope for this purpose. We find that, by appropriately tilting the shells of a Wolter-I X-ray telescope in different directions, the field of view increases, at the cost of a reduction of the on-axis performance. We draw a possible design made of two identical modules pointing at adjacent regions of the sky.
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All authors John Rankin, Daniele Spiga, Paolo Conconi, Sergio Campana, Giovanni Pareschi, Stefano Basso, Marta Maria Civitani, Vincenzo Cotroneo

Astrophysics of Galaxies

An updated census of the Vast Polar Structure member galaxies

Alberto Manuel Martínez-García

The Vast Polar Structure (VPOS) is a thin, planar arrangement of dwarf galaxies oriented almost perpendicular to the Milky Way (MW) disc. Since its discovery, the census of VPOS member galaxies has progressively expanded thanks to continuous findings of new dwarfs in the vicinity of the MW and increasingly precise measurements of their phase-space coordinates. In this work, we present the largest census to date of VPOS member galaxies, building on a sample of 73 MW dwarfs for which positional and kinematic data are available in the literature. Based on their orbital poles, we identify 22 VPOS members: 12 MW satellites, the Large Magellanic Cloud (LMC), and 9 LMC satellites. With the exception of Bootes III, Kim 1, and Sculptor, all the on-plane dwarfs are co-rotating. Our revised census increases the known VPOS member population by nearly 50%, introducing Delve 4, Kim 1, Kim 3, Eridanus III, Pictor II, and YMCA-1 (3 MW and 3 LMC satellites, respectively) as new on-plane dwarfs. From this updated census, we revise the structural parameters of the VPOS, confirming its planar ($c/a \sim$0.27) and remarkably thin ($\sim$15 kpc) nature.
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High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph

Instabilities in Cylindrical Geometry Using the Minimalist Approach: Formalism and Rotational Instabilities

Nektarios Vlahakis

The minimalist approach for linear stability analysis is applied to fluids and magnetized ideal plasmas in cylindrical geometry. In this approach, the dispersion relation is obtained by integrating a single first-order differential equation - referred to as the principal equation - subject to appropriate boundary conditions. We first derive the principal equation for a general unperturbed state with radially varying density and pressure, axial and azimuthal components of both the velocity and magnetic field, and a radially directed gravitational field. We then use this formulation to analyze rotating flows with axial magnetic fields, addressing both wall-bounded and interface-driven axisymmetric instabilities. In addition to exact results for selected unperturbed states, we obtain approximate dispersion relations using the WKBJ method in the incompressible and compressible limits. The analysis encompasses centrifugal, magnetorotational, and buoyancy-driven instabilities as special cases, and it clarifies how compressibility modifies their stability properties.
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Instrumentation and Methods for Astrophysics

Scientific performances of the XGIS instrument on-board THESEUS

E. Arrigoni, S. Mereghetti, R. Campana et al. (+6 more)

The Transient High Energy Sky and Early Universe Surveyor (THESEUS) satellite, currently undergoing a Phase-A study for the M7 ESA mission selection, will mainly rely on the XGIS (X and Gamma Imaging Spectrometer) instrument to discover and precisely localise gamma-ray bursts and other high-energy transients. The XGIS instrument has been designed to provide accurate sky images in a wide field of view (>2 steradians) in the 2-150 keV band, coupled to coverage of nearly half of the sky with good timing and spectroscopic capabilities up to several MeV. This will be achieved thanks to the combination of two identical cameras, based on the coded mask imaging technique, oriented to provide partially overlapping fields of view. We present the capabilities of the XGIS, focussing in particular on the sensitivity and source location accuracy. We discuss the expected scientific advances in the GRB field, estimated through detailed Monte-Carlo simulations which take into account the design of the XGIS imaging system and the properties of the GRB population at high redshifts.
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All authors E. Arrigoni, S. Mereghetti, R. Campana, C. Labanti, A. Pisapia, P. Calabretto, G. Mattioli, E. Virgilli, L. Amati

Astrophysics of Galaxies

Is the Nuclear Star Cluster a Bulge Fossil Fragment?

R. Michael Rich, Brian Thorsbro and Christian Johnson

The Milky Way nuclear star cluster (NSC) is unlike a conventional globular cluster: it contains a broad metallicity distribution and stellar populations formed over an extended interval, while its detailed abundances show a close connection to the inner Galactic bulge. We ask whether the NSC should instead be compared with the proposed "bulge fossil fragments" Terzan 5 and Liller 1, complex stellar systems interpreted as surviving remnants of massive structures involved in early bulge assembly. We place this comparison against the field-bulge metallicity distribution measured by the Blanco DECam Bulge Survey and against high-resolution infrared abundance measurements in the NSC. A broad metallicity distribution by itself is not diagnostic, because the bulge field is intrinsically broad and strongly structured. More discriminating tests are the presence of chemically narrow and age-coherent subpopulations, the relation between [alpha/Fe] and [Fe/H], light-element abundance patterns, spatial segregation, and chemo-dynamical differences among populations. Existing NSC data establish strong chemical links with the bulge but do not support a simple one-to-one analogue of either Terzan 5 or Liller 1. In particular, metal-rich alpha-enhanced stars in the NSC provide an important contrast with the near-solar [alpha/Fe] metal-rich populations of the best-studied fossil-fragment candidates. We argue that the BFF hypothesis is most useful as a falsifiable framework for identifying an early bulge-building component within a composite NSC assembled through in-situ star formation, migration, and cluster infall.
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Instrumentation and Methods for Astrophysics

Demonstrating the Time-Domain Capabilities of the 4-m International Liquid Mirror Telescope: An Early Census of Transient and Variable Detections

Kumar Pranshu, Kuntal Misra, Bhavya Ailawadhi et al. (+11 more)

The PyLMT transient detection pipeline has been operational since November 2023, detecting transient and variable objects in the ILMT images in almost real time. Using the image subtraction technique, nearly 3700 CCD frames have been analyzed by the automated pipeline, generating nearly 23,000 alerts for the detection of verified transient candidates and cataloged variable sources. Around 21,000 of the alerts correspond to known MPC asteroids, nearly 2000 correspond to variable stars (including eclipsing binaries, RR Lyrae, Delta Scuti, T-Tauri, etc.), 509 correspond to variable AGNs (including QSOs, Seyfert galaxies, and blazars), 21 supernova candidates, and several other interesting candidates. We provide a concise overview of the detections and their significance, emphasizing the surveys potential contributions to a broad class of astrophysical and scientific cases. A transient detection dashboard called DART was developed using Streamlit to visualize and categorize candidates based on PyLMT and SIMBAD classifications. It includes cone-search functionality and displays key metadata, offering an intuitive interface that is publicly accessible. Our results demonstrate the viability of liquid mirror telescopes such as the ILMT for time-domain astronomy, emphasizing the important role that small-field survey facilities can play in systematic transient science programs.
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All authors Kumar Pranshu, Kuntal Misra, Bhavya Ailawadhi, Monalisa Dubey, Naveen Dukiya, Sara Filali, Paul Hickson, Priyanshi Kumari, Gokul Singh Mehra, Vibhore Negi, Jeewan C. Pandey, Anna Pospieszalska-Surdej, Jean Surdej, Sarvesh Kumar Yadav

Solar and Stellar Astrophysics

The relationship between solar and stellar tachoclines, dynamos, and spin-down

Loren I. Matilsky, Lydia Korre and Nicholas Brummell

The solar tachocline, a thin shear layer separating the differentially rotating convective zone (CZ) from the underlying rigidly rotating radiative zone (RZ), remains a dynamical mystery. Under the influence of "radiative spreading" (the process by which meridional circulation, baroclinicity, and differential rotation burrow through a stably stratified fluid), the tachocline should have spread significantly by the current age of the Sun. Some unknown torque must therefore rigidify the whole solar interior below the CZ and keep the tachocline confined to a thin layer. At the same time, the spin-down process (through which cool stars shed angular momentum via surface magnetic torques) must extract angular momentum from the solar RZ, presenting a second mystery: solar spin-down must be communicated from the near-surface layers to the deep interior, all the while leaving the tachocline intact. In this work, we explicitly analyze the dynamics of radiative spreading in two 3D, spherical-shell, fully nonlinear fluid simulations of a solar-like CZ–RZ system, one without a magnetic field (hydrodynamic—HD) and one with a small random seed magnetic field (magnetohydrodynamic—MHD). We find that radiative spreading is unmitigated in the HD case (as expected), but in the MHD case, a self-excited dynamo not only confines the tachocline, but also extracts angular momentum from the RZ, thereby communicating the spin-down downward. We thus speculate that solar and stellar tachoclines may be intimately linked to both the spin-down process and global dynamo.
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Earth and Planetary Astrophysics

Double Gravity-Assist Rendezvous Trajectory to Halley's Comet Using Deep-Space Low Thrust

Roberto Flores, Alessandro Beolchi, Chiara Pozzi et al. (+4 more)

The perihelion of comet 1P/Halley in 2061 is an excellent chance to revisit this object of outstanding scientific and cultural relevance. During its 1986 approach to the Sun, it was targeted by several flyby missions. Due to its retrograde, highly-inclined orbit, the relative velocities during the encounter were large, limiting the scientific return due to the short time spent inside the coma. A rendezvous trajectory would overcome this limitation, but the design is challenging due to the limitations of current propulsion technology. Given the lead times of spacecraft development and the long duration of the interplanetary transfer to the comet, it is imperative to start mission planning as soon as possible. We present a novel rendezvous strategy, combining unpowered Jupiter and Saturn gravity-assists with deep-space low-thrust arcs. It minimizes launch energy and propellant budget, constraining the arrival to occur before the onset of high activity. The double flyby strategy reduces the otherwise prohibitive cost of the plane change maneuver. Closed expressions for the optimal flyby geometry, together with an explicit low-thrust transcription technique, reduce the number of design parameter to three, improving computational efficiency. Crucially, this is the first rendezvous mission concept achievable with well-proven technology (standard radioisotope thermoelectric generators and a Hall-effect thruster) and compatible with several existing launchers. We describe the trajectory optimization strategy and perform a comprehensive exploration of the design space. Finally, we present two promising proof-of-concept trajectories in detail.
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All authors Roberto Flores, Alessandro Beolchi, Chiara Pozzi, Mauro Pontani, Ivano Bertini, Cesare Barbieri, Elena Fantino

Astrophysics of Galaxies

Disc-Based Estimation of the Local Dark Matter Density and Velocity Distribution in IllustrisTNG50

Hatsume Chujo, Shogo Masaki, Keiko I. Nagao et al. (+1 more)

We study the dark matter (DM) density and velocity distribution in the solar neighborhood of Milky Way-like galaxies using the TNG50-1 run of the IllustrisTNG simulation suite. Milky Way-like galaxies are selected according to both their halo mass and their bulge-to-total stellar mass ratio, and the solar-neighborhood region within each galaxy is identified from the positions and number density of stars, so that DM particles associated with the galactic disc are extracted while contributions from the halo component are suppressed. Averaging over the selected galaxies, we obtain a local DM density of $\rho \simeq 0.47\pm0.02~{\rm GeV\,cm^{-3}}$, consistent with the range inferred from observations. The disc-based extraction gives a higher peak density, $0.41\pm0.02~{\rm GeV\,cm^{-3}}$, than the value $0.34\pm0.02~{\rm GeV\,cm^{-3}}$ from a simple distance-based extraction, probably because it excludes the low-density DM in the halo. The width of the density distribution, on the other hand, is nearly unchanged. The velocity distribution is well described by an isotropic Maxwellian with a peak velocity of about $226~{\rm km~s^{-1}}$, close to the value assumed in the standard halo model. The differences in the density and velocity distributions between our disc-based and simple distance-based extractions are not so large as to significantly affect the interpretation of direct-detection experiments.
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All authors Hatsume Chujo, Shogo Masaki, Keiko I. Nagao, Takuho Nakabayashi

Astrophysics of Galaxies

Constraints on the Intranight Optical Variability of Intermediate-Mass Black Hole Candidates

Wenwen Zuo, Hengxiao Guo, Wanling Liu et al. (+12 more)

Intermediate-mass black holes (IMBHs) provide a unique regime for studying accretion variability at the low-mass end of the black hole population, yet their intranight optical variability (INOV) remains poorly constrained. We present a systematic investigation of INOV in an optically selected sample of IMBH candidates using high-cadence observations from the Zwicky Transient Facility (ZTF). From a parent sample of 1,447 broad H$\alpha$-selected candidates, we identify 64 IMBH candidates (median $f_{\mathrm{AGN}}\sim0.06$) with 163 intranight monitoring sessions. Apparent INOV signals identified by conventional ZTF PSF-fit photometry are largely associated with seeing-dependent changes in the relative contributions of compact nuclear and extended host components, which can mimic intrinsic short-timescale variability. In contrast, no robust INOV is detected with difference-image analysis. An ensemble structure function spanning $\Delta t\sim0.003$–$1600$ days reveals long-term variability in a small subsample of sources, whereas intrinsic variability remains unresolved at intranight timescales. Monte Carlo simulations further show that ZTF-like single-night monitoring has a low INOV recovery probability ($\sim1.2%$) for the variability amplitudes inferred from the long-term analysis. The recovery probability is primarily controlled by source brightness, AGN contribution, intrinsic variability amplitude, and photometric precision. These results demonstrate that the absence of detected INOV does not imply the absence of rapid accretion variability, but can reflect the limited detectability of low-amplitude signals under current observing capabilities. Our findings highlight the importance of robust photometric methodologies for future high-cadence variability studies of low-mass accreting black holes.
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All authors Wenwen Zuo, Hengxiao Guo, Wanling Liu, Wenke Ren, Jingbo Sun, Patricia Arévalo, Luis C. Ho, Alok C. Gupta, Vineet Ojha, Mouyuan Sun, Shuangliang Li, Haicheng Feng, Qi Yuan, Minfeng Gu, Xuebing Wu

Astrophysics of Galaxies

The Intermediate-Mass Black Hole Reverberation Mapping Project: Scientific Overview and Sample Characteristics

Hengxiao Guo, Jiancheng Wu, Wenwen Zuo et al. (+38 more)

Recent discoveries with the James Webb Space Telescope of massive black holes at high redshift have highlighted fundamental questions about black hole seed formation and the coevolution of black holes with their host galaxies. Because the initial seed population cannot yet be observed directly, nearby intermediate-mass black holes provide a complementary fossil record of black hole formation and early growth. Motivated by this opportunity, we present the Intermediate-Mass Black Hole Reverberation Mapping (IMBH-RM) project and construct a homogeneous Sloan Digital Sky Survey sample of active broad-line IMBHs by uniformly reanalyzing literature candidates with consistent spectral decomposition and black hole mass estimation. Our sample contains 192 reliable IMBH candidates at $z\lesssim0.3$ with $\log(M_{\rm BH}/M_\odot)<6$, including four particularly compelling sources with $\log(M_{\rm BH}/M_\odot)<5$. The primary goal of IMBH-RM is to obtain reliable black hole masses from direct measurements and characteristic sizes of the broad-line region and accretion disk for a carefully selected subsample. These measurements will provide robust low-mass anchors for calibrating single-epoch black hole mass estimates and extending black hole–galaxy scaling relations into the IMBH regime. By building a statistically meaningful reverberation-mapped sample spanning $10^4-10^6\,M_\odot$, we aim to constrain the local IMBH mass distribution and place observational constraints on competing black hole seed formation scenarios. The future Multi-Channel Imager aboard the Chinese Space-station Survey Telescope provides a particularly promising platform for achieving these goals.
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All authors Hengxiao Guo, Jiancheng Wu, Wenwen Zuo, Ruining Tian, Xuechen Zheng, Meicun Hou, Paulina Lira, Philip G. Edwards, Vivian U, Shu Wang, Mar Mezcua, Luis C. Ho, Minfeng Gu, Tao An, Samuzal Barua, Colin J. Burke, Zhen-yi Cai, Xuheng Ding, Haicheng Feng, Alok C. Gupta, ShaSha Li, Wanling Liu, Wen-juan Liu, Ru-sen Lu, Dragana Ilić, Andjelka B. Kovačević, Yu Pan, Luka Č. Popović, Wenke Ren, Paula Sánchez-Sáez, Jamie Stevens, Jingbo Sun, Mouyuan Sun, Chizhuo Wang, Junxian Wang, Rongfeng Shen, Xuebing Wu, Yong Shi, Zhefu Yu, Zhenya Zheng, Ling Zhu

Astrophysics of Galaxies

Empirical Near-Infrared Spectral Templates from SPHEREx: Disentangling AGN and Host-Galaxy Emission

Wenke Ren, Hengxiao Guo, Zhenya Zheng et al. (+9 more)

SPHEREx conducts the first all-sky near-infrared spectral survey over 0.75-5.0 $\mu$m, spanning the transition from host-galaxy starlight to AGN-heated torus emission and enabling spectroscopic identification of active galactic nuclei (AGNs). We develop a data-driven framework combining weighted non-negative matrix factorization with forward modeling to learn empirical rest-frame templates from 2,777 normal galaxies and 1,064 AGNs in the North Ecliptic Pole (NEP) field. The resulting 14-component dictionary contains seven galaxy templates spanning stellar-population continua and nebular emission and seven AGN templates capturing emission lines and warm and hot torus continua, providing an additive, operational decomposition. Inferred near-infrared host fractions correlate with independent SDSS spectral and HSC imaging decompositions (at Pearson $r=0.68$ and $r=0.59$), comparable to the SDSS-HSC correlation ($r=0.66$) and supporting the reliability of the AGN-host separation. In the NEP deep field, the same templates recover redshifts with $|z_{\rm fit}-z_{\rm spec}| < 0.01$ for 93.0% of galaxies and 93.5% of AGNs and distinguish galaxies, narrow-line AGNs, and broad-line AGNs with 81.3% accuracy. At all-sky depth, classification retains 72.9% accuracy. The near-infrared coefficients also flag questionable DESI spectral classifications and redshifts, showing how SPHEREx complements optical spectroscopy. Learned directly from survey spectrophotometry and extending beyond the $K$ band, this empirical dictionary fills a long-standing gap in near-to-mid-infrared templates and provides a data-driven foundation for population-scale studies of AGN activity and its connection to host galaxies across the SPHEREx all-sky survey.
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All authors Wenke Ren, Hengxiao Guo, Zhenya Zheng, Minfeng Gu, Wenwen Zuo, Junxian Wang, Weida Hu, Zhen-Bo Su, Shi-Jiang Chen, Lin Long, Jiaqi Lin, Chi-Zhuo Wang

Instrumentation and Methods for Astrophysics

Simulation of the electron escape ratio for keV alpha-particle ionization tracks in liquid helium

Zihuai Hu, Junhui Liao, Zhuo Liang et al. (+6 more)

The electron escape ratio for 5.3 MeV alpha-particle ionization tracks in liquid helium under varying external electric fields has been measured in several experiments. However, to the best of our knowledge, the corresponding ratio for keV-scale alpha tracks in the same medium has not yet been reported. In this article, we demonstrate for the first time that this ratio can be accurately characterized using COMSOL-based simulations. Our simulation framework was developed in two stages. In Stage I, we aimed to verify consistency between our simulated results and published experimental data for 5.3 MeV alpha particles. Following successful verification in Stage I, we proceeded to Stage II, in which the 5.3 MeV track was replaced by 2, 5, and 10 keV tracks. Our simulated results reveal that (a) keV-scale tracks exhibit electron escape ratios approximately 1.5-2.5 times higher than that of the 5.3 MeV track, and (b) the escape ratios for all track energies (2, 5, 10 keV, and 5.3 MeV) exhibit a linear dependence on the ion number density at the simulation's T0, but not on the electron number density.
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All authors Zihuai Hu, Junhui Liao, Zhuo Liang, Guangpeng An, Zhaohua Peng, Jian Zheng, Lifeng Zhang, Lei Zhang, Yuanning Gao

Solar and Stellar Astrophysics

Electron acceleration by turbulent reconnection in solar flares

Zining Ren, Xin Cheng, Yulei Wang et al. (+1 more)

Solar flares can release magnetic energy explosively in the corona and produce high-energy particles on short timescales. However, how and where these particles are accelerated remains an open question. Here, we investigate the acceleration and transport of electrons during self-developed three-dimensional turbulent reconnection of solar flares by solving Parker's transport equation in the framework of high-resolution MHD simulations. We find that thermal electrons at both the flare current sheet and loop top are rapidly accelerated up to ~90keV, with energy spectra exhibiting a power-law feature. Although the population of accelerated electrons at the flare loop top is larger than that at the current sheet, their spectral indices are similar, close to the values usually observed. More importantly, the acceleration is achieved by turbulence-driven compression structures of various scales rather than the supposed termination shock, particularly at the flare loop top. A portion of compression structures even forms shocks. These results highlight the critical role of turbulent reconnection in accelerating electrons, thereby shedding new light on the acceleration and transport of particles in other high-energy phenomena.
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All authors Zining Ren, Xin Cheng, Yulei Wang, Mingde Ding

Instrumentation and Methods for Astrophysics

Overview of multi-conjugate adaptive optics reconstructors

Clémentine Béchet

Multi-Conjugate Adaptive Optics (MCAO) systems aim at correcting for the atmospheric turbulence uniformly over wide-field observations. Compared to classical AO, this requires a tomographic reconstruction of the turbulence perturbations, that is to say a reconstruction of the atmosphere in its volume, and the control of several deformable mirrors optically conjugated to various altitudes. During the last two decades, many tomographic reconstructors have been proposed in the AO literature and some have been implemented on sky on existing MCAO systems. This paper presents an overview of MCAO reconstructors. Four categories of reconstructors are considered: i) the reconstructors based on interaction matrix; ii) the minimum-variance static reconstructors; iii) the 3-step recontructors and iv) the Kalman-based reconstructors. We discuss their relative advantages and drawbacks.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Quasicrystalline Inflation: From the Cosmological Dipole to Primordial Diffraction

Jiro Soda

We propose quasicrystalline inflation. Six quasiperiodic phases decompose into three phonons and three phasons. It turns out that a coherent pure-phason displacement can generate a local power dipole while the linear traceless quadrupole vanishes. From spatially varying quadratic effective field theory, we derive off-diagonal correlations whose momentum transfer is restricted to integer combinations of the six icosahedral wavevectors. These correlated off-diagonal signals provide a characteristic observational signature of primordial quasiperiodic order, primordial diffraction.
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Instrumentation and Methods for Astrophysics

Optimization of adaptive optics correction during observations: Algorithms and system parameters identification in closed-loop

Clémentine Béchet, Michel Tallon and Éric Thiébaut

The adaptive optics (AO) on the European Extremely Large Telescope, as well as earlier pathfinders like the Adaptive Optics Facility, at the Very Large Telescope in 2014, will no longer be stationary systems. AO is no longer isolated on a bench; some elements are directly in the optical train of the telescope, suffering environment and constrains changes during the observations. To guarantee good performance at any observing time, we investigate a self-calibration strategy. We focus here on one of the most challenging aspects: the identification of system parameters during closed-loop observations without introducing any additional disturbance. Such problem is known in the identification theory to be difficult to solve. We have recently presented (Béchet et al., AO4ELT2 Conference, 2011) an identification method for this, with promising results obtained in simulations. To consolidate these advances, we come back in the present paper to the equations and provide a theoretical analysis to justify the choice of the algorithm. We highlight the benefit of using incremental data and commands to decorrelate the disturbance. We also present 2 implementations of the method, currently studied at the European Southern Observatory.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Cosmological implications for hairy black holes via spontaneous symmetry breaking: Are Hairy Black Holes Primordial?

Suruj Jyoti Das and Miok Park

We investigate whether hairy black holes generated through spontaneous symmetry breaking in Einstein-Scalar-Gauss-Bonnet (ESGB) theory, involving a complex scalar field with a global $U(1)$ symmetry, can be compatible with cosmological evolution. To this end, we introduce the ESGB theory with a scalar self-interaction that becomes relevant on cosmological scales while remaining negligible near the black hole. Owing to the time dependence of the GB term on cosmological scales, the scalar field dynamics in the evolving FLRW background differ qualitatively from those in the nearly static black hole background. In particular, for scalar-GB couplings compatible with hairy black hole formation, the effective potential supports a symmetry-broken vacuum throughout inflation. However, after inflation, a decelerated expansion changes the sign of the GB term, temporarily making the effective potential unbounded from below. As the GB contribution subsequently decreases, the scalar self-interaction eventually dominates and restores the symmetry. Within this schematic framework, we derive stringent constraints on the coupling strengths, the cutoff scale, and the black hole mass, which primarily arise for avoiding efficient tachyonic amplification of the scalar field perturbations during the unbounded phase. For cutoff scales compatible with both cosmological evolution and scalar hair formation, we find that only ultralight black holes with masses of the order of a few grams can develop scalar hair, identifying them as hairy primordial black holes.
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Instrumentation and Methods for Astrophysics

BICEP/Keck XXII: Analysis of the South Pole Atmosphere for CMB Observations

P. A. R. Ade, Z. Ahmed, M. Amiri et al. (+92 more)

The South Pole is among the driest sites on Earth, and the resulting high atmospheric transparency makes it an excellent site for millimeter-wave astronomical observations. Nevertheless, for bolometric surveys of the cosmic microwave background (CMB), fluctuations in line-of-sight water vapor drive variable atmospheric emission, which has a significant impact on survey sensitivity. We have deployed a water vapor radiometer (WVR) to characterize these fluctuations in space and time and to compare atmospheric and CMB signals with other sites. This WVR has been monitoring conditions from the South Pole over the past nine years, co-located and co-observing with the BICEP series of telescopes. In this work, we analyze the performance of the WVR and the characteristics of the South Pole atmosphere and demonstrate coherent wind-driven transport of water vapor structures across the site. We show that fluctuations in CMB detector timestreams are well correlated with fluctuations in atmospheric water vapor, providing independent justification for baseline filtering procedures used to remove these fluctuations and providing a new pathway to detect and mitigate the temperature-to-polarization leakage that currently limits the precision of ground-based CMB polarization measurements.
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All authors P. A. R. Ade, Z. Ahmed, M. Amiri, D. Barkats, D. Barron, R. Basu Thakur, I. Birdwell, C. A. Bischoff, D. Beck, J. J. Bock, V. Buza, B. Cantrall, J. R. Cheshire IV, J. Connors, J. Cornelison, M. Crumrine, A. J. Cukierman, E. Denison, L. Duband, M. A. Echter, M. Eiben, B. D. Elwood, S. Fatigoni, J. P. Filippini, A. Fortes, M. Gao, C. Giannakopoulos, N. Goeckner-Wald, D. C. Goldfinger, S. Gratton, J. A. Grayson, A. Greathouse, P. K. Grimes, G. Halal, M. Halpern, E. Hand, S. A. Harrison, S. Henderson, T. D. Hoang, J. Hubmayr, H. Hui, K. D. Irwin, J. H. Kang, K. S. Karkare, S. Kefeli, J. M. Kovac, C. Kuo, K. Lasko, K. Lau, M. Lautzenhiser, T. Liu, S. C. Mackey, N. Maher, K. G. Megerian, L. Minutolo, L. Moncelsi, Y. Nakato, H. T. Nguyen, R. O'Brien, S. N. Paine, A. Papen, A. Patel, M. A. Petroff, A. R. Polish, N. Precup, T. Prouve, C. Pryke, C. D. Reintsema, T. Romand, M. Salatino, A. Schillaci, B. Schmitt, C. D. Sheehy, B. Singari, A. Soliman, T. St. Germaine, A. Steiger, B. Steinbach, R. Sudiwala, G. Teply, K. L. Thompson, C. Tucker, A. D. Turner, C. Verges, A. G. Vieregg, A. Wandui, A. C. Weber, J. Willmert, C. L. Wong, W. L. K. Wu, H. Yang, C. Yu, L. Zeng, C. Zhang, S. Zhang

Cosmology and Nongalactic Astrophysics

Calculating the squeezed bispectrum in stochastic inflation by Monte Carlo simulation

Koichi Miyamoto and Yuichiro Tada

The bispectrum of cosmological perturbations is an important probe of inflation and the underlying particle physics. However, calculating it becomes challenging in inflation models where inflaton dynamics is dominated by quantum diffusion rather than slow-roll, especially in the multi-field case. In this paper, employing the stochastic-$\delta \mathcal{N}$ formalism, we propose a Monte Carlo-based method to calculate the bispectrum in the squeezed limit, as an extension of the method for the power spectrum that we previously proposed. Our method involves generating paths of inflatons' time evolution that branch only several times, avoiding nested path generation, which incurs a prohibitive computational cost. As numerical demonstrations, we apply the proposed method to single- and double-field chaotic inflation for validation, and to hybrid inflation with mild waterfall, for which, to the best of our knowledge, the bispectrum is calculated for the first time in this work.
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Instrumentation and Methods for Astrophysics

Lightweight Soft X-ray Imager (LSXI) with glass-based coded mask

Dali Zhang, Chao Zheng, Lu Wang et al. (+23 more)

The coded mask technique has been widely used in X-ray and Gamma-ray imagers, especially in space astronomy. However, the traditional design of coded mask imagers usually has problems with large size and heavy weight. Here, we propose a novel design for a coded mask imager made of glass based on microchannel plate (MCP) technology, making it lightweight (within 1 kg), compact, and self-supporting, which is very suitable for space exploration satellites. The design is initially demonstrated by reconstructing encoded patterns from measurements at the X-ray beamline. Monte Carlo simulations of the module integrated into a 6U CubeSat are conducted to assess its in-orbit detector performance, including sensitivity and source localization.
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All authors Dali Zhang, Chao Zheng, Lu Wang, Haopeng Li, Jinpeng Zhang, Xinqiao Li, Shaolin Xiong, Longhui Li, Zhenghua An, Sheng Yang, Xiaoqing Cong, Zhixing Ling, Hailing Qin, Xiangyang Wen, Ke Gong, Yaqing Liu, Xiaojing Liu, Xiang Ma, Xiaoyun Zhao, Yanbing Xu, Junhao Yin, Dejun Gong, Jiacong Liu, Chenwei Wang, Min Gao, Jinzhou Wang

High Energy Astrophysical Phenomena

Are Repeaters Prevalent Among the Known Fast Radio Burst Sources?

Xiao-Fei Dong, Qing Pan, Yong-Feng Huang et al. (+10 more)

Fast radio bursts (FRBs) are millisecond radio pulses of unknown origin. Despite extensive follow-up observations, only $\sim3\%$ of FRBs have been confirmed as repeaters. It remains unclear whether the rest are truly one-off bursts, or essentially repeating sources that have only been detected once due to limited monitoring time. Using the second CHIME/FRB catalog, we test this debate by comparing non-repeaters with two repeater-based subsamples: the first-detected bursts of repeaters and their highest-fluence bursts. A non-parametric method that accounts for selection effects is employed to derive the energy functions and event rates of these samples. All samples are well described by broken power-law energy distributions with comparable break energies ($\sim 5\times10^{38}$ erg), but with significantly different slopes between repeating and non-repeating populations. Their event-rate evolution also differs significantly. Assuming $\rho(z) \propto (1+z)^B$, we have $B = -5.57^{+0.15}_{-0.15}$ for non-repeaters and $B = -8.63^{+0.46}_{-0.41}$ and $-9.10^{+0.55}_{-0.56}$ for the two repeater samples. Size-matched resampling shows that the repeater event-rate indices lie far outside the 5$\sigma$ range expected from non-repeater subsamples, ruling out sample size as the reason for the observed difference. These results indicate that at least a subset of one-off FRBs are intrinsically non-repeating, implying that repeating sources may represent a distinct and possibly less common population.
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All authors Xiao-Fei Dong, Qing Pan, Yong-Feng Huang, Zhi-Bin Zhang, Hao-Xuan Gao, Jin-Jun Geng, Xue-Feng Wu, Lang Cui, Xiu-Juan Li, Song-Bo Zhang, Abdusattar Kurban, Chen-Ran Hu, Chen Deng

Instrumentation and Methods for Astrophysics

A measurement-based approach to EPFD calculation, to quantify the impact of satellite mega-constellations on low-frequency radio astronomy

Steven J. Tingay, Gregory Hellbourg, Daniel Sheen et al. (+4 more)

Context: Satellite mega-constellations generate Unintended Electro-Magnetic Radiation (UEMR) impacting low frequency radio astronomy. The Radio Regulations of the International Telecommunications Union Radiocommunication Sector (ITU-R) contain the basis for addressing UEMR, but enforcement mechanisms are absent. Aims: To adapt compatibility study methods based on satellite constellation simulations, in particular the Equivalent Power Flux-Density (EPFD) framework, to radio telescope measurements. Methods: We adapt the ITU-R EPFD calculation framework to measurement data obtained from all-sky interferometric imaging. We address the conceptual differences between forward-model EPFD calculations and measurement-based approaches. In particular, we consider low frequency systems, which are typically wide field-of-view and interferometric instruments. Results: For the first time, we demonstrate that all-sky interferometric observations enable a direct adaptation of the EPFD formalism to measurement data. We thus confirm previous estimations (Di Vruno et al. 2023) that the resulting measurement-based EPFD distributions exceed the radio astronomy interference threshold levels defined in Recommendation ITU-R RA.769-2 in 50-70% of samples. These exceedance fractions are well above the 2% single-system data-loss criterion in Recommendation ITU-R RA.1513-2. Expressed using the conventional 2% compatibility margin, the corresponding margins are negative, ranging from -18.6 to -16.3 dB, equivalent to a required uniform attenuation of 16.3-18.6 dB. Conclusions: Measurement-based implementations provide a practical pathway toward verification and long-term monitoring at low radio frequencies, which could form an important component of enforceability. We suggest instrumentation approaches to support measurement.
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All authors Steven J. Tingay, Gregory Hellbourg, Daniel Sheen, Dylan Grigg, Benjamin Winkel, Federico Di Vruno, Balthasar Indermuehle

Instrumentation and Methods for Astrophysics

Scalability in Simulating a Large-Aperture, Fresnel Zone Plate Lens for a Conceptual Space Telescope

Maneesha Dushmantha De Zoysa, Yangwoo Seong, Ho Xuan Vinh et al. (+2 more)

As ambitious space telescope concepts such as ultra-lightweight planar diffractive optical elements (DOEs) emerge, validating the performance remains a major computational challenge. Conventional Fourier propagation algorithms were observed to fail at meter-class apertures due to severe memory limits caused by rigid grid-sampling requirements, and the scaled-down proxy models used for reflector telescopes cannot be applied, since scaling compresses the outermost zones that govern resolution. We benchmarked five Fourier-based propagators against a common Fresnel diffraction integral and found that only those decoupling the focal-plane grid from the input aperture converge within a 1% error threshold. With these findings, we implemented an optimized, stripe-processed Chirp Z-Transform (CZT) framework, evaluating the focal spot strictly within a fixed region of interest to reduce peak memory usage. Applied to five full-aperture configurations from 1.0 m to 5.0 m at f/# = 5, the framework predicted spatial resolution and diffraction efficiency to within 0.001% and 0.16% of analytical references, with modulation transfer function results cross-checked by two analytical extraction methods, all within 6.4 GB of memory on a single consumer-grade GPU. This simulation study represents first steps toward quantifying the expected results of ambitious space telescope concepts and aids the mission development (or selection) phase. With a highly accurate, memory-efficient validation tool, the findings obtained will be used to guide the fabrication decisions of future hardware, optical testing, and physical deployment mechanisms of large-scale diffractive telescopes.
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All authors Maneesha Dushmantha De Zoysa, Yangwoo Seong, Ho Xuan Vinh, Jae Hung Han, Hyun Jung Kim

Cosmology and Nongalactic Astrophysics

Inflationary Magnetogenesis with $f(R,\phi)$ Coupling

Shuang Liu, Bo-yu Zhao, Yu Li et al. (+1 more)

Inflationary magnetogenesis provides a promising mechanism for generating primordial large-scale magnetic fields, but faces challenges such as the strong coupling problem and backreaction issues. In this paper, we extend the Ratra model by introducing a coupling between the electromagnetic field and the background geometry, parameterized as $K(R)I^2(\phi)$. Starting from a general action with $f^2(R,\phi)F_{\mu\nu}F^{\mu\nu}$, we adopt $f^2(R,\phi)=K(R)I^2(\phi)$ as a concrete realization. Rather than focusing on the slow-roll inflationary stage (which reduces to the standard Ratra scenario), we concentrate on the post-inflationary reheating epoch, where the broken-power-law evolution of the scale factor and coupling function across the inflation-to-reheating transition allows us to derive analytic expressions for the magnetic and electric energy density spectra. Three key theoretical constraints are imposed on the model parameter space: the strong coupling condition, the backreaction constraint, and the CMB isotropy requirement. We obtain predictions for the present-day magnetic field strength $B_0$ and coherence length $L_{c0}$ for various combinations of the inflationary energy scale $H_f$ and the reheating temperature $T_r$. By comparing with observational constraints from radio observations and Fermi-LAT gamma-ray data, we demonstrate that the inflationary energy scale $H_f$, the reheating temperature $T_r$, the parameter $\beta$, and the e-folding numbers $N_f$, $N_r$ must satisfy stringent joint constraints. This work provides a viable theoretical framework for inflationary magnetogenesis that simultaneously satisfies theoretical consistency conditions and current observational bounds, with the reheating-stage nonlinear MHD evolution serving as a crucial ingredient for producing observationally compatible magnetic fields.
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All authors Shuang Liu, Bo-yu Zhao, Yu Li, Yao-chuan Wang

Tuesday 1 September

Instrumentation and Methods for Astrophysics

Photon-Ring Retarded- Time Tomography: The Mahakal Phenomenon

Hina Dixit and Abhinav Chauhan

Near-critical null geodesics generate image-order channels with distinct mappings, delays, and weights, so one observer-time data set samples multiple source epochs. We organize the inverse problem by historical reach, dimension, and held-out recovery. Using continuum-noise-consistent, matrix-free Kerr/Schwarzschild operators for orders n = 0, 1, 2, we audit 12 spin-inclination geometries. At normalized SNR0 = 100, resolved orders extend anchor-connected history beyond direct imaging in all cells by 40 M, 24 M, and one 4 M grid step at inclinations 20 degrees, 50 degrees, and 75 degrees. Operational rank rises from 153 to 202 and old-age innovation from 8.29 M to 40.72 M; complete order summation retains only 9.66 M. Compact temporal support gives an exact result: temporal basis functions outside the direct retarded-time footprint generate identically zero direct columns, while higher orders can lift those old-epoch blind blocks. Direct old-structure rank is zero, while resolved orders support 38, 93, and 185 operational directions across three classes. Yet source enrichment leaves reach nearly fixed while rank fraction and singular-value stability collapse; this is the Mahakal phenomenon. Held-out tests show bounded benefit, not a movie. Resolved orders extend stable baseline-inclusive emissivity-level span from 48 M to 80 M, but that endpoint is level dominated. On 60 histories, physical morphology error falls by 13.3 percent with TSVD and 16.4 percent with ridge. Reliable two-feature recovery fails and the stable morphology interval is zero. Complete order summation yields no material morphology gain. The positive results are therefore best-case, known-geometry image-domain benchmarks under ideal order separation; SNR0 is an operator normalization, not an observation.
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