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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 30 December

Astrophysics of Galaxies

photoD with Rubin's Data Preview 1: first stellar photometric distances and deficit of faint blue stars. Stellar distances with Rubin's DP1

L. Palaversa, E. Donev, Ž. Ivezić et al. (+96 more)

Aims: We investigate the utility of Rubin's Data Preview 1 for estimating stellar number density profile in the Milky Way halo. Methods: Stellar broad-band near-UV to near-IR $ugrizy$ photometry released in Rubin's Data Preview 1 is used to estimate distance and metallicity for blue main sequence stars brighter than $r=24$ in three $\sim$1.1. sq.~deg. fields at southern Galactic latitudes. Results: Compared to TRILEGAL simulations of the Galaxy's stellar content by (Dal Tio, 2022), we find a significant deficit of blue main sequence turn-off stars with $22 < r < 24$. We interpret this discrepancy as a signature of a much steeper halo number density profile at galactocentric distances $10-50$ kpc than the cannonical $\sim1/r^3$ profile assumed in TRILEGAL simulations. Conclusions: This interpretation is consistent with earlier suggestions based on observations of more luminous, but much less numerous, evolved stellar populations, and a few pencil beam surveys of blue main sequence stars in the northern sky. These results bode well for the future Galactic halo exploration with Rubin's Legacy Survey of Space and Time.
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All authors L. Palaversa, E. Donev, Ž. Ivezić, K. Mrakovčić, N. Caplar, M. Jurić, T. Jurkić, S. Campos, M. DeLucchi, D. Jones, K. Malanchev, A.I. Malz, S. McGuire, B. Abel, L. Girardi, G. Pastorelli, M. Trabucchi, S. Zaggia, E. Acosta, C.L. Adair, J. Andrew, É. Aubourg, A.E. Bauer, W. Beebe, E.C. Bellm, R.D. Blum, M.T. Booth, A. Boucaud, D. Branton, D.L. Burke, D. Calabrese, J.L. Carlin, H-F. Chiang, Y. Choi, A.J. Connolly, S. Dagoret-Campagne, P.N. Daly, F. Daruich, G. Daubard, E. Dennihy, H. Drass, O. Eiger, A.M. Eisner, L.P. Guy, J. Hoblitt, P. Ingraham, F. Jammes, B.T. Jannuzi, M.J. Jee, T. Jenness, R.L. Jones, C. Juramy-Gilles, S.M. Kahn, Y. Kang, A. Kannawadi, L.S. Kelvin, I.V. Kotov, G. Kovács, N.R. Kurita, T. Lange, D. Laporte, J.C. Lazarte, S. Liang, M. Lopez, N.B. Lust, M. Lutfi, O. Lynn, G. Mainetti, F. Menanteau, M. Miller, M. Moniez, N. Sedaghat, E. Nourbakhsh, H.Y. Park, J.R. Peterson, R. Plante, A. Plazas Malagón, M.N. Porter, K.A. Reil, V.J. Riot, A. Roodman, E.S. Rykoff, R.H. Schindler, J. Sebag, R.A. Shaw, A. Shugart, K.B. Siruno, J.A. Smith, J.D. Swinbank, J.G. Thayer, S. Thomas, R. Tighe, D.L. Tucker, M. Turri, E.K. Urbach, B. Van Klaveren, W. van Reeven, C.Z. Waters, B. Willman

High Energy Astrophysical Phenomena

SSC Radiation in the ICMART Model: Spectral Simulations and Application to the Record-Breaking GRB 221009A

Xueying Shao and He Gao

This paper presents simulations of the synchrotron self-Compton (SSC) spectrum within the Internal-Collision-induced Magnetic Reconnection and Turbulence (ICMART) model. We investigate how key parameters like the magnetization $\sigma_0$ shape the broadband spectral energy distribution by regulating the electron distribution and magnetic field strength. The overall spectrum typically comprises two components: synchrotron radiation peaking at $E_{\rm p}$ with a low-energy spectral index $\alpha$ between -1 and -1.5, and an SSC component peaking at $E_{\rm ssc}$. At high energies, Klein-Nishina suppression causes an exponential cutoff. The flux ratio Y between these components is critical: when Y is small, the SSC peak can be suppressed. Spectral features of the synchrotron component reveal the underlying physical conditions: harder spectra with $\alpha\sim-1$ indicate a large Y parameter and strong KN suppression. We find a positive correlation between Y and $\sigma_0$, contrasting with internal shock model predictions. Applied to GRB 221009A, our model suggests $\sigma_0\leq20$ can reproduce the MeV-TeV observations. This study underscores the value of combined MeV-TeV observations in probing GRB emission mechanisms.
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Instrumentation and Methods for Astrophysics

Antarctic TianMu Staring Observation Project II: Data reduction and preliminary results

Hubiao Niu, Jing Zhong, Yu Zhang et al. (+6 more)

The Antarctic TianMu Staring Observation Program is a time-domain optical sky survey project carried out in Antarctica, capable of large sky coverage, high-cadence sampling, and long-period staring. It utilizes the exceptional observing conditions in Antarctica to conduct high-cadence time-domain sky surveys. At present, we have successfully developed an 18-cm aperture Antarctic TianMu prototype, which has been deployed at Zhongshan Station in Antarctica for two consecutive years of trouble-free observations, during which more than 300,000 original images were obtained. This paper systematically outlines the commissioning data of the prototype telescope in 2023, the primary data processing pipeline, and the preliminary data products. The core pipeline encompasses four key stages: Data preprocessing, instrumental effect correction, astrometric solution, and full-field stellar photometry. Here, we release the 2023 data products, which specifically include reduced image data and a photometric catalog, for which, preliminary analyses demonstrate robust performance. Using Gaia Data Release 3 as a reference catalog, the astrometric precision, quantified by the root mean square of positional errors, is determined to be better than approximately 2 arcseconds, validating the observational capabilities of the system. For a 30-second exposure, the detection limit in the G-band is achieved at 15.00~mag, with a detection threshold of 1.5~$\sigma$. The photometric errors are below 0.1~mag for the majority of stars brighter than 14.00~mag. Furthermore, it improves significantly, reaching better than 0.01~mag for most stars brighter than 11.00~mag and 12.00~mag when employing the adaptive aperture photometry and point spread function photometry methods, respectively.
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All authors Hubiao Niu, Jing Zhong, Yu Zhang, Jianchun Shi, Rui Rong, Jinzhong Liu, Shiyin Shen, Zhenghong Tang, Dan Zhou

Instrumentation and Methods for Astrophysics

Antarctic TianMu Staring Observation Project I: Overview and Implementation of the Prototype Telescope

Dan Zhou, Jing Zhong, Jianchun Shi et al. (+31 more)

Wide-field rapid sky surveys serve as critical observational methods for time-domain astronomical research. The Antarctic region, with several months of continuous dark nights annually, is an ideal site for time-domain astronomical observations. The Antarctic TianMu Staring Observation Project aims to deploy a fleet of small telescopes, adopting an array observation model to conduct time-domain optical observations in Antarctica, featuring wide-sky coverage, high-cadence sampling, long-period staring, and simultaneous multi-band measurements. Considering the severe challenges optical telescopes face in Antarctica, including extremely low temperatures, unattended operation, and limited power supply and network transmission, we have designed and developed the Antarctic TianMu prototype telescope based on drift-scan charge-coupled device technology. In October 2022, our prototype (with an aperture of 18 cm), named AT-Proto was transported to Zhongshan Station in Antarctica aboard China's 39th Antarctic Research Expedition. It has since operated stably and reliably in the frigid environment for over two years, demonstrating the significant advantages of this technology in polar astronomical observations. The experimental observation results of AT-Proto provide a solid foundation for the subsequent construction of a time-domain astronomy observation array in Antarctica.
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All authors Dan Zhou, Jing Zhong, Jianchun Shi, Zhenghong Tang, Shiyin Shen, Peng Jiang, Jie Zhu, Yong Yu, Lixin Zheng, Jianjun Cao, Guoping Chen, Xinyu Yao, Congcong Zhang, Lurun Shen, Hui Zhang, Xiang Pan, Chenwei Yang, Tuo Ji, Xian Shi, Hengxiao Guo, Zhen Yan, Donghai Zhao, Liang Chen, Jianeng Zhou, Minfeng Gu, Fuguo Xie, Wenbiao Han, Jinliang Hou, Bixuan Zhao, Wenwen Zuo, Chun Xu, Zhengyi Shao, Lei Hao, Jian Fu

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Kinematic Anisotropies in PTA Observations: Analytical Toolkit

Maximilian Blümke, Kai Schmitz, Tobias Schröder et al. (+2 more)

The reported evidence for an isotropic gravitational-wave background (GWB) from pulsar timing array (PTA) collaborations has motivated searches for extrinsic and intrinsic anisotropies. Kinematic anisotropies may arise as a consequence of a boosted observer moving with respect to the frame in which the GWB appears isotropic. In this work, we present an analytical toolbox to describe the effects of kinematic anisotropies on the overlap reduction function. Our analytical results differ from previous findings at the quadrupole order and are detailed in three appendices. For the first time, we also derive the corresponding auto-correlation using two approaches, taking the pulsar distances to be infinite or finite, respectively. Our formulas can be used in forecasts or Bayesian analysis pipelines.
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All authors Maximilian Blümke, Kai Schmitz, Tobias Schröder, Deepali Agarwal, Joseph D. Romano

High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph

The role of particle feedback on particle acceleration in magnetic reconnection

Shimin Liang and Nianyu Yi

Magnetic reconnection is a ubiquitous process in astrophysical plasmas and an efficient mechanism for particle acceleration. Using 2.5D magnetohydrodynamic (MHD) simulations with a co-evolving fluid-particle framework, we investigate how particle feedback affects reconnection and acceleration. Our simulations demonstrate that particle feedback to the fluid amplifies shear flows within magnetic islands, which strengthens the convective electric field and thereby boosts particle acceleration. This mechanism results in a higher maximum particle energy and a harder non-thermal energy spectrum. The guide field suppresses both the increase in gas internal energy and particle acceleration. These findings highlight the complex interplay between feedback, guide fields, and reconnection dynamics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Inflationary QCD phase diagram

Kohei Fujikura and Toshifumi Noumi

Motivated by the cosmological collider program, which aims to probe high-energy physics through inflation, we investigate the phase diagram of multi-flavor QCD in de Sitter spacetime with a flavor-universal axial chemical potential induced by a rolling inflaton coupled to fermions. We determine the first-order critical line and a critical point as functions of the Hubble parameter and the axial chemical potential, employing an effective description of chiral symmetry breaking within the framework of the Nambu–Jona-Lasinio model. We find that a first-order chiral phase transition may occur during inflation or at its end when the axial chemical potential is sufficiently large and crosses the critical line. This provides a cosmological collider analogue of the QCD phase diagram explored in heavy-ion colliders.
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Earth and Planetary Astrophysics

Atmospheric Mass Flux as a Function of Ionospheric Emission on Unmagnetized Earth

P. C. Hinton, D. A. Brain, N. R. Schnepf et al. (+3 more)

We explore ion escape from, and solar ion deposition to, \hll{an unmagnetized Earth-like planet}. We use RHybrid, an ion-kinetic electron-fluid code to simulate the global plasma interaction of unmagnetized Earth with the solar wind. We vary the global ionospheric emission rate, and quantify the resultant planetary ion escape rates ($O^+$ and $H^+$) and the solar wind deposition rate ($H^+$). We use these results to compute the net mass flux to the atmosphere and find that the solar ion deposition rate could be comparable to planetary ion escape rates. For the emission rates simulated, our results show that under typical solar wind conditions ($v_{sw} = 400 \ km \ s^{-1}$, $n_{sw} = 5 \ cm^{-3}$), the mass of the atmosphere would decrease by less than 3% over a billion years, indicating that Earth's intrinsic magnetic field may be unnecessary for retention of its atmosphere. Lastly, we present a hypothesis suggesting that ionospheric emission may evolve through time towards a critical emission rate that occurs at a net mass flux of zero.
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All authors P. C. Hinton, D. A. Brain, N. R. Schnepf, R. Jarvinen, J. Cessna, F. Bagenal

High Energy Astrophysical Phenomena

Machine-learning approaches to dispersion measure estimation for fast radio bursts

Hosein Rajabi, Zhejian Liu, Fereshteh Rajabi et al. (+1 more)

Fast radio bursts (FRBs) are bright, mostly millisecond-duration transients of extragalactic origin whose emission mechanisms remain unknown. As FRB signals propagate through ionized media, they experience frequency-dependent delays quantified by the dispersion measure (DM), a key parameter for inferring source distances and local plasma conditions. Accurate DM estimation is therefore essential for characterizing FRB sources and testing physical models, yet current dedispersion methods can be computationally intensive and prone to human bias. In this proof-of-concept study, we develop and benchmark three deep-learning architectures, a conventional convolutional neural network (CNN), a fine-tuned ResNet-50, and a hybrid CNN-LSTM model, for automated DM estimation. All models are trained and validated on a large set of synthetic FRB dynamic spectra generated using CHIME/FRB-like specifications. The hybrid CNN-LSTM achieves the highest accuracy and stability while maintaining low computational cost across the investigated DM range. Although trained on simulated data, these models can be fine-tuned on real CHIME/FRB observations and extended to future facilities, providing a pathway toward real-time, data-driven DM estimation in large FRB surveys with further development.
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All authors Hosein Rajabi, Zhejian Liu, Fereshteh Rajabi, Martin Houde

High Energy Astrophysical Phenomena

Time-Dependent Accretion Disks with Magnetically Driven Winds: Green's Function Solutions

Mageshwaran Tamilan

We present Green's function solutions for a geometrically thin, one-dimensional Keplerian accretion disk that includes angular momentum extraction and mass loss due to magnetohydrodynamic (MHD) winds. The disk viscosity is assumed to vary radially as $\nu \propto r^{n}$. We derive solutions for three types of boundary conditions applied at the inner radius $r_{\rm in}$: (i) zero torque, (ii) zero mass accretion rate, and (iii) finite torque and finite accretion rate, and investigate the time evolution of a disk with an initial surface density represented by a Dirac-delta function. The mass accretion rate at the inner radius decays with time as $t^{-3/2}$ for $n = 1$ at late times in the absence of winds under the zero-torque condition, consistent with Lynden-Bell & Pringle (1974), while the presence of winds leads to a steeper decay. All boundary conditions yield identical asymptotic time evolution for the accretion and wind mass-loss rates, though their radial profiles differ near $r_{\rm in}$. Applying our solutions to protoplanetary disks, we find that the disk follows distinct evolutionary tracks in the accretion rate-disk mass plane depending on $\psi$, a dimensionless parameter that regulates the strength of the vertical stress driving the wind, with the disk lifetime decreasing as $\psi$ increases due to enhanced wind-driven mass loss. The inner boundary condition influences the evolution for $\psi < 1$ but becomes negligible at higher $\psi$, indicating that strong magnetically driven winds dominate and limit mass inflow near the boundary. Our Green's function solutions offer a general framework to study the long-term evolution of accretion disks with magnetically driven winds.
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Astrophysics of Galaxies

Variation of the 2175 Å extinction feature in Andromeda galaxy

Bing Yan, Shu Wang, Jian Gao et al. (+2 more)

Extinction curves contain key information on interstellar dust composition and size distribution, with the 2175 Å bump being the most prominent feature. We analyze 20 sightlines toward M31 using HST/STIS UV spectroscopy combined with multi-band photometry to characterize this feature. The extinction curves show substantial diversity, from MW-like shapes to flatter profiles with $R_V$ reaching up to $\sim5.8$. The strength of the 2175 Å feature varies widely, including two sightlines where the bump is essentially absent. The bump central wavelength spans a broader range than previously reported, while its width remains consistent with earlier studies. A moderate positive correlation is found between bump strength ($c_3$) and width ($\gamma$). We derive an average UV extinction curve toward M31 with $R_V \approx 3.53$. These results provide new constraints on dust properties and their spatial variations in this galaxy.
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All authors Bing Yan, Shu Wang, Jian Gao, Yuxi Wang, Bingqiu Chen

Monday 29 December

Cosmology and Nongalactic Astrophysics

The Tianlai-WIYN North Celestial Cap Redshift Survey

Reza Ansari, Gabriela A. Marques, John P. Marriner et al. (+13 more)

We present the results of a small, low redshift spectroscopic survey of galaxies within 3 degrees of the North Celestial Pole (NCP) selected using V-band photometry obtained from the North Celestial Cap Survey (NCCS) (Gorbikov & Brosch 2014). The purpose of the current survey is to create a redshift space template for 21 cm emission from neutral hydrogen with which to correlate radio line intensity observations by the Tianlai dish and cylinder interferometers. A total of 898 redshifts were obtained from the 2102 extended objects in the NCCS with m_V < 19 in the survey area. After accounting for extinction, the survey geometry and selection effects, the number density and clustering pattern of galaxies in the redshift catalog are consistent with other low redshift surveys. We were also able to identify 11 galaxy cluster candidates from this redshift catalog.
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All authors Reza Ansari, Gabriela A. Marques, John P. Marriner, Olivier Perdereau, Elena Pinetti, Lily Robinthal, Albert Stebbins, Haoxuan Sun, Peter Timbie, Gregory S. Tucker, Eli Doyle, Jocelyn Chu, E. Revsen Karaalp, Xuelei Chen, Jixia Li, Fengquan Wu

Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Control and read-out of the HEPD-02 tracking system onboard CSES-02 satellite

S. Bartocci, R. Battiston, S. Beolè et al. (+42 more)

The High Energy Particle Detector (HEPD-02) is a payload of the second China Seismo-Electromagnetic Satellite (CSES-02), designed and built by the Italian Limadou collaboration. Its purpose is to detect cosmic rays and trapped particles of radiation belts, in the kinetic energy range 3-100 MeV for electrons, 30-200 MeV for protons. HEPD-02 is the first space detector to use a tracking detector based on Monolithic Active Pixel Sensors (MAPS). The MAPS provides high spatial resolution, low noise, increased robustness, and low production costs. Operating MAPS in space presents a significant challenge due to strict power consumption requirements. To meet such constraints, a custom Tracker Data Acquisition (TDAQ) board and firmware have been designed and implemented, by using a commercial low-power Field Programmable Gate Array (FPGA). This paper addresses the design features of the TDAQ unit, enabling the tracking detector to be operated efficiently, with particular focus on the power consumption performance.
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All authors S. Bartocci, R. Battiston, S. Beolè, F. Benotto, P. Cipollone, S. Coli, A. Contin, M. Cristoforetti, C. De Donato, C. De Santis, A. Di Luca, F. Dumitrache, F. M. Follega, S. Garrafa Botta, G. Gebbia, R. Iuppa, A. Lega, M. Lolli, G. Masciantonio, M. Mergè, M. Mese, R. Nicolaidis, F. Nozzoli, A. Oliva, G. Osteria, F. Palma, F. Palmonari, B. Panico, S. Perciballi, F. Perfetto, P. Picozza, M. Pozzato, E. Ricci, M. Ricci, S. B. Ricciarini, Z. Sahnoun, U. Savino, V. Scotti, E. Serra, A. Sotgiu, R. Sparvoli, P. Ubertini, V. Vilona, S. Zoffoli, P. Zuccon

Astrophysics of Galaxies

The ionization structure and chemical history in isolated H ii regions of dwarf galaxies with VIMOS/IFU II. The Leo A galaxy

A. Andrade, I. Saviane, L. Monaco et al. (+1 more)

Study the ionized gas in metal-poor environments is key to understanding the mechanisms regulating galaxy evolution. However, most of the previous studies of extragalactic HII regions rely on unresolved observations of gaseous structures. We study the south-western, spatially resolved, HII region of Leo A, one of the most studied isolated dwarf galaxies in the Local Group. Using archival VIMOS-IFU/VLT data, we explored its gaseous structure through optical emission lines to gain insights into the present-day drivers of gas physics in this dIrr, and we place constraints on the chemical evolution scenario responsible for this low chemical enrichment. The emission line maps reveal that the strongest emission comes from the south-west region. A stratified distribution of ionic species was detected, likely powered by the young star cluster at the nebular centre. HST/ACS data show that the brightest star is in the centre of both the HII region and the star cluster. Photoionization production rates derived indicate that this star can sustain the ionization budget to power the HII region, although subject to the assumed electron density. Using the direct method, we derived a metallicity of $12+\log(\mathrm{O/H})=7.29\pm0.06$ dex, increasing to $7.46\pm0.09$ dex after correcting for temperature fluctuations, placing Leo A in the low-mass end of the MZR. Chemical evolution models suggest that, under constant accretion, the stellar mass growth and metal enrichment over the last 10 Gyr are successfully reproduced by both leaky-box and gas-regulator models. Those results are similar to those found in SagDIG, supporting a picture in which the present-day evolution of Leo A is dominated by stellar feedback processes. The combination of mass loss mechanisms and accretion events reproduces its chemical evolution, suggesting that Leo A has evolved under a gas equilibrium regime across its lifetime.
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All authors A. Andrade, I. Saviane, L. Monaco, M. Gullieuszik

Astrophysics of Galaxies

A clustering-based search for substructures in the Galactic plane and bulge using RR Lyrae stars as tracers

N. Cristi-Cambiaso, C. Navarrete, M. Catelan et al. (+2 more)

Although many globular clusters (GCs) have been identified in the Galaxy, their population is estimated to be incomplete, especially in regions with strong crowding and interstellar extinction such as the Galactic bulge and plane.RR Lyrae stars, as bright standard candles and tracers of old stellar populations, are powerful tools for finding GCs in these regions, and large catalogs of such stars have recently become available. We aim to construct a sample of RR Lyrae stars with six-dimensional information (three-dimensional positions, proper motions, and metallicities) in the Galactic plane and bulge, and to exploit it using a hierarchical clustering algorithm to search for Galactic substructures. We build a sample of fundamental-mode RR Lyrae (RRab) stars with positions, distances, proper motions, and photometric metallicity estimates from Gaia and VVV data. Using a clustering algorithm calibrated to optimize GC recovery, we identify groups of RRab stars with similar locations in the six-dimensional parameter space. The most promising groups are selected by comparison with the properties of known GCs. We recover many RRab groups associated with known Galactic GCs and derive the first RR Lyrae-based distances for BH 140 and NGC 5986. We also detect small groups of two to three RRab stars at distances up to ~25 kpc that are not associated with any known GC, but display GC-like distributions in all six parameters. Several of these groups, mostly pairs, lie toward the Galactic bulge but show distinct proper motions or distances, suggesting they may not belong to the bulge population. Overall, our approach identifies dozens of GC-like RRab groups in the Galactic plane and bulge, which are excellent targets for follow-up observations. Future radial velocity measurements can test whether the RRab members of these groups are truly co-moving.
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All authors N. Cristi-Cambiaso, C. Navarrete, M. Catelan, M. Zoccali, C. Quezada

High Energy Astrophysical Phenomena

A secondary orbiter under collisions with an accretion disk

Vladimir Karas

Dynamics of stellar orbits in dense stellar systems and nuclear star clusters (NSC) with an embedded supermassive black hole (SMBH) is governed a complex interplay of different forces. In particular, star–star gravitational collisions (relaxation), physical collisions between stars, and the hydrodynamical interaction with any surrounding gaseous environment, such as an accretion disk. These processes influence the stellar distribution, the feeding of the central black hole, and the generation of observable phenomena. Furthermore, the self-gravity of the accretion medium modulates the long-term evolution, adding significant complexity to the system's dynamics. By employing elementary arguments we outline the mentioned influences in their mutual competition.
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High Energy Astrophysical Phenomena

COBIPLANE: A Systematic Search for Compact Binary Millisecond Pulsars at Low Galactic Latitudes

Marco Turchetta, Manuel Linares, Karri Koljonen et al. (+2 more)

We present the main results obtained from the COmpact BInary Pulsar search in the low-LAtitude NEighborhood (COBIPLANE), an optical photometric survey designed to find new `spider' binary millisecond pulsars. We conducted observations targeting 30 unidentified sources from the 4FGL-DR3 Fermi Large Area Telescope (Fermi-LAT) catalog, selected for their pulsar-like $\gamma$-ray properties. Extending to Galactic latitudes as low as $\pm3^{\circ}$, this survey reaches closer to the Galactic plane than its predecessor survey, the COmpact BInary PULsar SEarch (COBIPULSE). We report the discovery of five optical variables coincident with the localizations of 4FGL J0821.5-1436, 4FGL J1517.9-5233, 4FGL J1639.3-5146, 4FGL J1748.8-3915, and 4FGL J2056.4+3142. These systems show optical flux modulation at the presumed orbital periods of $0.41576(6) \ \mathrm{d}$, $0.305(2) \ \mathrm{d}$, $0.204(7) \ \mathrm{d}$, $0.3(2) \ \mathrm{d}$, and $0.4395(1) \ \mathrm{d}$, respectively, and photometric temperatures of $4000$–$6000 \ \mathrm{K}$, consistent with the companion stars of `redback' subtype of spider pulsar binaries. Based on their optical light curve shapes and X-ray properties characteristic for spider systems – namely, a luminosity of $1.5 \times 10^{32} \ (D / 3.9 \ \mathrm{kpc})^2 \ \mathrm{erg} \ \mathrm{s}^{-1}$ ($0.3$–$10 \ \mathrm{keV}$) for 4FGL J1748.8-3915, and upper limits of $\sim10^{31}$–$10^{33} \ \mathrm{erg} \ \mathrm{s}^{-1}$ ($0.2$–$12 \ \mathrm{keV}$) for the others – we classify these sources as new spider candidate systems.
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All authors Marco Turchetta, Manuel Linares, Karri Koljonen, Paulo A. Miles-Páez, Jordan A. Simpson

Cosmology and Nongalactic Astrophysics

Clustering of cosmic string loops within a Milky-way like halo

Itamar Allali, Mudit Jain and Shi Yan

Loops of cosmic string experience a recoil from anisotropic gravitational radiation, known as the rocket effect, which influences the extent to which they are captured by galaxies during structure formation. Analytical studies have reached different conclusions regarding loop capture in galaxies: early treatments argued for efficient capture, while later analyses incorporating the loop rocket force throughout halo formation found that capture efficiency is reduced and strongly dependent on loop size. In this work, we employ the N-body simulation code GADGET-4, introducing non-backreacting tracer particles subject to a constant recoil force to model cosmic string loops with the rocket effect. We simulate the formation of a Milky-Way-like halo from redshift $z=127$ to $z=0$, considering loop populations characterized by a range of length parameters $\xi$, inversely proportional to the rocket acceleration. We find that the number of captured loops exhibits a pronounced peak at $\xi_{\textrm{peak}}\simeq 12.5$, arising from the competition between rocket-driven ejection at small $\xi$ and the declining intrinsic loop abundance at large $\xi$. For fiducial string tensions, this corresponds to $\mathcal{O}(10^6)$ loops within the halo. We further find that loops with weak rocket forces closely trace the dark-matter distribution, while those subject to stronger recoil but still captured – particularly the most abundant loops near $\xi_{\textrm{peak}}$ – are preferentially concentrated toward the central regions of the halo.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Strongly Coupled Sectors in Inflation: Gapped Theories of Unparticles

Yikun Jiang, Guilherme L. Pimentel and Chen Yang

We consider a novel scenario for a strongly coupled spectator sector during inflation, that of a higher dimensional conformal field theory with large anomalous dimensions – “unparticles” – and compactify the extra dimensions. More specifically, we take generalized free fields in five dimensions, where the extra dimension is compactified to a circle. Due to the usual Kaluza-Klein mechanism, the resulting excitations carry properties of both particles and unparticles, so we dub this scenario “gapped unparticles”. We derive a two-point function of the gapped unparticles by performing dimensional reduction. We then compute, in the collapsed limit, the four-point correlation function of conformally coupled scalars exchanging a gapped unparticle, which are used as seed functions to obtain the correlation function of primordial density perturbations. The phenomenology of the resulting correlators presents some novel features, such as oscillations with an envelope controlled by the anomalous dimension, rather than the usual value of 3/2. Depending on the value of the five-dimensional scaling dimension and effective mass of the gapped unparticles, we find a clear strategy to distinguish gapped unparticles from heavy massive scalars. If we assume the interactions are localized on a brane, gapped unparticles with different effective masses will share a universal coupling, and their exchanges produce an interesting interference pattern.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Dark Recipe for the First Giants: From Population III Stars to Early Supermassive Black Holes via Dark Matter Capture

Sulagna Bhattacharya, Debajit Bose, Basudeb Dasgupta et al. (+2 more)

The presence of supermassive black holes (SMBHs) at high redshifts ($z>5$), as revealed by James Webb Space Telescope (JWST), challenges standard black hole (BH) formation scenarios. We propose a mechanism in which non-annihilating dark matter (DM) with non-gravitational interactions with the Standard Model (SM) particles accumulates inside Population III (Pop III) stars, inducing their premature collapse into BH seeds having the same mass as the parent star. Owing to their early formation, these seeds can accrete for longer periods and grow into the SMBHs observed at early cosmic times. Focusing on spin-dependent (SD) DM-proton interactions, we identify regions of parameter space that account for the observed high-redshift SMBH population, their mass function, and the SMBH-stellar mass relation. Portions of this parameter space are testable by forthcoming direct detection experiments. The scenario may lead to distinctive gravitational wave (GW) signatures from SMBH mergers, accessible to Laser Interferometer Space Antenna (LISA) and pulsar timing array (PTA) observations.
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All authors Sulagna Bhattacharya, Debajit Bose, Basudeb Dasgupta, Jaya Doliya, Ranjan Laha

Instrumentation and Methods for Astrophysics

Galaxy Zoo Evo: 1 million human-annotated images of galaxies

Mike Walmsley, Steven Bamford, Hugh Dickinson et al. (+17 more)

We introduce Galaxy Zoo Evo, a labeled dataset for building and evaluating foundation models on images of galaxies. GZ Evo includes 104M crowdsourced labels for 823k images from four telescopes. Each image is labeled with a series of fine-grained questions and answers (e.g. "featured galaxy, two spiral arms, tightly wound, merging with another galaxy"). These detailed labels are useful for pretraining or finetuning. We also include four smaller sets of labels (167k galaxies in total) for downstream tasks of specific interest to astronomers, including finding strong lenses and describing galaxies from the new space telescope Euclid. We hope GZ Evo will serve as a real-world benchmark for computer vision topics such as domain adaption (from terrestrial to astronomical, or between telescopes) or learning under uncertainty from crowdsourced labels. We also hope it will support a new generation of foundation models for astronomy; such models will be critical to future astronomers seeking to better understand our universe.
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All authors Mike Walmsley, Steven Bamford, Hugh Dickinson, Tobias Géron, Alexander J. Gordon, Annette M.N. Ferguson, Lucy Fortson, Sandor Kruk, Natalie Lines, Chris J. Lintott, Karen L. Masters, Robert G. Mann, James Pearson, Hayley Roberts, Anna M.M. Scaife, Stefan Schuldt, Brooke Simmons, Rebecca Smethurst, Josh Speagle, Kyle Willett

High Energy Astrophysical Phenomena

Classification and Characteristics of Double-trigger Gamma-ray Bursts

Liang Li

Over the past two decades, the Swift and Fermi missions have identified a rare class of “double-trigger” gamma-ray bursts (GRBs) that produce two independent trigger events. These events are characterized by a sufficiently long quiescent period during which the on-board trigger system can reset, resulting in the subsequent emission being recorded as a second independent event. Consistent sky localization confirms that both trigger events originated from the same astrophysical source. Here, we present a systematic classification and characteristics study of three such cases: GRB 091024A, GRB 110709B, and GRB 220627A. We investigate each trigger episode emission independently using standard classification diagnostics, including duration ($T_{90}$), hardness ratio, minimum variability timescale (MVT), spectral lag ($\tau_{\rm lag}$), peak energy ($E_{\rm p}$), and energetics. We compare these properties with those of typical long GRBs (LGRBs) and with single-trigger LGRBs that exhibit extended quiescent periods. Our analysis reveals that all sub-bursts from the three double-trigger events consistently lie within the LGRB classification region. These results indicate that double-trigger GRBs are not a physically distinct subclass, but rather products of LGRB central engines that undergo extended dormancy and subsequent reactivation.
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Earth and Planetary Astrophysics

Precise Physical Parameters, Habitability, and Orbital Stability of Sun-like SB2 Systems: HD 130669, HD 184467, HD 191854, and HD 214222

Ahmad Abushattal, Nikolaos Georgakarakos, Mashhoor A. Al-Wardat et al. (+5 more)

This work analyzes four Sun-like double-lined spectroscopic binary (SB2) systems by combining visual and spectroscopic observational data with Al-Wardat's atmospheric modeling method to accurately determine their fundamental parameters. For each system, we determine stellar masses, orbital parallaxes, effective temperatures, spectral types, semimajor axes, and eccentricities with high precision, resolving discrepancies between astrometric and spectroscopic measurements. Moreover, we assess the potential for stable planetary orbits in these systems. We also calculate habitable zones around these binaries based on the orbital evolution of planetary orbits. These systems may represent promising targets for future extrasolar planet searches around Sun-like stars due to their robust physical and orbital parameters that can be used to determine planetary habitability and stability.
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All authors Ahmad Abushattal, Nikolaos Georgakarakos, Mashhoor A. Al-Wardat, Bilal Algnamat, Hassan B. Haboubi, Deshinta Arrova Dewi, Enas M. Abu-Alrob, Abdallah M. Hussein

Solar and Stellar Astrophysics

The 24 Aqr triple system: A closer look at its unique high-eccentricity hierarchical architecture

Ahmad Abushattal, Mashhoor A. Al-Wardat, Elliott P. Horch et al. (+4 more)

As its periastron passage occurred during the third quarter of 2020, system 24 Aqr is of particular significance. New visual solutions for the latest speckle interferometry observations collected by the Lowell Discovery Telescope (LTD) with its new QWSSI speckle camera are presented here. A variety of techniques were used to analyze the system, including ORBITX code for orbital solution, Al-Wardat's method for analyzing multiple stellar systems, and Edwards' method for analyzing visual and spectroscopic binaries. We derive precise masses and the complete set of its fundamental parameters for the three components, and we introduce a new orbital solution, and a new dynamical parallax, which is very close to the measured value given by Hipparcos 2007 and from that of Gaia DR2. In the next section, we discuss the possibility of a coplanar orbit. In conclusion, we demonstrate that we need a 65-m telescope to resolve the inner binary visually, although an array of telescopes could be used instead.
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All authors Ahmad Abushattal, Mashhoor A. Al-Wardat, Elliott P. Horch, Nikolaos Georgakarakos, Hatem A. Al-Ameryeen, Enas M. Abu-Alrob, Abdallah M. Hussein

High Energy Astrophysical Phenomena

Limits on dark matter existence in neutron stars from recent astrophysical observations and mass correlation analysis

Jing Fu Hu, Hang Lu and Bao Yuan Sun

Dark matter admixed neutron stars (DANSs) serve as a specific astrophysical laboratory for probing the features of dark matter (DM) and have emerged as a promising candidate for interpreting recent astrophysical observations (e.g., by NICER and LIGO/Virgo). Accurately constraining the internal DM content of DANSs is therefore of critical importance. In this work, we construct the equations of state (EoS) for DANS matter by employing twelve nuclear matter (NM) models within the covariant density functional (CDF) theory and a self-interacting fermionic model for DM. Using these EoSs as input, we solve the two-fluid Tolman-Oppenheimer-Volkov (TOV) equations to systematically investigate the influence of DM on the global properties of neutron stars (NSs). By incorporating recent observational constraints on NS properties, the maximum DM mass fraction $f_\chi^{\mathrm{max}}$ in DANSs is determined for each NM EoS model. Our analysis reveals a strong linear correlation (Pearson coefficient $r=0.98$) between $f_\chi^{\mathrm{max}}$ and the maximum mass of a pure NS, $M_{\rm{NS}}^{\mathrm{max}}$, described by $f_{\chi}^{\mathrm{max}} = 0.22 M_{\mathrm{NS}}^{\mathrm{max}} - 0.44$. Leveraging this correlation and the observed NS maximum mass distribution, $P(M_{\text{NS}}^{\max} \mid \text{EM})$, we derive the probability distribution function (PDF) for the maximum DM mass, $P(M_{\chi}^{\max} \mid \text{EM})$, in DANSs. We find that at the 68% confidence level, $M_{\chi}^{\mathrm{max}}=0.150^{+0.070}_{-0.051}\ M_{\odot}$. This quantitative constraint on the DM mass provides a critical prior for interpreting potential observational signatures of DANSs, such as anomalous tidal deformabilities and distinctive gravitational-wave signals.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc

The new generation lunar gravitational wave detectors: sky map resolution and joint analysis

Xiaolin Zhang, Chengye Yu, Haoran Li et al. (+3 more)

Lunar-based gravitational-wave interferometry is a fascinating endeavor, and was proposed as a promising approach to bridge the observational gap between space-borne and ground-based detectors. In this work, we adopt the Fisher-matrix method to examine the angular-resolution performance of the newly proposed Crater Interferometry Gravitational-wave Observatory (CIGO) on the lunar crater rim near the north pole, together with TianQin and LISA, for monochromatic sources in the 0.1-10 Hz band. We find that above 0.1 Hz, CIGO achieves better localization accuracy than the other two space-based missions and dominates the combined detector network's performance, provided that lunar noise mitigation is achieved in the 0.1-2.87 Hz frequency range. We further explore an upgraded Tetrahedron configuration, TCIGO, with a fourth station at the bottom of a crater, which forms a regular tetrahedral constellation on the lunar surface. The result shows that TCIGO yields a five-fold improvement in angular-resolution capability over CIGO and gets better sky coverage across the target frequency band.
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All authors Xiaolin Zhang, Chengye Yu, Haoran Li, Sobhan Kazempour, Mingqiu Li, Sichun Sun

Instrumentation and Methods for Astrophysics · Cross-listed from hep-ph

Defect Formation in NaI Crystals: A Novel Pathway to Dark Matter Detection

G. Angloher, M. R. Bharadwaj, A. Böhmer et al. (+43 more)

Sodium iodide (NaI) is a widely used scintillator in direct dark matter searches. In particular, NaI-based cryogenic scintillating calorimeters have emerged as promising candidates, like in the COSINUS experiment, for testing the annually modulating signal reported by DAMA/LIBRA. In this study, we investigate defect formation within NaI crystals and its impact on the dark matter detection signal. Using molecular dynamics simulations and density functional theory techniques, we simulate a DM particle collision on an NaI crystal, focusing on the possible defects formation and their structural and electronic properties. Our analysis includes a detailed study of the electronic states associated with the interstitial atoms and vacancies, the energetic cost of defect formation, and the anisotropic threshold displacement energy. Finally, we highlight the potential to exploit dark matter-induced defects as a novel detection channel, enabled by the introduction of new states within the electronic band gap.
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All authors G. Angloher, M. R. Bharadwaj, A. Böhmer, M. Cababie, I. Colantoni, I. Dafinei, N. Di Marco, C. Dittmar, F. Ferella, F. Ferroni, S. Fichtinger, A. Filipponi, T. Frank, M. Friedl, D. Fuchs, L. Gai, M. Gapp, M. Heikinheimo, M. N. Hughes, K. Huitu, M. Kellermann, R. Maji, M. Mancuso, L. Pagnanini, F. Petricca, S. Pirro, F. Pröbst, G. Profeta, A. Puiu, F. Reindl, K. Schäffner, J. Schieck, P. Schreiner, C. Schwertner, P. Settembri, K. Shera, M. Stahlberg, A. Stendahl, M. Stukel, C. Tresca, S. Yue, V. Zema, Y. Zhu, N. Zimmermann M. Di Giambattista, F. Giannessi, R. Rollo

Earth and Planetary Astrophysics

Not Just Gas: How Solid-Driven Torques Shaped the Migration of the Galilean Moons

Lucas Gonzalez-Rivas, Leonardo Krapp, Ximena Ramos et al. (+1 more)

Surviving rapid inward orbital migration is a crucial aspect of formation models for the Jupiter's Galilean moons. The primary aim of this study is to investigate the orbital migration of the Galilean moons by incorporating self-consistent solid dynamics in circumjovian disk models. We perform two-fluid simulations using the FARGO3D code on a 2D polar grid. The simulations model a satellite with the mass of a proto-moon, Europa, or Ganymede interacting with a circumjovian disk. The dust component, coupled to the gas via a drag force, is characterized by the dust-to-gas mass ratio ($\epsilon$) and the Stokes number ($T_s$). The effect of solids fundamentally alter the satellites' evolution. We identify a vast parameter space where migration is slowed, halted, robustly reversed -leading to outward migration-, or significantly accelerated inward. The migration rate is dependent on satellite mass, providing a natural source of differential migration. Solid dynamics provides a robust and self-consistent mechanism that fundamentally alters the migration of the Galilean moons, potentially addressing the long-standing migration catastrophe. This mechanism critically affects the survival of satellites and could offer a viable physical process to explain the establishment of resonances through differential migration. These findings establish that solid torques are a critical, non-negligible factor in shaping the final architecture of satellite systems.
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All authors Lucas Gonzalez-Rivas, Leonardo Krapp, Ximena Ramos, Pablo Benitez-Llambay

Instrumentation and Methods for Astrophysics

Sidelobe Modification for an Offset Gregorian Reflector System using a Reconfigurable Intelligent Surface-Equipped Subreflector

S.W. Ellingson and A.J. Yip

In past work, we described the use of a reconfigurable intelligent surface (RIS) mounted on the rim of an axisymmetric prime focus-fed reflector to create nulls in the close-in sidelobes. In this paper, we show that similar performance is possible in an offset Gregorian reflector system using a RIS on the rim of the subreflector. Applications include radio astronomy, where offset Gregorian reflectors are common and observations are subject to deleterious levels of interference from satellites entering through sidelobes. We show that an efficient RIS replacing the outer one-third of the subreflector surface, employing passive elements with 1-bit phase-only control, can create a null in the peak of the second sidelobe in the quiescent pattern. This is achieved using a simple unconstrained optimization algorithm to set the states of the RIS elements. The algorithm yields a deep null with just 0.2~dB reduction in main lobe directivity, despite lacking any constraints on main lobe pattern. Compared to our previous approach of mounting the RIS on the rim of the main reflector, the subreflector-based approach demonstrated in this paper requires a much smaller RIS and can implemented in existing systems by replacing the subreflector.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Frozen Neutron Stars in Four-Dimensional Non-polynomial Gravities

Chen Tan and Yong-Qiang Wang

This paper investigates the structure and properties of neutron stars in four-dimensional non-polynomial gravities. Solving the modified Tolman-Oppenheimer-Volkoff equations for three different equations of state (BSk19, SLy4, AP4), we confirm that neutron star solutions remain in existence. As the modification parameter $\alpha$ increases, neutron stars grow in both radius and mass. We find that, when the parameter $\alpha$ is sufficiently large, a frozen state emerges at the end of the neutron-star sequence. In this state, the metric functions approach zero extremely close to the stellar surface, forming a critical horizon, making it nearly indistinguishable from a black hole to an external observer. Such a frozen neutron star constitutes a universal endpoint of the neutron-star sequence in this theory, independent of the choice of the equation of state. Based on our results and current observational constraints, we derive bounds on the modification parameter $\alpha$ and show that frozen neutron stars remain allowed in the bounds.
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