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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 9 December

High Energy Astrophysical Phenomena

A search for successful and choked jets in nearby broad-lined Type Ic supernovae

Tanner O'Dwyer, Alessandra Corsi, Sheng Yang et al. (+16 more)

The observational link between long gamma-ray bursts (GRBs) and broad-lined stripped-envelope core-collapse supernovae (SNe Ic-BL) is well established. Significant progress has been made in constraining what fraction of SNe Ic-BL may power high- or low-luminosity GRBs when viewed at small off-axis angles. However, the GRB-SN connection still lacks a complete understanding in the broader context of massive-star evolution and explosion physics. Models predict a continuum of outcomes for the fastest ejecta, from choked to ultra-relativistic jets, and observations from radio to X-rays are key to probing these scenarios across a range of viewing angles and velocities. Here, we present results from a coordinated radio-to-X-ray campaign targeting nearby (z<=0.1) SNe Ic-BL designed to explore this diversity. With eight new radio-monitored events and updated data for one previously observed SN, we further tighten constraints on the fraction of SNe Ic-BL as relativistic as SN 1998bw/GRB 980425. We identify SN 2024rjw as a new radio-loud event likely powered by strong interaction with circumstellar material (CSM), and add evidence supporting a similar interpretation for SN 2020jqm. We also establish new limits on the properties of radio-emitting ejecta with velocities consistent with cocoons from choked jets, highlighting SN 2022xxf as a promising cocoon-dominated candidate. These results refine our understanding of the continuum linking ordinary SNe Ic-BL, engine-driven explosions, and GRBs, and contribute to building a sample that will inform future multi-messenger searches for electromagnetic counterparts to high-energy neutrinos.
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All authors Tanner O'Dwyer, Alessandra Corsi, Sheng Yang, Shreya Anand, S. Bradley Cenko, Gokul P. Srinivasaragavan, Anna Y.Q.Ho, Jesper Sollerman, Bei Zhou, Arvind Balasubramanian, Po-Wen Chang, Marc Kamionkowski, Daniel Perley, Russ R. Laher, Kohta Murase, Frank J. Masci, Mansi M. Kasliwal, Josiah N. Purdum, Matthew J. Graham

Solar and Stellar Astrophysics

Exploring the binary origin of B and Be rapid rotators

Jonathan Labadie-Bartz, Mark Suffak, Carol Jones et al. (+8 more)

Observational evidence has continued to mount that a significant fraction of rapidly rotating early-B type stars are products of binary mass transfer. However, very few mid- and late-type B stars with rapid rotation have been demonstrated to be post-interaction products, despite a growing sample of SB1 binaries among stars within this range of spectral types. By considering the currently available information over the entire range of rapidly rotating B-type binaries, we argue that a significant fraction of the mid- and late-type rapid rotators found in binaries are also likely the result of past mass transfer episodes. The observed properties of this sample are compared to the predictions from the Binary Population and Spectral Synthesis code (BPASS), with attention given to the expected evolutionary pathways of stripped stars and the stellar and binary properties of both components of post-interaction systems across a range of initial conditions. Prospects for directly detecting and characterizing the stripped cores of the previous mass donors in such systems are described, and the implications for the role of binary interaction in causing rapid rotation are discussed. An accurate description of prevalence of binary interaction, the physics of mass transfer, and the post-interaction configuration of systems over a range of initial conditions has far-reaching implications including double-degenerate binaries and their eventual mergers, the output of ionizing UV flux of stellar populations, and the supernova explosions that can arise from stripped or rapidly-rotating progenitors.
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All authors Jonathan Labadie-Bartz, Mark Suffak, Carol Jones, Yaël Nazé, Ken Gayley, Geraldine Peters, Rina Rast, Anusha Ravikumar, Asif ud-Doula, Coralie Neiner, Jeremy J. Drake

Cosmology and Nongalactic Astrophysics

Probing the environment around GW170817 with DESI: insights on galaxy group peculiar velocities for standard siren measurements

A. J. Amsellem, A. Palmese, K. Douglass et al. (+56 more)

We present a new measurement of the Hubble constant, $H_0$, following the gravitational wave event GW170817 and Dark Energy Spectroscopic Instrument (DESI) observations. A standard siren measurement with a nearby (luminosity distance $\sim 40 $ Mpc) event such as GW170817 is typically sensitive to the peculiar motion of the host galaxy due to local dynamics. Previous measurements from this event have taken advantage of peculiar velocity measurements of nearby galaxies, including a handful of objects in the galaxy group that the host of the event, NGC 4993, has been associated with. Still, the group's properties and NGC 4993's membership were debated. We present DESI observations of thousands of galaxies in the vicinity of NGC 4993, resulting in 39 group galaxies and a five-fold increase in galaxies compared to previous observations with many of these galaxies contributing to a peculiar velocity measurement. Examining the local dynamics, our observations support the presence of a galaxy group of which NGC 4993 is part with a halo mass of order $\sim$$10^{13}~M_\odot$. Using peculiar velocity measurements from our Fundamental Plane galaxies observations, we find $H_0 =70.9^{+6.4}_{-8.5}$ km s$^{-1}$ Mpc$^{-1}$. In addition, using a peculiar velocity measurement for NGC 4993 from Surface Brightness Fluctuations in Cosmicflows-4 we find $H_0 =73.4^{+3.3}_{-3.9}$ km s$^{-1}$ Mpc$^{-1}$. We study the impact of different galaxy selection criteria on the determination of the peculiar velocity and, in turn, on the $H_0$ measurement. Our results highlight the importance of multiplexed spectroscopic observations of the environments of gravitational wave events to probe local dynamics, which can ultimately affect standard siren measurements.
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All authors A. J. Amsellem, A. Palmese, K. Douglass, C. Howlett, Juliana S. M. Karp, I. Magaña Hernandez, J. Moustakas, R. H. Wechsler, J. Aguilar, S. Ahlen, S. Benzvi, D. Bianchi, D. Brooks, A. Carr, T. Claybaugh, A. Cuceu, Tamara M. Davis, A. de la Macorra, Arjun Dey, Biprateep Dey, P. Doel, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, K. Honscheid, M. Ishak, R. Joyce, R. Kehoe, T. Kisner, A. Kremin, O. Lahav, A. Lambert, M. Landriau, L. Le Guillou, M. Manera, V. Manwadkar, A. Meisner, R. Miquel, A. D. Myers, S. Nadathur, G. Niz, N. Palanque-Delabrouille, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, A. Raichoor, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, H. Seo, J. Silber, D. Sprayberry, G. Tarlé, R. Zhou, the DESI Collaboration

Astrophysics of Galaxies

FIRESTORM I: Stellar Feedback and Gas Kinematics in the Evolved W40 Hub-Filament System

Ming-Kang Lim, Ram K. Yadav, L. K. Dewangan et al. (+12 more)

The FIRESTORM project–Feedback-Induced Regions and Emission from Star-forming Tracers of ObseRvable Molecular Gas–has targeted four star-forming regions to quantify the impact of stellar feedback on star formation. In this paper, we present multiwavelength results for one of the targets, the nearby high-mass star-forming region W40. Using dense-gas tracers C$^{18}$O(1–0) and H$^{13}$CO$^+$(1–0), we identified six velocity-coherent filaments: five at \vlsr $\sim$\,7.5\kms\! and one at \vlsr $\sim$\,5\kms. Four of these converge towards an infrared-bright cluster hosting the most massive star of the region (IRS 1A South, O9.5V), forming a hub-filament system (HFS). Key physical parameters, including filament lengths, widths, masses, velocity dispersions, and line masses, are derived. Five dense clumps traced by N$_2$H$^+$(1–0) exhibit subsonic to transonic turbulence, contrasting with the supersonic motions of their parental filaments, indicating turbulence dissipation. A deficit of emission at \vlsr $\sim$\,7\kms\! in several molecular lines, along with a blueshifted absorption dip in the HCN(1–0) profile, suggests that emission from OB-heated gas is being absorbed by a cold foreground cloud. A bridge-like feature in position-velocity space connects the \vlsr $\sim$\,5 and $\sim$\,7.5\kms\! filaments, and spatially coinciding with dense condensations and radio continuum peaks. These findings suggest that a past interaction–likely a cloud-cloud collision–triggered the formation of HFS and ultimately the central massive cluster.
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All authors Ming-Kang Lim, Ram K. Yadav, L. K. Dewangan, Kee-Tae Kim, A. Zavagno, Jedsada Maklai, Nicola Schneider, D. Arzoumanian, Arshia M. Jacob, L. E. Pirogov, Jihye Hwang, D. K. Ojha, Gyuho Lee, Affan Adly Nazri, Saurabh Sharma

Astrophysics of Galaxies

Euclid Quick Data Release (Q1): Euclid spectroscopy of quasars. 1. Identification and redshift determination of 3500 bright quasars

Euclid Collaboration: Y. Fu, R. Bouwens, K. I. Caputi et al. (+353 more)

The slitless spectroscopy mode of the NISP onboard Euclid has enabled efficient spectroscopy of objects within a large FoV. We present a large and homogeneous sample of bright quasars identified from the Euclid Quick Data Release (Q1) by combining high-purity candidate selections from Gaia and WISE with the NISP spectra. Through visual inspection of the Euclid spectra of these quasar candidates, we identify approximately 3500 quasars with reliable redshifts at $0<z\lesssim 4.8$. Of these, 2686 are new spectroscopic identifications relative to existing public compilations. We generate the first Euclid composite spectrum of quasars covering rest-frame NUV to NIR wavelengths without telluric lines, which will be pivotal to NIR quasar spectral analysis. We obtain an empirical spectroscopic depth of $J_{\rm E}\lesssim 21.5$ and $H_{\rm E}\lesssim 21.3$ at the sensitivity of the Wide Field Survey, beyond which the number of securely identified quasars declines sharply. We analyse VIS morphologies using Sersic and CAS metrics, and a deep-learning PSF fraction to track nuclear dominance. At low redshift ($z<0.5$), obvious host structures are common and a single Sersic model fits about half of the sources; at intermediate redshift ($0.5<z<2$), the nuclear component dominates, with 90% of the Sersic fits saturating at the upper index limit. In this intermediate redshift regime, $f_{\rm PSF}$ is available, and we use it as a more reliable compactness measure than the single-Sersic and CAS parameters to quantify nuclear versus host emission. We also explore the novel Euclid NIR colour space and discuss the role of these quasars in refining AGN selection techniques for future Euclid data releases. The spectroscopic bright quasar catalogue of this work, and the composite quasar spectrum, will be available at https://cdsarc.cds.unistra.fr/. (abridged)
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All authors Euclid Collaboration: Y. Fu, R. Bouwens, K. I. Caputi, D. Vergani, M. Scialpi, B. Margalef-Bentabol, L. Wang, M. Bolzonella, M. Banerji, E. Bañados, A. Feltre, Y. Toba, J. Calhau, F. Tarsitano, P. A. C. Cunha, A. Humphrey, G. Vietri, F. Mannucci, S. Bisogni, F. Ricci, H. Landt, L. Spinoglio, T. Matamoro Zatarain, D. Stern, M. J. Page, D. M. Alexander, G. Zamorani, W. Roster, M. Salvato, Y. Copin, J. G. Sorce, D. Scott, Y.-H. Zhang, E. Lusso, J. Wolf, D. Yang, H. J. A. Rottgering, B. Laloux, M. Siudek, S. Belladitta, Q. Liu, V. Allevato, K. Kuijken, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, J. Brinchmann, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, A. Costille, F. Courbin, H. M. Courtois, M. Cropper, A. Da Silva, H. Degaudenzi, G. De Lucia, C. Dolding, H. Dole, F. Dubath, C. A. J. Duncan, X. Dupac, S. Dusini, S. Escoffier, M. Fabricius, M. Farina, R. Farinelli, S. Ferriol, F. Finelli, P. Fosalba, N. Fourmanoit, M. Frailis, E. Franceschi, P. Franzetti, M. Fumana, S. Galeotta, K. George, W. Gillard, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, E. Keihänen, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, R. Laureijs, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, S. Marcin, O. Marggraf, K. Markovic, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, R. Nakajima, C. Neissner, R. C. Nichol, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, R. Rebolo, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, E. Rossetti, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, T. Schrabback, M. Scodeggio, A. Secroun, E. Sefusatti, G. Seidel, S. Serrano, P. Simon, C. Sirignano, G. Sirri, L. Stanco, J.-L. Starck, J. Steinwagner, C. Surace, P. Tallada-Crespí, D. Tavagnacco, A. N. Taylor, H. I. Teplitz, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, A. Veropalumbo, D. Vibert, Y. Wang, J. Weller, A. Zacchei, E. Zucca, M. Ballardini, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, D. Di Ferdinando, J. A. Escartin Vigo, L. Gabarra, W. G. Hartley, M. Huertas-Company, J. Martín-Fleitas, S. Matthew, N. Mauri, R. B. Metcalf, A. A. Nucita, A. Pezzotta, M. Pöntinen, C. Porciani, I. Risso, V. Scottez, M. Sereno, M. Tenti, M. Viel, M. Wiesmann, Y. Akrami, S. Alvi, I. T. Andika, S. Anselmi, M. Archidiacono, F. Atrio-Barandela, E. Aubourg, D. Bertacca, M. Bethermin, L. Bisigello, A. Blanchard, L. Blot, M. Bonici, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, B. Camacho Quevedo, F. Caro, C. S. Carvalho, T. Castro, F. Cogato, S. Conseil, A. R. Cooray, O. Cucciati, G. Daste, F. De Paolis, G. Desprez, A. Díaz-Sánchez, J. J. Diaz, S. Di Domizio, J. M. Diego, P. Dimauro, P.-A. Duc, M. Y. Elkhashab, A. Enia, Y. Fang, A. G. Ferrari, A. Finoguenov, F. Fontanot, A. Franco, K. Ganga, J. García-Bellido, T. Gasparetto, V. Gautard, E. Gaztanaga, F. Giacomini, F. Gianotti, G. Gozaliasl, M. Gray, M. Guidi, C. M. Gutierrez, A. Hall, C. Hernández-Monteagudo, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, S. Kruk, V. Le Brun, J. Le Graet, L. Legrand, M. Lembo, F. Lepori, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, A. Loureiro, J. Macias-Perez, M. Magliocchetti, C. Mancini, R. Maoli, C. J. A. P. Martins, L. Maurin, M. Miluzio, P. Monaco, C. Moretti, G. Morgante, S. Nadathur, K. Naidoo, P. Natoli, A. Navarro-Alsina, S. Nesseris, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, A. Pisani, D. Potter, S. Quai, M. Radovich, P.-F. Rocci, G. Rodighiero, S. Sacquegna, M. Sahlén, D. B. Sanders, E. Sarpa, C. Scarlata, A. Schneider, D. Sciotti, E. Sellentin, F. Shankar, L. C. Smith, E. Soubrie, K. Tanidis, C. Tao, G. Testera, R. Teyssier, S. Tosi, A. Troja, M. Tucci, C. Valieri, A. Venhola, G. Verza, P. Vielzeuf, A. Viitanen, N. A. Walton, J. R. Weaver

Astrophysics of Galaxies

Predicting Infall Time of Milky-Way Satellites via Machine Learning

Seungyeon Kim, Myoungwon Jeon and Seongjun Hyung

The properties of dwarf galaxies provide essential insight into galaxy formation and evolution in a hierarchical universe. Among various physical quantities, identifying their infall times to host galaxies is crucial, as these times encode key information such as star formation histories. However, estimating infall times remains challenging due to the complex interplay between different physical processes and the lack of consensus among existing methods. We propose a fast and interpretable method to predict the infall time of dwarf satellites using LightGBM, a gradient-boosting decision tree algorithm. Our model is trained on satellites from 30 Milky Way (MW)-like host galaxies generated by A-SLOTH, a semi-analytic model calibrated using observational constraints, including those from the MW and its satellites. To balance predictive ability and observational applicability, we adopt $\tau_{90}$, [Fe/H], and $M_{\star}$ as input features. Since satellites with prior group membership hinder accurate MW infall predictions, we exclude them from the training data. As a result, the model achieves the best average mean squared error (MSE) of 5.04 in the A-SLOTH data set. Our model also shows good agreement with existing observational studies of MW satellites, although some discrepancies remain due to a few outliers such as CVn II and UMa I. In addition, for satellites experiencing prior infall events before MW-like host infall, the model predicts the timing of the first infall with a significantly lower MSE of 1.66, indicating the importance of the earliest infall in the quenching process of satellite galaxies.
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High Energy Astrophysical Phenomena

The Radius of PSR J0437-4715 from NICER Data

M. C. Miller, A. J. Dittmann, I. M. Holt et al. (+12 more)

Neutron star Interior Composition Explorer (NICER) data have been used to estimate the masses and radii of the rotation-powered millisecond pulsars PSR J0030$+$0451, PSR J0740$+$6620, PSR J0437$-$4715, PSR J1231$-$1411, and PSR J0614$-$3329, sometimes in joint analyses with X-ray Multi-Mirror (XMM-Newton) data. These measurements provide invaluable information about the properties of cold, catalyzed matter beyond nuclear saturation density. Here we present the results of our modeling of NICER data on PSR J0437$-$4715 using several different models of hot thermal X-ray emitting spots on the stellar surface. For this pulsar, previous Nuclear Spectroscopic Telescope Array (NuSTAR) observations established that there is also a modulated nonthermal component to the emission, but the previously published analysis of NICER data did not model this component. We find that the Bayesian evidence is significantly higher when the modulated nonthermal component is included, and that omission of this component leads to poor fits to the bolometric NICER data and thus risks bias in the resulting radius estimates. Our models, which we pursue to inferential convergence, therefore have modulated nonthermal emission, and our headline model has in addition three uniform-temperature thermally-emitting circular spots. Using this model, the symmetric 68% credible range in the radius is 11.8 km to 15.1 km, which at the independently-measured mass of $M=1.418\pm 0.044~M_\odot$ is consistent with previous reports of the radius of the $\sim 1.4~M_\odot$ pulsar PSR J0030$+$0451. We discuss the implications of this measurement for the equation of state of dense matter.
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All authors M. C. Miller, A. J. Dittmann, I. M. Holt, F. K. Lamb, C. Chirenti, Z. Arzoumanian, J. Berteaud, S. Bogdanov, K. C. Gendreau, W. C. G. Ho, S. M. Morsink, P. S. Ray, R. A. Remillard, Z. Wadiasingh, M. T. Wolff

High Energy Astrophysical Phenomena

Neutrino pair bremsstrahlung due to electromagnetic collisions in neutron star cores revisited

P.S. Shternin

We reconsider the problem of neutrino pair bremsstrahlung emission originating from the electromagnetic collisions of charged particles in nucleonic ($npe\mu$) neutron star cores. Two limiting cases are considered: (i) protons are in the normal state and (ii) protons are in the superconducting state. In both cases, the dominant contribution to the bremsstrahlung emissivity $Q^{\mathrm{em}}_{\mathrm{Br}}$ comes from the transverse part of in-medium electromagnetic interactions. For non-superconducting matter, we obtain an unusual $Q^{\mathrm{em}}_{\mathrm{Br}}\propto T^{23/3}$ temperature dependence due to the dynamical character of plasma screening in the transverse channel, but considerably smaller values of $Q^{\mathrm{em}}_{\mathrm{Br}}$ than in previous studies, rendering the considered process unimportant in practice. In contrast, for superconducting and superfluid matter, the neutrino emission processes involving nucleons are suppressed and $Q^{\mathrm{em}}_{\mathrm{Br}}$ due to lepton collisions provides the residual contribution to the neutrino emissivity of neutron star core matter. In the superconducting case, the plasma screening becomes static and the standard $Q^{\mathrm{em}}_{\mathrm{Br}}\propto T^{8}$ temperature scaling is restored. Simple analytical expressions for $Q^{\mathrm{em}}_{\mathrm{Br}}$ in both limiting cases are provided.
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High Energy Astrophysical Phenomena

Backwards Gamma-Ray Bursts: Searching for Exploding Primordial Black Holes in Short-Duration GRB Catalogs

Stefano Profumo and Kally Wen

We present a systematic search for signatures of terminal black-hole evaporation in short gamma-ray burst (sGRB) catalogs. An exploding primordial black hole (PBH) undergoing final-stage Hawking radiation is predicted to produce a distinctive "backwards burst"-a very short, spectrally hard transient with monotonically increasing flux and little or no longer-wavelength afterglow. We develop a forward-modeling framework that directly compares theoretical PBH evaporation light curves, computed with full Standard Model particle content and detector response folding, against empirical GRB pulse templates. Analyzing 39 well-characterized Swift sGRBs with non-detected or extremely faint afterglows, we find that all events exhibit fast-rise, slow-decay temporal profiles inconsistent with the PBH prediction. Model comparison via Akaike and Bayesian information criteria decisively favors conventional FRED or ERCA fits over the PBH template for every burst. No candidates for terminal PBH evaporation are identified. The null result yields an upper bound on the local PBH explosion rate density $R_{\mathrm{PBH}} \lesssim 10^5~\mathrm{pc}^{-3}~\mathrm{yr}^{-1}$, comparable to constraints from dedicated TeV $\gamma$-ray searches. Our methodology establishes a robust template-matching approach that can be scaled to larger multi-instrument catalogs, providing a foundation for future searches targeting this unique signature of quantum gravity and early-Universe physics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Single-field D-type inflation in the minimal supergravity in light of Planck-ACT-SPT data

Yermek Aldabergenov and Sergei V. Ketov

The minimal supergravity framework is applied to a construction of new D-type single-field models of inflation in agreement with precision measurements of the cosmic microwave background radiation by Planck Collaboration, BICEP/Keck Collaboration, Atacama Cosmology Telescope and South Pole Telescope. The inflaton potential, the power spectrum of scalar perturbations, the cosmological observables and the reconstruction procedure can be very simple when using the e-folds as the running variable.
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Cosmology and Nongalactic Astrophysics

Neutrino mass constraints in the context of 4-parameter dark energy equation of state and DESI DR2 observations

Gowri S Nair, Amlan Chakraborty, Luca Amendola et al. (+1 more)

Cosmological constraints on the total neutrino mass, $\sum m_\nu$, are strongly shaped by assumptions about the dark-energy equation of state due to the well-known degeneracy between massive neutrinos and late-time cosmic acceleration. In this work, we move beyond the two-parameter Chevallier-Polarski-Linder (CPL) form adopted in recent DESI analyses and re-examine neutrino mass constraints using a flexible four-parameter dark energy equation of state (4pDE). We implement the 4pDE model in a modified version of CLASS and perform a full MCMC analysis using Planck, DESI DR2 BAO, and Pantheon+ data. Relative to our previous 4pDE study based on pre-DESI BAO datasets, the inclusion of DESI DR2 substantially tightens the constraints on the transition parameters while still yielding a relaxed neutrino-mass bound compared to $\Lambda$CDM, $\sum m_\nu < 0.101$ eV ($95\%$ C.L.). This upper limit is more stringent than the DESI DR2 constraint obtained within the $w_0w_a$CDM framework. From the best-fit parameters, we reconstruct the evolution of the 4pDE equation of state along with both $68\%$ and $95\%$C.L. We do not find a statistically significant phantom-crossing at $z \sim 0.5$, consistent with the conclusion from the DESI collaboration; at higher redshifts, the reconstructed $w(z)$ follows the CPL evolution and deviates only at low redshift. Additionally we also find reduction in $\Delta \chi^2_{\rm min}=-7.3$ compared to $\Lambda$CDM model.
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All authors Gowri S Nair, Amlan Chakraborty, Luca Amendola, Subinoy Das

High Energy Astrophysical Phenomena

Optical polarimetry of the accreting black hole X-ray binary Swift J1727.8$-$1613 over the state transition and radio ejections

Anagha P. Nitindala, Alexandra Veledina, Vadim Kravtsov et al. (+7 more)

We present the first optical ($BVR$) polarimetric observations of Swift J1727.8$-$1613 during its 2023–2024 outburst. Observations were performed during the X-ray hard-to-soft state transition, the soft state and the decaying hard state of the source. For the vast majority of nights, we detect statistically significant polarization of ${\approx}1$%, a fraction of which is of interstellar origin. We find a significant change of polarization coinciding in time with discrete radio ejections. The direction of this polarization variation differs from the directions inferred from the X-ray, sub-mm and radio polarization angles, as well as from the resolved jet orientation. After correcting for the interstellar component, we find that the intrinsic polarization degree remained approximately constant at PD $\approx 0.3$% throughout the hard-intermediate state. We explore several possible origins for the polarization and conclude that it is most plausibly produced by scattering within the optically thin accretion disk wind. The intrinsic polarization angle, PA $\approx-15\deg$, is notably offset from the jet axis, which we interpret as evidence for a misalignment between the black hole spin and the orbital axis.
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All authors Anagha P. Nitindala, Alexandra Veledina, Vadim Kravtsov, Andrei V. Berdyugin, María Alejandra Díaz Teodori, Vilppu Piirola, Takeshi Sakanoi, Masato Kagitani, Svetlana V. Berdyugina, Juri Poutanen

Instrumentation and Methods for Astrophysics

Thermal design of focal plane assembly of wavefront camera for exoplanet imaging corona module

Chengcheng Wen, Shu Jiang, Mingming Xu et al. (+2 more)

The focal plane assembly of wavefront camera is the key imaging device of wavefront detection camera and the key load of the exoplanet imaging coronagraph module. In order to ensure the imaging quality and reduce the dark current and thermal noise, it is necessary to effectively dissipate the heat of the focal plane CCD and other high-power electronic devices to ensure the working performance and reliability of the focal plane assembly. Based on the limited space and cooling resources, this paper adopts the flexible graphene heat conducting cable and grooved heat pipes, and carries out detailed thermal design and thermal analysis of its cooling path. The finite element model is established by thermal analysis software and thermal simulation is carried out. in that steady state, the work temperature range of the CCD chip is -12.8 to -10.9 celsius, which meets the temperature control index, and the work temperatures of other components are also within the design requirements, which indicate that the thermal design scheme is reasonable and feasible, and meets the task requirements.
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All authors Chengcheng Wen, Shu Jiang, Mingming Xu, Lingyi Kong, Jinning He

Cosmology and Nongalactic Astrophysics

The frame-dragging vector potential on galaxy scales from Dark-Matter-only Newtonian $N$-body simulations

William Beordo, Marco Bruni, Cristian Barrera-Hinojosa et al. (+1 more)

Effects of General Relativity are usually neglected in the non-linear evolution of structures, where Newtonian $N$-body simulations are traditionally employed. In the post-Friedmann expansion framework, a weak-field relativistic approximation purpose-built for cosmology, a frame-dragging gravito-magnetic vector potential arises at leading order, sourced by momentum currents. At this order, the vector potential contributes to the metric while leaving the dynamics of the matter fields unaffected, as it does not appear in the Euler equation. It can therefore be extracted a posteriori from standard N-body simulations, where the dynamics is purely Newtonian. Using the Delaunay Tessellation Field Estimator code on the IllustrisTNG simulations, here we extend previous work in order to compute the power spectrum of this vector potential down to galactic scales. The magnitude of the vector potential is two orders of magnitude larger than predicted by perturbation theory, and is a $1\% \sim 0.1\%$ effect compared to the non-linear Newtonian scalar gravitational potential. In the redshift range considered here, the gravito-magnetic effect remains subdominant, without showing any enhancement during a particular phase in the evolution of structures, aside from the continuous growth of non-linearity at low redshift. Although this seems to suggest that, within the $\Lambda$CDM model, no significant gravito-magnetic effects contribute to the non-linear evolution of cosmic structures, i.e. to the dynamics of massive particles, possible observational consequences, e.g. in lensing, deserve further exploration.
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All authors William Beordo, Marco Bruni, Cristian Barrera-Hinojosa, Mariateresa Crosta

High Energy Astrophysical Phenomena

A magnetar outburst with atypical evolution: the case of Swift J1555.2-5402

A. Borghese, F. Coti Zelati, M. Imbrogno et al. (+12 more)

The magnetar Swift J1555.2-5402 was discovered in outburst on 2021 June 3 by the Burst Alert Telescope on board the Swift satellite. Early X-ray follow-up revealed a spin period P~3.86 s, a period derivative Pdot~3e-11 s/s, dozens of short bursts, and an unusually flux decline. We report here on the X-ray monitoring of Swift J1555.2-5402 over the first ~29 months of its outburst with Swift, NICER, NuSTAR, INTEGRAL and Insight-HXMT, as well as radio observations with Parkes soon after the outburst onset. The observed 0.3-10 keV flux remained at levels >~1e-11 erg/cm^2/s for nearly 500 days before dropping by a factor of ~10 from its June 2021 peak towards the end of the monitoring campaign. During this time span, the spectrum was dominated by a single blackbody, with temperature attaining approximately a constant value (~1.2 keV) while the inferred radius shrank from ~1.7 km to ~0.3 km (assuming a source distance of 10 kpc). The long-term spin-down rate (Pdot~3.6e-11 s/s) is only ~15 % higher than that measured in the first 30 days. No periodic or burst-like radio emission was detected, in line with what has been previously reported using different radio facilities. The persistently high temperature, shrinking hotspot, and a prolonged bright flux plateau followed by a fast dimming observed during the outburst evolution pose a challenge for the outburst mechanisms proposed so far.
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All authors A. Borghese, F. Coti Zelati, M. Imbrogno, G. L. Israel, D. De Grandis, D. P. Pacholski, M. Trudu, M. Burgay, S. Mereghetti, N. Rea, P. Esposito, M. Pilia, A. Possenti, R. Turolla, L. Ducci

High Energy Astrophysical Phenomena

Low-Mass Neutron Stars and Effective Phase Transitions from a Hybrid Van der Waals-Polytropic Equation of State

P. H. F. Arruda and S. D. Campos

We study phase-transition-like behavior in neutron stars using a simplified, piecewise equation of state that couples a modified van der Waals-type core to a polytropic crust. The model remains analytically tractable while allowing for nonlinear density dependence. We impose thermodynamic and causal consistency conditions and determine the critical densities at which the curvature of the pressure-energy density relation changes. In the non-relativistic limit, the generalized Lane-Emden equations describe a smooth core-crust transition layer. We integrate the Tolman-Oppenheimer-Volkoff equations across different $(\tau_1,\sigma_1)$ regimes, where these parameters encode thermal and interaction effects in the core. The resulting mass-radius sequences yield low neutron star masses $(0.99-2.05)M_{\odot}$, and the chemical potential exhibits the characteristic signatures of phase-transition behavior at densities well above the matching point. Our results show that analytic EOS models can reproduce the key phenomenology of phase transitions and provide a controlled framework for exploring low-mass neutron star configurations.
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Cosmology and Nongalactic Astrophysics

Stochastic gravitational-wave background search using data from five pulsar timing arrays

Wang-Wei Yu and Bruce Allen

Using public pulse time-of-arrival data from five pulsar timing arrays (PTAs), we search for a stationary, isotropic, and unpolarized nHz stochastic gravitational-wave background (SGWB). This analysis is more sensitive than previous individual PTA searches because the combined 121-pulsar dataset is about four times larger than any single PTA's. For pulsars observed by multiple PTAs, we employ a new "direct combination" method to merge their astrophysical models and data. This avoids the challenge of reconciling different PTA timing models to obtain a single "best" model. A central result of our analysis is the posterior distribution of the amplitude $A_{gw}$ and exponent $\gamma_{gw}$ of the putative SGWB energy-density spectrum, modeled as a power law in frequency. While these results are consistent with a nonzero SGWB amplitude $A_{gw}$, the statistical significance-assessed via a Bayesian odds ratio and noise-marginalized false-alarm probabilities ($p$-values) for three detection statistics-remains below the conventional $5\sigma$ threshold for a confident detection. The inter-pulsar timing-residual correlation, reconstructed as a function of angle $\theta$ between the pulsar lines of sight, matches the Hellings and Downs (HD) prediction.
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Solar and Stellar Astrophysics · Cross-listed from physics.flu-dyn

Centrifugal instability of Taylor-Couette flow in stratified and diffusive fluids

Junho Park

The linear and non-linear dynamics of centrifugal instability in Taylor-Couette flow are investigated when fluids are stably stratified and highly diffusive. One-dimensional local linear stability analysis (LSA) on cylindrical Couette flow confirms that the stabilising role of stratification on centrifugal instability is suppressed by strong thermal diffusion (i.e. low Prandtl number $Pr$). For $Pr\ll1$, it is verified that the instability dependence on thermal diffusion and stratification with the non-dimensional Brunt-Väisälä frequency $N$ can be prescribed by a single rescaled parameter $P_{N}=N^{2}Pr$. From direct numerical simulation (DNS), various non-linear features such as axisymmetric Taylor vortices at saturation, secondary instability leading to non-axisymmetric patterns or transition to chaotic states are investigated for various values of $Pr\leq1$ and the Reynolds number $Re_{i}$. Two-dimensional bi-global LSA on axisymmetric Taylor vortices, which appear as primary centrifugal instability saturates nonlinearly, is also performed to find the secondary critical Reynolds number $Re_{i,2}$ at which the Taylor vortices become unstable by non-axisymmetric perturbation. The bi-global LSA reveals that $Re_{i,2}$ increases (i.e. the onset of secondary instability is delayed) in the range $10^{-3}<Pr<1$ at $N=1$ or as $N$ increases at $Pr=0.01$. Secondary instability leading to highly non-axisymmetric or irregular chaotic patterns is further investigated by the 3D DNS. The Nusselt number $Nu$ is also computed from the torque at the inner cylinder for various $Pr$ and $Re_{i}$ at $N=1$ to describe how the angular momentum transfer increases with $Re_{i}$ and how $Nu$ varies differently for saturated and chaotic states.
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High Energy Astrophysical Phenomena

Pulsars identified in the LOFAR Two-metre Sky Survey at 144 MHz

G. A. C. Rijkers, C. G. Bassa, J. R. Callingham et al. (+1 more)

We present the astrometric identification of 80 known radio pulsars as unresolved continuum sources detected at 144 MHz in the second data release of the LOFAR Two-metre Sky Survey (LoTSS DR2), which covers 27% of the Northern hemisphere. These identifications represent the majority ($\geq$ 86%) of radio pulsars present in the LoTSS DR2 footprint and provide independent celestial positions and flux densities at 144 MHz. We compare LoTSS flux densities with literature values from various image and time-domain observations and find good agreement for all but two pulsars. We attribute these flux density deviations to intrinsic pulsar properties (nulling and off-pulse emission). We investigate criteria to select promising pulsar candidates using data from the upcoming LoTSS release of the entire Northern sky ($\delta>0^\circ$), as well as the LOFAR LBA Sky Survey (LoLSS) at 54 MHz (covering $\delta>24^\circ$). Of the 80 detections, 35 (44%) were blindly redetected based on their linear or circular polarization. Therefore we conclude that candidate selection based on polarization properties is a promising approach. Candidate selection can be supplemented with spectral indices via cross-matching to LoLSS sources at 54 MHz, as the high sensitivity of LoTSS is not matched by image-domain surveys at higher frequencies.
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All authors G. A. C. Rijkers, C. G. Bassa, J. R. Callingham, T. Shimwell

Astrophysics of Galaxies

Predicting Quasar Counts Detectable in the LSST Survey

Guodong Li, Roberto J. Assef, W.N. Brandt et al. (+11 more)

The Legacy Survey of Space and Time (LSST), being conducted by the Vera C. Rubin Observatory, is a wide-field multi-band survey that will revolutionize our understanding of extragalactic sources through its unprecedented combination of area and depth. While the LSST survey strategy is still being finalized, the Rubin Observatory team has generated a series of survey simulations using the LSST Operations Simulator to explore the optimal survey strategy that best accommodates the majority of scientific goals. In this study, we utilize the latest simulated data to predict the number of detectable quasars by LSST in each band and evaluate the impact of different survey strategies. We find that the number of quasars and lower luminosity AGNs detected in the baseline strategy (v4.3.1) in the redshift range z=0.3-6.7 will be highest in the i-band and lowest in the u-band. Over 70% of quasars are expected to be detected within the first year in all bands, as LSST will have already reached the break of the luminosity function at most redshifts. With a limiting magnitude of 25.7 mag, we expect to detect 184 million AGNs in the z-band over the 10-year survey, with quasars constituting only 6% of the total AGNs in each band. This arises because, considering that the luminosities of most low-luminosity AGNs are affected by contamination from their host galaxies, we set a magnitude threshold when predicting the number of quasars. We find that variations in the u-band strategy can impact the number of quasar detections. Specifically, the difference between the baseline strategy and that with the largest total exposure in u is 15%. In contrast, changes in rolling strategies, DDF strategies, weather conditions, and Target of Opportunity observations result in variations below 2%. These results provide valuable insights for optimizing approaches to maximize the scientific output of quasar studies.
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All authors Guodong Li, Roberto J. Assef, W.N. Brandt, Matthew J. Temple, Franz E. Bauer, Marcin Marculewicz, Swayamtrupta Panda, Alessandro Peca, Claudio Ricci, Gordon T. Richards, Sarath Satheesh Sheeba, Chao-Wei Tsai, Jingwen Wu, Ilsang Yoon

Astrophysics of Galaxies

HI-detected Dwarf Galaxies in the FASHI Survey: Insights from Single- and Double-Peaked Emission-Line Samples

Cheng Cheng, Jia-Sheng Huang, Wei Du et al. (+4 more)

We present a sample of low HI mass dwarf galaxies ($M_{\rm HI} < 10^8 M_\odot$) detected by The FAST All Sky HI Survey (FASHI) project. Due to the faint and irregular morphology of these galaxies, the default photometry is often inaccurate. Therefore, we utilized The Dark Energy Camera Legacy Survey (DECaLS) data to perform careful photometric measurements, and find that the low HI mass galaxies have similar stellar mass densities to dwarf elliptical (dE) galaxies. Compared to other dwarf galaxy populations, the HI-selected dwarfs exhibit higher stellar mass densities than ultradiffuse galaxies, and similar densities to HI-selected low-surface-brightness galaxies, albeit with lower stellar masses, suggesting a possible evolutionary connection among these populations. By classifying the galaxies according to their HI spectral-line profiles, we show that the double-peaked sources conform closely to the Tully-Fisher relation, whereas the single-peaked sources follow the Faber-Jackson relation but with large scatter. This indicates that the single-peaked systems are likely dispersion dominated and that the relationship between stellar mass and halo mass in such systems may remain consistent across both low- and high-mass regimes. These findings suggest that HI-selected dwarf galaxies with single-peaked HI profiles may share a similar dynamical state with massive ellipticals, offering new insights into their structural evolution and the diversity of formation pathways for low-mass galaxies.
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All authors Cheng Cheng, Jia-Sheng Huang, Wei Du, Hong-Xin Zhang, Chuan-Peng Zhang, Ming Zhu, Gustavo Orellana

Earth and Planetary Astrophysics

The Two-Dimensional Structure of Circumplanetary Disks and their Radiative Signatures

Aster G. Taylor, Fred C. Adams and Nuria Calvet

During their formative stages, giant planets are fed by infalling material sourced from the background circumstellar disk. Due to conservation of angular momentum, the incoming gas and dust collects into a circumplanetary disk that processes the material before it reaches the central planet itself. This work investigates the complex vertical structure of these circumplanetary disks and calculates their radiative signatures. A self-consistent numerical model of the temperature and density structure of the circumplanetary environment reveals that circumplanetary disks are thick and hot, with aspect ratios $H/R\sim0.1-0.25$ and temperatures approaching that of the central planet. The disk geometry has a significant impact on the radiative signatures, allowing future observations to determine critical system parameters. The resulting disks are gravitationally stable and viscosity is sufficient to drive the necessary disk accretion. However, sufficiently rapid mass accretion can trigger a thermal instability, which sets an upper limit on the mass accretion rate. This paper shows how the radiative signatures depend on the properties of the planetary system and discuss how the system parameters can be constrained by future observations.
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Astrophysics of Galaxies

High-Redshift Galactic Outflows: Orientation Effects, Kinematics, and Metallicity in TNG50 and SERRA

Ivan Kostyuk, Stefano Carniani, Mahsa Kohandel et al. (+1 more)

Context: Recently, JWST/NIRSpec observations have provided the first detections of warm ionised outflows in low-mass galaxies at high redshifts (z>3), revealing an occurrence rate of 25-40% depending on the intensity of the emission lines. This fraction is lower than predicted by simulations, which suggest that fast outflowing gas should be a common feature of all star-forming galaxies in the early Universe. Aims: In order to better understand the discrepancies between simulations and observations, we identify and characterize outflows in high-redshift galaxies using the TNG50 cosmological and SERRA zoom-in simulations. Our study examines how outflow detectability depends on the line of sight, explores the properties of the fast gas, and investigates its relationship with key galactic properties. Methods: We analyse approximately 60000 galaxies from TNG50 and 3000 galaxies from SERRA over the redshift ranges z=3-5 and z=4-5, respectively, spanning stellar masses of Mstar=10^7.5-10^11Msun. Outflows in the immediate vicinity of each galaxy are identified using a Gaussian mixture model algorithm that uses the gas velocity, star-formation-rate, and location as input parameters. We subsequently compare the simulated outflows to those observed in the JWST/JADES NIRSpec survey. Results: Outflow masses in both TNG50 and SERRA broadly reproduce the JWST/JADES measurements within roughly 0.5dex, though simulations tend to predict slightly higher values, suggesting that optical emission lines capture only a fraction of the multiphase outflow. However, simulated outflow velocities are typically an order of magnitude lower than those inferred from observations. TNG50 indicates a clear orientation dependence as outflows in face-on galaxies are approximately 15% more likely to be detected than in edge-on systems, with this difference increasing to nearly 40% for more massive, disc-shaped galaxies.
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All authors Ivan Kostyuk, Stefano Carniani, Mahsa Kohandel, Andrea Pallottini

Earth and Planetary Astrophysics

Astrometric Reconnaissance of Exoplanetary Systems (ARES). I. Methodology validation with HST point-source images of Proxima Centauri

M. Libralato, L. Bedin and A. Burgasser

We present the first results of the Astrometric Reconnaissance of Exoplanetary Systems (ARES) project, aimed at validating and characterizing candidate exoplanets around the nearest systems using multi-epoch Hubble Space Telescope (HST) data. In this first paper, we focus on Proxima Centauri, leveraging archival and recent HST observations in point-source imaging mode. We refine the geometric-distortion calibration of the HST detector used, and develop a robust methodology to derive high-precision astrometric parameters by combining HST measurements with the Gaia DR3 catalog. We determine Proxima's position, proper motion, and parallax with uncertainties at the $\sim$0.4-mas, 50-$\mu$as yr$^{-1}$, and 0.2-mas level, respectively, achieving consistent results with what measured by Gaia within $\sim$1$\sigma$. We further investigate the presence of the candidate exoplanet Proxima c by analyzing the proper-motion anomaly derived from combining long-term HST-based and short-term Gaia astrometry. Under the assumption of a circular, face-on orbit, we obtain an estimated mass of $m_c = 3.4^{+5.2}_{-3.4}$ $M_\odot$, broadly consistent with radial-velocity constraints but limited by our current uncertainties. These results establish the foundation for the next phase of ARES, which will exploit HST spatial-scanning observations to achieve astrometric precisions of a few tens of $\mu$as and enable a direct search for astrometric signatures of low-mass companions.
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High Energy Astrophysical Phenomena

NICER Perspective on TeV Blazar Mrk~421: X-ray Variability and Particle Acceleration

Sangeetha Kizhakkekalam, Gopal Bhatta, Navaneeth P K et al. (+1 more)

Mrk~421 is one of the most fascinating blazars, widely studied across the electromagnetic spectrum using observations at various wavebands, from radio to the TeV gamma ray bands. We present the first detailed spectral and timing analysis of the TeV blazar Mrk~421 based on 45 X-ray observations from the NICER X-ray telescope, collected over two years from 2022 to 2024. The source exhibits strong X-ray variability across intraday and long-term timescales. During this period, we observe a dramatic change in flux, from $\sim 50$ to $\sim 1380$~cts~s$^{-1}$, representing a $\sim 28$-fold increase. Spectral modeling with power-law, broken power-law, and log-parabolic functions shows that the log-parabola provides the most accurate description of the X-ray spectra. The hardness ratio analysis confirms a harder-when-brighter trend, consistent with the anticorrelation between flux and photon index($\Gamma$). Correlation studies reveal a positive relation between the photon index ($\alpha$) and the curvature parameter ($\beta$) of the log-parabola model, a negative correlation between $\beta$ and synchrotron peak energy ($E_{\mathrm{p}}$), and a positive correlation between $E_{\mathrm{p}}$ and flux. In addition, the observed rapid variability indicates that the X-ray emission originates from a compact region located close to the central engine. Furthermore, using a log-parabolic electron energy distribution within the synchrotron jet scenario, we simulate the observed anti-correlation between the $E_{\rm p}$ and $\beta$. These features can be interpreted within the framework of energy-dependent particle acceleration in blazar jets, which are often associated with turbulence, strong magnetic fields, and relativistic outflows.
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All authors Sangeetha Kizhakkekalam, Gopal Bhatta, Navaneeth P K, Tek P. Adhikari

Earth and Planetary Astrophysics

A Search for Transit Duration Variations in M dwarf Multi-Planet Systems

Kohhei Bessho, Sarah Ballard and Natalia Guerrero

The nominal habitable zone for exoplanets orbiting M dwarfs lies close to the host star, making dynamical considerations especially important. One consequence of this proximity is the expectation of spin synchronization, with implications for atmospheric circulation. Several mechanisms can maintain non-zero obliquities over long timescales in compact multi-planet systems, including capture into Cassini State 2 (CS2) and other forms of secular spin-orbit coupling; such pathways are plausible in the orbital architectures of close-in M-dwarf planets. In this study, we search for transit duration variations (TDVs) consistent with the nodal precession rates predicted by Laplace-Lagrange secular theory in compact M-dwarf multi-planet systems. Our sample includes 23 exoplanets orbiting 12 stars. We compare recent, high-precision transit durations obtained from JWST white-light curves with measurements published at the discovery epoch and afterward. The resulting transit duration variation ranges from seconds to minutes, and we fit a linear trend to duration versus time for each planet. All systems are consistent with flat (no TDV) at the 3{\sigma} level. The strongest candidate is TRAPPIST-1d, whose fitted slope differs from zero with 2.2{\sigma} confidence. We calculate the expected TDV signals predicted by secular precession and compare them to the observed limits. Our null detection is consistent with the low-impact-parameter regime, where theoretical TDVs are only a few seconds per decade and below our sensitivity. Higher-impact-parameter configurations predict substantially larger TDVs and are disfavored: under uniformly distributed geometries, at least half of the allowed configurations would be excluded.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Dark Photons in the Early Universe: From Thermal Production to Cosmological Constraints

Xun-Jie Xu and Boting Zhou

Dark photons, a generic class of light gauge bosons that interact with the Standard Model (SM) exclusively through kinetic mixing, arise naturally in many gauge extensions of the SM. Motivated by these theoretical considerations, we present a comprehensive analysis of their thermal production in the early universe. Our calculation covers a broad range of dark photon masses from 0.1 keV to 100 MeV and include inverse decay, annihilation, and semi-Compton processes. Wherever possible, we present analytical estimates of the production rates and yields, and verify their accuracy numerically. For dark photons lighter than twice the electron masses (around 1 MeV), we find that our analytical estimate of the freeze-in yield based on resonant production is very accurate, implying that off-resonance contributions can be neglected in practice. For heavy dark photons, although this conclusion no longer holds, we derive an interesting ratio, $4\pi e/27\approx0.14$, with $e$ the coupling constant of QED, that can be used to estimate the relative importance of on- and off-resonance contributions. Finally, using the calculated abundance of dark photons in the early universe, we derive cosmological constraints on the dark photon mass and kinetic mixing. Compared with bounds from stellar cooling and supernovae, the cosmological constraints are most stringent in the mass range from 0.1 MeV to 6 MeV, within which kinetic mixing at the level of $10^{-12}\sim10^{-10}$ can be probed.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Superluminal constraints from ultra-high-energy neutrino events

J. M. Carmona, J. L. Cortés and M. A. Reyes

The $220^{+570}_{-100}\,$PeV neutrino detected by KM3NeT marks the beginning of ultra-high-energy neutrino astronomy and provides a powerful probe of Lorentz Invariance Violation (LIV). In superluminal scenarios, neutrinos can decay through vacuum $e^-e^+$ pair emission or neutrino splitting. Previous analyses of the KM3-230213A event relied on simplified survival-probability estimates and, in some cases, used inaccurate decay-width expressions or neglected redshift and threshold effects. In this work we present a unified and self-consistent framework that corrects these issues and applies to both the energy-independent ($n=0$) and quadratic ($n=2$) superluminal cases. We collect and recast the decay-width and threshold expressions, clarify their flavor dependence, and include a consistent treatment of cosmological propagation. We also assess the impact of cascade regeneration and show that cascade effects are negligible for the purpose of setting LIV bounds. The survival-probability approximation adopted in previous works is therefore justified, while our framework provides a coherent basis for future analyses of superluminal neutrino constraints, which should consistently include possible time-delay signatures.
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Astrophysics of Galaxies

Measuring the diffuse Galactic synchrotron spectral index and curvature between 45 and 2300 MHz

Melis O. Irfan and Giuseppe Puglisi

We present an all-sky map of the synchrotron spectral index and curvature between 45 and 2300 MHz at a resolution of 1 degree calculated from a combination of numerous partial sky empirical measurements. We employ a least-squares parametric fit which relies on removing a free-free emission template and a component separation technique which fits for both synchrotron and free-free emission. We compare our diffuse sky model estimates against those derived from the models widely used in the community (e.g. pysm3 and GSM) employing external datasets that were not included in the estimation process. Our evaluation focuses on identifying the enhanced consistency at both the map level and in pixel-to-pixel correlations, allowing for a more robust verification of our model's performance. We find our parametric, least-squares synchrotron estimate to be the most reliable across radio frequencies as it consistently provides sky models with average accuracies (when compared to empirical data) of around 20 per cent, whilst other model performances range on average between 10 and 70 per cent accurate. The results obtained have been made publicly accessible online and can be utilized to further develop and refine models of Galactic synchrotron emission.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Time-Averaged Template for Stochastic Gravitational-Wave Background Detection in Space-Based Interferometers

Jing-yi Wu and Yong Tang

Stochastic gravitational-wave background (SGWB) poses significant challenges for data analysis and parameter inference in future space-based gravitational-wave missions, such as LISA and Taiji, as it appears as an additional stochastic component along with instrumental noise. Previous studies have developed various approaches to distinguish the SGWB from instrumental noise, often under simplified assumptions such as static or equal-arm configurations. However, in realistic scenarios, time-varying arm-lengths introduce additional complexities that require careful modeling. In this work, we investigate the impact of template construction on SGWB parameter estimation under realistic orbital configurations. Using the simulated SGWB signals and dominant instrumental noise sources, we compare three template strategies: time-averaged template constructed from segmented data, equal-arm template, and a template treating the arm-lengths as a free parameter. Our results show that the time-averaged template yield improves parameter estimation accuracy under time-varying arm-lengths, whereas introducing the effective arm-length as a free parameter increases estimation uncertainty. These findings highlight the importance of realistic template construction for high-precision SGWB analysis in future space-based missions.
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