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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 8 June

High Energy Astrophysical Phenomena

Limits on primordial black holes from the extragalactic gamma-ray background; current status and future projections

Ilias Cholis, Iason Krommydas and John Carlini

Primordial black holes (PBHs), possibly formed from the collapse of early universe perturbations, will evaporate via Hawking radiation with a lifetime comparable to the age of the universe, if their mass is $O(10^{14})$ g. Such black holes can contribute to the observed gamma-ray fluxes in the MeV and GeV range. Using the observed extragalactic gamma-ray background (EGRB) from the Fermi Large Area Telescope, the EGRET, and the COMPTEL telescopes that cover gamma-ray energies from 0.5 MeV to 1 TeV, we evaluate limits on the abundance of PBHs with masses of $10^{14}$ to $10^{17}$ g. We study both monochromatic and extended mass distributions of PBHs. To model the EGRB spectrum, we calculate the contribution from extragalactic sources including blazars, star-forming galaxies and radio galaxies and also account for ultra-high-energy cosmic rays that produce gamma rays when interacting with the infrared background. Our EGRB modeling uses information from the Fermi gamma-ray point sources catalog, from observations at X-rays, the visible spectrum, the infrared and radio waves, and also accounts for modeling uncertainties and variations on the properties within each class of these sources. Moreover, we use recent work on the modeling of the PBHs' gamma-ray emission, that includes the direct Hawking radiation, gamma rays produced in the hadronization and decay of unstable particles, final state radiation and gamma rays from pair annihilations in the interstellar medium. As the contribution of final state radiation and the annihilation of positrons enhances the low-energy part of the produced gamma-ray spectra from PBHs, we find that the EGRB observations can set the tightest limits on their abundance among all indirect dark matter probes, within the mass range of interest.[abridged]
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Earth and Planetary Astrophysics

Complex gas flows in magnetized protoplanetary disks promote the formation of dust traps at low fragmentation velocities

Vignesh Vaikundaraman, Joanna Drazkowska, Nerea Gurrutxaga et al. (+1 more)

Non-ideal magnetohydrodynamic simulations of protoplanetary disks show a plethora of complex gas structures, including winds, rings, and gaps. These affect dust transport and help form dust traps, which are essential for planetesimal formation. Although studies have explored the evolution of dust in such systems, they have done so either in 1D or without dust coagulation, and the effect of such systems on dust growth is still an active area of research. This work aims to investigate the effect of a complex gas flow architecture on global dust evolution, including dust growth and transport. We examine the timescales of different processes impacting dust evolution and discuss prospects of forming planetesimals. We post-process gas velocity output from a 2D non-ideal magnetohydrodynamic simulation using a 2D (r-z) Monte Carlo dust coagulation code to perform global simulations of dust growth and evolution. We perform three runs, one with a typical steady-state disk and two with the gas velocity from the MHD simulation, where we vary the fragmentation velocity. Our results show that the advection of small particles by the gas due to strong gas velocities can play an important role in setting the dust size distributions around protoplanetary disks. The gas flow structure has a transition region, and this region acts as a location of a dust pile-up, increasing the pebble-to-gas ratio by a factor of 2.5 when compared to the steady state disk. Lowering the fragmentation velocity improves the stability of the pile-up, but the pebble concentration is not as high. This scenario acts as a way to form a dust trap in a disk without a pressure bump. We discuss the possibilities for planetesimal formation in such a trap.
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All authors Vignesh Vaikundaraman, Joanna Drazkowska, Nerea Gurrutxaga, Xue-Ning Bai

High Energy Astrophysical Phenomena

A Multi-Wavelength View of the First Type Ic-BL Supernova with an Einstein Probe X-ray Shock Breakout

Jillian C. Rastinejad, Gokul Srinivasaragavan, Nikhil Sarin et al. (+36 more)

In March 2026, the Einstein Probe (EP) discovered its most nearby (z = 0.0343) Fast X-ray Transient (FXT), EP260321a, the first EP FXT to provide a strong match to expectations for X-ray "shock breakout'" (SBO) emission. Here, we present our multi-wavelength follow-up campaign of EP260321a and its broad-line Type Ic (Ic-BL) supernova (SN) counterpart, SN2026gzf. We show that our radio follow-up extending over 5.8 - 54.5 days post-FXT rules out an on-axis jet counterpart of isotropic-equivalent kinetic energy $E_{K} \gtrsim 10^{49}$ erg for circumburst densities $n > 10^{-2}~{\rm cm}^{-3}$ and assuming microphysical parameters $\epsilon_e = \epsilon_B = 0.1$. Our radio data also constrains a median mass-loss rate of $\dot{M} \lesssim 1.2 \times 10^{-5} M_{\odot}~{\rm yr}^{-1}$ for a Wolf-Rayet progenitor. In addition, we derive SN2026gzf's properties, including $^{56}$Ni mass, diffusion timescale, and expansion velocities, from our $\sim$nightly-cadence optical data and compare them with those of optically discovered Type Ic-BL SNe, finding that SN 2026gzf is well within the 90% confidence interval across all properties. We further fit SN2026gzf's light curve and determine that combined emission from both interaction with CSM and $^{56}$Ni radioactive decay provides the best fit with plausible model parameters. Finally, using the rate of Ic-BL SNe from the ZTF Bright Transient Survey and assuming all Type Ic-BL SNe produce EP260321a-like FXTs, we infer an expected rate of EP-detected SBOs of 4.4 - 16 year$^{-1}$. This is inconsistent at the 90% confidence level with current EP detection rates, potentially indicating that most Type Ic-BL SNe produce less luminous X-ray SBO signals compared to EP260321a.
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All authors Jillian C. Rastinejad, Gokul Srinivasaragavan, Nikhil Sarin, Tanner O'Dwyer, S. Bradley Cenko, James K. Leung, Anya E. Nugent, Daniel A. Perley, Genevieve Schroeder, Shreya Anand, Tomas Ahumada, Igor Andreoni, Aleksandra Bochenek, Alessandra Corsi, Christoffer Fremling, Anna Y. Q. Ho, Mansi M. Kasliwal, Geoffrey Mo, Anirudh Salgundi, Kendall I. Sippy, J. Sollerman, Eric C. Bellm, Tracy X. Chen, Michael W. Coughlin, Michael C. Davis, Fabio De Colle, Danielle Frostig, Christopher L. Fryer, Michael J. Graham, Xander J. Hall, K. -R. Hinds, Luca Izzo, Wynn Jacobson-Galan, Nathan P. Lourie, Keiichi Maeda, Josiah Purdum, Ben Rusholme, Avinash Singh, Robert Stein

High Energy Astrophysical Phenomena

Decadal pre-explosion activity and circumstellar interaction in a supernova

Ting-Wan Chen, Amar Aryan, Sheng Yang et al. (+52 more)

When a massive star explodes as a supernova, crucial information about its immediate environment is lost within hours. Here we report rapid optical observations from Lulin Observatory of the broad-lined Type Ic supernova SN 2026gzf, beginning 1.25 hours after Einstein Probe detected the X-ray transient EP260321a. Our data led to the discovery of the optical counterpart and showed a luminous blue first-day excess that cannot be reproduced by standard radioactive models. We find that interaction between the ejecta and $\approx 0.02$ M$_{\odot}$ of circumstellar material accounts for the early excess. Archival Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) images show variability at the explosion site over the previous $\sim 12$ years, with the source brightening by a factor of $\sim 1.5$ in the final $\sim 3$ years before explosion, providing rare evidence for pre-explosion activity in a stripped-envelope progenitor system. The precursor brightening suggests enhanced eruptive mass loss during late-stage oxygen burning before core collapse, while an additional silicon-burning episode shortly before explosion may have created the compact nearby material responsible for the X-ray shock-breakout signal. SN 2026gzf therefore offers the first view of how a stripped progenitor modifies its immediate environment shortly before death, linking long-term precursor variability, circumstellar interaction and the explosion itself.
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All authors Ting-Wan Chen, Amar Aryan, Sheng Yang, Stephen J. Smartt, Takashi J. Moriya, Seán J. Brennan, Maximilian D. Stritzinger, Bailey Martin, Matt Nicholl, Albert K. H. Kong, James H. Gillanders, Anirban Dutta, Brian P. Schmidt, Yu-Chi Cheng, Mark E. Huber, Cheng-Han Lai, Chien-Hsiu Lee, Yu-Hsing Lee, Chow-Choong Ngeow, Ken W. Smith, Christopher Ashall, Katie Auchettl, Chris R. Burns, Kenneth C. Chambers, Zhi-Yue Chen, Thomas de Boer, Eric Y. Hsiao, Khoa Ngo Thanh Ho, Willem B. Hoogendam, David O. Jones, Erkki Kankare, Tom L. Killestein, Hanindyo Kuncarayakti, Meng-Han Lee, Chuan-Jui Li, Chien-Cheng Lin, Christopher Lidman, Thomas B. Lowe, Eugene A. Magnier, Kyle Medler, Anais Möller, Thomas Moore, Nidia Morrell, Gregory S. H. Paek, Cameron M. Pfeffer, Da-Chun Qiang, Liana Rauf, Thomas M. Reynolds, Aiswarya Sankar.K, Shubham Srivastav, Jack Tweddle, Richard Wainscoat, Ze-Ning Wang, Huangfei Xiao, Zonghong Zhu

Cosmology and Nongalactic Astrophysics

Mixed Dark Matter: Limits from the Milky Way Satellite Galaxies

Wendy Crumrine, Dominic Pang, Ethan O. Nadler et al. (+2 more)

The Standard Model of particle physics contains a diverse set of particle species, motivating the possibility of a similarly complex dark sector. Here we study two-component dark matter (DM) mixtures, in which one component behaves as standard CDM while the other suppresses the formation of small-scale structure, either through an astrophysically relevant de~Broglie wavelength (fuzzy DM; FDM) or collisional damping from temperature-independent scattering (interacting DM; IDM). Using the observed population of Milky Way satellite galaxies, we derive new leading constraints on the parameter spaces of mixed FDM and of mixed IDM coupled to photons ($\gamma$-DM), neutrinos ($\nu$-DM), or baryons ($p$-DM), for beyond-CDM fractions down to $50\%$. We require that the linear matter power spectra of allowed models remain less suppressed than a constrained reference model. The resulting $95\%$ confidence bounds on FDM mass and IDM cross section weaken systematically with decreasing fraction, following distinct power-law scalings. At $50\%$ fraction, IDM cross section bounds weaken by a factor of $\sim$2–6 and FDM mass bounds by $\sim$1.5, relative to the $100\%$ case. We forecast that idealized future satellite surveys, which adopt approximate LSST sensitivity thresholds, can improve these $100\%$ bounds by a factor of $\sim$1.6–14 for IDM and $\sim$3 for FDM. Self-consistent cosmological simulations of mixed DM scenarios will be essential to more robustly characterize the degeneracy between particle physics parameters and fractional contribution, to extend constraints to lower fractions, and to identify signatures beyond satellite abundance to further inform these models.
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All authors Wendy Crumrine, Dominic Pang, Ethan O. Nadler, Andrew Benson, Vera Gluscevic

Astrophysics of Galaxies

On Cross-Correlating Line Intensity Maps from SPHEREx during Reionization

Abigail E. Ambrose, Eli Visbal and Matthew McQuinn

We have simulated Ly{\alpha}, H{\alpha}, H{\beta}, [OII], and [OIII] intensity maps which are observable by SPHEREx during cosmic reionization. We simulate these intensity maps including all significant sources of emission for each line, and include radiative transfer for the Ly{\alpha} intensity maps. We also include a simple model of dust extinction based on observations of galaxies at z<5. One of the main challenges of intensity mapping is interloping lines from galaxies at lower redshifts, which makes producing an auto-power spectrum challenging. We focus on cross-correlations between different lines, as this eliminates such foreground contamination of the signal. We have cross-correlated the simulated SPHEREx intensity maps to find the most observable cases. This includes modeling of interloping lines and masking bright interloping galaxies. Testing a range of cases motivated by observations, we find total signal-to-noise values up to 99 for the highest case of H{\alpha} cross-correlated with [OIII] at z=5 assuming no dust extinction. We also find cases which will not be detectable. We find that the dominant noise source in these intensity maps on most scales is from the instrument, except for Ly{\alpha} and [OII] and then only on the largest scales the interlopers are the dominant source. We find through intensity mapping we can probe galaxies with masses $M<4x10^{10}~M_{\odot}$ which are below the necessary luminosity for a 3{\sigma} signal-to-noise direct detection of galaxies by SPHEREx. However, the majority of our observable signal is dominated by large, directly detectable galaxies, rather than the smaller, fainter galaxies. We find marginal detections of the clustering portion of the power spectrum at z=5 for H{\alpha}x[OIII]. Detections of the clustering signal from other lines or at z>6 will require more sensitive instruments, such as the Cosmic Dawn Intensity Mapper.
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High Energy Astrophysical Phenomena

Failed jet breakout in the metal-poor broad-lined type Ic supernova 2026gzf

Antonio Martin-Carrillo, Christina C. Thöne, James K. Leung et al. (+103 more)

A long-standing question in the death of massive stars is the role of relativistic jets. While many gamma-ray bursts and some fast X-ray transients seem to be associated with broad-lined type Ic supernovae, the opposite is not true. The lack of observable jet emission in those Ic-BL SNe can be explained by invoking off-axis jets, choked jets that inject all their energy into the stellar envelope, baryon-loaded jets for which the prompt high-energy emission is strongly suppressed, or non-jetted SNe. The lack of exact explosion time in the majority of SNe presents an obstacle to distinguish between these scenarios. Here we report the properties of SN 2026gzf associated with the X-ray thermal Einstein Probe shock-breakout EP260321a at z=0.0343. The absence of compelling shocked cocoon and radio emission up to 54 days, combined with initial expansion velocities of ~30,000 km/s and a circumstellar shell of ~0.07 M$_\odot$, favour a scenario for SN 2026gzf in which a jet was choked in the circumstellar shell. Our high-spatial resolution images of the SN environment show that the progenitor was located between two highly star-forming regions with a metallicity lower than any previously known Ic-BL SN. As the first case of a Ic-BL SN associated with high-energy prompt emission without the signature of a jet, SN 2026gzf provides a unique perspective to understand the successful launch of relativistic jets during the deaths of massive stars.
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All authors Antonio Martin-Carrillo, Christina C. Thöne, James K. Leung, Gregory Corcoran, Antonio de Ugarte Postigo, Peter G. Jonker, Luca Izzo, Andrew J. Levan, Benjamin P. Gompertz, Stéphane Basa, Nikhil Sarin, Jonathan Quirola-Vásquez, Rob A. J. Eyles-Ferris, Riccardo Brivio, Alan M. Watson, Laura Cotter, Jennifer Alexandra Chacón, Andrea Rossi, Andrea Melandri, Piramon Kumnurdmanee, Nial R. Tanvir, Anshika Gupta, Franz E. Bauer, Jean-Grégoire Ducoin, Andrea Reguitti, Kuntal Misra, Dong Xu, Susanna D. Vergani, Wen-fai Fong, Kendall Ackley, Edilberto Aguilar-Ruiz, Dalya Akl, Miguel Ángel Aloy, Jie An, Camila Angulo-Valdez, Sarah Antier, Jean-Luc Atteia, Rosa L. Becerra, Rene P. Breton, Nathaniel R. Butler, Sergio Campana, Francesco Carotenuto, Jorge Casares Velázquez, Ashley A. Chrimes, Valerio D'Elia, Joyce N. D. van Dalen, Fabio De Colle, Massimiliano De Pasquale, Vik S. Dhillon, Damien Dornic, Martin J. Dyer, Matteo Ferro, Morgan Fraser, Andrew S. Fruchter, Francis Fortin, Duncan K. Galloway, Leonardo García-García, Stefan Geier, Ramandeep Gill, Noémie Globus, Roberto Gualandi, Marion Guelfand, Francesco Guidolin, Dieter H. Hartmann, Agnes P. C. van Hoof, Pall Jakobsson, Divyanshu Janghel, Tom L. Killestein, Sylvio Klose, Shiho Kobayashi, Rubina Kotak, Amit Kumar, Asuka Kuwata, Tanmoy Laskar, William H. Lee, Massimiliano Lincetto, Gianluca Lombardi, Diego López-Cámara, Joseph D. Lyman, Elisabetta Maiorano, Keiichi Maeda, Nikos Mandarakas, Francesco Magnani, Jirong Mao, Enrique Moreno Méndez, Ana María Nicuesa Guelbenzu, Kanthanakorn Noysena, Laura K. Nuttall, Paul T. O'Brien, David O'Neill, Paolo Ochner, Margarita Pereyra, Giovanna Pugliese, Gavin Ramsay, Lauren Rhodes, Andrea Saccardi, Ruben Salvaterra, Fredd Sánchez Álvarez, Benjamin Schneider, Steve Schulze, Rhaana L. C. Starling, Danny Steeghs, Kzrysztof Ulaczyk, Chiara Ventura, Tayyaba Zafar, Zi-Pei Zhu

Astrophysics of Galaxies

From Dense Gas Clouds to Supermassive Black Hole Seeds: Hybrid Hydro/Direct $N$-body Simulations of Runaway Collision-driven Intermediate-mass Black Hole Formation

Eunwoo Chung, Yongseok Jo, Ji-hoon Kim et al. (+2 more)

A population of dense stellar systems at high redshift has recently been uncovered by the JWST. To investigate the formation of supermassive black hole (SMBH) seeds in these dense environments without invoking any ad hoc seeding mechanisms, we present star cluster-scale simulations performed with an updated version of the hydrodynamics code Enzo-Abyss, which self-consistently integrates the gravity using a direct $N$-body method coupled with stellar evolution. By modeling initially dense, metal-poor gas clouds with varying turbulence, we consistently find the formation of dense clusters resembling early-stage nuclear star clusters (NSCs), as well as the formation of very massive stars (VMSs) ranging from $343\;\mathrm{M_\odot}$ to $5108\;\mathrm{M_\odot}$ via runaway collisions, irrespective of stellar wind feedback strength. Following the direct collapse of these VMSs, the resulting intermediate-mass black holes (IMBHs) grow through Eddington-limited gas accretion and tidal disruption events (TDEs). In our most optimistic model, we find a mass accretion rate of $1.64\times10^{-4}\;\mathrm{M_\odot\;yr^{-1}}$, with TDEs contributing $23\%$ of the total accretion over $\sim10\;\mathrm{Myr}$. Assuming a steady gas supply into the NSC driven by rapid structural assembly in the high-redshift environment, together with a constant TDE rate, we project that an IMBH with an initial mass of $6747\;\mathrm{M_\odot}$ at the center of the NSC can grow to $\sim62000\;\mathrm{M_\odot}$ within $100\;\mathrm{Myr}$ of its formation. Our numerical study, conducted within a single self-consistent framework that incorporates the essential physical processes, suggests that VMSs can form in dense gas clouds, collapse into IMBHs, and subsequently provide viable seeds for the SMBHs observed at high redshift.
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All authors Eunwoo Chung, Yongseok Jo, Ji-hoon Kim, Minyong Jung, Oh-kyoung Kwon

Astrophysics of Galaxies

Individual Star Sampling in Star Formation Simulations: A Semi-Deterministic Model

Yunwei Deng, Hui Li, Zhiqiang Yan et al. (+2 more)

In modern simulations that include star formation, it is common to use a universal and invariant initial mass function (IMF) to represent star populations or sample individual stars. However, stellar masses are determined by local and environmental processes that operate over a wide dynamical range and remain unresolved in simulations. We introduce a semi-deterministic (SDT) scheme for sampling individual stars from star-forming gas in numerical simulations. We represent unresolved molecular cores and protostellar disks with reservoir particles (RsvPs) and employ an on-the-fly friends-of-friends algorithm to identify star clusters. The instantaneous IMF for newly formed stars is then derived from the current cluster mass. We test the performance of this method in simulations of isolated molecular clouds and a major merger between two dwarf galaxies. Compared to existing IMF sampling methods, our SDT scheme naturally reproduces the observed $m_{\star,\text{max}}$-$M_\text{ecl}$ relation and yields numbers of massive stars consistent with optimal sampling theory. It also exhibits the smallest run-to-run variation among simulations with different random seeds. The regulated star formation results in a small ($\sim0.15$ Myr) but coherent time delay in the emergence of massive stars, reduces the large scatter arising from Poisson noise, and produces initial mass segregation within the clusters. On galactic scales, the SDT method predicts a steeper high-mass IMF slope at low star formation rates (SFRs), with the slope negatively correlated with the SFR. As the specific abundance of massive stars declines, our model naturally explains the systematically low H$\alpha$-based SFRs, where the H$\alpha$ indicator for Milky Way-like galaxies underestimate the intrinsic SFR owing to the reduced population of massive stars.
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All authors Yunwei Deng, Hui Li, Zhiqiang Yan, Chuizheng Kong, Zhi-Yu Zhang

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

Constraints and Projections for Millicharged Dark Matter in the Sun with Water Cherenkov Neutrino Detectors

Thong T.Q. Nguyen

Millicharged particles are well-motivated dark matter candidates that have been extensively investigated in terrestrial experiments. Recent studies proposed using the IceCube Neutrino Observatory to search for high-energy neutrinos produced by the capture and annihilation of millicharged dark matter in the Sun, deriving new constraints in the strong interaction regime where the millicharge is $q_\chi \sim 10^{-3}$-$10^{-2}$, which extend to small fractional abundances where all existing constraints lose sensitivity. In this work, I point out that the lower energy threshold of water Cherenkov detectors makes Super-Kamiokande and the future Hyper-Kamiokande sensitive to neutrinos from the annihilation of lighter millicharged dark matter, complementing the high-mass reach of IceCube. I find that Super-Kamiokande can constrain previously unexplored parameter space at $m_{\chi}=5$-28 GeV for dark matter fraction of $f_{\chi}=10^{-4.5}$, while Hyper-Kamiokande can improve these constraints and will be sensitive to fractional abundances as small as $f_{\chi}\simeq 5\times 10^{-6}$, nearly an order of magnitude below current IceCube limits.
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Cosmology and Nongalactic Astrophysics

A universal model for the accretion rates and formation times of dark matter halos

Ankita Bera and Benedikt Diemer

The formation histories of halos set the baseline rate at which galaxies accrete gas over cosmic time. While a number of models describe these histories and their derivative, the mass accretion rate (MAR), a simple and universal formula has remained elusive. Here we measure the median MARs and half-mass formation times of halos in dark matter-only and hydrodynamical simulations, in extremely different cosmologies ($\Lambda$CDM and Einstein-de Sitter), and across a wide range of redshifts ($z = 0$-$14$). We confirm that MARs increase with mass and redshift, and that they are virtually identical in hydrodynamical and dark matter-only simulations. We show that MARs are accurately described by a universal six-parameter function of three physical variables: the peak height $\nu$, the slope of the linear power spectrum $n_{\rm eff}$, and the effective linear growth rate $\alpha_{\rm eff}$. A complementary two-parameter fit for the formation redshift improves on the function of Lacey & Cole by fixing one parameter to its physical value and adding a dependence on $n_{\rm eff}$. Our model is broadly consistent with some prescriptions from the literature but provides a larger range and higher accuracy at high redshifts and low masses. Our fitting functions are implemented in the publicly available Colossus toolkit.
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Cosmology and Nongalactic Astrophysics

On the potential of pseudo-scalar dark energy

Andrea Minotti, Yunzhi Wu and Marco Regis

A cosmological pseudo-scalar field provides a compelling realization of dynamical dark energy (DE). If its coupling to photons is non-negligible, the cosmic microwave background acquires a rotation of its polarization plane, known as cosmic birefringence (CB). We present an extended analysis of several pseudo-scalar DE models and derive constraints on the parameters of their potentials by combining observations of the background expansion history with measurements of CB. We find that the axion-like potential constitutes a viable model only for large values of the anomaly coefficient. Scenarios in which the pseudo-scalar field rolls down a potential with quadratic, linear, or Ratra-Peebles forms can successfully explain DE and CB, with a symmetry-breaking scale close to the GUT scale.
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High Energy Astrophysical Phenomena

EP260321a/SN 2026gzf: The Faintest Shock Breakout Associated with a Broad-Lined Supernova

Brendan O'Connor, Xander J. Hall, Malte Busmann et al. (+33 more)

The explosion of a star is first marked by the shock wave breaking out of the stellar surface, producing a burst of ultraviolet and X-ray radiation. These events are observationally rare, despite likely accompanying the majority of supernovae. Here, we report on our multi-wavelength observing campaign of the closest Einstein Probe fast X-ray transient EP260321a at $z=0.0344$. The thermal ($kT=130$ eV) X-ray emission with peak luminosity $1.0\times10^{45}$ erg s$^{-1}$ points to a shock breakout origin. We demonstrate that EP260321a is accompanied by a broad-lined Type Ic supernova, SN 2026gzf. The supernova properties, including its spectral evolution, lightcurve evolution, and expansion velocities, are all typical of the energetic stripped-envelope supernovae associated with gamma-ray bursts. However, deep X-ray upper limits obtained with the Chandra X-ray Observatory do not detect an X-ray afterglow, and instead exclude the afterglow of known gamma-ray bursts or fast X-ray transients. If the stellar explosion launched a successful relativistic jet, we require that it had both a low Lorentz factor $\Gamma_0$\,$<$\,$30$ and a kinetic energy $E_\textrm{kin}$\,$<$\,$10^{49}$ erg for a stellar wind density of $A_*$\,$\gtrsim$\,$1$. We propose that EP260321a originated from a mildly relativistic, weak outflow that was choked by the progenitor star. This scenario is capable of naturally explaining its low X-ray luminosity and lack of prompt gamma-ray emission. EP260321a bridges the gap between SN 2008D and low-luminosity GRBs, suggesting a greater diversity in the physical parameters of stripped stars as they undergo terminal collapse.
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All authors Brendan O'Connor, Xander J. Hall, Malte Busmann, Daniel Gruen, Alberto Floris, Tomas Cabrera, Ziyuan Zhu, Antonella Palmese, Dylan Green, John Banovetz, Julius Gassert, Christopher L. Fryer, Roberto Ricci, Eleonora Troja, Surya Shivaprasad, Gregory R. Zeimann, Ariel J. Amsellem, Stephen Bailey, Segev BenZvi, Simone Dichiara, Hendrik van Eerten, Jeremy Hare, Lei Hu, Christopher M. Irwin, Keerthi Kunnumkai, Konstantin Malanchev, Mitra Maleki, Michael J. Moss, Adam D. Myers, Dheeraj Pasham, Christoph Ries, Geoffrey Ryan, David Schlegel, Michael Schmidt, Silona Wilke, Yu-Han Yang

Solar and Stellar Astrophysics

Mode Instability and a Massive, Isolated Outburst in the Pulsating White Dwarf GD 1212

J. J. Hermes, Keaton J. Bell, Andrew H. Dublin et al. (+8 more)

We analyze a large brightening event that lasted for roughly half a day in the pulsating hydrogen-atmosphere white dwarf GD 1212 during K2 Campaign 12 of the extended Kepler mission. For the other 80 days of K2 observations, GD 1212 exhibited a rich spectrum of long-period (~1100 s) pulsations that underwent rapid variations in frequency and amplitude but did not exhibit any additional outbursts. We refine previous attempts at mode identification and find a likely sequence of dipole and quadrupole splittings that reveal an overall rotation rate of roughly 17.0 hr. The outburst at Day 61 is fully resolved by the 60-second-cadence K2 data, with the entire white dwarf becoming up to 17.5% brighter overall, from an approximately 850 K increase in effective temperature, with pulsational variability during the outburst showing shorter periods and higher amplitudes. Outbursts are believed to be the result of nonlinear mode coupling via parametric instability, whereby energy stored in linearly excited parent modes is rapidly transferred to damped child modes that dissipate near the surface. Additionally, we characterize a "failed" outburst that caused correlated pulsation frequency changes, an approximately 5 microHz increase, with a small approximately 0.35% corresponding brightness increase. GD 1212 is now the eighth pulsating hydrogen-atmosphere DAV white dwarf to show outburst behavior, although it exhibited the largest outburst yet and has the longest inferred recurrence timescale. This high-signal-to-noise record tracing pulsations through both large and small temperature excursions in GD 1212 provides unique insights into parametric resonance and nonlinear mode coupling in white dwarf pulsations.
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All authors J. J. Hermes, Keaton J. Bell, Andrew H. Dublin, M. H. Montgomery, Steven D. Kawaler, Ian Clark, Zachary P. Vanderbosch, Bart H. Dunlap, P.-E. Tremblay, Paul Chote, Boris T. Gaensicke

High Energy Astrophysical Phenomena

The Curious Case of PHL 1811: Heavy Obscuration Versus Intrinsic X-ray Weakness

B. Luo, Xiaolei Chen, Jian Huang et al. (+2 more)

We present a systematic X-ray analysis of the narrow-line Type 1 quasar PHL 1811, which has long been regarded as the prototype of intrinsically X-ray weak quasars. A critical breakthrough came with the first detection of a bright X-ray flare from this source by the Einstein Probe (EP) in 2024. We utilize archival X-ray observations spanning 2001-2024, including the post-flare EP and Swift data. We confirm that PHL 1811 shows X-ray weakness factors $f_{\rm weak} \approx 23$-179 across all epochs before 2024. The 2024 EP flare marks the first detection of an X-ray nominal state with $f_{\rm weak} \approx 0.63$, followed by a rapid flux decline. We identify three key observational signatures that strongly support heavy obscuration: (1) a significant hard X-ray excess above $\approx5$ keV in the 2015 XMM-Newton spectrum; (2) relatively flat spectral shapes in two Swift observations; and (3) transitions between X-ray nominal and multiple X-ray weak states without corresponding optical/infrared variability, consistent with expectations from obscuration by a clumpy dust-free absorber. Fitting with a partial-covering obscuration model reproduces all multi-epoch spectra well. The observed steep spectra are dominated by a small leaked/scattered fraction of the intrinsic continuum, and variability is driven by changes in the leakage fraction and column density. Our results strongly favor the scenario where PHL 1811 is obscured by a radiatively driven accretion-disk wind from super-Eddington accretion, unifying PHL 1811 with the broader population of super-Eddington accreting AGNs under a single obscuration framework.
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All authors B. Luo, Xiaolei Chen, Jian Huang, W. N. Brandt, Qingling Ni

Earth and Planetary Astrophysics

Planet or brown dwarf? Constraints on the formation of H-type objects in IC348

Richard J. Parker and Catarina Alves de Oliveira

The formation mechanism(s) of substellar objects, such as brown dwarfs and free-floating planets, remains an ongoing puzzle in stellar and planetary physics. Recent observational and theoretical work points towards a star-like origin for brown dwarfs, though several authors posit that they could form like planets in a circumstellar disc, and then subsequently be ejected into a star-forming region or the Galactic field. Recently, JWST observations have discovered nine substellar objects in the IC348 star-forming region with a spectral absorption feature at 3.4$\mu$m from an unidentified aliphatic hydrocarbon, detected for the first time in planetary atmospheres outside of the Solar System. It is unclear whether these hydrocarbon absorption features in these 'H-type' objects indicate a different formation mechanism compared to more massive brown dwarfs. We quantify the spatial distribution of these objects and find they are indistinguishable from the spatial distribution of stars and other brown dwarfs in IC348. We use N-body simulations to test whether the H-type objects could have formed as planets in circumstellar discs and then been dynamically ejected by stellar fly-bys. We show that a similar number of free-floating planets could be produced if those planets initially resided at ~5au from their host stars. However, these free-floating planets have a much more dispersed spatial distribution than the stars and brown dwarfs, inconsistent with the spatial distribution of the H-type objects in IC348. We therefore conclude that the H-type objects are unlikely to have a planetary-like origin.
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Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

Too Heavy to Hide: Gamma-Ray Constraints on Annihilating Dark Matter beyond Unitarity

Abhishek Dubey, Deep Jyoti Das and Akash Kumar Saha

The measurement of high energy diffuse gamma rays by various ground-based air shower detectors have opened a new chapter for high energy particle physics and astrophysics. The broad range of viable dark matter candidates motivates extending indirect searches to heavier dark matter masses, opening new opportunities to uncover the nature of dark matter. If dark matter is composite rather than point-like, then the thermal unitarity bound can be relaxed, opening up the possibility of dark matter masses far beyond the electroweak scale. We perform a model agnostic search for heavy annihilating dark matter using the gamma-ray measurements and upper limits from Tibet AS$_\gamma$, LHAASO, KASCADE-Grande, Pierre Auger Observatory, and Telescope Array. These highest energy datasets enable us to probe new regions of parameter space and set world-leading limits on the annihilation cross sections for dark matter masses $10^5$–$10^{12}$ GeV. Our work highlights the power of high energy gamma-ray datasets in discovering heavy dark matter signatures in the near future.
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Astrophysics of Galaxies

Discovery and Spectroscopic Characterization of a Distant, Compact Milky Way Satellite in Gemini

K. Overdeck, W. Cerny, C. Y. Tan et al. (+27 more)

We present the discovery of a compact Milky Way satellite in the constellation of Gemini. This system was discovered by cross-matching detections from two independent search algorithms applied to Blanco/DECam data from the third data release of the DECam Local Volume Exploration survey (DELVE DR3), and confirmed with deeper imaging from Gemini/GMOS-N. Based on these data, we determine that the system is an ultra-faint ($M_V = -2.1^{+0.4}_{-0.6}$), compact ($r_{1/2} = 8.6^{+1.4}_{-1.2}$ pc) system located at a heliocentric distance of $120^{+7}_{-6}$ kpc. These physical properties place the system in the regime of ambiguous, ultra-faint compact Milky Way halo satellites that cannot be confidently classified as dwarf galaxies or star clusters from morphology alone; we therefore name the system DELVE 8/Gemini I. From medium-resolution Keck/DEIMOS spectroscopy, we securely identify four members including two blue horizontal branch stars, confirming the system as a bound satellite moving at a mean radial velocity of $v_{\rm hel} = -82.7^{+3.7}_{-3.9} {\rm km\,s}^{-1}$. We also use these spectra to place an upper limit of $\rm [Fe/H] \lesssim -2.5$ on the metallicity of DELVE 8/Gemini I's brightest star, supporting the classification of the system as either an ancient star cluster or ultra-faint dwarf galaxy. The discovery of faint, distant systems similar to DELVE 8/Gemini I is expected to become more common with upcoming surveys.
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All authors K. Overdeck, W. Cerny, C. Y. Tan, C. E. Martínez-Vázquez, A. B. Pace, J. A. Sharp, A. Drlica-Wagner, M. Geha, D. J. Sand, J. A. Carballo-Bello, Y. Choi, D. Crnojevíc, P. S. Ferguson, M. Hirschauer, D. J. James, N. Kallivayalil, G. Limberg, P. Massana, S. Mau, G. E. Medina, B. Mutlu-Pakdil, M. Navabi, D. L. Nidever, N. E. D. Noël, A. Pai, A. H. Riley, J. D. Sakowska, L. Santana-Silva, G. S. Stringfellow, A. K. Vivas

Instrumentation and Methods for Astrophysics

Flux Cube Reconstruction from Slitless Spectroscopy

M. Griggio, R. E. Ryan Jr., N. Pirzkal et al. (+19 more)

Slitless spectroscopy enables efficient, large-area surveys without target pre-selection, yet it faces challenges from source blending, higher noise, and lost spatial-spectral information. We present an advanced, non-parametric, data-driven algorithm that leverages multiple dispersion angles to reconstruct three-dimensional flux distributions, providing low-resolution Integral Field Unit (IFU) capabilities from slitless data. By treating each pixel as an independent element, our method naturally handles source confusion without requiring prior assumptions regarding redshifts, templates, or model libraries. We validate the algorithm using simulated Roman Space Telescope wide-field slitless spectroscopy images that are equivalent to what is expected from the High-Latitude Time-Domain Survey. First, we demonstrate that a host-galaxy model reconstructed from multiple dispersion angles can be used to accurately subtract host light from a transient, recovering a Type Ia supernova spectrum with minimal bias. Second, we showcase a high-fidelity flux-cube reconstruction of a complex galaxy, successfully measuring the redshift and recovering continuum, emission, and absorption features. This approach highlights the potential of multi-dispersion-angle slitless data to provide spatially resolved spectral information in a non-parametric way, which is traditionally accessible only with integral field spectroscopy, opening a new window into large, unbiased, and spatially-resolved studies of galaxy evolution.
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All authors M. Griggio, R. E. Ryan Jr., N. Pirzkal, T. L. Astraatmadja, S. Casertano, S. Perlmutter, D. Rubin, G. Aldering, J. M. DerKacy, O. D. Fox, A. S. Fruchter, L. Galbany, R. Hounsell, A. M. Isaacs, P. L. Kelly, R. S. Kessler, B. M. Rose, J. Roychowdhury, M. Sako, D. M. Scolnic, L.-G. Strolger, the Roman Supernova Cosmology Project Infrastructure Team

Earth and Planetary Astrophysics

Stellar Obliquities of Young Systems, Atmospheres Undergoing Contraction and Escape (SOYSAUCE) II: a 135 Myr planet on an aligned orbit with transit timing variations

Madyson G. Barber, Andrew W. Mann, Sydney Vach et al. (+16 more)

Young planets (<1 Gyr) provide opportunities to directly probe planet formation and evolution processes in action. However, due to heightened stellar activity, there is a lack of known transiting planets in adolescence (~100-500 Myr). Here we present the validation of TIC 150070085 b, a 3.6 R_E planet on a 10.47 day orbit, and report the candidate TIC 150070085 c, a 3.0 R_E planet on a 15.90 day orbit. While we are unable to validate the second signal, the proximity to mean motion resonance (3:2) and transit timing variations observed in the transits of TIC 150070085 b strongly suggest the signal is planetary. We confirm the host star as a member of Alessi 84 and combine the group's CMD, rotation, and variability properties to update the age to 135 +/- 10 Myr. We additionally use MAROON-X to observe the Rossiter-McLaughlin signal of TIC 150070085 b and measure the sky projected obliquity angle ($\lambda$). We find TIC 150070085 b is consistent with a near-aligned orbit with its host star (|$\lambda$| = 18 +/- 12$^\circ$), in line with similarly aged transiting planets with measured $\lambda$ values. Continued discovery and characterization of planets in this age regime are vital to link planetary infancy (<50 Myr) and maturity (>1 Gyr).
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All authors Madyson G. Barber, Andrew W. Mann, Sydney Vach, Leah J. Boff, Andrew W. Boyle, Andrew Vanderburg, Adam L. Kraus, Benjamin M. Tofflemire, Marshall C. Johnson, Allyson Bieryla, David W. Latham, Karen A. Collins, Steve B. Howell, Richard P. Schwarz, Gregorg Srdoc, Francis P. Wilkin, Felipe Murgas, Enric Palle, Chris Stockdale

Astrophysics of Galaxies

Through the Veil: Ly$\alpha$ Illuminates the Host Galaxies of Little Red Dots

Zhiyuan Ji, Yang Sun, Mauro Giavalisco et al. (+5 more)

Little Red Dots (LRDs) are enigmatic, compact red sources ubiquitous in JWST deep fields whose physical nature remains elusive. As one of the most sensitive tracers of neutral hydrogen in galaxy environments, Ly$\alpha$ is uniquely positioned to probe the gaseous structures proposed to explain LRDs' unusual properties. We present a systematic study of Ly$\alpha$ emission in LRDs, using a sample of 110 spectroscopically confirmed LRDs at $z \geq 4$ from the A. de Graaff et al. (2025) catalog, all with NIRSpec/PRISM coverage of the Ly$\alpha$ line. We detect Ly$\alpha$ at signal-to-noise S/N $\geq$ 3 in 32 LRDs, finding Ly$\alpha$ luminosities and the distribution of rest-frame equivalent widths consistent with normal star-forming galaxies at comparable redshifts. Yet the Ly$\alpha$/H$\alpha$ ratios fall systematically below those of star-forming galaxies, and the Ly$\alpha$ luminosity tracks [O III] luminosity more closely than [O III] equivalent width, together suggesting that Ly$\alpha$ is primarily associated with the host-scale component rather than the compact component responsible for the broad Balmer lines and red continuum. For 13 LRDs at $z \gtrsim 5.5$, we construct continuum-subtracted Ly$\alpha$ maps using broadband imaging from HST/ACS or JWST/NIRCam, revealing spatially extended, asymmetric, and often offset emission relative to the rest-optical light, consistent with resonant scattering through clumpy, anisotropic gas commonly observed in high-redshift Ly$\alpha$ emitters. These results support a two-component picture in which the compact rest-optical source is embedded within a more extended host-galaxy environment whose interstellar and circumgalactic gas shapes Ly$\alpha$ escape and spatial redistribution. Ly$\alpha$ opens a new window into the relation between the compact red component, the host galaxy, and the surrounding gas in LRDs.
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All authors Zhiyuan Ji, Yang Sun, Mauro Giavalisco, Anna de Graaff, Christina C. Williams, Yongda Zhu, George H. Rieke, Marcia Rieke

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

Radio Emission from High-Frequency Gravitational Wave Point Sources

Ethan Baker and Hongwan Liu

High-frequency gravitational waves (HFGWs) in the MHz to GHz regime can convert into radio photons in the presence of astrophysical magnetic fields through the inverse Gertsenshtein effect. We show that existing radio telescopes like CHIME and FAST are excellent tools for detecting HFGW sources, significantly outperforming many existing experiments at detecting primordial black hole (PBH) mergers, the most realistic sources of transient HFGWs. Radio telescopes are also uniquely sensitive to sources of monochromatic HFGW emission, such as ultralight boson clouds formed through superradiance around PBHs, and are likely to have excellent sensitivity to generic sources of detectable HFGWs.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Geometric Matching of Local Static Regions in Cosmological Spacetimes with an Evolving Lapse

Seokcheon Lee

The generalized cosmological time (GCT) framework introduces a modified lapse function, N(t)\propto a^{b/4}, as a geometric extension of the standard FLRW description. Like other departures from $\Lambda$CDM, such constructions must remain compatible with the observed stability of local gravitational and laboratory physics. In scalar–tensor theories, this compatibility is usually achieved through dynamical screening mechanisms that suppress additional degrees of freedom in dense environments. In this work, we examine whether a locally static spacetime region can be consistently embedded within a cosmological background described by a time-dependent lapse. By embedding a static Schwarzschild interior into an expanding GCT–FLRW exterior, the Israel junction conditions are used to determine the class of background expansions that admit such a matching in the absence of a thin shell. The continuity of the extrinsic curvature yields a Friedmann-type relation that coincides with the GCT background equations of motion. This relation should be interpreted not as a new dynamical equation, but as a geometric consistency condition (GCC) associated with the matching of the two spacetime regions. In this sense, the junction does not introduce new dynamics, but provides a GCC under which a region with fixed local clocks can be embedded in a cosmological spacetime with an evolving lapse. Therefore, the analysis clarifies how locally static gravitational systems can remain compatible with a cosmological time normalization that differs from that of local proper time while preserving the standard description of local physics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Limits of the Rastall–Einstein Equivalence: Matter-Action Compatibility, FLRW Dynamics, and Exceptional Sectors

José A. C. Nogales, Karen-Luz Burgoa Rosso and Marcelo H. Alvarenga

A regular Rastall metric equation can be written exactly as an Einstein equation with a conserved algebraic source. We examine whether this source redefinition also preserves a specified local matter-action class. For an isentropic barotropic fluid, keeping the particle-density variable and its conserved current fixed gives the compatibility condition $3n\rho_{,nn}-\rho_{,n}=0$, whose non-Einstein solutions are $\rho(n)=\rho_\Lambda+C n^{4/3}$. For a minimally coupled first-derivative scalar field with the same field and kinetic variable, preservation of the local $\mathcal L_\phi(X,\phi)$ class gives $X\mathcal L_{\phi,XX}-\mathcal L_{\phi,X}=0$, and hence $\mathcal L_\phi=\frac12\mathcal A(\phi)X^2+\mathcal B(\phi)$. These are off-shell functional compatibility tests within restricted continuum action classes; they do not by themselves establish equivalence of full solution spaces or observables. Throughout the analysis, $T_{\mu\nu}$ denotes the physical energy–momentum tensor of the specified matter model. Its Einstein-form algebraic image is $\Theta_{\mu\nu}[T]=T_{\mu\nu}-\alpha g_{\mu\nu}T$. We also complete the dictionary between two Ricci–trace parametrizations, including the coupling, and state a limited on-shell variational obstruction with its exceptions. The analysis includes Poisson-level weak-field matching for an operational rest-mass density, the singular FLRW branch $D(w)=0$, a classification of exceptional parameter sectors, and a comparison of Rastall gravity with standard unimodular gravity and nonconservative trace-free completions. The regular Rastall metric equation is therefore algebraically equivalent to an Einstein equation with a redefined source; equivalence of completed matter–gravity models is a separate, stronger requirement.
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Astrophysics of Galaxies

Satellite compaction pathways: environmental drivers shaping dwarf galaxy corpulence in the TNG50 simulation

Abhner P. De Almeida, Gary A. Mamon and Gastão B. Lima Neto

We explore the physical mechanisms driving dwarf galaxy corpulence, focusing on those that end up as compact satellites. We select dwarf galaxies at $z=0$ with $\log(M_\star/{\rm M}_\odot)$ between 8.4 and 9.2 from the TNG50 hydrodynamical simulation after excluding systems flagged as potentially spurious. Compact dwarfs are defined according to the $z=0$ size-mass relation as those on the lower envelope of its main branch or on its lower-size secondary branch, while "Normal" lie on the main branch spine. We identify two robust compaction pathways and a third, more tentative, channel: 1) Compact satellites that remain rich in dark matter (DM) inhabit poorer environments having fewer mergers, favouring the accretion of lower-angular-momentum gas. This allows gas inflows that drive concentrated inner star formation and compaction, as previously found for centrals. 2) Most DM-poor satellites (which typically end up red and metal-rich for their stellar mass) undergo compaction mainly caused by tidal stripping of outer stars. Their compaction is faster when gas is present, by at least 15 per cent after correcting for the stronger tidal field. 3) For most of our few very metal-rich DM-poor Compact satellites, the major compaction phase begins with a starburst driven by ram pressure compression near first pericentre, even if much of the compaction often occurs during subsequent tidal stripping. As a result, compact dwarf satellites in TNG50 arise through distinct pathways. We discuss how numerical effects can affect this conclusion.
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Solar and Stellar Astrophysics

ALMA measurements of mass loss and wind clumping in the massive stars of the Arches cluster

James P. Perry, Raman K. Prinja, Danielle M. Fenech et al. (+1 more)

We present the first Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 (100 GHz) and Band 6 (243 GHz) continuum observations of the Arches cluster, one of the youngest and most massive stellar clusters in the Milky Way. We detect and characterise millimetre emission from 23 massive stars, including WN7-9h Wolf-Rayet stars, O-type supergiants and hypergiants. By combining our ALMA measurements with archival Very Large Array data spanning 5-22.5 GHz, we derive broadband radio-millimetre spectral indices and investigate the radial structure of stellar winds through frequency-dependent clumping diagnostics. The majority of Wolf-Rayet stars exhibit spectral indices clustered around $\alpha \approx 0.7-0.8$, consistent with predominantly thermal free-free emission from dense, partially optically thick winds. In contrast, several O-type stars show flat or negative broadband spectral indices, indicative of non-thermal synchrotron emission likely associated with colliding-wind binaries. Using millimetre flux densities, we derive clumping-scaled mass-loss rates spanning $\log(\dot{M}/\mathrm{M}_{\odot}\,\text{yr}^{-1})\approx-4.1$ to $-4.9$ for the WN stars and $-4.9$ to $-5.4$ for the O super-/hypergiants, consistent with expectations for luminous massive stars in the Galactic Centre environment. We find significant evidence of structured wind clumping at millimetre wavelengths that generally decreases with increasing radius, supporting structured wind models with strong inner-wind inhomogeneities. These results demonstrate the power of combined radio-millimetre observations for constraining mass-loss and wind structure in massive stars, and provide new insight into stellar feedback in extreme cluster environments.
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All authors James P. Perry, Raman K. Prinja, Danielle M. Fenech, Francisco Najarro

Cosmology and Nongalactic Astrophysics

Inflationary interpretation of the gravitational-wave signal in the European Pulsar Timing Array DR2 with constraints

Philippe Turgeon, Chiara Caprini, Anton Chudaykin et al. (+5 more)

The second data release of the European Pulsar Timing Array (EPTA) collaboration provides evidence for the presence of a gravitational-wave (GW) background. In this work, we explore a potential cosmological interpretation of this signal in terms of inflationary scenarios. We parametrize the tensor power spectrum in terms of the tensor-to-scalar ratio $r$, the tensor spectral index $n_t$, the reheating temperature $T_{\text{rh}}$, and the cut-off frequency $f_{\text{end}}$. We incorporate all relevant observational constraints, including those from the Cosmic Microwave Background, Big Bang Nucleosynthesis, and LIGO-Virgo-KAGRA observations. We demonstrate that imposing these constraints consistently reduces the region of parameter space that provides a viable interpretation of the EPTA signal, to $-11.66 \lesssim \log_{10}r \lesssim -1.45$, $1.32 \lesssim n_t \lesssim 2.47$, $1.78\text{ MeV} \lesssim T_{\text{rh}} \lesssim 28.2\text{ GeV}$, and $75.86\text{ nHz} \lesssim f_{\text{end}} \lesssim 14.45\text{ Hz}$ at the 95% confidence level. This favours the scenario in which the GW spectrum in the EPTA frequency band originates from tensor modes that re-entered the Hubble radius during the radiation-dominated era, allowing for a higher $r$ and a flatter spectrum. However, $T_{\text{rh}}$ must take very low values, which are challenging to explain theoretically.
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All authors Philippe Turgeon, Chiara Caprini, Anton Chudaykin, Martin Kunz, Delphine Perrodin, Ismael Cognard, Lucas Guillemot, Gilles Theureau

Cosmology and Nongalactic Astrophysics

Universal Suppression of Gravitational Waves from Black Hole Evaporation Dynamics

Xin-Chen He, Xiao-Han Ma, Misao Sasaki et al. (+1 more)

Evaporating black holes can leave distinct imprints on gravitational wave (GW) backgrounds. We show that black hole populations with finite width mass distributions exhibit a universal late time evolution governed by the evaporation dynamics rather than the details of the initial mass distribution, leading to a characteristic power law suppression of the induced GWs. We demonstrate this for a broad class of mass functions in primordial black hole (PBH) scenarios featuring an early Universe matter-dominated era, and identify the suppression of PBH-induced GWs found for critical collapse distributions as a manifestation of this general phenomenon. Our results establish a direct connection between the asymptotic GW spectrum and the underlying law of black hole evaporation.
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All authors Xin-Chen He, Xiao-Han Ma, Misao Sasaki, Volodymyr Takhistov

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Neutron stars in Poincaré gauge gravity with quadratic torsion

Chaitanya Vashistha, Radouane Gannouji and Apratim Ganguly

We study static neutron stars in an algebraic sector of Poincaré gauge gravity with parity-even and parity-odd quadratic torsion invariants. Since torsion is non-propagating, the contorsion equation is algebraic and can be solved in terms of the spin current. For a Weyssenhoff fluid satisfying the Frenkel condition, the metric field equations reduce to ordinary Riemannian Einstein equations sourced by an effective fluid containing spin-squared corrections. We derive the effective energy density, radial pressure, and tangential pressure, allowing both isotropic and anisotropic spin correlations. In contrast with Einstein–Cartan theory, the coefficient of the effective spin-spin interaction is not fixed, but depends on the dimensionless quadratic-torsion couplings. In the Einstein–Cartan limit, using the metric definition of the stress-energy tensor, the unpolarized spin contribution gives $w_{\mathrm{spin}}=-1/3$. We then derive the corresponding modified Tolman–Oppenheimer–Volkoff equations and solve them numerically using the DD2 equation of state. For the positive effective spin-spin coupling branch considered here, the torsion correction makes the stellar configurations more compact, lowers the maximum mass, and reduces the binding energy relative to the general-relativistic sequence. For the smooth weak-polarization profiles considered, spin-correlation anisotropy has only a negligible effect on the mass–radius relation.
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Astrophysics of Galaxies

Mapping Interstellar Ice Inventory toward Class 0 Protostars in Star-forming Region Orion A with JWST Data

Igor Petrashkevich, Yaroslav Pavlyuchenkov, Anna Punanova et al. (+7 more)

We present a detailed study of the spatial distribution and chemical composition of interstellar ices toward six Class 0 protostars (HOPS-56, HOPS-60, HOPS-73, HOPS-91, HOPS-96, and HOPS-108) in the Orion A molecular cloud. Using high-resolution spectroscopic data from the JWST NIRspec and MIRI MRS instruments (4.3 - 8.1 $\mu$m), we have constructed the first pixel by pixel absorption maps with a resolution of $\sim$100~AU for key ice species, including $^{13}$CO$_2$, OCN$^-$, CO, H$_2$O, NH$_4^+$, and H$_2$CO. CH$_4$ and OCS were analyzed toward the continuum peaks. The column densities were derived by fitting the observed spectra with laboratory ice analogs. We employed radiative transfer modeling, which confirmed the reliability of our column density estimates within the protostellar envelopes. Our analysis reveals significant variations in ice abundances and distributions, reflecting the physical structure and energetic processes within the envelopes. Specifically, we observe the influence of protostellar heating and outflows on the ice mantles, most notably in HOPS-60. The total ice composition is consistent with astrochemical models and covers $\sim$90% of observed ice inventory suggesting that ice is primarily formed during the prestellar stage and subsequently inherited by the protostellar envelope. Based on the abundance relative to water, the sources can be categorized into two distinct groups, possibly indicating evolutionary differences or variations in envelope density and temperature profiles.
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All authors Igor Petrashkevich, Yaroslav Pavlyuchenkov, Anna Punanova, Maksim Ozhiganov, Ruslan Nakibov, Varvara Karteyeva, Svetlana Salii, Andrej Sobolev, Mikhail Medvedev, Anton Vasyunin