Current date: 2026-07-20
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Scoring abstracts
Number of records retrieved: 604
Keyword score statistics
score 17 -- 1 abstracts
score 15 -- 1 abstracts
score 8 -- 1 abstracts
score 6 -- 2 abstracts
score 5 -- 1 abstracts
score 4 -- 2 abstracts
score 3 -- 13 abstracts
score 2 -- 21 abstracts
in total -- 42 abstracts
Articles that appeared on 2026-07-20
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[abstract 1 / 42] Wow! (score: 17)
- Title: Dynamics and geometry of the inner sub-parsec-scale JET in 3C 279 observed with the Event Horizon TelescopeAuthors: Hendrik Mueller, Sebastiano D. von Fellenberg, Ai-Ling Zeng, Paul Tiede, Thomas P. Krichbaum, Roman Gold, Tuomas Savolainen, Jae-Young Kim, Sijia Peng, Teresa Toscano, Michael Janssen, Boris Georgiev, Dhanya G. Nair, Iniyan Natarajan, Lindy Blackburn, Kazunori Akiyama, Ezequiel Albentosa-Ruiz, Antxon Alberdi, Walter Alef, Juan Carlos Algaba, Rohan Ganesh Amanaganti, Richard Anantua, Eleni Antonopoulou, Keiichi Asada, Rebecca Azulay, Anne-Kathrin Baczko, David Ball, Bidisha Bandyopadhyay, John Barrett, Michi Bauböck, Bradford A. Benson, Dan Bintley, Raymond Blundell, Katherine L. Bouman, Geoffrey C. Bower, Michael Bremer, Roger Brissenden, Silke Britzen, Avery E. Broderick, Dominique Broguiere, Thomas Bronzwaer, Sandra Bustamante, Douglas F. Carlos, John E. Carlstrom, Andrew Chael, Chi-kwan Chan, Chin-Shin Chang, Dominic O. Chang, Koushik Chatterjee, Erandi Chavez, Ming-Tang Chen, Yongjun Chen, Xiaopeng Cheng, Paul Chichura, Ilje Cho, Nicholas S. Conroy, John E. Conway, Thomas M. Crawford, Geoffrey B. Crew, Alejandro Cruz-Osorio, Yuzhu Cui, Brandon Curd, Rohan Dahale, Jordy Davelaar, Joost de Kleuver, Mariafelicia De Laurentis, Roger Deane, Jason Dexter, Vedant Dhruv, Indu K. Dihingia, Sheperd S. Doeleman, Sergio A. Dzib, Razieh Emami, Heino Falcke, Joseph Farah, Vincent L. Fish, Edward Fomalont, H. Alyson Ford, Marianna Foschi, Raquel Fraga-Encinas, William T. Freeman, Per Friberg, Christian M. Fromm, Antonio Fuentes, Peter Galison, Charles F. Gammie, Roberto Garcia, Olivier Gentaz, Ciriaco Goddi, Arturo I. Gomez-Ruiz, Brissa Gomez Miller, Jose L. Gomez, Minfeng Gu, Mark Gurwell, Kazuhiro Hada, Daryl Haggard, Ronald Hesper, Dirk Heumann, Luis C. Ho, Paul Ho, Mareki Honma, Chih-Wei L. Huang, Lei Huang, David H. Hughes, Shiro Ikeda, C. M. Violette Impellizzeri, Makoto Inoue, Sara Issaoun, Yuhei Iwata, David J. James, Buell T. Jannuzi, Britton Jeter, Wu Jiang, Alejandra Jiménez-Rosales, Michael D. Johnson, Svetlana Jorstad, Adam C. Jones, Abhishek V. Joshi, Taehyun Jung, Tomohisa Kawashima, Garrett K. Keating, Mark Kettenis, Dong-Jin Kim, Jongsoo Kim, Junhan Kim, Motoki Kino, Jakob Knollmüller, Jun Yi Koay, Prashant Kocherlakota, Yutaro Kofuji, Patrick M. Koch, Shoko Koyama, Carsten Kramer, Joana A. Kramer, Michael Kramer, Cheng-Yu Kuo, Noemi La Bella, Deokhyeong Lee, Sang-Sung Lee, Aviad Levis, Shaoliang Li, Zhiyuan Li, Rocco Lico, Greg Lindahl, Michael Lindqvist, Mikhail Lisakov, Jun Liu, Kuo Liu, Elisabetta Liuzzo, Wen-Ping Lo, Andrei P. Lobanov, Laurent Loinard, Colin J. Lonsdale, Amy E. Lowitz, Ru-Sen Lu, Nicholas R. MacDonald, Jirong Mao, Nicola Marchili, Sera Markoff, Daniel P. Marrone, Alan P. Marscher, Ivan Marti-Vidal, Satoki Matsushita, Lynn D. Matthews, Lia Medeiros, Karl M. Menten, Hugo Messias, Izumi Mizuno, Yosuke Mizuno, Joshua Montgomery, Kotaro Moriyama, Monika Moscibrodzka, Wanga Mulaudzi, Cornelia Müller, Alejandro Mus, Gibwa Musoke, Ioannis Myserlis, Hiroshi Nagai, Neil M. Nagar, Masanori Nakamura, Gopal Narayanan, Antonios Nathanail, Santiago Navarro Fuentes, Joey Neilsen, Chunchong Ni, Andy Nilipour, Michael A. Nowak, Hiroki Okino, Hector Raul Olivares Sanchez, Feryal Özel, Daniel C. M. Palumbo, Georgios Filippos Paraschos, Jongho Park, Harriet Parsons, Nimesh Patel, Ue-Li Pen, Dominic W. Pesce, Vincent Pietu, Alexander Plavin, Aleksandar PopStefanija, Oliver Porth, Cora Prather, Giacomo Principe, Dimitrios Psaltis, Hung-Yi Pu, Alexandra Rahlin, Venkatessh Ramakrishnan, Ramprasad Rao, Mark G. Rawlings, Luciano Rezzolla, Angelo Ricarte, Luca Ricci, Bart Ripperda, Jan Röder, Freek Roelofs, Cristina Romero-Cañizales, Eduardo Ros, Arash Roshanineshat, Helge Rottmann, Alan L. Roy, Ignacio Ruiz, Chet Ruszczyk, Kazi L. J. Rygl, Leon D. S. Salas, Salvador Sanchez, David Sanchez-Argüelles, Miguel Sanchez-Portal, Ali SaraerToosi, Mahito Sasada, Kaushik Satapathy, Saurabh, Karl-Friedrich Schuster, Zhiqiang Shen, Sasikumar Silpa, Randall Smith, Bong Won Sohn, Jason SooHoo, Kamal Souccar, Joshua S. Stanway, He Sun, Alexandra J. Tetarenko, Remo P. J. Tilanus, Michael Titus, Kenji Toma, Pablo Torne, Efthalia Traianou, Sascha Trippe, Matthew Turk, Akhil Uniyal, Ilse van Bemmel, Bram van den Berg, Huib Jan van Langevelde, Daniel R. van Rossum, Jesse Vos, Jan Wagner, Zhiren Wang, Derek Ward-Thompson, John Wardle, Jasmin E. Washington, Jonathan Weintroub, Maciek Wielgus, Kaj Wiik, Michael F. Wondrak, George N. Wong, Jompoj Wongphexhauxsorn, Qingwen Wu, Paul Yamaguchi, Aristomenis Yfantis, Doosoo Yoon, Andre Young, Ziri Younsi, Wei Yu, Feng Yuan, Ye-Fei Yuan, J. Anton Zensus, Shuo Zhang, Brandon Zhao, Guang-Yao Zhao,Comments: accepted for publication by A&ASubjects: astro-ph.GACreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
The 2021 Event Horizon Telescope observations resolve the innermost JET region of the BLAZAR 3C279 with unprecedented detail. The reconstructed images consistently reveal a compact core elongated nearly orthogonal to the large-scale JET axis. This rarely observed morphology recurs across multiple epochs and from 22-230 GHz and is therefore intrinsic rather than an imaging artifact. Geometric model fitting identifies several components with apparent speeds up to 10c, requiring bulk Lorentz factors greater than 10.3 and constraining viewing angles to extremely small values (smaller than one degree). Rest-frame brightness temperatures are systematically low (between 10^9 and 10^10 K), consistent with optically thin emission at 230 GHz. These results suggest that the JET bends toward the observer on sub-parsec scales, producing strong RELATIVISTIC beaming. Possible drivers of the observed JET bending and temporal evolution include the JET's interaction with the interstellar medium, kink or Kelvin--Helmholtz instabilities, MAGNETic RECONNECTion near the horizon, or binary-induced precession. However, the current temporal coverage of VLBI data remains insufficient to distinguish between these mechanisms. Continued multifrequency VLBI monitoring will be essential to constraining the dynamics and geometry of the JET base in 3C279.
[abstract 2 / 42] Wow! (score: 15) - Title: A Multiwavelength Study of a Long-Duration VHE Flare from BL Lacertae with VERITASAuthors: Atreya Acharyya, Avery Archer, Priyadarshini Bangale, Joshua Bartkoske, Wystan Benbow, James Buckley, Yu Chen, Jodi Christiansen, Alisha Chromey, Anne Duerr, Manel Errando, Miguel Escobar Godoy, Juan Escudero Pedrosa, Abe Falcone, Sydney Feldman, Qi Feng, Simon Filbert, Lucy Fortson, Amy Furniss, William Hanlon, Olivier Hervet, Claire Hinrichs, Jamie Holder, Zach Hughes, Thomas Humensky, Weidong Jin, Madalyn Johnson, Philip Kaaret, Mary P. Kertzman, Maria Kherlakian, Tobias Kleiner, Nikolas Korzoun, Sanchari Kundu, Mark Lang, Matthew Lundy, Eileen Meyer, John Millis, Connor Mooney, Patrick Moriarty, Reshmi Mukherjee, Wenmeng Ning, Rene A. Ong, Ashwani Pandey, Martin Pohl, Elisa Pueschel, John Quinn, Pazit Rabinowitz, Kenneth J. Ragan, Paul Reynolds, Deivid Ribeiro, Leandro Rizk, Emmet Thomas Roache, Iftach Sadeh, Alberto Sadun, Lab Saha, Glenn Sembroski, Ruo Shang, Megan Splettstoesser, Donggeun Tak, Anjana Talluri, James Tucci, Janeth Valverde, David Williams, Sam Wong, Margo Aller, Masoud Asadi-Zeydabadi, Ryan Hickox, Svetlana Jorstad, Sebastian Kiehlmann, Piatra Lusen, Allen Marscher, Walter Max-Moerbeck, Philipe De La Parra, Anthony Readhead, Katie Riley,Comments: 19 pages, 8 figures. Accepted for publication in the Astrophysical Journal (ApJ)Subjects: astro-ph.HECreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
We report the first observations of a long-duration very-high-energy (VHE; $E > 100$ GeV) flare from BL Lacertae (VER J2202+422), taken with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). On October 15, 2022, the FERMI-Large Area Telescope (LAT) detected elevated GeV activity originating from this BLAZAR. This triggered a multiwavelength campaign, which includes observations from VERITAS, SWIFT, NUSTAR, and select optical and radio observatories. VERITAS observed the source for a total of $\sim 9.8$ hours between September 1, 2022 and December 1, 2022. An analysis of these data yields a $\sim 28 σ$ detection of the source. While previously observed VHE flares from BL Lacertae have lasted on time-scales of minutes to days, VERITAS continued to detect flaring activity from the source for over a month ($\sim 40$ days) after the original flaring activity was detected with FERMI-LAT. Broadband spectral modeling shows that a SYNCHROTRON self-Compton (SSC) model with an external inverse-Compton (EC) component is preferred over a one-zone SSC model.
[abstract 3 / 42] Wow! (score: 8) - Title: Stern--Gerlach Spin Sorting and Dynamical Feedback in Relativistic Pair-Plasma ReconnectionAuthors: K. Nykyri,Comments: 8 pages including six figures, supplementary material with 7 pages and 1 figure. This is a re-submission to PRL and companion paper, performing a relativistic sweep-study, SpinPIC2D code description, testing and validation has been submitted as companion paper to Physical Review ESubjects: physics.plasm-ph astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We derive a Stern--Gerlach control parameter, $Ξ$, comparing spin-driven cross-sheet displacement with the RELATIVISTIC Larmor radius. It places heliospheric plasmas and most astrophysical JETs in the negligible regime, some stellar-mass black-hole coronae in a transitional regime, and MAGNETar sheets in a strong, near-QED regime. Relativistic pair-plasma simulations at fixed $γ_{\rm tr}=2$ show that increasing $Ξ$ produces, within the coupled SG+$\mathbf J_M$ model, MAGNETic-moment sorting and MAGNETization-current feedback that enhance the normalized flux-growth rate through an additional spin-kinetic pathway beyond classical pressure- and geometry-controlled pair-plasma RECONNECTion.
[abstract 4 / 42] Yes (score: 6) - Title: Self-confinement of RELATIVISTIC pair beams in MAGNETized interstellar plasmas: the case of pulsar X-ray filamentsAuthors: Luca Orusa, Lorenzo Sironi,Comments: 8 pages, 7 figures. Added a few comments, clarifications, and numerical tests, results unchanged. Matches version published by PRLSubjects: astro-ph.HE physics.plasm-phCreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
The observation of filamentary X-ray structures near bow-shock pulsar wind nebulae (PWNe) -- such as the Guitar, Lighthouse, and PSR J2030$+$4415 nebulae -- and of slow-diffusion regions around pulsars like Geminga, Monogem, and PSR J0622$+$3749, challenges the standard picture of cosmic-ray transport in the interstellar medium, implying a diffusion coefficient two orders of magnitude smaller than the Galactic average. The suppressed diffusion can be attributed to self-generated MAGNETic turbulence, driven -- via the non-resonant streaming instability -- by electron-positron pairs escaping the PWNe. This instability requires a net current, yet the beam of escaping pairs is expected to be charge-neutral. We show that a charge-neutral pair beam propagating through an electron-proton plasma can spontaneously generate a net current. Using fully kinetic two-dimensional particle-in-cell simulations with realistic mass ratio, we find that beam electrons get focused into self-generated MAGNETic filaments produced by the nonlinear evolution of the Weibel instability, while beam positrons remain unconfined. We show that in three-dimensional simulations the resulting net (positron) current drives the non-resonant streaming instability, further amplifying the MAGNETic field. This mechanism provides a pathway for the onset of charge asymmetries in initially charge-neutral pair beams and for the growth of MAGNETic fluctuations that efficiently scatter the beam particles, with implications for the formation of X-ray filaments and, potentially, for particle self-confinement in TeV halos around PWNe.
[abstract 5 / 42] Yes (score: 6) - Title: Relativistic Scaling and Magnetization-Current Feedback in Stern Gerlach-Modified Pair-Plasma Reconnection: SpinPIC2D Validation and Nonlinear RegimesAuthors: K. Nykyri,Comments: This preprint contains 8 figures and 13 pages in the main text and 19 pages of supplementary material detailing the SpinPIC2D-code and its validation. This paper has been submitted to Physical Review E and is a companion paper to a submitted letter which is posted here https://arxiv.org/abs/2605.16243Subjects: physics.plasm-ph astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We investigate the RELATIVISTIC scaling and electroMAGNETic feedback of Stern--Gerlach (SG) force driven spin transport in pair-plasma RECONNECTion with SpinPIC2D. The model advances RELATIVISTIC proper momentum and MAGNETic BMT spin precession, applies the SG force, deposits spin MAGNETization, and includes $\mathbf J_M=\nabla\times\mathbf M$ in Ampere's law. In a weak-seed scan at fixed $γ_{\rm tr}=2$, the normalized global MAGNETic flux-growth remains near the classical control-run for $Ξ\le0.1$, is $0.016$ at $Ξ=0.4$, and reaches approximately $0.12$ and $0.25$ at $Ξ=0.7$ and 1, respectively over $3\le t/τ_{\rm sp}\le7$. Because $\partial/\partial y=0$ in the 2.5-D geometry, the direct $y$-directed SG term vanishes and the enhancement is indirect: sheet-normal SG sorting restructures branch-resolved electron and positron velocity distributions which results in changes in pressure moments and generates a layered MAGNETization current. Along a fixed-$χ_{\rm sim}$ family, increasing $γ_{\rm tr}$ reduces $Ξ$ and suppresses branch sorting, whereas the matched-control flux-growth enhancement remains positive for $γ_{\rm tr}=2,3,5$. Retuning $χ_{\rm sim}$ to hold $Ξ=1$ does not preserve nonlinear similarity: both the coupling and $J_{M,y}$ increase with $γ_{\rm tr}$, and the $γ_{\rm tr}=5$ case develops a multi-X-line state. Thus $Ξ$ orders the onset of SG-modified RECONNECTion, while the nonlinear response also depends on the absolute spin coupling and MAGNETization-current amplitude.
[abstract 6 / 42] Yes (score: 5) - Title: X-ray POLARIZATION of Z-type neutron star low-mass X-ray binaries -- II. Spectropolarimetric analysisAuthors: Andrea Gnarini, Francesco Ursini, Giorgio Matt, Stefano Bianchi, Fiamma Capitanio, Massimo Cocchi, Sergio Fabiani, Ruben Farinelli, Philip Kaaret, Lorenzo Marra, Antonella Tarana,Comments: 14 pages, 4 figures, 8 tablesSubjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
IXPE has provided for the first time detailed energy- and time-resolved X-ray polarimetry of Z-type neutron star low-mass X-ray binaries (NS-LMXBs) as they move along their color-color diagrams (CCDs). These sources can reach the highest POLARIZATION observed for NS-LXMBs in the 2-8 keV range when they move along the horizontal branch. In a previous paper, we characterized the spectral state of a sample of Z-sources using the CCD and estimated the POLARIZATION with model-independent analysis. Here, we present detailed spectropolarimetric analysis for each source on each branch using data from IXPE, NICER, and NUSTAR. The continuum X-ray emission of all the sources is well described with a combination of thermal accretion disk emission plus a harder Comptonized component. In addition, reflection features, in particular the RELATIVISTICally broadened Fe line, are observed for our sources, except GX 5-1. For most of the sources and branches, the main contribution to the X-ray emission and POLARIZATION is due to Comptonization: moving from the horizontal branch (HB) to the normal branch (NB), the POLARIZATION degree (PD) in the 2-8 keV band varies from about 6% to 3-4%, while the PD is loosely constrained in the flaring branch (FB), due to the shorter exposures. These PD values are significantly higher than theoretical expectations for typical spreading or boundary layer configurations. The POLARIZATION of the disk is generally lower (below 3%) but still higher than predictions for an electron scattering-dominated, plane-parallel atmosphere above the disk observed at the corresponding inclination. Moreover, the POLARIZATION angle (PA) of the disk seems to be significantly misaligned and not perpendicular to that of Comptonization. We find no correlation between the POLARIZATION signal and the inclination, nor with the contribution of reflected photons throughout the Z-track.
[abstract 7 / 42] Yes (score: 4) - Title: Triple radio flares from tidal disruption events: JET-wind collisions and the discovery of a third radio flare from AT2020vwlAuthors: Andrew Mummery, Adelle Goodwin, Colin Christy, Kate Alexander, Noah Franz,Comments: 20 pages plus Appendices, 8 Figures. First two authors contributed equally. Comments welcomeSubjects: astro-ph.HECreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Radio flares from tidal disruption events (TDEs) are observed on two distinct timescales: prompt (around the time of optical peak) and delayed (hundreds to thousands of days after optical peak). A recent framework put forward to explain this diversity suggests that super-Eddington winds produce prompt flares while JETs launched during a disk state transition at low accretion rates produce delayed flares. A unique observational prediction of this framework is that individual sources showing both types of flares may be expected to show a third flare. This third flare will occur when the (faster) JET catches up with the (slower) wind. The observational appearance of the third flare depends on the system parameters. As the two shock fronts collide the (brighter) JET encounters a change in density, modifying its SYNCHROTRON-self-absorption frequency and observed flux. Here we discuss the observational appearance of such a scenario, and then show, in new long-term monitoring radio observations of the TDE AT2020vwl, the discovery of a third radio flare. This flare is coincident with the time at which forward modeling of the first two flares in a wind-JET framework predicts a collision between the two shock fronts. We make predictions for the long-term radio evolution of two other TDEs showing double radio flares: ASASSN-15oi (which may show a weak flare or flattening of the lightcurve) and AT2024tvd (which is predicted to imminently undergo a third flare).
[abstract 8 / 42] Yes (score: 4) - Title: Radio-detected Lya emitters at 1.88 < z < 3.52: AGN fraction and Lya emissionAuthors: Sai Zhai, Huub Röttgering, Anniek J. Gloudemans, Erin Mentuch Cooper, Maya H. Debski, Gregory Zeimann, Matt J. Jarvis, Leah K. Morabito, Donald P. Schneider, Daniel J. Farrow, Gary J. Hill, Caryl Gronwall, Yuming Fu,Comments: 14 pages, 10 figures, 2 tables. Accepted for publication in Astronomy & Astrophysics (A&A)Subjects: astro-ph.GA astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Lya emitters (LAEs) are galaxies with strong Lya emission, tracing early STAR FORMATION and ionizing radiation. Their connection to ACTIVE GALACTIC NUCLEi (AGNs) is key to understanding the mechanisms behind (extended) Lya emission. In this work, we measure the fraction of LAEs identified as radio-emitting AGN (fAGN,radio) and the fraction of radio sources that exhibit Lya emission (fLya) to investigate the connection between radio AGN activity and Lya emission at 1.88 < z < 3.52. We identify 928 sources detected in both the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the LOw Frequency ARray (LOFAR) surveys. These matches are drawn from 55,109 spectroscopically confirmed LAEs and 27,625 radio sources. After applying completeness corrections, we obtain fAGN,radio = 1.77 $\pm$ 0.04% and fLya = 18.15 $\pm$ 0.14%. The fraction fAGN,radio increases from 0.4 $\pm$ 0.1% to 9.7 $\pm$ 1.3% with increasing Lya luminosity, while fLya rises from 0.7 $\pm$ 0.1% to 55.8 $\pm$ 14.5% with radio luminosity. `LAEs with radio AGN' and `optical AGN with Lya emission' show similar radio luminosities above the AGN threshold, although optical AGN have higher Lya luminosities. We find no significant correlation between Lya luminosity and either radio luminosity or spectral index. Lya line width increases with Lya luminosity but shows no correlation with radio size. Our results show that most Lya emission at 1.88 < z < 3.52 is powered by STAR FORMATION, with radio AGN activity confined to a small luminous subset (1.77 $\pm$ 0.04%). The absence of correlations between Lya and radio properties suggests that Lya emission is governed primarily by host-galaxy gas properties rather than direct AGN JET coupling.
[abstract 9 / 42] (score: 3) - Title: Dynamics of MAGNEToviscous warped discs around compact objectsAuthors: Arthur G. Suvorov, Kostas Glampedakis,Comments: 24 pages, 12 figures, 1 table. PRD in press; minor changes to title to match journal style, and final typos correctedSubjects: astro-ph.HE gr-qc hep-thCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Accretion discs that are tilted with respect to their compact hosts can warp out-of-plane through general RELATIVISTIC frame-dragging. Warp influences disc dynamics in ways that have been studied extensively, especially as regards instabilities that might lead to rapid angular-momentum cancellation between neighboring rings of fluid and mass infall. We provide a review of warped-disc phenomena here, revisiting key hydrodynamical assumptions that impact calculations of the shear viscosity controlling instability thresholds. Relativistic effects at the level of gas-parcel orbits are included, as are external Lorentz forces applied by the compact primary's MAGNETic field. Semianalytic analysis reveals that intense MAGNETic fields can bring about new branches of warp modes and avoided crossings that significantly reduce the perpendicular viscosity at sub-Eddington accretion rates. Critical strengths required for misaligned torques to tear a thin disc may thus relax for systems like neutron star X-ray binaries or radio-loud ACTIVE GALACTIC NUCLEi.
[abstract 10 / 42] (score: 3) - Title: Search for QUASAR pairs with Gaia astrometric data IV. Confirmation of 17 dual QUASARs and 143 projected QUASARsAuthors: Zhuojun Deng, Qihang Chen, Liang Jing, Xingyu Zhu, Jianghua Wu,Comments: 10 pages, 5 figuresSubjects: astro-ph.GACreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Dual QUASARs separated at the kiloparsec scale are widely regarded as precursors to binary supermassive BLACK HOLEs and offer a key insight into the dynamical evolution of galaxy mergers. Our series of studies focuses on searching for dual QUASARs by using a selection strategy of zero proper motion and zero parallax to isolate candidate QUASARs near known ones and by follow-up spectroscopy of the candidates. This paper, the fourth in the series, reports the spectroscopic confirmations of our QUASAR pair candidates based on the spectroscopic data of the SDSS and DESI DR1. We newly identified 17 dual QUASARs and 143 projected QUASARs. The redshifts of the 17 dual QUASARs range from 0.573 to 2.758, with a median of 1.512. One notable system, J0023+0417, exhibits nearly identical spectral features in the two members and shows evidence of a potential foreground galaxy, making it a high-confidence strong gravitational lensing system. The redshifts of the 143 projected QUASARs are from 0.301 to 4.030, with a median of 1.596. Among them, four have projected distances below 30 kpc, offering valuable opportunities to probe the circumgalactic medium (CGM) of the foreground host galaxy through absorption lines.
[abstract 11 / 42] (score: 3) - Title: Quenching of X-ray emission in little red dots by both Compton-thick gas and high accretion ratesAuthors: Albert Sneppen, Darach Watson, James H. Matthews, Stuart A. Sim,Comments: Accepted for publication in A&A, 7 pages, 5 figuresSubjects: astro-ph.GA astro-ph.HECreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Little red dots (LRDs) are candidate high-redshift supermassive BLACK HOLEs accreting in dense gas. They remain undetected in X-rays. In previous work, we provided the first quantitative models that reproduce the optical and near-infrared spectra of LRDs with the \sirocco radiative transfer code, thereby constraining the properties of the surrounding gas. Here, we use these constraints to predict the X-ray attenuation produced by dense gas cocoons, and explore its dependence on Balmer-break strength, metallicity, intrinsic X-ray spectral energy distribution, and observed bandpass as a function of redshift. The X-ray constraints are very tight, requiring extinction by a Compton-thick gas column ($N_{\rm H}\sim10^{25}\,{\rm cm}^{-2}$) with moderate metallicity $0.05$-$0.1\,Z_\odot$ and intrinsically weak X-ray emission (bolometric to X-ray luminosity ratio, $k_{\rm bol,X}\gtrsim 30$), as observed in narrow-line ACTIVE GALACTIC NUCLEi with high accretion rates, to make LRDs sufficiently faint to evade detection. Intrinsically bright X-ray emitters as seen in typical broad-line ACTIVE GALACTIC NUCLEi would be detected even behind the typical Compton-thick gas columns with modest metallicity that were inferred from the optical spectra. Very low metallicity objects might be detected in X-rays even with low intrinsic X-ray luminosities, suggesting that LRDs are not (currently) chemically pristine.
[abstract 12 / 42] (score: 3) - Title: Understanding Pulsar Magnetospheres with the SKAOAuthors: L. S. Oswald, A. Basu, M. Chakraborty, B. C. Joshi, N. Lewandowska, K. Liu, M. E. Lower, A. Philippov, X. Song, P. Tarafdar, J. van Leeuwen, A. L. Watts, P. Weltevrede, G. Wright, J. Benáček, A. Beri, S. Cao, P. Esposito, F. Jankowski, J. C. Jiang, A. Karastergiou, K. J. Lee, N. Rea, D. Vohl,Comments: Published in Advancing Astrophysics with the SKA II (AASKAII), 2026 (arXiv:2606.20366). Report-no:AASKAII/Oswald01. Advancing Astrophysics with the SKA II (AASKAII) outlines the transformative scientific advances that will be enabled by the SKA telescopes. N.B. a version of this article was previously published as part of a Special Issue, linked at arxiv:2512.16157Subjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make them the ideal instruments for studying the pulsar MAGNETosphere. This chapter describes the advances that have been made in pulsar MAGNETosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar MAGNETosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.
[abstract 13 / 42] (score: 3) - Title: Multimessenger prospects of quasi-periodic eruptionsAuthors: Vojtěch Witzany, Alessia Franchini, Matteo Bonetti, Luca Broggi,Comments: Invited chapter for the book "Mysterious Repeating Signals from Centers of Galaxies" (Eds. Dheeraj Pasham, Eric Coughlin, Riccardo Arcodia, Petra Sukova, Itai Linial, Springer Singapore, expected in 2027)Subjects: astro-ph.HE gr-qcCreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Quasi-Periodic Eruptions (QPEs) are recurring soft X-ray transients that may be generated by inspirals of stellar-mass objects spiraling into supermassive BLACK HOLEs, known as extreme mass ratio inspirals (EMRIs). Independently, EMRIs and the gravitational-wave signals they generate are one of the key targets for the Laser Interferometer Space Antenna (LISA). What is the potential of a coincident detection of EMRIs both as a QPE and by LISA? ElectroMAGNETic counterparts to LISA events would provide sky localization, enable standard siren measurements of the Hubble constant and constrain formation mechanisms of the corresponding inspirals. Combined observations would link the accurate measurements of BLACK HOLE masses and spins to their galactic nuclear environments and would thus enable lasting synergies with various observations across the electroMAGNETic spectrum. However, most of the currently known QPEs imply EMRI orbital periods that place the frequencies of the corresponding gravitational-wave signal out of the LISA sensitivity band. Additionally, the selection biases of QPE detections and the LISA instrument may preclude a coincident detection. Future searches should focus on expanding the QPE catalogs and ultimately hunt for ``golden'' short-period QPEs that correspond to EMRIs that fall within the LISA band.
[abstract 14 / 42] (score: 3) - Title: Large-scale emission from gamma-ray binaries: the case of LS 5039Authors: J. R. Martinez, V. Bosch-Ramon,Comments: 12 pages, 8 figures. Accepted for publication in Astronomy & AstrophysicsSubjects: astro-ph.HECreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Abridged abstract: Context: Gamma-ray binaries hosting a non-accreting neutron star and a massive star exhibit multi-wavelength emission on different spatial scales. The interaction between their winds produces an outflow that can inflate a bubble or form a bow shock as it interacts with the surrounding medium. LS 5039 shows extended (1 pc-scale) X-ray emission that may arise from one of these large-scale structures. Aims: We explain and predict the large-scale emission from LS 5039. Methods: We modelled the thermal and non-thermal emission from five scenarios, representing different evolutionary phases, assuming particle acceleration at the mixed-wind termination shock: three bubble scenarios, treated with a one-zone model, and two bow-shock scenarios, studied with a multi-zone approach. We also investigated the radiation from escaping particles. Results: The extended X-rays are best explained as SYNCHROTRON radiation. Some scenarios predict detectable radio emission, while escaping particles may provide a minor steady contribution to the gamma rays in the powerful bow-shock scenario. Escaping protons with energies of 0.1-1 PeV could also inject up to $\sim10^{36}$ erg s$^{-1}$ into Galactic COSMIC RAYs for optimistic injection luminosities. Conclusions: Gamma-ray binaries can efficiently accelerate particles on large scales, producing broadband emission and 0.1-1 PeV COSMIC RAYs. Our results can guide future multi-wavelength observations to constrain the large-scale interaction, age, and birthplace of LS 5039.
[abstract 15 / 42] (score: 3) - Title: Implications of the UV/optical Plateau of AT2018cowAuthors: Wenbin Lu, Anthony L. Piro,Comments: 15 pages, 5 figures, plus appendix. Comments, big or small, are very welcome!Subjects: astro-ph.HE astro-ph.SRCreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
AT2018cow, the prototypical luminous fast blue optical transient (LFBOT), shows a slowly fading plateau in the UV/optical light lasting at least 5 years after the explosion. The plateau SED is blackbody-like with temperature $\gtrsim$ 2e4 K and an emission radius ~40 Rsun, which has been attributed to a geometrically thin accretion disk around a compact object. Viscously powered disk models, however, require an unusually massive BLACK HOLE $\gtrsim$ 200 Msun (for viscosity parameter $α$ > 0.01). Moreover, accretion onto such a massive BLACK HOLE produces X-ray emission that is likely in tension with the XMM-Newton constraint, unless the X-ray is highly anisotropic or absorbed. We propose instead that the UV/optical emission arises from the photosphere of a super-Eddington wind launched from the inner disk, together with irradiation and reprocessing by the geometrically thin outer disk. Fitting the model to four-band HST photometry at t ~ 4 yr, we find that all accretors from 1.4 Msun neutron star to ~100 Msun BLACK HOLE produce similarly good fits. This degeneracy arises because the wind photospheric color temperature depends only weakly on the accretor mass. We also find that, at NIR-MIR wavelengths (1 to 10 um), wind free-free emission differs by an order of magnitude across the allowed mass range, providing a potential discriminant accessible to JWST. Another potential signature to differentiate the accretor mass and disk composition is the recombination line emission (HeII1640 or H$α$) from the disk wind. The inferred disk parameters from our model are consistent with a micro-tidal disruption event, either tidal disruption or merger with a companion star, in which an initially geometrically thick disk transitions to a thin phase within the first year and subsequently the thin outer disk evolves on the observed ~10 yr viscous timescale.
[abstract 16 / 42] (score: 3) - Title: 22 Newly Identified Repeating Changing-look AGNs and Evidence for Extreme Broad-line Region BreathingAuthors: Litao Zhu, Zhongxiang Wang, Alok C. Gupta, Yiyang Zeng, P. U. Devanand, Karan Dogra, Riya Bhowmick, Ju-Jia Zhang,Comments: 22 pages, 11 figures, 2 tables, submitted to ApJSubjects: astro-ph.GA astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Changing-look ACTIVE GALACTIC NUCLEi (CL AGNs) show the appearance or disappearance of broad emission lines on timescales of years. Among them, the repeating CL (RCL) AGNs may provide a clear clue for our understanding of the CL transitions because the same nucleus crosses some physical boundaries more than once. We search for RCL AGNs in known CL-AGN samples using long-term multi-band light curves, and selected 34 candidates for spectroscopic follow-up. We confirm 25 RCL AGNs, including 22 newly identified cases. Properties of these RCL AGNs are analyzed. The observed rest-frame intervals of the second transitions are mostly 3--4 yr, while the variations of the optical light curves suggest that some transitions might occur on timescales of several months. The latest spectra show that the on/off states correspond to higher/lower Eddington-ratio, in the expected direction relative to the parent CL-AGN samples. As seven RCL AGNs are well covered by nearly continuous single-band light curves, their on/off states can be found to follow multi-year optical excursions, and their Eddington ratios vary consistently with the photometric changes. We also find that the H$β$-only transitions occur at higher Eddington ratios than the transitions involving both H$α$ and H$β$, suggesting a line-dependent Broad-Line-Region (BLR) visibility threshold. These results support a picture in which different accretion-flow processes drive reversible changes in the central ionizing emissions, while the observed RCL transitions are produced by the BLR breathing across line-dependent visibility thresholds.
[abstract 17 / 42] (score: 3) - Title: Viscous Accretion Disks around Regular Black Holes Embedded in a Quintessence Dark Energy Field: Beyond the Novikov--Thorne ApproximationAuthors: Sandip Dutta,Comments: 12 pages, 5 figuresSubjects: gr-qc hep-thCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We develop a comprehensive RELATIVISTIC framework for geometrically thin, optically thick Shakura--Sunyaev $α$-viscous accretion disks around rotating Hayward regular BLACK HOLEs embedded in a quintessence DARK ENERGY (DE) field. The static, spherically symmetric building blocks of our spacetime are each exact solutions of the Einstein field equations, sourced respectively by the Hayward non-linear electroMAGNETic field and a quintessence fluid with equation-of-state parameter $ω<-1/3$; we combine and rotate them following standard practice for this class of models, and we are explicit throughout about the resulting metric's phenomenological status. Abandoning the stress-free inner boundary of the Novikov--Thorne--Page (NTP) model, we analytically incorporate a non-zero viscous torque $\Tcal_{\rm in}$ at the innermost stable circular orbit (ISCO) via the RELATIVISTIC vertical epicyclic frequency $\Obot(r)$. We prove that the bolometric efficiency $η=[1-E(\rISCO)]\times100\,\%$ is strictly independent of the viscosity parameter $α$ but sensitive to both the Hayward length scale $l$ and the DE density $ρ_0$, establishing a rigorous two-observable degeneracy-breaking strategy. At benchmark parameters ($j=0.4$, $l=0.5M_{\BH}$, $ρ_0=2\times10^{-4}$), the combined geometry yields $η=8.71\,\%$, substantially above the vacuum Kerr value $7.51\,\%$ at the same spin. The viscosity correction $δ\Fcal/\Fcal_{\rm NTP}$ diverges at $r\to\rISCO^+$, amplified by the geometric odification of the boundary pressure: the viscosity amplification ratio rises from $0.80$--$4.52\,\%$ (vacuum Kerr) to $0.87$--$6.76\,\%$ (Hayward+DE) at $α=0.1$, providing a clean, monotonic observational discriminator accessible to \textit{NICER} and \textit{NUSTAR}, independent of the bulk spectral normalisation.
[abstract 18 / 42] (score: 3) - Title: Stable X-ray reverberation lags in the BLACK HOLE X-ray binary SWIFT J1727.8-1613Authors: Wei Yu, Sinan Allak, Zi-Xu Yang, Xiao Fan, Andrea Santangelo, Tian-hao Xie,Comments:Subjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Aims. We investigate the evolution of X-ray reverberation lags in the BLACK HOLE X-ray binary SWIFT J1727.8-1613 during its 2023 outburst, with the aim of probing the inner accretion flow geometry across spectral states. Methods. We analyzed NICER observations covering the low-hard state (LHS) and hard-intermediate state (HIMS). The time lags were computed using Fourier-based techniques, and we constructed lag-frequency and lag-energy spectra. To obtain a robust estimate of the soft lag amplitude, we focused on a frequency range in which the reverberation signal dominates and remains stable, thereby minimizing contamination from hard lags and phase-wrapping effects. Results. The soft lag amplitude increases rapidly from the LHS to the early HIMS and then stays near 10 ms throughout the HIMS. In the frequency range in which reverberation lags prevail, the lag shows little dependence on Fourier frequency. On the other hand, the observed low-frequency lags change from hard-lag dominated to soft-lag dominated, with amplitudes comparable to those measured at higher frequencies. Conclusions. These results suggest that the reverberation lag varies little during the HIMS, consistent with a relatively stable inner accretion geometry during this state. The apparent evolution of the lag amplitude from the LHS to the HIMS can be largely explained by the diminishing effect of hard lags and does not necessarily require significant changes in the intrinsic light-travel timescale. SWIFT J1727.8-1613 therefore provides a case in which the reverberation signal can be studied with reduced contamination over a broad frequency range, offering new insight into the evolution of the accretion geometry in BLACK HOLE X-ray binaries.
[abstract 19 / 42] (score: 3) - Title: A cosmic-ray loaded nascent outflow driven by a massive star clusterAuthors: Marianne Lemoine-Goumard, Lucia Härer, Lars Mohrmann, Romain Bernet, Jim Hinton, Giada Peron, Brian Reville, Luigi Tibaldo, Thibault Vieu,Comments: Published by Nature CommunicationsSubjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Cosmic rays are widely held to drive outflows from star-forming galaxies and profoundly influence galaxy evolution. Direct evidence for cosmic-ray carrying outflows is however lacking. At the same time there is increasing awareness of the importance of massive star clusters in the acceleration of COSMIC RAYs in galaxies. Here we report on the discovery of a nascent outflow driven by the massive star cluster Westerlund 1. Giga-electronvolt gamma-ray emission coincident with a cavity visible in atomic hydrogen traces the emergence of a population of RELATIVISTIC electrons out of the Galactic Disc. The emission is offset from tera-electronvolt gamma-ray radiation surrounding the cluster, but connects to it smoothly spectrally and spatially. The implied energy density of co-accelerated protons and nuclei, assuming standard non-thermal electron/proton injection efficiencies, is at least an order of magnitude higher than that in the general interstellar medium. These particles therefore have the potential to dynamically influence the outflow. This discovery suggests that cosmic-ray loaded outflows may be a common feature of young massive star clusters, with implications for the transport of COSMIC RAYs into the halo of the Galaxy.
[abstract 20 / 42] (score: 3) - Title: Non-thermal emission from the vicinity of the MAGNETar CXOU J171405.7-381031Authors: Manoel F. Sousa, Rita. C. Anjos,Comments: Accepted for publication in MNRASSubjects: astro-ph.HE astro-ph.SR hep-phCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Magnetars are neutron stars with ultra-strong MAGNETic fields ($B \sim 10^{14}$-$10^{15}$ G) and are promising candidates for high-energy particle acceleration. We present a multiwavelength analysis of the region surrounding CXOU J171405.7-381031, a MAGNETar associated with the SUPERNOVA remnant (SNR) CTB 37B. The broadband spectral energy distribution spanning radio to TeV energies is modeled using leptonic and lepto-hadronic scenarios, with particle populations constrained using Markov Chain Monte Carlo techniques. Within an SNR framework, both scenarios provide acceptable descriptions of the gamma-ray data. The purely leptonic model reproduces the overall spectral shape but slightly underestimates the highest-energy flux measured by H.E.S.S., whereas a lepto-hadronic interpretation offers an improved description above $\sim 10$ TeV, with inverse-Compton scattering dominating the GeV emission and neutral-pion decay contributing at the highest energies. The required proton energy ($W_{\rm p} \gtrsim 10^{51}$ erg) can be substantially reduced if the remnant interacts with a dense ambient medium. A MAGNETar wind nebula scenario can reproduce the broadband spectrum but is strongly disfavored by the observed source morphology. Simulated Cherenkov Telescope Array Observatory (CTAO) observations indicate that exposures of $\sim 50$ h will constrain the proton cut-off energy, enabling a decisive test of hadronic emission in this region.
[abstract 21 / 42] (score: 3) - Title: Discovery of $γ$-Ray Pulsations from the Extreme-Spin-Down Millisecond Pulsar PSR J0435+3233Authors: Mengqing Zhang, Shengbin Pei, Pengfei Zhang,Comments: 6 pages, 3 figuresSubjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Motivated by the recent discovery of PSR~J0435+3233, a millisecond pulsar with an exceptionally large period derivative of $\dot{P}=4.9\times10^{-17}\ {\rm s\,s^{-1}}$ and a high spin-down luminosity of $\dot{E}=5.89\times10^{37}\ {\rm erg\,s^{-1}}$, we analyze $\sim$17~yr of observations obtained with the \textit{FERMI} Large Area Telescope for the pulsar. We identify the cataloged source 4FGL~J0435.5+3232, located only $0.01^{\circ}$ from the radio timing position, as the $γ$-ray counterpart of PSR~J0435+3233. Using $γ$-ray events collected within the validity interval of the radio timing ephemeris, we detect its $γ$-ray pulsations at a $\sim6.8σ$ confidence level. In this interval, the phase-resolved analysis shows that the pulsed emission is concentrated predominantly within the rotational-phase of $ϕ\sim0.44$--$0.69$. We also derive its $γ$-ray luminosity of $L_γ=6.26\times10^{32}\ {\rm erg\,s^{-1}}$, assuming a distance of 1.2~kpc and isotropic emission. This luminosity corresponds to an apparent $γ$-ray efficiency of $η_γ\sim1.1\times10^{-5}$, revealing an exceptionally low $γ$-ray output despite the pulsar's young-pulsar-like rotational-energy budget. Our detection establishes PSR~J0435+3233 as a $γ$-ray MSP, and the striking combination of its high spin-down power and low apparent $γ$-ray efficiency provides a new probe of particle acceleration, radiation beaming, and viewing geometry in the MAGNETospheres of millisecond pulsars with extreme rotational properties.
[abstract 22 / 42] (score: 2) - Title: Optical appearance of the Konoplya-Zhidenko rotating non-Kerr BLACK HOLE surrounded by a thin accretion diskAuthors: Ke-Jian He, Yi Liu, Chen-Yu Yang, Xiao-Xiong Zeng,Comments: 29 pages, 15 figuresSubjects: astro-ph.HE gr-qcCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
In this study, we investigate the optical appearance of rotating Konoplya-Zhidenko non-Kerr BLACK HOLEs in the presence of thin accretion disks, with the aim of examining whether the information of deformation parameters manifest in observable signatures. By employing a fisheye camera model in conjunction with backward ray-tracing techniques, we simulate images for both prograde and retrograde accretion scenarios. The results indicate that the deformation parameter $ξ$ can partially mitigate the shadow deformation induced by the rotation parameter $a$. The inner shadow displays characteristic morphological transformations at varying observation angles, transitioning from an axisymmetric circular form at low angles to a hat-like configuration at higher angles. Furthermore, at high observational inclination angles, the direct image and the lensed image become distinctly discernible, and an increase in the deformation parameter $ξ$ enhances the observed intensity of the image. Interestingly, the motion behavior of the accretion flow influences the observed intensity distribution on the screen, a finding that is consistent with the redshift distribution. Hence, variations in the deformation parameter $ξ$, the observation angles, and the motion behavior of the accretion flow collectively influence the observable appearance of the BLACK HOLE. We expect this work to provide valuable references for identifying observable signatures of spacetime deviations from general relativity.
[abstract 23 / 42] (score: 2) - Title: A framework for realisable data-driven active flow control using model predictive control applied to a simplified truck wakeAuthors: Alberto Solera-Rico, Carlos Sanmiguel Vila, Stefano Discetti,Comments: 38 pages, accepted versionSubjects: physics.flu-dynCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We present a data-driven active flow control framework designed for deployment with few non-intrusive sensors. The method builds upon Artificial Intelligence driven reduced-order predictive models based on Long-Short-Term Memory (LSTM) networks and efficient gradient-based Model Predictive Control (MPC). The model uses only surface-mounted pressure probes to infer the wake state, and is trained entirely offline on a dataset built with open-loop actuations, thus avoiding the complexities of online learning. Sparsification of the sensors needed for control from an initially large set is achieved using SHapley Additive exPlanations (SHAP). A parsimonious set of sensors is then deployed in closed-loop control with MPC. The framework is tested in numerical simulations of a two-dimensional truck model at Reynolds number 500, with pulsed-JET actuators placed in the rear of the truck to control the wake. The resulting LSTM-MPC achieved a drag reduction of 12.8\%.
[abstract 24 / 42] (score: 2) - Title: Padé Approximants for cosmic Dispersion MeasuresAuthors: Marios Kalomenopoulos, Jiaming Zhuge,Comments: Submitted in JCAP (updated version with applications on cosmological inference). Comments welcome!Subjects: astro-ph.HE astro-ph.COCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Fast Radio Bursts (FRBs) have become an indispensable tool for studying the ``missing baryons'', the Universe's ionisation properties, as well as the cosmological parameters. This is achieved by analysing the diffuse dispersion measure (${\rm DM}_{\rm diff}$) of FRBs as a function of redshift. However, the rapidly increasing data size requests more and more computational resources. In this work, we first develop an accelerated method for any cosmic dispersion measure by deriving an analytical approximation formula for flat, $Λ$CDM and $w$CDM universes. Focusing on FRBs, we show that our approximation works well for the ranges $0.01 \leq z \leq 2$, $0.2 \leq Ω_m \leq 1.0$ and $-3.0 \leq w \leq -0.5$, with relative error to a numerically evaluated ${\rm DM}_{\rm diff}$ always smaller than $3.5 \%$ (in the worst case scenario). This error remains below observationally relevant ${\rm DM}$ scatter and is especially small near the concordance $Λ$CDM cosmology. Additionally, we perform a cosmological analysis of simulated FRB data and show that our approximation gives robust and unbiased results, even when applied in regions of parameter space where its relative error becomes larger than $3\%$. Finally, the approximation is more than $15$ ($2$) times faster than the numerical solution of $Λ$CDM ($w$CDM), and can reach a timing improvement of a factor of $25$ when used in an MCMC cosmological inference.
[abstract 25 / 42] (score: 2) - Title: FROST-CLUSTERS -- III. Metallicity-dependent intermediate mass BLACK HOLE formation by runaway collisions in dense star clustersAuthors: Antti Rantala, Thorsten Naab, Natalia Lahén, Klaus Reuter, Markus Rampp, Martyna Chruślińska, Bastián Reinoso,Comments: 27 pages, 20 figures (including the appendix). Accepted for publication in MNRAS. Section 6 of the previous arXiv submission will be submitted as a separate studySubjects: astro-ph.GACreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We explore the formation of intermediate mass BLACK HOLEs (IMBHs), potential seeds for supermassive BLACK HOLEs (SMBHs), via runaway stellar collisions for a wide range of star cluster (surface) densities ($4\times10^3 M_\odot$ pc$^{-2} \lesssim Σ_\mathrm{h} \lesssim 4\times10^6 M_\odot$ pc$^{-2}$) and metallicities $(0.01 Z_\odot \lesssim Z \lesssim 1.0 Z_\odot)$. Our sample of isolated (>1400) and hierarchical (30) simulations of young, massive star clusters with up to $N=1.8\times10^6$ stars includes collisional stellar dynamics, stellar evolution, and post-Newtonian equations of motion for BLACK HOLEs using the BIFROST code. High stellar wind rates suppress IMBH formation at high metallicities ($Z\gtrsim0.2 Z_\odot$) and low collision rates prevent their formation at low densities ($Σ_\mathrm{h}\lesssim 3\times10^4 M_\odot$ pc$^{-2}$). The assumptions about stellar wind loss rates strongly affect the maximum final IMBH masses ($M_\bullet\sim 6000 M_\odot$ vs. $25000 M_\odot$). The total stellar mass loss from collisions and collisionally boosted winds before $t=3$ Myr can together reach up to $5$--$10\%$ of the final cluster mass. We present fitting formulae for IMBH masses as a function of host star cluster $Σ_\mathrm{h}$ and $Z$ which can be used to seed SMBHs in high resolution cosmological hydrodynamical simulations and in semi-analytic models for galaxy formation. Our results favour IMBH formation in dense low metallicity environments similar to $z\sim10$ James Webb Space Telescope (\textit{JWST}) proto globular clusters. IMBH formation is suppressed in the high metallicity and low density conditions of the local Universe.
[abstract 26 / 42] (score: 2) - Title: Little Red Dots as Obscured Little Blue Dots: A Super-Eddington Unification ModelAuthors: Piero Madau, Roberto Maiolino,Comments: 15 pages, 9 figures, submitted to A&A, revised versionSubjects: astro-ph.GA astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We investigate whether Little Red Dots (LRDs) are the dust-reddened, high-inclination counterparts of compact, blue broad-line AGNs (Little Blue Dots, LBDs) powered by super-Eddington accretion. We model the central engine as a geometrically thick, radiation-pressure supported accretion flow whose funnel produces strongly anisotropic, intrinsically blue ionizing continua, coupled to an equatorially concentrated BLR and dusty reprocessing clouds with modest covering factor. Using inclination-dependent spectral energy distributions (SEDs) as input to Cloudy, we show that the extreme broad Halpha EWs of JWST LRDs can be reproduced with global BLR covering factors of only 10%, fully consistent with standard Type~1 AGNs and far below unity. Large Balmer EWs arise because self-shadowing suppresses the high-inclination optical continuum while the BLR is illuminated by an ionizing-rich EUV SED. Weak high-ionization lines (e.g. HeII4686) follow from the orientation-dependent suppression of the XUV/soft X-ray continuum toward equatorial directions, without requiring a fully enclosing gaseous cocoon. Applying a gray dust attenuation law with AV~3 along high-inclination (LRD-selected) sightlines, our fiducial model reproduces the V-shaped UV-optical continua of LRDs and the large Balmer decrements; strong Balmer breaks arise only along the most obscured sightlines. A compact equatorial dust structure with modest global covering factor intercepts and reradiates only a small fraction of the bolometric luminosity, yielding a modest hot-dust bump and far-IR/sub-mm output consistent with current measurements and limits and implying small dust masses. This single-framework model links LRD and LBD observables through orientation, predicting correlated trends in Halpha EW, Balmer decrement, Balmer break, high-ionization line strengths, and IR emission.
[abstract 27 / 42] (score: 2) - Title: Stellarator island divertor shape optimization for reduced peak heat fluxesAuthors: Avigdor Veksler, Aaron Bader, Heinke Frerichs, Elizabeth Paul,Comments: 15 pages, 10 figuresSubjects: physics.plasm-phCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
An automated algorithm to construct island divertors for stellarators is presented and is used to find divertors that meet heat load requirements determined by material limits. The algorithm uses just two initial conditions: two starting coordinates on the island separatrix chosen by the user. We leverage the simplicity of the algorithm to explore the divertor parameter space in a fixed MAGNETic equilibrium. Heat loads are approximated using the field line diffusion model implemented in the \texttt{FLARE} code. Divertor solutions that satisfy heat load requirements while maintaining a high power fraction captured are found using a parameter scan and a Bayesian optimization routine. The optimization finds divertors that perform the same as the parameter scan, but with a 95\% reduction in computational cost. The resulting divertors satisfy heat load requirements across varying cross-field heat diffusivities. Optimization over various islands in the equilibrium shows that low-elongation islands are the easiest to find divertors that satisfy heat flux requirements. This algorithm presents a simple parameterization for island divertors and facilitates further physics and optimization studies.
[abstract 28 / 42] (score: 2) - Title: Ringdown and lensing of triple systemsAuthors: Vitor Cardoso, Giuseppe Ficarra, Jaime Redondo-Yuste, João Sieiro dos Santos,Comments: 19 pages, 10 figures. Matches the published versionSubjects: gr-qc astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Triple systems have progressively been recognized as ubiquitous in our Universe and provide a good testing ground for wave generation and propagation in nontrivial environments. We study the dynamics of triple systems in a fully nonlinear setting. In particular, we analyze numerical relativity simulations of head-on collisions of BLACK HOLEs in the presence of a companion. We show evidence for Doppler and gravitational redshift in the ringdown, and clear signs of amplification by lensing. In certain cases, we also show the appearance of a second image, with hints of resonant mode excitation. Our results pave the way for the understanding of mergers in the vicinity of massive companions. Even in extreme setups we do not find collapse to BLACK HOLEs from lensed gravitational radiation.
[abstract 29 / 42] (score: 2) - Title: Forest without Trees is still Fruitful: Constraints on the thermal state of the neutral IGM at $z\approx5.6$ with the 21-cm forest power spectrumAuthors: Tomáš Šoltinský, Arnab Chakraborty, Girish Kulkarni, Matteo Viel, Cathryn M. Trott, Rashmi Sagar, Nithyanandan Thyagarajan, James S. Bolton, Benedetta Ciardi, Emma V. Ryan-Weber, Soumak Maitra, Abhirup Datta, Nirupam Roy,Comments: 16+3 pages, 12+5 figures, Submitted to Nature Astronomy, Comments welcomeSubjects: astro-ph.COCreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Neutral regions of the intergalactic medium (IGM) during the Epoch of Reionization (EoR) remain largely unexplored due to the limitations of existing probes. Owing to discoveries of numerous high-redshift radio-bright sources, the 21-cm forest, a series of absorption features imprinted by the neutral IGM in the spectra of such sources, now offers an attractive probe of the thermal and ionization state of the predominantly neutral IGM at $z\gtrsim5.5$. We analyse archival upgraded Giant Metrewave Radio Telescope (uGMRT) observations of J352-15, the brightest known radio-loud QUASAR in the EoR ($z=5.82$), to measure the one-dimensional (1D) power spectrum of the 21-cm forest. By comparing the observed power spectrum with forward-modelled synthetic spectra generated from cosmological simulations spanning a wide range of ionization and X-ray pre-heating scenarios, we perform Bayesian inference even in the absence of a statistical detection. We also present an independent Murchison Widefield Array measurement, although its lower sensitivity prevents competitive constraints. Using uGMRT, we achieve a sensitivity of $3.62\,\rm mJy\,beam^{-1}$ per $6.1\,\rm kHz$ channel. While we do not detect the 21-cm forest statistically, the null detection jointly constrains the mean neutral hydrogen fraction, $\langle x_{\rm HI}\rangle$, and the mean temperature of the neutral IGM, $\langle T_{\rm HI}\rangle$. At the $68\%$ credible level, our analysis disfavours cold and substantially neutral IGM models at $z\approx5.6$, including models with $\langle T_{\rm HI}\rangle \lesssim 27\,\rm K$ for $\langle x_{\rm HI}\rangle=0.1$. These limits probe parameter space allowed by existing Ly$α$ and 21-cm observations, indicating substantial pre-heating of the neutral IGM above the adiabatic cooling floor. This demonstrates that the 21-cm forest has entered the regime of observationally informative statistics.
[abstract 30 / 42] (score: 2) - Title: Polarization geometry of MAGNETohydrodynamic turbulenceAuthors: Raphael Skalidis,Comments: SubmittedSubjects: astro-ph.SR physics.flu-dynCreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
We introduce a geometric framework that organizes the second-order statistics of the Elasser fields into POLARIZATION states on generalized Poincaré spheres. In this representation, energy, cross-helicity, residual energy, and the phase lag between counter-propagating wave packets emerge as complementary POLARIZATION parameters. We derive a Bloch-analogue equation governing the evolution of POLARIZATION states and show that distinct POLARIZATION geometries are associated with different cascade dynamics. The framework predicts that transitions in the turbulent spectral scaling coincide with changes in the POLARIZATION state of the interacting modes.
[abstract 31 / 42] (score: 2) - Title: Observations of X-ray quasi-periodic eruptionsAuthors: Thomas Wevers, Joheen Chakraborty, Erwan Quintin, Michal Zajaček, Margherita Giustini,Comments: Invited review chapter for the book "Mysterious Repeating Signals from Centers of Galaxies" (Eds. Dheeraj Pasham, Eric Coughlin, Riccardo Arcodia, Petra Sukova, Itai Linial, Springer Singapore, expected in 2027). 39 pages, 11 figuresSubjects: astro-ph.HE astro-ph.GACreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Quasi-periodic eruptions (QPEs) are a novel class of repeating nuclear transients, discovered exclusively in the X-ray band to date. Since their initial discovery in 2019, the QPE sample has grown to 13 sources, exhibiting large amplitude, quasi-regular eruptive variability patterns that are distinct from previously known modes of massive BLACK HOLE variability. In this chapter, we provide a comprehensive overview of their observational characteristics. We review the X-ray spectral and timing properties of QPE eruptions, their long-term evolution, as well as the underlying quiescent emission, which is well described by thermally dominated, compact accretion disks. We discuss population-level emerging trends and selection biases, and present an updated census of their host galaxy properties. We also highlight the growing body of evidence pointing to strong connections between QPEs and tidal disruption events. Finally, we briefly summarize the key observational constraints on proposed QPE model interpretations, before looking ahead to the observational challenges and opportunities that will shape future progress in understanding this emerging population of nuclear transients.
[abstract 32 / 42] (score: 2) - Title: Lattice Boltzmann Methods for Navier-Stokes Equations in General Orthogonal Coordinates for Efficient Flow Simulations using Nonuniform Clustered GridsAuthors: Eman Yahia, Kannan Premnath,Comments: 86 pages, 20 figuresSubjects: physics.flu-dyn physics.comp-phCreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Resolving multiscale fluid flows or boundary layers effectively requires the use of nonuniform meshes with local grid clustering. The standard lattice Boltzmann method (LBM), a kinetic theory-based approach for computational fluid dynamics, however, is restricted to the use of uniform Cartesian grids. We present new and improved formulations of the LBM that accommodate continuously varying spatial grids via coordinate transformations to simulate the Navier-Stokes equations (NSE) in the general orthogonal coordinates (GOC). They are constructed using a Chapman-Enskog analysis to specify the equilibrium moments of the distribution functions and the geometric force terms used in the collision step to be dependent on the local metric factors and their spatial derivatives, along with the density, momentum and their fluxes, and some correction terms related to the normal velocity gradients so as to accurately represent the NSE in the GOC. The resulting GOC-LBM importantly maintains the simplicity of the collide-and-stream approach and is Galilean invariant that is free of the cubic velocity artifacts. Our GOC-LBM is general and modular in that it can be used with any collision model with appropriate modifications to the equilibria and forcing terms. We present its implementation details for a variety of collision models while the central moments-based model using multiple relaxation times was found to be the most robust in practical implementations. We validate the GOC-LBM through numerical simulations for various benchmark flow problems. Moreover, we demonstrate significant computational advantages of our approach for a case study on simulating boundary layer flows efficiently that involves coupling the GOC-LBM for the NSE with a new GOC-LB scheme for solving the MAGNETic induction equation for MAGNETohydrodynamics (MHD), and for another case study involving orthogonal curvilinear grids.
[abstract 33 / 42] (score: 2) - Title: Uncovering Hierarchical Sub-Population of Binary Black HolesAuthors: Muhammad Zeeshan, Richard O'Shaughnessy,Comments:Subjects: astro-ph.HECreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Enabled by improved instruments with increasing sensitivity, the ongoing gravitational wave census now contains 259 binary BLACK HOLEs, numerous enough to unveil trends, substructure, and subpopulations which may provide key clues to their underlying formation mechanisms. In this work, motivated by evidence for multiple formation channels including hierarchical formation, we build a natively multi component mixture model for the binary BLACK HOLE population, in which each component has an independently recovered rate, mass, spin, and spin misalignment model. (The components share a common redshift distribution.) Using a model carefully tuned to avoid parameter degeneracies, a powerlaw model plus five successively higher mass gaussians, we recover overall merger rates versus mass and trends versus redshift which are consistent with previously published results. Too, we recover previously identified overall trends versus spin: preferential alignment and low spin at low mass; large spin and isotropic spins at high mass. Critically, however, our multi-component model disagrees with previously published results, finding all components except the lowest mass are consistent with isotropy. Too, our multi-component model has a roughly hierarchical spectrum of gaussian mass peaks, but without the expected correlations between spin and mass expected from naked hierarchical formation
[abstract 34 / 42] (score: 2) - Title: Assessing the waveform systematics from parameter estimation to population inference with eccentricityAuthors: Muhammad Zeeshan, Richard O'Shaughnessy, Natalie Malagon, Katelyn J. Wagner,Comments:Subjects: astro-ph.HECreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
While masses and spins are routinely used to constrain compact binary formation channels, eccentricity provides an additional and potentially powerful diagnostic of binary origin, particularly for dynamically assembled systems. Recent advances in eccentric waveform modeling now make it possible to search for eccentric signatures in gravitational wave data; however, differences between waveform models can introduce systematic effects that may propagate into astrophysical population inference. In this work, we analyze 153 binary BLACK HOLEs, 2 binary neutron stars and 7 neutron star BLACK HOLE binaries from the GWTC-4 catalog. We compare the source and population level inferences obtained with two eccentric waveform models, SEOBNRv5EHM and TEOBResumS-DALI, as well as with quasi circular waveform analyses. We find that the two eccentric models give broadly consistent source parameter estimates for most events, but some events exhibit subtle and coherent differences. These small, systematic offsets can accumulate in hierarchical population inference, leading to differences in inferred population properties, most notably in the redshift evolution and effective spin distribution. Because coherent event level biases can grow approximately as $\sqrt{N}$ for a catalog of N events, waveform systematics become increasingly important as gravitational wave catalogs expand. We also introduce a synthetic data framework that generates eccentric populations and corresponding RIFT posterior samples, enabling injection studies that test the recoverability of eccentric population properties.
[abstract 35 / 42] (score: 2) - Title: A JWST, ALMA and VLA survey of the Ophiuchus-A star-forming region: Unveiling hidden dust mass and connecting infrared outflows to their radio originsAuthors: Isaac C. Radley, John D. Ilee, Gemma Busquet, Hauyu Baobab Liu, Klaus M. Pontoppidan, Alvaro Ribas, Marc Audard, Eleonora Bianchi, Tyler L. Bourke, Claudio Codella, Audrey Coutens, Josep M. Girart, Melvin G. Hoare, Izaskun Jiménez-Serra, Doug Johnstone, Laurent Loinard, Olja Panić, Jaime E. Pineda, Linda Podio, John J. Tobin, David J. Wilner,Comments: Accepted for publication in AJSubjects: astro-ph.GA astro-ph.SRCreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
We present an infrared, millimetre, and radio survey of 20 Class 0-III young stellar objects in the Ophiuchus A L1688 star-forming cluster, combining high-resolution (7-25 au) VLA and JWST observations with archival ALMA data. We implement physically motivated models to derive dust and ionised gas properties, spectral behaviour and their relative contributions through the millimetre-centimetre radio spectral energy distribution. Our models reveal circumstellar dust disks that are, on average, tens to hundreds of times more massive than millimetre-only estimates (subject to uncertainties arising from the choice of dust opacity) and contain millimetre-sized grains even at the Class 0 stage. Owing to the VLA's high resolution we are able to connect outflows to their origins, detecting protostellar JET emission on scales of 10s-1000s au. Our results represent a homogeneous characterisation of the dust and ionised gas properties in Ophiuchus and present a potential solution to the long-standing 'missing disk mass' problem. However, our understanding is still limited by resolution and sensitivity at frequencies <40 GHz. Future facilities like the SKA and ngVLA are needed to provide the necessary capabilities to fully spatially resolve this emission (<0.18") even in one of the closest star-forming regions.
[abstract 36 / 42] (score: 2) - Title: Star formation, stellar evolution, and planets in high-resolution X-ray imagingAuthors: Hans Moritz Günther, Scott J. Wolk, Sean J. Gunderson, Ruchi Pandey, Keivan G. Stassun, Lynne Valencic,Comments: This is a report generated in response to a call by the X-ray Science Interest Group of the NASA Physics of the Cosmos Program Analysis Group (PhysPAG). A summary of all five reports can be found at https://doi.org/10.48550/arXiv.2606.28138Subjects: astro-ph.IM astro-ph.GACreated: 2026-07-16; Updated: 2026-07-20; Datestamp: 2026-07-20
Stars set the conditions for planet formation, planet evolution, and habitability -- all major topics in astronomy today. Stars are also important in their own right as the most visible component of galaxies. In cool stars, X-ray emission is powered by MAGNETic fields, and so far our Sun is the only system in which those fields are spatially resolved. High-resolution X-ray (HiReX) imaging can track the origin and evolution of those fields, see how they connect young stars to their disks and outflows, and measure the energy, mass, and momentum that radiation and coronal mass ejections (CMEs) carry into the circumstellar environment. This is crucial for understanding whether planets can form and survive in young stellar systems, whether life can develop on those planets, and how the star evolves over time. Intermediate-mass and high-mass stars blow winds and eventually evolve into degenerate objects such as white dwarfs, neutron stars, and BLACK HOLEs. Their evolution and death drive the chemical evolution of galaxies. High-resolution X-ray (HiReX) imaging can study the hottest components in those systems, such as the colliding winds of massive stars, accretion and nova explosions in CVs, and the shocks in outflows that form planetary nebulae. All these cases have in common that the X-ray emission is tracing the hottest, fastest, and most energetic components of the shocks. HiReX observations can reveal the temperature, spatial structures, and elemental abundances of different system components that no other wavelength can. While stars are physically small compared to more powerful objects such as accreting BLACK HOLEs and AGN, they are also much closer to us, allowing a HiReX mission to resolve a variety of physical phenomena fundamental to our understanding of how stellar systems form, evolve, and interact with their environment.
[abstract 37 / 42] (score: 2) - Title: High-Density Sound Speed and Post-Merger DynamicsAuthors: John Stroud, David Radice, Sanjay Reddy,Comments: 31 pages, 11 figuresSubjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
The density dependence of the speed of sound in cold neutron star matter remains poorly constrained and is central to determining the high-density equation of state (EOS). While binary neutron star (BNS) merger simulations increasingly incorporate detailed microphysics, the direct impact of the sound-speed in the neutron star core on observable signatures has not been systematically explored. We address this by introducing a simplified parametrization that suppresses microphysics while allowing controlled variation of the sound speed at supranuclear densities through its derivative with respect to the baryon chemical potential. Using the WhiskyTHC code, we perform a suite of fully RELATIVISTIC BNS merger simulations and identify correlations between the sound-speed slope parameter and key merger outcomes, including remnant properties and post-merger GW frequencies. These results demonstrate that multimessenger observables are sensitive to the behavior of matter at the highest densities reached in neutron star cores. We further analyze gravitational-wave signals from the CoRe database of binary neutron star merger simulations employing more realistic equations of state. Our analysis reveals approximately EOS-independent relations between the derivative of the sound speed and the peak post-merger gravitational-wave frequency. Although these relations cannot be considered truly quasi-universal, they nonetheless indicate that post-merger gravitational waves retain measurable information about the EOS at he highest densities. At the same time, the remaining EOS dependence highlights the difficulty of isolating the underlying high-density physics and motivates the development of targeted parameterized frameworks for interpreting future multimessenger observations.
[abstract 38 / 42] (score: 2) - Title: Linear Gyrokinetic Simulations of Micro-tearing Mode: Local versus GlobalAuthors: Yifei Liu, Haotian Chen, Yao Yao, Zhengji Li, Jiquan Li, Wei Chen,Comments:Subjects: physics.plasm-phCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
A systematic comparison of local and global linear gyrokinetic simulations of micro-tearing modes (MTMs) is performed using the GENE code. The analysis spans diverse plasma parameters, including the core regions with normal and weak MAGNETic shear, as well as the pedestal region with the strong plasma non-uniformity. The global simulations reveal a distinct MTM type characterized by a `parity mixing' mode structure, which can be significantly destabilized by trapped electrons. Moreover, in contrast to electrostatic drift wave instabilities, the current layer width ($ Δ_c $) is identified as the crucial factor determining the importance of global effects. The MTM in the core region exhibits the slab-like feature with narrow $ Δ_c $, leading to high consistency between local and global results. However, in the pedestal region, the steep pressure gradient broadens $Δ_c$, driving quantitative deviations when $Δ_c$ becomes comparable to the plasma pressure gradient scale length. For high-$n$ MTMs, $ Δ_c $ can exceed the distance between adjacent mode rational surfaces. The resulted overlapping of current layers enhances the toroidal mode coupling effect, accounting for the substantial discrepancies observed between local and global simulations.
[abstract 39 / 42] (score: 2) - Title: The weight of light: colliding pulses of radiation in General RelativityAuthors: Jorge Expósito Patiño, Vitor Cardoso, Hannes R. Rüter,Comments: 9 pages, 7 figuresSubjects: gr-qcCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We study the gravitational interaction of very strong pulses of electroMAGNETic radiation, up to and beyond gravitational collapse. We demonstrate the existence of very compact states close to the threshold of collapse, both for a single pulse, and a head-on collision of such pulses, and we measure their compactness to be above the maximum value proposed by the hoop conjecture. For a single pulse above the threshold of collapse, a fast BLACK HOLE is produced. Depending on the amount of tuning, head-on collisions can form two horizonless states, two small BLACK HOLEs or one big BLACK HOLE. Our results show that the gravitational interaction of massless fields can lead to nontrivial final or intermediate states, while giving rise to extremely high luminosity and compactness.
[abstract 40 / 42] (score: 2) - Title: Massless scalar scattering by Kerr-Bertotti-Robinson BLACK HOLEs:transparent-end channels and superradianceAuthors: Hai Huang, Xudong Sun, Juhua Chen,Comments:Subjects: gr-qcCreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
We formulate and numerically solve the real-frequency scattering problem for a neutral, minimally coupled, massless scalar on the rotating Kerr--Bertotti--Robinson (Kerr--BR) black-hole geometry, using a specified transparent boundary condition at the coordinate end. Since the Maxwell stress tensor of the background is traceless, the minimally coupled wave equation reduces to the four-dimensional conformal wave equation, enabling exact Carter-like separation after scaling the scalar field by the conformal factor. Unlike the asymptotically flat case, the coordinate end $r\to\infty$ lies at a finite tortoise distance. We show that the resulting reflection data are conditional on this boundary prescription rather than defining a unique, observer-independent cross section. Within the transparent-end model,open-channel superradiance is governed by a double-gate mechanism requiring both the local horizon condition and the outer propagation condition $q_\infty^2>0$. At the benchmark spin $a/M=0.9$, the co-rotating dipole amplification decreases as the external MAGNETic field increases. Crucially, the field narrows and closes the open superradiant window at $BM\simeq0.243$. Near the propagation threshold, the amplification coefficient vanishes linearly with the outer wave number.
[abstract 41 / 42] (score: 2) - Title: Impact of eccentricity and higher-modes on neutron star-BLACK HOLE parameter estimationAuthors: Snehal Tibrewal, Aasim Jan, Aaron Zimmerman, Hsin-Yu Chen,Comments:Subjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
Detections of gravitational waves from neutron star-BLACK HOLE systems provide avenues for studying extreme matter, constraining binary formation channels, and testing the nature of compact objects in strong gravity. Eccentric signatures in the signal further enhance this potential by improving parameter estimation and offering clues about binary formation. Because eccentricity is primarily imprinted during the inspiral phase, it is often weakly constrained or missed entirely in binary BLACK HOLE observations; in contrast, neutron star-BLACK HOLE systems produce longer in-band signals, enabling more precise measurements of eccentricity and leaving a distinct imprint on parameter inference. In this work, we present a systematic parameter-estimation study exploring the impact of eccentricity on inference using injections simulated with the state-of-the-art eccentric waveform model SEOBNRv5EHM. We find that for systems like GW200105_162426, the measurement precision of eccentricity and correlated parameters improves as eccentricity increases, yielding tighter constraints at larger eccentricities. For the highest eccentricity considered in this study, $e=0.25$, we recover eccentricity with $1σ$ uncertainty as low as $4\times10^{-4}$. In addition, the constraints on effective spin $χ_\mathrm{eff}$ and mass ratio $q$ improve relative to the quasi-circular case by factors of $\sim13$ and $\sim20$, respectively. On the other hand, we find no significant improvement in extrinsic parameters such as luminosity distance and sky localization, suggesting that for systems like GW200105_162426, the additional information provided by eccentricity in this sector is either negligible or degenerate with the information provided by higher-order modes.
[abstract 42 / 42] (score: 2) - Title: Eccentricity as a Magnifying Glass: Precision Population Inference Enabled by Eccentric Neutron Star--Black Hole MergersAuthors: Alberto Salvarese, Hsin-Yu Chen, Aaron Zimmerman, Snehal Tibrewal,Comments: 12 pages, 6 figures, 3 tables. Comments are welcomeSubjects: astro-ph.HECreated: 2026-07-17; Updated: 2026-07-20; Datestamp: 2026-07-20
The formation history of compact binary systems remains one of the key open questions in astrophysics. Theoretical studies generally favor isolated binary evolution for neutron star-BLACK HOLE (NSBH) systems, which tends to produce nearly circular orbits. However, recent analyses of the gravitational-wave event GW200105 indicate that its source has measurable eccentricity, suggesting that alternative formation channels may also contribute. It has been shown that the intrinsic parameters of eccentric NSBH mergers, such as the component masses and spins, are much better measured than circular mergers with LIGO-Virgo-KAGRA (LVK) observatories. We explore how such eccentricity-enhanced parameter measurements can affect the inference of NSBH formation channels. We find that sharper measurements of the effective spin parameter $χ_{\rm eff}$ increase the fraction of systems for which negative values can be confidently identified, allowing for the clear measurement of a spin-orbit misaligned event every $\sim 2.5$ eccentric NSBH detections for an isotropically distributed population in the fifth LVK observing run (O5). Improved NS mass measurements provide better constraining power for NS mass distributions, potentially revealing structure and tightening the bounds that can be drawn on their upper and lower masses. Similarly, the recovery of a metallicity-dependent BH mass distribution is improved by eccentricity-enhanced measurements. Finally, we show that the proposed population-level eccentricity distribution for dynamical-formation channels can be tested by the end of O5.
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