Current date: 2026-04-08

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Datestamp limit: 2026-04-08 (0 days ago)

Created/updated limit: 2026-04-01 (7 days ago)

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OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2026-04-08&until=2026-04-08&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 739

Keyword score statistics

score 13 -- 1 abstracts

score 9 -- 1 abstracts

score 7 -- 5 abstracts

score 6 -- 2 abstracts

score 5 -- 5 abstracts

score 4 -- 8 abstracts

score 3 -- 6 abstracts

score 2 -- 18 abstracts

in total -- 46 abstracts

Articles that appeared on 2026-04-08

[abstract 1 / 46] Wow! (score: 13)
arXiv:2603.19889 [pdf, ps, other]

Title: VHE gamma-ray intranight variability from BL Lacertae during the extreme flaring state of 2022

Authors: K. Abe, S. Abe, A. Abhishek, F. Acero, A. Aguasca-Cabot, I. Agudo, C. Alispach, D. Ambrosino, F. Ambrosino, L. A. Antonelli, C. Aramo, A. Arbet-Engels, C. Arcaro, T. T. H. Arnesen, P. Aubert, A. Baktash, M. Balbo, A. Bamba, A. Baquero Larriva, U. Barres de Almeida, J. A. Barrio, L. Barrios Jiménez, I. Batkovic, J. Baxter, J. Becerra González, J. Bernete, A. Berti, E. Bissaldi, O. Blanch, G. Bonnoli, P. Bordas, A. Briscioli, G. Brunelli, J. Buces, A. Bulgarelli, I. Burelli, L. Burmistrov, M. Cardillo, S. Caroff, A. Carosi, R. Carraro, F. Cassol, D. Cerasole, A. Cerviño Cortínez, Y. Chai, G. Chon, L. Chytka, G. M. Cicciari, J. L. Contreras, J. Cortina, H. Costantini, M. Croisonnier, M. Dalchenko, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, M. de Bony de Lavergne, R. Del Burgo, C. Delgado, J. Delgado Mengual, D. della Volpe, B. De Lotto, L. Del Peral, R. de Menezes, G. De Palma, V. de Souza, C. Díaz, L. Di Bella, A. Di Piano, F. Di Pierro, R. Di Tria, L. Di Venere, D. Dominis Prester, A. Donini, D. Dorner, L. Eisenberger, D. Elsässer, G. Emery, L. Feligioni, F. Ferrarotto, A. Fiasson, L. Foffano, Y. Fukazawa, S. Gallozzi, R. Garcia López, S. Garcia Soto, C. Gasbarra, D. Gasparrini, J. Giesbrecht Paiva, N. Giglietto, F. Giordano, N. Godinovic, T. Gradetzke, R. Grau, J. Green, G. Grolleron, S. Gunji, P. Günther, J. Hackfeld, D. Hadasch, M. Hashizume, T. Hassan, K. Hayashi, L. Heckmann, M. Heller, J. Herrera Llorente, N. Hiroshima, D. Hoffmann, D. Horns, J. Houles, D. Hrupec, R. Imazawa, T. Inada, S. Inoue, K. Ioka, M. Iori, T. Itokawa, A. Iuliano, J. Jahanvi, I. Jimenez Martinez, J. Jimenez Quiles, I. Jorge Rodrigo, J. Jurysek, M. Kagaya, V. Karas, H. Katagiri, D. Kerszberg, T. Kiyomoto, Y. Kobayashi, K. Kohri, P. Kornecki, H. Kubo, J. Kushida, B. Lacave, M. Lainez, A. Lamastra, L. Lemoigne, M. Linhoff, S. Lombardi, F. Longo, R. López-Coto, A. López-Oramas, S. Loporchio, J. Lozano Bahilo, F. Lucarelli, H. Luciani, P. L. Luque-Escamilla, M. Makariev, M. Mallamaci, D. Mandat, K. Mannheim, F. Marini, M. Mariotti, P. Marquez, G. Marsella, J. Martí, O. Martinez, G. Martínez, M. Martínez, M. Massa, D. Mazin, J. Méndez-Gallego, S. Menon, E. Mestre Guillen, D. Miceli, T. Miener, J. M. Miranda, M. Molero Gonzalez, E. Molina, T. Montaruli, A. Moralejo, A. Morselli, V. Moya, A. L. Müller, H. Muraishi, S. Nagataki, T. Nakamori, A. Neronov, D. Nieto Castaño, M. Nievas Rosillo, L. Nikolic, K. Noda, V. Novotny, S. Nozaki, M. Ohishi, Y. Ohtani, A. Okumura, R. Orito, L. Orsini, J. Otero-Santos, P. Ottanelli, M. Palatiello, G. Panebianco, D. Paneque, R. Paoletti, J. M. Paredes, M. Pech, M. Pecimotika, M. Peresano, F. Perrotta, F. Pfeifle, M. Pihet, G. Pirola, C. Plard, F. Podobnik, M. Polo, C. Pozo-Gonzaléz, E. Prandini, S. Rainò, R. Rando, W. Rhode, M. Ribó, G. Rodriguez Fernandez, M. D. Rodríguez Frías, A. Roy, A. Ruina, E. Ruiz-Velasco, T. Saito, S. Sakurai, D. A. Sanchez, H. Sano, E. Santos Moura, T. Šarić, Y. Sato, F. G. Saturni, V. Savchenko, F. Schiavone, F. Schussler, T. Schweizer, M. Seglar Arroyo, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, I. Sofia, J. Strišković, M. Strzys, Y. Suda, A. Sunny, H. Tajima, M. Takahashi, R. Takeishi, S. J. Tanaka, D. Tateishi, T. Tavernier, P. Temnikov, Y. Terada, K. Terauchi, T. Terzic, M. Teshima, M. Tluczykont, T. Tomura, D. F. Torres, F. Tramonti, P. Travnicek, G. Tripodo, A. Tutone, M. Vacula, M. Vázquez Acosta, G. Verna, I. Viale, A. Viana, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, G. Voutsinas, I. Vovk, T. Vuillaume, R. Walter, T. Yamamoto, R. Yamazaki, Y. Yao, T. Yoshida, T. Yoshikoshi, W. Zhang, N. Zywucka, the CTAO-LST collaboration, F. Aceituno, J. A. Acosta-Pulido, V. Casanova, J. Escudero Pedrosa, V. Fallah Ramazani, J. Jormanainen, S. Jorstad, G. Keating, P. M. Kouch, M. Gurwell, A. Lähteenmäki, E. Lindfors, A. Marscher, D. Morcuende, I. Myserlis, K. Nilsson, C. A. Ortega Hunter, R. Rao, A. Sota, M. Tornikoski, H. Zhang,

Comments: Accepted for publication in A&A. 13 pages + 8 pages of Appendix

Subjects: astro-ph.HE astro-ph.GA

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

BL Lacertae (BL Lac), the archetypal BLAZAR of its subclass and one of the most studied BLAZARs in the last decades, has undergone a series of major multi-wavelength outbursts since 2020, resulting in its highest recorded $γ$-ray flare to date between September and November 2022 together with those from August 2021 and October 2024. We characterised the $γ$-ray and multi-wavelength emission and spectral energy distribution (SED) of BL Lac, as well as their evolution during the major and extended $γ$-ray and multi-wavelength flare that occurred between September and November 2022. We evaluated the variability of the flare, focusing on the nights of October 20 and November 13, when clear intranight very-high-energy (VHE, $E>100$ GeV) $γ$-ray variability was observed. We modelled the $γ$-ray and broadband SEDs during periods of stable emission identified with a Bayesian block analysis and interpreted the flare's evolution in terms of the variability in the RELATIVISTIC particles and the JET's physical parameters. The VHE emission shows an average flux of 0.23 Crab Units (C.U.) above 200 GeV and a variability amplitude of more than a factor ten. We observe intranight flux-doubling variations as fast as $\sim$8 minutes during the nights of October 20 and November 13, 2022 with maximum fluxes of 4.4 C.U. above 100 GeV and 2.8 C.U. above 200 GeV. The spectral analysis reveals a transition of the X-ray emission from the high- to the low-energy SED peak and a shift of the $γ$-ray peak towards higher energies. We interpret the broadband emission within a leptonic two-zone model in which intranight variability is explained as MAGNETic RECONNECTion in a compact region closely oriented with the line of sight while variations in the RELATIVISTIC electron distributions and the injection of freshly accelerated particles explain the weekly scale variations.

[abstract 2 / 46] Wow! (score: 9)
arXiv:2604.05028 [pdf, ps, other]

Title: Characterizing the Gamma-ray Emission from Low-Luminosity AGN

Authors: Chris Karwin, Nikita Khatiya, Margot Boughelilba, Xiurui Zhao, Anita Reimer, Marco Ajello,

Comments: 22 pages, 12 figures, 2 tables. Accepted for publication in the Astrophysical Journal

Subjects: astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

A majority of the ACTIVE GALACTIC NUCLEi (AGN) in the local Universe are classified as low-luminosity AGN (LLAGN), having bolometric luminosities $\lesssim 10^{42} \ \mathrm{erg \ s^{-1}}$. Although high-energy gamma-ray emission is predicted from both the JETs and disks of LLAGN, to date only four have been detected by the FERMI Large Area Telescope (FERMI-LAT). In this work, we therefore conduct a comprehensive study of all the LLAGN from the Palomar spectroscopic survey of bright, northern galaxies, including both subthreshold and detected gamma-ray sources, using 14.4 years of LAT data. Our analysis results in a new detection of one LLAGN, as well as a detection of the subthreshold population using a stacking technique. We find that the signal from the subthreshold sample is consistent with being dominated by star-formation activity, although a contribution from compact JETs or a mixed contribution from JETted and non-JETted systems is also feasible. On the other hand, the individually detected LLAGN are likely dominated by JET emission. We perform detailed spectral modeling for a subset of these sources and find that the gamma-ray signal can be explained by SYNCHROTRON self-Compton radiation, if the inner JET emission region is weakly MAGNETized with its total energy density being strongly particle dominated, and only slowly moving. With this work we also publicly release our Python-based stacking library for analyzing subthreshold source populations with the LAT, based on a proven technique used in numerous studies.

[abstract 3 / 46] Wow! (score: 7)
arXiv:2512.08716 [pdf, ps, other]

Title: Optical polarimetry of the accreting BLACK HOLE X-ray binary SWIFT J1727.8$-$1613 over the state transition and radio ejections

Authors: Anagha P. Nitindala, Alexandra Veledina, Vadim Kravtsov, Andrei V. Berdyugin, María Alejandra Díaz Teodori, Vilppu Piirola, Takeshi Sakanoi, Masato Kagitani, Svetlana V. Berdyugina, Juri Poutanen,

Comments: Submitted to Astronomy & Astrophysics

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

We present the first optical ($BVR$) polarimetric observations of SWIFT J1727.8$-$1613 during its 2023--2024 outburst. Observations were performed during the X-ray hard-to-soft state transition, the soft state and the decaying hard state of the source. For the vast majority of nights, we detect statistically significant POLARIZATION of ${\approx}1$\%, a fraction of which is of interstellar origin. We find a significant change of POLARIZATION coinciding in time with discrete radio ejections. The direction of this POLARIZATION variation differs from the directions inferred from the X-ray, sub-mm and radio POLARIZATION angles, as well as from the resolved JET orientation. After correcting for the interstellar component, we find that the intrinsic POLARIZATION degree remained approximately constant at PD $\approx 0.3$\% throughout the hard-intermediate state. We explore several possible origins for the POLARIZATION and conclude that it is most plausibly produced by scattering within the optically thin accretion disk wind. The intrinsic POLARIZATION angle, PA $\approx-15°$, is notably offset from the JET axis, which we interpret as evidence for a misalignment between the BLACK HOLE spin and the orbital axis.

[abstract 4 / 46] Wow! (score: 7)
arXiv:2603.09562 [pdf, ps, other]

Title: Temporal Variation of the Coronal Radius Parameter in a Jetted Tidal Disruption Event: SWIFT J1644+57

Authors: Arka Chatterjee, Kimitake Hayasaki, Prantik Nandi, Neeraj Kumari, Skye R. Heiland, Arghajit Jana, Sachindra Naik, Samar Safi-Harb,

Comments: accepted for publication in ApJ, comments are welcome

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Tidal Disruption Events are exotic astrophysical phenomena where matter from a star or the interstellar medium is captured by a supermassive BLACK HOLE. The process liberates enormous energy, within a few months to a year timescale, enough to detect dormant BLACK HOLEs in near as well as the farthest galaxies. We revisit the long-term spectral variabilities associated with the JETted Tidal Disruption Event \source~by exploring the archival X-ray data obtained with SWIFT/XRT and XMM-Newton observatories. Our analysis reveals that the spectral indices decrease non-monotonically as \source~evolves with time. We also find that the soft (0.3-1.5 keV) and hard (1.5-10 keV) X-ray photon counts are highly correlated with a maximum correlation coefficient of 0.95 and peak at {\it zero} lag. Moreover, the soft and hard band variabilities obtained from XMM-Newton observations are highly correlated with a Pearson cross-correlation coefficient of 0.96. This indicates that the soft and hard X-ray photons are emitted from the same site, which is most likely a Compton cloud, i.e., the corona. Assuming the hard X-ray photons originate from the corona, we find that the coronal parameter undergoes rapid expansion during the early phases when accompanied by a RELATIVISTIC JET launching and subsequently evolves toward a state of saturation with minor fluctuations in the latter stages. The temporal variation of the coronal radius parameter ($R_{cor}$) is consistent with a simple theoretical conjecture. We also discuss the application of our analytical outcomes to other JETted and non-JETted tidal disruption events.

[abstract 5 / 46] Wow! (score: 7)
arXiv:2604.05020 [pdf, ps, other]

Title: ElectroMAGNETic Flares from Compact-Object Mergers in AGN Disks: Signatures and Predictions

Authors: Hiromichi Tagawa, Zoltán Haiman, Shigeo S. Kimura, Hassen M. Yesuf, Hengxiao Guo,

Comments: 29 pages, 15 figures

Subjects: astro-ph.HE astro-ph.GA

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Accretion disks in ACTIVE GALACTIC NUCLEi (AGN) are promising sites for mergers of stellar-mass BLACK HOLEs (BHs) detectable via gravitational waves (GWs). These environments facilitate both in-situ formation and dynamical capture of compact objects, and their subsequent mergers. The uncertain origin of GW events detected by LIGO, Virgo and KAGRA motivates searching for accompanying electroMAGNETic (EM) signatures. Here we investigate post-merger EM flares associated with JETs launched from merger remnants, as well as from the shocked ambient gas as the JET breaks out of the disk. We find that JET breakout produces luminous gamma-ray emission, detectable with MeV-band telescopes. Cooling emission from a shocked circum-BH minidisk, winds and background AGN-disk peaks in the UV and optical, with durations ranging from about an hour to a month, and can be identified through year-long monitoring of $\sim10^3$ AGNs with luminosities ranging from $\sim 10^{44}$ to $\sim 10^{45}~{\rm erg~s^{-1}}$. With a single set of parameters, this post-merger JET model produces gamma-ray, hard X-ray and optical flares similar to those claimed to be associated with GW events. Furthermore, by incorporating a transition from a high- to low-angular-momentum accretion state after the merger, the model avoids excessive BH growth, alleviating tensions with hyper-Eddington accretion scenarios.

[abstract 6 / 46] Wow! (score: 7)
arXiv:2604.05576 [pdf, ps, other]

Title: Extreme Blazars Observed with MAGIC: Second Catalog Release

Authors: K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, F. Acero, A. Aguasca-Cabot, I. Agudo, C. Alispach, D. Ambrosino, F. Ambrosino, T. Aniello, S. Ansoldi, L. A. Antonelli, C. Aramo, A. Arbet-Engels, C. Arcaro, T. T. H. Arnesen, P. Aubert, A. Babić, C. Bakshi, A. Baktash, M. Balbo, A. Bamba, A. Baquero Larriva, U. Barres de Almeida, J. A. Barrio, L. Barrios Jiménez, I. Batkovic, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, C. Bigongiari, A. Biland, E. Bissaldi, O. Blanch, G. Bonnoli, P. Bordas, Ž. Bošnjak, A. Briscioli, E. Bronzini, G. Brunelli, J. Buces, A. Bulgarelli, I. Burelli, L. Burmistrov, A. Campoy-Ordaz, M. Cardillo, S. Caroff, A. Carosi, R. Carosi, R. Carraro, M. Carretero-Castrillo, F. Cassol, A. J. Castro-Tirado, D. Cerasole, G. Ceribella, A. Cerviño Cortínez, Y. Chai, G. Chon, L. Chytka, G. M. Cicciari, A. Cifuentes Santos, J. L. Contreras, J. Cortina, S. Covino, H. Costantini, M. Croisonnier, M. Dalchenko, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, M. de Bony de Lavergne, R. Del Burgo, M. Delfino, C. Delgado, J. Delgado Mengual, D. della Volpe, B. De Lotto, L. Del Peral, R. de Menezes, G. De Palma, V. de Souza, C. Díaz, L. Di Bella, A. Di Piano, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsässer, G. Emery, L. Feligioni, J. Escudero, L. Fariña, F. Ferrarotto, A. Fiasson, L. Foffano, L. Font, F. Frías García-Lago, S. Fröse, Y. Fukazawa, S. Gallozzi, R. Garcia López, S. Garcia Soto, C. Gasbarra, D. Gasparrini, S. Gasparyan, M. Gaug, J. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, N. Godinovic, T. Gradetzke, R. Grau, J. Green, G. Grolleron, S. Gunji, P. Günther, J. Hackfeld, D. Hadasch, A. Hahn, G. Harutyunyan, M. Hashizume, T. Hassan, K. Hayashi, L. Heckmann, M. Heller, J. Herrera Llorente, N. Hiroshima, D. Hoffmann, D. Horns, J. Houles, D. Hrupec, R. Imazawa, T. Inada, S. Inoue, K. Ioka, M. Iori, D. Israyelyan, T. Itokawa, A. Iuliano, J. Jahanvi, I. Jimenez Martinez, J. Jimenez Quiles, I. Jorge Rodrigo, J. Jormanainen, J. Jurysek, M. Kagaya, S. Kankkunen, V. Karas, H. Katagiri, T. Kayanoki, D. Kerszberg, T. Kiyomoto, G. W. Kluge, Y. Kobayashi, K. Kohri, J. Konrad, P. Kornecki, P. M. Kouch, G. Koziol, H. Kubo, J. Kushida, B. Lacave, M. Lainez, A. Lamastra, L. Lemoigne, E. Lindfors, M. Linhoff, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, J. Lozano Bahilo, F. Lucarelli, H. Luciani, L. Lulić, P. L. Luque-Escamilla, E. Lyard, P. Majumdar, M. Makariev, M. Mallamaci, D. Mandat, G. Maneva, M. Manganaro, S. Mangano, K. Mannheim, S. Marchesi, F. Marini, M. Mariotti, P. Marquez, G. Marsella, J. Martí, D. Martin, O. Martinez, G. Martínez, M. Martínez, M. Massa, P. Maruševec, D. Mazin, S. Menchiari, J. Méndez-Gallego, S. Menon, E. Mestre Guillen, D. Miceli, T. Miener, J. M. Miranda, R. Mirzoyan, M. Molero Gonzalez, E. Molina, H. A. Mondal, T. Montaruli, A. Moralejo, A. Morselli, V. Moya, A. L. Müller, H. Muraishi, S. Nagataki, T. Nakamori, C. Nanci, A. Negro, A. Neronov, V. Neustroev, D. Nieto Castaño, M. Nievas Rosillo, C. Nigro, L. Nikolic, K. Noda, V. Novotny, S. Nozaki, M. Ohishi, A. Okumura, R. Orito, L. Orsini, J. Otero-Santos, P. Ottanelli, S. Paiano, M. Palatiello, G. Panebianco, D. Paneque, R. Paoletti, J. M. Paredes, M. Pech, M. Pecimotika, M. Peresano, F. Perrotta, M. Persic, F. Pfeifle, M. Pihet, G. Pirola, C. Plard, F. Podobnik, M. Polo, C. Pozo-Gonzaléz, P. G. Prada Moroni, E. Prandini, S. Rainò, R. Rando, W. Rhode, M. Ribó, J. Rico, G. Rodriguez Fer dez, M. D. Rodríguez Frías, A. Roy, A. Ruina, E. Ruiz-Velasco, N. Sahakyan, T. Saito, S. Sakurai, D. A. Sanchez, H. Sano, E. Santos Moura, T. Šarić, Y. Sato, F. G. Saturni, V. Savchenko, F. Schiavone, K. Schmitz, F. Schmuckermaier, F. Schussler, T. Schweizer, M. Seglar Arroyo, A. Sciaccaluga, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, I. Sofia, D. Sobczynska, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, A. Sunny, H. Tajima, M. Takahashi, R. Takeishi, S. J. Tanaka, D. Tateishi, T. Tavernier, P. Temnikov, Y. Terada, K. Terauchi, T. Terzic, M. Teshima, M. Tluczykont, T. Tomura, D. F. Torres, F. Tramonti, P. Travnicek, G. Tripodo, A. Tutone, S. Ubach, M. Vacula, M. Vázquez Acosta, S. Ventura, G. Verna, I. Viale, A. Viana, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, G. Voutsinas, I. Vovk, T. Vuillaume, R. Walter, C. Walther, F. Wersig, M. Will, T. Yamamoto, R. Yamazaki, Y. Yao, P. K. H. Yeung, T. Yoshida, T. Yoshikoshi, W. Zhang, N. Zywucka, F. D'Ammando, D. Linder, F. Wierda,

Comments: Accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Extremely high-peaked BL Lac objects - also named extreme BLAZARs - are among the most energetic and persistent extragalactic accelerators in the Universe, defined by a SYNCHROTRON emission peaking above $10^{17}$ Hz in X-rays. Such emission is then reprocessed and produces radiation extending deeply into very-high-energy (VHE, energy E>100 GeV) gamma rays. Observations in this energy band - optimally investigated by the Imaging Air-Shower Cherenkov telescopes - are crucial for probing the physical processes that drive their extreme behavior. This study extends our investigation of extreme BLAZARs in the VHE gamma-ray range, providing a second new mini-catalog of sources observed by the MAGIC telescopes. We report on the monitoring of seven targets between 2017 and 2025, including four newly observed sources and three that have been part of long-term observation campaigns, for a total of approximately 338 hours of observations. The analysis of MAGIC data reveals two new VHE detections of extreme BLAZARs, along with three additional sources showing hints of VHE emission. Joint observations of MAGIC and the first Large-Sized Telescope (LST-1) also confirmed a new VHE extreme BLAZAR. Our results are complemented by simultaneous multiwavelength observations in other energy bands, including optical-UV, X-rays, and high-energy gamma rays (100 MeVGeV). We confirm typical behavior of extreme BLAZARs, such as a modest variability and a ``harder-when-brighter'' trend in X-rays across the sample. This new set increases the population of extreme BLAZARs and their broadband analysis confirms the physical properties of these extreme sources.

[abstract 7 / 46] Wow! (score: 7)
arXiv:2604.06128 [pdf, ps, other]

Title: On the observational distinguishability of the Kerr and Kerr-Hayward metrics to EHT

Authors: Nikola Bukowiecka, Angelo Ricarte, Prashant Kocherlakota, Cora Prather,

Comments: 21 pages, 6 figures

Subjects: astro-ph.HE astro-ph.IM gr-qc

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Astrophysical BLACK HOLEs appear well-represented by the Kerr metric, but this metric has the philosophical problem of a ring-like curvature singularity. We show that a phenomenological correction to the Kerr metric known as the Kerr-Hayward metric can eliminate the curvature singularity while preserving in detail many features of polarized BLACK HOLE images now testable by the Event Horizon Telescope (EHT). To establish this, we produce new general RELATIVISTIC MAGNETohydrodynamics (GRMHD) simulations of a MAGNETized plasma in a Kerr-Hayward spacetime, then we extend the EHT analysis framework to perform polarized radiative transfer in this spacetime. We detail our methodology for implementing this modified spacetime into an open-source pipeline. From fluid quantities such as the MAGNETic flux parameter and JET efficiency, to image quantities such as the POLARIZATION pattern and the photon ring structure, our results for the Kerr-Hayward metric appear functionally indistinguishable from the Kerr metric. Our study finds that under certain conditions, the singularity-free correction to the Kerr metric can yield observables that are effectively indistinguishable in EHT measurements.

[abstract 8 / 46] Yes (score: 6)
arXiv:2508.18345 [pdf, ps, other]

Title: Hillas meets Eddington: The case for BLAZARs as ultra-high-energy neutrino sources

Authors: Xavier Rodrigues, Frank Rieger, Artem Bohdan, Paolo Padovani,

Comments:

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Blazars are promising high-energy neutrino source candidates. However, leptohadronic models face challenges in describing neutrino emission within a viable energy budget, and their predictive power is limited by the commonly used single-zone approximation and the reliance on phenomenological parameters. In this work, we present a new leptohadronic model where a sub-Eddington JET evolves from MAGNETically- to kinetically dominated. A small fraction of the electrons and protons picked up by the JET are continuously accelerated to a power-law spectrum, estimated based on the local MAGNETic field strength, turbulence, and ambient density, for which we assume power-law profiles. The model parameters are thus directly tied to the JET physics and are comparable in number to typical single-zone models. We then numerically calculate the emission along the JET. Applying the model to the IceCube candidate TXS 0506+056, we find that protons are accelerated to EeV energies in the inner JET, producing a neutrino flux up to order 100 PeV that is consistent with the 10 year IceCube point-source data. Proton emission at 0.1 pc describes the X-ray and gamma-ray data, while electron emission at the parsec scale describes the optical data. Protons carry a power of about 1% of the Eddington luminosity, showing that the model is energetically viable. The particle spectra follow $E^{-1.8}$, with diffusion scaling as $E^{0.3}$, ruling out Bohm-like diffusion. Additional particle injection near the broad line region can reproduce the 2017 flare associated to a high-energy neutrino. We also apply the model to BLAZAR PKS 0605-085, which may be associated with a recent neutrino detected by KM3NeT above 100 PeV. The results suggest that BLAZARs are efficient neutrino emitters at ultra-high energies, making them prime candidates for future experiments targeting this challenging energy range.

[abstract 9 / 46] Yes (score: 6)
arXiv:2604.05992 [pdf, ps, other]

Title: Occurrence of Flat-top Electron Velocity Distributions in Magnetotail Plasma Jets

Authors: Louis Richard, Yuri V. Khotyaintsev, Cecilia Norgren,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Non-Maxwellian electron velocity distributions (eVDFs) are ubiquitous in collisionless plasmas. For example, various types of non-Maxwellian eVDFs exist in MAGNETic RECONNECTion JETs in the Earth's MAGNETotail. At thermal energies, eVDF can be flat-topped due to electron trapping associated with MAGNETic RECONNECTion. However, the occurrence of such eVDFs in MAGNETotail RECONNECTion remains largely unconstrained. Here, we statistically investigate flat-top eVDFs in fast plasma JETs in the MAGNETotail using a new method for classifying eVDFs. We show that only $\sim 7\%$ of the eVDFs in the JETs are flat-tops. Nevertheless, we find that most JETs exhibit flat-top eVDFs, indicating that this signature of parallel acceleration and electron streaming is characteristic of the JETs. We find that these flat-top eVDFs are localized within an ion-inertial-length-scale region near the edges of the current sheet and close to the RECONNECTion region. Our results highlight the importance of flat-top eVDFs in non-local thermodynamic equilibrium collisionless plasmas.

[abstract 10 / 46] Yes (score: 5)
arXiv:2512.16638 [pdf, ps, other]

Title: Cygnus X-3: A variable petaelectronvolt gamma-ray source

Authors: The LHAASO Collaboration, Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, J. Blunier, A. V. Bukevich, C. M. Cai, Y. Y. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, E. S. Chen, G. H. Chen, H. K. Chen, L. F. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen, T. L. Chen, X. B. Chen, X. J. Chen, X. P. Chen, Y. Chen, N. Cheng, Q. Y. Cheng, Y. D. Cheng, M. Y. Cui, S. W. Cui, X. H. Cui, Y. D. Cui, B. Z. Dai, H. L. Dai, Z. G. Dai, Danzengluobu, Y. X. Diao, A. J. Dong, X. Q. Dong, K. K. Duan, J. H. Fan, Y. Z. Fan, J. Fang, J. H. Fang, K. Fang, C. F. Feng, H. Feng, L. Feng, S. H. Feng, X. T. Feng, Y. Feng, Y. L. Feng, S. Gabici, B. Gao, Q. Gao, W. Gao, W. K. Gao, M. M. Ge, T. T. Ge, L. S. Geng, G. Giacinti, G. H. Gong, Q. B. Gou, M. H. Gu, F. L. Guo, J. Guo, K. J. Guo, X. L. Guo, Y. Q. Guo, Y. Y. Guo, R. P. Han, O. A. Hannuksela, M. Hasan, H. H. He, H. N. He, J. Y. He, X. Y. He, Y. He, S. Hernández-Cadena, B. W. Hou, C. Hou, X. Hou, H. B. Hu, S. C. Hu, C. Huang, D. H. Huang, J. J. Huang, X. L. Huang, X. T. Huang, X. Y. Huang, Y. Huang, Y. Y. Huang, A. Inventar, X. L. Ji, H. Y. Jia, K. Jia, H. B. Jiang, K. Jiang, X. W. Jiang, Z. J. Jiang, M. Jin, S. Kaci, M. M. Kang, I. Karpikov, D. Khangulyan, D. Kuleshov, K. Kurinov, Cheng Li, Cong Li, D. Li, F. Li, H. B. Li, H. C. Li, Jian Li, Jie Li, K. Li, L. Li, R. L. Li, S. D. Li, T. Y. Li, W. L. Li, X. R. Li, Xin Li, Y. Li, Zhe Li, Zhuo Li, E. W. Liang, Y. F. Liang, S. J. Lin, B. Liu, C. Liu, D. Liu, D. B. Liu, H. Liu, J. Liu, J. L. Liu, J. R. Liu, M. Y. Liu, R. Y. Liu, S. M. Liu, W. Liu, X. Liu, Y. Liu, Y. Liu, Y. N. Liu, Y. Q. Lou, Q. Luo, Y. Luo, H. K. Lv, B. Q. Ma, L. L. Ma, X. H. Ma, I. O. Maliy, J. R. Mao, Z. Min, W. Mitthumsiri, Y. Mizuno, G. B. Mou, A. Neronov, K. C. Y. Ng, M. Y. Ni, L. Nie, L. J. Ou, Z. W. Ou, P. Pattarakijwanich, Z. Y. Pei, D. Y. Peng, J. C. Qi, M. Y. Qi, J. J. Qin, D. Qu, A. Raza, C. Y. Ren, D. Ruffolo, A. Sáiz, D. Savchenko, D. Semikoz, L. Shao, O. Shchegolev, Y. Z. Shen, X. D. Sheng, Z. D. Shi, F. W. Shu, H. C. Song, Yu. V. Stenkin, V. Stepanov, Y. Su, D. X. Sun, H. Sun, J. X. Sun, Q. N. Sun, X. N. Sun, Z. B. Sun, N. H. Tabasam, J. Takata, P. H. T. Tam, H. B. Tan, Q. W. Tang, R. Tang, Z. B. Tang, W. W. Tian, C. N. Tong, L. H. Wan, C. Wang, D. H. Wang, G. W. Wang, H. G. Wang, J. C. Wang, K. Wang, Kai Wang, Kai Wang, L. P. Wang, L. Y. Wang, L. Y. Wang, R. Wang, W. Wang, X. G. Wang, X. J. Wang, X. Y. Wang, Y. Wang, Y. D. Wang, Z. H. Wang, Z. X. Wang, Zheng Wang, D. M. Wei, J. J. Wei, Y. J. Wei, T. Wen, S. S. Weng, C. Y. Wu, H. R. Wu, Q. W. Wu, S. Wu, X. F. Wu, Y. S. Wu, S. Q. Xi, J. Xia, J. J. Xia, G. M. Xiang, D. X. Xiao, G. Xiao, Y. F. Xiao, Y. L. Xin, H. D. Xing, Y. Xing, D. R. Xiong, B. N. Xu, C. Y. Xu, D. L. Xu, R. F. Xu, R. X. Xu, S. S. Xu, W. L. Xu, L. Xue, D. H. Yan, T. Yan, C. W. Yang, C. Y. Yang, F. F. Yang, L. L. Yang, M. J. Yang, R. Z. Yang, W. X. Yang, Z. H. Yang, Z. G. Yao, X. A. Ye, L. Q. Yin, N. Yin, X. H. You, Z. Y. You, Q. Yuan, H. Yue, H. D. Zeng, T. X. Zeng, W. Zeng, X. T. Zeng, M. Zha, B. B. Zhang, B. T. Zhang, C. Zhang, H. Zhang, H. M. Zhang, H. Y. Zhang, J. L. Zhang, J. Y. Zhang, Li Zhang, P. F. Zhang, R. Zhang, S. R. Zhang, S. S. Zhang, S. Y. Zhang, W. Zhang, W. Y. Zhang, X. Zhang, X. P. Zhang, Yi Zhang, Yong Zhang, Z. P. Zhang, J. Zhao, L. Zhao, L. Z. Zhao, S. P. Zhao, X. H. Zhao, Z. H. Zhao, F. Zheng, T. C. Zheng, B. Zhou, H. Zhou, J. N. Zhou, M. Zhou, P. Zhou, R. Zhou, X. X. Zhou, X. X. Zhou, B. Y. Zhu, C. G. Zhu, F. R. Zhu, H. Zhu, K. J. Zhu, Y. C. Zou, X. Zuo, J. S. Wang,

Comments: Submitted to NSR

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

We report the discovery of variable $γ$-rays up to petaelectronvolt from Cygnus X-3, an iconic X-ray binary. The $γ$-ray signal was detected with a statistical significance of approximately 10 $σ$ by the Large High Altitude Air Shower Observatory (LHAASO). Its intrinsic spectral energy distribution (SED), extending from 0.06 to 3.7 PeV, shows a pronounced rise toward 1 PeV after accounting for absorption by the cosmic microwave background radiation. The detected month-scale variability,together with a 3.2$σ$ evidence for orbital modulation, suggests that the PeV $γ$-rays originate within, or in close proximity to, the binary system itself. The observed energy spectrum and temporal modulation can be naturally explained by $γ$-ray production through photomeson processes in the innermost region of the RELATIVISTIC JET, where protons need to be accelerated to tens of PeV energies.

[abstract 11 / 46] Yes (score: 5)
arXiv:2604.05046 [pdf, ps, other]

Title: Wide Jets or Low Rates: Reconciling Short GRB and Gravitational-Wave Neutron Star Merger Rates

Authors: Keerthi Kunnumkai, Antonella Palmese, Brendan O'Connor, Amanda Farah, Ignacio Magana Hernandez,

Comments: 22 pages, 6 figures, 1 table

Subjects: astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Gravitational wave (GW) and short Gamma Ray Burst (sGRB) observations provide us with complementary views of compact object mergers. The paucity of binary neutron star merger (BNS) detections in the latest LIGO/Virgo/KAGRA (LVK) observing run raises the question of whether the GW merger rates are sufficient to explain the observed sGRB rate with compact object mergers alone. We investigate this connection using the latest merger rate constraints from the fourth LVK observing run (O4) and published estimates of the local sGRB rate density. For an observed sGRB rate density of $ \sim 1-7~\mathrm{Gpc^{-3}\,yr^{-1}}$, if $>55\%$ of BNS mergers can successfully launch a JET, we find that the current LVK BNS merger rate can be reconciled with a sGRB merger population containing a significant fraction of relatively wide JETs with core half-opening angles $θ_j \geq 10^\circ$. Meanwhile, a narrow JET population ($θ_j \sim 6^\circ$) can only be matched with the O4 neutron star merger rate estimates for an observed sGRB rate density of $\lesssim 1~\mathrm{Gpc^{-3}\,yr^{-1}}$, which is broadly consistent with several of the latest available estimates. We also find that neutron star-BLACK HOLE mergers (NSBH) are expected to be a subdominant component of the sGRB population compared to BNS mergers, and they cannot help reconcile some of the highest available sGRB rate ($ >7~\mathrm{Gpc^{-3}\,yr^{-1}}$) with the GW rate estimates. However, they can still substantially contribute to the sGRB population, comprising $\sim 6-16\%$ of it for an observed sGRB rate density of $\sim 1-3~\mathrm{Gpc^{-3}\,yr^{-1}}$. Overall, our results indicate that present GW and sGRB observations remain broadly consistent with BNS mergers as the main progenitors of sGRBs.

[abstract 12 / 46] Yes (score: 5)
arXiv:2604.05058 [pdf, ps, other]

Title: Kinetic MAGNETohydrodynamics and Landau fluid closure in relativity

Authors: Abhishek Hegade K. R., James M. Stone,

Comments: 23 pages + appendices. Supplementary notebook in the source file. Comments are welcome!

Subjects: astro-ph.HE gr-qc physics.plasm-ph

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Diffuse accretion flows near a supermassive BLACK HOLE are fundamentally weakly collisional. In such weakly collisional plasmas, the ion and electron distribution functions can deviate significantly from thermal equilibrium, and particle kinetic effects can influence large-scale fluid motion by driving pressure anisotropy, heat conduction, and plasma instabilities. Modeling these plasma effects in highly RELATIVISTIC flows could be important for interpreting horizon-scale observations of BLACK HOLE images. In this paper, we present a theoretical framework for understanding weakly collisional plasmas in general relativity by deriving the RELATIVISTIC drift kinetic equations from the Vlasov-Maxwell equations. We present the evolution equations for the moments of the gyroaveraged distribution function and introduce a new analytic Landau fluid closure to capture anisotropic heat flow in RELATIVISTIC plasmas. Unlike standard (collisional) general RELATIVISTIC MAGNETohydrodynamics or extended MAGNETohydrodynamics, our model does not rely on strong collisions to enforce thermal equilibrium and consistently incorporates Landau damping in a fluid closure. The model introduced in this work provides a complementary approach to fully kinetic simulations in understanding weakly collisional effects in low-luminosity RELATIVISTIC BLACK HOLE accretion disks.

[abstract 13 / 46] Yes (score: 5)
arXiv:2604.05471 [pdf, ps, other]

Title: Galactic-scale evolution of classical and complex RADIO GALAXies. Impact of ambient morphology and JET geometry

Authors: Gourab Giri, Prajnadipt Ghosh, Ravi Joshi, Anderson Caproni, Paola Rossi, Gianluigi Bodo, Sayan Kundu, Kshitij Thorat, Swarna Chatterjee, Dario Borgogno, Valerio Vittorini, Marco Tavani,

Comments: Article accepted for publication in A&A journal. (19 Figs, 4 Tables)

Subjects: astro-ph.GA

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Extragalactic JETs exhibit a wide range of propagation orientations relative to the host galaxy's principal axis. This study investigate the spatiotemporal evolution of JETs as a function of their propagation direction within their triaxial hosts-introducing varying degrees of environmental hindrance-and as a function of internal JET properties (while maintaining identical JET power)-introducing varying collimation and thrust. Observational data on extended radio sources are re-analyzed to identify key traits arising from variations in JET orientation and intrinsic properties. These findings are then systematically tested using a suite of 3D RMHD simulations. When a JET propagates along host's major axis (path of maximal environmental resistance), it produces an X-shaped morphology with secondary lobe aligns along the minor axis, co-evolving actively alongside the active JET. At intermediate angles to the major axis, the JET morphology transitions into a double-boomerang structure with notably curved lobes. Such lobes are interestingly regenerative through both backflow and JET precession mechanisms, making it difficult to disentangle their origin. Jets propagating along the minor axis (path of minimal resistance) exhibit faster propagation, forming classical double-lobed sources. With increased thrust and improved collimation (keeping JET power constant), these JETs advance even more rapidly, potentially evolving into giant RADIO GALAXy candidates. Counterexample sources that deviate from these traits were also modeled. The spatial variation of internal turbulence shows significant fluctuations below 1 kpc, with stronger MAGNETic fields further suppressing these irregularities. Magnetic field plays a key role in the radiative appearance of these sources, modulating features like missing or one-sided (wing) lobe emission, filamentary structures, and warmspot versus hotspot formation.

[abstract 14 / 46] Yes (score: 5)
arXiv:2604.05905 [pdf, ps, other]

Title: Testing X-ray Periodicity and Long-Term Trend in PG 1553+113 via Targeted SWIFT-XRT Monitoring

Authors: P. Peñil, N. Torres-Albà, L. Marcotulli, A. Domínguez, M. Ajello, A. Rico, S. Buson, S. Adhikari,

Comments: 13 pages, 3 figures,

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

PG~1553+113 is the BLAZAR with the most-significantly detected periodic patter in its multiwavelength (MWL) emission, making it one of the most promising candidates for hosting a supermassive BLACK HOLE binary. However, the presence of this periodic behavior in the X-ray band remains under debate, largely due to the lack of continuous monitoring. This has led to differing conclusions in previous studies. In addition, we aim to examine whether the recently identified linear long-term trends in the gamma-ray and optical bands also exist in the X-ray regime. Here, we evaluate the 2.1-year period in the X-ray light curve of PG 1553+113 using two dedicated monitoring campaigns with SWIFT-XRT and UVOT, guided by predictions of future oscillation phases. We also examine whether the long-term trend is present in X-rays, the potential periodic behavior of the X-ray power-law photon index, and its potential correlation to the X-ray flux. As a result, we find tentative evidence for a correlation between the predicted high-emission states in the gamma-ray band and those observed in the X-ray and UV bands. Therefore, we do not find a strong evidence of the same periodic pattern in X-ray. In addition, we find that the X-ray light curve is consistent with the presence of a long-term linear trend, in agreement with those previously reported in gamma-ray, optical, and radio. Overall, these results indicate that the X-ray emission is likely to share the same long-term behavior observed in the gamma-ray and optical bands. Nevertheless, the pronounced stochastic variability that characterizes the X-ray light curve limits our ability to draw firm conclusions regarding the presence of the periodic behavior.

[abstract 15 / 46] Yes (score: 4)
arXiv:2502.07940 [pdf, ps, other]

Title: Temporary EHBL-like behavior of Markarian 501 during July 2014 VHE flaring

Authors: Sarira Sahu, A. U. Puga Oliveros, D. I. Páez-Sánchez, G. Sánchez-Colón, Subhash Rajpoot, M. E. Iglesias Martínez, José Guerra Carmenate, P. Fernández de Córdoba, Gaetano Lambiase,

Comments: 12 pages, 7 figures, 1 table

Subjects: astro-ph.HE hep-ph

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Markarian 501, a BL Lac object well-known as a high energy gamma-ray source, has exhibited several epochs of very high energy (VHE) gamma-ray flaring events when its SYNCHROTRON peak frequency shifted above $10^{17}$ Hz, a signature of extreme behavior. From July 16 to July 31, 2014 such flaring events were observed for 15 days by various telescopes. On July 19 (MJD 56857.98), the X-ray outburst from the source was at its highest and on the same day an intriguing narrow peak-like feature around 3 TeV was observed by the MAGIC telescopes, a feature inconsistent with standard interpretations. Using the well-known two-zone photohadronic model, we study these VHE gamma-ray spectra on a day-by-day basis and offer explanation. Our two-zone photohadronic scenario shows that, on MJD 56857.98, the peak-like feature appears at a cutoff energy of $E^c_γ=3.18$ TeV. Below this energy the VHE spectrum increases slowly and is in high emission state. However, for $E^c_γ\, > 3.18$ TeV, the spectrum falls faster, resulting in a mild peak-like feature, not prominent enough as claimed by the MAGIC collaboration.

[abstract 16 / 46] Yes (score: 4)
arXiv:2508.06341 [pdf, ps, other]

Title: Impact of BLACK HOLE spin on low-mass BLACK HOLE-neutron star mergers

Authors: Rahime Matur, Ian Hawke, Nils Andersson,

Comments: 15 pages, 10 figures, 2 table. Accepted for publication in MNRAS

Subjects: astro-ph.HE gr-qc

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

The recent detection of GW230529 suggests that BLACK HOLE-neutron star mergers may involve low-mass BLACK HOLEs, potentially producing detectable electroMAGNETic counterparts. Motivated by this, we perform eleven fully general-RELATIVISTIC hydrodynamic simulations with and without neutrino treatment, targeting the inferred chirp mass of GW230529. We systematically vary the BLACK HOLE spin from $a_{\mathrm{BH}} = 0.0$ to $0.8$ in steps of $0.1$, making this the most comprehensive study of spin effects in BLACK HOLE-neutron star mergers to date. We confirm our earlier findings of fast-moving ejecta ($v \geq 0.6\,c$) in this parameter regime and demonstrate a clear spin dependence, with fast-ejecta masses reaching up to $\qty{\sim e-3}{\Mass\Sun}$ for $a_{\mathrm{BH}} = 0.8$. Most notably, we identify for the first time the presence of spiral wave-driven ejecta in BLACK HOLE-neutron star mergers -- a phenomenon previously reported only in binary neutron star systems. The mass of this component grows significantly with spin, reaching levels up to $\qty{\sim 7e-3}{\Mass\Sun}$. These results establish a new spin-enhanced mechanism for powering blue kilonova emission in BLACK HOLE-neutron star mergers, significantly extending the range of systems expected to produce observable electroMAGNETic counterparts.

[abstract 17 / 46] Yes (score: 4)
arXiv:2601.05319 [pdf, ps, other]

Title: Accretion disc winds in X-ray binaries

Authors: Teo Muñoz-Darias, María Díaz Trigo, Chris Done, Gabriele Ponti, Ryota Tomaru,

Comments: To be published in Space Science Reviews. 86 pages in total, including references (56 pages of main text)

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Despite early theoretical expectations that large-scale, massive outflows would be triggered by accretion onto BLACK HOLEs and neutron stars, their presence was not firmly established until the 2000s. Since then, these accretion disc winds have been recognised as a common, perhaps ubiquitous, feature of accretion discs in X-ray binaries. Over the past two decades, our understanding of these outflows has expanded significantly, with their associated phenomenology now observed across the X-ray, ultraviolet, optical, and near-infrared regimes. In this review, we provide a comprehensive summary of the observational properties of both low- and high-ionisation winds, treating each separately as well as part of a broader phenomenon, and place these findings in the context of current theoretical modelling. We discuss their close connection with disc atmospheres, their impact on the accretion process, and their role within the broader framework that includes the radio JET and the different accretion flow configurations and states. We also address current challenges and outline some of the anticipated developments, particularly those linked to upcoming observational facilities.

[abstract 18 / 46] Yes (score: 4)
arXiv:2601.06278 [pdf, ps, other]

Title: VLBI Observations of SN 2012au Reveal a Compact Radio Source a Decade Post Explosion

Authors: Mattias Lazda, Kenzie Nimmo, Maria R. Drout, Benito Marcote, Jason W. T. Hessels, Eli Wiston, Raffaella Margutti, Omar Ould-Boukattine, Tanmoy Laskar, Jacco Vink, Ryan Chornock, James K. Leung, Deanne L. Coppejans, Dan Milisavljevic, Juan Mena-Parra, Dan Patnaude,

Comments: 35 pages, 10 figures, published in ApJ

Subjects: astro-ph.HE astro-ph.SR

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Three leading models have been put forth to justify the observed radio re-brightening associated with stripped-envelope SUPERNOVAe (SESNe) years post-explosion: radiation from an emerging pulsar wind nebula (PWN), shock interaction with a dense circumstellar medium (CSM), or emission from off-axis, RELATIVISTIC JETs. SN 2012au is a particularly intriguing SESN in this regard as observations obtained $\gtrsim$ 6 years post-explosion have shown both (i) optical emission features consistent with a young PWN and (ii) a radio re-brightening. We present the results of our Very-Long-Baseline-Interferometric (VLBI) observations of SN 2012au performed between 8 to 13 years post core-collapse. Our VLBI observations reveal a luminous, steadily fading radio source that remains compact ($\leq1.4\times10^{17}~\mathrm{cm}$) and stationary ($\leq0.36c$) over the course of our campaign. Overall, we find that our VLBI measurements can be readily explained by a $\sim$decade-old PWN, potentially explained by shock interaction with specific CSM geometries, and are unlikely to be explained by emission from an off-axis, RELATIVISTIC JET. Assuming a PWN origin, our observations require that the initial spin-down luminosity of the central pulsar be between $10^{36}~\mathrm{erg~s^{-1}}\leq\dot{E}_0\leq {4\times10^{42}}~\mathrm{erg~s^{-1}}$ and radio efficiency factor be $η_\mathrm{R}\geq {3\times10^{-7}}$ (both quoted at the $ {99.7\%}$ confidence interval). These results are consistent with independent inferences obtained using optical spectroscopy of SN 2012au, alongside inferences of known Galactic systems. If a PWN origin is confirmed, SN 2012au would represent the first extragalactic PWN emerging from a modern day SN, providing a novel opportunity to study the formation properties of a decade-old pulsar.

[abstract 19 / 46] Yes (score: 4)
arXiv:2603.00336 [pdf, ps, other]

Title: FRB scattering statistics through the CGM are sensitive to morphology and intermittency

Authors: Dylan L. Jow, Calvin Leung,

Comments:

Subjects: astro-ph.GA astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

The small-scale properties of circumgalactic gas in ordinary galaxies drive its bulk properties: the mass loading of cold neutral gas in galactic outflows affects their bulk momentum; gas cooling processes on small scales affect the spatial distribution of gas in the cool (T~$10^4$K) circumgalactic medium (CGM). However, hydrodynamical simulations have yet to resolve the CGM on such small scales. Spectroscopy remains our primary probe of the small-scale CGM, with which sub-parsec scales are challenging to resolve. Fast radio bursts (FRBs)--microsecond to millisecond duration radio pulses--are temporally broadened ("scattered") by gradients in the electron density transverse to the line of sight, often generated by fluctuations on the smallest spatial scales. This makes FRB scattering a powerful, complementary, and scalable probe of the small-scale CGM. We show that the distribution of scattering timescales introduced by density fluctuations within a single, foreground halo--the tau distribution function, or TDF--is sensitive to the small-scale spatial morphology of the gas. The TDF is readily measurable and is analogous to areal covering factors reported in QUASAR absorption statistics. We compute the TDF in two regimes: scattering from a turbulent, volume-filling medium ("volumetric scattering") distributed along the line of sight; and scattering from discrete structures localized along the line of sight ("intermittent scattering"). Within these regimes, the TDF is sensitive to whether the cool gas comprises primarily spherical, filamentary (1D), or sheet-like (2D) structures. This work sets the stage for upcoming observations which will use hundreds of sight-lines through nearby halos to probe the small-scale CGM, and points out a novel science case for FRB detectors like MeerKAT, Parkes, FAST, and the DSA-2000, which are exquisitely sensitive over a narrow field of view.

[abstract 20 / 46] Yes (score: 4)
arXiv:2603.27692 [pdf, ps, other]

Title: Strong-field focusing of high-energy particles in beam-multifoil collisions

Authors: Aimé Matheron, Doug Storey, Max F. Gilljohann, Sheldon Rego, Erik Adli, Igor A. Andriyash, Gevy J. Cao, Xavier Davoine, Claudio Emma, Frederico Fiuza, Spencer Gessner, Laurent Gremillet, Claire Hansel, Chan Joshi, Christoph H. Keitel, Alexander Knetsch, Valentina Lee, Michael D. Litos, Nathan Majernik, Yuliia Mankovska, Brendan O'Shea, Ivan Rajkovic, Pablo San Miguel Claveria, Viktoriia Zakharova, Chaojie Zhang, Mark J. Hogan, Matteo Tamburini, Sébastien Corde,

Comments:

Subjects: physics.acc-ph physics.plasm-ph

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Extreme beams of charged particles and photons, reaching ultrahigh densities or producing intense GAMMA-RAY BURSTs, are central to accelerator physics, laboratory astrophysics, and strong-field quantum electrodynamics research. Yet their generation is hindered by conventional focusing methods at multi-GeV energies that rely on massive MAGNETic assemblies, limiting compactness and attainable density. Here we report the first experimental observation of a fundamentally new focusing mechanism, in which a high-energy charged-particle beam is focused by its own MAGNETic field reflected from a stack of thin metallic foils via near-field coherent-transition-radiation. The experiment, performed at SLAC's FACET-II facility, reveals strong, cumulative focusing across a broad range of beam configurations, enabled by the delivered 10 GeV, 1 nC, 10 Hz electron beam. The measurements closely agree with predictions from an analytical model and particle-in-cell simulations. These results demonstrate that multifoil focusing is a remarkably straightforward, self-aligned approach to the generation of ultrahigh density beams, opening a path to explore unprecedented regimes of beam-matter interaction and high-energy radiation.

[abstract 21 / 46] Yes (score: 4)
arXiv:2604.05059 [pdf, ps, other]

Title: Implications of low neutron star merger rates for GAMMA-RAY BURSTs, r-process production and Galactic double neutron stars

Authors: Maya Fishbach, Alexander P. Ji, Wen-fai Fong, Tom Y. Wu, Jillian C. Rastinejad, Aditya Vijaykumar, Hsin-Yu Chen,

Comments:

Subjects: astro-ph.HE gr-qc

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

The first multimessenger discovery of a binary neutron star (BNS) merger, GW170817, proved that such mergers can source short GAMMA-RAY BURSTs (SGRBs) and produce \rprocess elements. The initial merger rate from this single event in the first two observing runs of the LIGO-Virgo observatory network, $110$--$3840\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$, was found to be broadly consistent with the SGRB rate, the Milky Way (MW) r-process mass, and the Galactic population of double neutron star (DNS) systems that will merge in a Hubble time. However, only one additional BNS merger has been detected since, and the BNS merger rate has been consistently revised downwards with the past few gravitational wave (GW) catalog updates. Analyzing GW data from the latest catalog GWTC-4, we find a total BNS merger rate of $28$--$300\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$ (consistent with the most recently published values from LIGO-Virgo-KAGRA) consisting of $53^{+176}_{-49}\,\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$ in GW170817-like $\sim(1.3,1.3)\,M_\odot$ BNSs (90\% credibility). In light of this updated GW rate, we revisit the consistency of the BNS merger rate with SGRBs, r-process and Galactic DNSs. In all cases, there is an emerging tension with the BNS (and EM-bright neutron star--BLACK HOLE, NSBH) merger rate. Comparing to a BNS merger rate of $100\,\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$, the cosmological SGRB rate is a factor of 3.6--18 higher, the r-process rate is a factor of 0.9--4.1 higher, and the rate inferred from Galactic DNSs is a factor of 2.3--5.1 higher than the BNS rate. We discuss how various uncertainties in the inferred rates either alleviate or exacerbate this tension, which point to the various physical processes that can be constrained by such rate comparisons.

[abstract 22 / 46] Yes (score: 4)
arXiv:2604.05879 [pdf, ps, other]

Title: Comments on "The impact of Solar MAGNETic field configurations on the production of gamma rays at the Solar disk'' (arXiv:2512.01403)

Authors: M. N. Mazziotta,

Comments: 4 pages, Comments on arXiv:2512.01403

Subjects: astro-ph.SR astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

In this short comment, I discuss the relationship between the results presented in arXiv:2512.01403 and those previously published in Phys.~Rev.~D~101,~083011~(2020). The 2020 study provides a full Monte Carlo simulation of cosmic-ray interactions with the solar atmosphere using the FLUKA code, including realistic solar-atmosphere models, PFSS/Parker/BIFROST MAGNETic-field configurations, and predictions for gamma rays, electrons, positrons, neutrons, and neutrinos. Given the substantial scientific overlap -- particularly in the modelling of hadronic interactions, MAGNETic-field effects, cascade development, and comparison with FERMI-LAT observations -- a direct comparison is relevant to assess consistency and complementarity. Here I summarize the main points of agreement, highlight differences in modeling assumptions, and outline how the two approaches can jointly contribute to understanding high-energy emission from the solar disk.

[abstract 23 / 46] (score: 3)
arXiv:2601.15452 [pdf, ps, other]

Title: The long quest for vacuum birefringence in MAGNETars: 1E 1547.0-5408 and the elusive smoking gun

Authors: Roberto Taverna, Roberto Turolla, Lorenzo Marra, Ruth M. E. Kelly, Alice Borghese, Gian Luca Israel, Sandro Mereghetti, Andrea Possenti, Silvia Zane, Michela Rigoselli,

Comments: 16 pages, 11 figures, revised version, accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Magnetars are now known to be among the most strongly polarized celestial sources in X-rays. Here we report on the $500\,\mathrm{ks}$ observation of the MAGNETar 1E 1547.0-5408 performed by the Imaging X-ray Polarimetry Explorer (IXPE) in March 2025. The IXPE spectrum is well reproduced by a single thermal component with blackbody temperature $kT_\mathrm{BB}\sim 0.67\,\mathrm{keV}$ and emission radius $R_\mathrm{BB}\sim 1.2\,\mathrm{km}$. The source exhibits a high linear POLARIZATION degree in the $2$--$6\,\mathrm{keV}$ band ($\mathrm{PD}=47.7\pm2.9\%$) with POLARIZATION angle $\mathrm{PA}=75^\circ.8 \pm 1.^\circ8$, measured West of celestial North. While $\mathrm{PA}$ does not appear to vary with energy, there is some evidence (at the $1σ$ confidence level) of a minimum in $\mathrm{PD}$ between $3$ and $4\,\mathrm{keV}$, compatible with what is expected by partial mode conversion at the vacuum resonance in a MAGNETized atmosphere. Phase-resolved spectral and polarimetric analyses reveal that X-ray thermal radiation likely originates from a single, fairly small hot spot with a non-uniform temperature distribution. Fitting the phase-dependent $\mathrm{PA}$ measured by IXPE with a rotating vector model (RVM) constrains the source geometry and indicates that both the dipole axis and line-of-sight are misaligned with respect to the spin axis. Under these conditions, the high POLARIZATION of the source cannot be regarded as compelling evidence for the presence of vacuum birefringence in the star MAGNETosphere. Nevertheless, the fact that the RVM successfully reproduces the modulation of the X-ray POLARIZATION angle and the behavior of $\mathrm{PD}$ with the energy hint once more to the presence of QED effects in MAGNETars.

[abstract 24 / 46] (score: 3)
arXiv:2602.11838 [pdf, ps, other]

Title: NE2025: An Updated Electron Density Model for the Galactic Interstellar Medium

Authors: S. K. Ocker, J. M. Cordes,

Comments: 34 pages, 18 figures, accepted for publication in ApJ

Subjects: astro-ph.GA astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Free electrons in the Galactic interstellar medium (ISM) disperse and scatter coherent radio waves, by amounts that depend on the distance to the radio source. Models of the Galactic electron density are thus widely used to predict distances and scattering of compact radio sources (including pulsars, fast radio bursts (FRBs), and long-period transients), in addition to mitigating ISM foregrounds in Galactic and extragalactic studies. We use a sample of 171 precise pulsar distances, based entirely on parallaxes and globular cluster associations, as well as scattering measurements of 568 pulsars, ACTIVE GALACTIC NUCLEi, and masers, to update the NE2001 Galactic electron density model. We refit the thick and thin disks and three of the spiral arms. The new parameters for these large-scale components significantly repartition free electrons between the thick disk and spiral arms, thereby correcting NE2001's systematic underestimation of pulsar distance and scattering. Sightlines with excessive dispersion and scattering are used to identify new clumps that are added to the model, in addition to refining clumps that were already included (e.g., Cygnus, Vela, and Gum). The Galactic Center component is revised, yielding scattering time predictions that are $10^3$ times smaller than the Galactic Center in NE2001. The updated model, NE2025, provides a factor of $20\times$ improvement in median distance prediction accuracy and $100\%$ median improvement in scattering predictions based on DM, relative to NE2001. There is a $15\times$ improvement in median distance prediction accuracy relative to YMW16. NE2025 is available on Github and the Python Package Interface.

[abstract 25 / 46] (score: 3)
arXiv:2603.04242 [pdf, ps, other]

Title: Active Galactic Nuclei-driven Metallicity Enrichment in the Interstellar Medium of Mrk 573

Authors: D. Ł. Król, P. Zhu, G. Fabbiano, M. Elvis, L. J. Kewley, N. Murray, R. Middei, A. Trindade-Falcão,

Comments: Accepted for publication in ApJ Letters

Subjects: astro-ph.GA astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

We present the first spatially resolved at $\sim20$ pc scale application of AGN-specific metallicity diagnostics for the nearby Compton-thick Seyfert 2 galaxy Mrk 573 ($z = 0.017$). We use Hubble Space Telescope narrow-band imaging, MUSE integral-field spectroscopy and apply AGN strong-line metallicity diagnostics based on [O III], [S II], H$β$, H$α$, and [N II] emission lines. We construct maps of $12 + \log$(O/H) for two different metallicity calibrations and two different N/O-O/H scaling relations out to $\sim1$ kpc and down to $\sim20$ pc scales. Our analysis reveals metallicity enhancement in AGN-dominated regions, with oxygen abundances reaching up to few times Solar. The metallicity shows a patchy spatial distribution, varying on $\sim100$ pc scales, appears to trace the high Seyfert/LINER index (SLI) value regions and the VLA 6 cm JET/radio lobe emission. These spatial correspondences and the lack of evidence for STAR FORMATION in the bicone region suggest that the enrichment originates from metals transported from the nuclear AGN regions by winds, outflows, or JETs.

[abstract 26 / 46] (score: 3)
arXiv:2604.05021 [pdf, ps, other]

Title: Ion Weibel Instability in the hybrid framework: the optimal resolution

Authors: Luca Orusa, Taiki Jikei,

Comments: 8 pages, 5 figures. Submitted to Physics of Plasmas

Subjects: physics.plasm-ph astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

The study of collisionless shocks and their role in cosmic-ray acceleration has gained increasing importance through both observations and simulations. Accurately modeling the shock transition region, where particle injection occurs, requires a proper description of the microinstabilities governing its structure. In high-Mach-number shocks, such as those associated with SUPERNOVA remnants, the ion Weibel instability is believed to provide the dominant dissipation mechanism. In this work, we investigate the ion Weibel instability driven by counterstreaming beams in the presence of an external perpendicular MAGNETic field. We employ hybrid simulations, in which ions are treated kinetically while electrons are modeled as a charge-neutralizing fluid. Although hybrid models are widely employed to study collisionless shocks, the resolution requirements needed to accurately capture ion-scale instabilities remain poorly understood. We address this issue by developing a linear theory of the ion Weibel instability tailored to the massless electron assumption of hybrid models and validating it with one- and two-dimensional simulations over a wide range of Alfvénic Mach numbers. We show that hybrid simulations can reliably reproduce the growth, saturation, and POLARIZATION of Weibel-generated MAGNETic fields in weakly MAGNETized regimes, provided that the relevant ion-scale modes are properly resolved. From the scaling of the dominant mode, we derive a minimum spatial resolution required as a function of Alfvénic Mach number. We also demonstrate that excessive resolution introduces unphysical small-scale whistler modes inherent to the massless-electron approximation. We validate the analysis by comparing the results with full particle-in-cell simulations. Together, these results provide practical guidance for hybrid simulations of collisionless shocks and beam-driven plasma systems.

[abstract 27 / 46] (score: 3)
arXiv:2604.05492 [pdf, ps, other]

Title: Remnant recoil and host environments of GWTC-4.0 binary black-hole mergers

Authors: Joan Llobera-Querol, Eleanor Hamilton, Neha Singh, Marta Colleoni, Felip A. Ramis Vidal, Abbas Askar, Tomasz Bulik, Aleksandra Olejak, Sascha Husa, Yumeng Xu, Jorge Valencia,

Comments: 20 pages, 16 figures, 4 tables

Subjects: astro-ph.HE gr-qc

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Determining the astrophysical origin of binary BLACK HOLEs and whether merger remnants are retained in their birth environments is essential for understanding hierarchical mergers and the growth of intermediate-mass BLACK HOLEs. We identified the gravitational-wave (GW) events most consistent with dynamical formation and assessed whether their merger remnants are retained in globular clusters, nuclear star clusters, or galactic potentials. We considered the 84 events consistent with binary-black-hole (BBH) mergers from the first part of the fourth observing run (O4a) of the LIGO-Virgo-KAGRA (LVK) GW detector network, and 3 selected events from the second part (O4b). We compared parameter-estimation posteriors with synthetic population models for field and cluster binaries using Bayes factors, accounting for the relative abundances of these formation channels in the local Universe. We computed recoil-velocity posteriors for all events using the IMRPhenomXPNR waveform model, which incorporates multipole asymmetries. We identified five events showing preference for a dynamical origin, including the most massive O4a event GW231123_135430, while excluding the high-spinning O4b event GW241011_233834. Typical recoil velocities of analyzed events are of order a few hundred km/s, with extended high-velocity tails. These kicks suggest that merger remnants are likely ejected from typical globular clusters, while retention in nuclear star clusters remains possible but not guaranteed. Our results disfavour efficient hierarchical growth in globular clusters, whereas nuclear star clusters remain viable environments for repeated mergers. Although results depend on the adopted astrophysical population models, this analysis highlights the importance of improved and larger population models, as well as higher-quality detections enabled by future developments in GW detectors.

[abstract 28 / 46] (score: 3)
arXiv:2604.06059 [pdf, ps, other]

Title: Spectroscopic confirmation of dual and offset QUASARs from the Subaru HSC-SSP program

Authors: Shenli Tang, John Silverman, Xavier Prochaska, Manda Banerji, Xuheng Ding, Masafusa Onoue, Knud Jahnke,

Comments:

Subjects: astro-ph.GA

Created: 2026-04-02; Updated: 2026-04-08; Datestamp: 2026-04-08

We present a spectroscopic follow-up program targeting closely-separated dual QUASAR candidates selected from imaging of SDSS QUASARs with the Subaru Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Using two-dimensional image decomposition, our selection identifies PSF-like companions within 0.6-4 arcsec separation (< 30 kpc) around the SDSS QUASAR. We newly confirm six broad-line dual QUASARs and eleven offset QUASARs (QUASAR-galaxy pairs), spanning 1.5 < z < 3.3 for the duals and predominantly z < 0.6 for the offset systems. No obvious lensed QUASARs were discovered from this program. We obtained 99 spectra of these candidates from NTT/EFOSC2, Gemini/GMOS-N, Keck/NIRES, and Subaru/FOCAS. From the spectra, we measure the emission-line properties of these dual BLACK HOLEs (BH). At z > 1.5, the confirmed duals exhibit high BLACK HOLE mass ($M_{\rm BH}$ $=10^{8.5}$-$10^{10} M_{\odot}$) with high bolometric luminosities ($L_{bol}$ $=10^{45.5}$-$10^{47.5}$ erg s$^{-1}$), yet accrete at moderate Eddington ratios ($λ_{\rm Edd}=$0.01-0.4). From the spectroscopically-confirmed samples, we estimate the dual fraction of SDSS QUASARs with separations of 0.6-4 arcsec to be 0.2%-1.2% at z<0.8, 0.08%-0.24% at 0.8

[abstract 29 / 46] (score: 2)
arXiv:2508.10627 [pdf, ps, other]

Title: Probing ultrafast heating and ionization dynamics in solid density plasmas with time-resolved resonant X-ray absorption and emission

Authors: Lingen Huang, Mikhail Mishchenko, Michal Šmíd, Oliver Humphries, Thomas R. Preston, Xiayun Pan, Long Yang, Johannes Hagemann, Thea Engler, Yangzhe Cui, Thomas Kluge, Carsten Baehtz, Erik Brambrink, Alejandro Laso Garcia, Sebastian Göde, Christian Gutt, Mohamed Hassan, Hauke Höppner, Michaela Kozlova, Josefine Metzkes-Ng, Masruri Masruri, Motoaki Nakatsutsumi, Masato Ota, Özgül Öztürk, Alexander Pelka, Irene Prencipe, Lisa Randolph, Martin Rehwald, Hans-Peter Schlenvoigt, Ulrich Schramm, Jan-Patrick Schwinkendorf, Monika Toncian, Toma Toncian, Jan Vorberger, Karl Zeil, Ulf Zastrau, Thomas E. Cowan,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-01; Updated: 2026-04-08; Datestamp: 2026-04-08

Heating and ionization are among the most fundamental processes in RELATIVISTIC LASER--solid interactions; however, their spatiotemporal evolution remains challenging to capture experimentally. Here we present detailed diagnosis of high-intensity LASER interactions with wire targets, leveraging the extreme spectral brightness of an X-ray free-electron LASER in sub-picosecond time-resolved resonant X-ray emission spectroscopy and absorption imaging. Experimental results are compared with comprehensive simulations using atomic collisional--radiative models, particle-in-cell, and MAGNETohydrodynamics codes to elucidate the underlying physics. These multi-scale simulations reveal extreme sensitivity of basic plasma parameters with widely used models, such as temperature and ionization depth, which are able to be constrained by incorporating a detailed accounting of LASER spatial profiles, pre-plasma conditions, and collisional processes. These results provide new insights into heating and ionization dynamics in the high-energy-density regime relevant to inertial fusion energy research, both as an experimental platform for accessing theoretically challenging conditions and as a benchmark for improving models of high-power LASER--plasma interactions.

[abstract 30 / 46] (score: 2)
arXiv:2510.12571 [pdf, ps, other]

Title: Low Reynolds number flow in a packed bed of rotated bars

Authors: Wojciech Sadowski, Christin Velten, Maximilian Brömmer, Hakan Demir, Kerstin Hülz, Francesca di Mare, Katharina Zähringer, Viktor Scherer,

Comments: submitted to Chemical Engineering & Technlogy

Subjects: physics.flu-dyn

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

The present study focuses on the gas flow through an experiment-scale modular packed bed reactor consisting of square bars, arranged in layers. Each layer is rotated by $30^\circ$ resulting in a complex shape of the void spaces between the bars. Particle Image Velocimetry measurement results inside and on top of the studied system are presented for particle-based Reynolds numbers of 100 and 200, and used as validation data for two sets of particle-resolved numerical simulations, using boundary conforming meshing strategy and treating the solid boundaries via the blocked-off method. The flow inside the bed is largely independent from the Reynolds number and seems to be determined by the geometry of the void spaces. The flow in the freeboard is dominated by the presence of slowly dissipating JETs downstream of the bed, which are characterized by unsteady oscillations at the higher Reynolds number. The numerical results obtained with both methods are in good agreement with the measurements, both inside and above the bed. However, stronger deviations between the results can be observed in the freeboard and can be traced to numerical properties of the current simulation approaches.

[abstract 31 / 46] (score: 2)
arXiv:2601.12614 [pdf, ps, other]

Title: Deterministic and probabilistic neural surrogates of global hybrid-Vlasov simulations

Authors: Daniel Holmberg, Ivan Zaitsev, Markku Alho, Ioanna Bouri, Fanni Franssila, Haewon Jeong, Minna Palmroth, Teemu Roos,

Comments:

Subjects: physics.space-ph cs.LG physics.plasm-ph

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

Hybrid-Vlasov simulations resolve ion-kinetic effects in the solar wind-MAGNETosphere interaction, but even 5D (2D + 3V) configurations are computationally expensive. We show that graph-based machine learning emulators can learn the spatiotemporal evolution of electroMAGNETic fields and lower order moments of ion velocity distribution in the near-Earth space environment from four 5D Vlasiator runs performed with identical steady solar wind conditions. The initial ion number density is systematically varied, while the grid spacing is held constant, to scan the ratio of the characteristic ion skin depth to the numerical grid size. Using a graph neural network (GNN) operating on the 2D spatial simulation grid comprising 670k cells, we demonstrate that both a deterministic forecasting model (Graph-FM) and a probabilistic ensemble forecasting model (Graph-EFM) based on a latent variable formulation are capable of producing accurate predictions of future plasma states. A divergence penalty is incorporated to encourage divergence-freeness in the MAGNETic fields. For the probabilistic model, a continuous ranked probability score objective is added to improve the calibration of the ensemble forecasts. The trained emulators achieve over two orders of magnitude speedup per time step on a single GPU compared to 100 CPU Vlasiator simulations. Most forecasted fields have Pearson correlations above 0.95 at 50 seconds lead time. However, we find that fields that exhibit near-zero degenerate distributions in the 5D setting are more challenging for the emulator to maintain high correlations for. Overall, these results demonstrate that GNNs provide a viable framework for rapid ensemble generation in hybrid-Vlasov modeling and highlight promising directions for future work.

[abstract 32 / 46] (score: 2)
arXiv:2602.23356 [pdf, ps, other]

Title: Revisiting the Perseus Cluster III: Role of Aspherical Explosions on its Chemical Composition and Extension to Metal-Poor Stars and Galaxies

Authors: Shing-Chi Leung, Henry Yerdon, Seth Walther, Ken'ichi Nomoto, Aurora Simionescu,

Comments: 23 pages, 39 figures. Submitted to the Astrophysical Journal on Nov 10 2025, revised on Feb 5 2026, accepted on Feb 7 2026, published on Apr 7 2026

Subjects: astro-ph.GA astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

The Perseus Cluster has been precisely measured by the legacy Hitomi telescope on the Si-group (Si, S, Ar, Ca) and Fe-group elements (Cr, Mn, Ni). These element abundance ratios provide insight into the typical behaviour of SUPERNOVAe. In Paper II, we presented new massive star explosion models at various metallicity, assuming spherical explosions. We show that while the fitting is improved, some features (e.g., Ni/Fe) remain to be improved. In this article, we extend our calculation to an aspherical explosion using the JET-induced explosion mechanism. The detailed pre- and post-explosion chemical profiles are calculated with a large post-processing network to capture the production of odd-number elements (V, Mn, Cu) and iron-group elements. We further explore how the JET-driven explosions create the diversity of models which could be compatible with the observed diversity in terms of $^{56}$Ni-mass vs ejecta mass, Ti-V relation, and stellar abundances. Finally, we apply the new collapsar models in the Galactic Chemical Evolution context. We study how the galactic stars, including the Zn-enriched star HE 1327-2326, can put constraints on the relative rates of collapsar and some of its model parameters. We show that collapsar could lead to significant changes in some elements, e.g., Zn. Our study shows that the collapsar is a necessary component to explain multiple elemental trends observed in the Milky Way Galaxy.

[abstract 33 / 46] (score: 2)
arXiv:2604.05085 [pdf, ps, other]

Title: A New Method for Testing Einstein's Theory of Gravity Close to Rapidly Spinning Black Holes

Authors: Shravan Vengalil Menon, Kun Hu, Henric Krawczynski,

Comments: 6 pages, 4 figures

Subjects: astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

The classical Penrose process and the collisional Penrose processes involve particles decaying or interacting very close to a spinning BLACK HOLE, in which some particles acquire negative energy and fall into the BLACK HOLE while others acquire that energy and can leave the system. Both processes involve an extreme form of frame dragging, i.e. the spinning BLACK HOLE drags spacetime with it, and the spacetime ejects some of the particles with a large energy gain, similar to a projectile in a slingshot. Such extreme forms of frame dragging had long been believed to be unobservable as the efficiency for a BLACK HOLE energizing particles in this way is very low. Here we report a new observational signature of this extreme sort of frame dragging. In rapidly spinning BLACK HOLEs in X-ray binaries, processes similar to collisional Penrose processes, but slightly less extreme, can give rise to a new spectral component with distinct spectral and polarimetric properties. Observations of this new spectral component with current or future broadband X-ray polarimeters will open a new window into testing Einstein's theory of gravity close to the edge of a BLACK HOLE and can be used to measure the BLACK HOLE spin.

[abstract 34 / 46] (score: 2)
arXiv:2604.05093 [pdf, ps, other]

Title: Great Walls of Cosmic Baryons in the Northern Sky

Authors: Vikram Ravi, Kritti Sharma, Liam Connor,

Comments: 10 pages, 4 figures, 1 table, submitted to ApJ Letters

Subjects: astro-ph.CO astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

The dispersion measures (DMs) of fast radio bursts (FRBs) encode the total ionized-gas column densities along their sightlines. Most observed FRBs originate at distances where the cosmological principle applies. Thus, variations in the DM distribution of FRBs observed in different regions on the sky trace local sources of anisotropy, such as the warm ionized medium and circum-galactic medium of the Milky Way, and local large-scale structure. We present a map of extragalactic DM variations across the Northern sky using a few thousand FRBs from the second \chime{} catalog. We detect a $\gtrsim 4σ$ excess of $\sim$150 pc cm$^{-3}$ above the global mean, extended over $\sim$30$^\circ$ scales and centered near $α\approx$ $12^{\rm h}$, $δ\approx$ $55^\circ$. This excess, termed Wall 1, is robust to variations in sample selection and jackknife resampling, and cannot be explained by Galactic-disk DM-model uncertainties. The excess is likely too large to correspond to anisotropy in the Milky Way halo. The signal spatially coincides with the Ursa Major supercluster and associated large-scale structures. A secondary, more tentative Wall 2 near $α\approx 2^{\rm h}$, $δ\approx$ $45^\circ$ is spatially coincident with the Perseus-Pisces supercluster. Although the spatial coincidences suggest that the Walls may correspond to baryons in the local large-scale structure, the probability of chance coincidence is likely too high ($\sim10-20\%$) to claim confident associations. These results highlight the potential of using FRB DMs to detect baryon overdensities associated with local large-scale structure, and have important implications for near-field baryon mapping and FRB cosmology.

[abstract 35 / 46] (score: 2)
arXiv:2604.05128 [pdf, ps, other]

Title: Identification of a Radio Counterpart to SN 2025ulz in the S250818k Localization Area

Authors: Tanner O'Dwyer, Alessandra Corsi, Deepika Yadav, Kunal P. Mooley, Raphael Baer-Way, Poonam Chandra, Gregg Hallinan, Mansi M. Kasliwal, Lauren Rhodes, Oleg M. Smirnov, Davide Lazzati, Joeri van Leeuwen, Adam Deller, Pikky Atri, Tanazza Khanam,

Comments: 15 pages, 7 figures

Subjects: astro-ph.HE astro-ph.CO

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

On 2025 August 18, the LIGO-Virgo-KAGRA collaboration reported S250818k, a sub-threshold gravitational-wave (GW) candidate consistent with a binary neutron star (NS) merger potentially involving a sub-solar-mass NS. Optical follow-up by the Zwicky Transient Facility identified AT2025ulz, a transient temporally coincident with the GW trigger that initially resembled a kilonova but was later classified as a young stripped-envelope Type IIb SUPERNOVA (SN), dubbed SN 2025ulz. A key question is whether SN 2025ulz harbors fast, possibly collimated, non-thermal ejecta indicative of a central engine, as invoked in "superkilonova" scenarios linking sub-solar-mass NSs to accretion-disk fragmentation or core fission. We present early-to-late-time multi-band radio observations of SN 2025ulz obtained with the Karl G. Jansky Very Large Array as part of the JAGWAR program, complemented by observations with the upgraded Giant Metrewave Radio Telescope and MeerKAT. We detect a faint but significant radio counterpart to SN 2025ulz at 6-10 GHz. The data are consistent with non-thermal emission from SN ejecta interacting with circumstellar material, favoring a compact progenitor and relatively fast ejecta akin to those of Type cIIb SNe. Our data are also consistent with emission from an off-axis JET peaking at about 50-100 days after the GW trigger. Overall, our radio detection is compatible with a superkilonova scenario and would motivate future systematic multi-wavelength follow-up of core-collapse events coincident with sub-solar NS GW candidates, should the association between S250818k and SN 2025ulz be supported by offline GW analyses.

[abstract 36 / 46] (score: 2)
arXiv:2604.05213 [pdf, ps, other]

Title: Local primordial non-Gaussianity using cross-correlations of DESI tracers

Authors: A. J. Rosado-Marín, A. J. Ross, H. Seo, E. Chaussidon, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. Cuceu, A. de la Macorra, A. de Mattia, R. Demina, B. Dey, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, C. Hahn, H. K. Herrera-Alcantar, D. Huterer, M. Ishak, R. Joyce, D. Kirkby, A. Kremin, O. Lahav, C. Lamman, M. Landriau, M. E. Levi, M. Manera, A. Meisner, R. Miquel, S. Nadathur, J. A. Newman, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, J. Silber, G. Tarlé, B. A. Weaver, C. Zhao, H. Zou,

Comments: 26 pages, 6 figures, 7 tables

Subjects: astro-ph.CO

Created: 2026-04-06; Updated: 2026-04-08; Datestamp: 2026-04-08

We constrain local primordial non-Gaussianity by a combined analysis of auto and cross-correlations of DESI DR1 tracers, leveraging LRGs and QSOs as well as ELGs between $0.8QUASARs can robustly improve the DESI DR1 $f^\mathrm{loc}_\mathrm{NL}$ constraints, by $\sim9\%$ to a measurement of $f^\mathrm{loc}_\mathrm{NL}=2.1_{-8.3}^{+8.8}$ at 68\% confidence. On the other hand, we do not find a clear improvement when including the DESI DR1 ELG sample. Mock tests predict an additional $\sim8\%$ gain with statistical scatter, and the lack of improvement in the data remains consistent with this expectation. This project serves as an exploratory analysis of DESI ELG clustering for $f^\mathrm{loc}_\mathrm{NL}$ through its cross-correlation in preparation for future DESI data analyses.

[abstract 37 / 46] (score: 2)
arXiv:2604.05392 [pdf, ps, other]

Title: Accurate POLARIZATION calibration of FAST spectral data for measurements of Zeeman splittings of OH megamasers in IRAS 02524+2046

Authors: L. G. Hou, X. Y. Gao, Tao Hong, J. L. Han,

Comments: 15 pages, 9 figures, 3 tables, Accepted for publication in A&A

Subjects: astro-ph.GA

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

An accurate POLARIZATION calibration is essential for a spectral data analysis and Zeeman splitting measurements. Two anomalies challenge our understanding of OH megamasers in IRAS 02524+2046: an unexplained 1667/1665 MHz flux-ratio deviation, and complex Stokes V signatures. Well-calibrated sensitive POLARIZATION observations are required to understand them. We develop a POLARIZATION calibration solution for the L-band 19-beam receiver installed on the Five-hundred-meter aperture spherical radio telescope (FAST) to achieve a high calibration accuracy and thus enable accurate measurements of the OH megamaser properties in IRAS 02524+2046. We determined the Mueller matrix solution for spectral observations across the 1050-1450 MHz frequency range with an accuracy of about 0.01%-0.08% for circular POLARIZATION. We then applied it to FAST observational data of IRAS 02524+2046. Our results show narrower emission line components in the OH megamasers than previously reported, which are indistinguishable in the total power spectrum, but are detected in the circular POLARIZATION spectrum. The 1667 MHz OH megamaser emissions probably span a wide velocity range from ~54750 to ~53580 km/s, indicating greater complexity than previously recognized. Our fit of the total power and circular POLARIZATION spectra for IRAS 02524+2046 revealed ten line components with significant Zeeman splitting (>3sigma), indicating in situ MAGNETic fields with a strength of approximately -24.5 mG to +20.6 mG, most of which (8/10) have positive values.

[abstract 38 / 46] (score: 2)
arXiv:2604.05425 [pdf, ps, other]

Title: Detectability of continuous gravitational waves from planetary-mass companions orbiting compact stars

Authors: Abdusattar Kurban, Xia Zhou, Na Wang, Yong-Feng Huang, Wenming Yan, Jianping Yuan, Ali Esamdin, Yu-Bin Wang, Zhigang Wen, Rai Yuen,

Comments: Accepted for publication in Astronomy and Astrophysics

Subjects: astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

Binary systems with ultrashort-period planetary-mass companions are expected to radiate continuous gravitational waves (GWs). However, earlier studies found that the detectability of such systems by the Laser Interferometer Space Antenna (LISA) is unlikely. In this study, we investigate the detectability of GWs from planetary-mass companions orbiting pulsars (PSRs) or white dwarfs (WDs) whose fundamental parameters, essential for calculating GW properties, have been measured. We compare the GW signals from our sample with the sensitivity curves of space-based GW detectors. We find that fourteen sources achieve a signal-to-noise ratio (\(\text{S/N}\)) of \(\gtrsim 5\) within four years of observations. Among these, three sources have PSR primaries (2S 0918-549 b, 4U 0513-40 b, and 4U 1543-62), and eleven systems possess WD primaries (BW Scl b, CP Eri b, CR Boo b, EF Eri b, GP Com b, GW Lib b, SDSS J0926+3624 b, SDSS J1507+5230 b, SMSS J1606-1000 b, SRGeJ0453 b, and WZ Sge b). We note that their detectability is less probable with near-term missions such as LISA, TianQin, and Taiji. Nevertheless, they could be detected by more advanced, future-generation observatories, such as the Deci-hertz Interferometer Gravitational wave Observatory (DECIGO) and the Big Bang Observer (BBO). This offers the potential to investigate the formation and evolution of ultrashort-period planetary-mass companions around compact stars through joint GW and electroMAGNETic surveys.

[abstract 39 / 46] (score: 2)
arXiv:2604.05479 [pdf, ps, other]

Title: One sightline, many systems: a FLASH discovery of HI towards scintillating QUASAR PKS 0405-385

Authors: E. F. Kerrison, H. Yoon, E. M. Sadler, Y. Kang, P. G. Edwards, A. Tuntsov, J. P. Pritchard, V. A. Moss, E. K. Mahony, H. Bignall, J. N. H. S. Aditya, J. R. Allison, S. Curran, R. D. Ekers, M. Glowacki, J. Stevens, R. Su, M. Whiting,

Comments: 11 pages, 5 figures and 1 table. Accepted for publication in PASA

Subjects: astro-ph.GA

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

We report the discovery of an intervening 21\,cm absorption line at z = 0.882 towards the z = 1.284 QUASAR PKS 0405-385, identified in the First Large Absorption Survey in HI (FLASH). This QUASAR once displayed the most rapid known intraday variability at radio frequencies, from which it earned the title of `the smallest radio QUASAR'. Although its size was revised upwards soon after based on updated scattering theory, PKS 0405-385 remains an important probe of Galactic plasma, and now also of intervening gas discovered through HI absorption. We present new long-slit spectroscopy spanning both PKS 0405-385 and the candidate host of the intervening HI gas. We identify MgII and FeII absorption lines in this spectrum consistent with the redshift of the intervening HI, as well as two additional, independent metal-line systems at z = 0.907 and z = 0.966, but we cannot accurately pinpoint the host(s) of this intervening gas in current data. We revisit the radio variability of PKS 0405-385 in light of advances in scintillation theory, as well as extended monitoring with the Australia Telescope Compact Array and the Australian SKA Pathfinder, and find a revised linear size >0.3 pc, but no new evidence of repeating intraday variability.

[abstract 40 / 46] (score: 2)
arXiv:2604.05604 [pdf, ps, other]

Title: Twisted doughnuts: Thick disk torus around equatorial asymmetric BLACK HOLE

Authors: Che-Yu Chen, Eva Hackmann, Audrey Trova,

Comments: 12 pages, 7 figures

Subjects: gr-qc astro-ph.GA astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

The Kerr BLACK HOLE spacetime is symmetric with respect to a well-defined equatorial plane. When such a symmetry is broken, for instance, by some putative effects beyond general relativity, the Keplerian circular orbits around the BLACK HOLE are distorted vertically away from the equatorial plane by an amount depending on the orbital radius. As a result, the Keplerian thin disk acquires a curved surface. In this work, we extend such results to thick tori configurations by considering non-self-gravitating Polish doughnut models. We show that due to the equatorial asymmetry of the spacetime, the centers and the cusps of tori are distorted away from the original equatorial plane toward the same direction as that experienced by the stable Keplerian orbits, and the entire tori configurations are twisted toward that direction as well. The shape of the distorted tori is demonstrated explicitly using a constant specific angular momentum profile $\ell(r,y)=\ell_0$ of the disk fluid. However, the result also applies to non-constant profiles of $\ell(r,y)$ generically in the sense that any asymmetric profile of $\ell(r,y)$ that attempts to produce a symmetric tori configuration either turns out to be ill-defined near the equatorial plane or suffers from fine-tuning issues.

[abstract 41 / 46] (score: 2)
arXiv:2604.05617 [pdf, ps, other]

Title: Persistence and Transition Varieties in Scalar Field Cosmology

Authors: Spiros Cotsakis,

Comments: 102 pages, 2 figures. Submitted to Classical and Quantum Gravity

Subjects: gr-qc math.DS

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

We develop a bifurcation-theoretic description of Friedmann--Robertson--Walker cosmologies with a scalar field $ϕ$, a barotropic fluid of index $γ$, and spatial curvature. For the strict exponential potential $V(ϕ)=V_{0}e^{λϕ}$, with $a=\sqrt{3/2}\,λ$, the local phase portrait is organised by five loci in the $(γ,a)$-plane: $|a|=3$, $a^{2}=3$, $a^{2}=9γ/2$, $γ=2/3$, and $γ=2$. Near these loci we compute translated JETs, centre(-like) reductions, and normal forms governing persistence and transitions. For the quadratic potential $V(ϕ)=(1/2)m^{2}ϕ^{2}$, the effective slope $λ$ is dynamical. Using the bounded variable $ζ=\arctanλ$, we obtain a regular autonomous $4$-dimensional system in $(X,Y,Ω_{k},ζ)$, where $Ω_{k}$ is the curvature variable. This reveals invariant gates, robust equilibrium continua, and vertical $γ$-thresholds for loss and recovery of normal hyperbolicity. We then construct an explicit stratification for the exponential class and a pull-back stratification for the massive case, together with the corresponding physical path maps into unfolding space. The resulting framework also organises slow-roll, ultra slow-roll, and oscillatory regimes.

[abstract 42 / 46] (score: 2)
arXiv:2604.05654 [pdf, ps, other]

Title: Probing the chiral MAGNETic effect via transverse spherocity event classification in RELATIVISTIC heavy-ion collisions

Authors: Somdeep Dey, Abhisek Saha,

Comments: 14 pages, 7 figures

Subjects: nucl-ex hep-ph nucl-th

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

We present the first study of the Chiral Magnetic Effect (CME) using transverse spherocity as an event-shape classifier in Pb+Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV, simulated with the A Multi-Phase Transport (AMPT) model with a realistic CME implementation. Transverse spherocity separates events into JETty and isotropic topologies based on the geometric distribution of transverse momentum. Unlike traditional event shape engineering methods, which use the flow vector as an event classifier that is itself contaminated by the very backgrounds it is intended to suppress, spherocity provides a cleaner, geometry-driven classification that avoids this circular limitation. CME inclusion shifts the spherocity distribution toward more isotropic events, confirming its sensitivity to CME-induced charge separation. The charge-dependent azimuthal correlator $Δγ$ and correlated background coupled with elliptic flow are consistently higher in JETty events. The scaled ratio $Δγ/v_2$ shows enhanced values for isotropic events, confirming effective background suppression after elliptic flow scaling. Our results demonstrate that isotropic event selection via transverse spherocity provides a cleaner and more reliable environment for CME searches by simultaneously suppressing flow-driven and resonance-decay backgrounds, making it a powerful complementary method to existing flow-vector-based methods.

[abstract 43 / 46] (score: 2)
arXiv:2604.05686 [pdf, ps, other]

Title: Strong Lensing and Quasinormal modes of BLACK HOLE around global monopole

Authors: Irengbam Roshila Devi, Ningthoujam Media, Yenshembam Priyobarta Singh, Telem Ibungochouba Singh,

Comments: 35 pages

Subjects: gr-qc

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

In this paper, we investigate various key aspects of a static and spherically symmetric BLACK HOLE with global monopole. Firstly, we analyze the deflection angle in the strong field limit of massive particle by the global monopole. It shows that the angle of deflection increases when the two characteristic parameters for monopole configuration increase. The influence of the global monopole parameter on the lensing observables and the BLACK HOLE shadow are studied. This shows that larger monopole parameter corresponds to larger shadow radii. The dynamics of timelike geodesics is also investigated in the spacetime. General circular orbits and the innermost stable circular orbits (ISCO) of timelike particles are discussed, highlighting that the monopole parameter significantly affects the circular orbits and the ISCO. In particular, it is observed that the radius of ISCO rises monotonically with $η$. In addition, the Lyapunov exponent is used to analyze the stability of timelike geodesics. The quasinormal modes for electroMAGNETic perturbation of the BLACK HOLE with varying $η$ is also investigated. Our findings indicate that increasing the monopole parameter gives rise to gravitational waves with slower damping oscillations. To further validate the derived quasinormal mode spectrum, we discuss the evolution of electroMAGNETic perturbations in the time domain profile, confirming the presence of the characteristic quasinormal ringing followed by late-time power-law tails.

[abstract 44 / 46] (score: 2)
arXiv:2604.06090 [pdf, ps, other]

Title: Posterior Predictive Checks for Gravitational-wave Populations: Limitations and Improvements

Authors: Simona J. Miller, Sophia Winney, Katerina Chatziioannou, Patrick M. Meyers,

Comments: 20 pages main text, 8 pages appendix (excluding references), 18 figures

Subjects: gr-qc astro-ph.HE

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

When selecting a model to characterize an astrophysical population, it is crucial to assess whether that model fits the data and, if not, how it can be improved. To this end, posterior predictive checks (PPCs) are a widely-used statistical test of model fit when inferring gravitational-wave source populations. However, PPCs exhibit limitations when assessing single-event parameters with large measurement uncertainty, like the spin tilt angles of the binary BLACK HOLEs (BBHs) observable with the LIGO-Virgo-KAGRA (LVK) detectors. When single-event inference is prior-dominated, traditional PPCs fail to flag even very poor model fits. In this work, we assess the efficacy of various alternative PPCs on poorly-constrained parameters. We compare PPCs conducted on event- vs.~data-level parameters (e.g. posterior samples vs. maximum likelihood points), and explore two additional event-level PPCs: partial predictive checks and split predictive checks. Independent of measurement uncertainty, we find that PPCs on maximum likelihood parameters are always more discerning of model misspecification than any event-level PPC. However, when investigating simulated GWTC-3.0-like catalogs, none of the alternative PPCs show significant improvement over those traditionally used, indicating that at that sensitivity, any limited information in the data about spin tilts is insufficient to diagnose model misspecification.Finally, we apply our suite of PPCs to the spin magnitude and tilt distributions inferred in the most recent LVK catalog, GWTC-4.0. We conclude that the Gaussian Component Spins model used therein under-predicts BBHs with large spin magnitudes and over-predicts those with perfectly anti-aligned tilts.

[abstract 45 / 46] (score: 2)
arXiv:2604.06096 [pdf, ps, other]

Title: Effects of Tungsten Radiative Cooling on Impurity, Heat and Momentum Transport in DIII-D Plasmas

Authors: A. Tema Biwole, T. Odstrčil, X. Litaudon, S. Shi, D. Ernst, C. F. B. Zimmermann, J. Lestz, N. T. Howard, P. Rodriguez-Fernandez, F. Khabanov, F. Turco, C. Perks, P. Manas, D. Fajardo, S. K. Kim, L. Schmitz, H. Wang, W. Boyes, S. Ding, B. Victor, C. Christal, C. Lasnier, T. M. Wilks, G. McKee,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

A first-of-its-kind experiment was conducted in the DIII-D tokamak under WEST similarity constraints on plasma shape and core parameters. This work presents a detailed transport study comparing a reference regime dominated by intrinsic carbon radiation and a high-radiation regime resulting from controlled tungsten (W) injection using the Laser Blow-Off system, with a core tungsten concentration $n_{\mathrm{W}}/n_e \sim 3\times 10^{-4}$ and a radiated-power fraction $f_\mathrm{rad}>0.5$. The W-induced radiative cooling lowered the electron temperature, thereby decreasing $T_e/T_i$ and stabilizing trapped-electron-mode (TEM) turbulence. This transition in turbulence regime reduced momentum and ion thermal diffusivities, yielding ion temperature peaking and a factor-of-two increase in toroidal rotation. At the outer plasma region, enhanced $E\timesB$ shear and increased collisionality further suppressed ion-scale turbulence, causing a sharp drop in ion heat flux. Consequently, impurity transport, predominantly turbulent in the low-radiation regime, acquired a strong neoclassical inward W convection during radiative cooling, bootstrapping the cooling cycle. Despite $f_\mathrm{rad}>0.5$, radiative collapse was not observed, likely owing to collisional ion-to-electron energy exchange acting as an electron-energy reservoir, together with $1/1$ MHD activity modulating the radiated power through core impurity neoclassical $T_i$-screening. These results support preparation for a tungsten wall change in DIII-D by elucidating tungsten-induced turbulence stabilization. They also provide key insights for interpreting plasma performance in WEST and are relevant to future reactors expected to operate with radiating tungsten-walled plasmas.

[abstract 46 / 46] (score: 2)
arXiv:2604.06121 [pdf, ps, other]

Title: Free Surface Enhancement of Droplet Rupture by Cavitation Bubble Collapse

Authors: Chenghao Xu, Zhengyu Yang, Jie Feng,

Comments:

Subjects: physics.flu-dyn

Created: 2026-04-07; Updated: 2026-04-08; Datestamp: 2026-04-08

The interaction between cavitation bubbles and surrounding droplets plays a central role in applications such as surface cleaning, ultrasonic emulsification, and therapeutic delivery. These processes depend on bubble-driven microJETs that drive the deformation and breakup of the droplets, which are significantly influenced by geometric confinements. Here, we investigate the hydrodynamic interaction between cavitation bubbles and oil droplets within a thin water layer considering the coupling confinements of a free surface and a rigid wall. We reveal two distinct regimes of droplet response to cavitation bubble collapse: the rupture regime, where oil droplets fragment into smaller droplets, and the no-rupture regime, where the droplet remains intact. By deriving a non-dimensional Kelvin impulse to represent the momentum of the bubble-induced JET, we establish a scaling law that correlates the criterion for droplet rupture to a characteristic Weber number and the bubble-to-droplet size ratio for the first time. This framework delineates the rupture boundary and even extends to predict the rupture of particle-laden droplets driven by cavitation bubbles. Our findings reveal the hydrodynamic principles underlying the cavitation bubble-driven droplet rupture and provide predictive criteria for controlling performance in engineering and biomedical systems involving cavitation bubble dynamics.