Current date: 2026-06-12

Setting default datestamp limit: 0

Datestamp limit: 2026-06-12 (0 days ago)

Created/updated limit: 2026-06-05 (7 days ago)

Suggested sets: physics, physics:astro-ph, physics:gr-qc, physics:physics

Setting default set: physics

OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2026-06-12&until=2026-06-12&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 734

Keyword score statistics

score 9 -- 1 abstracts

score 7 -- 3 abstracts

score 6 -- 3 abstracts

score 5 -- 3 abstracts

score 4 -- 4 abstracts

score 3 -- 12 abstracts

score 2 -- 16 abstracts

in total -- 42 abstracts

Articles that appeared on 2026-06-12

[abstract 1 / 42] Wow! (score: 9)
arXiv:2512.19259 [pdf, ps, other]

Title: Projected sensitivity of CTAO to axion-like particles from BLAZARs with a machine learning approach

Authors: Francesco Schiavone, Leonardo Di Venere, Francesco Giordano,

Comments: Accepted for publication in EPJC

Subjects: astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Blazars are a class of ACTIVE GALACTIC NUCLEi, supermassive BLACK HOLEs located at the centres of distant galaxies characterised by strong emission across the entire electroMAGNETic spectrum, from radio waves to gamma rays. Their RELATIVISTIC JETs, closely aligned to the line of sight from Earth, are a rich and complex environment, characterised by the presence of strong MAGNETic fields over parsec-scale lengths. Owing to their cosmological distance from Earth, these sources serve as ideal targets to probe non-standard gamma-ray propagation. In particular, axion-like particles (ALPs) could be detected through their coupling to photons, which enables ALP-photon conversions in external MAGNETic fields, leading to distinct signatures in the BLAZARs' gamma-ray spectra. In this work, we estimate the potential of the Cherenkov Telescope Array Observatory (CTAO) to constrain the ALP parameter space by simulating observations of two bright BLAZARs, Mrk 501 and PKS 2155$-$304. We obtain projected $2σ$ exclusion regions, demonstrating that CTAO will be able to consistently improve present limits thanks to its greater energy resolution and point-source sensitivity with respect to present ground-based gamma-ray telescopes. In addition to the standard statistical technique based on the likelihood ratio test, we further demonstrate the application of a new method based on machine learning classifiers, which may help in reducing the effect of systematic model-dependent uncertainties in future ALP searches.

[abstract 2 / 42] 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, V. Fallah Ramazani, D. Linder, F. Wierda,

Comments:

Subjects: astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

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 3 / 42] Wow! (score: 7)
arXiv:2606.12668 [pdf, ps, other]

Title: The X-ray photon index Eddington ratio relation in radio-quiet QUASARs from XMM-Newton and SDSS

Authors: SH. M. Shehata, Baraa Hany, Reham Mostafa,

Comments:

Subjects: astro-ph.GA

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

This study presents a comprehensive X-ray spectroscopic analysis of 642 QUASARs, obtained by cross-matching the XMM-Newton Serendipitous Source Catalog (DR11) with the Sloan Digital Sky Survey (DR16) QUASAR catalog. After stringent quality filtering and automated spectral reduction, we derived reliable photon indices ($Γ$) and intrinsic 2--10 keV X-ray luminosities. Using multiwavelength data, sources were classified into 561 radio-quiet (RQ) and 81 radio-loud (RL) QUASARs. We estimate the bolometric luminosity and Eddington ratio ($λ_{\mathrm{Edd}}$) from absorption-corrected X-ray measurements and virial BLACK HOLE masses. Our primary objective is to establish and characterize the fundamental relationship between the photon index and Eddington ratio for RQ population. We find that RQ QUASARs exhibit systematically higher Eddington ratios, peaking at $\log λ_{\mathrm{Edd}} \approx -1.2$, and softer spectra with $Γ\approx 2.0$. A statistically significant positive correlation between $Γ$ and $λ_{\mathrm{Edd}}$ is detected in RQ QUASARs, supporting disk--corona coupling models. To validate our results within the broader context of AGN evolution, we further examine the dependence of $λ_{\mathrm{Edd}}$ on redshift ($z$) and BLACK HOLE mass ($M_{\mathrm{BH}}$). For RQ QUASARs, $λ_{\mathrm{Edd}}$ increases with redshift and decreases with $M_{\mathrm{BH}}$, in strong agreement with recent results \cite{aggarwal2024evidence}, highlighting the universal nature of these accretion trends. By correlating spectral slope with accretion rate, this work provides new insights into the interplay between accretion physics, JET activity, and the cosmic evolution of QUASARs.

[abstract 4 / 42] Wow! (score: 7)
arXiv:2606.13493 [pdf, ps, other]

Title: The ultra low-frequency spectral properties of bright extended RADIO GALAXies in the 3CRR catalogue

Authors: J. M. Boxelaar, F. De Gasperin, M. J. Hardcastle, E. De Rubeis, R. J. van Weeren,

Comments: 16 pages, 9 figures

Subjects: astro-ph.GA

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Context. Active galactic nuclei (AGN) JETs are fundamental drivers of galaxy evolution, injecting kinetic energy into their environments. The large-scale morphology and spectral properties of these RADIO GALAXies are consequences of complex particle acceleration, energy loss, and absorption processes. While the shape of the SYNCHROTRON spectrum encodes the plasma's energetic history, understanding the physics of particle acceleration and duty cycles has historically been limited by a lack of well-resolved observations at ultra-low frequencies (< 100 MHz), where the oldest COSMIC RAY electron populations are traced. Aims. This study aims to perform the first comprehensive multi-frequency analysis of bright extended RADIO GALAXies down to 58 MHz. The goal is to study electron acceleration mechanisms, accurately measure the low-frequency spectral shape, and constrain the injection index for a sample of Fanaroff-Riley (FR) I and II galaxies using spectral ageing models. Methods. Utilising new 58 MHz observations from the LOFAR Low Band Antenna (LBA) combined with LOFAR High Band Antenna (HBA; 144 MHz) and Rapid ASKAP Continuum Survey (RACS, 887 MHz & 943.5 MHz & 1367.5 MHz) data, a sub-sample of 22 extended sources from the 3CRR catalogue was selected, requiring the largest angular size to be at least 2.5'. The analysis involves constructing detailed spectral index maps and utilising radio colour-colour diagrams to interpret spectral shapes and constrain ageing model parameters across the radio lobes. Results. This study presents the ultra-low frequency spectral index maps for this sample. For FR I galaxies, spectral indices range from ~0.5 near the core (consistent with first-order FERMI acceleration) to > 1.0 in the lobes. For FR II galaxies, hotspots exhibit steep low-frequency spectra (0.5 - 0.9), suggesting complex acceleration or absorption effects.

[abstract 5 / 42] Yes (score: 6)
arXiv:2606.12511 [pdf, ps, other]

Title: Unification models of Active Galactic Nuclei

Authors: Claudio Ricci,

Comments: Invited chapter for the Encyclopedia of Astrophysics (edited by I. Mandel, section editor S. McGee) to be published by Elsevier as a Reference Module

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

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

This chapter presents an overview of the unification models for Active Galactic Nuclei (AGN), focusing on the physical structures, classification schemes, and evolutionary processes that characterize accreting supermassive BLACK HOLEs. We introduce the fundamental components of AGN, including the supermassive BLACK HOLE, accretion disk, JETs, outflows, broad-line and narrow-line regions, polar dust and the dusty anisotropic obscurer. The traditional orientation-based unification model is reviewed, with a focus on the role of the covering factor of the obscuring material in shaping observed properties. We introduce the radiation-regulated unification model, which accounts for the influence of radiative feedback on the nuclear environment of SMBHs. We also examine the evolutionary aspects of AGN unification, including the impact of galaxy mergers, host galaxy properties, and redshift-dependent trends. Finally, we discuss changing-look AGN, which challenge conventional unification frameworks by exhibiting dramatic spectral variability.

[abstract 6 / 42] Yes (score: 6)
arXiv:2606.12518 [pdf, ps, other]

Title: Black Hole Polarimetry III: Universal Polarization of Synchrotron Radiation at the Horizon

Authors: Andrew Chael, Alexandru Lupsasca, George N. Wong, Zachary Gelles, Eliot Quataert,

Comments: 24 pages, 6 figures

Subjects: astro-ph.HE gr-qc

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

Polarized images of a BLACK HOLE encode the direction of electroMAGNETic energy flow near its event horizon. Measuring POLARIZATION from near-horizon emission can determine whether this energy flow is powered by the accreting plasma or the BLACK HOLE spin. Here we consider the linear POLARIZATION of SYNCHROTRON radiation emitted from the base of horizon-threading field lines in a time-stationary, axisymmetric, and degenerate Kerr MAGNETosphere. We show that the observed POLARIZATION pattern displays universal behavior: it is completely determined by the BLACK HOLE spin and observer inclination and is independent of the MAGNETic field geometry. We derive a simple analytic formula for this spin-dependent horizon POLARIZATION pattern. We find that this predicted pattern is also approached in time-averaged images from General Relativistic Magnetohydrodynamic simulations. Future observations with Very-Long-Baseline Interferometry at microarcsecond resolution could detect the trend of POLARIZATION toward the unique horizon value in M87*. Such observations may enable new measurements of BLACK HOLE spin and provide evidence that MAGNETic field lines thread the horizon and extract spin energy via the Blandford--Znajek process.

[abstract 7 / 42] Yes (score: 6)
arXiv:2606.12543 [pdf, ps, other]

Title: Spectral analysis of MAGNETized advective accretion flows around rotating BLACK HOLEs

Authors: Mayank Pathak, Shubhrangshu Ghosh, Banibrata Mukhopadhyay,

Comments: 20 pages including 16 figures (32 png files) and 2 tables; accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

The spectra of an accretion disk around BLACK HOLEs are the basic diagnostic tool to enlighten the underlying flows and then BLACK HOLEs. Accretion flows around BLACK HOLEs, however, are controlled by parameters like the MAGNETic field, spin of the BLACK HOLE, accretion rate and temperature of the flow. These quantities affect the (MAGNETo)hydrodynamics of the flow thus consequently lead to variations in the spectrum. We first consider numerical steady state MAGNETohydrodynamic (MHD) solutions of MAGNETized accretion flows around BLACK HOLEs to study the dependence of the spectra on these disk properties. The spectrum exhibits strong dependence on the spin of the BLACK HOLE, accretion rate, MAGNETic field and the electron temperature of the flow. Variations in these quantities influence the emission peaks and overall luminosity, which can be a tell-tale sign to extract physics of observed spectra. We further validate our results with general RELATIVISTIC MHD (GRMHD) simulations using the standard and normal evolution (SANE) and MAGNETically arrested disk (MAD) vector potentials. We consider two BLACK HOLE spins ($a=0.5$ and $a=0.9375$) to model the MAGNETic field configurations and study the resulting spectra by comparing MAD and SANE results. We find a large difference in the bolometric luminosities and the location of the emission peaks between SANE and MAD flows. Certain properties of the spectra, like, the ratio of SYNCHROTRON radiation to SYNCHROTRON self-Comptonization peaks in SANE and MAD, show drastically distinct features. The overall luminosity combined with such metrics can distinguish the MAGNETic field characteristics in astrophysical systems.

[abstract 8 / 42] Yes (score: 5)
arXiv:2602.09102 [pdf, ps, other]

Title: Polarization Signatures of Inspiraling Hotspots around Kerr Black Holes

Authors: Pablo Ruales, Delilah E. A. Gates, Alejandro Cárdenas-Avendaño,

Comments: v3: Fixed typo in Eq.II.10

Subjects: astro-ph.HE gr-qc

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Polarimetric interferometry is a powerful tool for probing both BLACK HOLE accretion physics and the background spacetime. Current models aimed at explaining the observed multiwavelength flares in Sgr A* often assume hotspots moving on geodesic, Keplerian orbits. In many scenarios, though, a hotspot may instead follow an inspiraling trajectory, potentially transitioning into a plunge toward the BLACK HOLE. In this work, we present a general framework to simulate the polarized emission from generic equatorial inspiraling hotspots in Kerr spacetime using a parametric four-velocity profile. This parametrization defines a continuous family of flows, ranging from Cunningham's disk model (fixed radius orbits outside the innermost stable circular orbit and plunging motion within the innermost stable circular orbit) to purely radial motion, thereby extending the standard assumptions. Within this framework, we show that inspiral motion produces a distinctive observational signature: a precessing, unwinding evolution of the polarimetric Stokes Q-U looping pattern, in sharp contrast with the closed Q-U loops associated with stable orbits at a fixed radius. We then explore how the morphology of these signatures depends on BLACK HOLE spin, observer inclination, and MAGNETic-field configuration. The presented model can be applied to current and near-future interferometric observations of linear POLARIZATION, offering a new avenue to probe the physics of matter spiraling inward and the RELATIVISTIC velocities of plunging plasma.

[abstract 9 / 42] Yes (score: 5)
arXiv:2606.11939 [pdf, ps, other]

Title: Detection of a parsec-scale, compact, and fading ejecta from an accreting massive BLACK HOLE

Authors: Chao Li, Ning Chang, Jun Yang, Lang Cui, Luis C. Ho,

Comments: 5 pages, 3 figures

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

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

Dwarf galaxies, characterized by their low luminosities and masses, are excellent candidates for searches for intermediate-mass BLACK HOLEs (IMBHs), particularly when they show strong accretion and ejection activity. The dwarf galaxy SDSS J101747.09+393207.7 has recently been found to display a very high X-ray luminosity and an X-shaped optical structure, possibly caused by a dwarf--dwarf merger. To explore its potential IMBH ejection activity, we performed very long baseline interferometry (VLBI) observations at 4.9 GHz. In this work, we present the detection of a milliarcsecond-scale, compact, sub-microjansky radio component near the optical centroid. According to some existing radio sky survey data, the radio component was not detected until 2015; it displayed an optically thin steep radio spectrum and declining flux densities across 0.8--5 GHz from 2019 to 2025. Therefore, we identify it as a short-lived and rarely seen ejecta that was produced by unstable accretion onto a massive BLACK HOLE and likely faded away in a few decades. These results indicate that short-lived, episodic JET activity from accreting IMBHs in dwarf galaxies might exist.

[abstract 10 / 42] Yes (score: 5)
arXiv:2606.12531 [pdf, ps, other]

Title: Gotta light? Illuminating AGN disks with LISA EMRIs

Authors: Federico Fantocolli, Francisco Duque, Jonathan Gair,

Comments: 8 pages, 4 figures

Subjects: gr-qc astro-ph.HE

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

We study the ability of the upcoming Laser Interferometer Space Antenna (LISA) to constrain gas torques acting on extreme-mass-ratio inspirals (EMRIs) when these are embedded in accretion disks, using recently developed RELATIVISTIC models for the binary-disk interaction. Using a fully Bayesian setup, we find that, contrary to previous forecasts based on Newtonian results, these observations can provide simultaneous estimates of the disk surface density and the accretion rate (or, equivalently, its total luminosity) without the need for an electroMAGNETic counterpart. Our analysis also indicates that simpler measurement constraints based on the linear-signal (Fisher matrix) approximation are not valid for these systems. For typical EMRI observations, the torque amplitude can be constrained to within ~10%, strengthening the prospect of probing accretion physics at (sub)microparsec scales, deep in the strong-field gravity regime and complementing electroMAGNETic observations. This also strengthens LISA's ability to help answering questions such as how massive BLACK HOLEs grow and coevolve with their host galaxies and, by helping to identify the EMRI's host galaxy through cross-correlation with AGN catalogues, to improve the use of these sources as (dark) sirens for cosmology.

[abstract 11 / 42] Yes (score: 4)
arXiv:2601.01763 [pdf, ps, other]

Title: When the Shadow Meets Its Measure: Assessing the Feasibility of Submillimeter Black Hole Shadow Imaging in Megamaser Disk AGN

Authors: Roman N. Burridge, Geoffrey C. Bower,

Comments: 25 pages, 7 figures, 9 tables. Revised version with updated 230 GHz flux standardization, astrometric feasibility analysis for NGC 4258, mass/distance/inclination treatment, references, and machine-readable table description

Subjects: astro-ph.GA astro-ph.IM

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Active galactic nuclei (AGN) hosting water megamaser disks provide precise geometric measurements of BLACK HOLE mass, distance, maser disk orientation, and dynamical center. In anticipation of space-based very long baseline interferometry, these systems offer a path to BLACK HOLE shadow (BHS) imaging beyond Sgr A* and M87*. We present new Submillimeter Array continuum observations of water megamaser galaxies, supplemented by archival ALMA and VLA measurements, to assess whether their AGN cores are bright enough for BHS-scale imaging. For a 21-source parent sample, we map the predicted BHS diameters of systems with published SMBH masses to submillimeter/millimeter (submm-mm) baseline requirements, estimate AGN core flux densities at 230 GHz while bounding thermal dust and extended-JET contamination and checking whether variability could affect the continuum estimates, and evaluate the astrometric precision required to detect spin-dependent BHS offsets for NGC 4258. NGC 4258 is the only source resolvable on Earth-L2 baselines; other targets require longer baselines approaching Earth-L4/L5 distances, and only a handful have $S_{230} \gtrsim 10$ mJy beam$^{-1}$. We also find a submillimeter excess in NGC 4258, suggesting that its disk remains geometrically thin to $\lesssim 100$ Schwarzschild radii before transitioning to an advection-dominated flow. Even for maximal spin, the formal 230 GHz BHS centroid precision is not the limiting term: the measurement would require locating the 22 GHz water maser dynamical center and registering it to the 230 GHz BHS image roughly seventy times more precisely than current maser astrometry allows, making the spin-offset measurement infeasible with present data.

[abstract 12 / 42] Yes (score: 4)
arXiv:2601.14391 [pdf, ps, other]

Title: Cold gas formation triggered by ACTIVE GALACTIC NUCLEi JET feedback in galaxy cluster cores

Authors: Stefano Sotira, Martin A. Bourne, Debora Sijacki, Franco Vazza, Fabrizio Brighenti,

Comments: 15 pages, 11 figures, 1 table. Accepted for publication in A&A

Subjects: astro-ph.GA

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Extended warm and cold gas nebulae, with complex morphologies and kinematics, have been observed in the centres of cool-core galaxy clusters. Their origin within the hot intracluster medium (ICM) is still puzzling, and among many mechanisms, positive feedback from the central ACTIVE GALACTIC NUCLEus (AGN) has been proposed. In this work, we performed a suite of very high-resolution hydrodynamic simulations of a Perseus-like cool-core galaxy cluster subject to self-regulated AGN JET feedback, which leads to realistic ICM properties. By explicitly following warm ionized, neutral, and molecular gas phases, we studied the complex interplay between AGN activity and the multi-phase ICM. While AGN feedback globally heats the ICM, we find that during the individual AGN JET bursts, hot material is also injected laterally to the JET axis, within the turbulent mixing layer. This material, as it expands, compresses the surrounding hot ICM, reducing the local cooling time, and leads to the formation of cold clumps on a characteristic timescale of $\sim 30$ Myr. By employing tracers, we explicitly track cooling within the affected regions, finding that very hot gas identified in high-compression, low-vorticity zones condenses in situ to form cold clumps. A statistical analysis reveals that the condensation of cold gas is highly promoted once the local turbulent Mach number, $σ_{hot}/c_{s,hot}$, in the hot gas component ($T \geq 10^7$ K) takes values around ~0.3. The presented process is a further important step in understanding the physical mechanisms that lead to the formation of cold gas in the cluster core. Our measured values of the characteristic turbulent Mach number, together with detailed multi-phase gas kinematics predictions, provide important theoretical tools to interpret future X-ray spectroscopy and deep radio data, ultimately to constrain the origin of cool-core cluster nebulae.

[abstract 13 / 42] Yes (score: 4)
arXiv:2606.12832 [pdf, ps, other]

Title: Data-driven modeling of Galactic diffuse emission with multi-wavelength observations

Authors: Xi Liu, Xiaodong Li, Sujie Lin, Yihan Liu, Chengyu Shao, Lili Yang, Le Zhang,

Comments: 13 pages, 9 figures, submitted to EPJC

Subjects: astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

We present a data-driven investigation of Galactic diffuse emission. Using multi-frequency Planck radio/microwave maps (30-857 GHz) and FERMI-LAT gamma-ray data (50 MeV-814 GeV), we construct a nonlinear mapping between radio emission and gamma-ray intensity through supervised machine learning. Our models achieve high predictive accuracy (R^2 > 0.90 in the 0.1-10 GeV range), demonstrating that multi-frequency radio observations encode sufficient information to reconstruct both spatial morphology and spectral properties of diffuse gamma-ray emission. By analyzing model performance across different frequency bands and spatial regions, we identify high-frequency radio bands as the dominant predictor, providing direct empirical support for the hadronic origin of Galactic 0.1-10 GeV gamma rays, while low-frequency radio bands for the leptonic origin above 10 GeV. Residual maps reveal coherent large-scale structures, including Loop I and III, highlighting regions where standard interstellar emission models are incomplete or biased. Compared with the GALPROP model, our machine learning approach yields a higher R^2=0.95 and lower mean absolute relative error (14.7%) in the inner Galactic disk and the Galactic center region. Our results illustrate that machine learning serves as a physically interpretable tool for multi-messenger astrophysics, providing a data-driven baseline for separating non-standard emission components and deriving new constraints on cosmic-ray propagation and interstellar medium structure.

[abstract 14 / 42] Yes (score: 4)
arXiv:2606.13398 [pdf, ps, other]

Title: A robust super-time-stepping scheme for Ohmic and ambipolar diffusion

Authors: Giancarlo Mattia, Mario Flock, David Melon Fuksman, Anastasia Tzouvanou, Vittoria Berta, Daniele Crocco,

Comments: 14 pages, 15 figures (+ appendix, 5 pages, 5 figures), under revision for A&A

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

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Context. Non-ideal MAGNETohydrodynamics (MHD) is a key tool for modeling MAGNETic flux transport in astrophysical systems such as molecular clouds, protostellar cores, and protoplanetary disks. Conventional explicit methods for non-ideal MHD diffusion are severely limited by timestep constraints, while substepping approaches can be unstable due to truncation errors near boundaries and strong MAGNETic-field gradients. Aims. Our main goal is to address these limitations by developing robust super-time-stepping methods for Ohmic and ambipolar diffusion. Methods. We present a super-time-stepping method based on the stability of the Gegenbauer polynomials. The method is designed to enhance robustness in the presence of strongly anisotropic resistivity and to reduce sensitivity to truncation errors near boundaries. We implement the scheme in the PLUTO code and assess its performance through dedicated Ohmic and ambipolar diffusion tests. We also compare this novel numerical scheme against two common astrophysical problems, namely MAGNETic RECONNECTion and the MAGNETorotational instability. Results. The novel Runge-Kutta-Gegenbauer scheme retains computational efficiency beyond purely explicit schemes while providing excellent stability compared with other traditional substepping methods. It remains stable in the presence of strongly anisotropic diffusion, enabling accurate MAGNETic-field evolution in regimes characteristic of protoplanetary disks and collapsing dense cores. Benchmark tests, including MAGNETic RECONNECTion and MAGNETorotational-instability setups, confirm the method's accuracy, efficiency, and suitability for large-scale non-ideal MHD simulations.

[abstract 15 / 42] (score: 3)
arXiv:2510.19822 [pdf, ps, other]

Title: Supermassive Black Hole Growth in Massive Galaxies at Cosmic Dawn

Authors: James Sunseri, Zachary L. Andalman, Romain Teyssier,

Comments: 17 pages, 7 figures, 1 table

Subjects: astro-ph.GA astro-ph.CO

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Among the emerging excess of massive, bright galaxies at Cosmic Dawn $z \gtrsim 9$ seen by the James Webb Space Telescope, several exhibit spectral features associated with ACTIVE GALACTIC NUCLEi (AGN). These AGN candidates suggest that supermassive BLACK HOLEs (SMBHs) grow rapidly in the early Universe. In a series of numerical experiments, we investigate how SMBHs grow within and influence the most massive galaxies at Cosmic Dawn using cosmological hydrodynamic zoom-in simulations run with the adaptive mesh refinement code \textsc{ramses}. Our suite of simulations explore how super-Eddington accretion, seed mass, and the strength of feedback influence SMBH-galaxy co-evolution in the most massive galaxies ($M_\star \gtrsim 10^8 M_\odot$) of the early Universe ($z \sim 15 - 9$). The environment which our numerical experiments reside in is an overdensity that collapses into a $\sim 10^{11} M_\odot$ halo by $z \sim 9$. Within this type of environment we find that SMBH growth is sensitive to stellar feedback which generates a turbulent-multiphase interstellar medium (ISM) that stochastically starves the SMBH. In the absence of AGN feedback, we find that the SMBH is starved $\sim 50\%$ of the time after the onset of STAR FORMATION in the galaxy. SMBH growth can become self-regulated by AGN feedback if the SMBH becomes massive enough, either by accretion or seeding, for its feedback to dominate the surrounding nuclear region. We find no evidence of galaxy-scale, AGN-driven quenching in the STAR FORMATION rate (SFR) across all simulations in our suite.

[abstract 16 / 42] (score: 3)
arXiv:2510.21709 [pdf, ps, other]

Title: From nuclear star clusters to Little Red Dots: BLACK HOLE growth, mergers, and tidal disruptions

Authors: Konstantinos Kritos, Joseph Silk,

Comments: 22 pages, 7 figures, accepted to ApJ

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

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Little Red Dots, discovered by the James Webb Space Telescope, are hypothesized to be ACTIVE GALACTIC NUCLEi containing a supermassive BLACK HOLE, possibly surrounded by a dense stellar cluster, large amounts of gas, and likely by a population of stellar-mass BLACK HOLEs. We develop a simple nuclear star cluster model to evolve the rapid mass growth of BLACK HOLE seeds into the supermassive regime. The combined processes of tidal disruption events, BLACK HOLE captures, and gas accretion are accounted for self-consistently in our model. Given the observed number density of Little Red Dots, and under reasonable assumptions, we predict at least a few tens of tidal disruption events and at least a few BLACK HOLE captures at z=4-6, with a tidal disruption event rate an order of magnitude larger than the BLACK HOLE capture rate. We also estimate the uncertainties in these estimates. Finally, we comment on the low x-ray luminosity of Little Red Dots.

[abstract 17 / 42] (score: 3)
arXiv:2512.03472 [pdf, ps, other]

Title: Quasi-linear theory of perpendicular ion heating by critically balanced turbulence

Authors: Zade Johnston, Jonathan Squire,

Comments: 57 pages, 25 figures. Accepted for publication in Journal of Plasma Physics

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

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

In collisionless astrophysical plasmas, turbulence mediates the partitioning of free energy among cascade channels and its dissipation into ion and electron heat. The resulting ion heating is often anisotropic, with ions observed to be preferentially heated perpendicular to the local MAGNETic field; understanding the mechanisms responsible for this heating is a key step in understanding the evolution of such plasmas. In this paper, we use the framework of quasi-linear theory to compute analytically the heating rates of ions interacting with turbulent, large-scale Alfvénic fluctuations. We show how the imbalance of the turbulence (the difference in energies between Alfvénic fluctuations travelling parallel and antiparallel to the MAGNETic field) modifies the spatiotemporal spectrum of these fluctuations, allowing the heating mechanism to smoothly transition between stochastic heating in balanced turbulence and cyclotron-resonant heating in imbalanced turbulence. The resultant heating rate is found to have a general form regardless of the level of imbalance, exhibiting a suppression related to the conservation of the ions' MAGNETic moment at small turbulent amplitudes and recovering previous empirical results in a formal calculation. The results of this work help to consolidate our qualitative understanding of ion heating within astrophysical plasmas, as well as yielding specific quantitative predictions to analyse simulations and observations.

[abstract 18 / 42] (score: 3)
arXiv:2605.06162 [pdf, ps, other]

Title: Vacuum POLARIZATION and cyclotron resonance effects on radiative transfer and plasma deceleration in subcritical X-ray pulsars

Authors: I. D. Markozov, A. Y. Potekhin, A. D. Kaminker, A. A. Mushtukov,

Comments: 20 pages, 14 figures, 1 table, submitted to MNRAS. The submitted version (v2) is substantially amended, partly due to the feedback on v1

Subjects: astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

We investigate the spectrum and POLARIZATION of radiation emerging from a subcritical X-ray pulsar using self-consistent radiation-hydrodynamic simulations of an accretion channel in a strong MAGNETic field. The polarized radiative transfer in the channel above the hot spot is simulated for the two normal modes, taking into account resonant Compton scattering in a strongly MAGNETized plasma and the effects of vacuum POLARIZATION. We show that the deceleration of the accreting matter in the subcritical regime is mainly governed by resonant scattering. Our simulations provide the velocity profiles of the plasma flow and demonstrate that vacuum POLARIZATION dominates over plasma birefringence, enhancing both the cyclotron spectral feature and the radiative deceleration of the plasma. We also find that the energy of the cyclotron feature increases with accretion luminosity, indicating a positive correlation consistent with previous observational results and theoretical interpretation.

[abstract 19 / 42] (score: 3)
arXiv:2606.12522 [pdf, ps, other]

Title: Magnetic fields at the dawn of structure formation I. The CARLA J1510+5958 proto-cluster

Authors: A. Pagliotta, A. Bonafede, C. Stuardi, C. J. Riseley, D. Vallés-Péerez, P. Tozzi, L. Di Mascolo,

Comments: 21 pages, 14 figures, accepted for publication in A&A, shortened abstract to meet arXiv characters requirement

Subjects: astro-ph.CO astro-ph.GA

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

Magnetic fields are a fundamental ingredient of the Universe, influencing the formation and evolution of cosmic structures. While MAGNETic fields in local galaxy clusters have been studied, their origin, amplification, and strength at high redshift are poorly understood. Proto-clusters represent the early stages of galaxy cluster formation, ideal for investigating the early MAGNETisation of the intra-cluster medium (ICM). We present a study of CARLA J1510+5958 proto-cluster at z = 1.72, observed with the JVLA in the L-band (1-2 GHz). We aim to investigate the MAGNETic field strength and structure in the proto-ICM and the role of AGN in MAGNETising the environment during early cluster formation. We analyse Faraday rotation on the polarised emission from the central radio-loud AGN using the Rotation Measure (RM) synthesis and QU fitting technique. We further interpret the observations with 3D simulations of gas density and turbulent MAGNETic fields, varying AGN orientation and path length. The two AGN lobes show different polarisation properties. The Western lobe exhibits a uniform RM (average $-115 \pm 32\text{ rad m}^{-2}$, dispersion $36 \pm 11\text{ rad m}^{-2}$), indicating a locally ordered MAGNETic field likely compressed by the lobe, while the Eastern lobe is depolarised. Although the asymmetry indicates a turbulent, MAGNETised medium, simulations rule out a purely isotropic random field for the Western lobe RM distribution. The QU fitting further suggests an internal Faraday component, interpreted as MAGNETised RELATIVISTIC plasma from the lobe mixed with the surrounding gas, indicating possible MAGNETisation of the ambient medium by the AGN. From this asymmetry, we constrain the average physical MAGNETic field in the proto-ICM to a lower limit of 0.4 $μ$G. These results confirm a MAGNETised proto-ICM at z = 1.72, proving early field amplification during cluster assembly.

[abstract 20 / 42] (score: 3)
arXiv:2606.12784 [pdf, ps, other]

Title: Constraining Kerr supermassive BLACK HOLE properties using gravitational waves from inspiraling stellar-mass binary BLACK HOLEs

Authors: Jie Wu, Jin-Tao Yao, Mengfei Sun, Jin Li, Zhoujian Cao,

Comments: 16 pages, 7 figures

Subjects: gr-qc

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

We study the capability of future space-based gravitational-wave (GW) detectors to constrain supermassive BLACK HOLE (SMBH) properties through observations of inspiraling stellar-mass binary BLACK HOLEs (BBHs) orbiting them. Focusing on stable hierarchical triple systems, we model the BBH motion in Kerr spacetime and compute the modulated GW signals using the post Newtonian waveform combined with moving-source transformation. Based on the LISA configuration and second-generation time delay interferometry technology, we estimate parameter uncertainties with the Fisher information matrix. Our results show that the outer semimajor axis has the strongest influence on parameter precision, while the SMBH spin and eccentricity mainly affect their own uncertainties. For high-SNR signals, the SMBH mass and orbital parameters can be measured with relative uncertainties on the order of $10^{-5}$, while the spin magnitude and its orientation can be constrained to within a few percentages. Applying the method to an M87*-like system, GW observations provide more precise measurements of the SMBH mass and spin compared with current electroMAGNETic observations, highlighting the potential of space-based GW astronomy to probe SMBH properties with high accuracy.

[abstract 21 / 42] (score: 3)
arXiv:2606.12846 [pdf, ps, other]

Title: Constraining inhomogeneities and asymmetries in SNe, FBOTs, and other high-energy transients from unresolved radio observations

Authors: Fabio De Colle, Rosa L. Becerra, Lizeth A. Meza, Nayana A. J., James K. Leung, Luca Izzo, Raffaella Margutti, Gerardo Urrutia, Enrique Moreno-Méndez, Leonardo García-García,

Comments: 12 pages, 8 figures, submitted to MNRAS

Subjects: astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Synchrotron emission in high-energy transients is produced by RELATIVISTIC electrons accelerated by shocks. As high-energy transients are often unresolved even on angular scales probed by very long baseline interferometry, it is difficult to obtain a full picture of the ejecta and circumstellar medium (CSM) properties that are probed by the radio SYNCHROTRON emission. Radio spectra of high-energy transients frequently show optically thick slopes shallower than the standard $F_ν\propto ν^{5/2}$ expected from SYNCHROTRON self-absorption (SSA) models, or broader spectra near the self-absorption frequency. Such deviations are often interpreted phenomenologically, without providing clear insights into the structure of the emitting region. We show how information on the homogeneity and symmetry of the emitting region can be directly inferred from SSA spectra, even when the source is unresolved. We discuss the circumstances under which inhomogeneities in the emitting region can change the spectrum below the self-absorption frequency, causing it to follow a different slope. We examine which parameters can be constrained from observations and which remain degenerate. We apply this method to the stripped-envelope SUPERNOVA (SN) 2016coi and to the fast blue optical transient (FBOT) AT2018cow, showing that SSA spectra constrain the degree of inhomogeneity in these systems, providing strong evidence for inhomogeneities in the emitting region in the SN 2016coi, and asymmetry in the case of AT2018cow, and we infer the characteristics of the emitting region. When well sampled spectra are available, our method can be applied as a general, model-independent, inference method. This approach can be used to constrain inhomogeneities in a variety of unresolved high-energy astrophysical transients, including SNe, FBOTs, tidal disruption events and GAMMA-RAY BURSTs.

[abstract 22 / 42] (score: 3)
arXiv:2606.12952 [pdf, ps, other]

Title: Gravitational wave background from extreme-mass-ratio inspirals

Authors: Haoyu Zhao, Yuanhao Zhang, Xilong Fan, Wenbiao Han,

Comments:

Subjects: astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

The gravitational wave background (GWB) produced by extreme-mass-ratio inspirals (EMRIs) serves as a powerful tool for probing the astrophysical and dynamical processes in galactic centers. EMRI systems are a primary target for the space-based detector LISA due to their long-lived signals and high signal-to-noise ratios. This study explores the statistical properties of the GWB from EMRI, focusing on the calculation methods for the GWB, the astrophysical distribution of EMRI sources, and the influence of key parameters, including the spin of supermassive BLACK HOLEs (SMBHs) and the masses of compact objects (COs). By analyzing these factors, we determine the distribution range of the characteristic strain of the GWB from EMRIs. We find that the final eccentricity distributions appear to have negligible effect on the intensity of the GWB due to rapid circularization before they become detectable and the spin of the SMBH enhances the GW characteristic strain by approximately 1$\%$ compared to cases without spin effects. The masses of COs can also significantly affect the characteristic strain of the GWB from EMRIs, with Black Hole (BH) as CO producing a GW signal intensity that is approximately one order of magnitude higher compared to cases where Neutron Star (NS) or White Dwarf (WD) are the COs.

[abstract 23 / 42] (score: 3)
arXiv:2606.13021 [pdf, ps, other]

Title: Enhanced Target Interaction Area of Helical Plasma Plumes in a Pulsed RF Atmospheric Plasma Jet

Authors: Radhika T P, Satyananda Kar,

Comments: 8 pages, 4 figures

Subjects: physics.plasm-ph

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Helical plasma plumes generated in pulsed radiofrequency atmospheric pressure plasma JETs exhibit unique flow dynamics arising from the coupling between Kelvin-Helmholtz instabilities and baroclinic torque. While the fundamental mechanism responsible for helical plume formation has been established, the implications of this morphology for plasma-target interaction remain largely unexplored. In this study, we experimentally investigate the interaction area of helical plasma plumes with different target configurations and compare it with the conventional conical plume produced under continuous RF excitation. High-speed imaging reveals that the helical plume significantly enlarges the effective plasma-target interaction region due to its rotating trajectory and enhanced air entrainment. The effect of different target materials and boundary conditions, including dielectric surfaces and metal-backed substrates, is systematically examined. The results demonstrate that helical plumes provide superior surface coverage, improved spatial distribution of reactive species, and enhanced plasma-surface coupling. These findings highlight the advantages of helical plasma JETs for applications requiring large-area plasma treatment, including plasma medicine, surface modification, and plasma-liquid interactions.

[abstract 24 / 42] (score: 3)
arXiv:2606.13090 [pdf, ps, other]

Title: Field line slippage rate signatures in nonlinear force-free field extrapolations

Authors: Sage Stanish, David MacTaggart,

Comments: Accepted for MNRAS

Subjects: astro-ph.SR

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Magnetic RECONNECTion plays a central role in solar flares and coronal mass ejections. Identifying where RECONNECTion is physically active within coronal MAGNETic field models is a key part of MAGNETic field analysis. We investigate the field line slippage rate as a physics-weighted proxy for three-dimensional RECONNECTion in nonlinear force-free field (NLFFF) extrapolations. The slippage rate measures the instantaneous deviation of MAGNETic field lines from ideal evolution, due to non-ideal terms in Ohm's law, providing a direct link between MAGNETic geometry and RECONNECTion physics. For NLFFFs, we show that the resistivity-induced slippage rate is governed by cross-field gradients of the field-aligned twist, thus establishing a clear connection between current structure and RECONNECTion signatures. We further examine its relationship to the squashing factor $Q$, used to identify quasi-separatrix layers (QSLs). By deriving a scaling estimate, we demonstrate that strong MAGNETic squashing amplifies slippage only insofar as it produces small transverse length scales; large values of $Q$ alone do not guarantee significant RECONNECTion. We apply this framework to a sequence of NLFFF extrapolations of NOAA active region 11158 spanning the X2.2 flare of 15 February 2011. The slippage rate reveals enhanced RECONNECTion signatures associated with distinct phases of the active region's evolution. In comparison with the squashing factor, we show that the field line slippage rate provides a physics-weighted complement to QSL analysis, distinguishing between regions that are geometrically favourable for RECONNECTion and those where RECONNECTion is physically significant.

[abstract 25 / 42] (score: 3)
arXiv:2606.13116 [pdf, ps, other]

Title: Deep optical spectroscopic monitoring of the pulsating ULX NGC 1313 X-2 with longslit Gemini observations

Authors: Rajath Sathyaprakash, Timothy. P. Roberts,

Comments: 12 pages, 10 figures

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

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

This study reports the nature of the companion star to the pulsating ULX NGC 1313 X-2, using long-slit spectroscopic data from Gemini-South observations, based on archival data from 2009. After stacking flux-calibrated spectra from ten nights of observations and fitting the spectra with stellar templates, we find a possible Balmer break in the GMOS-S spectrum below 4000 Angstroms, which is suggestive of an A-type supergiant donor. Using the inferred stellar radii, we report updated constraints on the orbital parameters of the system and on the nature of the binary. We also add some information on the accretion disc size scale by studying the X-ray and optical variability using the lag-frequency spectrum and corroborate on results from earlier studies for the gas bubble expansion rates by modelling the [O III] emission line profiles, allowing constraints on the kinetic power of the wind/JET relative to the accretion power. This study also expands on previous efforts to study the formation history of the binary using multi-wavelength observations.

[abstract 26 / 42] (score: 3)
arXiv:2606.13291 [pdf, ps, other]

Title: Automatic detection of Flare Ribbon Fine Structures as Proxies for Plasmoid Dynamics in Flare Reconnection

Authors: Georgios Chouliaras, Peter F. Wyper, Joel T. Dahlin,

Comments:

Subjects: astro-ph.SR

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Flare ribbons often display fine structures along their fronts that are commonly interpreted as signatures of intermittent RECONNECTion dynamics including plasmoid formation in the flare current sheet. We introduce an automated method that detects and tracks the spiral- and wave-like imprints of these structures and as a proof of concept apply it to maps of MAGNETic field-line length from a high-resolution 3D eruptive-flare simulation. The workflow applies the correlation-dimension method, density-based clustering, and a minimum-area ellipse fit to summarise each feature. We show that across the simulated flare, the detected spirals remain locked to the ribbon's outward motion while drifting coherently along the ribbon. The two ribbons show opposite along-ribbon drift and motion away from their hooks in accordance with theoretical expectations, with instantaneous speeds of 10-800 km s^1, all well below the local surface Alfven speed. Occurrence, lifetimes, and mean MAGNETic flux of the features peak during the impulsive phase. The distribution of per-spiral mean unsigned flux shows a scale-free tail above roughly 6x10^18 Mx with a power-law exponent near 3.4. Together, these results show that bursty, plasmoid-mediated flare RECONNECTion leaves a clear, measurable signature on the flare ribbons. The method provides a practical surface diagnostic of ribbon fine structure that can potentially be used to inform our understanding of three-dimensional MAGNETic RECONNECTion in the flare current sheet.

[abstract 27 / 42] (score: 2)
arXiv:2507.00113 [pdf, ps, other]

Title: Black-hole - neutron-star mergers: new numerical-relativity simulations and multipolar effective-one-body model with spin precession and eccentricity

Authors: Alejandra Gonzalez, Sebastiano Bernuzzi, Alireza Rashti, Francesco Brandoli, Rossella Gamba,

Comments: 40 pages, 30 figures

Subjects: gr-qc astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

In this paper, we present 52 new numerical-relativity (NR) simulations of black-hole-neutron-star merger (BHNS) mergers and employ the data to inform TEOBResumS-Dalí: a multipolar effective-one-body model also including precession and eccentricity. Our simulations target quasicircular mergers and the parameter space region characterized by significant tidal disruption of the star. Convergent gravitational waveforms are produced with a detailed error budget after extensive numerical tests. We study in detail the multipolar amplitude hierarchy and identify a characteristic tidal signature in the $(\ell,m)=(2,0)$, and $(3,0)$ modes. We also develop new NR-informed models for the remnant BLACK HOLE and for the recoil velocity. The numerical data is then used to inform next-to-quasicircular corrections and the ringdown of TEOBResumS-Dalí for BHNS. We show an overall order of magnitude improvement in the waveform's amplitude at merger and more consistent multipoles over our older TEOBResumS-GIOTTO for BHNS. TEOBResumS-Dalí is further validated with a new 12 orbit precessing simulation, showing phase and relative amplitude differences below $\sim 0.5$ (rad) throughout the inspiral. The computed mismatches including all the modes lie at the one percent level for low inclinations. Finally, we demonstrate for the first time that TEOBResumS-Dalí can produce robust waveforms with both eccentricity and precession, and use the model to identify the most urgent BHNS to simulate for waveform development. Our new numerical data are publicly released as part of the CoRe database.

[abstract 28 / 42] (score: 2)
arXiv:2511.00307 [pdf, ps, other]

Title: Spin-up and mass-gain in hyperbolic encounters of spinning BLACK HOLEs

Authors: Healey Kogan, Frederick C. L. Pardoe, Helvi Witek,

Comments: 23 pages, 23 figures; matches version published in PRD

Subjects: gr-qc astro-ph.HE

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

Scattering BLACK HOLEs spin up and gain mass through the re-absorption of orbital angular momentum and energy radiated in gravitational waves during their encounter. In this work, we perform a series of numerical relativity simulations to investigate the spin-up and mass-gain for equal-mass BLACK HOLEs with a wide range of equal initial spins, $χ_{\rm i}\in[-0.7,0.7]$, aligned (or anti-aligned) to the orbital angular momentum. We also consider a variety of initial momenta. Furthermore, we explore a range of incident angles and identify the threshold between scattering and merging configurations. The spin-up and mass-gain are typically largest in systems with incident angles close to the threshold value, large momenta, and negative (i.e. anti-aligned) initial spins. When evaluated at the threshold angle, we find that the spin-up decreases linearly with initial spin. Intriguingly, systems with initial spin $χ_{\rm i}=0.7$ sometimes experience a spin-down, in spite of an increase in the black-hole angular momentum, due to a corresponding gain in the black-hole mass. Across the simulation suite, we find a maximum spin-up of $0.3$ and a maximum increase in the black-hole mass of $15\%$.

[abstract 29 / 42] (score: 2)
arXiv:2511.15782 [pdf, ps, other]

Title: Trading oxygen for iron II. Oxygen- versus iron-dependent cosmic STAR FORMATION history

Authors: Martyna Chruślińska, Mirko Curti, Ruediger Pakmor, Annalisa De Cia, Jorryt Matthee, Aniket Bhagwat, Stephanie Monty,

Comments: updated to match the A&A accepted version

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

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Due to their different nucleosynthetic origin, a stellar population produces oxygen (O) and iron (Fe) on different timescales and their relative abundance can deviate strongly from solar. Galaxy formation models should treat these elements separately, as they play a distinct role in shaping physical phenomena. For example, oxygen mainly sets the gas cooling rate, while the iron abundance sets stellar atmosphere opacities impacting stellar evolution, spectra and feedback. Observations of star-forming galaxies usually only constrain gas-phase oxygen abundance, vastly limiting our capabilities of separating the cosmic evolution of oxygen and iron. Here, we present an observationally-motivated framework to scale the cosmic evolution of O and Fe abundances. We apply the relation between the alpha-enhancement and galaxies' specific STAR FORMATION rate ([O/Fe]-sSFR; Chruslinska et al. 2024) to derive the Fe and O-dependent cosmic STAR FORMATION history (cSFH). We find that STAR FORMATION with near-solar O/Fe is rare: at least 70% of the integrated cosmic stellar mass forms at non-solar O/Fe. The cosmic average metallicity is generally lower in [Fe/H] than in [O/H] (by up to a factor 3), with the offset increasing from redshifts z=0 to z~3 and then approaching the core-collapse O/Fe ratio. We validate our results against samples that probe the Fe-dependent cSFH in different regimes such as absorption-derived <[Fe/H]> from long GAMMA-RAY BURSTs. Our results impact the interpretations of stellar and galaxy spectra and the predicted rates of transients, especially those linked to metal-poor progenitors (e.g., BLACK HOLE mergers).

[abstract 30 / 42] (score: 2)
arXiv:2601.13831 [pdf, ps, other]

Title: The Dead Cone Effect in Heavy-Quark Jets: A Unified Study from Charm and Bottom to Top

Authors: Redamy Perez-Ramos, Stefan Kluth, Wolfgang Ochs,

Comments: 7 pages, contribution to International Workshop on Future Linear Colliders (LCWS---2025), Valencia, Spain, version accepted for publication with minor changes

Subjects: hep-ph hep-ex

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

We present a unified overview of recent progress in the study of QCD radiation in heavy-QUARK JETs, focusing on the dead-cone effect. Using precision data from LEP at $\sqrt{s}=91.2$~GeV, we demonstrate strong momentum-space suppression in charm and bottom QUARK JETs, supported by Monte Carlo simulations with \textsc{Pythia}8, and provide a quantitative interpretation within the Modified Leading Logarithmic Approximation (MLLA) of perturbative QCD. We then extend the analysis to top-QUARK JETs at $\sqrt{s}=1$~TeV, where finite lifetime effects and decay radiation introduce new conceptual challenges. A new method is presented to isolate the top-QUARK dead cone by separating production and decay radiation, and it is validated at both parton and hadron level using \textsc{Pythia}8. Together, these results establish a coherent framework for testing QCD radiation dynamics across all three heavy QUARKs.

[abstract 31 / 42] (score: 2)
arXiv:2606.12454 [pdf, ps, other]

Title: Hyperstatistical thermodynamics of the one-dimensional Klein-Gordon and Dirac oscillators: a closed-form q-generalized Boltzmann factor and a quantitative comparison with Beck's superstatistics

Authors: Abdelmalek Boumali,

Comments:

Subjects: physics.gen-ph

Created: 2026-06-05; Updated: 2026-06-12; Datestamp: 2026-06-12

We revisit the thermodynamics of the one-dimensional Klein-Gordon (KGO) and Dirac (DO) oscillators within two frameworks of generalized statistics: Beck's asymptotic superstatistics and the recently introduced hyperstatistics. In hyperstatistics, a $γ$-distribution of domain Boltzmann factors yields, after Laplace transformation and averaging over a normalisable density $f(β)$, the closed-form q-generalized Boltzmann factor $B_q(\varepsilon) = \exp_q(-\langleβ\rangle\varepsilon)$, independent of $f(β)$. We compute the partition function, entropy $S$, and specific heat $C_v$ for both 1D oscillators using excitation energies $\varepsilon_n = E_n - E_0$ to remove the rest-energy shift and enforce third-law behaviour $C_v \to 0$ as $T = 1/\langleβ\rangle \to 0$. Appropriate degeneracies ($g_n = 1$ for KGO; $g_0 = 1$, $g_n = 2$ for $n \geq 1$ for DO) are applied. Hyperstatistics successfully (i) reproduces the high-temperature Boltzmann limit $C_v \to 2k_B$, (ii) is structurally independent of $f(β)$, (iii) avoids the unphysical negative regions of the Beck polynomial bracket, and (iv) systematically distinguishes KGO from DO by capturing the enhanced entropy and sharper specific-heat structure caused by spin-induced degeneracy. The frameworks agree quantitatively for $q - 1 \ll 1$ and $\langleβ\rangle E \lesssim 2$, but diverge at high temperatures where Beck's polynomial expansion loses validity and the exact hyperstatistical q-exponential remains positive, monotonic, and analytic. Ultimately, hyperstatistics provides a numerically stable and analytically tractable alternative to asymptotic superstatistics for RELATIVISTIC oscillators, naturally extensible to higher dimensions and external MAGNETic fields.

[abstract 32 / 42] (score: 2)
arXiv:2606.12509 [pdf, ps, other]

Title: TBD LBD: The nature of `little blue dots'

Authors: Albert Sneppen, Darach Watson, James H. Matthews, Georgios Nikopoulos,

Comments: 5 pages, 5 figures, submitted. Comments are welcome

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

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

Previous Sirocco radiative-transfer models of gas-cocooned AGN predicted lower-column counterparts to little red dots (LRDs): compact, X-ray-weak sources with bluer continuum slopes and Balmer jumps rather than Balmer breaks. The recently identified population of little blue dots (LBDs) closely resembles this predicted phase. Here we explore these lower-column-density cocoons in which nebular recombination emission remains visible while strong Balmer-continuum absorption is avoided. We find that a sequence of increasing column density connects more classical AGN spectra, Balmer-jump LBD-like spectra at $N_{\rm H}\!\sim\!{\rm few}\times10^{24} \mathrm{cm^{-2}}$, and Balmer-break LRD-like spectra at higher columns. In this sequence, electron scattering produces exponential line wings and suppresses X-ray emission before strong Balmer absorption features, characteristic of higher column densities, appear. We therefore propose that LBDs are lower-column analogues of LRDs within a common gas-cocooned AGN sequence. This interpretation predicts that Balmer-jump emission, X-ray weakness, permitted lines with exponential wings, He II $λ$4686 emission, smaller H$α$ FWHM values and equivalent widths than in LRDs, and weak or absent absorption features are characteristic of LBDs. We compare to three example LBD spectra and identify Balmer-jump signatures in them.

[abstract 33 / 42] (score: 2)
arXiv:2606.12542 [pdf, ps, other]

Title: Implementation of multi-grid Poisson solver in numerical relativity and its application to gravitational collapse of massive star

Authors: Kenta Kiuchi, Hirotada Okawa,

Comments: 11 pages, 8 figures

Subjects: astro-ph.HE gr-qc

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

We develop a new grid-based multi-grid Poisson solver in numerical relativity. We report the performance of the multi-grid Poisson solver in the initial value problems for two-puncture BLACK HOLEs, a static spherical neutron star, a uniformly rotating neutron star in equilibrium, and a gravitationally collapsing massive star. As a demonstration, we conduct a numerical-relativity neutrino-radiation-transfer hydrodynamics simulation of the gravitational collapse of the $9M_\odot$ massive star in Ref.~\cite{Aguilera-Dena:2020mfh} up to the core bounce. During the simulation, we employ the constraint-preserving regird prescription with the newly developed multi-grid Poisson solver to improve the resolution. It shows that the baryonic mass, the Arnowit-Deser-Misner (ADM) mass, and the ADM-like angular momentum are, respectively, preserved with $O(10^{-3})\%$ and $O(10^{-2})$--$O(10^{-1})$\% accuracy.

[abstract 34 / 42] (score: 2)
arXiv:2606.12661 [pdf, ps, other]

Title: Finding Novel Precursors for Solar Wind Stream Interaction Regions with Interpretable Deep Learning

Authors: Prateek Mayank, Yogesh, Enrico Camporeale, D. Chakrabarty, Lan K Jian, Gregory G. Howes, Thomas E. Berger,

Comments: Manuscript Under Review. 22 pages with 8 figures, including appendix and references

Subjects: astro-ph.SR physics.plasm-ph physics.space-ph

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

Solar wind stream interaction regions (SIRs) drive recurrent geoMAGNETic storms, yet most existing catalogs rely on expert inspection and simple thresholds that are subjective and can miss events with complex morphologies. We present SIREN (SIR Encoder Network), a lightweight Transformer based model for per timestep SIR detection from in situ solar wind observations. The model ingests sequences of 11 solar wind parameters, spanning MAGNETic field, velocity, and thermodynamic properties. With approximately 100,000 trainable parameters in a two layer encoder architecture, SIREN is trained using weighted binary cross entropy loss and a cosine annealing learning rate. Platt scaling is applied to produce well-calibrated detection probabilities. On a held-out test set of 102 events, the calibrated model achieves a ROC-AUC of 0.93, F1 score of 0.78, and true skill statistic of 0.67. Analysis of the self-attention weights confirms that the model concentrates on the SIR, grounding its decisions in the physically relevant portion of each sequence. Integrated Gradients attribution reveals a quantifiable feature hierarchy: proton density (24.3%) and MAGNETic field magnitude (21.6%) dominate, followed by temperature (13.9%) and bulk speed (12.1%). Notably, the transverse velocity component Vy and east-west flow angle together contribute 13-17%, identifying flow deflection as a consistent but previously under-quantified SIR signature. By producing continuous probabilities rather than binary labels, SIREN enables flexible threshold tuning for operational use and provides a template for compact, interpretable deep-learning systems in space weather.

[abstract 35 / 42] (score: 2)
arXiv:2606.12732 [pdf, ps, other]

Title: X-ray Emission and Stellar Ages of Sun-Like Stars

Authors: Breanna A. Binder, Edward W. Schwieterman, Alison Farrish, Sarah Peacock, Margaret C. Turnbull, Stephen R. Kane, Katherine Garcia-Sage,

Comments: Accepted to ApJ; 16 pages, 9 figures

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

Created: 2026-06-10; Updated: 2026-06-12; Datestamp: 2026-06-12

We present an analysis of XMM-Newton and Chandra observations of 85 nearby main-sequence FGK stars with age estimates ranging from 0.2-12 Gyr. We measure quiescent 0.3-10 keV luminosities, variability metrics, and multi-temperature thermal plasma spectral parameters. Quiescent spectra are typically described by three characteristic plasma components ($kT\approx0.1$, 0.4, 0.8 keV); the fraction of flux from $T\ge7$ MK rises with X-ray surface flux, reaching $\sim$50% for $F_X\gtrsim10^6$ erg cm$^{-2}$ s$^{-1}$. We derive relations between emission measure-weighted coronal temperature and both $L_X$ and $F_X$, enabling temperature-informed count-rate conversions for faint sources. We quantify how bandpass conversions (ROSAT 0.1-2.4 keV vs. XMM-Newton 0.3-10 keV) depend on temperature, and show that inferred ROSAT-band $L_X$ broadly follows the canonical $t^{-1.5}$ decay, while the harder band exhibits increased scatter at $>$4 Gyr. Several stars show excess activity suggestive of age errors, inclination effects, or unresolved companions. Some of these "outlier" stars are potential direct imaging targets for the Habitable Worlds Observatory, and detailed characterization of these stars is needed to inform their likely influence on the atmospheric evolution of orbiting planets.

[abstract 36 / 42] (score: 2)
arXiv:2606.12760 [pdf, ps, other]

Title: The toroidal flux and separatrix effects in tokamaks

Authors: Allen H Boozer,

Comments:

Subjects: physics.plasm-ph

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

The toroidal MAGNETic flux enclosed by MAGNETic surface has remarkably little prominence in the tokamak literature. Nevertheless, it is required to properly interpret Faraday's Law, which gives the slippage of the poloidal relative to the toroidal MAGNETic flux through the loop voltage. The toroidal flux also simplifies and makes more precise the equilibrium conditions when a tokamak plasma is bounded by a separatrix. This paper illustrates the effect of a separatrix on equilibria using an analytic model in which the $z$ Cartesian coordinate is assumed to define a periodicity direction. Using 95\% of the poloidal flux between the axis and the separatrix to define the edge rotational transform, $q_{95}$, gives the definition an unnecessary sensitivity to the current profile in the central part of the plasma. The required avoidance of disruptions places great importance on identifying parameters that can be both measured and controlled in tokamak power plants. This identification would be clarified by the use of the toroidal rather than the poloidal flux as the radial coordinate.

[abstract 37 / 42] (score: 2)
arXiv:2606.13128 [pdf, ps, other]

Title: Multi-Epoch X-Ray Detection of SLSN-I 2018bsz: Constraints on the Powering Mechanism and Ejecta Structure

Authors: Julia Ahlvind, Josefin Larsson, Dennis Alp, Ragnhild Lunnan,

Comments: 18 Pages, 5 Figures, 3 Tables. Accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

SN 2018bsz is the closest known stripped superluminous SUPERNOVA (SLSN-I) to date, making it an ideal laboratory for investigating the physical mechanisms powering this class of extreme explosions. We present a multi-epoch X-ray spectroscopic study of SN 2018bsz based on four Chandra observations followed by one XMM observation, spanning 87 to 1253 days after explosion. The source is detected at all Chandra epochs and is also tentatively detected in the late XMM observation, although more uncertain due to nearby contaminating sources. Regardless of the XMM detection, this makes SN 2018bsz the second X-ray detected SLSN-I and the third X-ray detected SLSN overall. We explore potential power sources for the observed X-ray emission and find that a millisecond (ms) MAGNETar central engine underpredict most of the observed X-ray luminosities and fail to reproduce the relatively flat light curve. Accounting for ejecta absorption further increases the discrepancy. While asymmetries and MAGNETar-driven ionization could reduce the effective absorption, ionization breakout is expected years after our observational window. Instead, the observations are more readily explained by early-time interaction between the ejecta and the circumstellar medium, while the MAGNETar emission is absorbed by the ejecta. This scenario is supported by the flat temporal evolution, previous optical results, and inferred mass-loss rates which resemble those of stripped SNe that later evolve into interacting systems. Our results thus favor the scenario where SN 2018bsz is part of a distinct group of SLSN-I, where interaction is crucial for the strong emission.

[abstract 38 / 42] (score: 2)
arXiv:2606.13325 [pdf, ps, other]

Title: Solar-System Bounds on Ricci-flat Spindle Deformations of Schwarzschild

Authors: Zhong-Xi Yu, Hong-Da Lyu, Shoulong Li,

Comments: 15 pages

Subjects: gr-qc

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Recently, a new class of deformed black-hole exact solutions was constructed in four-dimensional general relativity. The deformation is controlled by a parameter $B$, which survives after deMAGNETizing a BLACK HOLE immersed in an external Bertotti-Robinson MAGNETic field and changes the global structure of the spacetime into a non-asymptotically flat spindle geometry. Although no astrophysical mechanism for generating such a deformation is currently known, it is natural to ask phenomenologically how large such a geometric deformation could be if it extended over the weak-field solar exterior. Using two classical Solar-System tests, we derive the leading corrections to planetary perihelion precession and to the light travel time in a Shapiro-type configuration. Requiring the \(B\)-induced perihelion advance to be smaller than the observational uncertainties in the supplementary perihelion precessions of planets gives the strongest bounds, \( |B|\lesssim 10^{-24}\text{--}10^{-23}\ {\rm cm}^{-1}\), while a Cassini time delay estimate gives a complementary null-geodesic sensitivity at the level \( |B|\lesssim 10^{-21}\ {\rm cm}^{-1}\). These results show that any such spindle deformation, if extended to the solar exterior geometry, must be extremely suppressed on Solar-System scales.

[abstract 39 / 42] (score: 2)
arXiv:2606.13326 [pdf, ps, other]

Title: Feasibility of a Flexible, Hybrid Tokamak-Stellarator Experiment using an Axisymmetric Dipole Coil Array

Authors: Jacob Halpern, Mohammed Haque, Elizabeth Paul, Carlos Paz-Soldan, Rithik Banerjee, Talia Angles, Frederick Sheehan, Ian Stewart,

Comments: 25 pages, 14 figures

Subjects: physics.plasm-ph

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

We demonstrate the design of a flexible, university-scale hybrid tokamak-stellarator experiment based on an axisymmetric array of planar HTS dipole coils. Because the coil array has few geometric degrees of freedom, we use single-stage optimization of the coil currents initialized from two-stage solutions to obtain mutually consistent equilibria and coil sets within realistic engineering limits. We find that the field error and coil current thresholds set minimum and maximum coil-plasma distances that confine the boundary to a roughly fixed axisymmetric envelope, within which rotational transform, volume, coil current, and quasi-symmetry (QS) error trade off against one another. Tighter current limits delocalize the non-axisymmetric shaping and raise QS error at fixed transform. From this single coil array we obtain a broad range of equilibria-quasi-axisymmetric vacuum stellarators with $ι$ up to 0.2, finite-$β$ hybrids with realistic profiles reaching on-axis $ι$ $\approx$ 1 and vacuum transform relevant for MHD stabilization, and strongly shaped tokamaks with elongation $κ$ = 1.7 and triangularity $δ$ = $\pm$0.6, all at peak pointwise coil forces well below the HTS tolerance. We show the same array can additionally correct toroidal field (TF) coil ripple, reducing the number of TF coils required compared to the equivalent tokamak. These results establish the design as a promising platform for hybrid tokamak-stellarator research.

[abstract 40 / 42] (score: 2)
arXiv:2606.13462 [pdf, ps, other]

Title: A symmetry theorem for localizable steady solutions of the 3D Euler equations

Authors: Daniel Peralta-Salas, Radu Slobodeanu,

Comments: 27 pages, no figures

Subjects: math.AP math-ph math.MP physics.plasm-ph

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

A steady Euler flow is localizable if the pressure function is constant along its stream lines. This property was used by Gavrilov to construct the first smooth compactly supported steady states of 3D Euler. We prove that any analytic localizable 3D Euler flow in a bounded domain $Ω$ is axisymmetric and $Ω$ is a rotationally symmetric domain whose transverse section is a disk or an annulus with convex boundary curves. To the best of our knowledge, this is the first symmetry theorem for 3D steady Euler flows. In the context of MHD equilibria, this result shows that Grad's conjecture holds true for MAGNETic fields satisfying the isodynamic condition, a property introduced by Palumbo in the 1960's to minimize the effect of particle drifts in plasma confinement devices.

[abstract 41 / 42] (score: 2)
arXiv:2606.13635 [pdf, ps, other]

Title: Geometrically Regular Black Object Solutions in Lower-Dimensional Gauss-Bonnet Gravity and Its Unimodular Extension

Authors: G. Alencar, T. M. Crispim, C. R. Muniz,

Comments: 23 pages; Comments are welcome

Subjects: gr-qc

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

We investigate the construction of regular compact objects in the recently proposed lower-dimensional Einstein--Gauss--Bonnet (EGB) gravity obtained through regularized dimensional reduction. Unlike the standard BTZ BLACK HOLE, the corresponding vacuum EGB solution develops a genuine curvature singularity at the origin, providing an interesting setting in which higher-curvature corrections deteriorate the ultraviolet behavior of spacetime. To address this issue, we reconstruct matter sectors capable of restoring regularity while preserving the BTZ-like asymptotic structure. First, we derive regular black-hole solutions supported by nonlinear electrodynamics and determine the corresponding electroMAGNETic Lagrangians directly from the field equations. We then extend the analysis to Simpson--Visser black-bounce geometries, obtaining smooth throat configurations with finite curvature invariants throughout the spacetime. As an alternative regularization mechanism, we formulate a unimodular extension of lower-dimensional EGB gravity and show that standard Maxwell fields can support regular geometries through a dynamical exchange between the vacuum and matter sectors mediated by a spacetime-dependent cosmological function. We further investigate the thermodynamic properties of the regular black-hole and black-bounce solutions, showing that the matter sector modifies the evaporation process, allows for remnant formation, and produces nontrivial phase transitions. In the black-bounce case, the thermodynamic quantities smoothly recover the EGB-BTZ behavior in the appropriate limit. These results demonstrate that lower-dimensional EGB gravity provides a useful laboratory for exploring the interplay between higher-curvature corrections, regular compact objects, nonlinear electrodynamics, and unimodular gravity.

[abstract 42 / 42] (score: 2)
arXiv:2606.13661 [pdf, ps, other]

Title: Robust Control of ECH Deposition Profiles on DIII-D

Authors: A. Rothstein, H. J. Farre-Kaga, K. Yasoda, J. Lestz, N. Chen, S. K. Kim, A. Jalalvand, E. Kolemen,

Comments: 20 pages, 9 figures

Subjects: physics.plasm-ph

Created: 2026-06-11; Updated: 2026-06-12; Datestamp: 2026-06-12

Electron Cyclotron Heating (ECH) is a key actuator in DIII-D and future tokamaks that provides auxiliary heating, localized current drive for scenario development and MHD stability, and even impurity pump-out. Due to its control flexibility and applications, a gyrotron optimization algorithm was developed to multitask and fine-tune the deposition location and heating power of each gyrotron while providing robustness to hardware failure. The ECH Optimization (ECHO) algorithm finds the optimal gyrotron mirror angle and power to achieve a target ECH radial deposition profile. This optimization is accomplished in real-time using a parallelized neural network surrogate of the TORBEAM code combined with a genetic optimizer. This has been deployed in a DIII-D experiment and has been validated with experimental ECE measurements and post-experiment offline ray tracing, showing the algorithm's reliability despite gyrotron failures and significant changes to plasma parameters.