Current date: 2026-03-19
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Datestamp limit: 2026-03-19 (0 days ago)
Created/updated limit: 2026-03-12 (7 days ago)
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Suggested sets: physics, physics:astro-ph, physics:gr-qc, physics:physics
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Scoring abstracts
Number of records retrieved: 641
Keyword score statistics
score 10 -- 2 abstracts
score 9 -- 1 abstracts
score 7 -- 1 abstracts
score 6 -- 2 abstracts
score 5 -- 5 abstracts
score 4 -- 6 abstracts
score 3 -- 8 abstracts
score 2 -- 11 abstracts
in total -- 36 abstracts
Articles that appeared on 2026-03-19
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[abstract 1 / 36] Wow! (score: 10)
- Title: Numerical simulations of JET launching and breakout from collapsarsAuthors: Gerardo Urrutia, Agnieszka Janiuk, Hector Olivares,Comments: 19 pages, 13 figures, accepted for publication in JHEAPSubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Long Gamma-Ray Bursts (LGRBs) are often associated with the collapse of stripped-envelope massive stars. Powerful RELATIVISTIC JETs drill through the stellar envelope before the gamma emission. Previous hydrodynamical studies imposed JETs artificially, neglecting accretion dynamics, while the central engine simulations have reproduced JET launching via the Blandford-Znajek mechanism focusing on the inner core regions. However, both the central engine and the progenitor structure are crucial to determining the JET's evolution. In this study, we present axisymmetric (2.5-D) GRMHD simulations that self-consistently follow JET formation from the black-hole horizon to breakout at the stellar surface ($R_\star \sim 10^{10}$~cm). The setup assumes a Kerr BLACK HOLE with spin $a \sim 0.9$ in the centre of three progenitor models, varying the MAGNETic-field strength and geometry. Relativistic JETs are successfully launched by a strong dipolar MAGNETic field ($B_0 \gtrsim 10^{12}$-$10^{14}$~G) from MAGNETically arrested disks. These JETs, initially MAGNETically dominated, convert energy into thermal and kinetic during their propagation. We found breakout times within $1.8 \lesssim t_{\rm bo} \lesssim 3.5$~s and luminosities $L_j \sim 5\times10^{49}-7\times10^{52}$~erg\,s$^{-1}$. Our results highlight the role of the initial MAGNETic field strength and its geometry, emphasizing the progenitor's density distribution as a key factor impacting the final structure and dynamics of LGRB JETs.
[abstract 2 / 36] Wow! (score: 10) - Title: VERITAS Observations Contemporaneous with the LHAASO Detection of NGC 4278Authors: The VERITAS Collaboration, A. Archer, P. Bangale, J. T. Bartkoske, W. Benbow, J. H. Buckley, Y. Chen, J. L. Christiansen, A. J. Chromey, A. Duerr, M. Errando, M. Escobar Godoy, S. Feldman, Q. Feng, S. Filbert, L. Fortson, A. Furniss, W. Hanlon, O. Hervet, C. E. Hinrichs, J. Holder, Z. Hughes, T. B. Humensky, M. Iskakova, W. Jin, M. N. Johnson, M. Kertzman, M. Kherlakian, D. Kieda, T. K. Kleiner, N. Korzoun, S. Kumar, S. Kundu, M. J. Lang, M. Lundy, G. Maier, C. McSorley, P. Moriarty, R. Mukherjee, W. Ning, S. O'Brien, M. Ohishi, M. A. Ong, A. Pandey, C. Poggemann, M. Pohl, E. Pueschel, J. Quinn, P. L. Rabinowitz, K. Ragan, P. T. Reynolds, D. Ribeiro, L. Rizk, E. Roache, I. Sadeh, L. Saha, H. Salzmann, M. Santander, G. H. Sembroski, R. Shang, M. Splettstoesser, D. Tak, A. K. Talluri, I. Thoreson, J. V. Tucci, J. Valverde, D. A. Williams, S. L. Wong, T. Yoshikoshi,Comments: 11 pages, 2 figures, Accepted for publication in the Astrophysical Journal (ApJ)Subjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Significant gamma-ray emission between 1 TeV and 20 TeV from a point source, 1LHAASO J1219+2915, consistent with the location of the LINER/LLAGN galaxy NGC 4278 was recently reported by the LHAASO collaboration. These data were later split into active and quasi-quiet states, with most of the LHAASO significance coming from the active state (MJD 59449-59589). Subsequent analysis of FERMI-LAT and SWIFT-XRT observations have been used to explore the double-peaked broad-band emission. Models of the spectral energy distribution (SED) are currently unconstrained due to the lack of contemporaneous multi-wavelength data at either peak. Here we report serendipitous observations of NGC 4278 with VERITAS, made possible by the contemporaneous observations of the nearby BLAZARs 1ES 1218+304, 1ES 1215+303, and W Comae, each of which are located within $2^\circ$ of NGC 4278. VERITAS did not detect any gamma-ray emission and a flux upper limit was calculated. The flux upper limits constrain the photon spectrum of the quasi-quiet period, and together with FERMI-LAT, indicate a peak in the SED between 100 GeV and 2 TeV. We present an interpretation of the broadband SED that is based on acceleration of protons in the corona of the AGN, followed by p-$γ$ interactions and optically thin $γ$-ray emission. Within this framework, the implied neutrino signal is slightly below the current sensitivity of IceCube.
[abstract 3 / 36] Wow! (score: 9) - Title: Ultraviolet variability in Radio-Loud Active Galactic Nuclei observed by UVIT onboard AstroSatAuthors: M. Reshma, C. S. Stalin, Amit Kumar Mandal, S. B. Gudennavar, Senorita Benedict, Prajwel Joseph,Comments: 46 pages, 6 figures and 5 tables; Accepted for publication in Journal of High Energy AstrophysicsSubjects: astro-ph.GACreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
Radio-loud ACTIVE GALACTIC NUCLEi (AGN) are among the most luminous objects in the Universe, emitting radiation from low-energy radio waves to high energy $γ$-rays. They are well known to exhibit flux variations at nearly all accessible wavelengths. However, their variability properties in the ultraviolet (UV) band remain relatively less explored compared to other wavebands. Here, we present the results of a systematic investigation of the UV flux and spectral variability characteristics of 24 radio-loud AGN spanning the redshift range 0.018 $\le$ $z$ $\le$ 2.218. The sample comprises 17 BL Lac objects, 6 flat spectrum radio QUASARs (FSRQs) and one radio-loud narrow line Seyfert 1 galaxy. We used observations obtained with the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat during its first ten years of operation, covering both the far-UV (FUV; 1300$-$1800 Å) and near-UV (NUV; 2000$-$3000 Å) bands. Of the 24 sources analysed, 18 showed significant UV variability on hour timescales. We found a bluer when brighter (BWB) spectral trend in two sources: the FSRQ CTA 102 and the BL Lac PKS 0447$-$439. The observed UV variability in our sample of radio-loud AGN, together with the BWB trend detected in these two sources, supports a scenario in which the hour timescale UV variations are driven by intrinsic processes within their RELATIVISTIC JETs.
[abstract 4 / 36] Wow! (score: 7) - Title: A high-resolution X-ray view of the ultra-fast outflow in MAXI J1810-222Authors: C. Pinto, M. Del Santo, A. D'Aì, F. Pintore, T. D. Russell, M. Parra, J. Ferreira, P. -O. Petrucci, K. Fukumura, A. Marino, T. Muñoz-Darias, G. A. Rodríguez Castillo, A. Segreto,Comments: 11 pages, 8 figures, accepted for publication in A&ASubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
In previous work, it was reported that the Galactic BLACK HOLE candidate MAXI J1810-222 exhibited a notable absorption spectral feature at around 1 keV in low-resolution X-ray spectra of CCD-like detectors. The feature was correlated with the spectral state of the source, being stronger in the soft states, as it occurs in the typical Fe K winds of X-ray binaries (XRBs). However, the results hinted towards rather extreme wind velocities of up to ~0.1 c. We therefore requested and obtained an observation with XMM-Newton to take advantage of the 10-fold higher spectral resolution (R ~200-400) provided by the RGS detector in order to resolve the lines and break the degeneracy between different models and interpretations. We applied state-of-the-art models of plasma in photoionisation equilibrium and multiphase interstellar medium. Further comparisons are performed with a re-analysis of NICER and NUSTAR data. The XMM-Newton/RGS spectrum is consistent with the presence of a mildly RELATIVISTIC wind, confirming the earlier indications obtained with NICER, but places tighter constraints on the outflow properties, with the lines being intrinsically broad. The data would then favour MAGNETically driven winds, although thermal effects may still contribute to mass loading. NUSTAR and XMM-Newton (EPIC) show a further hotter component indicating a stratified or multiphase outflow. Fe K spectra taken with calorimetric detectors (e.g., Resolve on XRISM) will enable a high-resolution view of the complex extreme outflow in this source and shed new light on outflow processes in XRBs.
[abstract 5 / 36] Yes (score: 6) - Title: Ultrahigh-Energy Gamma-Ray Sources Need Not Be Hadronic PeVatronsAuthors: Zachary Curtis-Ginsberg, Dan Hooper, Justin Vandenbroucke,Comments: 17 pages, 8 figuresSubjects: astro-ph.HE astro-ph.GACreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
Ultrahigh-energy gamma rays ($E_γ>100 \, {\rm TeV}$) have been detected from a handful of astrophysical sources. Due to the Klein-Nishina suppression of inverse Compton scattering at such high energies, it has sometimes been argued that these sources must be accelerators of PeV-scale protons, making them the long-sought-after Galactic ''PeVatrons.'' Here, we challenge this conclusion, demonstrating that these sources can be straightforwardly explained by simple leptonic models. In this context, we consider the microQUASAR SS 433, the Galactic Center, and TeV halos, showing in each case that the observation of PeV-scale gamma rays from these sources does not indicate that they are accelerators of hadronic COSMIC RAYs. We also note that the measured angular extension of SS 433 is in good agreement with the predictions of our model, favoring a leptonic origin for the gamma-ray emission from this source. A definitive identification of a PeVatron would require additional information, such as the combined observation of the pion bump and SYNCHROTRON peak, the spatial correlation of gamma-ray emission with gas, or the detection of neutrinos with $E_ν \gtrsim 100 \, {\rm TeV}$.
[abstract 6 / 36] Yes (score: 6) - Title: Radiative GRMHD simulations of puffy accretion discs: Numerical versus analytical models of sub-Eddington accretionAuthors: Debora Lančová, Maciek Wielgus, Marek Abramowicz, Agata Różańska, Włodek Kluźniak, Jiří Horák, David Abarca, Aleksander Sądowski, Gabriel Török,Comments: 12 pages, 8 figures, submitted to MNRASSubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
A widely accepted picture of an accretion flow in the luminous soft spectral state of X-ray binary systems is a geometrically thin disc structure much like the classic analytic solution of Shakura \& Sunyaev. Although the analytic models are troubled by instabilities and miss important aspects of physics, such as MAGNETic fields, they are successfully used as a framework for interpreting observational data. Here, we compare the results of general RELATIVISTIC radiative MAGNETohydrodynamic (GRRMHD) simulations of optically thick, mildly sub-Eddington accretion on a stellar-mass BLACK HOLE (the puffy disc) with established analytic and semi-analytic accretion models in the same regime. From the simulations, we find that the accretion flow is stabilised by the MAGNETic field, with a puffed-up, optically thick region resembling a warm corona surrounding a denser and cooler disc core. However, the stratified vertical structure of the disc significantly influences the observational picture of such a system. We analyse the inner disc structure, flow properties, effective viscosity, and inner edge position, and compare them to the predictions of standard models. We find that the simulated discs share some similarities with the models; however, they differ in several important aspects, most notably: the photosphere is geometrically thick, the inner edge is located closer to the central BLACK HOLE than the analytic models assume, the surface density is significantly lower than analytically predicted, and the effective viscosity parameter is not constant but rises steeply in the innermost region.
[abstract 7 / 36] Yes (score: 5) - Title: Do plasmoids induce fast MAGNETic RECONNECTion in well-resolved current sheets in 2D MHD simulations?Authors: G. H. Vicentin, G. Kowal, E. M. de Gouveia Dal Pino, A. Lazarian,Comments: 25 pages, 17 figures, 1 tableSubjects: physics.plasm-ph astro-ph.HE hep-thCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
We investigate the development of tearing-mode instability using the highest-resolution two-dimensional MAGNETohydrodynamic simulations of RECONNECTing current sheets performed on a uniform grid, for Lundquist numbers of $10^3 \le S \le 5 \times 10^5$ , reaching up to $65,536^2$ grid cells. We demonstrate a Sweet--Parker scaling of the RECONNECTion rate $V_{\text{rec}} \sim S^{-1/2}$ up to Lundquist numbers $S \sim 10^4$. For larger values of Lundquist number, between $2\times 10^4\le S \le 2 \times 10^5$, plasmoid formation sets in, leading to a slight enhancement of the RECONNECTion rate, $V_{\text{rec}} \sim S^{-1/3}$, consistent with the prediction from linear tearing mode induced RECONNECTion, indicating that RECONNECTion remains resistivity-dependent and therefore slow. In this range of $S$-values, the plasmoids do not undergo a merger cascade, as they are rapidly advected out of the RECONNECTion layer. Only for $S > 2 \times 10^5$, we observe the nonlinear development of the tearing-mode instability, with plasmoid coalescence and a saturation of the RECONNECTion rate at $V_\text{rec} / V_A \sim 0.01$. At such high $S$, however, the corresponding Reynolds number is large, reaching $\text{Re} > 2000$ even on scales comparable to the current-sheet thickness. We therefore conclude that, in astrophysical systems, it is essential to account for the dominant influence of turbulence and three-dimensional effects in the RECONNECTion process.
[abstract 8 / 36] Yes (score: 5) - Title: The impact of Solar MAGNETic field configurations on the production of gamma rays at the Solar diskAuthors: Julien Dörner, Frederic Effenberger, Horst Fichtner, Julia Becker Tjus, Meng Jin, Wei Liu, Vahe' Petrosian,Comments:Subjects: astro-ph.HE astro-ph.SRCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
The Sun produces a steady signal of high-energy gamma rays through interactions of Galactic COSMIC RAYs (GCRs) with its atmosphere. Observations with FERMI-LAT and HAWC have revealed a gamma-ray flux significantly higher than early theoretical predictions, with unexpected temporal and spectral features that suggest a crucial role of the solar MAGNETic field. In this work, we model GCR-induced gamma-ray emission at the solar disk using the CRPropa framework with realistic hadronic interactions, chromospheric density profiles, and several MAGNETic field configurations over the solar cycle. This allows us to quantify the gamma-ray emission of the entire solar disk for different phases of the solar activity cycle and we present, for the first time, maps of the production locations of gamma rays on the solar surface. We consider both mono-energetic and realistic power-law injection spectra in a simplified dipole-quadrupole current sheet model and potential-field source surface (PFSS) extrapolations for Carrington rotations during solar maximum and minimum. Our results show that MAGNETic mirroring and large-scale field topology strongly affect the spectral shape and spatial distribution of the emission, with slightly enhanced fluxes predicted at solar minimum. While our simulated baseline fluxes remain below observations, additional effects, such as heavier nuclei, Parker-field mirroring, and deeper atmospheric interactions, could result in further enhancements of fluxes closer to observational values. Hadronic interactions do not only produce gamma rays but also neutrinos. We estimate the expected neutrino flux from the Sun based on our gamma-ray predictions. We find that the expected flux is slightly below current upper limits from IceCube.
[abstract 9 / 36] Yes (score: 5) - Title: Optical outburst evolution of the transient BLACK HOLE X-ray binary SWIFT J1727.8-1613: Disc response to JET ejections and late-outburst emergence of powerful disc windsAuthors: N. Castro Segura, K. Solomons, J. M. Corral-Santana, C. Knigge, P. A. Charles, M. Brigitte, S. Fijma, M. Diaz-Trigo, A. Gúrpide, D. A. H. Buckley, F. Carotenuto, A. J. Castro-Tirado, D. L. Coppejans, M. Georganti, A. Hughes, K. S. Long, J. Matthews, I. Monageng, I. Pelisoli, T. D. Russell, D. Steeghs, J. Svoboda, A. J. Tetarenko, F. M. Vincentelli, A. G. W. Wallis,Comments: 15 pages, 7 figures, submitted to MNRASSubjects: astro-ph.HECreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
SWIFT J1727.8$-$1613 is a newly discovered transient low-mass X-ray binary harbouring a stellar-mass ($\sim 10M_\odot$) BLACK HOLE. We present state-resolved VLT/X-Shooter optical spectroscopy of its 2023 outburst, sampling the luminous hard-to-soft and late soft-to-hard transitions. During the onset of the brightest radio flare, He\,\textsc{ii} flux rises relative to adjacent epochs, with reduced peak-to-peak separation and full-width-half-maximum, consistent with enhanced irradiation shifting line emissivity to larger radii. We detect no contemporaneous change in the line base tracing the inner disc. The most dramatic change occurs at the onset of the dim-hard state, when strong, broad (higher-order) Balmer lines appear in absorption, and He\,\textsc{ii} remains in emission, but becomes highly asymmetric. While the hardening of the X-ray spectrum likely promotes the reappearance of an underlying disc photosphere, the kinematic alignment between the Balmer absorption ($v_w\sim-750\,\mathrm{km\,s^{-1}}$) and the suppressed blue peak of He\,\textsc{ii} suggests a unified origin in a massive, cool ($T\lesssim10^{4}\,\mathrm{K}$) accretion disc wind. Radiative transfer simulations demonstrate that such asymmetric He\,\textsc{ii} profiles are naturally produced in a rotating and accelerating outflow. Using the Sobolev approximation, we estimate the wind mass-loss rate to be $\dot{M}_w\gtrsim10^{-9}\,M_\odot\,\mathrm{yr^{-1}}$, comparable to the instantaneous accretion rate and a significant fraction of the secular mass-transfer rate from the donor. If persistent at quiescent-level X-ray luminosities, this outflow could strongly impact the system's secular evolution.
[abstract 10 / 36] Yes (score: 5) - Title: RABBITS - III. Modelling RELATIVISTIC accretion discs around spinning BLACK HOLEs in galaxy formation simulationsAuthors: Dimitrios Irodotou, Shihong Liao, Theodoros Nakas, Geoffrey Compère, Roberto Oliveri, Jessica M. Hislop, Alexander Rawlings, Sonja Soininen, Aswin P. Vijayan,Comments: The accretion model is publicly available at https://github.com/DimitriosIrodotou/RABBITS-III. Published in the Open Journal of AstrophysicsSubjects: astro-ph.GA astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
In this third study of the 'Resolving supermAssive Black hole Binaries In galacTic hydrodynamical Simulations' (RABBITS) series we develop and implement a geometrically thin RELATIVISTIC accretion disc model, which self-consistently evolves the mass and spin vector of BLACK HOLEs via analytically modelling the structure of steady-state accretion discs. The model employs a suite of RELATIVISTIC, local solutions where pressure is dominated by either gas or radiation, while opacity is primarily governed by either electron scattering or free-free absorption. These local solutions are piece-wisely combined to form the global structure of the accretion disc based on each solution's range of validity. By explicitly modelling the structure of accretion discs, the model mitigates the stochasticity inherent in Bondi-type prescriptions, resulting in an approach where every episode of BLACK HOLE mass accretion is derived from first principles. For the first time, our model enables galaxy formation simulations to place constraints on accretion disc sizes and structures. In addition, flux and temperature radial profiles can be directly extracted from the simulation, enabling the generation of spectral energy distributions. Consequently, by incorporating the thermal structure and spacetime geometry around spinning BLACK HOLEs, our model more accurately captures the energetic output of QUASARs, overcoming critical limitations of classical approaches. Along with this manuscript, we make public a C version of the model appropriate to be used as a module in simulations, a Python version of the model that can be used independently to post-process any simulation and build mock accretion discs, and an updated version of the Relagn model that has the capability of producing SEDs by building an accretion disc for a given set of parameters and extracting its surface density, temperature, and opacity profiles.
[abstract 11 / 36] Yes (score: 5) - Title: Energy extraction from a rotating Buchdahl star via MAGNETic RECONNECTionAuthors: Ikhtiyor Eshtursunov, Sanjar Shaymatov,Comments: 10 pages, 7 captioned figuresSubjects: gr-qcCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
In this work, we investigate the MAGNETic RECONNECTion (MR) process as a mechanism for energy extraction from a rapidly rotating Buchdahl star (BS), one of the most compact horizonless objects that can, in principle, possess a spin parameter exceeding the extremal limit of a BLACK HOLE (BH). We explore the energetics of the BS by focusing on the newly proposed MR mechanism developed by Comisso and Asenjo (the Comisso-Asenjo mechanism). Within this framework, we evaluate the energy extraction efficiency and the associated power output from a rapidly rotating BS. We show that the ergoregion of the BS exists only when the spin parameter satisfies $β>1/\sqrt{2}$. Consequently, the extraction of rotational energy through MR becomes possible only under this condition. Furthermore, we analyze the rate of energy extraction driven by fast MAGNETic RECONNECTion and compare the resulting power with that predicted by the Blandford-Znajek mechanism. Our results indicate that the energy extraction rate increases significantly when the BS spin parameter exceeds the extremal limit for a BH, highlighting that MR can be substantially more efficient than the Blandford-Znajek mechanism. We demonstrate that MR can greatly enhance energy extraction efficiency from rapidly rotating BS with a large spin, making such an object potentially more efficient engines of high-energy astrophysical processes than BH.
[abstract 12 / 36] Yes (score: 4) - Title: Astrophysical Black holes: An Explanation for the Galaxy QuenchingAuthors: Jay Verma Trivedi, Pankaj S. Joshi, Gopal-Krishna, Peter L. Biermann,Comments: 10 pages, 1 figureSubjects: gr-qc astro-ph.GA astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
In light of increasing observational evidence supporting the existence of ultra-compact objects, we adopt the term astrophysical BLACK HOLE to refer to any object having a huge mass confined within a sufficiently small region of spacetime. This terminology encompasses both the classical BLACK HOLE solutions predicted by general relativity, as well as alternative compact objects that may not possess an event horizon. We propose models of Astrophysical Black holes (ABHs) without event horizons (EHs), as a more viable explanation for the long-term quenching phenomenon in galaxies. At the same time, the short-term quenching is explained here in terms of an efficient feedback expected in the models of stellar-mass astrophysical BLACK HOLEs (StMABHs). We have calculated the radiative flux from the disk in a general spherically symmetric metric background and used it to contrast the distinctive features of the BHs and ABHs scenarios. We demonstrate the relative ease of wind generation from the accretion disk surrounding an ABH without an event horizon, compared to a BH, and highlight the significant strength of these winds. The nature of the feedbacks arising from accretion onto a BH and an ABH in the `QUASAR' and `radio' modes are compared and some possible observational signatures of the StMABHs are pointed out.
[abstract 13 / 36] Yes (score: 4) - Title: Global Non-Axisymmetric Hall Instabilities in a Rotating PlasmaAuthors: Alexandre Sainterme, Fatima Ebrahimi,Comments:Subjects: physics.plasm-ph astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Non-axisymmetric, flow-driven instabilities in the incompressible Hall-MHD model are studied in a differentially rotating cylindrical plasma. It is found that in the Hall-MHD regime, both whistler waves and ion-cyclotron waves can extract energy from the flow shear, resulting in two distinct branches of global instability. The non-axisymmetric whistler modes grow significantly faster than non-axisymmetric, ideal MHD modes. A discussion of the global whistler instability mechanism is presented in the large-ion-skin-depth, `electron-MHD' limit. When the MAGNETic field is azimuthal, a subset of the whistler modes having zero axial wave number are uncovered to be destabilized by the `co-rotation amplifier' mechanism. It is observed that the effect of the Hall term on the non-axisymmetric modes can be appreciable when $d_i$ is on the order of a few \% of the width of the cylindrical annulus. Distinct global modes emerge in the strong Hall-MHD regime at significantly stronger MAGNETic fields than those required for unstable global MHD modes, as the Hall effect weakens the stabilizing `field-line bending' by decoupling ion motion from the MAGNETic field. These global non-axisymmetric modes may play an important role in weakly ionized accretion disks.
[abstract 14 / 36] Yes (score: 4) - Title: The imitation game (r)evolutions: $Q$-star effective shadow from GRMHD analysisAuthors: Víctor Jaramillo, Laura Meneses, Héctor R. Olivares Sánchez, Carlos Herdeiro, Darío Núñez, Shuang-Yong Zhou,Comments: 18 pages, 7 figuresSubjects: gr-qc astro-ph.HECreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
$Q$-stars are a class of BOSON stars arising in scalar-field theories with interacting potentials, minimally coupled to gravity. We show that, in certain regions of parameter space, the angular velocity of stable timelike circular geodesics around $Q$-stars can attain a maximum at a nonzero radius. Notably, this behaviour may occur for stable configurations. This feature has been argued to produce effective shadows, but so far it has only been investigated for unstable solutions. We test this possibility by performing general RELATIVISTIC MAGNETohydrodynamic evolutions for a representative stable $Q$-star model. A low-density, low-luminosity central region is indeed observed to form and persist -- at least until the evolution becomes affected by numerical viscosity. As a proof of principle, this suggests that families of stable BOSONic stars can act as BLACK HOLE mimickers. Moreover, for the model at hand, a heuristic analysis shows that the effective shadow has a comparable size to that of a Schwarzschild BLACK HOLE with the same mass. Importantly, this mechanism for generating an effective shadow does not rely on the object being ultracompact, or an ad hoc chosen accretion disk.
[abstract 15 / 36] Yes (score: 4) - Title: Compton-thick AGN in the NUSTAR Era. XI. Analyzing 11 CT-AGN Candidates Selected with Machine LearningAuthors: Ross Silver, Nuria Torres-Alba, Stefano Marchesi, Vittoria Gianolli, Isaiah Cox, Dhrubojyoti Sengupta, Indrani Pal, Marco Ajello, Xiurui Zhao, Kouser Imam, Anuvab Banerjee,Comments:Subjects: astro-ph.GACreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
This work discusses the broadband X-ray spectral analysis of 11 candidate heavily-obscured ACTIVE GALACTIC NUCLEi (AGN) selected based on their infrared and X-ray properties by a recently published machine learning algorithm. This paper is part of a larger work to identify and characterize all AGN in the local universe (z < 0.1) with the largest line-of-sight (los) column densities (NH), the so-called Compton-thick (CT-, NH,los >= 1024 cm-2) AGN. We modeled the X-ray spectra using two physically- motivated models, UXClumpy and RXTorusD. Of the 11 AGN in our sample, we found three to be obscured with 22.7 < LogNH,los <= 23.0, five have 23.0 < LogNH,los <= 23.25, and three have 23.4 < LogNH,los <= 23.9, according to UXClumpy. Meanwhile, according to RXTorusD, we found three AGN to be obscured with 22.7 < LogNH,los <= 23.0, four with 23.0 < LogNH,los <= 23.4, and four with 23.85 < LogNH,los <= 23.96. Additionally, this work served as a comparison between UXClumpy and RXTorusD. We found broad agreement between the two, with 8/11 sources agreeing on the value of the photon index Gamma, while only 5/11 sources agreeing on the NH,los value within the 90% confidence level.
[abstract 16 / 36] Yes (score: 4) - Title: State-dependent broadband X-ray timing reconfiguration in the changing-look AGN NGC 1566Authors: Yu Tao, Jie Tang, Xuan Wei, Xiaohan Zhang,Comments: 5 pages, 4 figures. Submitted to MNRAS:LettersSubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
NGC 1566 has exhibited dramatic state changes in its X-ray spectrum, but the evolution of its broadband timing properties remains poorly constrained. We combine long-term SWIFT monitoring with high-time-resolution XMM-Newton observations to model the broadband X-ray power spectral density (PSD) in the dim and bright states. In the hard band, the PSD bend frequency shifts by about 1 dex between the two states, implying a substantially longer characteristic variability timescale in the bright state. The relative timing behaviour of the soft and hard bands also changes with state. In the dim state, the soft-band bend frequency is higher than the hard-band value by about 0.49 dex, whereas in the bright state the two become broadly consistent. The broadband variability evolution of NGC 1566 therefore involves not only an overall shift in characteristic timescale, but also a state-dependent change in the soft-hard timing relation, from a more stratified to a more tightly coupled configuration. Combined with previous spectral results, this supports a genuine reconfiguration of the inner radiative structure during the changing-look transition.
[abstract 17 / 36] Yes (score: 4) - Title: The Potential for Hadronic Particle Acceleration in Galactic Pulsar Wind NebulaeAuthors: Alison M. W. Mitchell, Samuel T. Spencer,Comments: Review article, accepted for publication in Universe. 21 pages, 3 figures, 1 tableSubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Pulsar wind nebulae (PWNe), formed when the wind originating from a rapidly rotating neutron star flows out into its surroundings, have now been observed across the electroMAGNETic spectrum from the radio to the PeV gamma-ray regime. For most of these sources, leptonic processes, where electrons interacting with background photon fields produce high-energy photons through inverse Compton scattering, are believed to be the origin of associated very-high-energy gamma-ray emission. As such, these objects cannot contribute significantly to the galactic hadronic COSMIC RAY flux at ~TeV-PeV energies. However, in a handful of cases, the possibility for an energetically sub-dominant hadron population being accelerated and producing very to ultra-high energy gamma-rays through pion decay has not yet been comprehensively excluded. Such scenarios have received renewed attention in the light of recent results from the Large High Altitude Air Shower Observatory (LHAASO). In this review we explore the theoretical background positing hadronic acceleration in galactic PWNe, considering cases where the hadrons escape from the pulsar surface and/or are accelerated in the wind, as well as potential 'shock mixing' scenarios. We also explore current and future possible constraints on a hadronic component to PWNe from observations.
[abstract 18 / 36] (score: 3) - Title: Origin of radio POLARIZATION in pulsar polar capsAuthors: Jan Benáček, Axel Jessner, Martin Pohl, Tatiana Rievajová, Lucy S. Oswald,Comments: 15 pages, 9 figures, 2 tables; Published in A&ASubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
It is crucial to know the POLARIZATION properties of coherent radio waves that escape from pulsar polar caps to calculate the radiative transfer through the MAGNETosphere and to predict observable radio properties. We describe pair cascades in the pulsar polar cap, and we determine for the first time the Stokes parameters of the escaping radio waves from first-principle kinetic simulations for a pulsar with a MAGNETic obliquity of $60^{\circ}$. We present 3D particle-in-cell kinetic simulations that include quantum-electrodynamic pair cascades in a charge-limited flow from the stellar surface. Our model quantitatively and qualitatively explains the observed pulsar radio powers and spectra, the pulse profiles, POLARIZATION curves, their temporal variability, the strong Stokes-$L$ and weak Stokes-$V$ POLARIZATION components, the decline in the linear POLARIZATION with frequency, and the nonexistence of a radius-to-frequency relation. The observable properties of radio emission from the polar cap can vary and include single- or double-peaked profiles. Most of the Stokes~$V$ curves from our simulations appear to be antisymmetric, but symmetric curves are also present at some viewing angles. Although the POLARIZATION-angle (PA) swing of the radiation from the polar cap fits the rotating vector model (RVM) for most viewing angles, the angles obtained from the RVM do not correspond to the dipole geometry of the MAGNETic field. Instead, the PA is directly related to the plasma flows in the polar cap. Our simulations demonstrate that pair discharges close to the surface of the polar cap cause the radio emission of pulsars and determine the majority of their typically observed properties. The merits of RVM for estimations of the MAGNETic field geometry from observations need to be reevaluated.
[abstract 19 / 36] (score: 3) - Title: Revisiting the Radio Lateral Distribution Function: An amplitude dependence on $X_{\rm max}$ and primary compositionAuthors: Washington R. Carvalho, Lech Wiktor Piotrowski,Comments:Subjects: astro-ph.HECreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
We show that there is a strong dependence of the radio LDF electric field amplitudes at ground level on the position of $X_{\rm max}$ in the atmosphere, even accounting for differences in the EM energy of the showers. Since an $X_{\rm max}$ dependence leads to a primary composition dependence, this implies that information on the mass composition is encoded not only in the LDF shape but also in its amplitude. This $X_{\rm max}$ dependence can be explained in terms of two competing scalings of the measured electric field: One goes with $(1/ρ)^J$, where $ρ$ is the air density at $X_{\rm max}$ and $J$ is a zenith dependent non-linearity factor describing coherence loss. This density scaling tends to decrease the geoMAGNETic emission of deeper showers. The other scaling goes with $(1/R)$, where $R$ is the distance from $X_{\rm max}$ to the core at ground, and instead increases the measured electric field of deeper showers. At low zenith angles, the $(1/R)$ scaling is stronger and leads to larger measured electric fields as $X_{\rm max}$ increases. The picture at higher zeniths, i.e., lower densities, is more nuanced. In this region, the deflections due to the Lorentz force are much larger and introduce extra time delays between the particle tracks, decreasing the coherence of the emission. This loss of coherence is highly dependent on the strength of the geoMAGNETic field and can slow down, or even reverse the increase of the radio emission with decreasing air density. This strong, yet historically overlooked LDF amplitude dependence on $X_{\rm max}$/composition could be used to directly infer, even bypassing any $X_{\rm max}$ reconstruction, the COSMIC RAY primary composition on an event-by-event basis. It could also have some repercussions on other radio reconstruction methods, such as a possible $X_{\rm max}$/composition bias on shower electroMAGNETic energy reconstruction methods.
[abstract 20 / 36] (score: 3) - Title: Search For a Counterpart to the Subsolar Mass Gravitational Wave Candidate S251112cmAuthors: Nicholas Vieira, Noah Franz, Bhagya Subrayan, Charles D. Kilpatrick, David J. Sand, Wen-fai Fong, Griffin Hosseinzadeh, Kate D. Alexander, K. Azalee Bostroem, Jillian Rastinejad, Kerry Paterson, Manisha Shrestha, Phillip Noel, P. Darc, Jeniveve Pearson, Aysha Aamer, A. Souza Santos, Luidhy Santana-Silva, Clecio R. Bom, Regis Cartier, Hemanth Bommireddy, Ósmar Rodríguez, Jennifer E. Andrews, Conor Ransome, Vasileios Paschalidis, Jay Strader, Aldana Grichener, J. Quirola-Vásquez, Sergiy Vasylyev, Marcelle Soares-Santos, Collin T. Christy, Brian Hsu, D. Carson Fuls, Yize Dong, Daniel E. Reichart, Jonathan Pineda-García, Kathryne J. Daniel, Daryl Janzen, C. E. Fields, Ann Zabludoff, Nicolas Meza, Felipe Olivares E., Kristine Spekkens, Benjamin Weiner, Maia Williams, Alex R. Gibbs, Frank Shelly, Aravind P. Ravi, Saurabh W. Jha, Stefano Valenti, Joshua Haislip, David E. Trilling,Comments: 20 pages, 8 figures in body; submitted to ApJ; comments welcome!Subjects: astro-ph.HECreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
The recent gravitational-wave (GW) alert from a compact object merger involving at least one subsolar mass (SSM) object has prompted questions about their origins. S251112cm is reported by LIGO/Virgo with a false alarm rate of 1 per 6.2 years, nearby luminosity distance $93 \pm 27$ Mpc, probability of containing a SSM object of 100%, and probability of containing a $1-3~M_\odot$ object of just 8%. Such a system likely did not involve the supersolar neutron stars or BLACK HOLEs invoked to explain kilonovae. One must then also invoke hitherto unobserved and speculative models to produce SSM mergers and the resultant electroMAGNETic (EM) counterparts. We introduce a framework which vets and scores candidate counterparts to SSM GW events to inform follow-up in search of any among the zoo of potential EM transients: kilonovae, kilonovae-within-SUPERNOVAe, super-kilonovae, or AGN flares from binary BLACK HOLE mergers. We use a suite of telescopes to perform tiling, galaxy-targeted observations, and photometric/spectroscopic follow-up of promising candidates. In near-real time, we ingest candidates reported by the community, including some of the first observations reported by the Vera C. Rubin Observatory. We vet and score a total of 248 candidates, including 67 from Rubin, but find no likely counterpart. We nonetheless highlight candidates which demonstrate the ability of our framework to distinguish between different transient types and describe strategies to maximize the chances of detecting a counterpart to the next SSM event. Our framework will be implemented in the forthcoming Multimessenger Tool for Rapid Object Vetting and Examination (TROVE).
[abstract 21 / 36] (score: 3) - Title: Pair-loaded electron-only MAGNETic RECONNECTion using LASER-driven capacitor coilsAuthors: Brandon K. Russell, Qian Qian, Rebecca Fitzgarrald, Yang Zhang, Stepan S. Bulanov, Sergei V. Bulanov, Hui Chen, Lan Gao, Gabriele M. Grittani, Xiaocan Li, Kian Orr, Geoffrey Pomraning, Kevin M. Schoeffler, Alexander G. R. Thomas, Hantao Ji,Comments: 8 pages, 3 figuresSubjects: physics.plasm-phCreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
We propose and simulate a laboratory platform to study the effects of positrons in MAGNETic RECONNECTion using LASER-driven capacitor coils. Using particle-in-cell simulations, we show that externally injected MeV electron-positron pairs are trapped in the coil current sheet, significantly modifying the RECONNECTion dynamics and particle acceleration. These pairs increase the RECONNECTion rate by a factor of approximately 8, which Ohm's law decomposition reveals to be driven by the divergence of the generalized pressure tensor. Based on their high energy and MAGNETization, the pairs also substantially broaden the diffusion region. Particle tracking simulations in realistic coil MAGNETic fields further demonstrate that injected pairs can remain confined for several picoseconds, providing conditions for sustained interaction with the RECONNECTion region. These results establish a near-term pathway to laboratory studies of positron-influenced RECONNECTion, bridging high-energy-density experiments with pair-dominated astrophysical environments.
[abstract 22 / 36] (score: 3) - Title: Optical variability and optical--mid-infrared dust lags in Type~1 changing-look AGNsAuthors: Yu Tao, Jie Tang, Xuan Wei,Comments: 9 pages, 9 figures. Submitted to MNRASSubjects: astro-ph.GACreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Changing-look ACTIVE GALACTIC NUCLEi (CL AGNs) show large changes in luminosity and optical spectral state on time-scales of a few years, and provide a valuable probe of time-dependent accretion in the disc-BLR-torus system. We present a systematic statistical study of their optical variability in a well-defined Type-1 phase, using g- and r-band light curves from the Zwicky Transient Facility for 165 CL AGNs. A subsample of 34 objects also has NEOWISE W1 and W2 light curves, which we use to measure optical-mid-infrared time lags. We use structure functions and a damped random-walk model to characterize variability amplitudes and time-scales on rest-frame scales from tens to a few hundred days, and examine their dependence on BLACK HOLE mass, luminosity, and Eddington ratio. In the Type-1 phase, the short-time-scale optical variability amplitude on about 30-day time-scales shows little dependence on BLACK HOLE mass, luminosity, or Eddington ratio. By contrast, the longer-term amplitudes on 150-300 day time-scales, as well as the damped random-walk time-scales, increase slowly with BLACK HOLE mass and luminosity, but still show no clear dependence on Eddington ratio. The sample shows a ubiquitous bluer-when-brighter trend and larger variability at shorter wavelengths, consistent with continuum variability from a multi-temperature accretion disc. For the NEOWISE subsample, the dust lag-luminosity relation inferred from the optical-mid-infrared lags is similar to that of normal Type-1 AGNs. Overall, CL AGNs in the Type-1 phase behave like normal Type-1 AGNs within the standard disc-BLR-dusty torus framework, but are more prone to large continuum reconfigurations on year-like time-scales.
[abstract 23 / 36] (score: 3) - Title: Magnetic field measurements in a sample of Class I and Flat-Spectrum protostars observed with SPIRouAuthors: L. Drouglazet, E. Alecian, A. Sousa, P. I. Cristofari, E. Artigau, J. Bouvier, A. Carmona, N. J. Cook, C. Dougados, G. Duchêne, C. P. Folsom, H. Nowacki, K. Perraut, S. H. P. Alencar, L. Amard, M. Audard, S. Cabrit, J. -F. Donati, K. Grankin, N. Grosso, O. Kochukhov, Á. Kóspál, V. J. M. Le Gouellec, L. Manchon, G. Pantolmos, P. Petit, L. Petitdemange, R. Devaraj, H. Shang, M. Takami,Comments:Subjects: astro-ph.SRCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Magnetic fields play a crucial role throughout stellar evolution, regulating angular momentum, channelling accretion, and launching JETs and outflows. While the MAGNETic properties of Classical T Tauri Stars (CTTS) are well characterised, those of their progenitors, Class I and Flat-Spectrum (FS) protostars, remain poorly constrained due to observational challenges linked to their embedded nature. We aim to detect and characterise large-scale MAGNETic fields in a sample of Class I and FS protostars, which are expected to host strong dynamo-generated fields. Using SPIRou, a high-resolution near-infrared spectropolarimeter, we analysed polarised spectra and applied the Least Squares Deconvolution (LSD) technique to extract MAGNETic signatures and measure longitudinal fields from Stokes V profiles. We report new detections of large-scale MAGNETic fields in 5 FS protostars. Including the previously known MAGNETic FS protostar V347 Aur, 40% of our sample (15 objects) is confirmed to be MAGNETic. These stars exhibit clear Zeeman signatures, with longitudinal field strengths ranging from ~80 to ~200 G. The remaining targets show no detectable Stokes V signature, with upper limits on dipolar fields between 500 G and >5 kG. These results indicate that Class I and FS protostars can host large-scale MAGNETic fields, possibly weaker than in CTTS, supporting the idea that MAGNETic processes are already active during the main accretion phase and may influence star-disk interactions from the earliest stages.
[abstract 24 / 36] (score: 3) - Title: The Engine and its Flows: Little Red Dot spectra are shaped by the column densities of their gas envelopesAuthors: Jorryt Matthee, Alberto Torralba, Gabriele Pezzulli, Rohan P. Naidu, John Chisholm, Sara Mascia, Jenny E. Greene, Yuzo Ishikawa, Max Gronke, Stijn Wuyts, Rongmon Bordoloi, Gabriel Brammer, Seok-Jun Chang, Anna-Christina Eilers, Anna de Graaff, Raphael E. Hviding, Edoardo Iani, Garth Illingworth, Daichi Kashino, Ivo Labbe, Yilun Ma, Michael V. Maseda, Romain Meyer, Erica Nelson, Pascal Oesch, Mengyuan Xiao,Comments: 19 pages, 13 figures. Main results in Figs 2 & 10. Submitted to A&A. Comments welcome!Subjects: astro-ph.GA astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
JWST data have enabled the abundant identification of compact broad Balmer line sources nicknamed the Little Red Dots. While they share broad lines with ACTIVE GALACTIC NUCLEi, they are unusually X-ray and infrared weak. We investigate the origin of the Balmer line profiles based on an empirical analysis of 18 broad H$α$-selected sources with high quality spectra at $z\approx3-7$. The H$α$ line profiles vary systematically with Balmer break strength: sources with blue UV to optical colors show a narrow core profile, redder sources with Balmer breaks a blue shifted absorption (P Cygni shape), and the reddest sources display absorption-dominated cores. All H$α$ lines have symmetric exponential wings, which are more dominant and slightly broader in red sources. Balmer absorption is present in $\sim60$ % of the sample, with H$β$ showing relatively stronger absorption. Drawing upon empirical analogies with stellar phenomena, we interpret these trends as being due to radiative processes that depend on variations in the optical depth, ionisation state and column density of a clumpy, partially ionised envelope. We unveil a correlation between the absorber velocity and Balmer break strength, with the densest absorbers inflowing and bluer sources having faster outflows. This indicates viewing angle or evolutionary effects where optically thick gas is inflowing, as suggested in models of super-Eddington accretion, and the engine can more easily drive outflows in directions with lower column densities. This new understanding of Balmer line profiles as tracing gas properties rather than dynamical broadening helps resolve tensions associated with high inferred BLACK HOLE masses from standard virial calibrations, and reveals the complex gas environment around the hot central engine.
[abstract 25 / 36] (score: 3) - Title: JWST Reveals Two Overmassive Black Hole Candidates in Dwarf Galaxies at z $\approx$ 0.7: Pushing Black Hole Searches into the Dwarf-Galaxy RegimeAuthors: E. Iani, P. Rinaldi, A. Torralba, J. Lyu, R. Navarro-Carrera, G. H. Rieke, F. Sun, C. Willott, Y. Zhu, A. Alonso-Herrero, M. Annunziatella, P. Bergamini, K. Caputi, M. Catone, L. Colina, R. Cooper, L. Costantin, A. Crespo Gómez, G. Desprez, C. Di Cesare, M. J. Hayes, I. Jermann, G. Kotiwale, I. Kramarenko, D. Langeroodi, S. Mascia, J. Matthee, J. Melinder, A. Muzzin, B. Navarrete, G. Noirot, G. Östlin, F. Pacucci, G. Rodighiero, M. Sawicki, Y. Sun, Z. Wu, G. Yang,Comments: 16 pages (main text), 9 figures (+2 in the appendix), 2 tables (+6 in the appendix)Subjects: astro-ph.GACreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
We report the discovery and characterization of two compact galaxies, Pelias and Neleus, at z ~ 0.71 and z ~ 0.75, identified in MACS J0416.1-2403 and GOODS-North. Both exhibit unusual spectral energy distributions (SEDs), with very blue rest-frame UV-optical emission and a steep rise toward near- and mid-infrared wavelengths. JWST/NIRISS and JWST/NIRSpec spectroscopy show strong rest-frame optical lines ([O III] 4959,5007 and Halpha) with extreme equivalent widths (>= 1000 Angstrom), indicating young burst-dominated populations with low metallicities (Z ~ 0.1-0.4 Zsun), low dust attenuation (Av ~ 0.2 mag), and stellar masses of Mstar ~ 10^7 Msun. Nonetheless, JWST/MIRI photometry reveals a strong mid-infrared excess that cannot be explained by stellar populations or star-formation-heated dust alone, requiring a hot-dust component most naturally associated with a deeply embedded ACTIVE GALACTIC NUCLEus (AGN). SED modelling yields log10(Lbol [erg/s]) ~ 43.7-44.0, implying BLACK HOLE masses of log10(MBH [Msun]) ~ 5.7-6.7 under the assumption of Eddington-limited accretion. Given the very low stellar masses of the hosts, this corresponds to black-hole-to-stellar mass ratios of about 6-60%, well above the extrapolation of local scaling relations. The lack of X-ray detections suggests that the accretion may be either heavily obscured or intrinsically X-ray weak. Their SEDs also resemble those of Blue Excess Hot Dust Obscured Galaxies and show the characteristic V-shaped continuum seen in Little Red Dots, although with the inflection occurring at redder wavelengths.
[abstract 26 / 36] (score: 2) - Title: Properties of current sheets in two-dimensional tearing-mediated incompressible MAGNETohydrodynamic turbulenceAuthors: Chen Shi, Marco Velli, Nikos Sioulas, Zijin Zhang,Comments:Subjects: astro-ph.SR physics.space-phCreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
It is well known that the nonlinear evolution of MAGNETohydrodynamic (MHD) turbulence generates current sheets. In the solar wind turbulence, current sheets are frequently observed and they are believed to be an important pathway for the turbulence energy to dissipate and heat the plasma. In this study, we perform a comprehensive analysis of current sheets in a high-resolution two-dimensional simulation of balanced, incompressible MHD turbulence. The simulation parameters are selected such that tearing mode instability is triggered and plasmoids are generated throughout the simulation domain. We develop an automated method to identify current sheets and accurately quantify their key parameters including thickness ($a$), length ($L$), and Lundquist number ($S$). Before the triggering of tearing instability, the current sheet lengths are mostly comparable to the energy injection scale. After the tearing mode onsets, smaller current sheets with lower Lundquist numbers are generated. While power-law scaling relations between $L$ and $a$ and between $a/L$ and $S$ are observed, no clear correlation is found between the upstream MAGNETic field strength and thickness $a$. Finally, although the turbulence energy shows anisotropy between the directions parallel and perpendicular to the local MAGNETic field increment, we do not observe a direct correspondence between the shape of the current sheets and that of the turbulence ``eddies.'' These results suggest that one needs to be cautious when applying the scale-dependent dynamic alignment model to the analysis of current sheets in MHD turbulence.
[abstract 27 / 36] (score: 2) - Title: The two shadows of a single BLACK HOLE: Vacuum birefringence phenomena within Einstein-Nonlinear-ElectrodynamicsAuthors: Marco A. A. de Paula, Haroldo C. D. Lima, Pedro V. P. Cunha, Carlos A. R. Herdeiro, Luís C. B. Crispino,Comments: 20 pages, 15 figuresSubjects: gr-qc hep-thCreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
One of the main features of nonlinear electrodynamics (NED) is the existence of an effective geometry that describes the geodesic motion of photons. A detailed analysis of the properties of effective geometry is of utmost importance for a better understanding of NED theories and their possible imprints on physics, especially in the context of BLACK HOLEs (BHs). We consider a NED model that depends on the two electroMAGNETic scalar invariants and obtain that the motion of photons in NED exhibits \textit{vacuum birefringence}, i.e., photons can propagate along two distinct paths, depending on their POLARIZATION. As a consequence of this phenomenon, we show that static BLACK HOLE solutions sourced by NED can admit two distinct unstable light rings, leading to the formation of two distinct shadows. Moreover, to explore the potential astrophysical relevance of our results, we also compare them with the astrophysical observations for the shadow radius of Sagittarius A*. We place upper limits on the charge-to-mass ratio of the NED-sourced BLACK HOLE. We also show that the motion of photons in this context can be interpreted as nongeodesic curves subjected to a four-force term from the perspective of an observer in the spacetime metric, generalizing previous results in the literature for NED models that depend on a single electroMAGNETic scalar invariant.
[abstract 28 / 36] (score: 2) - Title: Diffuse X-ray Emission in the Sagittarius C ComplexAuthors: Zhenlin Zhu, Mark R. Morris, Gabriele Ponti, Ping Zhou,Comments: 18 pages, 9 figures, accepted for publication in ApJSubjects: astro-ph.HE astro-ph.GACreated: 2026-03-17; Updated: 2026-03-19; Datestamp: 2026-03-19
The Sagittarius C (Sgr C) complex, located on the western edge of the Central Molecular Zone (CMZ), hosts a mixture of star-forming and non-thermal activity whose X-ray properties remain poorly understood. Using deep archival Chandra and XMM-Newton observations, we resolve the diffuse X-ray emission in Sgr C into two components: an H II region coincident with the radio peak and a brighter diffuse feature located to its southwest. Spatially resolved spectroscopy reveals the presence of a soft (kT <= 1 keV) plasma with metal abundances consistent with the elevated metallicity expected in the CMZ in both regions, along with a harder (~ 8 keV) thermal component within the H II region. The observed diffuse X-ray emission and its association with an expanding [C II] shell suggest that the hot gas may originate from a young SUPERNOVA remnant (SNR) embedded in the H II region. Under this interpretation, the inferred shock velocity (~ 800 km/s) and SNR age (>= 1.7 kyr) are consistent with a core-collapse SNR in the Galactic Center. These results reveal Sgr C as a potential host of a SNR and highlight the complex interplay between massive-star feedback, MAGNETic fields, and molecular gas in the CMZ.
[abstract 29 / 36] (score: 2) - Title: Low-dimensional geometry learning for turbulence prediction in optimized stellaratorsAuthors: Xishuo Wei, Handi Huang, Haotian Chen, Hongxuan Zhu, Zhe Bai, Samuel Williams, Zhihong Lin,Comments:Subjects: physics.plasm-phCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
The optimized stellarator is an attractive concept for which the averaged particle radial drift is zero, and the single particle loss can be significantly reduced. But for the reactor design, global physics such as turbulent transport also need to be optimized besides the confined single particle orbit, or properties estimated using local estimations and heuristic formulations. The first-principle global transport code is too computationally expensive to integrate into the optimization process. The fast surrogate global transport model based on machine learning is a good alternative choice, but the amount of data required to train the surrogate model is numerous due to the high degree-of-freedom of the stellarator design. The work shows that the stellarator design with quasi-helically(QH) symmetric geometry is approximately distributed in a low dimensional latent space, which can be explicitly found by deep learning. This discovery makes it possible to generate global gyrokinetic simulation data for training surrogate models to directly optimize the stellarator geometry for turbulent transport, energetic particle instability, and MHD modes. Using the low dimensional latent space and data analysis methods, the relation between linear zonal residues and axis-excursion is found, providing a simple guide to optimize low turbulent transport QH stellarators.
[abstract 30 / 36] (score: 2) - Title: Revealing the Spectral Properties of Galactic Interstellar Medium by Survey ObservationsAuthors: Ya-Wen Xiao, Jian-Fu Zhang, Alex Lazarian,Comments: 8 pages, 4 figures, Accepted for publication in ApJSubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Based on multi-frequency radio POLARIZATION survey datasets, we investigate the spectral characteristics of the Galactic interstellar medium (ISM) using the POLARIZATION frequency analysis (PFA) method, referred to as POLARIZATION variance. By comparing this novel PFA technique with the traditional power spectrum approach, and by cross-examining data from two distinct surveys, we aim to reinforce the robustness of our findings. Our analysis reveals that the ISM scaling slope in the Galactic disk is steeper than the classic Kolmogorov slope, whereas the ISM scaling slope in the Galactic halo aligns with the Kolmogorov slope. We suggest a distinct turbulence cascade process operating in the Galactic halo compared to the Galactic disk.
[abstract 31 / 36] (score: 2) - Title: Tightening Cosmological Constraints Within and Beyond $Λ$CDM Using Gamma-Ray Bursts Calibrated with Type Ia SupernovaeAuthors: Wei Hong, Luca Izzo, Massimo Della Valle, Orlando Luongo, Marco Muccino, Tong-Jie Zhang,Comments: 12+7 pages, 5+10 figuresSubjects: astro-ph.CO astro-ph.HE gr-qcCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Context. Gamma-ray bursts (GRBs) reach redshifts beyond Type Ia SUPERNOVAe (SNe Ia) and can extend distance measurements into the early Universe, but their use as distance indicators is limited by the circularity problem in calibrating empirical luminosity relations. Aims. We present a model-independent methodology to overcome this circularity by combining Pantheon$+$ SNe Ia, a distance reconstruction based on artificial neural networks (ANNs), and two GRB correlations (Amati and Combo) into a distance ladder from low to high redshift, with the goal of constraining cosmological parameters in $Λ\mathrm{CDM}$ and $w_0 w_a \mathrm{CDM}$. Methods. We use the ReFANN to reconstruct the luminosity distance $d_L(z)$ and distance modulus $μ(z)$ from the Pantheon$+$ dataset, with hyperparameters optimized via approximate Bayesian computation rejection and a risk function. This model-independent reconstruction calibrates the Amati and Combo relations using a low-redshift ($z<1$) GRB sample from FERMI GBM and SWIFT-XRT. The calibrated relations then provide distance estimates for GRBs at $z \geq 1$. Finally, a joint Bayesian analysis simultaneously constrains the cosmological and GRB correlation parameters, ensuring self-consistent uncertainty propagation. Results. We obtain consistent cosmological constraints from two independent GRB correlations. The Hubble constant $H_0$ agrees with SNe Ia values, though potentially influenced by Pantheon$+$ dataset. High-redshift GRBs favour a higher matter density $Ω_m$ than the Pantheon$+$ and hint at possible DARK ENERGY evolution.Conclusions. We present a framework that mitigates GRB cosmology's circularity problem, extending the distance ladder to $z \sim 9$ and establishing GRBs as a high-redshift probe.
[abstract 32 / 36] (score: 2) - Title: Optical transients from non-explosive double white-dwarf mergers: the case of a central neutron star remnantAuthors: Ridha Fathima M. M., Alexandre M. R. Almeida, Mattia Bulla, Jaziel G. Coelho, Cristiano Guidorzi, Jorge A. Rueda,Comments: 12 pages, 6 figures, Accepted for publication in JHEAPSubjects: astro-ph.HECreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Discoveries of ultra-massive MAGNETic white dwarfs (WDs) and peculiar pulsars have been proposed to originate in double white dwarf (DWD) mergers. There are three possible post-merger central remnants of non-explosive mergers: 1) a stable sub-Chandrasekhar WD; 2) a rapidly rotating super-Chandrasekhar WD; 3) a neutron star (NS). In this work, we explore the thermal transient arising from non-explosive DWD mergers that leave an NS remnant from the prompt collapse of the merged core. The transient is powered by the cooling of the expanding dynamical ejecta, with energy injection from MAGNETic dipole radiation, which depends on the dipole factor $D = B_d^2/P_0^4$, with $B_d$ and $P_0$ being the surface MAGNETic field strength and initial rotation period of the newborn NS. We simulate lightcurves in the Legacy Survey of Space and Time (LSST) bands and estimate the horizon and detection rates for these transients across a range of model parameters. We find LSST detection horizons upper limits ranging $30$--$1020$ Mpc and corresponding detection rates $10^2$--$10^6$ yr$^{-1}$ for $\log D = 24$--$40$. Accounting for the survey cadence, we find that only configurations with $\log D = 36$--$40$ are detectable within $240$--$990$ Mpc, with detection rates $10^4$--$10^6$ yr$^{-1}$. Combined searches across surveys can compensate for the low cadence and improve the detection rates of fast and less energetic sources. Multi-wavelength campaigns can aid in detecting the spindown radiation at higher energies observable after the optical transient. Observations of these transients will provide direct evidence of the non-explosive DWD mergers, characterise the remnants and progenitor parameters, and the fraction of explosive and non-explosive mergers.
[abstract 33 / 36] (score: 2) - Title: ElectroMAGNETic radiation-reaction near BLACK HOLEs: orbital widening and the role of the tailAuthors: Bakhtinur Juraev, Arman Tursunov, Zdeněk Stuchlík, Martin Kološ, Dmitri V. Gal'tsov,Comments: 15 pages, 8 figures. Under review since 7 October 2025Subjects: gr-qcCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
We investigate the orbital evolution of a classical charged particle around a Schwarzschild BLACK HOLE immersed in an external, uniform MAGNETic field, taking into full account both local radiation-reaction and the nonlocal tail self-force arising in curved spacetime. Starting from the DeWitt-Brehme equation and its Landau-Lifshitz reduction, we derive analytic expressions for the conservative and dissipative components of the electroMAGNETic self-force in both the weak-field (Newtonian) and strong-field regimes. By implementing backward-in-time integration of the third-order DeWitt-Brehme equation alongside the second-order Landau-Lifshitz equation, we demonstrate that the so-called orbital widening effect persists even when the tail term is included, and that for astrophysically realistic charge-to-mass ratios the tail contribution to the trajectory is negligible. We further show that this widening is directly controlled by the product of the MAGNETic field and radiation-reaction parameters and can be captured in the Newtonian limit. Finally, we identify a scaling symmetry showing that simulations with moderate parameter values can accurately represent the dynamics in realistic astrophysical conditions, confirming that orbital widening is a robust phenomenon that can persist even in astrophysical BLACK HOLE environments.
[abstract 34 / 36] (score: 2) - Title: Enhanced foreground mitigation in thermal SZ Compton-$y$ maps via POLARIZATION and deprojectionAuthors: Jyothis Chandran, Mathieu Remazeilles, R. B. Barreiro,Comments: 38 pages, 14 figures, and 3 tables. Public data products available at Zenodo (https://doi.org/10.5281/zenodo.18876142)Subjects: astro-ph.CO astro-ph.GACreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
Residual foreground contamination in thermal Sunyaev-Zeldovich (SZ) Compton-$y$ parameter maps ($y$-maps) arises mainly from Galactic emissions -- thermal dust and SYNCHROTRON radiation -- on large angular scales, and from cosmic infrared background (CIB) anisotropies on small scales. Unlike the thermal SZ effect, Galactic foregrounds are strongly polarized. Exploiting this distinction, we introduce a hybrid Needlet Internal Linear Combination (Hybrid NILC) method that combines Planck total-intensity and POLARIZATION frequency maps in the component-separation pipeline, thereby improving the suppression of residual Galactic emission while preserving the unpolarized SZ signal by leveraging the intrinsic $TE$ and $TB$ correlations of thermal dust and SYNCHROTRON. Using Planck PR4 data, we find that the Hybrid NILC $y$-map exhibits about $40\,\%$ lower cross-correlation with the IRAS dust tracer than the standard temperature-only Planck $y$-map, indicating reduced residual Galactic contamination. Simulations further indicate that, for future high-sensitivity surveys such as LiteBIRD, the Hybrid NILC will become increasingly effective at suppressing Galactic residuals. We further address small-scale extragalactic contamination by selectively deprojecting specific moments of the CIB using a Constrained Hybrid NILC variant, achieving an improved balance between CIB suppression and noise penalty compared to previous implementations in the literature. These novel approaches -- particularly the joint use of temperature and POLARIZATION in component separation -- offer a powerful framework for disentangling polarized and unpolarized signals.
[abstract 35 / 36] (score: 2) - Title: Characterization of molecular outflows at core-scale in the massive clump AGAL G345.0029-0.224Authors: E. Cohen Arazi, M. E. Ortega, S. Paron, P. F. Velázquez, A. Rodríguez-González, E. Alquicira,Comments: Accepted for publicacion in Boletín de la Asociación Argentina de Astronomía (February 2026)Subjects: astro-ph.GACreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
High-mass stars, with their powerful winds and intense radiation fields, are fundamental in regulating galactic dynamics and evolution; however, despite their great relevance, the mechanisms involved in their formation are still not fully understood. In this context, molecular outflows, which are essential for removing angular momentum and allowing accretion onto the central object, are a crucial phenomenon for characterizing their formation. Previous studies reveal a discrepancy in the masses of outflows associated with high-mass clumps between works conducted at the clump scale ($\sim$ pc) and those at the core scale ($\sim$ subpc). This suggests that the high-mass outflow activity observed at the clump scale might be the result of the contribution from several lower-mass outflows linked to individual molecular cores. This work presents a study of the molecular gas toward a high-mass clump associated with an Extended Green Object (EGO). EGOs are indicators of JETs associated with high-mass protostars. Employing high angular resolution data from the Atacama Large Millimeter/submillimeter Array (ALMA), the presence of several hot cores with outflow activity was observed in the source. A characterization of the outflows at the core scale is presented within the context of the physical parameters of the molecular clumps.
[abstract 36 / 36] (score: 2) - Title: On the Astrophysical Origin of Binary Black Hole Subpopulations: A Tale of Three Channels?Authors: Anarya Ray, Shirsha Mukherjee, Michael Zevin, Vicky Kalogera,Comments:Subjects: astro-ph.HE astro-ph.GA gr-qcCreated: 2026-03-18; Updated: 2026-03-19; Datestamp: 2026-03-19
There is increasing evidence for multiple binary BLACK HOLE~(BBH) subpopulations in the cumulative gravitational wave catalog by the LIGO-Virgo-KAGRA Collaboration. The astrophysical interpretation of this complex underlying population is subject to theoretical uncertainties in treatments of binary stellar evolution, core collapse, and host environments. In this \textit{Letter}, using parametrized mixture models, we show that the BBH detection sample comprises three astrophysical subpopulations that are likely dominated by specific formation channels. In particular, we show that the $10M_{\odot}$ peak and the $35M_{\odot}$ feature in the BBH mass spectrum correspond to distinct mass-ratio, spin alignment, spin precession, and redshift evolution properties. We show that mass-based transitions reported in the distribution of BBH parameters naturally emerge from our inferred distributions without explicit modeling. Our results are consistent with the current observed population arising from specific relative abundances of isolated binary evolution, dynamical formation in globular clusters, and higher-generation BBH mergers. Under this interpretation, we constrain the relative underlying fraction of these channels to be $79.0^{+11.5}_{-10.9}\%$, $14.5^{+11.6}_{-8.0}\%$, and, $2.5^{+5.5}_{-1.8}\%$, respectively, and find these relative fractions to be evolving over cosmic time with more than $1σ$ confidence. Our interpretation relies on simple theoretical predictions that are mostly robust against uncertainties in BBH formation, with more definite conclusions expected in the near future.
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