Current date: 2026-04-27
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Number of records retrieved: 553
Keyword score statistics
score 8 -- 1 abstracts
score 7 -- 1 abstracts
score 6 -- 1 abstracts
score 5 -- 2 abstracts
score 4 -- 3 abstracts
score 3 -- 3 abstracts
score 2 -- 12 abstracts
in total -- 23 abstracts
Articles that appeared on 2026-04-27
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[abstract 1 / 23] Wow! (score: 8)
- Title: Synchrotron POLARIZATION of anisotropic electron distribution in GRB prompt emissionAuthors: Kang-Fa Cheng, Kai-Xian Luo, Xiao-Hong Zhao, Jirong Mao, Hong-Bang Liu, Yu-Hang Mo, Jin-Rong Huang, Rong-Li Weng, Wen-Jie Xie, Gao-Jin Yu,Comments: 13 pages, 6 figures, 1 table. Accepted for publication in ApJSubjects: astro-ph.HECreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
In GAMMA-RAY BURSTs (GRBs), the electron pitch angle ($α$) is usually assumed to be isotropically distributed. However, recent numerical simulations indicate that only the high-energy electrons (with Lorentz factors $γ>γ_{iso}$) are distributed isotropically, whereas the low-energy electrons (with $γ<γ_{iso}$) follow an energy-dependent anisotropic distribution during MAGNETic RECONNECTion. The mean value of $\sin^2 α$ approximately follows the relation $\langle \sin^2 α\rangle \propto γ^{m}$ for $γ<γ_{iso}$. In principle, POLARIZATION measurements may help us constrain the pitch-angle distribution of electrons in GRBs, since different pitch-angle distributions produce distinct SYNCHROTRON POLARIZATION signatures. The POLARIZATION of GRBs produced by isotropically distributed electrons has been extensively studied. In this paper, we investigate SYNCHROTRON POLARIZATION produced by anisotropically distributed electrons within a globally toroidal MAGNETic field in GRB prompt emission. Our results show that the SYNCHROTRON PDs in the $γ$-ray and X-ray bands produced by anisotropically distributed electrons are systematically lower than those produced by isotropically distributed electrons, while the PD in the optical band could be either lower or higher than that of isotropically distributed electrons, depending primarily on the value of the energy slope $m$. In addition, we compared our numerical results with observational data, and the comparison suggests that an anisotropic distribution of electrons may offer a potential explanation for the PD and spectral data of some GRBs.
[abstract 2 / 23] Wow! (score: 7) - Title: ElectroMAGNETic Precursors to Binary Neutron Star Mergers: Kinetic Simulations of Magnetospheric FlaringAuthors: Jasmine Parsons, Anatoly Spitkovsky, Alexander Philippov, Hayk Hakobyan,Comments: 14 pages, 7 figures, submitted to ApJLSubjects: astro-ph.HE astro-ph.SR physics.plasm-phCreated: 2026-04-23; Updated: 2026-04-27; Datestamp: 2026-04-27
We present the first 3D global kinetic simulations of the interacting MAGNETospheres of pre-merger binary neutron stars. The stars, whose MAGNETic moments are anti-aligned, twist the field lines connecting them, leading to periodic eruptions. Each eruption consists of an expanding MAGNETic flux tube with a RECONNECTing current sheet trailing behind it, topologically analogous to coronal mass ejections. We predict two novel classes of electroMAGNETic precursor signals powered by the efficient dissipation of MAGNETic energy in these periodically forming trailing current sheets. First, particles accelerated in the sheets produce nonthermal gamma-ray signals peaking at $\sim16\,\mathrm{MeV}$, which escape minutes to seconds before merger while the sheets are still optically thin to pair production, with modest characteristic luminosities of $L_\mathrm{obs}\gtrsim 10^{42}\,\mathrm{erg/s}$, detectable only for nearby mergers. Second, merging plasmoids in the sheets could produce fast radio burst-like transients in the final seconds before merger, with characteristic luminosities $L_\mathrm{radio}\sim 10^{38-40}\,\mathrm{erg/s}$. These coherent radio precursors would be detectable by upcoming instruments, either in untargeted surveys by wide-field instruments such as CHORD, or through targeted follow-up of gravitational-wave early-warning alerts with instruments such as DSA or SKA-mid.
[abstract 3 / 23] Yes (score: 6) - Title: The no-hair theorems at work in the tidal disruption event AT2020afhdAuthors: Lorenzo Iorio,Comments: LaTex2e, 20 pages, 1 table, 6 figures. Section added. Accepted for publication in UniverseSubjects: astro-ph.HE gr-qc physics.space-phCreated: 2026-04-23; Updated: 2026-04-27; Datestamp: 2026-04-27
Recently, the coprecession of both the accretion disk and the JET formed following the tidal disruption event associated with the optical transient AT2020afhd, driven by a supermassive BLACK HOLE of almost ten million solar masses, were independently measured in both the X and radio bands, respectively, showing a periodicity of nearly 20 days over about 300 days. An analytical model of the general RELATIVISTIC gravitoMAGNETic Lense-Thirring precession of the effective orbit of a fictitious test particle revolving about a spinning primary can explain the observed precessional features. It yields allowed regions in the system's parameter space which, as far as the hole's dimensionless spin parameter is concerned, are essentially in agreement with those obtained in the literature with general RELATIVISTIC MAGNETohydrodynamic simulations. The present analytical approach can be extended to include the precession due to the hole's quadrupole mass moment as well. It breaks the degeneracy in the allowed regions occurring for negative and positive values of the spin parameter when only the Lense-Thirring effect is considered. The best estimate for the hole's mass yields the range $0.185-0.215$ for the dimensionless spin parameter. Using the same strategy with the gravitoMAGNETic frequency for an extended disk of finite size with a parameterized power-law mass density yields to distinct, generally non-overlapping allowed regions for each value of the power-law index adopted.
[abstract 4 / 23] Yes (score: 5) - Title: VLTI-GRAVITY observations of BLAZARsAuthors: Talvikki Hovatta, Elina Lindfors, Heidi Korhonen, Preeti Kharb, Markus Wittkowski, Aaron Labdon, Tapio Pursimo, Kaj Wiik,Comments: Accepted for publication in A&A. 6 pages of main text with 4 figures. V2 includes minor language edits and updated referencesSubjects: astro-ph.GA astro-ph.HECreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Parsec-scale JETs of BLAZARs have so far been spatially resolved only in millimeter and submillimeter wavelengths, where very long baseline interferometry can be used to obtain milliarcsecond-scale images of the JETs. We have attempted to spatially resolve the near-infrared emission in JET-dominated BLAZARs for the first time. We used the VLTI-GRAVITY instrument to obtain milliarcsecond-scale near-infrared interferometric observations of a flaring BLAZAR Ton 599. Additionally, we observed four non-flaring BLAZARs using the GRAVITY-wide mode, where a nearby bright star is used as a fringe tracker. We modeled the squared visibilities of Ton 599 and found that they are incompatible with a single unresolved point source unless there is a significant amount of additional unknown coherence loss in the instrument. With the present data, we cannot distinguish between a model with an unresolved point source and extended emission or coherence loss and a model with a single Gaussian component. This suggests that we are seeing the unresolved or only partially resolved JET-base in near-infrared wavelengths. The wide-field mode of GRAVITY was challenging for the additional relatively faint targets, resulting in either non-detections or poor-quality data that could not be modeled. Our observations demonstrate that it is possible to detect the compact JET emission in BLAZARs with near-infrared interferometry, suggesting that with the improved GRAVITY+ instrument it will be possible to spatially resolve and image the near-infrared emission of BLAZAR JETs.
[abstract 5 / 23] Yes (score: 5) - Title: Repeated Sunspot Light Bridge Jets Associated with Slipping Base BrighteningsAuthors: Yadan Duan, Xiaoli Yan, Yuhang Gao, Jincheng Wang, Zhe Xu, Yongyuan Xiang,Comments: 13 pages, 6 figures, Accepted for publication in ApJLSubjects: astro-ph.SRCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Light bridge (LB) JETs offer a unique window into small-scale eruptive phenomena within sunspots, the Sun's strongest MAGNETic environments; however, their generation mechanism remains a subject of debate. Using high-resolution observations from the New Vacuum Solar Telescope (NVST), we investigated six recurrent light bridge JETs and the slipping motions of their JET base points (JBPs). Analogous to coronal JETs, our observations show that these LB JETs are characterized by a preceding JBP followed by a collimated JET spire. The JBP of each repeated JET along the LB displays apparent slipping motion at velocities of 0.6-1.5 km/s, which is temporally correlated with quasi-periodic enhanced photospheric horizontal motion of 1.3-6.5 km/s. Following the slipping JBPs, the resulting JET spires' fronts display similar slipping behaviors within the upper solar atmosphere. The Chinese Ha Solar Explorer (CHASE) reveals Ellerman-bomb-like spectral signatures at the JBPs, confirming that MAGNETic RECONNECTion is operating at the JET base. Based on these results, we propose that repeated 3D RECONNECTion occurring between the horizontal LB field and the ambient vertical umbral field may drive these LB JETs. This process appears to be driven and/or modulated by quasi-periodic horizontal motion fueled by convective upflows and the transport of MAGNETic flux along the light bridge. This work suggests that some LB JETs share a common RECONNECTion-driven mechanism with coronal JETs and provides direct evidence of slipping RECONNECTion occurring along the sunspot light bridge.
[abstract 6 / 23] Yes (score: 4) - Title: Anisotropic diffusion modeling of cosmic-ray lepton propagationAuthors: V. D. Borisov, I. A. Kudryashov,Comments:Subjects: astro-ph.HECreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
We analyze DAMPE and H.E.S.S. measurements of the total cosmic-ray electron-positron spectrum, together with the AMS-02 positron fraction, using an anisotropic, spatially varying diffusion framework. The diffusion-tensor components are computed via numerical integration of test-particle trajectories in a prescribed Galactic MAGNETic-field model. We show that simultaneously accounting for the spatial dependence and anisotropy of the diffusion tensor yields an accurate description of the local electron and positron data up to TeV energies. The inferred injection spectral index, $γ=2.169$, is fully consistent with expectations from diffusive shock-acceleration theory. In this approach, the observed spectral softening arises naturally from enhanced energy losses experienced by leptons propagating over larger effective distances along the large-scale MAGNETic field.
[abstract 7 / 23] Yes (score: 4) - Title: Signature of iron line profile from a Kerr-like WORMHOLEAuthors: Cheng Liu, Hoongwah Siew, Hong-Xuan Jiang, Yosuke Mizuno, Tao Zhu,Comments:Subjects: astro-ph.HE gr-qcCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Broad, skewed iron K$α$ emission lines in the X-ray spectra of accreting BLACK HOLEs encode key information about the spacetime geometry of the innermost disk. While the Kerr metric is standard for spin measurements, horizonless alternatives like traversable "Kerr-like" WORMHOLEs can mimic many BLACK HOLE signatures, challenging current data interpretations. We develop a RELATIVISTIC reflection framework incorporating Kerr-like WORMHOLE geometries to predict iron line distortions and assess the feasibility of distinguishing event horizons from WORMHOLE throats.Using a custom ray-tracing subroutine, we implement two \textsc{XSPEC} modules: \texttt{kwline} for $δ$-function profiles and \texttt{kwconv} for full reflection spectra, parameterized by spin, throat radius, and shape-function coefficients. We compute a dense grid of line profiles and generate synthetic \textit{NUSTAR} spectra with realistic response matrices. By fitting these simulations with canonical Kerr models, we quantify deviations attributable to WORMHOLE geometries.We find that Kerr-like WORMHOLEs produce narrower Fe K$α$ lines with suppressed red wings as the throat parameter $λ$ increases. In 50 ks \textit{NUSTAR} simulations ($λ=0.9, a_*=0.998$), simple convolutional models (\texttt{kerrconv}) can mimic the WORMHOLE spectrum. However, self-consistent models like \texttt{relxillCp} result in statistical failure, yielding structured residuals and unphysical parameter pegging (e.g., emissivity $q_{\rm in} \to 10$). We conclude that large-throat WORMHOLEs are detectable in high-quality X-ray spectra if analyzed with fully consistent reflection models rather than post-processing approximations.
[abstract 8 / 23] Yes (score: 4) - Title: A Quasar--Companion System Without AGN Outflow at $z \sim 6$: The Case of PSO J083+11Authors: Muhammad Akmal Husain, Irham Taufik Andika, Mochamad Ikbal Arifyanto,Comments: 16 pages, 13 figuresSubjects: astro-ph.GACreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
PSO J083.8371+11.8482, a QUASAR at $z = 6.34$ with a nearby companion galaxy, provides an opportunity to study the impact of ACTIVE GALACTIC NUCLEus (AGN) activity on the surrounding environment during the epoch of reionization. We analyze ALMA observations of the [C\,\textsc{ii}] 158~$μ$m emission line and the far-infrared (FIR) continuum, which trace cold interstellar gas and dust-reprocessed radiation from STAR FORMATION and AGN heating. The QUASAR host shows STAR FORMATION rates (SFRs) of $544$--$3764~\mathrm{M_{\odot}~yr^{-1}}$ from [C\,\textsc{ii}] and $1861$--$2932~\mathrm{M_{\odot}~yr^{-1}}$ from FIR emission, while the companion galaxy exhibits lower SFRs of $21$--$145$ and $76$--$211~\mathrm{M_{\odot}~yr^{-1}}$ from the same diagnostics. Both galaxies follow typical $L_{\mathrm{[C\,II]}}/L_{\mathrm{FIR}}$ ratios observed in star-forming galaxies and show no evidence for a [C\,\textsc{ii}] deficit, indicating that stellar heating dominates the interstellar medium energetics. The [C\,\textsc{ii}] moment maps reveal compact emission with centrally peaked intensity and ordered rotational kinematics in both systems. Velocity dispersions remain well below values associated with powerful AGN-driven outflows, and no significant morphological asymmetries or disturbed velocity fields indicative of AGN feedback or major mergers are detected, although marginal kinematic substructure in the QUASAR's high-velocity channels warrants further investigation. Although the companion lies at a projected distance of $18.248 \pm 0.277$~kpc within the QUASAR proximity zone, neither morphological nor kinematic signatures indicate AGN-driven outflows affecting the circumgalactic medium. We therefore interpret this system as being observed in a pre-outflow accretion phase, where rapid supermassive BLACK HOLE growth precedes the development of large-scale AGN feedback.
[abstract 9 / 23] (score: 3) - Title: The Effects of Complex Accretion Disk Geometry on Broadened Iron K$α$ LinesAuthors: William Surgent, Daniel R. Wilkins,Comments:Subjects: astro-ph.HECreated: 2026-04-23; Updated: 2026-04-27; Datestamp: 2026-04-27
X-rays are emitted from the corona above the orbiting matter of the accretion disk and travel either directly to us or illuminate the disk. This illumination of the inner disk is enhanced by gravitational light bending, which focuses the rays towards the BLACK HOLE and therefore towards the inner radii of the disk. These rays that hit the inner radii are reflected back to us, and we observe them in the X-ray reflection spectrum. In this work, we create novel general RELATIVISTIC ray tracing simulations to investigate the effects of altering the geometry of the accretion disks of BLACK HOLEs on the most dominant part of the reflection spectrum, the iron K$α$ line. Work demonstrating the effect of disk geometry on the iron line has been performed, though many previous analyses have assumed a simplistic system, consisting of a point-source corona with a flat and infinitesimally thin accretion disk. We extend these models to more realistic accretion disk approximations. These include a constant aspect ratio disk, a radiation-pressure-dominated Shakura-Sunyaev disk, an expanded inner disk that has a non-negligible scale height in its inner regions due to radiation pressure, as well as various warped disks. Using measurement uncertainties from XRISM, we find that non-negligible thickness in accretion disks underestimates the BLACK HOLE spin, corona height, and inclination angle if fitted with a flat disk model. The warped disk model could not be fit with the flat disk approximation.
[abstract 10 / 23] (score: 3) - Title: Ultra-high-energy $γ$-ray imprints from PeV particles accelerated by SUPERNOVA remnantsAuthors: Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, J. Blunier, A. V. Bukevich, C. M. Cai, Y. Y. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, E. S. Chen, G. H. Chen, H. K. Chen, L. F. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen, T. L. Chen, X. B. Chen, X. J. Chen, X. P. Chen, Y. Chen, N. Cheng, Q. Y. Cheng, Y. D. Cheng, M. Y. Cui, S. W. Cui, X. H. Cui, Y. D. Cui, B. Z. Dai, H. L. Dai, Z. G. Dai, Danzengluobu, Y. X. Diao, A. J. Dong, X. Q. Dong, K. K. Duan, J. H. Fan, Y. Z. Fan, J. Fang, J. H. Fang, K. Fang, C. F. Feng, H. Feng, L. Feng, S. H. Feng, X. T. Feng, Y. Feng, Y. L. Feng, S. Gabici, B. Gao, Q. Gao, W. Gao, W. K. Gao, M. M. Ge, T. T. Ge, L. S. Geng, G. Giacinti, G. H. Gong, Q. B. Gou, M. H. Gu, F. L. Guo, J. Guo, K. J. Guo, X. L. Guo, Y. Q. Guo, Y. Y. Guo, R. P. Han, O. A. Hannuksela, M. Hasan, H. H. He, H. N. He, J. Y. He, X. Y. He, Y. He, S. Hernández-Cadena, B. W. Hou, C. Hou, X. Hou, H. B. Hu, S. C. Hu, C. Huang, D. H. Huang, J. J. Huang, X. L. Huang, X. T. Huang, X. Y. Huang, Y. Huang, Y. Y. Huang, A. Inventar, X. L. Ji, H. Y. Jia, K. Jia, H. B. Jiang, K. Jiang, X. W. Jiang, Z. J. Jiang, M. Jin, S. Kaci, M. M. Kang, I. Karpikov, D. Khangulyan, D. Kuleshov, K. Kurinov, Cheng Li, Cong Li, D. Li, F. Li, H. B. Li, H. C. Li, Jian Li, Jie Li, K. Li, L. Li, R. L. Li, S. D. Li, T. Y. Li, W. L. Li, X. R. Li, Y. Li, Zhe Li, Zhuo Li, E. W. Liang, Y. F. Liang, S. J. Lin, B. Liu, C. Liu, D. Liu, D. B. Liu, H. Liu, J. Liu, J. L. Liu, J. R. Liu, M. Y. Liu, R. Y. Liu, S. M. Liu, W. Liu, X. Liu, Y. Liu, Y. Liu, Y. N. Liu, Y. Q. Lou, Q. Luo, Y. Luo, H. K. Lv, B. Q. Ma, L. L. Ma, X. H. Ma, I. O. Maliy, J. R. Mao, Z. Min, W. Mitthumsiri, Y. Mizuno, G. B. Mou, A. Neronov, K. C. Y. Ng, M. Y. Ni, L. Nie, L. J. Ou, Z. W. Ou, P. Pattarakijwanich, Z. Y. Pei, D. Y. Peng, J. C. Qi, M. Y. Qi, J. J. Qin, D. Qu, A. Raza, C. Y. Ren, D. Ruffolo, A. Sáiz, D. Savchenko, D. Semikoz, L. Shao, O. Shchegolev, Y. Z. Shen, X. D. Sheng, Z. D. Shi, F. W. Shu, H. C. Song, Yu. V. Stenkin, Y. Su, D. X. Sun, H. Sun, J. X. Sun, Q. N. Sun, X. N. Sun, Z. B. Sun, N. H. Tabasam, J. Takata, P. H. T. Tam, H. B. Tan, Q. W. Tang, R. Tang, Z. B. Tang, W. W. Tian, C. N. Tong, L. H. Wan, C. Wang, D. H. Wang, G. W. Wang, H. G. Wang, J. C. Wang, K. Wang, Kai Wang, Kai Wang, L. P. Wang, L. Y. Wang, L. Y. Wang, R. Wang, W. Wang, X. G. Wang, X. J. Wang, X. Y. Wang, Y. Wang, Y. D. Wang, Z. H. Wang, Z. X. Wang, Zheng Wang, D. M. Wei, J. J. Wei, Y. J. Wei, T. Wen, S. S. Weng, C. Y. Wu, H. R. Wu, Q. W. Wu, S. Wu, X. F. Wu, Y. S. Wu, S. Q. Xi, J. Xia, J. J. Xia, G. M. Xiang, D. X. Xiao, G. Xiao, Y. F. Xiao, Y. L. Xin, H. D. Xing, Y. Xing, D. R. Xiong, B. N. Xu, C. Y. Xu, D. L. Xu, R. F. Xu, R. X. Xu, S. S. Xu, W. L. Xu, L. Xue, D. H. Yan, T. Yan, C. W. Yang, C. Y. Yang, F. F. Yang, L. L. Yang, M. J. Yang, R. Z. Yang, W. X. Yang, Z. H. Yang, Z. G. Yao, X. A. Ye, L. Q. Yin, N. Yin, X. H. You, Z. Y. You, Q. Yuan, H. Yue, H. D. Zeng, T. X. Zeng, W. Zeng, X. T. Zeng, M. Zha, B. B. Zhang, B. T. Zhang, C. Zhang, H. Zhang, H. M. Zhang, H. Y. Zhang, J. L. Zhang, J. Y. Zhang, Li Zhang, P. F. Zhang, R. Zhang, S. R. Zhang, S. S. Zhang, S. Y. Zhang, W. Zhang, W. Y. Zhang, X. Zhang, X. P. Zhang, Yi Zhang, Yong Zhang, Z. P. Zhang, J. Zhao, L. Zhao, L. Z. Zhao, S. P. Zhao, X. H. Zhao, Z. H. Zhao, F. Zheng, T. C. Zheng, B. Zhou, H. Zhou, J. N. Zhou, M. Zhou, P. Zhou, R. Zhou, X. X. Zhou, X. X. Zhou, B. Y. Zhu, C. G. Zhu, F. R. Zhu, H. Zhu, K. J. Zhu, Y. C. Zou, X. Zuo, Y. Li,Comments: 31 pages, 8 figures, 3 TablesSubjects: astro-ph.HECreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
The quest for the origin of COSMIC RAY (CRs) is a fundamental issue in astrophysics. Shocks of SUPERNOVA remnants (SNRs) have been considered as the dominant contributors to Galactic CRs below the spectral knee near $\sim 3$ petaelectronvolt (PeV). Whether SNRs are efficient accelerators of particles beyond PeV energies has long been debated. Here we report observations of very-high-energy $γ$-ray emission up to hundreds of TeV from two middle age shell-type SNRs, G150.3$+$4.5 and $γ$-Cygni, with the Large High Altitude Air Shower Observatory (LHAASO). Two (or three) distinct morphological/spectral components with convex spectral shapes are observed in both sources, with the low-energy one being more extended than the high-energy one. %Although it is possible that these high-energy components may be driven by powerful pulsars, The likely association of the high-energy component with molecular clouds at similar distances, and the weakness/absence of pulsar wind nebulae (PWNe) inside these SNRs clearly indicate for the first time that the highest energy emission is produced by collision of hadronic CRs up to PeV energies with the clouds. These results are compatible with the classic model prediction that PeV particles accelerated near the end of the free expansion phase of SNR evolution can illuminate nearby molecular clouds (MCs) to produce strong $γ$-ray emission.
[abstract 11 / 23] (score: 3) - Title: Variability of Sagittarius A* at 3 GHz on minute-scale with MeerKATAuthors: K. Kaur, I. Rammala-Zitha, A. Basu, G. Witzel, M. Wielgus, V. Balakrishnan, E. D. Barr, A. Brunthaler, S. Buchner, D. J. Champion, M. Hoeft, S. Khan, H. -R. Klöckner, C. König, M. Kramer, V. Venkatraman Krishnan, Y. K. Ma, S. A. Mao, P. V. Padmanabh, S. Ranchod, S. S. Sridhar, J. D. Wagenveld, R. S. Wharton, O. Wucknitz,Comments: 8 pages, 10 figures, 1 table. Accepted for publication in Astronomy & AstrophysicsSubjects: astro-ph.GA astro-ph.HECreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
The supermassive BLACK HOLE Sagittarius A* (Sgr A*) exhibits temporal and spectral variability across the electroMAGNETic spectrum. However, variability at radio frequencies below ~ 5 GHz for timescales shorter than a day remains largely unexplored. We investigate the variability of Sgr A* at 2.79 GHz on short timescales (1 min), to probe an under-explored regime of its emission process. Through point-source model fitting in the uv-domain, we analyse the flux density variation of Sgr A* over an 8 h observation. We detect flux variation on a few tens of minute timescale with a modulation index of 6.11 %, a mean flux density of ($827 \pm 0.1_{\mathrm{stat}} \pm 33_{\mathrm{sys}}) \, \mathrm{mJy}$, and a mean spectral slope of $0.08\pm0.03$. Furthermore, we measure the slope of the structure function of the observed light curve as $0.81 \pm 0.05$ with a characteristic timescale of about 120 min. Our study at low radio frequencies is a critical step toward constraining the physical mechanisms that drive Sgr A*'s variable emission and its spectral energy distribution. Our study suggests that variability at centimetre and millimetre wavelengths is likely more closely related than previously thought.
[abstract 12 / 23] (score: 2) - Title: The Decoupling of Binaries from Their Circumbinary DisksAuthors: Alexander J. Dittmann, Geoffrey Ryan, M. Coleman Miller,Comments: 10 pages, 5 figures. Submitted to ApJL, comments welcomeSubjects: astro-ph.HE astro-ph.GA gr-qcCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
We have investigated, both analytically and numerically, accreting supermassive BLACK HOLE binaries as they inspiral due to gravitational radiation to elucidate the decoupling of binaries from their disks and inform future multi-messenger observations of these systems. Our numerical studies evolve equal-mass binaries from initial separations of $100 GM/c^2$ until merger, resolving scales as small as $\sim0.04 GM/c^2$, where $M$ is the total binary mass. Our simulations accurately capture the point at which the orbital evolution of each binary decouples from that of their circumbinary disk, and precisely resolve the flow of gas throughout the inspiral. We demonstrate analytically and numerically that timescale-based predictions overestimate the binary separations at which decoupling occurs by factors of $\sim3$, and illustrate the utility of a velocity-based decoupling criterion. High-viscosity ($ν\gtrsim0.03 GM/c$) circumbinary systems decouple late ($a_b\lesssim 15 GM/c^2$) and have qualitatively similar morphologies near merger to circumbinary systems with constant binary separations. Lower-viscosity circumbinary disks decouple earlier and exhibit qualitatively different accretion flows, which lead to precipitously decreasing accretion onto the binary. If detected, such a decrease may unambiguously identify the host galaxy of an ongoing event within a LISA error volume. We illustrate how accretion amplitude and variability evolve as binaries gradually decouple from their circumbinary disks, and where decoupling occurs over the course of binary inspirals in the LISA band. We show that, even when dynamically negligible, gas may leave a detectable imprint on the phase of gravitational waves.
[abstract 13 / 23] (score: 2) - Title: Sensing Gravity with Polarized ElectroMAGNETic RadiationAuthors: Kjell Tangen,Comments: 19 pagesSubjects: gr-qc astro-ph.COCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Polarization wiggling is an observational effect of a gravitational field on the POLARIZATION of electroMAGNETic radiation traversing it. We find that in linear gravity, the POLARIZATION wiggle rate contributions from scalar, vector and tensor perturbations are independent and gauge invariant. While vector and tensor perturbations do induce POLARIZATION wiggling, scalar perturbations do not. This poses two natural questions: Can polarized electroMAGNETic radiation be used to measure vectorial and tensorial components of gravitational fields directly? And if so, how? Polarization wiggling is studied for an arbitrary vector perturbation to the spacetime metric. In a stationary spacetime, the POLARIZATION wiggle rate is proportional to the difference in frame dragging rate around the direction of propagation between radiation emission and measurement events. We show how this can be used to measure the angular momentum of a gravitational source if the emitter orbits the gravitational source on a known orbit. Finally, the POLARIZATION wiggling effect induced by a gravitational tensor mode with arbitrary POLARIZATION is analyzed. The effect is demonstrated for two cases: A spacetime with a flat Minkowski background and an expanding cosmology with a conformally flat background. In both cases, the POLARIZATION wiggling frequency equals the frequency of the gravitational tensor mode, while the other state parameters of the gravitational tensor mode are encoded in the POLARIZATION wiggling amplitude and phase of the polarized radiation. We show that measurements of POLARIZATION wiggling frequency, amplitude and phase of polarized electroMAGNETic radiation emitted by multiple sources at known positions from different directions enables all state parameters of a gravitational tensor mode to be determined.
[abstract 14 / 23] (score: 2) - Title: Comprehensive study of solar type II radio bursts and the properties of the associated shock wavesAuthors: K. Bhandari, D. E. Morosan, S. Normo,Comments: 13 pages (9 page main body, 4 page appendix), 13 figuresSubjects: astro-ph.SRCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Type II radio bursts are solar radio emissions generated by electrons accelerated by coronal shocks. These bursts are typically found close to expanding coronal mass ejections (CMEs), making them valuable for studying the properties and dynamics of CME-driven shocks in the solar corona. Here, we aim to determine the regions in the solar corona where shock waves accelerate electrons and determine their characteristic properties. To do this, we combine radio observations of type II solar radio bursts with MAGNETo-hydrodynamic (MHD) simulations of the solar corona. We analyse ten type II radio bursts from Solar Cycle 25 exhibiting emissions. The novelty of this study lies in using radio imaging data for all type II bursts to examine the positions of the radio sources. The radio source positions, combined with a geometrical fitting of the CME shock and the MHD simulations, are used to determine essential shock parameters at the acceleration region, such as the Alfvén Mach number $(M_{\rm A}$ and $θ_{\rm BN}$. The shock parameters are then combined with the properties of the radio emission and the associated eruption in a comprehensive study. We found that for all events, the type II bursts are located near or inside coronal streamers. The estimated shock speeds are high, resulting in the formation of super-critical shocks ($3.8~\leq~M_{\rm A}~\leq~7.7$) at the type II locations. In most events, type II bursts are located at oblique shocks rather than near-perpendicular geometries, suggesting that the shock structure is more complex at local scales than the simple spherical shock models usually applied to CME shocks. Our results suggest that CME-streamer interaction regions are necessary for the generation of type II bursts, as they provide ideal plasma conditions for the formation of super-critical shocks and the subsequent acceleration of electrons.
[abstract 15 / 23] (score: 2) - Title: Subsolar mass BLACK HOLEs from stellar collapse induced by primordial BLACK HOLEsAuthors: Thomas W. Baumgarte, Stuart L. Shapiro,Comments: 5 pagesSubjects: astro-ph.HE gr-qcCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
While no gravitational-wave detection of subsolar mass BLACK HOLEs has been confirmed to date, a number of candidate detections invite us to speculate on the origin of such BLACK HOLEs should a detection be confirmed. It is generally assumed that the observation of a BLACK HOLE with subsolar mass $M_{\rm obs}$ would provide strong evidence for primordial BLACK HOLEs (PBHs). The mass $M_{\rm PBH}$ of the PBH, however, does not necessarily have to be equal to $M_{\rm obs}$, as it would in what we term a ``direct PBH scenario". Instead, a BLACK HOLE of mass $M_{\rm obs}$ may form in a capture of a much smaller primordial BLACK HOLE, $M_{\rm PBH} \ll M_{\rm obs}$, by a dwarf star of mass $M_* \simeq M_{\rm obs}$, followed by the total consumption of the star by the PBH. We provide some rough estimates and demonstrate that such an ``indirect PBH scenario" may also lead to significant populations of BLACK HOLEs with mass $M_{\rm obs}$, especially in dwarf galaxies, and may be able to explain rare subsolar mass events.
[abstract 16 / 23] (score: 2) - Title: Backlighting the Cosmic Web with Fast Radio Bursts: An Anthology of Dispersion Measure Cross-Correlations with Large-Scale Structure and Baryon TracersAuthors: Kritti Sharma, Elisabeth Krause, Vikram Ravi, Dhayaa Anbajagane, Liam Connor, W. L. Kimmy Wu, Simone Ferraro, Sebastian Grandis, David Alonso, Yi-Kuan Chiang, Casey J. Law, Pranjal R. S., Samuel McCarty, Shivam Pandey,Comments: 25 pages, 6 figuresSubjects: astro-ph.CO astro-ph.GA astro-ph.HECreated: 2026-04-23; Updated: 2026-04-27; Datestamp: 2026-04-27
Fast Radio Bursts (FRBs) probe baryons permeating the cosmic web through their dispersion measures (DMs), which encode the integrated electron density along cosmological sightlines. Using 3,455 unique FRB sources from CHIME/FRB with $\sim 15$ arcmin localizations, we present an anthology of DM correlations with tracers of large-scale structure and baryonic matter at redshifts $z \lesssim 1.5$. We measure statistically significant correlations at $2.6-5σ$ with ten probes, including galaxies ($2.8σ$), weak gravitational lensing ($2.6σ$), cosmic infrared background ($4.0σ$), cosmic microwave background (CMB) lensing ($3.3σ$), thermal Sunyaev Zel'dovich (tSZ) effect ($3.8σ$), X-ray emission tracing galaxy clusters ($5.0σ$) and superclusters ($3.3σ$), soft X-ray background (SXRB, $4.1σ$), and radio continuum emission ($3.2σ$). These measurements reveal a consistent picture in which FRB sightlines intersecting overdense environments carry systematically larger DMs. Correlations with hot-gas tracers provide additional leverage on the strength of feedback, as they are strongly weighted towards the dense, bound gas. The measured amplitude of tSZ$\times$DM and SXRB$\times$DM correlations are consistent with theoretical predictions of baryon distribution from a DM-$z$ relation-inferred model with moderate feedback at $\sim 0.5σ$ level. Weaker feedback scenario is ruled out at $\sim 3.5σ$ by the SXRB$\times$DM correlation. Taken together, these measurements constitute a quantitative multi-tracer foundation for a new era in which FRBs from next generation facilities, such as BURSTT, CHORD, DSA, and SKA, in harmony with other probes, will map the baryon content of the full extent of the cosmic web.
[abstract 17 / 23] (score: 2) - Title: Quiescent and flaring states of three active stars: V834 Tau, LQ Hya, and BY DraAuthors: Gurpreet Singh, Jeewan C. Pandey, Subhajeet Karmakar,Comments: Accepted for pulication in ApJSubjects: astro-ph.SRCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
We present a detailed X-ray study of the quiescent and flaring coronae of three active main-sequence K-type stars, V834 Tau, LQ Hya, and BY Dra, using \textit{XMM-Newton} observations. The quiescent coronae are well described by two-temperature thermal plasma models, with cool and hot components at 0.26-0.30 keV and 0.93-1.01 keV, respectively. Despite similar coronal temperatures, X-ray luminosities (10$^{29.18\mbox{--}29.75}$ erg s$^{-1}$) and overall abundances, the relative emission measures of the cool and hot components differ among the stars. High-resolution spectroscopy reveals significant iron depletion by factors of 5-10 relative to photospheric values, and an inverse first-ionisation-potential effect in all three stellar coronae. Six energetic flares are detected, with peak temperatures of 30 -- 133 MK and released energies of $0.6\mbox{--}4.2\times$10$^ {33}$ erg, classifying them as superflares. Most flares exhibit decay times roughly twice their rise times, although one event shows a decay phase nearly twenty times longer than its rise. Time-resolved spectroscopy and loop scaling laws yield flare parameters consistent with previous studies of active stars. LQ Hya displays recurrent superflares at the same rotational phase across observations separated by six months, suggesting a long-lived, complex MAGNETic field structure. These results provide insights into the MAGNETic activity and flare energetics in active stars, and their implications for stellar and exoplanetary environments.
[abstract 18 / 23] (score: 2) - Title: How lonely are the Binary Compact Objects Detected by the LIGO-Virgo-KAGRA Collaboration?Authors: Devesh Giri, Suvodip Mukherjee,Comments: 24 pages, 10 figures, 3 tablesSubjects: astro-ph.HE astro-ph.CO gr-qcCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Gravitational-wave (GW) observations of compact binary coalescences (CBCs) are traditionally interpreted under the assumption that the binary evolves in isolation. However, in realistic astrophysical environments, brief three-body encounters may perturb the binary's orbital evolution and imprint deviations on the emitted GWs. We develop a physically motivated model for such interactions, retaining Newtonian three-body dynamics supplemented by leading-order ($2.5$PN) radiation-reaction within the binary. We show that such encounters produce a distinctive morphology of dephasing and amplitude modulation in GWs. We search for this kind of distortion from the LIGO--Virgo--KAGRA (LVK) GW catalog GWTC-4 on three events: GW170817, GW190814, and GW230627\_015337, chosen based on high SNR and in-band duration $\gtrsim 10~\mathrm{s}$. We find no statistically significant deviation in the data, which translates into constraints on the absence of any intermediate-mass BLACK HOLE in the mass range above $\sim 10^2$ M$_\odot$ in the vicinity of these binaries of radius approximately $10^{-1}~\mathrm{AU}$. This arises from robust exclusions arising from fly-by interactions that would dynamically disrupt the binary and are directly ruled out independent of waveform modelling, placing the first upper bound on intermediate-mass BLACK HOLEs near these GW events. In future, with the availability of long-duration GW signals, this new avenue can probe encounters of the binary GW sources with compact objects of lighter masses at distances farther away than 1 AU and hence opens a new window to probe the population of individual compact objects of both astrophysical and primordial origin in astrophysical systems of dense environments ranging from galactic centers to dense globular clusters.
[abstract 19 / 23] (score: 2) - Title: Radial evolution of Alfvén wave Parametric Decay Instability in the near-Sun solar wind: Effects of Temperature AnisotropyAuthors: Hayato Saguchi, Yohei Kawazura, Munehito Shoda, Yuto Katoh,Comments:Subjects: astro-ph.SR physics.space-phCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Parametric decay instability (PDI) of Alfvén wave is thought to play an important role in the dissipation of the large-amplitude Alfvén waves and in the heating of MAGNETized plasmas. Temperature anisotropy is frequently observed by spacecraft, including Parker Solar Probe (PSP), in the near-Sun solar wind, yet its impact on PDI in the near-Sun solar wind has been understudied. We calculate the maximum growth rates of PDI, $γ_{\max}/ω_{0}$, where $ω_0$ is the frequency of the parent wave, by solving the linear dispersion relation of Chew-Goldberger-Low (CGL) equations under several expanding background models. To assess the effect of temperature anisotropy, the growth rate is compared with that derived from ideal MAGNETohydrodynamics (MHD). From $R_0$ ($ \sim 1.02R_\odot$) to $30R_0$, we consider three expansion cases: (i) spherically symmetric adiabatic expansion with constant wind speed, (ii) Multi-source observation- and model-constrained expansion, and (iii) a PSP-constrained profile of $(β_{\parallel},ξ)$, where $β_\parallel=8πp_{\parallel0}/B_0^2$ is the parallel plasma beta and $ξ=T_{\perp0} / T_{\parallel0}$ is the temperature anisotropy, that includes Parker-spiral effects. We find that temperature anisotropy increases $γ_{\max}/ω_{0}$ for $β\lesssim 0.1$ in the near-Sun solar wind: in the case of (iii), temperature anisotropy with $T_{\perp0} > T_{\parallel0}$ increases $γ_{\max}/ω_{0}$ by factors of $\sim 1.5$ over $R\simeq 1$--$15\,R_0$, whereas temperature anisotropy with $T_{\parallel0}>T_{\perp0}$ decreases $γ_{\max}/ω_{0}$ at larger $R$. Our results suggest that the temperature anisotropy plays an important role in the onset of PDI even in low-$β$ regimes, such as the near-Sun solar wind.
[abstract 20 / 23] (score: 2) - Title: 3D modelling of thermal loads during unmitigated vertical displacement events in ITER and JETAuthors: F. J. Artola, A. Redl, S. N. Gerasimov, R. A. Pitts, I. S. Carvalho, M. Kong, G. Simic, A. Loarte, J. Van Blarcum, the JOREK team, the JET contributors, the EUROfusion Tokamak Exploitation Team,Comments: submitted as preprint to Nuclear FusionSubjects: physics.plasm-phCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Predicting three-dimensional thermal loads during tokamak disruptions is essential for ITER yet remains weakly developed. We present a physics-based workflow that couples MHD simulations of vertical displacement events with field line tracing on a realistic 3D first wall model and a transient wall thermal response. The approach is validated against JET discharges with beryllium main chamber armour, reproducing key global dynamics, non-axisymmetric current features, and the occurrence (or absence) of melting, thereby building confidence in the methodology. We then apply the same workflow to ITER-relevant conditions with tungsten (W) armour, consistent with the new 2024 ITER re-baseline, to assess disruption heat loads and their 3D localization. The resulting analysis demonstrates the resilience of the ITER W first wall against these events and provides predictions for the energy deposition and current flow profiles. Beyond these studies, the workflow enables scenario-by-scenario estimates of disruption-induced thermal loading, allowing to assess the disruption-budget consumption for these events in future devices.
[abstract 21 / 23] (score: 2) - Title: Constraints on the Primordial Black Hole Abundance using Pulsar Parameter DriftsAuthors: Yan-Chen Bi, Yu-Mei Wu, Qing-Guo Huang,Comments: 9 pages, 2 figuresSubjects: astro-ph.CO astro-ph.HECreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Primordial BLACK HOLEs (PBHs) provide a compelling interpretation for the binary BLACK HOLEs (BBHs) observed by ground-based gravitational-wave (GW) detectors, especially for those BBHs in the theoretical mass gap. In the early Universe, the scalar perturbations required to produce such PBHs inevitably generate scalar-induced GWs (SIGWs). These SIGWs peak in the sub-nanohertz band, and manifest secularly as measurable jerk-like drifts in the second derivative of pulsar spin periods. In this Letter, we perform the first search for SIGWs using pulsar parameter drifts, and place a 95\% confidence-level upper limit on the PBH abundance of $f_{\mathrm{PBH}} < 10^{-10}$ over the mass range $[3 \times 10^{-1}, 4 \times 10^{4}] M_{\odot}$. Our results strongly disfavor a PBH origin for the BBHs currently detected by the LIGO-Virgo-KAGRA (LVK) Collaborations.
[abstract 22 / 23] (score: 2) - Title: Quasinormal Modes and Neutrino Energy Deposition for a Magnetically Charged Black Hole in a Hernquist Dark Matter HaloAuthors: Ali Ovgun, Reggie C. Pantig, Joel Saavedra,Comments: 30 pages, 7 figures, 6 tablesSubjects: gr-qcCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
We investigate quasinormal modes, shadow observables, weak gravitational lensing, and neutrino--antineutrino annihilation for a static, spherically symmetric BLACK HOLE that carries a nonlinear-electrodynamics MAGNETic charge and is embedded in a Hernquist dark-matter halo. The geometry is controlled by the black-hole mass $M$, MAGNETic charge $g$, and halo parameters $(α,β)$, and provides a simple analytic setting in which compact-object and environmental deformations can be studied simultaneously. We derive the scalar, electroMAGNETic, and axial gravitational master equations and compute the corresponding quasinormal spectra using a high-order WKB expansion supplemented by Pade resummation. The MAGNETic charge raises the real oscillation frequency and slightly increases the damping rate, whereas the Hernquist halo shifts the spectrum in the opposite direction; for suitable parameters the two effects partially cancel at the level of individual modes. We then connect the eikonal spectrum with the photon sphere and shadow radius, emphasizing the distinction between comparisons performed at fixed bare mass and at fixed asymptotic mass $\mathcal{M}=M+α$. At fixed asymptotic mass, the residual NED and halo-concentration terms reduce the shadow and the weak-deflection angle relative to Schwarzschild at the first nontrivial order. Finally, we formulate neutrino-pair annihilation in the same background, including the angular factor, Tolman-redshifted $T^9$ kernel, integrated deposition rate, and reduced shell profile. The MAGNETic sector suppresses the annihilation efficiency, while the halo sector enhances it through its lowering of the lapse. These results show that ringdown, imaging, lensing, and high-energy deposition probe the same underlying competition between near-horizon MAGNETic structure and extended dark-matter environment, but with different parameter weights.
[abstract 23 / 23] (score: 2) - Title: Revisiting confinement scalings and fusion performance with a perspective optimized for extrapolationAuthors: Jalal Butt, Geert Verdoolaege, Ghent University, Stanley M. Kaye, Egemen Kolemen,Comments:Subjects: physics.plasm-phCreated: 2026-04-24; Updated: 2026-04-27; Datestamp: 2026-04-27
Recent advances in high-temperature-superconductor technology have made substantially higher toroidal MAGNETic fields technologically accessible, reopening the design space for compact, high-field tokamak reactors. Because reactor performance projections remain anchored to empirical confinement scalings, the recent update to the ITPA global H-mode confinement database raises an important question: what does the present experimental record and its uncertainty imply for the path to reactor-grade fusion performance? In this work, we revisit confinement extrapolation from an explicitly extrapolation-oriented perspective and, to complement its implications in terms of a direct reactor performance measure, present a cross-machine empirical scaling for fusion power. We systematically search for a minimally complex confinement scaling that optimizes the tradeoff between variance capture and extrapolative robustness. We find that low-order models centered near $N=3$ to $N=4$ optimize this tradeoff, with plasma current, machine size, heating power, and elongation emerging as the dominant engineering levers, together with an empirically inferred confinement penalty associated with metallic walls. Recast in reactor-performance terms, the results indicate that both the fusion triple product and fusion power are governed primarily by plasma current: the triple product scales approximately as $I_p^2$, and the empirical fusion power scaling exhibits a similarly near-quadratic dependence over a survey of the highest performing discharges across several machines. Projecting to reactors, these results suggest that high-field devices with metal walls may require higher plasma current than standard IPB98$(y,2)$-based expectations imply, and that gigawatt-class tokamak performance likely demands operation at $I_p \gtrsim 20\mathrm{MA}$.
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