Current date: 2025-12-29
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Scoring abstracts
Number of records retrieved: 532
Keyword score statistics
score 15 -- 1 abstracts
score 12 -- 1 abstracts
score 8 -- 1 abstracts
score 7 -- 2 abstracts
score 4 -- 4 abstracts
score 3 -- 3 abstracts
score 2 -- 12 abstracts
in total -- 24 abstracts
Articles that appeared on 2025-12-29
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[abstract 1 / 24] Wow! (score: 15)
- Title: MiniJETs and Broken Stationarity in a Blazar : Novel Insights into the Origin of $γ$-ray Variability in CTA 102Authors: Agniva Roychowdhury,Comments: 8 pages, 8 figures. Accepted for publication in The Astrophysical JournalSubjects: astro-ph.HE physics.plasm-phCreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
High-energy BLAZAR light curves, in X-rays and beyond, have historically preferred a log-normal flux distribution, signifying multiplicative processes either in the JET itself or due to connection(s) with accretion. Here we present 18 year archival FERMI-LAT light curves (0.1-100 GeV) of the flat spectrum radio QUASAR (FSRQ) CTA 102 from August 2008 to November 2025, which underwent a huge flare in 2017, with a $\sim$ factor of 100 jump in $γ$-ray flux, along with similar flaring in X-rays. Our statistical analyses confirm that neither the pre nor the post-flare total GeV light curves follow a strictly log-normal distribution. Instead, we observe a statistically significant reduction in skewness from the pre to the post-flare light curves, which implies the BLAZAR transitioned from an energetic state with frequent flaring to a more plateaued state with occasional flaring. We further find that this state transition can be explained through MAGNETic relaxation, where many RECONNECTion events caused the 2017 flare, after which the MAGNETic field was ordered and its energy reached a minimum. To explain this further, we use a Monte Carlo simulation of a modified miniJETs-in-a-JET model where GeV flares are produced only when a maximum number of miniJETs move toward the broad line region and towards the line of sight, in the context of an external Compton model. The flux distributions (both observed and simulated) could be fit by a modified log-normal power-law distribution, implying our miniJETs model can reproduce the GeV flares in CTA 102 as well as their flux distributions.
[abstract 2 / 24] Wow! (score: 12) - Title: Multiband optical variability on diverse timescales of the BLAZAR Ton 599 from 2011 to 2023Authors: O. Vince, C. M. Raiteri, M. Villata, A. C. Gupta, J. Kovačević-Dojčinović, M. Lakićević, L. Č. Popović, P. Kushwaha, D. O. Mirzaqulov, S. A. Ehgamberdiev, D. Carosati, S. G. Jorstad, A. P. Marscher, Z. R. Weaver, J. R. Webb, P. S. Smith, W. P. Chen, A. Tsai, H. C. Lin, G. A. Borman, T. S. Grishina, V. A. Hagen-Thorn, E. N. Kopatskaya, E. G. Larionova, V. M. Larionov, L. V. Larionova, D. A. Morozova, S. S. Savchenko, I. S. Troitskiy, Y. V. Troitskaya, A. A. Vasilyev, A. V. Zhovtan, E. V. Shishkina, O. M. Kurtanidze, M. G. Nikolashvili, S. O. Kurtanidze, R. Ivanidze, J. A. Acosta-Pulido, M. I. Carnerero, G. Damljanović, M. Stojanovic, M. D. Jovanovic, V. V. Vlasyuk, O. I. Spiridonova, A. S. Moskvitin, T. Pursimo, D. Elsässer, M. Feige, L. Kunkel, J. Ledermann, D. Reinhart, A. Scherbantin, K. Schoch, R. Steineke, C. Lorey, I. Agudo, J. Escudero Pedrosa, F. J. Aceituno, G. Bonnoli, V. Casanova, D. Morcuende, A. Sota, V. Bozhilov, A. Valcheva, E. Zaharieva, M. Minev, A. Strigachev, R. Bachev, B. Mihov, L. Slavcheva-Mihova, A. C. Sadun, A. Takey, A. Shokry, M. A. El-Sadek, A. Marchiniand G. Verna,Comments: 22 pages, 12 figures (+1 in Appendix), 9 tables (+1 in Appendix)Subjects: astro-ph.HE astro-ph.GACreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
(Shortened)Context: We analyze the optical variability of the FSRQ Ton 599 using BVRI photometry from the WEBT collaboration (2011-2023), complemented by photometric and spectroscopic data from the Steward Observatory.\\ Aims: To characterize short- and long-term optical variability -- including flux distributions, intranight changes, color evolution, and spectra -- to constrain physical parameters and processes in the central engine.\\ Methods: We tested flux distributions in each filter against normal and log-normal, explored the RMS-flux relation and derived PSDs. We quantified intranight variability using a $χ^2$ test and fractional variability. From variability timescales, we estimated the emitting region size and MAGNETic field. Long-term variability was studied by segmenting the light curve into 12 intervals and analyzing flux statistics. For multi-filter flares, we computed spectral slopes, redshift-corrected fluxes, monochromatic luminosities and generated Color-magnitude and color-time diagrams. From low-flux spectra, we measured Mg II line and estimated the BLACK HOLE mass.\\ Results: Ton 599 showed strong optical variability. Log-normal distributions fit the fluxes better, and all bands show a positive RMS-flux relation with red-noise PSDs.Intranight variability is detected, and used in constraining the emission region and MAGNETic field.The R band reaches a peak flux of 23.5 mJy, corresponding to a monochromatic luminosity of $log(νLν)= 48.48 [erg/s]$. We found a redder-when-brighter trend at low fluxes (thermal), achromatic behavior at intermediate levels (possibly due to JET orientation changes), and a bluer-when-brighter trend at high fluxes (SYNCHROTRON). Long-term color changes are modest, short-term are significant, with a negative correlation between the amplitude of color changes and the average flux. The estimated SMBH mass is order of $10^8 M_\odot$.
[abstract 3 / 24] Wow! (score: 8) - Title: VLBI Diagnostics of Off-axis Jets in Radio Flares of Tidal Disruption EventsAuthors: Tatsuya Matsumoto,Comments: 13 pages, 9 figures, 1 table, submitted to ApJ, comments welcome!!!Subjects: astro-ph.HECreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
The origin of late-time radio flares in tidal disruption events remains unclear. In particular, the peculiar radio flare observed in AT2018hyz has motivated two leading scenarios: a delayed outflow launched $\sim1000\,\rm days$ after discovery, or an off-axis RELATIVISTIC JET directed far from our line of sight. Very long baseline interferometry (VLBI) imaging provides the most direct way to distinguish between these scenarios. In this paper, we calculate synthetic radio images for both models and examine their observational signatures. The motion of the emission centroid is the most powerful diagnostic for breaking the degeneracy. In the delayed-outflow scenario, the centroid motion is confined within a non-RELATIVISTIC distance, whereas in the off-axis JET scenario it exhibits apparent superluminal motion. Detecting such superluminal motion would therefore provide a smoking-gun signature of the off-axis JET interpretation. We also find that the JET image exhibits characteristic features, including a non-monotonic evolution of the image aspect ratio. These results are expected to be generic and applicable to other JETted explosions, such as microQUASARs and GAMMA-RAY BURSTs.
[abstract 4 / 24] Wow! (score: 7) - Title: Detection of very high-energy gamma-ray emission from the RADIO GALAXy M87 with LHAASOAuthors: Zhen Cao, F. Aharonian, Axikegu, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, A. V. Bukevich, Q. Cao, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, A. M. Chen, E. S. Chen, H. X. Chen, Liang Chen, Lin Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen, T. L. Chen, Y. Chen, N. Cheng, Y. D. Cheng, M. C. Chu, M. Y. Cui, S. W. Cui, X. H. Cui, Y. D. Cui, B. Z. Dai, H. L. Dai, Z. G. Dai, Danzengluobu, 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, C. D. 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, X. L. Guo, Y. Q. Guo, Y. Y. Guo, Y. A. Han, O. A. Hannuksela, M. Hasan, H. H. He, H. N. He, J. Y. He, Y. He, Y. K. Hor, B. W. Hou, C. Hou, X. Hou, H. B. Hu, Q. Hu, S. C. Hu, C. Huang, D. H. Huang, T. Q. Huang, W. J. Huang, X. T. Huang, X. Y. Huang, Y. Huang, Y. Y. Huang, X. L. Ji, H. Y. Jia, K. Jia, H. B. Jiang, K. Jiang, X. W. Jiang, Z. J. Jiang, M. Jin, M. M. Kang, I. Karpikov, D. Khangulyan, D. Kuleshov, K. Kurinov, B. B. Li, C. M. Li, Cheng Li, Cong Li, D. Li, F. Li, H. B. Li, H. C. Li, Jian Li, Jie Li, K. Li, S. D. Li, W. L. Li, W. L. Li, X. R. Li, Xin Li, Y. Z. 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, H. D. Liu, J. Liu, J. L. Liu, M. Y. Liu, R. Y. Liu, S. M. Liu, W. Liu, Y. Liu, Y. N. Liu, Q. Luo, Y. Luo, H. K. Lv, B. Q. Ma, L. L. Ma, X. H. Ma, J. R. Mao, Z. Min, W. Mitthumsiri, H. J. Mu, Y. C. Nan, A. Neronov, K. C. Y. Ng, L. J. Ou, P. Pattarakijwanich, Z. Y. Pei, J. C. Qi, M. Y. Qi, B. Q. Qiao, J. J. Qin, A. Raza, D. Ruffolo, A. Sáiz, M. Saeed, D. Semikoz, L. Shao, O. Shchegolev, X. D. Sheng, F. W. Shu, H. C. Song, Yu. V. Stenkin, V. Stepanov, Y. Su, D. X. Sun, Q. N. Sun, X. N. Sun, Z. B. Sun, J. Takata, P. H. T. Tam, Q. W. Tang, R. Tang, Z. B. Tang, W. W. Tian, L. H. Wan, C. Wang, C. B. Wang, G. W. Wang, H. G. Wang, H. H. Wang, J. C. Wang, Kai Wang, Kai Wang, L. P. Wang, L. Y. Wang, P. H. Wang, R. Wang, W. Wang, X. G. Wang, X. Y. Wang, Y. Wang, Y. D. Wang, Y. J. Wang, Z. H. Wang, Z. X. Wang, Zhen Wang, Zheng Wang, D. M. Wei, J. J. Wei, Y. J. Wei, T. Wen, C. Y. Wu, H. R. Wu, Q. W. Wu, S. Wu, X. F. Wu, Y. S. Wu, S. Q. Xi, J. Xia, G. M. Xiang, D. X. Xiao, G. Xiao, Y. L. Xin, Y. Xing, D. R. Xiong, Z. Xiong, D. L. Xu, R. F. Xu, R. X. Xu, W. L. Xu, L. Xue, D. H. Yan, J. Z. Yan, T. Yan, C. W. Yang, C. Y. Yang, F. Yang, F. F. Yang, L. L. Yang, M. J. Yang, R. Z. Yang, W. X. Yang, Y. H. Yao, Z. G. Yao, L. Q. Yin, N. Yin, X. H. You, Z. Y. You, Y. H. Yu, Q. Yuan, H. Yue, H. D. Zeng, T. X. Zeng, W. Zeng, M. Zha, B. B. Zhang, F. Zhang, H. Zhang, H. M. Zhang, H. Y. Zhang, J. L. Zhang, Li Zhang, P. F. Zhang, P. P. Zhang, R. Zhang, S. B. Zhang, S. R. Zhang, S. S. Zhang, X. Zhang, X. P. Zhang, Y. F. Zhang, Yi Zhang, Yong Zhang, B. Zhao, J. Zhao, L. Zhao, L. Z. Zhao, S. P. Zhao, X. H. Zhao, F. Zheng, W. J. Zhong, 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,Comments: Update the list of authorsSubjects: astro-ph.HECreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
The nearby RADIO GALAXy M87 is a very-high-energy (VHE) gamma-ray emitter established by observations with ground-based gamma-ray detectors. Here we report the long-term monitoring of M87 from 2021 to 2024 with Large High Altitude Air Shower Observatory (LHAASO). M87 has been detected by LHAASO with a statistical significance $\sim 9σ$. The observed energy spectrum extends to 20 TeV, with a possible hardening at $\sim 20$ TeV and then a clear softening at higher energies. Assuming that the intrinsic spectrum is described by a single power law up to 20 TeV, a tight upper bound on the extragalactic background light (EBL) intensity is obtained. A strong VHE flare lasting eight days, with the rise time of $τ_{r}^{\rm rise} = 1.05\pm0.49$~days and decay time of $τ_{d}^{\rm decay} = 2.17\pm0.58$~days, was found in early 2022. A possible GeV flare is seen also in the FERMI-LAT data during the VHE flare period. The variability time as short as one day seen in the LHAASO data suggests a compact emission region with a size of $\sim 3\times 10^{15}δ\, {\rm cm}$ ($δ$ being the Doppler factor of the emitting region), corresponding to a few Schwarzschild radii of the central supermassive BLACK HOLE in M87. The continuous monitoring of the source reveals a duty cycle of $\sim 1\%$ for VHE flares with a flux above $ 10^{-11}{\rm~erg~cm^{-2}~s^{-1}}$.
[abstract 5 / 24] Wow! (score: 7) - Title: A self-consistent 3D MHD model producing a solar blowout JETAuthors: Yajie Chen, Hardi Peter, Damien Przybylski, Lakshmi Pradeep Chitta, Sudip Mandal,Comments: Accepted for publication in A&ASubjects: astro-ph.SR astro-ph.HECreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
Context. Solar blowout JETs are a distinct subclass of ubiquitous extreme-ultraviolet (EUV) and X-ray coronal JETs. Aims. Most existing models of blowout JETs prescribe an initial MAGNETic field configurations and apply ad-hoc changes in the photosphere to trigger the JETs. In contrast, we aim for a self-consistent MAGNETo-convective description of the JET initiation. Methods. We employ a 3D radiation MAGNETohydrodynamic (MHD) model of a solar coronal hole region using the MURaM code. The computational domain extends from the upper convection zone to the lower corona. We synthesize the emission in the extreme UV and X-rays for a direct comparison to observations and examine the evolution of the MAGNETic field structure of the event. Results. In the simulation a twisted flux tube forms self-consistently, emerges through the surface and interacts with the pre-existing open field. Initially the resulting JET is of the standard type with a narrow spire. The release of the twist into the open field causes a broadening of the JET spire turning the JET into a blowout type. At the same time this creates a fast heating front propagating at the local Alfvén speed. The properties of the modeled JET closely match observations of blowout JETs: a slow (180 km/s) mass upflow and a fast (500 km/s) propagating front form, the latter being a signature of the heating front. Also the timing of the JET with respect to the flux emergence and subsequent cancellation matches observations. Conclusions. The near-surface MAGNETo-convection self-consistently generates a twisted flux tube that emerges through the photosphere. The tube then interacts with the pre-existing MAGNETic field by means of interchange RECONNECTion. This transfers the twist to the open field region and produces a blowout JET that matches the main characteristics of this type of JET found in observations.
[abstract 6 / 24] Yes (score: 4) - Title: Sombrero Galaxy as an Accelerator of Ultrahigh Energy Cosmic Ray NucleiAuthors: Luis A. Anchordoqui, Karem Peñaló Castillo,Comments: Matching version to be published in PRDSubjects: astro-ph.HECreated: 2025-12-24; Updated: 2025-12-29; Datestamp: 2025-12-29
Motivated by a recent proposal that points to the Sombrero galaxy as a source of the highest energy COSMIC RAYs, we investigate the feasibility of accelerating light and heavy nuclei in the supermassive BLACK HOLE located at the center of this dormant galaxy. We show that COSMIC RAY nuclei concentrated in the immediate vicinity of the supermassive BLACK HOLE could be efficiently accelerated up to the maximum observed energies without suffering catastrophic spallations. Armed with our findings we stand against the conventional wisdom and conjecture that accelerators of the highest energy COSMIC RAYs must anti-correlate with the (electroMAGNETic) source power.
[abstract 7 / 24] Yes (score: 4) - Title: Impact of the EPOS.LHC-R hadronic interaction model on the Centaurus A ultrahigh-energy cosmic-ray scenarioAuthors: Silvia Mollerach, Esteban Roulet,Comments:Subjects: astro-ph.HECreated: 2025-12-24; Updated: 2025-12-29; Datestamp: 2025-12-29
We discuss the impact of the recent EPOS.LHC-R hadronic interaction model on the scenario in which most of the COSMIC RAYs with energies above 5 EeV originate in the nearby Centaurus A RADIOGALAXy. The heavier composition inferred when considering this hadronic model implies that the amount of H and He emitted by the source is reduced compared to what was found with previous hadronic models. The elements of the CNO group play a more predominant role in the instep region just above the ankle while the elements of the Si and Fe groups can contribute significantly in the suppression region of the energy spectrum above 50 EeV. We also obtain the predictions for the amplitude of the dipolar anisotropy in different energy bins above 4 EeV, showing that they can be well consistent with the measurements for appropriate values of the extragalactic turbulent MAGNETic field and source lifetime. A new method to extract the information on the COSMIC RAY masses from that of the depth of the maximum development of the air showers is also introduced.
[abstract 8 / 24] Yes (score: 4) - Title: Spectral State Switching in Mrk 421: Results from the AstroSat LAXPC/SXT ObservationsAuthors: Sikandar Akbar, Zahir Shah, Ranjeev Misra, Naseer Iqbal,Comments: submitted to Journal of High Energy Astrophysics(JHEAP)Subjects: astro-ph.HECreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
We carried a detailed time and flux resolved X-ray spectral analysis of the high-SYNCHROTRON-peaked BLAZAR Mrk\,421 using simultaneous AstroSat and LAXPC20/SXT observations. The 100\,s binned LAXPC20 light curve obtained during 3--8 January 2017 reveals pronounced flux variability. The source exhibits a fractional variability amplitude of $F_{\mathrm{rms}} = 0.210 \pm 0.005$ in the SXT band and $F_{\mathrm{rms}} = 0.316 \pm 0.006$ in the LAXPC20 band. During this interval, the source reached a peak count rate of 122.94\,counts\,s$^{-1}$. This enabled us to carry flux resolved spectroscopy by selecting ten flux states, S1--S10 each having a width of 8\,counts\,s$^{-1}$. We noted that the spectra in these flux states are well described by a SYNCHROTRON-convolved broken power-law (BPL), which consistently provides a better fit than a log-parabola. The low-energy particle index (index before the break) is found to cluster around two discrete values across flux states indicating two spectra states in the source. The break energy consistently moves to high energy with increase in flux level in these states. Time-resolved spectroscopy (10-ks segments) confirms that the flux histogram is best modelled as a double lognormal distribution and the index histogram is bimodal. Inclusion of two additional long observations spanning 2017-2019 shows the same double-state behaviour on longer timescales. Together, the results indicate that Mrk\,421 routinely occupies two dominant spectral; in a leptonic SYNCHROTRON framework this can be explained by Gaussian-like fluctuations in acceleration conditions producing lognormal flux states.
[abstract 9 / 24] Yes (score: 4) - Title: The First X-ray Polarimetry of GRS 1739--278 Reveals Its Rapidly Spinning Black HoleAuthors: Qing-Chang Zhao, Michal Dovciak, Han-Cheng Li, Lian Tao, Hua Feng, Federico Vincentelli, Giorgio Matt, Philip Kaaret, Shuang-Nan Zhang,Comments: Acceptance for publication in APJLSubjects: astro-ph.HECreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
We present a joint spectro-polarimetric analysis of the BLACK HOLE X-ray binary GRS~1739--278 during its 2025 mini-outburst, using simultaneous observations from \ixpe\ and \nustar. The \ixpe\ data show a POLARIZATION degree of ${\rm PD} = (2.3 \pm 0.4)\%$ and a POLARIZATION angle of ${\rm PA} = 62^\circ \pm 5^\circ$ in the 2--8~keV range. The model-independent analysis reveals that the PD increases from $\sim 2\%$ at 2~keV to $\sim 10\%$ in the 6--8~keV band, while the PA remains stable across the \ixpe\ band within statistical uncertainties. Broadband spectral modeling of the combined \ixpe\ and \nustar\ datasets shows that hard Comptonization contributes negligibly in this soft-state observation, while a substantial reflected component is required in addition to the thermal disk emission. We then model the \ixpe\ Stokes spectra using the \texttt{kynbbrr} model. The best-fitting results indicate that high-spin configurations enhance the contribution of reflected returning radiation, which dominates the observed POLARIZATION properties. From the \texttt{kynbbrr} modeling, we infer an extreme BLACK HOLE spin of $a = 0.994^{+0.004}_{-0.003}$ and a system inclination of $i = 54^\circ{}^{+8^\circ}_{-4^\circ}$. Owing to the large contribution from returning radiation, the observed POLARIZATION direction is nearly parallel to the projected system axis, the position angle of which is predicted to be $58^\circ \pm 4^\circ$. Our results demonstrate that X-ray polarimetry, combined with broadband spectroscopy, directly probes the geometry and RELATIVISTIC effects in accretion disks around stellar-mass BLACK HOLEs.
[abstract 10 / 24] (score: 3) - Title: The Effect of Magnetic Field Dissipation in the Inner Heliosheath: Reconciling Global Heliosphere Model and Voyager DataAuthors: Sergey D. Korolkov, Igor I. Baliukin, Merav Opher,Comments:Subjects: astro-ph.SRCreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
Global ideal MAGNETohydrodynamic models of the heliosphere typically predict a greatly exaggerated MAGNETic field pile-up in the inner heliosheath (IHS), the region between the termination shock and heliopause. However, Voyager 1 and 2 observations show only a gradual increase throughout this region. This mismatch is largely attributed to the simplified assumption of a unipolar solar MAGNETic field in many global models, which neglects the complex, folded structure of the heliospheric current sheet (HCS). The IHS, especially at low heliolatitudes, contains these compressed sector boundaries, widely considered prime locations for MAGNETic dissipation via RECONNECTion. To align global model simulations with observations without incurring the prohibitive computational cost of resolving the kinetic-scale current sheet, this work introduces a phenomenological term into the MAGNETic field induction equation. This term captures the macroscopic effect of MAGNETic energy dissipation due to unresolved HCS dynamics. It is designed to mitigate the artificial MAGNETic pile-up, preserve the topological integrity of the MAGNETic field lines, and avoid explicit MAGNETic diffusion. This study demonstrates that incorporating a phenomenological dissipation term into global heliospheric models helps to resolve the longstanding discrepancy between simulated and observed MAGNETic field profiles in the IHS. The proposed mechanism reduces exaggerated MAGNETic energy (converts it into thermal energy), aligns model output with Voyager measurements of both MAGNETic field and proton density, and produces the outward shift in termination shock position and a reduction of the IHS thickness. We found that the characteristic time for MAGNETic field dissipation of about 6 years provides improved agreement with Voyager data in the IHS.
[abstract 11 / 24] (score: 3) - Title: Compact Ca II K Brightenings Precede Solar Flares: A Dunn Solar Telescope Pilot StudyAuthors: Aman Priyadarshi M. Kumar, Juie Shetye, Sean G. Sellers, Damian J. Christian,Comments: Accepted to ApJ LettersSubjects: astro-ph.SRCreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
We present a uniform analysis of compact Ca II K (3934 Å) brightenings that occur near flare kernels and assess their value as short-lead indicators of solar flare onset. Using high-cadence imaging from the Rapid Oscillations in the Solar Atmosphere (ROSA) instrument at the Dunn Solar Telescope (DST), we examine eight flare sequences (seven C-class and one B-class) obtained between 2021 and 2025. Fixed, detector-coordinate regions of interest are used to generate mean-intensity light curves, which are detrended and smoothed to isolate impulsive brightenings. In every event, a compact Ca II K brightening is detected within or adjacent to the flaring region that peaks 10--45 min before the primary kernel and the corresponding rise in GOES 1--8 Å flux. The measured temporal offsets scale with the deprojected separation between the brightening and flare kernels, implying an apparent propagation speed of $\sim$30--35 km s$^{-1}$ that is consistent with chromospheric RECONNECTion. Complementary Spectropolarimeter for Infrared and Optical Regions (SPINOR) spectropolarimetry for one event shows topological reconfiguration from closed to open or extended connectivity, supporting a RECONNECTion-driven origin. These results demonstrate that compact Ca II K brightenings are reproducible, physically meaningful precursors to flare onset. Their simplicity and cadence make them attractive chromospheric indicators, and future work will evaluate their predictive skill alongside established UV/EUV and MAGNETic diagnostics.
[abstract 12 / 24] (score: 3) - Title: Long-term monitoring of repeating FRB 20220912A with the uGMRT at low radio frequenciesAuthors: Ajay Kumar, Yogesh Maan, Banshi Lal, Yash Bhusare, Shriharsh P. Tendulkar, Visweshwar Ram Marthi, Puja Majee,Comments: 22 Pages, 16 Figures, 1 Table, Submitted to ApJ, Comments are welcomeSubjects: astro-ph.HECreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
Some repeating FRBs exhibit occasional extreme repetition rates, but very few show a sustained high activity level. One such hyperactive repeater is FRB 20220912A, which was discovered by CHIME/FRB Collaboration on 2022 September 12. Here, we present results from a long-term monitoring campaign of FRB 20220912A using the upgraded Giant Metrewave Radio Telescope (uGMRT) in the frequency range from 300 to 750 MHz. Over the course of nearly two years, we detected a total of 643 bursts in this frequency range. The source exhibited extreme activity for a few months after its discovery and sustained its active phase for over 500 days, with unsystematic modulations in the activity during this phase. The cumulative energy distributions in both bands show a break, consistent with other active repeaters like FRB 20121102A, FRB 202011124A, etc., suggesting common underlying emission mechanisms. Moreover, we show that the energy distribution shape for FRB 20220912A remains broadly same across a large range of frequencies and over time. Overall, the extended high activity, estimated total energy output, persistent power-law tails in the energy distributions, and the lack of detectable short timescale periodicity favor progenitor models invoking young dynamic MAGNETars, potentially emitting pulses across large rotation phase ranges.
[abstract 13 / 24] (score: 2) - Title: Search for Lorentz Invariance Violation with spectral lags of GRB 190114C using profile likelihoodAuthors: Vyaas Ramakrishnan, Shantanu Desai,Comments: 14 pages, 4 figures. Accepted in Int J. of Modern Physics DSubjects: astro-ph.HE astro-ph.IMCreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
We search for Lorentz invariance violation (LIV) using the spectral lag data for GRB 190114C using frequentist analysis, where we deal with the astrophysical nuisance parameters using profile likelihood. For this use case, we find a global minima for the $χ^2$ as a function of energy scale of LIV ($E_{QG}$), well below the Planck scale. The best-fit $2σ$ central intervals for $E_{QG}$ are given by $2.81^{+0.96}_{-0.72}\times 10^{14}$ GeV and $9.10^{+2.59}_{-0.64}\times 10^{5}$ for linear and quadratic LIV, respectively and agree with the Bayesian estimates hitherto obtained in a previous work. Therefore, the results from frequentist analysis GRB 190114C agrees with Bayesian analysis and presents yet another proof of principles applications of profile likelihood in the search for LIV.
[abstract 14 / 24] (score: 2) - Title: Observational signatures of quantum-corrected RN blackholeAuthors: Nikko John Leo S. Lobos, Virginia C. Fernandez,Comments: 7 pages, 3 figuresSubjects: gr-qcCreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
We investigate the observational signatures of a quantum-corrected Reissner-Nordstr"om (RN) BLACK HOLE to constrain Planck-scale modifications to spacetime geometry using current astrophysical data. By analyzing the null geodesic structure, we demonstrate that the quantum correction parameter, $\mathrm{a}$, acts as a repulsive geometric potential that opposes the gravitational compactification induced by the electric charge, $Q$. This competition leads to a parameter degeneracy wherein a highly charged, quantum-corrected BLACK HOLE can mimic the shadow size of a classical Schwarzschild BLACK HOLE. To resolve this, we employ the strong-field limit formalism to derive the deflection angle and the observables associated with RELATIVISTIC Einstein rings. Our analysis reveals that while the electric charge enhances the deflection angle, the quantum correction suppresses it, providing a theoretical mechanism to distinguish the two effects. Confronting these predictions with the latest Event Horizon Telescope (EHT) observations, we derive robust constraints on the dimensionless parameter $Π= \mathrm{a}/Q$. We find that consistency with the shadow angular diameter of Sgr A* requires $0 \le Π\lesssim 0.7$, implying that quantum geometric corrections cannot exceed approximately $70\%$ of the BLACK HOLE charge without violating empirical bounds. These results highlight the potential of strong-field lensing to place precise phenomenological limits on quantum gravity candidates.
[abstract 15 / 24] (score: 2) - Title: Magnetic Field Line Chaos, Cantori, and Turnstiles in Toroidal PlasmasAuthors: Allen H Boozer,Comments:Subjects: physics.plasm-phCreated: 2025-12-24; Updated: 2025-12-29; Datestamp: 2025-12-29
Although MAGNETic field line chaos, cantori, and turnstiles underlie the physics of tokamak disruptions, runaway electron damage, stellarator non-resonant divertors, and the most important electroMAGNETic correction to what are called electrostatic micro-instabilities, these concepts are not well known. These concepts will be defined and applications that illustrate their importance will be discussed.
[abstract 16 / 24] (score: 2) - Title: NICER Magnetar Burst CatalogAuthors: Che-Yen Chu, Chin-Ping Hu, Teruaki Enoto, George A. Younes, Andrea Sanna, Sebastien Guillot, Rachael Stewart, Zaven Arzoumanian, Matthew G. Baring, Marlon L. Bause, Tolga Güver, Wynn C. G. Ho, Chryssa Kouveliotou, Alex Van Kooten, Zorawar Wadiasingh, Keith C. Gendreau,Comments: 12 pages of main body, 5 pages of appendix tables, 10 figures, submitted to ApJSSubjects: astro-ph.HECreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
In this paper, we present a comprehensive catalog of short bursts from MAGNETars based on eight years of NICER observations. A total of 1130 bursts were identified, making this the largest MAGNETar burst catalog to date. The sample is dominated by SGR 1935+2154, which contributes 76% of all detected bursts. We analyzed burst durations, spectral properties, and their correlations across multiple sources. Bursts from SGR 1935+2154 exhibit significantly longer durations, with a mean of 317 ms, compared to a mean of 23 ms for bursts from other MAGNETars. Two microsecond-scale bursts were detected for the first time, originating from 1E 1048.1-5937 and CXOU J010043.1-721134. Spectral analysis in the 0.5--8 keV range using both blackbody and power-law models shows that bursts with higher fluences have harder spectra. In contrast, correlations between burst duration and spectral parameters are weak or absent. This catalog provides a valuable dataset for studying MAGNETar short bursts, enabling future modeling efforts and improving our understanding of the diversity and physical mechanisms of MAGNETar bursts.
[abstract 17 / 24] (score: 2) - Title: ESO Expanding Horizons White Paper: ElectroMAGNETic counterparts of massive BH mergers with LISAAuthors: M. Dotti, F. Mannucci, R. Buscicchio, M. Colpi, Q. D'Amato, A. Franchini, A. De Rosa, Z. Haiman, . Izquierdo-Villalba, A. Mangiagli, M. Scialpi P. Severgnini, C. Vignali, M. Volonteri,Comments: ESO "Expanding Horizons" white paperSubjects: astro-ph.IM astro-ph.GA astro-ph.HE gr-qcCreated: 2025-12-23; Updated: 2025-12-29; Datestamp: 2025-12-29
The Laser Interferometer Space Antenna (LISA), adopted by ESA and scheduled for the second half of the next decade, will drive a new revolution in the rapidly growing field of gravitational-wave astronomy, by extending GW observations into the hiterto unexplored millihertz regime. One of the key source classes of LISA is merging massive BLACK HOLE binaries in the 1e4-1e7 Msun mass range detectable to very high redshifts $z\sim 15$. MBHBs lighter than 1e6 Msun can potentially be identified during their inspiral weeks before coalescence, allowing for complementary electroMAGNETic observations before, during, and after the two MBHs merge. This white paper aims at defining the optimal strategy to maximize the number of detected EM counterparts of LISA MBHB events.
[abstract 18 / 24] (score: 2) - Title: Numerical Simulations of the Circularized Accretion Flow in Population III Star Tidal Disruption Events. I. The Accretion Flow and the WindAuthors: Yu-Heng Sheng, De-Fu Bu, Xiao-Hong Yang, Yi-Ren Chang, Liang Chen,Comments: 23pages,21figures,accepted by ApJSubjects: astro-ph.HE astro-ph.GACreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
Tidal Disruption Events (TDEs) have recently been proposed as potential probes for Population III stars. However, the properties of the accretion flow and the wind from the Pop III star TDE system are not clear. By performing radiative hydrodynamic simulations, we study the 'circularized' accretion flow of the Pop III star TDE system. The masses of the BLACK HOLE (BH) and the disrupted star are $10^6$ and $300$ solar masses, respectively. We focus on the properties of the wind. We find that the BLACK HOLE accretion rate is highly super-Eddington. A strong wind is driven by radiation pressure. Due to the presence of a strong wind, only $25\%$--$35\%$ of the fallback debris is accreted by the BH. The remaining part is taken away by the wind. The kinetic power of the wind can be as high as $10^{46} {\rm \ erg \ s^{-1}}$. The properties of the wind obtained in this paper may be useful for understanding the radiation properties of Pop III star TDEs in the context of the wind 'reprocessing' model.
[abstract 19 / 24] (score: 2) - Title: Multiband Gravitational Wave Detection Prospects for M31 UCXB-1 System in Low and Middle Frequency BandAuthors: Xiao Guo, Zhoujian Cao, Zhiwei Chen,Comments: 10 pages, 11 figures, comments are welcome!Subjects: astro-ph.HE gr-qcCreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
The recent discovery of M31 UCXB-1, the first extragalactic ultracompact X-ray binary (UCXB) with an orbital period of $T_{\rm orb} \sim 465$ s, presents a unique laboratory for studying close binary evolution and an unprecedented target for continuous gravitational wave (GW) searches. Its identification as a strong candidate BLACK HOLE-white dwarf (BH-WD) system, combined with its exceptionally short period and high X-ray luminosity, suggests it may be one of the most vital low-frequency GW sources in M31. In this \textit{Letter}, we investigate the detectability of its GW signal for future space-borne detectors in multiband GW detection. We find that while its signal-to-noise ratio (S/N) for low-frequency detectors remains marginal for high-confidence detection, middle-frequency detectors such as DECIGO and BBO are far more promising, potentially achieving S/N $\varrho>8$ within reasonable observational duration. With a primary mass of only $m_1 > 5.4M_\odot$ (or $6.6M_\odot$), the network of all low and middle frequency detector (or BBO alone) is capable of detecting GW from this system with a $\varrho > 8$, during 10-year observation. Furthermore, orbital eccentricity can enhance the GW strain at higher harmonics, further improving its detectability, especially for middle-frequency detectors. This study establishes M31 UCXB-1 as a key prototype of short-period UCXBs, cementing its role as a cornerstone for multiband, multi-messenger astrophysics and a vital bridge between X-ray astronomy and the future GW era.
[abstract 20 / 24] (score: 2) - Title: Investigating the signs of evolutionary characteristics in the energy spectrum of shock wave accelerationAuthors: Xu-Lin Dong, Wei-Kang Gao, Yi-Qing Guo, Shu-Wang Cui,Comments:Subjects: astro-ph.HECreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
Under ideal conditions, the theory of shock acceleration for COSMIC RAYs predicts that different elements should exhibit strictly identical spectral indices when accelerated to the same rigidity (R). However, recent high-precision measurements of elemental energy spectra have definitively established the existence of variations in spectral indices across different elements. This study constrains the spectral indices of cosmic-ray elements using AMS-02 and DAMPE observations within the Spatially Dependent Propagation (SDP) model. For elements with A/Z = 2, spectral indices shows significant positive correlations with both atomic number Z and mass number A, likely due to A or Z-dependent fragmentation cross-sections. Predictions indicate that the observed spectra of Ni and Zn will align with the Fe spectrum, while their injection spectra will exhibit slightly softer spectral indices compared to Fe. Future observations from AMS-02, DAMPE and HERD are expected to verify these findings, while theoretical models are needed to systematically explain this phenomenon.
[abstract 21 / 24] (score: 2) - Title: Golden and Silver Dark Sirens for precise H0 measurement with HETDEXAuthors: Yixuan Dang, Ish Gupta, Robin Ciardullo, Erin Mentuch Cooper, Shiksha Pandey, Dustin Davis, Surhud More, Rachel Gray, Hsin-Yu Chen, Daniel J. Farrow, Caryl Gronwall, Donghui Jeong, Shun Saito, Donald P. Schneider, B. S. Sathyaprakash,Comments:Subjects: astro-ph.CO gr-qcCreated: 2025-12-25; Updated: 2025-12-29; Datestamp: 2025-12-29
Gravitational waves (GWs) from compact binary coalescences are standard sirens that provide a direct measure of the source's luminosity distance, enabling an independent measurement of the Hubble constant (H0). While a bright siren -- a GW event with an identified electroMAGNETic (EM) counterpart -- provided the first such constraint, most detections, currently dominated by BLACK HOLE mergers, lack EM signatures. A measurement of H0 is still possible with these dark sirens by statistically associating GW events with galaxies in existing catalogs based on the sky localization. In this work, we explore the potential of two subsets of sirens: rare golden dark sirens, for which a single galaxy dominates the H0 posterior, and silver dark sirens, which are far more common but have a larger set of plausible host galaxies. Using the fifth internal data release of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), we assess the suitability of the Visible Integral-field Replicable Unit Spectrograph (VIRUS) for spectroscopic follow-up of dark sirens. VIRUS exposures of the standard HETDEX depth provide precise redshifts and exquisite completeness within z = 0.2. After a single year of observations with the upgraded LIGO-A# network, the combined sample of golden and silver dark sirens with z < 0.2 and follow-up VIRUS observations can potentially yield a few-percent constraint on H0. Our predictions suggest that spectroscopic redshift surveys such as HETDEX can play a key role in realizing high-precision cosmology with dark sirens in the near future. Standard-siren distance measurements offer a critical, fully independent path to the local value of H0 to resolve the Hubble tension.
[abstract 22 / 24] (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: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
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 $(3.6~\leq~M_{\rm A}~\leq~6.4$) 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 23 / 24] (score: 2) - Title: A Rare Millisecond Pulsar with Cross-Pole Emission: Single-Pulse Insights from PSR J1857+0943Authors: Shi-jun Dang, Ji-guang Lu, Peng Jiang, Yu-lan Liu, Jin-tao Xie, Habtamu Menberu Tedila, Fei-fei Kou, Jian-ping Yuan, Zhi-gang Wen, Shuang-qiang Wang, Lun-hua Shang, Zu-rong Zhou, Wen-ming Yan, Qi-jun Zhi, Na Wang,Comments: 11 pages,8 fiugres,submitted to ApJSubjects: astro-ph.HE hep-phCreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
Studies of subpulse variability in millisecond pulsars (MSPs) offer important constraints on their emission physics. Using the high sensitivity of FAST, we present the first identification of distinct single pulse fluctuation behaviour in PSR J1857+0943. We find that the third component(MP\_C3) of the main pulse may originate from a different region than the other two main-pulse components and may instead share a common origin with the interpulse. This conclusion is supported by four observational evidence as follows: First, the LRCCF shows a clear anticorrelation between MP\_C3 and the interpulse. Second, the single-pulse POLARIZATION at the main-pulse longitude reveals obvious component mixing. Third, the modulation period of the interpulse components is roughly twice that of MP\_C3. Fourth, the reduced modulation index in MP\_C3 suggests possible mixing of emission from different regions. The interpretation in this letter contrasts with the usual assumption that the main pulse and interpulse originate from opposite MAGNETic poles. Hence, PSR J1857+0943 provides a rare laboratory for probing component-dependent plasma behaviour in an MSP MAGNETosphere. Our results offer direct evidence that the main pulse can include emission associated with more than one MAGNETic pole and highlight the importance of single-pulse diagnostics for understanding the geometry and dynamics of pulsars with interpulse emission. In addition, we analyse the jitter properties of this pulsar and measure a one-hour jitter of $σ_{J,1\rm h} = 78 \pm 3~\mathrm{ns}$ at 1.25 GHz, consistent with previous studies.
[abstract 24 / 24] (score: 2) - Title: Revealing the transient ionization dynamics and mode-coupling mechanisms of helicon discharge through a self-consistent multiphysics modelAuthors: Jing-Jing Ma, Lei Chang, Ming-Yang Wu, Hua Zhou, Yi-Wei Zhang, Ilya Zadiriev, Elena Kralkina, Shogo Isayama, Shin-Jae You,Comments:Subjects: physics.plasm-phCreated: 2025-12-26; Updated: 2025-12-29; Datestamp: 2025-12-29
Helicon plasma sources play a central role in applications ranging from material treatment to space propulsion and fusion, yet the physical processes governing their ignition, transient ionization, and mode evolution remain incompletely understood. Here we develop a self-consistent, fully coupled multiphysics framework that integrates Maxwell equations, electron energy transport, drift-diffusion kinetics, and heavy-species chemistry to capture the complete spatiotemporal evolution of helicon discharges. The model reproduces experimental measurements across pressure, MAGNETic field, and frequency ranges, and reveals a previously unresolved transient ionization stage characterized by a rapid density rise within ~10-4 s, accompanied by a two-peak electron temperature structure that governs the formation of the dense plasma core. By tracking the RF power flow and field topology, we characterize the transient redistribution of RF energy during ignition. A short-lived phase of localized energy deposition accompanies the onset of ionization, followed by an evolution toward helicon-like field characteristics together with rapid density growth and profile restructuring. Systematic parametric scans further reveal the sensitivity of this mode-coupling process to gas pressure, MAGNETic field strength, and driving frequency. These results provide a unified picture of the ignition and mode-transition physics in helicon plasmas and establish a predictive tool for the design and optimization of RF plasma sources across space propulsion, manufacturing, and fusion technologies.
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