Transition from Fireball to Poynting-flux-dominated Outflow in Three-Episode GRB 160625B
B. -B. Zhang, B. Zhang, A. J. Castro-Tirado, Z. G. Dai, P. -H. T. Tam, X. -Y. Wang, Y. -D. Hu, S. Karpov, A. Pozanenko, F. -W. Zhang, E. Mazaeva, P. Minaev, A. … 展开作者
B. -B. Zhang, B. Zhang, A. J. Castro-Tirado, Z. G. Dai, P. -H. T. Tam, X. -Y. Wang, Y. -D. Hu, S. Karpov, A. Pozanenko, F. -W. Zhang, E. Mazaeva, P. Minaev, A. Volnova, S. Oates, H. Gao, X. -F. Wu, L. Shao, Q. -W. Tang, G. Beskin, A. Biryukov, S. Bondar, E. Ivanov, E. Katkova, N. Orekhova, A. Perkov, V. Sasyuk, L. Mankiewicz, A. F. Zarnecki, A. Cwiek, R. Opiela, A. Zadrozny, R. Aptekar, D. Frederiks, D. Svinkin, A. Kusakin, R. Inasaridze, O. Burhonov, V. Rumyantsev, E. Klunko, A. Moskvitin, T. Fatkhullin, V. V. Sokolov, A. F. Valeev, S. Jeong, I. H. Park, M. D. Caballero-Garcia, R. Cunniffe, J. C. Tello, P. Ferrero, S. B. Pandey, M. Jelinek, F. K. Peng, R. Sanchez-Ramirez, A. Castellon
备注：
Revised version reflecting the referees' comments. 27 pages, 11 figures, 5 tables. The final edited version will appear in Nature Astronomy
The ejecta composition is an open question in gamma-ray bursts (GRB) physics. Some GRBs possess a quasi-thermal spectral component in the time-resolved spectral analysis, suggesting a hot fireball origin. Others show a featureless non-thermal spectrum known as the "Band" function, consistent with a synchrotron radiation origin and suggesting that the jet is Poynting-flux-dominated at the central engine and likely in the emission region as well. There are also bursts showing a sub-dominant thermal component and a dominant synchrotron component suggesting a likely hybrid jet composition. Here we report an extraordinarily bright GRB 160625B, simultaneously observed in gamma-rays and optical wavelengths, whose prompt emission consists of three isolated episodes separated by long quiescent intervals, with the durations of each "sub-burst" being $\sim$ 0.8 s, 35 s, and 212 s, respectively. Its high brightness (with isotropic peak luminosity L$_{\rm p, iso}\sim 4\times 10^{53}$ erg/s) allows us to conduct detailed time-resolved spectral analysis in each episode, from precursor to main burst and to extended emission. The spectral properties of the first two sub-bursts are distinctly different, allowing us to observe the transition from thermal to non-thermal radiation between well-separated emission episodes within a single GRB. Such a transition is a clear indication of the change of jet composition from a fireball to a Poynting-flux-dominated jet.
The Origin of the Photospheric Emission of GRB 220426A
GRB 220426 A是一个以光球辐射为主的明亮的伽马射线暴。我们进行了几次测试，以推测这种光球发射的起源。无量纲熵$η$很大，如果我们假设它是由中微子-反中微子湮灭机制发射的纯热火球，这是不寻常的。此外，流出具有较大的$η$，在最初的几秒内具有较低的光度$L$，使得时间分辨的$η-L$的趋势不能被描述为$η$和$L$之间的单调正相关。几乎完全热化坡印亭通量的混合流出可以解释准热谱以及大的$η$。更重要的是，磁场的存在可以影响质子密度和中子-质子耦合效应，从而可以解释观测到的时间分辨$η-L$的变化趋势。光球发射的其他来源，如非耗散混合流出或磁重联，不支持，因为它们的辐射效率低，这与GRB 220426 A的余辉未检测到不一致。因此，我们认为混合外流可能是最有可能的来源。
Intrinsic properties of the engine and jet that powered the short gamma-ray burst associated with GW170817
GRB 170817 A是一个亚亮短伽马射线暴，在中子星合并产生的引力波信号GW 170817之后约1.74 s被探测到。现在，它被理解为一个离轴事件，由指向观察方向15至30度的相对论性喷流茧提供动力。茧是由初始喷流与合并残余物的非相对论重子风相互作用而激发的，导致了具有窄核和宽翼的结构化流出。在本文中，我们耦合的结构化外流与模型的喷风相互作用的观测约束约束的内在属性，喷气发动机发射的中央，包括其时间延迟的合并事件。使用磁化BNS合并模拟的启发风处方，我们发现，喷气发动机在约0.4秒的合并，这意味着1.74秒观察到的延迟主要是由火球传播到光球半径。我们还约束，第一次为任何伽马射线暴，喷射开口角在注射，并设置一个下限，其渐近洛伦兹因子。这些发现表明，最初坡印廷通量占主导地位的射流，通过电磁过程发射。如果喷流是由吸积黑洞提供动力的，它们也会对亚稳态中子星遗迹的生存时间产生重大限制。
Multi-epoch afterglow rebrightenings in GRB 250129A: Evidence for successive shock interactions
Université de la Côte d’Azur（蔚蓝海岸大学）；New York University Abu Dhabi（阿布扎比纽约大学）；Center for Astrophysics and Space Science (CASS), New York University Abu Dhabi（阿布扎比纽约大学天体物理学与空间科学中心）；IJCLab, Univ Paris-Saclay, CNRS/IN2P3（巴黎萨克雷大学IJCLab实验室）；Institute of Physics and Astronomy, Theoretical Astrophysics, University Potsdam（波茨坦大学物理与天文学研究所理论天体物理系）；Nikhef（尼赫夫国家粒子物理研究所）；Institute for Gravitational and Subatomic Physics (GRASP), Utrecht University（乌得勒支大学引力与亚原子物理研究所）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México（墨西哥国立自治大学射电天文学与天体物理研究所）；Physics Department, Nazarbayev University（纳扎尔巴耶夫大学物理系）；Energetic Cosmos Laboratory, Nazarbayev University（纳扎尔巴耶夫大学高能宇宙实验室）；Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM（巴黎萨克雷大学、巴黎西岱大学、法国原子能与替代能源委员会、法国国家科学研究中心）；E.Kharadze Georgian National Astrophysical Observatory（E.哈拉泽格鲁吉亚国家天文台）
GRB 250129A表现出多个晚期时间X射线和光学波段的再变亮现象，研究通过分析促发辐射和近红外数据，揭示后光再变亮可能由延迟碰撞刷新冲击波引起。
