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Rapid spectral variability of a giant flare from a magnetar in NGC 253
Nature ( IF 64.8 ) Pub Date : 2021-01-13 , DOI: 10.1038/s41586-020-03077-8
O J Roberts 1 , P Veres 2 , M G Baring 3 , M S Briggs 2, 4 , C Kouveliotou 5, 6 , E Bissaldi 7, 8 , G Younes 5, 6 , S I Chastain 5, 6 , J J DeLaunay 9 , D Huppenkothen 10 , A Tohuvavohu 11 , P N Bhat 2, 4 , E Göğüş 12 , A J van der Horst 5, 6 , J A Kennea 13 , D Kocevski 14 , J D Linford 15 , S Guiriec 5, 6, 16 , R Hamburg 2, 4 , C A Wilson-Hodge 14 , E Burns 17
Affiliation  

Magnetars are neutron stars with extremely strong magnetic fields (1013 to 1015 gauss)1,2, which episodically emit X-ray bursts approximately 100 milliseconds long and with energies of 1040 to 1041 erg. Occasionally, they also produce extremely bright and energetic giant flares, which begin with a short (roughly 0.2 seconds), intense flash, followed by fainter, longer-lasting emission that is modulated by the spin period of the magnetar3,4 (typically 2 to 12 seconds). Over the past 40 years, only three such flares have been observed in our local group of galaxies3,4,5,6, and in all cases the extreme intensity of the flares caused the detectors to saturate. It has been proposed that extragalactic giant flares are probably a subset7,8,9,10,11 of short γ-ray bursts, given that the sensitivity of current instrumentation prevents us from detecting the pulsating tail, whereas the initial bright flash is readily observable out to distances of around 10 to 20 million parsecs. Here we report X-ray and γ-ray observations of the γ-ray burst GRB 200415A, which has a rapid onset, very fast time variability, flat spectra and substantial sub-millisecond spectral evolution. These attributes match well with those expected for a giant flare from an extragalactic magnetar12, given that GRB 200415A is directionally associated13 with the galaxy NGC 253 (roughly 3.5 million parsecs away). The detection of three-megaelectronvolt photons provides evidence for the relativistic motion of the emitting plasma. Radiation from such rapidly moving gas around a rotating magnetar may have generated the rapid spectral evolution that we observe.



中文翻译:

来自 NGC 253 磁星的巨大耀斑的快速光谱变化

磁星是具有极强磁场(10 13至 10 15高斯)1,2的中子星,它偶尔会发出大约 100 毫秒长且能量为 10 40至 10 41尔格的 X 射线爆发。偶尔,它们还会产生极其明亮和充满活力的巨型耀斑,这些耀斑以短暂(大约 0.2 秒)、强烈的闪光开始,然后是更微弱、持续时间更长的发射,由磁星3,4(通常为 2 )的自旋周期调制到 12 秒)。在过去的 40 年里,在我们的本地星系群3,4,5,6中只观测到三个这样的耀斑,并且在所有情况下,耀斑的极端强度都会导致探测器饱和。有人提出,河外巨型耀斑可能是短 γ 射线爆发的子集7、8、9、10、11 ,因为当前仪器的灵敏度使我们无法检测到脉动的尾巴,而最初的明亮闪光很容易可观测到大约 10 到 2000 万秒差距的距离。在这里,我们报告了对 γ 射线暴 GRB 200415A 的 X 射线和 γ 射线观测,它具有快速爆发、非常快的时间变化、平坦的光谱和大量的亚毫秒光谱演化。考虑到 GRB 200415A 在方向上相关 13 ,这些属性与河外磁星 12 巨大耀斑的预期属性非常匹配13与星系 NGC 253(距离大约 350 万秒差距)。三兆电子伏特光子的探测为发射等离子体的相对论运动提供了证据。来自旋转磁星周围如此快速移动的气体的辐射可能产生了我们观察到的快速光谱演化。

更新日期:2021-01-13
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