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arXiv 0811.1044astro-ph
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GRB 080503:由扩展发射主导的裸短伽马射线暴的意义

GRB 080503: Implications of a Naked Short Gamma-Ray Burst Dominated by Extended Emission

D. A. Perley, B. D. Metzger, J. Granot, N. R. Butler, T. Sakamoto, E. Ramirez-Ruiz, A. J. Levan, J. S. Bloom, A. A. Miller, A. Bunker, H. -W. Chen, A. V. Filipp… 展开作者

D. A. Perley, B. D. Metzger, J. Granot, N. R. Butler, T. Sakamoto, E. Ramirez-Ruiz, A. J. Levan, J. S. Bloom, A. A. Miller, A. Bunker, H. -W. Chen, A. V. Filippenko, N. Gehrels, K. Glazebrook, P. B. Hall, K. C. Hurley, D. Kocevski, W. Li, S. Lopez, J. Norris, A. L. Piro, D. Poznanski, J. X. Prochaska, E. Quataert, N. Tanvir

摘要:

我们报告GRB 080503的观测,一个短的伽马射线暴,具有非常明亮的扩展发射(约30倍的初始尖峰的伽玛射线注量),结合与其他短斯威夫特事件的全面比较。然而,尽管它的发射亮度很低,但光学对应物非常微弱,在BAT触发后约1小时开始的深度观测中从未超过25等。光学亮度在约1天达到峰值,然后急剧下降,其方式类似于Li & Paczynski(1998)对致密双星合并后类似超新星发射的预测。然而,一个浅的光谱指数和类似的演变,从钱德拉观测推断的X射线更符合余辉的解释。相对于明亮的伽玛射线辐射,这种可能的余辉非常微弱,这表明爆发周围有一个非常低密度的介质(一个“裸露的”伽玛暴),这与在深度HST成像中缺乏一个28.5等的重合宿主星系相一致。我们的观测结果加强了这样一种观点,即短伽玛暴通常发生在活跃的恒星形成区域之外,但表明在某些情况下,扩展的即时发射的光度可以大大超过短尖峰,这可能会限制这类事件的理论解释。由于大多数以前没有观测到扩展发射的BAT短爆发太微弱,即使它以典型水平存在,也无法检测到这种特征,因此仅根据现有Swift样本中观测到的扩展发射的存在或不存在得出结论是不成熟的。(节略)

英文摘要:

We report on observations of GRB 080503, a short gamma-ray burst with very bright extended emission (about 30 times the gamma-ray fluence of the initial spike) in conjunction with a thorough comparison to other short Swift events. In spite of the prompt-emission brightness, however, the optical counterpart is extraordinarily faint, never exceeding 25 mag in deep observations starting at ~1 hr after the BAT trigger. The optical brightness peaks at ~1 day and then falls sharply in a manner similar to the predictions of Li & Paczynski (1998) for supernova-like emission following compact-binary mergers. However, a shallow spectral index and similar evolution in X-rays inferred from Chandra observations are more consistent with an afterglow interpretation. The extreme faintness of this probable afterglow relative to the bright gamma-ray emission argues for a very low-density medium surrounding the burst (a "naked" GRB), consistent with the lack of a coincident host galaxy down to 28.5 mag in deep HST imaging. Our observations reinforce the notion that short GRBs generally occur outside regions of active star formation, but demonstrate that in some cases the luminosity of the extended prompt emission can greatly exceed that of the short spike, which may constrain theoretical interpretation of this class of events. Because most previous BAT short bursts without observed extended emission are too faint for this signature to have been detectable even if it were present at typical level, conclusions based solely on the observed presence or absence of extended emission in the existing Swift sample are premature. (abridged)

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