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arXiv 0706.1273astro-ph
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短/硬GRB 050724余辉的多色观测

Multicolor observations of the afterglow of the short/hard GRB 050724

D. Malesani, S. Covino, P. D'Avanzo, V. D'Elia, D. Fugazza, S. Piranomonte, L. Ballo, S. Campana, L. Stella, G. Tagliaferri, L. A. Antonelli, G. Chincarini, M. … 展开作者

D. Malesani, S. Covino, P. D'Avanzo, V. D'Elia, D. Fugazza, S. Piranomonte, L. Ballo, S. Campana, L. Stella, G. Tagliaferri, L. A. Antonelli, G. Chincarini, M. Della Valle, P. Goldoni, C. Guidorzi, G. L. Israel, D. Lazzati, A. Melandri, L. J. Pellizza, P. Romano, G. Stratta, S. D. Vergani

摘要:

由于发现了短/硬伽马射线暴(GRB)的光学和X射线余辉,人们正在收集有关它们的新信息。然而,一些关键方面仍然知之甚少,包括外流的准直水平,中央引擎活动的持续时间以及祖系统的属性。我们希望限制短伽玛暴050724和它的宿主星系的物理性质,并对全球短伽玛暴的人口作出一些推断。我们目前的余辉GRB 050724和它的宿主星系的光学观测,显着扩大了现有的数据集,这一事件。我们将我们的结果与模型进行比较,并与文献中的可用测量值进行补充。我们研究了余辉光变曲线和光谱,包括X射线数据。我们还提出了观测的主机星系。观测到的光辐射可能与X射线光变曲线中观测到的大耀斑有关。因此,明显的急剧衰减不是由于喷流效应。现有的数据确实与低准直一致,这反过来又意味着一个大的能量释放,与长伽玛暴的能量释放相当。耀斑的性质也限制了内部激波机制,需要在碰撞的壳层之间有一个大的洛伦兹因子对比。这意味着中央发动机在较晚的时候是活跃的,而不是同时发射所有炮弹。宿主星系呈红色,没有正在形成的恒星,这与以前对GRB的发现一致。然而,它不是一个纯粹的椭圆,并有一些微弱的螺旋结构。GRB 050724提供了一个最令人信服的案例,说明短爆发和一个拥有古老恒星星族的星系之间存在联系。因此,它在限制祖细胞模型方面发挥着关键作用,这些模型应该允许出生和爆发之间的长时间延迟。

英文摘要:

New information on short/hard gamma-ray bursts (GRBs) is being gathered thanks to the discovery of their optical and X-ray afterglows. However, some key aspects are still poorly understood, including the collimation level of the outflow, the duration of the central engine activity, and the properties of the progenitor systems. We want to constrain the physical properties of the short GRB 050724 and of its host galaxy, and make some inferences on the global short GRB population. We present optical observations of the afterglow of GRB 050724 and of its host galaxy, significantly expanding the existing dataset for this event. We compare our results with models, complementing them with available measurements from the literature. We study the afterglow light curve and spectrum including X-ray data. We also present observations of the host galaxy. The observed optical emission was likely related to the large flare observed in the X-ray light curve. The apparent steep decay was therefore not due to the jet effect. Available data are indeed consistent with low collimation, in turn implying a large energy release, comparable to that of long GRBs. The flare properties also constrain the internal shock mechanism, requiring a large Lorentz factor contrast between the colliding shells. This implies that the central engine was active at late times, rather than ejecting all shells simultaneously. The host galaxy has red colors and no ongoing star formation, consistent with previous findings on this GRB. However, it is not a pure elliptical, and has some faint spiral structure. GRB 050724 provides the most compelling case for association between a short burst and a galaxy with old stellar population. It thus plays a pivotal role in constraining progenitors models, which should allow for long delays between birth and explosion.

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