Orphan afterglows in the Universal structured jet model for ?-ray bursts
Orphan afterglows in the Universal structured jet model for ?-ray bursts
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DOI：
10.1111/j.1365-2966.2008.13736.x
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发表时间：
2007-11
影响因子：
4.8
通讯作者：
E. Rossi;R. Perna;F. Daigne
中科院分区：
文献类型：
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作者：
E. Rossi;R. Perna;F. Daigne
在γ射线暴余辉光变曲线中缺乏可靠的消色差突变，促使人们对喷流孔径进行独立的测量。偶然寻找余辉，特别是在无线电波的波长上，一直是经典的选择。这些调查数据已被解释为假设一个均匀发射的射流与尖锐的边缘（'顶帽'射流），在这种情况下，弱相对论光束余辉伽玛暴比例与射流立体角。在本文中，我们考虑，而不是，一个非常广泛的流出的亮度，减少整个发射表面。特别是，我们采用通用结构射流（USJ）模型，这是一个替代的顶帽模型的射流结构。然而，对调查数据的解释是非常不同的：在USJ模型中，我们只观察到喷流孔径内的发射，并且观察到的即时发射率与余辉率的比率应该完全取决于选择效应。我们计算的馀辉的数量和率预计在全天空快照观测作为一个功能的调查灵敏度。我们发现OA搜索的当前（负面）结果与我们的预期一致。在无线电和X射线波段，这主要是由于调查的灵敏度低，而在光学波段，天空覆盖不足。在一般情况下，我们发现，X射线的调查是穷人的OA搜索工具，如果喷气机的结构。另一方面，20厘米射电巡天的微弱图像和未来的仪器，如艾伦望远镜阵列（在射电波段），特别是GAIA，全景巡天望远镜和快速反应系统以及大型综合巡天望远镜（在光学波段）将有机会探测到余辉。
The paucity of reliable achromatic breaks in γ-ray burst afterglow light curves motivates independent measurements of the jet aperture. Serendipitous searches of afterglows, especially at radio wavelengths, have long been the classic alternative. These survey data have been interpreted assuming a uniformly emitting jet with sharp edges (‘top-hat’ jet), in that case the ratio of weakly relativistically beamed afterglows to GRBs scales with the jet solid angle. In this paper, we consider, instead, a very wide outflow with a luminosity that decreases across the emitting surface. In particular, we adopt the universal structured jet (USJ) model, which is an alternative to the top-hat model for the structure of the jet. However, the interpretation of the survey data is very different: in the USJ model, we only observe the emission within the jet aperture and the observed ratio of prompt emission rate to afterglow rate should solely depend on selection effects. We compute the number and rate of afterglows expected in all-sky snapshot observations as a function of the survey sensitivity. We find that the current (negative) results for OA searches are in agreement with our expectations. In radio and X-ray bands, this was mainly due to the low sensitivity of the surveys, while in the optical band the sky coverage was not sufficient. In general, we find that X-ray surveys are poor tools for OA searches, if the jet is structured. On the other hand, the Faint Images of the Radio Sky at Twenty-cm radio survey and future instruments like the Allen Telescope Array (in the radio band) and especially GAIA, Panoramic Survey Telescope and Rapid Response System and Large Synoptic Survey Telescope (in the optical band) will have chances to detect afterglows.