GRB 050502B optical afterglow: a jet-break at high redshift
GRB 050502B optical afterglow: a jet-break at high redshift
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DOI：
10.1051/0004-6361/200913965
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发表时间：
2010-10
影响因子：
6.5
通讯作者：
P. Afonso;J. Greiner;E. Pian;S. Covino;D. Malesani;A. Yoldaş;T. Krühler;C. Clemens;S. McBreen;A. Rau;D. Giannios;J. Hjorth
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文献类型：
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作者：
P. Afonso;J. Greiner;E. Pian;S. Covino;D. Malesani;A. Yoldaş;T. Krühler;C. Clemens;S. McBreen;A. Rau;D. Giannios;J. Hjorth
目标。雨燕GRB 050502 B以其X射线光变曲线中非常明亮的耀斑而闻名。然而，尽管有广泛的研究，光学光变曲线从未被讨论过，它的红移是不受约束的。光学和X射线数据之间可能的相关性进行了分析。方法.从TNG在R和I波段的光度数据被用来比较的光学余辉与X射线光变曲线。使用HyperZ软件包和后期VLT主机观测来获得红移估计。结果I波段余辉衰减遵循指数α = 2.1 ± 0.6的幂律，在101.3 × 105 s处有一个晚期的衰减。R ― I颜色明显为红色，宽谱指数β OX = 0.9±0.1与X射线谱斜率β X一致。虽然光度红移z > 4是最保守的结果，但在主体中没有消光的情况下，光度红移z = 5.2 ± 0.3，由此导出各向同性能量E γ，iso =（3.8 ± 0.7）× 1052 erg和喷流张开角θ = 3.7°。结论.结合X射线和光学数据表明一个消色差的休息，我们解释为喷流休息。射流破碎后的斜率大致服从射流缓慢冷却模型的闭合关系。由于余辉的颜色非常红，为了使红移较低（z < 1），如果存在于宿主中，消光必须非常高。由于光-X射线指数与X射线光谱一致，而且没有XRT证据表明存在过量的NH，因此GRB 050502 B可能处于高红移。
Aims. Swift GRB 050502B is well known for the very bright flare displayed in its X-ray light curve. Despite extensive studies, however, the optical light curve has never been discussed and its redshift is unconstrained. Possible correlations between optical and X-ray data are analysed. Methods. Photometric data from TNG in the R and I bands were used to compare the optical afterglow with the X-ray light curve. The HyperZ package and a late-time VLT host observation were used to derive redshift estimates. Results. The I-band afterglow decay followed a power law of index α = 2.1 ± 0.6, after a late break at∼ 1.3 x 10 5 s. The R ― I colour is remarkably red and the broadband spectral index β OX = 0.9±0.1 is consistent with the X-ray spectral slope β X . Although a photometric redshift of z > 4 is the most conservative result to consider, a photometric redshift of z = 5.2 ± 0.3 is suggested with no extinction in the host, based on which an isotropic energy E γ,iso = (3.8 ± 0.7) x 10 52 erg and a jet opening angle θ ∼ 3.7° are subsequently derived. Conclusions. The combined X-ray and optical data suggest an achromatic break, which we interpret as a jet-break. The post jet-break slope roughly obeys the closure relation for the jet's slow cooling model. Because of the afterglow's very red colour, in order for the redshift to be low (z < 1), extinction must be significantly high if present in the host. Since the optical-to-X-ray index is consistent with the X-ray spectrum, and there is no XRT evidence for excess N H , GRB 050502B was likely at high redshift.