Identifying the Environment and Redshift of Gamma-Ray Burst Afterglows from the Time Dependence of Their Absorption Spectra
Identifying the Environment and Redshift of Gamma-Ray Burst Afterglows from the Time Dependence of Their Absorption Spectra
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DOI：
10.1086/305865
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发表时间：
1997-12
期刊：
影响因子：
--
通讯作者：
R. Perna;A. Loeb
中科院分区：
文献类型：
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作者：
R. Perna;A. Loeb
伽马射线暴(GRB)余辉的发现揭示了一类新的光学和无线电波长的可变源。目前，探测到的余辉的环境和精确的红移仍然是未知的。我们发现，如果伽玛射线源位于致密的(≲100pC)富气环境中，由于余辉辐射使周围介质逐渐电离，余辉光谱将呈现出随时间变化的吸收特征。这种时间相关性的检测可以用来限制周围气体系统的大小和密度。例如，如果吸收发生在源周围大小为≲100pC的气体云中，在伽马射线暴970508中探测到的镁II吸收线在第一个月应该已经大大减弱。依赖于时间的HI或金属吸收特征提供了对伽玛暴红移的精确测定。
The discovery of gamma-ray burst (GRB) afterglows revealed a new class of variable sources at optical and radio wavelengths. At present, the environment and precise redshift of the detected afterglows are still unknown. We show that if a GRB source resides in a compact (≲100 pc) gas-rich environment, the afterglow spectrum will show time-dependent absorption features due to the gradual ionization of the surrounding medium by the afterglow radiation. Detection of this time dependence can be used to constrain the size and density of the surrounding gaseous system. For example, the Mg II absorption line detected in GRB 970508 should have weakened considerably during the first month if the absorption occurred in a gas cloud of size ≲100 pc around the source. The time-dependent H I or metal absorption features provide a precise determination of the GRB redshift.