高电离金属作为伽马射线暴起源区环爆气体的探针
Highly-ionized metals as probes of the circumburst gas in the natal regions of gamma-ray bursts
摘要：
本文介绍了用VLT/X-射手摄谱仪获得的长持续时间伽马射线暴（GRB）余辉谱中的高电离吸收线。我们的主要目标是研究伽玛暴诞生区的环暴介质。我们的主要重点是NV 1238，1242线跃迁，但我们也讨论了其他高电离线，如OVI，CIV和SiIV。我们没有发现NV的柱密度和中性气体的属性，如金属丰度，HI柱密度和尘埃耗尽之间的相关性，但是NV的相对速度，通常是相对于中性气体的蓝移，被发现与HI的柱密度。如果NV气体是GRB所在的HII区域的一部分，则可以解释这一点，该区域的膨胀受到GRB宿主星系中致密中性气体的限制。我们发现了初步的证据（在2 σ显著性下），X射线导出的柱密度N_H，X可能与NV的柱密度相关，这将表明这两种测量对位于GRB附近的气体的柱密度敏感。我们调查的情况下，NV（和OVI）产生的重组后，相应的原子已完全剥离其电子的初始即时发射，在以前的模型中，高度电离的气体产生的光电离从伽玛射线暴余辉。
英文摘要：
We present here a survey of high-ionization absorption lines in the afterglow spectra of long-duration gamma-ray bursts (GRBs) obtained with the VLT/X-shooter spectrograph. Our main goal is to investigate the circumburst medium in the natal regions of GRBs. Our primary focus is on the NV 1238,1242 line transitions, but we also discuss other high-ionization lines such as OVI, CIV and SiIV. We find no correlation between the column density of NV and the neutral gas properties such as metallicity, HI column density and dust depletion, however the relative velocity of NV, typically a blueshift with respect to the neutral gas, is found to be correlated with the column density of HI. This may be explained if the NV gas is part of an HII region hosting the GRB, where the region's expansion is confined by dense, neutral gas in the GRB's host galaxy. We find tentative evidence (at 2-sigma significance) that the X-ray derived column density, N_H,X, may be correlated with the column density of NV, which would indicate that both measurements are sensitive to the column density of the gas located in the vicinity of the GRB. We investigate the scenario where NV (and also OVI) is produced by recombination after the corresponding atoms have been stripped entirely of their electrons by the initial prompt emission, in contrast to previous models where highly-ionized gas is produced by photoionization from the GRB afterglow.
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