Coward 2008 余辉响应时间对红移测量的偏差

主要内容:
趋势就是光学余辉被观测的时间越长, 越能确定高红移的暴.
注意这里的响应时间是整个观测的duration, 而不是第一次follow的反应时间.

精彩摘抄:
响应时间和红移的统计关系.

可是如果响应时间在100分钟左右的就没有红移大于2的, 这也太夸张了吧. 难道就不能通过宿主星系来确定一下红移? 同样大于1000分钟的就没有红移比较小的暴. 我怀疑这不是选择效应, 而是一个真实的趋势了

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Title:		GRB optical afterglow and redshift selection effects: The learning curve effect at work
Authors:		Coward, D. M.
Publication:		eprint arXiv:0811.3443
Publication Date:		11/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		5 pages, 4 figures, MNRAS Letter (accepted)
Bibliographic Code:		2008arXiv0811.3443C

Abstract

We show how the observed gamma ray burst (GRB) optical afterglow (OA) and redshift distributions are changing in time from selection effects. For a subset of {\it Swift} triggered long duration bursts, we show that the mean time taken to acquire spectroscopic redshifts for a GRB OA has evolved to shorter times. We identify a strong correlation between the mean time taken to acquire a spectroscopic redshift and the measured redshift. This correlation reveals that shorter response times favour smaller redshift bursts. This is compelling evidence for a selection effect that biases longer response times with relatively brighter high redshift bursts. Conversely, for shorter response times, optically fainter bursts that are relatively closer are bright enough for spectroscopic redshifts to be acquired. This selection effect could explain why the average redshift, $\approx2.8$ measured in 2005, has evolved to $\approx2$, by mid 2008. Understanding these selection effects provides an important tool for separating the contributions of intrinsically faint bursts, those obscured by host galaxy dust and bursts not seen in the optical because their OAs are observed at late times. The study highlights the importance of rapid response telescopes capable of spectroscopy, and identifies a new redshift selection effect that has not been considered previously, namely the response time to measure the redshift.

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