Graham 2008 短暴GRB 070714B的观测

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z=0.9，目前最高红移了

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Title:		GRB 070714B - Discovery of the Highest Spectroscopically Confirmed Short Burst Redshift
Authors:		Graham, J. F.; Fruchter, A. S.; Levan, A. J.; Melandri, A.; Kewley, L. J.; Levesque, E. M.; Nysewander, M.; Tanvir, N. R.; Dahlen, T.; Bersier, D.; Wiersema, K.
Publication:		eprint arXiv:0808.2610
Publication Date:		08/2008
Origin:		ARXIV
Keywords:		Astrophysics
Bibliographic Code:		2008arXiv0808.2610G

Abstract

We detect the afterglow and host galaxy of GRB 070714B. Our observations of the afterglow show an initial plateau in the lightcurve for approximately the first 5 to 25 minutes, then steepening to a powerlaw decay with index alpha = 0.86 +/- 0.10 for the period between 1 to 24 hours post burst. This is consistent with the X-ray light-curve which also shows an initial plateau followed by similar subsequent decay. Such an initial plateau, commonly observed with both long and short GRBs, is suggestive of ongoing central engine activity. We also detect a host galaxy at the location of the optical transient. Our Gemini Nod & Shuffle spectroscopic observations of the host show a single emission line at 7167 angstroms which, based on a grizJHK photometric redshift, we conclude is the 3727 angstrom [O II] line. This places the host at a redshift of z=0.923 which, along with the subsequent probable spectroscopic redshift determination on GRB 070429B of z=0.904 by another group, significantly exceeds the previous highest spectroscopically confirmed short burst redshift of z=0.546 held by GRB 051221. This dramatically moves back the time at which we know short bursts were being formed, and suggests that the present evidence for an old progenitor population may be observationally biased.

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