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Title: GRB 070714B - Discovery of the Highest Spectroscopically Confirmed Short Burst Redshift
Authors: J. F. Graham (1 and 2), A. S. Fruchter (1), A. J. Levan (3), A. Melandri (4), L. J. Kewley (5), E. M. Levesque (5), M. Nysewander (1), N. R. Tanvir (6), T. Dahlen (1), D. Bersier (4), K. Wiersema (6), D. G. Bonfield (7), A. Martinez-Sansigre (8) ((1) Space Telescope Science Institute, (2) Johns Hopkins University, (3) University of Warwick, (4) Liverpool John Moores University, (5) University of Hawaii, (6) University of Leicester, (7) NASA Goddard Space Flight Centre, (8) Max Planck Institute for Astronomy)
(Version v3)

We detect the optical 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 shows an initial plateau followed by a similar subsequent decay. At late time, we detect a host galaxy at the location of the optical transient. 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. We therefore find a redshift of z=0.923. This redshift, as well as a subsequent probable spectroscopic redshift determination of GRB 070429B at z=0.904 by two other groups, significantly exceeds the previous highest spectroscopically confirmed short burst redshift of z=0.546 for 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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U.S. astronomers detected a cosmic explosion that took place 7.4 billion years ago -- making it the oldest known short gamma-ray burst.
The explosion was discovered using NASA's Swift satellite and the Gemini Observatory, astronomers said Wednesday in a release.

"This discovery dramatically moves back the time at which we know short GRBs were exploding. The short burst is almost twice as far as the previous confirmed record holder" - John Graham of The Johns Hopkins University.

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GRB 070714B.kmz
Google Sky file (2kb, km)

GRB 070714B_
Expand (53kb, 560 x 414)

Position(2000): RA 03 51 22.33, Dec +28 17 51.7

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Using the powerful one-two combo of NASAs Swift satellite and the Gemini Observatory, astronomers have detected a mysterious type of cosmic explosion farther back in time than ever before. The explosion, known as a short gamma-ray burst (GRB), took place 7.4 billion years ago, more than halfway back to the Big Bang.
The record-setting short burst is known as GRB 070714B, since it was the second GRB detected on July 14, 2007. Swift discovered the GRB in the constellation Taurus. The bursts high energy and 3-second duration firmly place it in the short GRB category. Rapid follow-up observations with the 2-meter Liverpool Telescope and the 4-meter William Herschel Telescope found an optical afterglow in the same location as the burst, which allowed astronomers to identify the GRBs host galaxy.

GRB 070714B
Swifts Ultraviolet/Optical Telescope captured this image of the afterglow of GRB 070714B, the farthest short gamma-ray burst with a measured distance.
Credit: Swift/UVOT Science Team/NASA

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