[vsnet-grb-info 4821] GRB070612A: Gemini Spectroscopic Redshift

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6556
SUBJECT: GRB070612A: Gemini Spectroscopic Redshift
DATE:    07/06/19 04:37:40 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko (Caltech), D. B. Fox, A. Cucchiara (Penn State), B. P. Schmidt
(Australia National University), E. Berger (Carnegie), P. A. Price (IfA),
and K. C. Roth (Gemini) report on behalf of a larger collaboration:

Starting on 2007 June 17 at 06:10 UT we used GMOS on the Gemini North
telescope to obtain a 600 s spectrum of the afterglow + host galaxy of GRB
070612A (Grupe et al., GCN 6509).  The spectrum was taken in twilight at
very high airmass (~ 3.2) and covers the wavelength range ~ 4000-8120 A.

We find a strong, broad (~ 10 A) emission line at ~ 6229 A that, based on
the lack any blueward emission features, we identify as [O II] 3727 at
z=0.617.  We also notice another possible emission feature at the very red
edge of our spectrum corresponding to H-beta at the same redshift.  No
other features are detected either in emission nor in absorption.

We note that this redshift is significantly larger than the original SDSS
photometric redshift (z ~ 0.1) noted by Cenko, Ofek, and Fox (GCN
6525), and is more consistent with the larger redshift (z ~ 0.4) noted by
Malesani et al. (GCN 6555).  The larger distance would naturally explain
the faintness of any associated SN emission, as noted by these authors.

We wish to thank and acknowledge the effort of the staff at Gemini North
in undertaking these difficult observations.