[vsnet-grb-info 1765] GRB 050709: Spectroscopy

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3605
SUBJECT: GRB 050709: Spectroscopy
DATE:    05/07/13 23:32:35 GMT
FROM:    Paul Price at IfA,UH  <price at ifa.hawaii.edu>

P.A. Price (IfA, Hawaii), K. Roth (Gemini), and D.W. Fox (Caltech)
report on behalf of a larger collaboration:

We have observed a candidate host galaxy of GRB 050709 with the Gemini
North telescope and GMOS spectrograph at 2005 July 13.58 UT.  The
observations were made under clouds, at high airmass, and with morning
twilight interfering with the some of the observations.

The source acquired is the brighter of the two sources reported by
Jensen et al. (GCN #3589; "Source B").  The long slit likely does not
cover the position of the fainter of the two sources which is coincident
with the Chandra source ("Source A").

We have reduced 2x900 sec integrations and identify emission lines at
approximate observed wavelengths of 7617A and 5810A which we associate
with Halpha and [O III]5007 at an approximate redshift of z = 0.16.
Fainter emission lines are observed at 5754A and 5641A, corresponding to
[O III]4959 and Hbeta, and thus we believe the redshift is secure.

If source A is the afterglow of GRB 050709, then it is seen in
projection about 3 kpc from Source B, suggesting that Source B may be
the host galaxy.  The similarity of this case with the previous
potential association of the short/hard GRB 050509B with a low-redshift
galaxy (Bloom et al., GCN #3386) is suggestive.  If GRB 050709 is at z =
0.16, then the isotropic-equivalent energy release is about 6 x 10^49
erg (based on Butler et al., GCN #3570).

A definitive measurement of the distance scale to short/hard GRBs awaits
the demonstration of variability of the X-ray or optical emission.  We
encourage deep observations to ascertain the nature of Source A and, in
particular, to search for variability.



We thank the staff of the Gemini North telescope for outstanding support
for these observations.