[AAVSO-HEN] GRB 070810B: Keck spectroscopy of possible host galaxies

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
For an archive and more information on circulars visit:
http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/bacodine/gcn3_archive.html

TITLE:   GCN CIRCULAR
NUMBER:  6756
SUBJECT: GRB 070810B: Keck spectroscopy of possible host galaxies
DATE:    07/08/12 03:25:02 GMT
FROM:    Christina Thoene at Niels Bohr Institute,DARK Cosmo Ctr  <cthoene at astro.ku.dk>

Christina C. Thoene (DARK, UC Berkeley), Joshua S. Bloom, Nathaniel R.
Butler (UCB) and Peter Nugent (LBL) report:

We obtained spectra of several sources around the reported XRT positions
of GRB70810B (GCN 6754 , Starling et al.) on Aug. 11, 12:30 UT, using Keck
I + LRIS. No new source is seen in imaging of the field at the same time.
At the position of source 1 ("S1") from Starling et al., there is no
optical counterpart visible. From further analysis of the X-ray data, we
detect another weak X-ray source at RA 00:35:46.892, DEC 08:51:05.96
("S3") which includes a weak optical source.
Within the BAT error circle, there is an early type galaxy (LEDA 1354367)
as noted first in Marshall et. al, GCN 6743, for which we determined a
redshift of z=0.0385 derived from Ca H&K absorption lines.
Around source 2 ("S2"), there are four galaxies of which two show strong
emission lines leading to a redshifts around z=0.49 from OII, OIII and the
Balmer series. The two other galaxies have marginal detections of emission
lines at the same redshift and these galaxies might therefore be part of a
cluster or even interacting.

An image indicating the different XRT positions and galaxies observed can
be found at:
http://lyra.berkeley.edu/~cthoene/GRBs/GRB070810B.png


CT wants to thank Keck support astronomer Greg Wirth and his wife for
excellent dinner support during the observations. Tusend tak!