C. C. Thoene (DARK, UC Berkeley), D. A. Perley (UCB), J. Cooke (UC
Irvine), J. S. Bloom (UC Berkeley), H.-W. Chen (Univ. Chicago) and E.
Barton (UCI) report:
We took 2x10min spectra of the afterglow of GRB 070810 (GCN 6734, Swan et
al.; GCN 6735, Chester et al.) with Keck I + LRIS on Aug. 10, starting
05:46:32 UT (3.58h after the burst) in twilight. From a DLA and several
absorption lines including Fe II, OI, SiII and CII, we infer a redshift of
z=2.17 for that burst.
In addition, we obtained 2x120 s imaging in R band and 2x150 s in g band,
starting at 06:13:26 UT.
Calibrating relative to five USNO-B1.0 stars, we measure a magnitude of
R=20.45 +/- 0.5, dominated by the systematic uncertainty relative to the