GCN Circular 12225

N. R. Tanvir, K. Wiersema (U. Leicester), A. J. Levan (U. Warwick), S. B. Cenko (U. Berkeley)
and T. Geballe (Gemini) report on behalf of a larger collaboration:

We observed the location of GRB 110731A (Oates et al. GCN12215
Not found
 
 
) with
the GMOS-N instrument on Gemini-North (Mauna Kea), beginning at 1 Aug 2011
09:07 UT.�� Spectroscopic observations totalling 3600s were obtained in good
conditions using the B600 grating (spanning approximately 3800 A to 6650 A).��
We identify a broad Ly-alpha absorption feature and several absorption lines of
O, C, Si and Al at a common redshift of z=2.83.�� This includes fine structure lines
of O, C and Si, as seen in other GRB sight-lines, confirming that this is the
redshift of the burst.

Provisional calibration of the acquisition image gives a magnitude of R=22.0 for
the afterglow (uncorrected for foreground extinction of A_R ~ 0.5),�� suggesting
a fairly shallow rate of decay since the NOT epoch (Malesani et al. GCN12220
Not found
 
 
).