TITLE:   GCN CIRCULAR
NUMBER:  13606
SUBJECT: GRB 120804A: Gemini-North detection of an optical afterglow and putative host galaxy
DATE:    12/08/07 16:04:57 GMT
FROM:    Wen-fai Fong at CFA  <wfong@cfa.harvard.edu>

W. Fong, R. Chornock, and E. Berger (Harvard) report:

"We re-observed the location of the short-duration GRB 120804A (GCN
13573) with the Gemini Multi-Object Spectrograph (GMOS) mounted on the
Gemini-North 8-meter telescope to check for the presence of a fading
optical source. We obtained 16x180-sec of i-band observations in good
seeing conditions (FWHM=0.65") starting on 2012 August 07.30 UT, 3.3
days after the BAT trigger and 3.0 days after our initial observations
(GCN 13586).

Digital image subtraction of the two GMOS epochs using the ISIS
software package reveals a fading source slightly offset from the
center of S1, suggesting this to be the optical afterglow of GRB
120804A. There are no additional residuals in or around the refined
XRT position (improved upon from GCN 13577;
http://www.swift.ac.uk/xrt_positions/00529686/). Both S1 and S2 appear
to be extended, indicating that S1 is likely to be the
host galaxy of GRB 120804A and S2 is likely unrelated to the GRB.

We thank the Gemini staff for their assistance with these
observations."