TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2650 SUBJECT: GRB 040812: Optical counterparts of CXO sources DATE: 04/08/18 17:45:40 GMT FROM: Edo Berger at Caltech E. Berger (Carnegie Observatories) reports on behalf of a larger collaboration: "We inspected the positions of Chandra sources CXO 1-7 (GCN #2648), detected in the error circle of GRB 040812 (GCN #2640), in our Keck LRIS and Las Campanas Du Pont 2.5-m I-band images (GCN #2645): CXO# RA Dec Counterpart? --------------------------------------------------- 1 16 26 00.47 -44 41 22.6 star 2 16 26 02.25 -44 43 49.4 ---- * 3 16 26 06.48 -44 43 20.8 star 4 16 26 08.44 -44 41 25.2 none ** 5 16 25 54.65 -44 42 49.4 star/galaxy 6 16 25 58.73 -44 41 47.0 star/galaxy 7 16 26 1.21 -44 42 46.6 star * CXO-2 is located about 20" away from a very bright star, and this position is saturated in all of our images ** CXO-4 is located about 2" away from a galaxy/star In addition, none of the optical counterparts (excluding CXO-2) exhibit any significant variability either between the two Keck epochs (taken 47 and 104 minutes after the burst) or between the Keck and LCO observations (taken 1.75 days after the burst)."