TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1000 SUBJECT: GRB010222 - Optical observation DATE: 01/03/02 02:16:03 GMT FROM: Christian Veillet at CFHT The optical counterpart of GRB010222 has been observed using the CFHT Multi Object Spectrograph in imaging mode at the Cassegrain focus of the 3.6-m CFH Telescope on the night of Feb. 28 to March 1. Two 10 mn images were obtained in much better conditions than the night before (GCN #998) with a seeing of about 0.8". There are only a few point like sources in the vicinity of the OT. A star like object ~11" S of the OT has been carefully measured with respect to the two stars used in GCN #998 and has a very consistent R magnitude on the MOS exposures (R = 20.13 +/- 0.02). A fainter object 8" from the OT is used for internal consistency checks at R = 22.35. Precise reduction of the images from Feb. 28 and March 1 gives the following results: Feb. 28.653 UTC R = 22.73 +/- 0.10 Mar. 01.628 UTC R = 22.96 +/- 0.10 The index of the power law decay given in GCN #998 is not significantly modified and found as 1.25 +/- 0.06. There is not structure found on the OT, which is still seen as a point source on the March 1 combined image. More information (with the new images of the OT) can be found at http://www.cfht.hawaii.edu/~veillet/grb.html M. Pakull, L. Mirioni, and J. McDonald are acknowledged for their help in this observation. This message may be cited. -- ************************************************************ Dr. Christian Veillet, CFHT Senior Resident Astronomer Phone: (808) 885-3161 http://www.cfht.hawaii.edu/~veillet/ ************************************************************