TITLE: GCN GRB OBSERVATION REPORT NUMBER: 998 SUBJECT: GRB010222: Optical observation and decay DATE: 01/03/01 09:21:10 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. 27 to 28. One image was obtained in relatively poor conditions (seeing ~ 1.5"). A preliminary reduction using stars (223.008250,43.006507) and (223.098277,42.994077) from Henden's list (GCN #987) gives: Feb. 28.653 UTC R = 22.60 +/- 0.15 The relative photometry of the two stars used is consistent with our image within 0.02 magnitudes. Using all the measurements of the R magnitude of the OT published in the GCN's (corrected if needed to put them back in the photometric system of Henden's list), the R magnitude is following a nice power law decay with an index of 1.20 +/- 0.07 since 0.6 days after the burst. An image of the OT and a graph of the decay are available at http://www.cfht.hawaii.edu/~veillet/grb.html S. Lilly 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/ ************************************************************