TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1363 SUBJECT: GRB 020331 Kyoto observation on March 31 DATE: 02/04/12 08:33:28 GMT FROM: Taichi Kato at Kyoto U T. Kato (Kyoto U.), H. Yamaoka (Kyushu U.), R. Ishioka, M. Uemura (Kyoto U.) report on behalf of the VSNET GRB team: We observed GRB 020331 (=H1963, the "Easter" burst detected by HETE, GCN 1315) using unfiltered ST-7E CCD cameras on 25-cm and 30-cm telescopes located at Kyoto University. The initial exposure started at 17h 19m 42s (7 min after the burst localization, 47 min after the burst detection). PSF photometry of measurable 24 images yielded 2.0-sigma detection at the reported afterglow (GCN 1339). The object was found to be 6.4 mag (on 31.734 UT, average of exposures) fainter than GSC 6166.129. After a link with field photometry by Henden (GCN 1319), we obtained a magnitude of 17.9 (system close to Rc), with 1-sigma limits of 17.5-18.7. The magnitude seems to be marginally brighter than the extrapolation with the reported power index (GCN 1346). The observation not only makes the earliest positive detection of a GRB afterglow detected by HETE, but also makes the first evidence that a GRB optical afterglow within ~1 hour of the burst can be at least as bright as expected from the later power-law decay. This message may be cited.