TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1312 SUBJECT: SN 2002ap - peak brightness date (SN/GRB?) DATE: 02/03/28 10:57:54 GMT FROM: Eran Ofek at Tel Aviv U. A. Gal-Yam, E. O. Ofek, O. Shemmer report: Using the Wise Observatory 1m telescope we have obtained UBVRI photometry of SN 2002ap during February 2002. Using our most conservative estimate for the date of the $B-$band peak, Feb. $7.1_{-1.3}^{+7.6}$ days, and assuming that the lag between a hypothetical GRB (that might have been associated with this SN) and the time of $B-$band maximum is similar to that measured for SN 1998bw (14.3 days, Galama et al. 1998), we would expect the GRB trigger to have occurred around Jan. $23.8_{-1.3}^{+7.6}$ days. However, if we use instead our estimated $U-$band peak date, Feb. $4.7_{-1.9}^{+1.1}$ days, which is best constrained by our photometry, along with the appropriate $U-$band time lag from Galama et al. 1998 (13.7 days), the resulting GRB trigger time is Jan. $22.0_{-1.9}^{+1.1}$ days. Hurley et al. (GCN 1252) found no candidate GRB that might be associated with SN 2002ap in an intensive search of gamma-ray data from the IPN, starting Jan. 21. Our results suggest that the GRB trigger may have occurred outside the time frame searched. If the GRB-peak magnitude time lag for SN 2002ap was just one day longer than the lag measured for SN 1998bw, the trigger is likely to have been missed by Hurley et al. We conclude that in order to detect, or set a secure upper limit to the fluence of a GRB associated with SN 2002ap, a search similar to the one reported by Hurley et al. should be extended to include data taken several days prior to January 21. This message may be cited.