GCN Circular 11882
M. Yoshida (HASC, Hiroshima Univ.), M. Yagi and Y. Komiyama (NAOJ) We performed R band imaging observation of the optical counterpart of GRB 110328A / Swift J164449.3+573451 (Cummings et al. GCN 11823) with LRIS attached to Keck-I telescope. The observation was made at 2011-04-01 15:22 UT. We obtained two 30 sec exposure frames and clearly detected the source (Cenko et al. GCN 11827; Leloudas et al. GCN 11830; Volnova et al. GCN 11837; Im et al. GCN 11839) in both frames. Using GSC2.3: N4JF005367 and N4JF005228 (F-magnitude = 15.90 and 17.13, respectively) for flux calibration, we obtained R-band AB magnitude of 22.61 +- 0.09. Taking into account photometric error of the GSC catalog, we consider that this result is consistent with the HST photometry done on 2011-04-04 (Fruchter et al. GCN 11881) and the OT shows no significant variation between our observation and the HST observation.