TITLE: GCN CIRCULAR NUMBER: 7413 SUBJECT: GRB 080310: GAO 150cm telescope Optical Observation DATE: 08/03/12 14:09:55 GMT FROM: Kenzo Kinugasa at Gunma Astro. Obs/Japan K. Kinugasa (Gunma Astronomical Observatory) report: The position of GRB 080310 (Chornock et al. GCN 7381; Cummings et al., GCN 7382) was observed with the 150 cm telescope of Gunma Astronomical Observatory. Starting at 15:09 and 18:01 UT (6.5 and 9.4 hours after the burst), Rc and Ic frames were acquired for sets of 5 x 3-min and 5 x 3-min exposures. We clearly detected the optical counterpart in all frames. We estimated the R magnitute below and confirmed the fading trend. The decay index of single power-law is consistent with the result reported by Urata et al. (GCN 7412). mid-UT exp Rc ----------------------------------- 15:18:50 5 x 3-min 20.1+-0.1 18:09:42 5 x 3-min 20.5+-0.1 -----------------------------------