TITLE: GCN CIRCULAR NUMBER: 31765 SUBJECT: GRB 220310A: MITSuME Akeno optical observation DATE: 22/03/18 00:15:23 GMT FROM: Ryohei Hosokawa at Tokyo Institute of Technology R. Hosokawa, Y. Imai, K. L. Murata, M. Niwano, N. Ito, Y. Takamatsu, R. Noto, S. Sato, M. Takaku, R. Yamaguchi, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 220310A (H. Negoro et al. GCN Circular #31725, A. Yoshida et al. GCN Circular #31730, P. A. Evans et al. GCN Circular #31731, V. Lipunov et al. GCN Circular #31732, H. Kumar et al. GCN Circular #31738, D. Svinkin et al. GCN Circular #31748, Ahmed M. Fouad et al. GCN Circular #31750, S. Belkin et al. GCN Circular #31751, A.S. Kozyrev et al. GCN Circular #31756) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope Akeno. The observation with a series of 60 sec exposures started at 2022-03-10 15:13:33 UT (14.7 hours after MAXI trigger). We stacked the images with good conditions. We marginally detected the optical counterpart candidate at the position reported previously (V. Lipunov et al. GCN Circular #31732, H. Kumar et al. GCN Circular #31738, Ahmed M. Fouad et al. GCN Circular #31750). The magnitudes of the source are as follows. T0+[hour] | Band | MID-UT | T-EXP[sec] | candidate magnitude ------------------------------------------------------------ 16.1 | g' |2022-03-10 16:32:13 | 6720.0 | 19.62+/-0.18 16.1 | Rc |2022-03-10 16:32:13 | 6780.0 | 19.67+/-0.18 16.1 | Ic |2022-03-10 16:32:13 | 6780.0 | 19.05+/-0.23 ------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).