TITLE: GCN CIRCULAR NUMBER: 31891 SUBJECT: GRB 220412A: MITSuME Akeno optical upper limits DATE: 22/04/13 05:35:44 GMT FROM: Katsuhiro L. Murata at Nagoya U K. L. Murata, M. Niwano, Y. Imai, N. Ito, Y. Takamatsu, S. Sato, R. Hosokawa, M. Sasada, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 220412A (Klingler et al. GCN Circular #31881, Watson et al. GCN Circular #31882, Breeveld and Klingler et al. GCN Circular #31885, Evans et al. GCN Circular #31887, D'Ai et al. GCN Circular #31888) 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 2022-04-12 10:10:00 UT (214 minutes after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any uncatalogued sources within the enhanced XRT error region (Evans et al. GCN Circular #31887). We obtained the 5-sigma limits of the stacked images as follows. T0+[min] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 214 2022-04-12 10:53:37 3960 g'>19.0, Rc>19.3, Ic>18.8 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used the 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).