TITLE: GCN CIRCULAR NUMBER: 31889 SUBJECT: GRB 220412B: MITSuME Akeno optical upper limits DATE: 22/04/13 05:34:06 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 220412B (Gropp et al. GCN Circular #31886) 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 18:28:16 UT (82 minutes after the Swift/BAT trigger). We stacked the images with good conditions. We did not detect any uncatalogued sources within the BAT error region (Gropp et al. GCN Circular #31886). We obtained the 5-sigma limits of the stacked images as follows. T0+[min] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 82 2022-04-12 18:55:21 2820 g'>17.9, Rc>19.0, Ic>18.5 ------------------------------------------------------------------------------------------------ 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).