TITLE: GCN CIRCULAR NUMBER: 32101 SUBJECT: GRB 220521A: MITSuME Akeno optical upper limits DATE: 22/05/24 09:32:51 GMT FROM: Naohiro Ito at Tokyo Tech S. Sato, M. Sasada, K. L. Murata, R. Hosokawa, Y. Imai, N. Ito, M. Niwano, Y. Takamatsu, M. Tateda, T. Hattori, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 220521A (The Fermi GBM team GCN Circular #32075, Dichiara et al. GCN Circular #32076, Evans et al. GCN Circular #32077, Malesani and Pursimo et al. GCN Circular #32078, Fynboet al. GCN Circular #32079, Evans et al. GCN Circular #32081, Goranskij et al. GCN Circular #32082, Kuin and Dichiara GCN Circular #32085, Tohuvavohu et al. GCN Circular #32086, Watson et al. GCN Circular #32087, Nazarov et al. GCN Circular #32088, Poolakkil and Meegan GCN Circular #32089, Lien et al. GCN Circular #32090, Strausbaugh et al. GCN Circular #32091) 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 2022-05-22 11:56:05 UT (12.6 hours after the Fermi/GBM trigger). We stacked the images with good conditions. We did not detect the optical afterglow (Malesani et al. GCN Circular #32078, Goranskij et al. GCN Circular #32082, Strausbaugh et al. GCN Circular #32091, Rastinejad et al. GCN Circular #32097, Cucchiara et al. GCN Circular #32099). We obtained the 5-sigma limits of the stacked images as follows. T0+[hour] | MID-UT | T-EXP[sec] | 5-sigma limits ------------------------------------------------------------------------------------------------ 16.6 | 2022-05-22 15:56:34 | 6780 | g' > 19.3, Rc > 19.1, Ic > 18.6 ------------------------------------------------------------------------------------------------ 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).