GCN Circular 32101

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).