TITLE: GCN CIRCULAR NUMBER: 31031 SUBJECT: GRB 211023B: MITSuME Akeno optical upper limits DATE: 21/11/02 11:51:41 GMT FROM: Yuri Imai at Tokyo Inst of Tech imai@hp.phys.titech.ac.jp

R. Hosokawa, Y. Imai, K. L. Murata, M. Niwano, Y. Takamatsu, N. Ito, R. Noto, S. Sato, M. Takaku, R. Yamaguchi, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 211023B (S. Dichiara et al. GCN Circular #30960, V. Lipunov et al. GCN Circular #30964, A.P. Beardmore et al. GCN Circular #30966, A.P. Beardmore et al. GCN Circular #30967, A. Pozanenko et al. GCN Circular #30972, Alan M. Watson et al. GCN Circular #30973, N. P. M. Kuin et al. GCN Circular #30975, Y.-D. Hu et al. GCN Circular #30976, S. Laha et al. GCN Circular #30979, D. A. Kann et al. GCN Circular #30992, B. O'Connor et al. GCN Circular #31000, J. Rastinejad et al. GCN Circular #31002, A. Pozanenko et al. GCN Circular #31003, B. Grossan et al. GCN Circular #31016) 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 21-10-24 17:18:57 UT (20.2 hours after Swift trigger). We stacked the images with good conditions. We did not detect any uncatalogued sources within the UVOT error region (S. Dichiara et al. GCN Circular #30960). We obtained the 5-sigma limits of the stacked images as follows.

T0+[days] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 2.9 2021-10-26 19:25:18 2160 g'>19.5, Rc>19.6, Ic>18.7 3.9 2021-10-27 19:10:47 4020 g'>19.5, Rc>20.1, Ic>19.4 4.9 2021-10-28 19:02:53 7020 g'>19.8, Rc>20.1, Ic>19.3 5.9 2021-10-29 18:56:59 6120 g'>20.3, Rc>20.5, Ic>19.9 ------------------------------------------------------------------------------------------------ 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).