TITLE: GCN CIRCULAR NUMBER: 31217 SUBJECT: GRB 211211A: MITSuME Akeno optical observation DATE: 21/12/12 13:18:20 GMT FROM: Naohiro Ito at Tokyo Tech N. Ito, R. Hosokawa, K. L. Murata, Y. Imai, Y. Takamatsu, M. Takaku, M. Niwano, R. Noto, S. Sato, R. Yamaguchi, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 211211A (The Fermi GBM team GCN Circular #31201, A. D'Ai et al. GCN Circular #31202, WeiKang Zheng and Alexei V. Filippenko GCN Circular #31203, A.P. Beardmore et al. GCN Circular #31205, V. Lipunov et al. GCN Circular #31206, M. Stamatikos et al. GCN Circular #31209, J.Mangan et al. GCN Circular #31210, J.P. Osborne et al. GCN Circular #31212, S.Q. Jiang et al. GCN Circular #31213, R. Strausbaugh and A. Cucchiara GCN Circular #32214) 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 was carried out from 2021-12-11 17:32:12 UT (~4.4 hours after the Fermi trigger) to 2021-12-11 21:20:21 UT. We stacked the images with good conditions. We marginally detected the optical afterglow candidate reported by the KAIT observation (WeiKang Zheng and Alexei V. Filippenko GCN Circular #31203), Nanshan/NEXT observation (S.Q. Jiang et al. GCN Circular #31213) and LCO observation (R. Strausbaugh and A. Cucchiara GCN Circular #32214) in our g'-, Rc- and Ic- band images. The candidate in our images is blended with the nearby SDSS galaxy (SDSS ID: 1237665429707096375, reported by GCN Circular #31203). We performed forced photometry at the position of the candidate against the nearby galaxy. The magnitudes and the 5-sigma limits of the stacked images are as follows. T0+[hour] | MID-UT | T-EXP[sec] | candidate magnitude | 5-sigma limits ------------------------------------------------------------------------------------------------ 6.3 | 2021-12-11 19:25:34 | 6600 | g'=20.4 +/- 0.2, Rc=20.3 +/- 0.1, Ic=20.4 +/- 0.3 | g'>20.2, Rc>20.7, Ic>19.7 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used id 141492123232234127 of PS1 catalog for flux calibration. The conversion from PS1 r and i band to our Rc and Ic band is by the equation of Tonry et al. (2012), Table. 6. 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).