[vsnet-grb-info 27984] GRB 210527A: MITSuME Akeno optical upper limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30087
SUBJECT: GRB 210527A: MITSuME Akeno optical upper limits
DATE:    21/05/28 05:47:33 GMT
FROM:    Ryohei Hosokawa at Tokyo Institute of Technology  <hosokawa at hp.phys.titech.ac.jp>

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

We observed the field of GRB 210527A (S. Laha et al. GCN Circular
#30081, J.P. Osborne et al. GCN Circular #30082, P.A. Evans et al. GCN
Circular #30083, Nat Butler et al. GCN Circular #30084, V. D'Elia et
al. GCN Circular #30085, V. Lipunov et al. GCN Circular #30086) 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 2021-05-27
10:23:37 UT (3.3 hours after the triggers). We stacked the images with
good conditions. We did not detect any sources within the enhanced XRT
error region (P.A. Evans et al. GCN Circular #30083) in all three
bands. We obtained the 5-sigma limits of the stacked images as
follows.

T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
3.3 2021-05-27 15:28 1980 g'>18.0, Rc>18.6, Ic>18.1
------------------------------------------------------------------------------------------------
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).