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GCN Circular 30718

Subject
GRB 210824A: MITSuME Akeno optical upper limits
Date
2021-08-26T09:48:44Z (3 years ago)
From
Masafumi Niwano at Tokyo Institute of Tech <niwano@hp.phys.titech.ac.jp>
M. Niwano, K. L. Murata, R. Hosokawa, N. Ito, Y. Imai, H. Takamatsu, 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 210824A (Fermi GBM team, GCN Circular 
#30699, K. L. Page et al. GCN Circular #30700, M.R. Goad et al. GCN 
Circular #30702, V. D'Elia et al. GCN Circular #30704, X. Liu et al. GCN 
Circular #30705, V. Lipunov et al. GCN Circular #30706, S. Lesage et al. 
GCN Circular #30707, Y.-D. Hu et al. GCN Circular #30708, V. Lipunov et 
al. GCN Circular #30709) 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 2021-08-25 
10:20:44 UT (30.1 hours after Fermi trigger). We stacked the images with 
good conditions. We did not detect any uncatalogued sources within the 
XRT error region (V. D'Elia et al. GCN Circular #30706). We obtained the 
5-sigma limits of the stacked images as follows.

T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------ 

31.3 2021-08-25 12:29:20.71 4740 g'>18.6, Rc>19.0, Ic>18.3
------------------------------------------------------------------------------------------------ 

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).
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