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GCN Circular 33087

Subject
GRB 221218A: MITSuME Akeno optical upper limits
Date
2022-12-20T10:21:15Z (a year ago)
From
Ichiro Takahashi at Tokyo Tech <itakahashi@hp.phys.titech.ac.jp>
I. Takahashi, M. Niwano, R. Hosokawa, K. L. Murata, Y. Imai, N. Ito,
S. Sato, N. Higuchi, M. Tateda, M. Sasada, Y. Yatsu, and N. Kawai
(Tokyo Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 221218A (S. Mereghetti et al. GCN
Circular #33082, WeiKang Zheng et al. GCN Circular #33085, Y.-D. Hu et
al. GCN Circular #33086) 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
2022-12-18 08:37:35 UT (1405 seconds after the INTEGRAL trigger). We
stacked the images with good conditions. We did not detect any
uncatalogued sources within the error region (S. Mereghetti et al. GCN
Circular #33082). We obtained the 5-sigma limits of the stacked images
as follows.

T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
1405 | 2022-12-18 08:51:23 | 1140.0 | g'>19.1, Rc>19.0, Ic>18.4
------------------------------------------------------------------------------------------------
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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