GCN Circular 33666

N. Higuchi, I. Takahashi, M. Sasada, S. Sato, R. Hosokawa, M. Niwano, Y.
Yatsu (Tokyo Tech), K. L. Murata (Kyoto U) and N. Kawai (Riken) report on
behalf of the MITSuME collaboration:

We observed the field of GRB 230420A (N. J. Klingler et al. #33658, J.P.
Osborne et al. #33661,R. Strausbaugh et al. #33662, Y.-D. Hu et al.
#33663, S.Y.
Fu et al. #33664, S.Y. Fu et al. #33665) 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 2023-04-20
10:23:41 UT (280 seconds after the Swift/BAT detection). We stacked the
images with good conditions. Here we report the Rc and Ic band magnitudes
by the forced-photometry at the enhanced Swift/XRT position (J.P. Osborne
et al. GCN Circular #33661), and the 5-sigma limit of the stacked images in
the g' band.

T0+[sec] |MID-UT | T-EXP[sec] | magnitudes of forced-photometry

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 588 | 2023-04-20 10:28:49| 540 | g'>18.3, Rc=18.3+/- 0.3, Ic=17.3 +/- 0.2

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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).