GCN Circular 33690

I. Takahashi, S. Hayatsu, N. Higuchi, M. Sasada, R. Hosokawa, S. Sato,
M. Niwano, H. Seki, H. Takei, 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 230427A (Troja et al. GCN Circular
#33687, Beardmore et al. GCN Circular #33688) with the optical three
color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm
telescope Akeno.

The observation started at 2023-04-27 10:33:23 UT (91 seconds after
the Swift/BAT trigger). We stacked the images with good conditions. We
did not detect any uncatalogued sources within the error region (Troja
et al. GCN Circular #33687). We obtained the 5-sigma limits of the
stacked images as follows.

T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
263 | 2023-04-27 10:36:15 | 160.0 | g'>17.8, Rc>17.4, Ic>17.0
753 | 2023-04-27 10:44:25 | 540.0 | g'>18.7, Rc>18.7, Ic>18.2
2391 | 2023-04-27 11:11:43 | 2220.0 | g'>19.6, Rc>19.4, Ic>19.0
------------------------------------------------------------------------------------------------
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).