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GCN Circular 33690

Subject
GRB 230427A: MITSuME Akeno optical upper limits
Date
2023-04-27T15:34:00Z (a year ago)
From
Ichiro Takahashi at Tokyo Tech <itakahashi@hp.phys.titech.ac.jp>
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).


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