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GCN Circular 31837

Subject
GRB 220403B: Kitab optical observations
Date
2022-04-05T21:24:30Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
N. Pankov (HSE), A. Zhornichenko (KIAM), A. Pozanenko (IKI), V. 
Agletdinov (KIAM), S. Belkin (IKI), Sh. Ehgamberdiev (UBAI) report on 
behalf of IKI-GRB-FuN:

We observed the field of  GRB 220403B  (Klingler  et al., GCN 31820) 
with Kitab RC-36  telescope in Clear filter.  Observation started on 
April, 03  (UT) 21:23:55 and ended on April, 04 (UT) 00:00:11. We 
clearly detect the optical afterglow (Klingler  et al., GCN  31820; 
Jelinek  et al., GCN 31821; Zhu  et al., GCN 31823; Rossi  et al., GCN 
31826; see also early upper limits in Lipunov et al., GCN 31825; Grossan 
  et al., GCN 31830) in the combined images of an initial part of 
observations and do not detect it in the final part.
Preliminary photometry of the  combined images is following

  Date,      UT start, t-T0,   Exp.,  Filter, OT,    Err,  UL(3 sigma)
                     (mid, days)

2022-04-03  21:23:55 0.05178   40*60  CR      19.24  0.19   20.2
2022-04-03  22:30:39 0.10640   87*60  CR      n/d    n/d    20.5

The photometry is based on nearby USNO-B1.0 stars, R2 magnitude
USNO-B1.0_id R2
1791-0003982 16.77
1791-0003984 17.83
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