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GCN Circular 32103

GRB 220521A: ISON-Castelgrande observatory optical observations
2022-05-24T13:31:23Z (2 years ago)
Alexei Pozanenko at IKI, Moscow <>
S. Belkin (IKI, HSE), A. Pozanenko (IKI), S. Schmalz (KIAM RAS), A. 
Schmalz (KIAM RAS),  N. Pankov (HSE), Filippo Graziani (GAUSS Srl), 
Riccardo Di Roberto (GAUSS Srl)  report on behalf of IKI GRB FuN:

We observed  the GRB 220521A (Fermi GBM Team, GCN 32075; Dichiara et 
al., GCN 32076;  Poolakkil and Meegan, GCN 32089) with ORI-22 telescope 
of ISON-Castelgrande observatory. Observation started on 2022-05-21 (UT) 
23:25:00, i.e. 4.65 min after GRB trigger. The series consists of 60 
images with an exposure of 60 s in a Clear filter.

The optical afterglow (Malesani et al., GCN 32078; Fynbo et al., GCN 
32079; Goranskij et al., GCN 32082; Strausbaugh et al., GCN 32091; 
Rastinejad et al., GCN 32097) is not detected in the initial part of the 
series and is marginally detected in the stacked image of the second 
part of the series.

Preliminary photometry of the stacked images is following

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

2022-05-21 23:25:00   0.012951  Clear 28*60    n/d   n/d   20.5
2022-05-21 23:57:00   0.035868  Clear 30*60    20.3  0.4   20.2

The photometry is based on nearby USNO-B1.0 (R2) stars
18:21:04.76880 +10:21:04.7232 16.26
18:21:07.39800 +10:20:37.5000 16.73
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