TITLE: GCN CIRCULAR NUMBER: 39427 SUBJECT: GRB 250221A: continued Assy optical observations, brightening afterglow confirmation DATE: 25/02/23 11:51:11 GMT FROM: Alexei Pozanenko at IKI, Moscow grb.alex@gmail.com
N. Pankov (HSE, IKI), V. Kim (FAI), M. Krugov (FAI), Y. Aimuratov (FAI), A. Volnova(IKI), A. Pozanenko (IKI) report on behalf of IKI GRB FuN:
We observed the optical afterglow (Francile et al., GCN 39395; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418; Pankov et al., GCNs 39422,39424; Ghosh et al., GCN 39425) of the Swift GRB 250221A (Caputo et al., GCN 39396) with AZT-20 telescope of Assy-Turgen observatory starting on 2025-02-22 (UT) 15:01:45 in r' filter.
The afterglow is clearly detected. Preliminary photometry of the afterglow in the stacked image is the following
Date UT start t-T0 Exp. Filter OT Err. UL(3sigma)
2025-02-22 15:01:45 1.49280 45x60 r' 20.50 0.05 22.7
The photometry is based on nearby PS1 stars. Compared to our previous observations (Pankov et al., GCNs 39422, 39424, 39426) we can confirm the afterglow brightening. We can estimate the time of the maximum earlier than 2025-02-22 (UT) 12:29:44
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