TITLE: GCN CIRCULAR NUMBER: 39426 SUBJECT: GRB 250221A: continued Mondy optical observations, brightening afterglow DATE: 25/02/23 11:47:30 GMT FROM: Alexei Pozanenko at IKI, Moscow grb.alex@gmail.com

N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunlo (ISZF), A. Volnova (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-33IK telescope of Mondy observatory starting on 2025-02-22 (UT) 12:29:44 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 12:29:44 1.38790 18x120 R 19.95 0.05 21.6

The photometry is based on nearby USNO-B1.0 (R2) stars. Compared to our previous observations (Pankov et al., GCNs 39422,39424) the afterglow has apparently become brighter.

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