TITLE:   GCN CIRCULAR
NUMBER:  35826
SUBJECT: GRB 240225B: Mondy afterglow observations
DATE:    24/02/28 07:44:44 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>

N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI, HSE) 
report on behalf of IKI-GRB-FuN:

We observed the field of GRB 240225B (Nakajima et al., GCN 35796; Evans, GCN 35797, 
Joshi et al., GCN 35798; D'Ai et al., GCN 35810; Kawakubo et al., GCN 35811) with 
AZT-33IK telescope of Sayan observatory (Mondy) equipped with CMOS-photometer 
ANDOR NEO. We took 60x120 sec frames in the R-filter starting on 2024-02-26 (UT) 
12:30:03. The optical afterglow (Gompertz et al., GCN 35805; Liu et al., GCN 35812; 
Malesani et al., GCN 35819; Wise et al., GCN 35820; Gompertz & Malesani, GCN 35824) 
is well detected in the stacked frame with a total exposure of 59x120 sec. Photometry 
of the optical afterglow is following:

Date       UT-start t-T0    Exp    Filter OT    Err   UL         FWHM
(UT)          (mid.)        (nxT)                   (3sigma)   (arcsec)
2024-02-27 13:01:23 1.71919 59x120 R      19.16 0.09  22.8       2.1

The magnitudes were calibrated using nearby USNO-B1.0 stars (R2 magnitudes).