TITLE: GCN CIRCULAR NUMBER: 42477 SUBJECT: GRB 251017A: INASAN-Kislovodsk optical observations DATE: 25/10/27 13:36:52 GMT FROM: Alina Volnova at IKI RAS alinusss@gmail.com
A. Volnova (IKI), A.N. Tarasenkov (INASAN), A. Pozanenko (IKI), N. Pankov (HSE) report on behalf of IKI GRB-FuN:
We observed the field of the Swift GRB 251017A (Gupta et al., GCN 42322) with RC500 telescope of the INASAN-Kislovodsk observatory. We took several 120-seconds frames in the R-band starting Oct. 17, 2025, 15:09:15 (UT). In the stacked image the optical counterpart (Perez-Garcia et al., 42323; Antier et al., 42325; Sasada et al., 42329; Lipunov et al., 42330; Fu et al., 42331; Mo et al., 42336; Adami et al., 42339; Xin et al., 42341; Izzo et al., 42350; Shilling et al., 42355; Akl et al., 42368; Midavaine et al., 42370) is clearly detected. Preliminary photometry is the following:
Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-10-17 15:09:15 0.34348 100*120 R 21.45 0.16 22.0
The photometry is based on several nearby PS1 stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction.
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