TITLE: GCN CIRCULAR NUMBER: 42711 SUBJECT: GRB 251025B: further Mondy optical observations DATE: 25/11/17 08:08:51 GMT FROM: Alina Volnova at IKI RAS <alinusss@gmail.com> A. Volnova (IKI), E. Klunko (ISTP), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN: We continued observations of the field of the GRB 251025B (Hussein et al., GCN 42437) in the R-filter with the AZT-33IK 1.5m telescope of the Sayan Solar Observatory (Mondy) taking several frames with 120 s exposures on Oct. 27-29 and Nov. 1, 2025. The optical counterpart (Wu et al., GCN 42438; Gress et al., GCN 42439; Wu et al., GCN 42440; Beardmore et al., GCN 42445; Mohan et al., GCN 42447; Hernández Funget al., GCN 42450; Pereyra et al., GCN 42452; Li et al., GCN 42453; Mo et al., GCN 42459; Rakotondrainibe et al., GCN 42460; Rajabov et al., GCN 42466; Saccardi et al., GCN 42472; Freeberg et al., GCN 42474; Volnova et al., GCN 42475; Gupta et al., GCN 42500; Mohan et al., GCN 42503; Adami et al., GCN 42547) is clearly detected in the stacked frame of every epoch. Preliminary photometry is the following: Date UT start t-T0 Exp. Filter OT Err. UL (mid,days) (n*s) (3sigma) 2025-20-27 15:53:18 2.08280 30*120 R 21.22 0.07 22.8 2025-10-28 16:11:51 3.11396 29*120 R 21.82 0.17 22.3 2025-10-29 15:14:24 4.03841 5*120 R 21.95 0.25 22.2 2025-11-01 15:12:37 7.07680 60*120 R 22.94 0.26 23.2 The photometry is based on several nearby SDSS stars (R-magnitudes Lupton's transformation) and is not corrected for the Galactic extinction, all magnitudes are in Vega system. View this GCN Circular online at https://gcn.nasa.gov/circulars/42711. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...