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.