TITLE:   GCN CIRCULAR
NUMBER:  40761
SUBJECT: GRB 250617B: SAO RAS optical observations
DATE:    25/06/17 22:54:57 GMT
FROM:    Alexander Moskvitin at SAO RAS <mosk@sao.ru>

A. Moskvitin, O. Spiridonova, Yu. Sotnikova (SAO RAS),
A. Ghosh, S. Razzaque (CAPP, University of Johannesburg)

We observed the field of the GRB 250617B (Page et al., GCN 40760) 
with SAO RAS 1-m telescope Zeiss-1000 equipped with CCD-photometer.
We obtained series of 60, 120 and 300 sec. exposures in Rc band 
and also one BVIc series. Observations started on 21:28:06 UT, 
since 26 minutes after the trigger.

The OT (Page et al., GCN 40760) is clearly visible in individual images 
with the brightness of R = 18.31 +/- 0.04 (t_mid - T0 = 0.5444 hours) 
and R = 18.66 +/- 0.04 (t_mid - T0 = 0.7635 hours).

This preliminary photometry is calibrated against R2 magnitudes 
of following nearby USNO-B1 stars and not corrected for the Galaxy 
extinction.

R.A.       Dec. (2000)   R2
22:11:38.4 +32:43:48.4   14.880 
22:11:19.9 +32:44:17.5   15.280 
22:11:41.0 +32:40:41.2   15.070 
22:11:45.2 +32:42:19.8   14.690

Observations are ongoing.