TITLE:   GCN CIRCULAR
NUMBER:  41859
SUBJECT: GRB 250916A: SAO RAS optical observations
DATE:    25/09/17 23:24:23 GMT
FROM:    Alexander Moskvitin at SAO RAS <mosk@sao.ru>

A. Moskvitin, O. Spiridonova (SAO RAS), A. Pozanenko (IKI), 
A. Ghosh, S. Razzaque (CAPP, University of Johannesburg),
Tao An and Yuanqi Liu (Shanghai Astronomical Observatory) 
report on behalf of GRB follow-up collaboration and IKI-GRB-FuN.

We observed the field of the GRB 250916A (Fermi GBM team, GCN 41839; 
Arya et al., GCN 41843; Cheung et al., GCN 41855) with the 1-m SAO RAS 
telescope Zeiss-1000 equipped with CCD-photometer.
We obtained series of 300 sec. images in BVRcIc bands on September 17, 
20:21:44--21:42:59 UT.

The OT (Belkin et al., GCN 41847; Mohan et al., GCN 41858) is clearly 
detected in the individual and stacked frames with the brightness 
of R = 19.60 +/- 0.02 (t_mid - T0 = 1.3059 days = 31.3419 hours).

Preliminary photometry is based on the nearby objects from PanSTARRS 
(magnitudes converted with Lupton 2005 equations) 
and has not corrected for the Galactic extinction.