TITLE:   GCN CIRCULAR
NUMBER:  41934
SUBJECT: GRB 250916A: SAO RAS Zeiss-1000 optical observations
DATE:    25/09/22 09:39:39 GMT
FROM:    Alexander Moskvitin at SAO RAS <mosk@sao.ru>

A. Moskvitin, O. Spiridonova (SAO), N. Pankov (HSE), 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; Osborne et al., 
GCN 41862; Waratkar and Grefenstette, GCN 41871; Godwin and Meegan, 
GCN 41876) with the 1-m SAO RAS telescope Zeiss-1000 equipped 
with the CCD-photometer. We obtained 9 x 300 sec. images Rc band 
on September 21, 23:36:57 -- September 22, 00:47:22 UT 
(t_mid - T0 = 5.44639 days).

The optical transient (Belkin et al., GCN 41847; Mohan et al., 
GCN 41858; Moskvitin et al., GCN 41859; Burkhonov et al., GCN 41860;
de Ugarte Postigo et al., GCN 41863; Moskvitin et al., GCN 41870;
Zheng and Filippenko, GCN 41873; Pankov et al., GCN 41892; 
Hall et al., GCN 41921) is clearly detected in the stacked frame 
with the brightness of R = 22.6 +/- 0.1.

Date        UT start  t-T0     Exp.  Filter  OT     Err. UL (3sigma)
                      (mid, d) (s)       
2025.09.21  23:36:57  5.44639  9 x 300 Rc  22.6 +/- 0.1 23.3
                      
Preliminary photometry is based on the nearby objects from PanSTARRS 
(magnitudes converted with Lupton 2005 equations) 
and has not corrected for the Galactic extinction.