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.

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