TITLE: GCN CIRCULAR NUMBER: 38762 SUBJECT: GRB 250101A: SAO RAS optical observations DATE: 25/01/01 19:20:35 GMT FROM: Moskvitin Alexander at SAO RAS mosk@sao.ru

A. S. Moskvitin and O. I. Spiridonova (SAO RAS), report on behalf of the GRB follow-up team.

We observed the field of Swift GRB 250101A (Page et al., GCN 38752) with the 1-m telescope of SAO RAS, Zeiss-1000 + CCD-photometer. On January 1, 16:18:20--16:51:10 UT (t_mid - T0 = 3.1986 hours) we obtained first set of 6 x 300 sec. images in Rc band. At 18:43:29--18:59:33 UT (t_mid - T0 = 5.4781 hours) we obtained second set of data, 3 x 300 sec. images in Rc band.

The OT (Page et. al., GCN 38752; Li et al., GCN 38753; Mohan et al., GCN 38754; Zhu et al., GCN 38755, GCN 38759; Budnev et al., GCN 38756; WU et al., GCN 38758) is clearly detected in our stacked frames with the brightness of R = 19.76 +/- 0.01 (t_mid - T0 = 3.1986 hours) and R = 19.84 +/- 0.02 (5.4781 hours), calibrated against nearby PS1 stars (magnitudes were converted with the Lupton 2005 equations and not corrected for the MW extinction).

Observations are ongoing.

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