TITLE: GCN CIRCULAR NUMBER: 38805 SUBJECT: GRB 250103B: LCOGT Optical Upper Limit DATE: 25/01/03 19:44:52 GMT FROM: Robert Strausbaugh at Eastern Illinois University rstrausbaugh@eiu.edu

R. Strausbaugh (Eastern Illinois University), A. Cucchiara (NASA) report on behalf of a larger collaboration:

We observed the Swift GRB 250103B field (Eyles-Ferris et al., GCN 38796) with the LCOGT 1-meter Sinistro instrument at the South African Astronomical Observatory site, on January 3, from 18:51 to 19:23 UT (corresponding to 4.12 to 4.65 hours after the GRB trigger time) with the Bessel I and R filters.

We performed a series of 3x300s exposures in I-band and R-band. We do not detect a source within the XRT error region in either band.

The following 5-sigma upper limits are calculated using the USNO-B1.0 catalog as reference:

R > 23.0 I > 22.1

These magnitudes are not corrected for galactic extinction.

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