TITLE: GCN CIRCULAR NUMBER: 42074 SUBJECT: GRB 251003A: LCOGT Optical Detection DATE: 25/10/03 04:04:06 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 251003A field (Beardmore et al., GCN 42070) with the LCOGT 1-meter Sinistro instrument at the McDonald Observatory, USA site, on October 3, from 03:07 to 03:39 UT (corresponding to 1.15 to 1.68 hours after the GRB trigger time) with the SDSS i and r filters.

We performed a series of 3x300s exposures in i-band and r-band. We detect an uncatalogued source in the XRT enhanced error region (Evans et al. GCNC 42071) consistent with other optical counterpart observations (Aceituno et al., GCN 42072; Méndez et al., GCN 42073) in both bands. We note that the r-i color of this event may indicate a moderate redshift source (z>4).

The following magnitudes are calculated using the PanSTARRS catalog as reference:

r = 20.97 +/- 0.12 i = 19.25 +/- 0.04

These magnitudes are not corrected for galactic extinction.

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