TITLE: GCN CIRCULAR NUMBER: 42043 SUBJECT: GRB 251001B: LCOGT Optical Observations DATE: 25/10/01 15:44:16 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 251001B field (Beardmore et al., GCN 42039) with the LCOGT 1-meter Sinistro instrument at the Siding Spring Observatory, Australia site, on October 1, from 14:51 to 15:23 UT (corresponding to 0.57 to 1.10 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 consistent with other optical counterpart observations (Gompertz et al., GCN 42040; An et al., GCN 42041) in both bands. We note that our r-band measurement implies a rapidly fading source.

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

r = 20.26 +/- 0.04 i = 19.81 +/- 0.03

These magnitudes are not corrected for galactic extinction.

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