TITLE:   GCN CIRCULAR
NUMBER:  30027
SUBJECT: GRB 210504A: LCO Optical Afterglow Detection
DATE:    21/05/16 17:00:44 GMT
FROM:    Robert Strausbaugh at U. of the Virgin Islands  <robert.strausbaugh@uvi.edu>

R. Strausbaugh (U. of the Virgin Islands), A. Cucchiara (U. of the Virgin Islands/College of Marin) report on behalf of a larger collaboration:

We observed Swift GRB 210504A (Beardmore, et al., GCN 29929) with the LCO 1-m Sinistro instrument at the South African Astronomical Observatory site, on May 5, from 18:49 to 18:56 UT (corresponding to 4.92 to 5.03 hours from the GRB trigger time) with the Bessel R filter.

We performed a series of 3x180s exposures in R. We detect an uncatalogued optical source in the coadded images consistent with the UVOT position (Breeveld, et al., GCN 29933).  Using the USNO-B.1 catalog as reference, we calculate the following magnitude:

R=20.29+/-0.18

These magnitudes are not corrected for galactic extinction.

R.S. is funded by NSF AST grant #1831682