TITLE:   GCN CIRCULAR
NUMBER:  29802
SUBJECT: GRB 210411C: LCO Optical Afterglow Candidate
DATE:    21/04/11 22:59:47 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 210411C (Sbarrato, GCN 29794) with the LCO 1-m Sinistro instrument at the Siding Spring Observatory, Australia site, on April 11, from 16:18 to 16:42 UT (corresponding to 1.22 to 1.62 hours from the GRB trigger time) with the Bessel R and I filters.

We performed a series of 4x180s exposures in R and I. We detect an optical source in R and I band images at a location consistent the initial UVOT detection (Sbarrato, GCN 29794) and enhanced XRT position (Goad, GCN 29800), that is not present in either USNO or 2MASS catalogs.  Using the USNO-B.1 catalog as reference, we calculate the following magnitudes:

R = 18.51 +/- 0.03

I = 18.01 +/- 0.03

These magnitudes are not corrected for galactic extinction.  These magnitudes may also be contaminated by a bright foreground star.

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