TITLE:   GCN CIRCULAR
NUMBER:  29613
SUBJECT: GRB 210307A: LCO Optical Upper Limits
DATE:    21/03/07 13:44:16 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 210307A (Ambrosi et al., GCN 29610) with the LCO 1-m Sinistro instrument at the Sutherland Observatory, South Africa site, on March 7, from 09:28 to 09:59 UT (corresponding to 0.60 to 1.18 hours from the GRB trigger time) with the Bessel R and I filters.

We performed a series of 4x240s exposures in R and I. We do not detect an uncatalogued optical source in either band in single frames, or in stacked images at a location consistent the initial XRT detection (Ambrosi et al., GCN 29610).  Using the USNO-B.1 catalog as reference, we calculate the following upper limits:

R > 20.72

I > 20.66

These magnitudes are not corrected for galactic extinction.

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