TITLE:   GCN CIRCULAR
NUMBER:  30849
SUBJECT: GRB 210919A: LCO Optical Upper Limit
DATE:    21/09/19 04:55:40 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 210919A (Tohuvavohu, et al., GCN 30846) with the LCO 1-m Sinistro instrument at the South African Astronomical Observatory site, on September 19, from 01:41 to 02:08 UT (corresponding to 1.22 to 1.67 hours from the GRB trigger time) with the Bessel R and I filters.

We performed a series of 4x200s exposures in R and 3x200s in I. In the large XRT detection region (Tohuvavohu, et al., GCN 30846) we find no obvious optical counterpart could be detected down to the following upper limits (consistent with previous reports (Tohuvavohu et al., GCNC 30846; Lipunov et al., GCNC 30847; Hu et al., GCN 30848)), calculated using the USNO-B.1 catalog as reference:

R>20.5
I>18.7

These magnitudes are not corrected for galactic extinction.

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