TITLE: GCN CIRCULAR NUMBER: 30769 SUBJECT: GRB 210905A: LCO Optical Detection DATE: 21/09/05 03:00:50 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 210905A (Sonbas, et al., GCN 30765) with the LCO 1-m Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on September 5, from 01:09 to 01:36 UT (corresponding to 0.95 to 1.40 hours from the GRB trigger time) with the Bessel R and I filters. We performed a series of 3x300s exposures in R and I. In the XRT detection region (Sonbas, et al., GCN 30765) we detect an uncatalogued source in I band at the following coordinates (309.0481637, -44.4402618). Using the USNO-B.1 catalog as reference, we calculate the following magnitudes and upper limits: R>22.44 I=19.52+/-0.09 These magnitudes are not corrected for galactic extinction. The detection in I and the lack of detection in R is suggestive of a high-z source. As such additional follow-up is encouraged. Additional LCO measurements are underway. R.S. is funded by NSF AST grant #1831682