TITLE:   GCN CIRCULAR
NUMBER:  30770
SUBJECT: GRB 210905A: Continued LCO Optical Observations
DATE:    21/09/05 04:33:24 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 02:32 to 02:53 UT (corresponding to 2.37 to 2.72 hours from the GRB trigger time) with the Bessel I filter.

We performed a series of 5x300s exposures in I band. We detect the same uncataloged source (Strausbaugh, et al., GCN 30769) at the following coordinates (309.0481637, -44.4402618).  Using the USNO-B.1 catalog as reference, we calculate the following magnitude:

I=20.4+/-0.1

These magnitudes are not corrected for galactic extinction.  There is clear evidence of fading from the first epoch (I=19.52+/-0.09) providing strong evidence that this is the afterglow of this burst.

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