TITLE:   GCN CIRCULAR
NUMBER:  25971
SUBJECT: GRB 191004A: Optical Detection with LCO
DATE:    19/10/07 16:14:13 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 191004A (Barthelmy et al., GCN 25945) with
the LCO 1-m Sinistro instrument on September 4, from 20:12 to 20:47 UT
(corresponding to 1.70 to 2.28 hours from the GRB trigger time)
with the Bessel R and I filters.

We performed a series of 10x180s exposures in each band.  We do not detect a significant source in individual frames, but we do  detect a source in co-added frames that is not present in either USNO-B1.0 or 2MASS surveys and is consistent with the optical afterglow location (Evans et al., GCN 25950) with the following magnitudes:

R = 22.89 +/- 0.10
I = 21.00 +/- 0.09


This flux is calibrated against several USNO-B1.0 objects near the GRB location but is not corrected for Galactic Extinction.

These observations were possible thanks to the USVI NASA-EPSCoR
Research Infrastructure Development (RID) grant NNX16AL44A.