[vsnet-grb-info 24531] GRB 191228A: Early Optical Upper Limits from LCO

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26630
SUBJECT: GRB 191228A: Early Optical Upper Limits from LCO
DATE:    20/01/02 12:22:34 GMT
FROM:    Robert Strausbaugh at U. of the Virgin Islands  <robert.strausbaugh at 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 191228A (Barthelmy et al., GCN 26601) with the LCO 1-m Sinistro instrument at the McDonald Observatory, Texas, USA site, on December 28, from 00:59 to 01:31 UT (corresponding to 0.66 to 1.22 hours from the GRB trigger time) with Bessel R and I filters.

We performed a series of 5x180s exposures in both bands. We do not detect any sources in the individual frames (nor in 5 stacked images in each band) in the enhanced Swift error region (Barthelmy et al., GCN 26607).  Using the USNO-B.1 catalog as reference, we obtain the following 3-sigma upper limits:

R > 14.69
I > 14.79

The low limiting magnitudes are most likely due to high sky background in the images in both bands.