TITLE:   GCN CIRCULAR
NUMBER:  22803
SUBJECT: GRB 180620A: LCO McDonald observations
DATE:    18/06/20 12:01:56 GMT
FROM:    Cristiano Guidorzi at Ferrara U,Italy  <guidorzi@fe.infn.it>

C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), 
A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU), A. Cucchiara (U. of 
Virgin Islands) on behalf of a large collaboration report:

The LCO 1-m unit at McDonald Observatory began observing Swift GRB 
180620A (Evans et al. GCN 22798) on June 20, 08:55 UT (20 min since the 
GRB trigger time) with the SDSS griz filters. The optical counterpart 
(Evans et al.; Butler et al. GCN 22799; Elenin et al. GCN 22800; Tyurina 
et al. GCN 22801) is clearly detected in each individual frame with the 
following magnitudes:

Mid Time since GRB    Exposure         Filter        Magnitude
(hrs)                  (s)
------------------------------------------------------------------
0.349                 1x120            SDSS-R        18.63 +- 0.04
0.583                 1x120            SDSS-I        18.27 +- 0.04
------------------------------------------------------------------

as calibrated against nearby PanSTARRS objects.