[vsnet-grb-info 21259] GRB 181020A: LCO Cerro Tololo observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23358
SUBJECT: GRB 181020A: LCO Cerro Tololo observations
DATE:    18/10/21 15:54:44 GMT
FROM:    Cristiano Guidorzi at Ferrara U,Italy  <guidorzi at fe.infn.it>

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

We observed Swift GRB 181020A (Moss et al. GCN 23349) with one of the 
LCO 1-m unit at Cerro Tololo Observatory on October 20, from 23:55 to 
Oct 21, 00:49 UT (corresponding to 4.9 to 5.8 hours from the GRB trigger 
time) with the SDSS r' and i' filters. We clearly detect the optical 
afterglow (Moss et al. GCN 23349) in both filters with the following 
magnitudes for the first half of the observation run:

Mid time from GRB      Exposure         Filter          Magnitude
trigger time (hrs)     (s)
---------------------------------------------------------------------
5.0                   5x120             SDSS r'         17.55 +- 0.03
5.2                   5x120             SDSS i'         17.2  +- 0.1
---------------------------------------------------------------------

as calibrated against nearby USNO UCAC4 objects.