TITLE:   GCN CIRCULAR
NUMBER:  23362
SUBJECT: GRB 181020A: REM detection
DATE:    18/10/22 12:16:45 GMT
FROM:    Andrea Melandri at INAF-OAB  <andrea.melandri@brera.inaf.it>

A. Melandri, S.Covino, P. D'Avanzo, D. Fugazza (INAF-OAB), on behalf of the REM team, report:

We observed the optical counterpart of GRB 181020A (Moss et al. GCN 23349; Axelsson GCN 23350; Veres GCN 23352; Fynbo et al. GCN 23356; Cucchiara et al. GCN 23358; Gropp et al. GCN 23360) with the REM 60cm robotic telescope located at the ESO premise of La Silla (Chile). The observations were performed starting on 2018 October 20 at 23:51 UT (i.e. 4.86 hrs after the burst) and were carried in the g, r, i, z, J, H and K bands. 

The GRB afterglow is detected in the first set of optical and NIR images. From preliminary photometry we estimate the following magnitudes:

r = 17.3 +/- 0.2 
i = 16.8 +/- 0.1 

at a mean time of 294 min from the GRB time (AB magnitudes, calibrated against the USNO UCAC4 catalogue).