GCN Circular 29474

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

We observed the field of GRB 210211A (Troja et al., GCN Circ. 29472
Not found
 
 
) with the REM 60cm robotic 
telescope located at the ESO premise of La Silla (Chile). The observations were performed starting 
on 2021 February 11 at 08:44:54 UT (i.e. 96 seconds after the burst) and were carried in the g, r, i, z, H 
bands simultaneously. 

From a preliminary analysis of the first set of images, obtained at a mid time of t-t0 = 101 s we detect in 
all filters an uncatalogued object at the following position: 

RA (J2000), Dec (J2000) = 17:57:45.67, -46:16:01.8 (+/- 0.5")

with a magnitude r = 16.9 +/- 0.1 (AB; calibrated against the APASS catalogue). This source is found about 
1.5 magnitudes fainter in a subsequent set of images obtained at t-t0 = 204 s. 

The source position lies about 8" outside the current available XRT error circle (https://www.swift.ac.uk/xrt_positions/). 
However, the observed brightness and rapid fading suggests that it is the optical/NIR afterglow of GRB 210211A. 
We also note the presence of an optical/NIR source inside the XRT error circle whose magnitude does not show significant 
variation in our dataset. 
 
Further analysis is in progress.