[vsnet-grb-info 27371] GRB 210211A: REM optical/NIR afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29474
SUBJECT: GRB 210211A: REM optical/NIR afterglow detection
DATE:    21/02/11 11:19:34 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <pda.davanzo at gmail.com>

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) 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.