[vsnet-grb-info 21476] GRB 181228A: REM NIR detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23575
SUBJECT: GRB 181228A: REM NIR detection
DATE:    18/12/28 09:35:37 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo at brera.inaf.it>

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

We observed the field of GRB 181228A (Moss et al. GCN 23570) with the REM 60cm robotic telescope located at the ESO premise of La Silla (Chile). 
The observations were performed starting on 2018 December 28 at 02:54:10 UT (i.e. 53 seconds after the burst) and were carried in the g, r, i, z, J, H 
and K bands. 

In the first set of NIR images (carried out in the H band) we detect an uncatalogued, fading source at the following position: 

RA (J2000): 03:19:15.05
Dec (J2000): +13:12:06.7

+/- 0.5". 

This position is consistent with the enhanced XRT position reported by Beardmore et al. (GCN 23574). The NIR source we detect is not present in the 
2MASS catalogue. We propose this source as the NIR afterglow of GRB 181228A.  

>From preliminary photometry we estimate the following magnitudes:

H = 14.3 +/- 0.1 at t-t0 = 122 s
H = 16.4 +/- 0.3 at t-t0 = 601 s

(Vega; calibrated against the 2MASS catalogue). At the same epochs, the source is not detected in the optical down to a 3sigma limiting magnitude of 
r ~ 18.0 (AB; calibrated against the pan-STARRS catalogue). This is consistent with the early optical non-detection reported by Zheng & Filippenko 
(GCN 23571).