[vsnet-grb-info 15912] GRB 141220A: Photometry from OSIRIS/GTC

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17200
SUBJECT: GRB 141220A: Photometry from OSIRIS/GTC
DATE:    14/12/20 11:08:46 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte at iaa.es>

A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), C.C. Thoene (IAA-CSIC),
J. Gorosabel (IAA-CSIC, UPV-EHU), N.R. Tanvir (U. Leicester), 
J.P.U. Fynbo (DARK/NBI), P. Pesev (GRANTECAN), G. Gomez Velarde 
(GRANTECAN), and D. Perez Valladares (GRANTECAN) report on behalf 
of a larger collaboration:

Photometric observations of the afterglow of GRB 141220A (Cummings et al. 
GCN 17196, Gorosabel et al. GCN 17197, de Ugarte Postigo et al. GCN 17198) 
were obtained by OSIRIS/GTC starting 20.6 min after the GRB onset. The 
afterglow was detected at r' = 18.11+/-0.05 mag in the first image and had 
decayed by 0.6+/-0.1 mag 38.7 min after the burst. Using our photometric data 
we derive a decay slope of alpha=0.96+/-0.11 (where F_nu ~ t^-alpha). These 
results are consistent with the observations reported by Guidorzi et al. (GCN 
17199). Our photometry was performed using SDSS stars as reference.

We encourage further observations and in particular spectroscopy of the 
afterglow, in particular to check for possible variability of the FeII* features 
between 5400 and 6100 A.