TITLE:   GCN CIRCULAR
NUMBER:  31229
SUBJECT: GRB 211211A: Very fast decay observed from CAFOS/2.2mCAHA
DATE:    21/12/14 16:25:45 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte@iaa.es>

A. de Ugarte Postigo (Obs. Cote d’Azur), D.A. Kann, C. Thoene, 
J.F. Agui Fernandez, M. Blazek (HETH/IAA-CSIC), I. Vico and 
A. Guijarro (CAHA) report: 

We obtained further i-band imaging of the afterglow of GRB 211211A 
(Fermi team GCN31201; D’Ai et al. GCN31202; Zheng and Filipenko 
GCN 31203) from CAFOS/2.2m CAHA 2.66 days after the burst onset.

The observation consisted of 20x120s exposures under good seeing 
and yielded a faint detection. The light curve decay, compared to our 
previous observation from Calar Alto (de Ugarte Postigo et al., GCN 
31228) indicates an extreme decay index of alpha = 3.25+/-0.40. 
This is similar to what is observed from the XRT light curve, which 
currently decays with an index of 3.2 (-0.7,+0.8) 
(https://www.swift.ac.uk/xrt_live_cat/01088940/ <https://www.swift.ac.uk/xrt_live_cat/01088940/>; Evans et al. 2007; 
Evans et al. 2009). We note that this is amongst the fastest post-break
decays that are normally observed for GRB afterglows.

Further observations with larger telescopes are encouraged.