TITLE:   GCN CIRCULAR
NUMBER:  31228
SUBJECT: GRB 211211A: Further observations from CAFOS/2.2m CAHA 
DATE:    21/12/13 17:22:44 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 a second imaging observation of the optical afterglow 
of GRB 211211A (Fermi team GCN31201; D’Ai et al. GCN31202; 
Zheng and Filipenko GCN 31203) with CAFOS, mounted on the 
2.2m telescope, at the Calar Alto Observatory (Almería, Spain). 

The observation started at 04:47 UT (39.6 hr after the GRB) and 
consisted of 30x90s in i-band. The optical afterglow is still detected, 
at a magnitude (AB) of i = 22.45+/-0.09, as compared to field stars 
from the SDSS catalogue. With respect to our earlier CAFOS 
photometry (de Ugarte Postigo et al. GCN 31218) this implies a 
rapid decay rate of alpha = 1.65, where F_nu ~ t^-alpha, which 
would indicate a post-jet break evolution.