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GCN Circular 31229

GRB 211211A: Very fast decay observed from CAFOS/2.2mCAHA
2021-12-14T16:25:45Z (3 years ago)
Antonio de Ugarte Postigo at IAA-CSIC <>
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) 
( <>; 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.
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