TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4412
SUBJECT: GRB 051227: optical afterglow
DATE:    05/12/29 05:45:00 GMT
FROM:    Daniele Malesani at SISSA-ISAS,Trieste,Italy  <malesani@sissa.it>

D. Malesani (SISSA), S. Covino (INAF/OABr), E. Depagne, C. Lidman, C. 
Melo (ESO), S. Piranomonte, L.A. Antonelli (INAF/OARm), S. Campana, G. 
Tagliaferri (INAF/OABr), G. Chincarini (Univ. Milano-Bicocca), M. Della 
Valle (INAF/OAA), F. Fiore and L. Stella (INAF/OAR), report on behalf of 
the MISTICI collaboration:

We observed again the field of GRB 051227 (Barbier et al., GCN 4397; 
Hullinger et al., GCN 4400; Barthelmy et al., GCN 4401) with the ESO 
VLT-UT2 equipped with FORS1. Observations started on 2005 Dec 29.1899 
(1.4 d after the GRB), and secured 1 hour of net exposure in the R band.

Analysis of the first 6 frames (30 min exposure) reveals that the source 
S1 individuated in the previous VLT images (Malesani et al., GCN 4404, 
4407; see also Bloom et al., GCN 4408; Berger et al., GCN 4410; Roming 
et al., GCN 4411) has dimmed by 1.1 +- 0.3 mag in the R band. Assuming a 
power law decay, the decay slope is alpha = 0.9 +- 0.3.

This suggests that very likely S1 is the optical afterglow of GRB 051227.

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