[AAVSO-HEN] GRB 080212: VLT optical rapid decay

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TITLE:   GCN CIRCULAR
NUMBER:  7311
SUBJECT: GRB 080212: VLT optical rapid decay
DATE:    08/02/14 19:37:21 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo at brera.inaf.it>

P. D'Avanzo, D. Fugazza (INAF-OAB), L.A. Antonelli (INAF-OAR), S. 
Covino, G. Chincarini, C. Guidorzi, G. Tagliaferri (INAF-OAB), V. 
D'Elia, F. Fiore, S. Piranomonte, L. Stella (INAF-OAR), M. Della Valle 
(INAF-OAA), S. D. Vergani (DIAS-DCU) report on behalf of the MISTICI 
collaboration:

We observed the optical afterglow of GRB 080212 (Ziaeepour et al., GCN 
7296) with the ESO-VLT equipped with the FORS2 camera in imaging mode at 
three different epochs. Observations have been carried out in R-band on 
Feb 13.3101 UT, Feb 13.3682 UT and Feb 14.2838 UT (0.58, 0.64 and 1.55 
days after the burst, respectively).

We found that between the first two epochs the afterglow faded very 
rapidly, with a decay index of alpha ~ 5.5. Very likely, the afterglow 
underwent a remarkable increase of its optical/NIR flux, probably 
related to the brightening observed in the X-rays about 4 hours before 
our VLT observations (see D'Avanzo et al., GCN 7310).

Assuming the above decay index, we estimate R ~ 20.8 at the epoch of the 
REM detection (D'Avanzo et al., GCN 7302) with an implied colour R-H~5

The decay of the afterglow then slowed down between the last two epochs 
and we measure R~25 in our last observation.