GCN Circular 6338

M. Jel�nek (IAA-CSIC Granada), P. Tristram (MOA,
Univ. of Canterbury), A. de Ugarte Postigo, J.
Gorosabel, (IAA-CSIC), F. Hale (Earth & Sky,
Tekapo), A. Gilmore, P. Kilmartin (Univ.  of
Canterbury) and A. J. Castro-Tirado (IAA-CSIC), 
on behalf of a larger collaboration,

report:

"Following the detection by Swift of the GRB070420
(Stamatikos et al. GCNC 6330), we obtained V(26),
R (14) and I (1) -band images at the 0.6m B&C
telescope at the Mt. John Observatory on Lake
Tekapo. They were taken starting on Apr 20.33 UT
(i.e. 1.6 hr post-burst) and continued until Apr
20.51 UT (~6 hours after the burst).

Our preliminary V-band lightcurve shows a simple
powerlaw decay between 1.6 and 3.5 hours after the
burst with alpha~-1.2+-0.2 which is somewhat stee-
per than the value reported from UVOT (Immler et al.
GCNC 6336).

At 4 hours after the GRB we see a sudden rebrigh-
tening of the order of 1 magnitude in 40min above
the value extrapolated from the previous decay.

Further analysis is in progress."

This message can be quoted.

[GCN OPS NOTE(22apr07): Per author's request,
the "(Stamatikos et al. GCNC 6330)" was changed to
"(Immler et al GCNC 6336)".]