Light curve of the RXTE giant flare of SGR  1806−20 observed on 2004 Dec. 27. The general decay of the giant flare with a bumpy structure on top of it, namely a strongly periodic signal due to rotation (7.56 s). The inset panel shows the rotational modulated light curve (filled circles), together with fitted piecewise constant model (solid line, Hutter 2007), shown here only for 2.5 rotational cycles, with a very complex light curve structure (see text for details).