  The 2011 outburst of Swift J1822.3--1606 was extraordinary; periodic
modulations at the spin period of the underlying neutron star were clearly
visible, remarkably similar to what is observed during the decaying tail of
magnetar giant flares. We investigated the temporal characteristics of X-ray
emission during the early phases of the outburst. We performed a periodicity
search with the spectral hardness ratio (HR), and found a coherent signal near
the spin period of the neutron star, but with a lag of about 3 radians.
Therefore, the HR is strongly anti-correlated with the X-ray intensity, which
is also seen in the giant flares. We studied time evolution of the pulse
profile and found that it evolves from a complex morphology to a much simpler
shape within about a month. Pulse profile simplification also takes place
during the giant flares, but on a much shorter timescale of about few minutes.
We found that the amount of energy emitted during the first 25 days of the
outburst is comparable to what was detected in minutes during the decaying tail
of giant flares. Based on these similarities, we suggest that the triggering
mechanisms of the giant flares and the magnetar outbursts are likely the same.
We propose that the trapped fireball that develops in the magnetosphere at the
onset of the outburst radiates away efficiently in minutes in magnetars
exhibiting giant flares, while in other magnetars, such as Swift J1822.3--1606,
the efficiency of radiation of the fireball is not as high and, therefore,
lasts much longer.
