  (Abridged) We present an analysis of a 10-day continuous ASCA observation of
the narrow-line Seyfert 1 galaxy IRAS 13224-3809. The soft (0.7-1.3 keV) and
hard (1.3-10 keV) X-ray band light curves binned to 5000s reveal trough-to-peak
variations by a factor >25 and 20, respectively. The light curves in the soft
and hard bands are strongly correlated without any significant delay. However,
this correlation is not entirely due to changes in the power-law flux alone but
also due to changes in the soft X-ray hump emission above the power law. The
presence of a soft X-ray hump below 2 keV, previously detected in ROSAT and
ASCA data, is confirmed. Time resolved spectroscopy using daily sampling
reveals changes in the power-law slope, with Gamma in the range 1.74-2.47,
however, day-to-day variations in Gamma are not significant. The Soft hump
emission is found to dominate the observed variability on a timescale of a
week, but on shorter timescales (20000s) the power-law component appears to
dominate the observed variability. Flux resolved spectroscopy reveals that at
high flux levels the power law becomes steeper and the soft hump more
pronounced. The steepening of the photon index with the fluxes in the soft and
hard bands can be understood in the framework of disk/corona models in which
accretion disk is heated by viscous dissipation as well as by reprocessing of
hard X-rays following an X-ray flare resulting from coronal dissipation through
magnetic reconnection events.
