Some low-mass X-ray transients show a secondary maximum in their
light curve during the outburst decay which occur after the transition to
the hard state. While some of these secondary outbursts could be jet
related, historically, they are attributed to the response of the outer disk
to the increased X-ray emission from the inner disk.

We hypothesize that as the corona grows during the transition to the
hard state, previously shadowed parts of the outer disk get irradiated,
hence leading to an increase in the mass ow towards the black hole,
leading to a secondary outburst.

To test this hypothesis, we solve the diffusion equation governing the
evolution of the geometrically thin accretion disks around black holes.
The disk instability model, irradiation of the disk by a lamppost-like
source (representing the corona), self-shadowing of the disk, and realistic
opacities have been included in the model for self-consistent calculations.

Using realistic corona formation timescales we simulated light curves
with different corona sizes and corona luminosities and characterized the
properties of the resulting secondary outbursts. We determine parameters
that provide observed formation timescale of the secondary outbursts.
Most importantly, we observe that secondary outbursts can only occur if
the size of the corona is greater than 200 gravitational radii. This may
explain why these secondary outbursts are only observed in some cases
and can provide a constraint on the corona geometry.