  Many of the directly imaged self-luminous gas giant exoplanets have been
found to have cloudy atmospheres. Scattering of the emergent thermal radiation
from these planets by the dust grains in their atmospheres should locally give
rise to significant linear polarization of the emitted radiation. However, the
observable disk averaged polarization should be zero if the planet is
spherically symmetric. Rotation-induced oblateness may yield a net non-zero
disk averaged polarization if the planets have sufficiently high spin rotation
velocity. On the other hand, when a large natural satellite or exomoon transits
a planet with cloudy atmosphere along the line of sight, the asymmetry induced
during the transit should give rise to a net non-zero, time resolved linear
polarization signal. The peak amplitude of such time dependent polarization may
be detectable even for slowly rotating exoplanets. Therefore, we suggest that
large exomoons around directly imaged self-luminous exoplanets may be
detectable through time resolved imaging polarimetry. Adopting detailed
atmospheric models for several values of effective temperature and surface
gravity which are appropriate for self-luminous exoplanets, we present the
polarization profiles of these objects in the infrared during transit phase and
estimate the peak amplitude of polarization that occurs during the inner
contacts of the transit ingress/egress phase. The peak polarization is
predicted to range between 0.1 and 0.3 % in the infrared.
