The interaction of the expanding shock from a supernova explosion with the
surrounding environment is a powerful source of radiation in various
spectral bands at different stages in the development of the supernova
remnant. Studying the X-rays generated by such objects is therefore likely
to reveal details of these on going interactions. For example, the X-ray
emission from the relatively old supernova remnant PKS1209-52 is highly
asymmetric – 75% of the total emission arises from the eastern side of the
shock. We describe a possible model that can explain this extra emission
from the eastern lobe of the remnant as resulting from a recent encounter
between the shock front and a small, dense, interstellar cloud. The
particular mechanism is a plasma streaming instability known as the
modified two-stream instability. The presence of the cloud makes it
possible to extract some of the kinetic energy of the shock wave and
convert this into X-ray emission via high-energy electrons generated from
lower hybrid waves in the plasma interaction region. We have carried out
2-D fluid simulation of the interaction which agrees very well with the
observed geometry of the source. Finally, the neutron star remnant of the
original supernova explosion is seen to generate cyclotron absorption
features in its X-ray emission spectrum that reveal the detailed dynamics
of the magnetic field of the neutron star itself. Planned laboratory
experiments to study the results will be outlined.