  It is an open issue how the surrounding environment of supernova remnant
shocks affect nonthermal X-rays from accelerated electrons, with or without
interacting dense material. We have conducted spatially resolved X-ray
spectroscopy of the shock-cloud interacting region of RCW 86 with XMM-Newton.
It is found that bright soft X-ray filaments surround the dense cloud observed
with 12CO and HI emission lines. These filaments are brighter in thermal X-ray
emission, and fainter and possibly softer in synchrotron X-rays, compared to
those without interaction. Our results show that the shock decelerates due to
the interaction with clouds, which results in an enhancements of thermal X-ray
emission. This could possibly also explain the softer X-ray synchrotron
component, because it implies that those shocks that move through a low density
environment, and therefore decelerate much less, can be more efficient
accelerators. This is similar to SN 1006 and Tycho, and is in contrast to RX
J1713.7-3946. This difference among remnants may be due to the clumpiness of
dense material interacting with the shock, which should be examined with future
observations.
