  Thin non-thermal X-ray filaments are often seen in young supernova remnants.
We used data from the 1 Ms Chandra observation of Cassiopeia A to study
spectral properties of some of the filaments in this remnant. For all the cases
that we examined, the X-ray spectrum across the filaments hardens, at about 10%
level, going outward, while observed filament widths depend only weakly on the
photon energy. Using a model that includes radiative cooling, advection and
diffusion of accelerated particles behind the shock, we estimated the magnetic
field, turbulence level and shock obliquity.
