The auto and cross angular power spectrum of the Cas A supernova remnant
  in radio and X-ray
  The shell type supernova remnant (SNR) Cas A exhibits structures at nearly
all angular scales. Previous studies show the angular power spectrum
$(C_{\ell})$ of the radio emission to be a broken power law, consistent with
MHD turbulence. The break has been identified with the transition from 2D to 3D
turbulence at the angular scale corresponding to the shell thickness.
Alternatively, this can also be explained as 2D inverse cascade driven by
energy injection from knot-shock interactions. Here we present $C_{\ell}$
measured from archival VLA $5$GHz (C band) data, and Chandra X-ray data in the
energy ranges ${\rm A}=0.6-1.0 \, \, {\rm keV}$ and ${\rm B} =4.2-6.0 \, \,
{\rm keV}$, both of which are continuum dominated. The different emissions all
trace fluctuations in the underlying plasma and possibly also the magnetic
field, and we expect them to be correlated. We quantify this using the cross
$C_{\ell}$ between the different emissions. We find that X-ray B is strongly
correlated with both radio and X-ray A, however X-ray A is only very weakly
correlated with radio. This supports a picture where X-ray A is predominantly
thermal bremsstrahlung whereas X-ray B is a composite of thermal bremsstrahlung
and non-thermal synchrotron emission. The various $C_{\ell}$ measured here, all
show a broken power law behaviour. However, the slopes are typically shallower
than those in radio and the position of the break also corresponds to smaller
angular scales. These findings provide observational inputs regarding the
nature of turbulence and the emission mechanisms in Cas A.
