Angular power spectrum of supernova remnants: effects of structure,
  geometry and diffuse foreground
  The study of the intensity fluctuation power spectrum of individual supernova
remnants (SNRs) can reveal the structures present at sub-pc scales, and also
constrain the physical process that generates those structures. There are
various effects, such as the remnant shell thickness, projection of a
three-dimensional structure onto a two-dimensional observational plane, and the
presence of diffuse "foreground" emission, which causes the observed power
spectrum to deviate from the intrinsic power spectrum of the fluctuations.
Here, we report results from a systematic study of these effects, using direct
numerical simulations, in the measured power spectrum. For an input power-law
power spectrum, independent of the power-law index, we see a break in the
observed power law at a scale which depends on the shell thickness of a
shell-type SNR, and the three-dimensional turbulence changes to two-dimensional
turbulence beyond that scale. We also report how the estimated power spectrum
is expected to deviate from the intrinsic SNR power spectrum in the presence of
additional diffuse Galactic synchrotron emission (DGSE) around the remnant
shell. For a reasonable choice of the parameters, if the intrinsic SNR power
spectrum is shallower than the DGSE power spectrum, the SNR contribution
dominates at small angular scales of the estimated power spectra. On the other
hand, if the SNR power spectrum is relatively steeper, the original power
spectra is recovered only over a small window of angular scales. This study
shows how detailed modeling may be used to infer the true power spectrum from
the observed SNR intensity fluctuations power spectrum, which in turn can be
used to constrain the nature of the turbulence that gives rise to these small
scale structures.
