A Galactic Dust Devil: far-infrared observations of the Tornado
  Supernova Remnant candidate
  We present complicated dust structures within multiple regions of the
candidate supernova remnant (SNR) the `Tornado' (G357.7-0.1) using observations
with Spitzer and Herschel. We use Point Process Mapping, PPMAP, to investigate
the distribution of dust in the Tornado at a resolution of 8", compared to the
native telescope beams of 5-36". We find complex dust structures at multiple
temperatures within both the head and the tail of the Tornado, ranging from 15
to 60K. Cool dust in the head forms a shell, with some overlap with the radio
emission, which envelopes warm dust at the X-ray peak. Akin to the terrestrial
sandy whirlwinds known as `Dust Devils', we find a large mass of dust contained
within the Tornado. We derive a total dust mass for the Tornado head of 16.7
solar masses, assuming a dust absorption coefficient of kappa_300 =0.56m^2
kg^1, which can be explained by interstellar material swept up by a SNR
expanding in a dense region. The X-ray, infra-red, and radio emission from the
Tornado head indicate that this is a SNR. The origin of the tail is more
unclear, although we propose that there is an X-ray binary embedded in the SNR,
the outflow from which drives into the SNR shell. This interaction forms the
helical tail structure in a similar manner to that of the SNR W50 and
microquasar SS433.
