New perspectives on the supernova remnant Puppis A based on a radio
  polarization study
  We present a polarization study towards the supernova remnant (SNR) Puppis A
based on original observations performed with the Australia Telescope Compact
Array (ATCA). Based on the analysis of a feature detected outside the SNR shell
(called `the tail' throughout the paper), it was possible to disentangle the
emission with origin in Puppis A itself from that coming from the foreground
Vela SNR. We found a very low polarization fraction, of about 3 percent on
average. The upper limit of the magnetic field component parallel to the line
of sight is estimated to be B$_\parallel \sim$ 20 $\mu$G. The statistical
behavior of the magnetic vectors shows two preferential directions, almost
perpendicular to each other, which are approximately aligned with the flat
edges of Puppis A. A third, narrow peak oriented perpendicular to the Galactic
plane suggests the existence of an interstellar magnetic field locally aligned
in this direction. There is evidence that the magnetic vectors along the shell
are aligned with the shock front direction. The low polarization fraction and
the statistical behavior of the magnetic vectors are compatible with a scenario
where the SNR evolves inside a stellar wind bubble with a box-like morphology,
produced by the interaction of the different stellar winds, one of them
magnetized, launched by the SN progenitor. This scenario can furthermore
explain the morphology of Puppis A, rendering little support to the previously
accepted picture which involved strong density gradients to explain the flat,
eastern edge of the shell.
