##
Axisymmetric Circumstellar Interaction in Supernovae

Blondin, John M.; Lundqvist, Peter; Chevalier, Roger A.
*Published in:*
ApJ, 472, 257

### Abstract

Multiwavelength observations of Type II supernovae have shown evidence of the
interaction between
supernovae and the dense slow winds from the red supergiant progenitor stars.
Observations of planetary
nebulae and the nebula around SN 1987A show that the slow winds from extended
stars frequently have an
axisymmetric structure with a high density in the equatorial plane. We have
carried out numerical
calculations of the interaction of a supernova with such an axisymmetric density
distribution. For small
values of the angular density gradient at the pole, the asymmetry in the
interaction shell is greater than, but
close to, that expected from purely radial motion. If the angular density
gradient is above a moderate value,
then the flow qualitatively changes and a protrusion emerges along the axis. For
a power-law supernova
density profile, the flow approaches a self-similar state in which the
protrusion length is 2-4 times the
radius of the main shell. The critical density gradient is larger for steeper
density profiles of the ejecta.
Most of our calculations are axisymmetric, but we have carried out a
three-dimensional calculation to
show that the protrusion is not a numerical artifact along the symmetry axis.
For typical supernova
parameters, the protrusions take ~> several years to develop. The appearance of
the shell with protrusions is
similar to that observed in VLBI radio images of the remnant 41.9 + 58 in M82
and possibly of SN 1986J.
We also considered the possibility of asymmetric ejecta and found that it had a
relatively small effect on
the asymmetry of the interaction region.