A High-Resolution X-Ray and Optical Study of SN 1006: Asymmetric
  Expansion and Small-Scale Structure in a Type Ia Supernova Remnant
  We introduce a deep (670 ks) X-ray survey of the SN1006 remnant from Chandra,
plus a deep H-alpha image from the 4m telescope at CTIO. Comparison with
Chandra images from 2003 gives the first measurement of X-ray proper motions
around the entire rim. We find that the expansion velocity varies significantly
with azimuth: the highest velocity of ~7400 km/s (almost 2.5 times that in the
NW) is found along the SE rim, where both kinematics and spectra indicate that
most of the X-rays stem from undecelerated ejecta. Asymmetries in the
distribution of ejecta are seen on a variety of spatial scales. Si-rich ejecta
are especially prominent in the SE quadrant, while O and Mg are more uniformly
distributed, indicating large-scale asymmetries arising from the explosion
itself. Ne emission is strongest in a sharp filament just behind the primary
shock along the NW rim, where the preshock density is highest. Here the Ne is
likely interstellar, while Ne within the shell may include a contribution from
ejecta. Within the interior of the projected shell we find a few isolated
"bullets" of what appear to be supernova ejecta that are immediately preceded
by bowshocks seen in H-alpha--features we interpret as ejecta knots that have
reached relatively dense regions of the surrounding ISM. Recent 3-dimensional
hydrodynamic models for SN Ia display small-scale features that resemble the
ones seen in X-rays in SN1006; an origin in the explosion itself or from
subsequent instabilities both remain viable options. We have expanded the
search for precursor X-ray emission ahead of a synchrotron-dominated shock
front. Profiles along both NE and SW rims require that a precursor be thinner
than about 3 arcsec and fainter than about 5% of the post-shock peak. These
limits suggest that the magnetic field is amplified by a factor of 7 or more in
a narrow precursor region, promoting diffusive particle acceleration.
