A High-Resolution X-Ray and Optical Study of SN 1006: Asymmetric Expansion and Small-Scale Structure in a Type Ia Supernova Remnant

摘要

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 withChandra images from 2003 gives the first measurement of X-ray proper motionsaround the entire rim. We find that the expansion velocity varies significantlywith azimuth: the highest velocity of ~7400 km/s (almost 2.5 times that in theNW) is found along the SE rim, where both kinematics and spectra indicate thatmost of the X-rays stem from undecelerated ejecta. Asymmetries in thedistribution of ejecta are seen on a variety of spatial scales. Si-rich ejectaare especially prominent in the SE quadrant, while O and Mg are more uniformlydistributed, indicating large-scale asymmetries arising from the explosionitself. Ne emission is strongest in a sharp filament just behind the primaryshock along the NW rim, where the preshock density is highest. Here the Ne islikely interstellar, while Ne within the shell may include a contribution fromejecta. Within the interior of the projected shell we find a few isolated"bullets" of what appear to be supernova ejecta that are immediately precededby bowshocks seen in H-alpha--features we interpret as ejecta knots that havereached relatively dense regions of the surrounding ISM. Recent 3-dimensionalhydrodynamic models for SN Ia display small-scale features that resemble theones seen in X-rays in SN1006; an origin in the explosion itself or fromsubsequent instabilities both remain viable options. We have expanded thesearch for precursor X-ray emission ahead of a synchrotron-dominated shockfront. Profiles along both NE and SW rims require that a precursor be thinnerthan about 3 arcsec and fainter than about 5% of the post-shock peak. Theselimits suggest that the magnetic field is amplified by a factor of 7 or more ina narrow precursor region, promoting diffusive particle acceleration.