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We report the results of an X-ray proper motion measurement for the NW rim ofSN1006, carried out by comparing Chandra observations from 2001 and 2012. TheNW limb has predominantly thermal X-ray emission, and it is the only locationin SN1006 with significant optical emission: a thin, Balmer-dominated filament.For most of the NW rim, the proper motion is about 0.30 arcsec/yr, essentiallythe same as has been measured from the H-alpha filament. Isolated regions ofthe NW limb are dominated by nonthermal emission, and here the proper motion ismuch higher, 0.49 arcsec/yr, close to the value measured in X-rays along themuch brighter NE limb, where the X-rays are overwhelmingly nonthermal. At the2.2 kpc distance to SN1006, the proper motions imply shock velocities of about3000 km/s and 5000 km/s in the thermal and nonthermal regions, respectively. Alower velocity behind the H-alpha filament is consistent with the picture thatSN1006 is encountering denser gas in the NW, as is also suggested by itsoverall morphology. In the thermally-dominated portion of the X-ray shell, wealso see an offset in the radial profiles at different energies; the 0.5-0.6keV peak dominated by O VII is closer to the shock front than that of the 0.8-3keV emission--due to the longer times for heavier elements to reach ionizationstates where they produce strong X-ray emission.

X-ray Proper Motions and Shock Speeds along the Northwest Rim of SN 1006