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

TL;DR

This study measures X-ray proper motions along the NW rim of SN 1006, revealing different shock velocities in thermal and nonthermal regions, and provides insights into the remnant's interaction with surrounding gas.

Contribution

It presents the first detailed proper motion measurements of SN 1006's NW rim using Chandra data, highlighting differences in shock speeds between thermal and nonthermal regions.

Findings

Proper motions of 0.30 and 0.49 arcsec/yr in thermal and nonthermal regions.

Shock velocities of approximately 3000 km/s and 5000 km/s.

Evidence of denser gas interaction in the NW region.

Abstract

We report the results of an X-ray proper motion measurement for the NW rim of SN1006, carried out by comparing Chandra observations from 2001 and 2012. The NW limb has predominantly thermal X-ray emission, and it is the only location in 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, essentially the same as has been measured from the H-alpha filament. Isolated regions of the NW limb are dominated by nonthermal emission, and here the proper motion is much higher, 0.49 arcsec/yr, close to the value measured in X-rays along the much brighter NE limb, where the X-rays are overwhelmingly nonthermal. At the 2.2 kpc distance to SN1006, the proper motions imply shock velocities of about 3000 km/s and 5000 km/s in the thermal and nonthermal regions, respectively. A lower velocity behind the H-alpha filament is consistent with the picture that SN1006 is encountering denser gas in the NW, as is also suggested by its overall morphology. In the thermally-dominated portion of the X-ray shell, we also see an offset in the radial profiles at different energies; the 0.5-0.6 keV peak dominated by O VII is closer to the shock front than that of the 0.8-3 keV emission--due to the longer times for heavier elements to reach ionization states where they produce strong X-ray emission.