Publication Date:
2013-09-26
Description:
We present a proper motion study of the eastern shock-region of the supernova remnant RCW 86 (MSH 14-6 3 , G315.4–2.3), based on optical observations carried out with Very Large Telescope/FOcal Reducer and low dispersion Spectrograph 2 in 2007 and 2010. For both the north-eastern and south-eastern regions, we measure an average proper motion of Hα filaments of 0.10 ± 0.02 arcsec yr –1 , corresponding to 1200 ± 200 km s –1 at 2.5 kpc. There is substantial variation in the derived proper motions, indicating shock velocities ranging from just below 700 km s –1 to above 2200 km s –1 . The optical proper motion is lower than the previously measured X-ray proper motion of north-eastern region. The new measurements are consistent with the previously measured proton temperature of 2.3 ± 0.3 keV, assuming no cosmic ray acceleration. However, within the uncertainties, moderately efficient (〈27 per cent) shock acceleration is still possible. The combination of optical proper motion and proton temperature rule out the possibility that RCW 86 has a distance less than 1.5 kpc. The similarity of the proper motions in the north-east and south-east is peculiar, given the different densities and X-ray emission properties of the regions. The north-eastern region has lower densities and the X-ray emission is synchrotron dominated, suggesting that the shock velocities should be higher than in the south-eastern, thermal X-ray dominated, region. A possible solution is that the Hα emitting filaments are biased towards denser regions, with lower shock velocities. Alternatively, in the north-east the shock velocity may have decreased rapidly during the past 200 yr, and the X-ray synchrotron emission is an afterglow from a period when the shock velocity was higher.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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