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 VLT/FORS2 in 2007 and 2010 .
For both the northeastern and southeastern regions , we measure an average proper motion of H \alpha filaments of 0.10 \pm 0.02 ″ yr ^ { -1 } , corresponding to 1200 \pm 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 northeastern region .
The new measurements are consistent with the previously measured proton temperature of 2.3 \pm 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 northeast and southeast is peculiar , given the different densities and X-ray emission properties of the regions .
The northeastern region has lower densities and the X-ray emission is synchrotron dominated , suggesting that the shock velocities should be higher than in the southeastern , thermal X-ray dominated , region .
A possible solution is that the H \alpha emitting filaments are biased toward denser regions , with lower shock velocities .
Alternatively , in the northeast 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 .