We have used a set of archived HST/WFPC2 exposures of the inner regions of the Crab Nebula to obtain a new measurement of the pulsar proper motion , the first after the original work of Wyckoff & Murray , more than 20 years ago .
Our measurement of the pulsar displacement , \mu = 18 \pm 3 mas yr ^ { -1 } , agrees well with the value obtained previously .
This is noteworthy , since the data we have used span less than 2 years , as opposed to the 77 years required in the previous work . With a position angle of 292 ^ { \circ } \pm 10 ^ { \circ } , the proper motion vector appears aligned with the axis of symmetry of the inner Crab nebula , as defined by the direction of the X-ray jet observed by ROSAT .
Indeed , if the neutron star rotation is to be held responsible both for the X-ray jet and for the observed symmetry , the Crab could provide an example of alignment between spin axis and proper motion .