A new HST measurement of the Crab Pulsar proper motion

Abstract

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 +/- 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(deg) +/- 10(deg) , 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. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555