The Proper Motion of the Neutron Star in Cassiopeia A

Abstract

Images from the High Resolution Camera on the Chandra X-ray Observatory were used to measure the proper motion of the neutron star in Cassiopeia A over a baseline of 10 years (1999-2009). One background source and 13 quasi-stationary flocculi were chosen to register the two images. Pixel offsets between features at each epoch were measured using four different statistical methods: Gaussian fitting, centroiding, cross correlation, and the Cash statistic. In many cases the offset measurements disagree in magnitude and/or direction by as much as 1 arcsecond, resulting in large uncertainties. As a result, the measurement for the motion of the neutron star is marginal at 390 +/- 400 km/s in the southeast direction. This motion is typical of the birth velocities of young pulsars and is consistent with the inferred proper motion based on the offset of the neutron star from the center of expansion of the optical ejecta.