Updated Proper Motion of the Neutron Star in the Supernova Remnant Cassiopeia A

Abstract

Abstract In this paper, we present updated estimates of the velocity of the neutron star (NS) in the supernova remnant Cassiopeia A using over two decades of Chandra observations. We use two methods: (1) recording the NS positions from dozens of Chandra observations, including the astrometric uncertainty estimates on the data points, but not correcting the astrometry of the observations; and (2) correcting the astrometry of the 13 Chandra observations that have a sufficient number of point sources with identified Gaia counterparts. For method #1, we observe a heliocentric velocity of 275 ± 121 km s−1, with an angle of 177° ± 22° east of north. For method #2, we observe a heliocentric velocity of 436 ± 89 km s−1 at an angle of 158° ± 12°. Correcting for galactic rotation and the Sun’s peculiar motion decreases these estimates to 256 km s−1 at 167° and 433 km s−1 at 151°, respectively. Both of our estimates match with the explosion-center-estimated velocity of ∼350 km s−1 and the previous 10 yr baseline proper-motion measurement of 570 ± 260 km s−1, but our use of additional data over a longer baseline has led to a smaller uncertainty by a factor of 2–3. Our estimates rule out velocities ≳600 km s−1 and better match with simulations of Cassiopeia A that include NS kick mechanisms.