The Proper Motion of the High Galactic Latitude Pulsar Calvera

Abstract

Calvera (1RXS J141256.0+792204) is a pulsar of characteristic age 285 kyr at a high Galactic latitude of b = +37°, detected only in soft thermal X-rays. We measure a new and precise proper motion for Calvera using Chandra High Resolution Camera observations obtained 10 yr apart. We also derive a new phase-connected ephemeris using 6 yr of NICER data, including the astrometric position and proper motion as fixed parameters in the timing solution. Calvera is located near the center of a faint, circular radio ring that was recently discovered by LOFAR and confirmed as a supernova remnant (SNR) by the detection of γ-ray emission with Fermi Large Area Telescope. The proper motion of 78.5 ± 2.9 mas yr−1 at position angle 241.°3 ± 2.°2 (in Galactic coordinates) points away from the center of the ring, a result which differs markedly from a previous low-significance measurement, and greatly simplifies the interpretation of the SNR/pulsar association. It argues that the supernova indeed birthed Calvera <10 kyr ago, with an initial spin period close to its present value of 59 ms. The tangential velocity of the pulsar depends on its uncertain distance, v t = (372 ± 14)d 1 kpc km s−1, but is probably dominated by the supernova kick, while its progenitor could have been a runaway O or B star from the Galactic disk.