Proper Motion and Timing of Two Unusual Pulsars: Calvera and 1E 1207.4-5209

TL;DR

This study measures the proper motions and timing of two unusual pulsars, Calvera and 1E 1207.4-5209, revealing their velocities, magnetic fields, and implications for their origins and evolution.

Contribution

It provides the first proper motion measurements for these pulsars and updates their timing solutions, offering insights into their magnetic fields and evolutionary paths.

Findings

1E 1207.4-5209 has negligible proper motion, indicating its offset is not due to high velocity.

Calvera has a marginal proper motion, moving away from the Galactic plane.

Calvera's magnetic field suggests it may be evolving towards typical pulsar magnetic fields.

Abstract

Using pairs of images from the Chandra High-Resolution Camera we examine the proper motion of the central compact object (CCO) 1E 1207.4-5209 in the supernova remnant (SNR) PKS 1209-51/52, and the unusual pulsar Calvera that is possibly a CCO descendant. For 1E 1207.4-5209, an insignificant proper motion of 15+/-7 mas/yr is measured, corresponding to a corrected tangential velocity of <180 km/s at the distance of 2 kpc. This proves that the previously noted large offset of the pulsar from the apparent geometric center of the SNR is not due to high proper motion; evidently the symmetry of the remnant does not indicate its center of expansion. Calvera has a marginally significant proper motion of 69+/-26 mas/yr, corresponding to 86+/-33 km/s for a hypothetical distance of 0.3 kpc. Notably, its vector is away from the Galactic plane, although its high Galactic latitude of b = +37 deg may be more a consequence of its proximity than its velocity. We also provide updated timing solutions for each pulsar. Spanning 14.5 yr, the ephemeris of 1E 1207.4-5209 has a small and steady frequency derivative that, because of the negligible proper motion, requires no kinematic correction. The derived surface dipole magnetic field strength of 1E 1207.4-5209 thus remains B_s = 9.8e10 G. Calvera has B_s = 4.4e11 G, intermediate between those of ordinary young pulsars and CCOs, suggesting that it may be on a trajectory of field growth that could account for the absence of descendants in the neighborhood of CCOs in the P-Pdot diagram.