A proper motion for the pulsar wind nebula G359.23-0.82, the "mouse," associated with the energetic radio pulsar J1747-2958

Abstract

The "Mouse" (PWN G359.23-0.82) is a spectacular bow shock pulsar wind nebula, powered by the radio pulsar J1747-2958. The pulsar and its nebula are presumed to have a high space velocity, but their proper motions have not been directly measured. Here we present 8.5 GHz interferometric observations of the Mouse nebula with the Very Large Array, spanning a time baseline of 12 years. We measure eastward proper motion for PWN G359.23-0.82 (and hence indirectly for PSR J1747-2958) of 12.9 ± 1.8 mas yr-1, which at an assumed distance of 5 kpc corresponds to a transverse space velocity of 306 ± 43 km s-1. Considering pressure balance at the apex of the bow shock, we calculate an in situ hydrogen number density of approximately 1.0+0.4-0.2cm-3 for the interstellar medium through which the system is traveling. A lower age limit for PSR J1747-2958 of 163+28-20 kyr is calculated by considering its potential birth site. The large discrepancy with the pulsar's spin-down age of 25 kyr is possibly explained by surface dipole magnetic field growth on a timescale ≈ 15 kyr, suggesting possible future evolution of PSR J1747-2958 to a different class of neutron star. We also argue that the adjacent supernova remnant G359.1-0.5 is not physically associated with the Mouse system but is rather an unrelated object along the line of sight. © 2009. The American Astronomical Society. All rights reserved.