Simulations of glitches in pulsars

Abstract

Pulsar glitches are thought to represent variable coupling between the neutron star and its superfluid interior. With the aim of distinguishing among different theoretical explanations for the glitch phenomenon, we study the response of a neutron star to two types of perturbations to the vortex array that exists in the superfluid interior: 1) thermal excitation of vortices pinned to inner crust nuclei by sudden heating of the crust, (e.g., a starquake), and 2) mechanical motion of vortices, (e.g., from crust cracking by superfluid stresses). The thermal glitch model adequately fits the timing data of the 1989 glitch in the Crab pulsar (Fig. 1), while both models fit the Vela “Christmas” glitch of 1988 (Fig. 2). The two models make different predictions for the generation of internal heat and subsequent enhancement of surface emission. The mechanical glitch model predicts a negligible temperature increase. For a pure and highly-conductive crust, the thermal glitch model predicts a surface temperature increase of ∼0.2% in the Crab (Fig. 3) and ∼1.5% in Vela (Fig. 4), occurring several weeks after the glitch. If the thermal conductivity of the crust is lowered by a high concentration of impurities, however, the surface temperature increase is ∼10% for a thermal glitch, and occurs about a decade after the glitch. A thermal glitch in an impure crust is consistent with the surface emission measurements following the January 2000 glitch in the Vela pulsar (Fig. 4). Future surface emission measurements coordinated with radio observations will constrain glitch mechanisms and the conductivity of the crust. See Larson & Link (2001) for a detailed description of this work.