Spindown of an oblique rotator with a currentstarved outer magnetosphere
Abstract
A variant of the vacuumdipole model of rotationpowered pulsars is presented that accounts for the observed spindown properties of all three pulsars with braking indices measured from absolute pulse numbering (the Crab, PSR B054069 and PSR B150958). In the model, the neutron star and inner magnetosphere are treated phenomenologically as a single unit, a magnetized, perfectly conducting sphere of radius r_v rotating rigidly in vacuo. The `vacuum radius' r_v corresponds to the innermost point in the magnetosphere where fieldaligned flow breaks down and the plasma becomes threedimensional, that is, the point where cyclotron losses occur slowly enough to allow electrons (or positrons) to move an appreciable distance before decaying to the <e1>l=0 Landau state. For young, Crablike pulsars, one typically finds r_*<<r_v< r_L</e1>, where r_* is the stellar radius, and r_L is the lightcylinder distance. The model therefore differs from standard vacuumdipole theories, in which the dipole has radius r_* and is treated as pointlike. Three observable pulsar parameters  the rotation frequency omicron, its time derivative /omicron, and the angle alpha between the rotation and magnetic axes  uniquely determine r_v and hence the electromagnetic braking torque exerted on the star, calculated from the Deutsch radiation fields of the rotating dipole. With no free parameters, the theory yields braking index values n=omicron,omicron//omicron^2 for the Crab, PSR B054069 and PSR B150958 that agree with timing data to 4 per cent. The second deceleration parameter m=omicron^2omicron...//omicron^3 is also predicted for each object, but cannot be verified to useful precision using data available at present. The relationship between our idealized yet successful spindown model and a genuine pulsar magnetosphere is discussed, and further observational tests of the theory are proposed.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 July 1997
 DOI:
 10.1093/mnras/288.4.1049
 Bibcode:
 1997MNRAS.288.1049M
 Keywords:

 STARS: NEUTRON;
 PULSARS: GENERAL;
 STARS: ROTATION.