The diffuse gamma-ray background and the pulsar magnetic window

Abstract

An investigation of the hypothesis that the Ruderman and Sutherland (1975) model's spark discharges are triggered by diffuse background gamma rays has shown that such triggering can be effective only within a narrow range, around 2.5 × 10 to the 12th gauss, of the surface magnetic field. The position of this magnetic window is insensitive to neutron star radius and polar gap size scaling with radius, and results in a pulsar long period cutoff at 4 secs. Assuming (1) a role for gamma-ray triggering and (2) the dipolarity of the fields, neutron stars whose surface magnetic fields are within the window will have higher probability of functioning as pulsars. It is noted that this explains the peaking, near this value, of derived pulsar magnetic fields. It is suggested that the observed spread in magnetic fields, which is derived from pulsar slowdown rates on the assumption of both dipole braking and a constant radius, is attributable to the presence of multiple components and neutron star radii spread.