$γ$-Ray Pulsars: Emission Zones and Viewing Geometries, A Computer Animation

Abstract

The computer animation illustrates the geometries described in a paper by the same authors. The preprint is available as number 9401045. The opening scene shows dipole field lines emanating from the polar caps of a rotating neutron star. The dipole axis is inclined along the green rods. The field lines shown are defined from the condition that they be tangent to the light cylinder (the cylindrical radius at which the tangential velocity of rotation reaches the speed of light). The static dipole field lines are smoothly morphed into the correct retarted-potential vacuum solutions. A red surface spanning these field lines is painted. In the next scene the blue surfaces represent the outer gaps above the surface of last closed field lines. High energy emission (blue) is produced in these outer gaps, and is beamed tangentially along the field lines. The radio emission (green) originates close to the surface of the star and is beamed along the dipole axes. The inclination angle $α$ of the dipole and the viewing angle $ζ$ are chosen to match the Crab parameters; $α$ = 70, $ζ$ = 65. The corresponding light curve is computed and shown for these angles, and the red dot traces rotation phase. The next scene shows the situation for angles appropriate to PSR1706-44; $α$ = 45, $ζ$ = 65. The final scene is a possibility for Geminga; $α$ = 20, $ζ$ = 75. These angles are poorly constrained as there is no radio emission.