Pulsar X‐Ray and Gamma‐Ray Pulse Profiles: Constraint on Obliquity and Observer Angles

We model the thermal X-ray profiles of Geminga, Vela and PSR 0656+14, whichhave also been detected as gamma-ray pulsars, to constrain the phase space ofobliquity and observer angles required to reproduce the observed X-ray pulsedfractions and pulse widths. These geometrical constraints derived from theX-ray light curves are explored for various assumptions about surfacetemperature distribution and flux anisotropy caused by the magnetizedatmosphere. We include curved spacetime effects on photon trajectories andmagnetic field. The observed gamma-ray pulse profiles are double peaked withphase separations of 0.4 - 0.5 between the peaks. Assuming that the gamma-rayprofiles are due to emission in a hollow cone centered on the magnetic pole, wederive the constraints on the phase space of obliquity and observer angles, fordifferent gamma-ray beam sizes, required to produce the observed gamma-ray peakphase separations. We compare the constraints from the X-ray emission to thosederived from the observed gamma-ray pulse profiles, and find that theoverlapping phase space requires both obliquity and observer angles to besmaller than 20-30 degrees, implying gamma-ray beam opening angles of at most30-35 degrees.Comment: 29 pages, 9 embedded figures, AASTEX v.4, To appear in ApJ, June 20, 1998 (Vol. 499