ELECTRON-ENERGY LOSSES NEAR PULSAR POLAR CAPS

We present results of a model for the energetics of electrons accelera ted by the large electric fields generated by a rotating highly magnet ized neutron star. The energy-loss mechanisms we consider in our calcu lations include magnetic Compton scattering of thermal X-ray photons, triplet pair production, and curvature radiation emission. The electro n acceleration mechanism is assumed to operate only to a height above the polar cap approximately equal to the polar cap radius. We find sev eral interesting results. First, magnetic Compton scattering is the do minant energy-loss process when the electron Lorentz factors are less than a few x 10(6) for typical gamma-ray pulsar magnetic fields and su rface temperatures measured by ROSAT. The amount of energy converted t o photons by accelerated electrons ranges from similar to 10% to simil ar to 100% of y(0) m(e)c(2), where y(0) is the maximum Lorentz factor an electron can attain with no radiative losses. We also find that if B > 10(13) G and T > 3 x 10(6) K, the Lorentz factors of the electrons can be limited to values less than or similar to 10(3), assuming valu es for the size of the neutron star thermal polar cap comparable to th e polar cap size determined by the open field lines. Such small Lorent z factors may be capable of explaining the gamma-ray emission from PSR 1509-58 which is observed only at energies less than or similar to 1 MeV. We calculated the fraction of the electron's kinetic energy that is converted to gamma rays for the three gamma-ray pulsars which show thermal X-ray spectra, namely, Vela, Geminga, and PSR 1055-52. Using t he pulsar parameters derived by Ogelman (1995), we found that we can e xpect these pulsars to have between similar to 5% (Geminga) and simila r to 60% (Vela) of the accelerated electron luminosity converted to ga mma-ray luminosity.