Gamma-ray emission from CGRO pulsars

Observations with the gamma-ray telescopes on CGRO have so far revealed gamma-ray emission above an energy of 1 MeV from 7, possibly 8 pulsars: 6 (7) radio pulsars and the radio quiet or radio dim pulsar Geminga. All except one of these pulsars have also been detected at energies above 100 MeV - the low-energy pulsar PSR B1509-58 has only been seen up to several MeV. The observed gamma-ray Light curves show mostly double-peaked emission patterns; only PSR B1706-44 and PSR B1509-58 have more complex light curves. The gamma-ray photon number spectra between 30 MeV and several GeV can be described with power law distributions with indices from -1.2 to -2.2, although a moderate bend in some spectra cannot be excluded. Above a few GeV several pulsars show a marked spectral break. gamma-ray pulsars are characterised by their high rotational energy loss and their relative proximity ton a galactic scale) to the Earth. In terms of derived parameters, gamma-ray pulsars are young (tau proportional to root P(P) over dot 10(6) years), have strong magnetic fields (B proportional to root P(P) over dot approximate to 10(12)G), and high voltages available over the pulsar's open field lines (Phi proportional to root(P) over dot/P-3 approximate to 3 x 10(14) - 4 x 10(16)V). Their efficiency to convert rotational energy into high-energy radiation increases systematically with age and the observed gamma-ray spectra in the EGRET energy range become correspondingly harder. For several of the brighter pulsars, phase resolved spectra have been derived showing significant spectral changes over the pulsar's rotation. Multi-wavelength beaming patterns, i.e., light curves observed throughout the electromagnetic spectrum, reinforce this picture that young pulsars have an extremely rich phenomenology in shaping their emission. While the gamma-ray light curves of most pulsars are quite similar, emission at lower energies appears unrelated in all cases except the Crab pulsar. The underlying physics describing the high-energy radiation processes in the pulsar's magnetosphere and close to the neutron star's surface is still in a state of development. Competing models have achieved explanations for many individual features of pulsars but a comprehensive, self-consistent treatment of particles, fields, and radiation is not yet available. Progress in understanding the emission processes is critical for questions related to the detection and population statistics of more high-energy pulsars, and the total contribution of high-energy pulsars to the galactic gamma-ray emission.