The Crab pulsar in the 0.75-30 MeV range as seen by CGRO COMPTEL - A coherent high-energy picture from soft X-rays up to high-energy gamma-rays

We present the time-averaged characteristics of the Crab pulsar in the 0.75 -30 MeV energy window using data from the imaging Compton Telescope COMPTEL aboard the Compton Gamma-Ray Observatory (CGRO) collected over its 9 year mission. Exploiting the exceptionally long COMPTEL exposure on the Crab all owed us to derive significantly improved COMPTEL spectra for the Crab nebul a and pulsar emissions, and for the first time to accurately determine at l ow-energy gamma -rays the pulse profile as a function of energy. These timi ng data, showing the well-known main pulse and second pulse at a phase sepa ration of similar to0.4 with strong bridge emission, are studied together w ith data obtained at soft/hard X-ray energies from the ROSAT HRI, BeppoSAX LECS, MECS and PDS, at soft gamma -rays from CGRO BATSE and at high-energy gamma -rays from CGRO EGRET in order to obtain a coherent high-energy pictu re of the Crab pulsar from 0.1 keV up to 10 GeV. The morphology of the puls e profile of the Crab pulsar is continuously changing as a function of ener gy: the intensities of both the second pulse and the bridge emission increa se relative to that of the first pulse for increasing energies up to simila r to1 MeV. Over the COMPTEL energy range above 1 MeV an abrupt morphology c hange happens: the first pulse becomes again dominant over the second pulse and the bridge emission loses significance such that the pulse profile abo ve 30 MeV is similar to the one observed at optical wavelengths. A pulse-ph ase-resolved spectral analysis performed in 7 narrow phase slices consisten tly applied over the 0.1 keV-10 GeV energy interval shows that the pulsed e mission can empirically be described with 3 distinct spectral components: i ) a power-law emission component (1 keV-5 GeV; photon index 2.022+/-0.014), present in the phase intervals of the two pulses; ii) a curved spectral co mponent required to describe soft (less than or similar to 100 keV) excess emission present in the same pulse-phase intervals; iii) a broad curved spe ctral component reflecting the bridge emission from 0.1 keV to similar to 1 0 MeV. This broad spectral component extends in phase over the full pulse p rofile in an approximately triangular shape, peaking under the second pulse . Recent model calculations for a three-dimensional pulsar magnetosphere wi th outer magnetospheric gap acceleration by Cheng et al. (2000) appear at p resent most successful in explaining the above complex high-energy characte ristics of the Crab pulsar.