Reanalyzing COMPTEL Data: The Gamma-Ray Sky up to 50 MeV

A decade after de-orbiting CGRO, COMPTEL's 1-30 MeV all-sky imaging data set remains unsurpassed, and no current or planned mission is capable of challenging COMPTEL's performance in the near future. Since the nineties, when the original COMPTEL data analysis techniques were developed, the performance of state-of-the-art computers has increased by orders of magnitude, enabling new and improved techniques that were out of reach at that time. These techniques include Geant4 simulations, Bayesian event selections, and partially-binned-response list-mode ML-EM imaging techniques. Besides others, the new methods offer the possibility to extend COMPTEL's upper energy limit from 30 to 50 MeV. The high energy range (above 10 MeV) is particularly challenging due to the low scattering cross-section for Compton telescopes and the coarse angular resolution of standard pair-conversion telescopes such as FERMI. First results in the energy range from 30 to 50 MeV are promising: Using COMPTEL data through November 1997, the Crab pulsar can be detected with 6-7 sigma and an angular resolution of 1.6 degrees is achieved. In this presentation we report on the analysis methods and present results from various strong gamma-ray sources in the high energy band from 10 to 50 MeV and compare them to the original COMPTEL results.