Editing Compton Gamma Ray Observatory (section)

===COMPTEL===
The '''Imaging Compton Telescope''' ('''COMPTEL''') by the [[Max Planck Institute for Extraterrestrial Physics]], the [[University of New Hampshire]], [[Netherlands Institute for Space Research]], and ESA's Astrophysics Division was tuned to the 0.75-30 MeV energy range and determined the angle of arrival of photons to within a degree and the energy to within five percent at higher energies. The instrument had a field of view of one [[steradian]]. For cosmic gamma-ray events, the experiment required two nearly simultaneous interactions, in a set of front and rear scintillators. Gamma rays would [[Compton scattering|Compton scatter]] in a forward detector module, where the interaction energy ''E<sub>1</sub>'', given to the recoil electron was measured, while the Compton scattered photon would then be caught in one of the second layers of scintillators to the rear, where its total energy, ''E<sub>2</sub>'', would be measured. From these two energies, ''E<sub>1</sub>'' and ''E<sub>2</sub>'', the Compton scattering angle, angle θ, can be determined, along with the total energy, ''E<sub>1</sub> + E<sub>2</sub>'', of the incident photon. The positions of the interactions, in both the front and rear scintillators, was also measured. The [[Euclidean vector|vector]], '''V''', connecting the two interaction points determined a direction to the sky, and the angle θ about this direction, defined a cone about '''V''' on which the source of the photon must lie, and a corresponding "event circle" on the sky. Because of the requirement for a near coincidence between the two interactions, with the correct delay of a few nanoseconds, most modes of background production were strongly suppressed. From the collection of many event energies and event circles, a map of the positions of sources, along with their photon fluxes and spectra, could be determined.