The COMPTEL experiment on the Compton Gamma-Ray Observatory measures γ–radiation in the energy range from 0.75 to 30 MeV . X-ray binaries form one category of potential γ-ray sources. Up to now only two X-ray binaries, Cyg X-l and Nova Per, have been seen by COMPTEL.
Cyg X-l. Preliminary results were reported by  and indicate that (i) there was no evidence for any hardening of the spectrum near lMeV, (ii) the plasma temperature suggested by a Wien spectral model was much higher than that implied by hard X-ray observations. This latter conclusion seems to require a revision in the standard spectral model for Cyg X-l.
The α–ray flux from Cyg X-l is constant up to several MeV. The time history of the flux in the 0.75… 2.0 MeV energy range shows that there are no significant variations near 1 MeV. The average photon spectrum derived from all observations up to 1994 July shows evidence for significant emission extending well above 2 MeV, with a data point in the 2…5 MeV range at 4.3 σ significance. However, the observed flux near 1 MeV is significantly below that reported by HEAO-3 and several other balloon observations . The COMPTEL spectral data show a broad line-like feature around ~ 4 MeV with the best fit of a single power law plus Gaussian. If we assume that the Gaussian represents a single broadened nuclear line of 12C*, then the width of 1.38 MeV demands a temperature of ~ 2 1012 K .