GAMMA-RAYS FROM THE GEMINGA PULSAR - VARIATIONS WITH TIME AND PHASE

Pulsed gamma radiation from the Geminga pulsar was recorded by the COS B satellite from 50 MeV to 5 GeV between 1975 and 1982. It has been a nalysed to derive the source spectral properties as a function of time and phase. The two main peaks are separated by 0.50 +/- 0.01 in phase . Significant pulsed emission has also been detected in both phase reg ions between the two main peaks. Significant spectral differences with phase have been found; the emission from the first peak is slightly s ofter than from the second one and the Interpeak 2 radiation is extrem ely soft. The first peak emission remained stable within the statistic s over 7 years while the flux from the other phase intervals changed s ignificantly with time. The phase dependence of the variability implie s that all the observed source emission should be pulsed and that it c onsists of four discrete beams with different apertures and spectra. T he beams characteristics are strikingly similar to those of four gamma -ray beams generated by the Vela pulsar.