Evidence for an increasing 59-s period in the X-ray emission from Geminga

Einstein Observatory and Exosat X-ray data from 1E0630 + 178 reveal a ~50% periodic emission at >=59 s. This confirms the earlier SAS 2 and COS B findings on 2CG195 + 4 at E> 50 MeV, and provides the temporal signature for the identification of Geminga. The observations, spanning over a decade (1973-83), also suggest a very high positive period derivative, P, which has become still higher between 1979 and 1983. A simple source scenario is proposed, based on a binary system containing a compact object responsible for the high energy emission, and also taking into account recent ultra high energy γ-ray measurements.