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 ≳59s. This confirms the early SAS-II and COS-B findings on 2CG 195+04 atE>50 MeV and provides the temporal signature for the identification of Geminga. The observations, spanning over a decade (1973–1983), also suggest a very high positive $$\dot P$$ which has become still higher in 1979–1983.