HEAO-1 observations of the X-ray pulsar 1E2259 + 586

Summary We have analysed HEAO-1 scanning observations of the X-ray pulsar 1E2259 + 586, obtaining a pulse period from 1978 January of 6.978586 ± 0.6 s. This extends the spindown trend seen by later observers to earlier times. No evidence is found for a second derivative to the period. The luminosity and pulse profile we derive are similar to those of subsequent observations, with no evidence for large-scale variability on a time-scale of days or months. We discuss how the conventional picture of the source as an accreting neutron star can be modified to accommodate the very stable spin period derivative, and assess various models for the pulsar’s formation and subsequent evolution.