A 23h EXOSAT observation of the X-ray pulsar 1E 2259+586 and the associated supernova remnant G 109.1-1.0

Abstract

The X-ray pulsar, 1E 2259+586, and the associated supernova remnant, G 109.1-1.0 were observed with the EXOSAT on 1984 December 1/2. The pulse period at this epoch was 6.978720±0.000006(1σ) s, indicating that between 1981 and 1984 the pulsar was spinning down with an average secular rate of change of the spin period given by P/P = +[3.3±0.2]×10^-6yr^-1. The pulse shape is stable on a time-scale of hours and shows some energy dependence. The measured Pis sufficiently small to enable to exclude the possibility that this source is an isolated pulsar powered by rotational energy losses and so the pulsar is probably powered by accretion from a low mass companion. In the context of theories of accretion disk torques, 1E 2259+586 is a fast rotator spinning at close to its equilibrium period. The pulsed spectrum of 1E 2259+586 is softer than that of any other known binary X-ray pulsar.