Detection of X – Ray Emission from the PSR 1259 – 63 / SS 2883 Binary System ∗

Nonpulsed but variable X-ray emission has been detected from the binary system containing the radio pulsar PSR 1259–63 during two pointed ROSAT observations, taken five months apart. This 47.7 ms radio pulsar is in a highly eccentric (2 ∼ .85) binary system with the 10 to 15 M ̄ Be star SS2883. It is the first radio pulsar found to be in a binary system with a massive main sequence companion; it is also the most highly eccentric binary system known to contain a neutron star. The level of X-ray flux detected in the ROSAT observations has increased with orbital phase by a factor of at least ten between 1992 February and 1993 February. The X-ray flux is significantly greater than expected from the Be star’s corona and seems likely to originate either from low-level stellar wind accretion onto the neutron star or from the shock between the stellar wind and the relativistic pulsar wind. The system may be the progenitor of the more slowly rotating Be X-ray binary pulsar systems. To appear in the Astrophysical Journal ∗Work supported in part by Department of Energy contract DE–AC03–76SF00515 (SLAC) and by a grant from the NASA ROSAT Guest Observer Program, NAG 5–1684. †Permanent address: Sonoma State University; Visiting Professor, Stanford Linear Accelerator Center.