X-ray emission from the PSR B1259–63 system near apastron

The PSR B1259–63 system contains a 47 ms radio pulsar in a highly eccentric binary with a Be-star companion. Strongly time variable X-ray emission was reported from this system as the pulsar was near apastron in 1992-early 1993. The variability was primarily deduced from an apparent non-detection of the PSR B1259-63 system during a first pre-apastron ROSAT observation in February 1992. We have re-analyzed the ROSAT observations of the PSR B1259-63 system. Contrary to the results of a previous analysis, we find that the PSR B1259-63 system was detected by ROSAT during the first off-axis February 1992 observation. The intensity of the soft X-ray emission of the PSR B1259-63 system before and after the 1992 apastron appears to vary at most by a factor ∼ 2. Our results sensibly constrain theoretical models of X-ray emission from the PSR B1259-63 system. Subject headings: binaries: close – pulsars: individual (PSR 1259-63) – stars: emissionline, Be – stars: mass loss – X-rays: stars. 1 New address: Columbia Astrophysics Laboratory, Pupin Hall, Columbia University, New York, NY 10027.