The geometric distance and binary orbit of PSR B1259-63

Understand

The pulsar/massive star binary system PSR B1259-63 / LS 2883 is one of the best-studied gamma-ray binaries, a class of systems whose bright gamma-ray flaring can provide important insights into high-energy physics.

• Using the Australian Long Baseline Array we have conducted very long baseline interferometric observations of PSR B1259-63 over 4.4 years, fully sampling the 3.4-year orbital period.
• From our measured parallax of $0.38\pm0.05$ mas we use a Bayesian approach to infer a distance of $2.6^{+0.4}_{-0.3}$ kpc.
• We find that the binary orbit is viewed at an angle of $154\pm3$ degrees to the line of sight, implying that the pulsar moves clockwise around its orbit as viewed on the sky.