The Eclipsing Pulsar PSR J1023+0038

© @Anne Archibald 2013

PSR J1023+0038 is an unusual binary pulsar: in 2000-2001 it had an accretion disc, which disappeared in 2002. It is again showing signs of activity - we're still trying to understand what has happened - but in the mean time it ticked along steadily almost like a normal pulsar. We say "almost" because its radio emission did show some very unusual features.

The left diagram shows the pulse phase (vertical) at three frequencies, for three five-hour orbits (horizontal) each. A normal pulsar would just look like smooth horizontal strips. This system shows eclipses and delays, where the signal either disappears completely or arrives late. Even though there's no accretion, there's still some plasma passing between us and the pulsar.

The right diagram shows the system geometry. The top panel shows an edge-on view of the system. The companion is to scale and distorted into that teardrop shape by gravity and centrifugal force. Our viewing angle towards the pulsar during the full orbit varies between the dashed lines, meaning that the companion never actually blocks our view. The bottom panel shows a face-on view of the system. The wedges show the angles that are eclipsed at 1400 (blue) and 350 (red) MHz. Even though the pulsar produces a powerful wind, the plasma from the companion reaches most of the orbit.

In Archibald et al. 2013, we try to understand what is going on. We think the companion may have a magnetic field like that of our Sun, and that the plasma flows along these field lines just like the solar wind. This would also slow the companion's rotation and make it draw closer to the pulsar, so accretion should continue. It's a mystery, though, why the accretion was so weak. Our planned multi-wavelength future observations will help answer that question.