| The pulsar PSR J1023+0038 is doing something peculiar: in June it disappeared as a pulsar and lit up in gamma rays. Unfortunately at the time it was too close to the Sun to observe with major optical telescopes or space-based X-ray telescopes. In October, though, as soon as it became possible, we observed the pulsar with the Swift X-ray telescope to try to determine what had happened.
What we found was that the X-rays and ultraviolet had gotten much brighter. We think what happened was that the system, which contains a pulsar and a slightly distorted main-sequence star in a very close orbit, formed an accretion disc: material is overflowing from the main-sequence star and falling towards the pulsar and growing extremely hot in the process. This hot material blazes in the ultraviolet and even the X-rays.
The image shows a still-mysterious aspect of the X-ray data: although the X-rays are generally bright, once in a while the X-ray flux drops down to the very limit of detectability for a few minutes at a time. It's not clear what could cause these short dropouts. A few minutes is roughly how long it should take to refill the inner hundred kilometers or so of the disc, so perhaps when the flow is weaker than usual the pulsar can turn on for a little while, clearing out the inner part of the disc?
This picture is drawn from Patruno et al. 2013. We announced the pulsar's disappearance in Stappers et al. 2013, and described its behaviour when it doesn't have an accretion disc in Archibald et al. 2013. We are carrying out a multiwavelength observing campaign to clarify what is happening in this puzzling system.