PSR B1931+24 (J1933+2421) behaves as an ordinary isolated radio pulsar during active phases that are 5-10 days long. However, the radio emission switches off in less than 10 seconds and remains undetectable for the next 25-35 days, then it switches on again. This pattern repeats quasi-periodically. The origin of this behaviour is unclear. Even more remarkably, the pulsar rotation slows down 50% faster when it is on than when it is off. This indicates a massive increase in magnetospheric currents when the pulsar switches on, proving that pulsar wind plays a substantial role in pulsar spin-down. This allows us, for the first time, to estimate the currents in a pulsar magnetospheric during the occurrence of radio emission.
@article{arxiv.astro-ph/0604605,
title = {A periodically active pulsar giving insight into magnetospheric physics},
author = {M. Kramer and A. G. Lyne and J. T. O'Brien and C. A. Jordan and D. R. Lorimer},
journal= {arXiv preprint arXiv:astro-ph/0604605},
year = {2009}
}