On the nature of the intermittent pulsar PSR B1931+24
  PSR B1931+24 is the first intermittent radio pulsar discovered to date, characterized by a 0.8 s pulsation which turns on and off quasi-periodically every ~35 days, with a duty cycle of ~10%. We present here X-ray and optical observations of PSR B1931+24 performed with the Chandra X-ray Observatory and Isaac Newton Telescope, respectively. Simultaneous monitoring from the Jodrell Bank Observatory showed that this intermittent pulsar was in the radio-on phase during our observations. We do not find any X-ray or optical counterpart to PSR B1931+24 translating into an upper limit of ~2x10^{31} erg/s on the X-ray luminosity, and of g' > 22.6 on the optical magnitude. If the pulsar is isolated, these limits cannot constrain the dim X-ray and optical emission expected for a pulsar of that age (~1.6 Myr). We discuss the possibility that the quasi-periodic intermittent behavior of PSR B1931+24 is due to the presence of a low mass companion star or gaseous planet, tight with the pulsar in an eccentric orbit. In order to constrain the parameters of this putative binary system we re-analysed the pulsar radio timing residuals and we found that (if indeed hosted in a binary system), PSR B1931+24 should have a very low mass companion and an orbit of low inclination. 
N. Rea (1,2), M. Kramer (3), L. Stella (4), P. Jonker (2,5), C. Bassa   (2,6), P. Groot (6), G. Israel (4), M. Mendez (7), A...