* Astronomy

Title: On the nature of the intermittent pulsar PSR B1931+24
Authors: N. Rea (1,2), M. Kramer (3), L. Stella (4), P. Jonker (2,5,6), C. Bassa (6), P. Groot (7), G. Israel (4), M. Mendez (8), A. Possenti (9), A. Lyne (3) ((1) U. Amsterdam, (2) SRON-Utrecht, (3) Jodrell Bank Observatory, (4) INAF-OAR, (5) CfA, (6) U. Utrecht, (7) U. Nijmegen, (8) U. Groningen, (9) INAF-OAC)
(Version v2)

We present X-ray and optical observations of the intermittent pulsar PSR B1931+24 performed with the Chandra X-ray Observatory and the Isaac Newton Telescope, respectively. Simultaneous monitoring of the pulsar from the Jodrell Bank Observatory showed that this intermittent radio pulsar was in its radio-on phase during our observations. PSR B1931+24 is in fact the first radio pulsar discovered to date, characterized by a 0.8s pulsed radio emission which turns on and off quasi-periodically every ~30days with a duty cycle of ~10%. We did not find any X-ray or optical counterpart for PSR B1931+24 (during the radio-on phase) with an upper limit on the X-ray luminosity of ~2x10^{31} erg/s and on the optical magnitude of i'> 22.6. If the pulsar is isolated, these limits show that PSR B1931+24 behaves in the X-ray and optical bands as almost all of the normal radio pulsars of its age (~1.6 Myr). However, we discuss here the possibility of the PSR B1931+24 quasi-periodic intermittent behaviour being due to the presence of a low mass companion star or gaseous planet, tight with the pulsar in an eccentric binary system. In order to constrain the parameters of this putative binary system we re-analysed the pulsar radio timing residuals and we find that (if indeed hosted in a binary), PSR B1931+24 should have a very low mass companion and a low inclined orbit.

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