Towards a theory of extremely intermittent pulsars II. Asteroids at a close distance

Aims. We investigate whether there may be one or many companions orbiting at close distance to the light cylinder around the extremely intermittent pulsars PSR B1931+ 24 and PSR J1841-0500. These pulsars, behaving in a standard way when they are active, also switch off for durations of several days, during which their magnetospheric activity is interrupted or reduced. Methods. We constrained our analysis on eight fundamental properties of PSR B1931+ 24 that summarise the observations. We considered that the disruption/activation of the magnetospheric activity would be caused by the direct interaction of the star with the Alfven wings emanating from the companions. We also considered the recurrence period of 70 days to be the period of precession of the periastron of the companions orbit. We analysed in which way the time scale of the on/off pseudo-cycle would be conditioned by the precession of the periastron and not by the orbital time scale, and we derived a set of orbital constraints that we solved. We then compared the model, based on PSR 1931+24, with the known properties of PSR 1841+0500. Results. We conclude that PSR B1931+ 24 may be surrounded at a close distance to the star by a stream of small bodies of kilometric or sub-kilometric sizes that could originate from the tidal disruption of a body of moderate size that fell at a close distance to the neutron star on an initially very eccentric orbit. This scenario is also compatible with the properties of PSR J1841-0500, although the properties of PSR J1841-0500 are, as of now, less constrained. Conclusions. These results raise new questions. Why are the asteroids not yet evaporated? What kind of interaction can explain the disruption of the magnetospheric activity? These questions are the object of two Papers in preparation that will complete the present analysis.