Rocking the Lighthouse: Circumpulsar Asteroids and Radio Intermittency

We propose that neutral, circumpulsar debris entering the light cylinder canaccount for many time-dependent pulsar phenomena that are otherwise difficultto explain. Neutral material avoids propeller ejection and injects sufficientcharges -- after heating, evaporation, and ionization -- to alter current flowsand pair-production and thus trigger, detune, or extinguish coherent emission.Relevant phenomena, with time scales from seconds to months, include nulls,rotating radio transients (RRATs), rapid changes in pulse profile (``modechanges''), variable subpulse drift rates, quasi-periodic bursts from B1931+24,and torque variations. Over the 10 Myr lifetime of a canonical pulsar withtrillion-gauss surface magnetic field, less than a millionth of an Earth massof material is needed to modulate the Goldreich-Julian current by 100%.Circumpulsar material originates from metal-rich, supernova fallback gas thataggregates into asteroids. Debris disks can inject sufficient material on timescales of interest, yet be too tenuous to form large planets detectable inpulse timing data. Asteroid migration results from collisions and theradiation-driven Yarkovsky and Poynting-Robertson effects. For B1931+24, anasteroid in a $\sim 40$~day elliptical orbit pollutes the magnetospherestochastically through collisions with other debris. Injection is less likelyfor hot, young and highly magnetized pulsars or millisecond pulsars thatpre-ionize any debris material well outside their small magnetospheres.Injection effects will therefore be most prominent in long-period, coolerpulsars, consistent with the distribution of relevant objects in perid andperiod derivative. A pulsar's spin history and its radiation-beam orientationmay influence whether it displays nulling, RRATs and other effects.Comment: 20 pages, 6 figures, submitted to Ap