Physics of Drifting Sub-pulses in Radio Pulsars

Abstract

Sophisticated analysis of single pulses from radio pulsars with the most sensitive radio telescopes available have taught us that most pulsars exhibit the phenomenon of drifting sub-pulses [43], see Figs. 20.1 and 20.2. Already as early as 1970 [41], it has been proposed that these `marching' sub-pulses circulate around the pulsar magnetic axis, and are caused by short-period waves which form part of a long-period wave which circulates about the star at the same angular velocity. Let P1 be the rotation period of the pulsar, P2 the period between sub-pulses within the primary-pulse envelope, P3 the time interval between drifting bands of sub-pulses, and P4 the circulation period around the magnetic axis, all expressed in units of time, then [41], see Fig. 20.2, 1 {$}{$}P{_}4 {\}approx {{}{{}P{_}1 P{_}3 {}} {\}over {{}P{_}2 (1 + NP{_}3 /P{_}1 ){}}{}} = {{}{{}P{_}1 P{_}3 {}} {\}over {{}P{_}2 {}}{}}{$}{$} if, in the last equality, the integer N is put to zero. After all these years, in a few cases, such a carousel of emission columns drifting around the magnetic axis has been constructed from the observations [4, 11,12], see Fig. 20.7. Understanding the phenomenon of drifting sub-pulses may, therefore, well be crucial to our understanding of radio pulsar electrodynamics which despite the largely classical nature of the relevant physics is still shrouded in mysteries, to date 40 years after the discovery of pulsars.