Physics of Drifting Sub-pulses in Radio Pulsars
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 h
- PDF / 4,723,850 Bytes
- 32 Pages / 439.095 x 666.249 pts Page_size
- 70 Downloads / 241 Views
Physics of Drifting Sub-pulses in Radio Pulsars Jan M.E. Kuijpers
20.1 Introduction 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 longperiod 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, P4 ≈
P1 P3 P1 P3 = P2 (1 + NP3 /P1 ) P2
(20.1)
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. In this Chapter I will show how drifting sub-pulses allow us to get a grip on the detailed geometry of the electric circuit and the sources of radio emission on the open field lines in the light of a number of proposed interpretations of drifting sub-pulses. In Sect. 20.2, we summarize the common characteristics of radio J.M.E. Kuijpers Department of Astrophysics, IMAPP, Radboud University Nijmegen, The Netherlands e-mail: [email protected] W. Becker (ed.), Neutron Stars and Pulsars, Astrophysics and Space Science Library 357, c Springer-Verlag Berlin Heidelberg 2009
543
544
J.M.E. Kuijpers
Fig. 20.1 Sequences of drifting sub-pulses are clearly visible at 328 MHz in stacked pulse observations of PSR B0031-07 (pulse period 0.943 s) taken with the Westerbork Synthesis Radio Telescope and the PuMa backend (courtesy of Dr. Roy Smits). The horizontal axis runs from 60 to 120◦ in ‘longitude’
Pulse number
20 Physics of Drifting Sub-pulses in Radio Pulsars
545
P3
P2
Pulse phase Fig. 20.2 Schematic picture of drifting sub-pulses in a stacked pulse diagram. P2 and P3 are measured in seconds and the pulse phase or conventional ‘longitude’ Φ corresponds to time according to the formula Φ = 360◦ t/P1
pulsar models to date, and the open questions, and sketch the basic properties which any steady circuit in the magnetosphere must have. Confrontation with individual models of drifting sub-pulses will then allow us to draw conclusions regarding the details of the electric circuit, and answer some of the open questions. This is done in Sect. 20.3 where we review the existing interpretations [8, 19, 22, 26, 39, 42, 44
Data Loading...
