The exact mechanism by which a pulsar radiates the energy observed as radio pulses is still a subject of vigorous debate. The basic picture of a misaligned magnetic dipole, with coherent radiation from charged particles accelerated along the open field lines above the polar cap [57, 127], will serve adequately for the purposes of this article, in which pulsars are treated as a tool to probe other physics. While individual pulses fluctuate severely in both intensity and shape (see Figure 1), a profile “integrated” over several hundred or thousand pulses (i.e., a few minutes) yields a shape – a “standard profile” – that is reproducible for a given pulsar at a given frequency. (There is generally some evolution of pulse profiles with frequency, but this can usually be taken into account.) It is the reproducibility of time-averaged profiles that permits high-precision timing.
Of some importance later in this article will be models of the pulse beam shape, the envelope function that forms the standard profile. The collection of pulse profile shapes and polarization properties have been used to formulate phenomenological descriptions of the pulse emission regions. At the simplest level (see, e.g.,  and other papers in that series), the classifications can be broken down into Gaussian-shaped “core” regions with little linear polarization and some circular polarization, and double-peaked “cone” regions with stronger linear polarization and S-shaped position angle swings in accordance with the “Rotating Vector Model” (RVM; see ). While these models prove helpful for evaluating observed changes in the profiles of pulsars undergoing geodetic precession, there are ongoing disputes in the literature as to whether the core/cone split is physically meaningful, or whether both types of emission are simply due to the patchy strength of a single emission region (see, e.g., ).
© Max Planck Society and the author(s)