Towards explanation of pulsar radio spectra

Institute of Radio Astronomy, Chervonopraporna St. 4, 61002 Kharkov, Ukraine

Corresponding author: rai@ira.kharkov.ua

Received: 15 June 2001
Accepted: 11 December 2001

Abstract

Refraction of radio waves in the ultrarelativistic highly magnetized pulsar plasma is considered. The influence of the effect on the observed pulsar spectra is studied. It is shown that refraction can cause a marked redistribution of the intensity in the emission beam. For a given sight-line trajectory across the beam this affects not only the apparent profile morphology but also the total intensity detected. As refraction is frequency-dependent, it can modify the pulsar spectrum. The spectral changes are peculiar to both the core and conal components. For the typical parameters of the magnetospheric plasma the effect is found to be efficient at the frequencies above 1 GHz. It is demonstrated that refraction can lead to the high-frequency steepening of the core-component spectrum with the subsequent flattening at still higher frequencies. In addition, the effect can account for the inversion of the intensity ratio of the conal components and the consequent break in the spectra of the conal-double pulsars. The high-frequency features of the pulsar spectra are compared with the other observational consequences of refraction. The conclusion is made that at the frequencies above 1 GHz the properties of pulsar radiation are mainly determined by the propagation effects in the magnetospheric plasma.