Fine structure of the pulsar decameter radiation as the probe of the propagation media

Abstract

Pulsars radiate short pulsed signals (a typical period of an ordinary pulsar is about 1 s) that are good probes of propagation media. Propagation medium includes pulsar magnetosphere, interstellar medium (ISM), interplanetary medium (IPM) and the Earth's ionosphere, it has turbulent nature with variation of the electron density along the line-of-sight. During pulses propagation they are influenced by free electrons, irregularities of the electron concentration and magnetic field. It causes the propagation effects that are called frequency dispersion delay, scattering and the Faraday rotation respectively. At low frequencies all the propagation effects are most contrasted and this imposes restrictions on the pulsar observations in this frequency range. In fact, we are able to investigate only the nearest to the Earth pulsars with low dispersion measures (DM, describes amount of free electrons on the line of sight). Fortunately, at low frequency about 1 – 2 % of all pulsar pulses are ten or hundred times more intensive than average pulses. This phenomenon is called the pulsar anomalously intense pulses (AIP) [1] and gives opportunities to study fine structures of pulsar individual pulses at these frequencies. Fine structure of the pulsar radiation is short pulses inside the main pulse, it was detected by Hankins [2]. Characteristic time scale of the fine structure is frequency dependent, at decameters it is the widest, in the paper [3] authors detected the fine structure of pulsar B0809+74 with time-scale 2 – 4 ms, using radio telescope UTR-2.