Interstellar Plasma Turbulence Spectrum Toward the Pulsars PSR B0809+74 and B0950+08

Interstellar scintillations of pulsars PSR B0809+74 and B0950+08 have been studied using observations at low frequencies (41, 62, 89, and 112 MHz). Characteristic temporal and frequency scales of diffractive scintillations at these frequencies have been determined. The comprehensive analysis of the frequency and temporal structure functions reduced to the same frequency has shown that the spectrum of interstellar plasma inhomogeneities toward both pulsars is described by a power law. The exponent of the spectrum of fluctuations of interstellar plasma inhomogeneities toward PSR B0950+08 (n = 3.00 +- 0.05) appreciably differs from the Kolmogorov exponent. Toward PSR B0809+74 the spectrum is a power law with an exponent n = 3.7 +- 0.1. A strong angular refraction has been detected toward PSR B0950+08. The distribution of inhomogeneities along the line of sight has been analyzed; it has been shown that the scintillations of PSR B0950+08 take place on a turbulent layer with enhanced electron density, which is localized at approximately 10 pc from the observer. For PSR B0809+74 the distribution of inhomogeneities is quasi-uniform. Mean-square fluctuations of electron density on inhomogeneities with a characteristic scale rho_0 = 10^7 m toward four pulsars have been estimated. On this scale the local turbulence level in the 10-pc layer is 20 times higher than in an extended region responsible for the scintillations of PSR B0809+74.Comment: 13 pages, 11 figure

The Asymmetry Coefficient for Interstellar Scintillation of Extragalactic Radio Sources

Comparing the asymmetry coefficients and scintillation indices for observed time variations of the intensity of the radiation of extragalactic sources and the predictions of theoretical models is a good test of the nature of the observed variations. Such comparisons can be used to determine whether flux-density variations are due to scintillation in the interstellar medium or are intrinsic to the source. In the former case, they can be used to estimate the fraction of the total flux contributed by the compact component (core) whose flux-density variations are brought about by inhomogeneities in the interstellar plasma. Results for the radio sources PKS 0405-385, B0917+624, PKS 1257-336, and J1819+3845 demonstrate that the scintillating component in these objects makes up from 50% to 100% of the total flux, and that the intrinsic angular sizes of the sources at 5 GHz is 10-40 microarcseconds. The characteristics of the medium giving rise to the scintillations are presented