V. I. Shishov

Laser irradiance propagation in turbulent media

The results obtained in recent years on laser irradiance propagation in random weakly inhomogeneous media with large scale index of refraction fluctuations are reviewed. Of particular concern are the problems of the cozrelation theory of fluctuations of irradiance propagating over large distances, where the effects of multiple scattering are greatly pronounced. Much attention is paid to the results on laser beams spread and phase fluctuations. Consideration is given to problem of the study of spatial spikes of irradiance that had passed through a turbulent media; which is comparatively new but important for practical applications. Systematic comparison of the theory with experiment is given where appropriate. The methods of analyses reviewed in this paper are applicable to a class of stochastic and dynamic partial differential equations and thus may be of interest in other areas of engineering reseach.

Radio sounding of the circumsolar plasma using polarized pulsar pulses

We present the results of radio sounding observations probing the inner solar wind near the minimum of the solar-activity cycle, using polarized pulses from PSR B0525+21 and PSR B0531+21 received when the lines of sight toward these pulsars were close to the Sun. The observations were obtained in June 2005 and June 2007 on the Large Phased Array of the Lebedev Physical Institute at 111 MHz. An upper limit for the scattering of giant pulses from PSR B0531+21 due to their passage through the turbulent solar-wind plasma is determined. The arrival-time delays for pulses from PSR B0531+21 are used to derive the radial dependence of the mean density of the circumsolar plasma. The resulting density distribution indicates that the acceleration of fast, high-latitude solar-wind outflows continues to heliocentric distances of 5–10R⊙, where R⊙ is the solar radius. The mean plasma density at heliocentric distances of about 5R⊙ is 1.4 × 104 cm−3, substantially lower than at the solar-activity maximum. This is associated with the presence of polar coronal holes. The Faraday rotation measure at heliocentric distances of 6–7R⊙ is estimated. Deviations of the spatial distribution of the magnetic field from spherical symmetry are comparatively modest in the studied range of heliocentric distances.

Effect of refraction scintillations on the response of an interferometer

Fluctuations of the interferometric response, averaged partly with an integration time much greater than the temporal scale of the diffraction scintillations and less than the temporal scale of the refraction scintillations, are discussed. The second moments of the interferometric response are obtained using a perturbation series for the partly-averaged coherence function. The correlations between the fluctuations of the partly-averaged flux and the coherence-length estimates are also obtained. The variances of these values are determined.

Interstellar scintillation of the radio source associated with the gamma-ray burst of May 8, 1997

The variability of the radio source associated with the gamma-ray burst of May 8, 1997, detected using the VLA, is analyzed. This variability can be explained as weak scintillations at 4.86 and 8.46 GHz and the refractive component of saturated scintillations at 1.43 GHz. Possible distances for the source are discussed. The scintillation parameters are in best agreement with the observations if the source is at a cosmological distance and has an angular size ∼2 microarcseconds (µas) at 4.86 GHz and an expansion speed of the order of 25 µas/year.

The asymmetry coefficient for interstellar scintillation of extragalactic radio sources

Comparing the asymmetry coefficients γ and scintillation indices m 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 caused 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 are 10–40 microarcseconds. The characteristics of the medium giving rise to the scintillations are presented.

Pulsar investigation using interstellar scintillation

We discuss the resolution of pulsar magnetospheres using interstellar scintillation. The two-dimensional spatial structure of pulsar emission zones can be obtained from analysis of diffractive scintillations at low frequencies. Based on refractive and diffractive scintillation of pulsars we can also reconstruct the distribution of turbulent plasma along the line of sight, and using this analysis a new approach to pulsar distance estimation can be made.

INTERSTELLAR SCINTILLATION AND CLOUDS OF THE INTERSTELLAR TURBULENT PLASMA

Data on interstellar diffraction and refraction scintillation of pulsars are analyzed. Comparison between theory and the observational data shows that two types of spectra for electron density fluctuations are realized in the interstellar medium: pure power law and piecewise with a break. The distribution of turbulent plasma in the Galaxy has a three component structure. Component A is diffuse and it is distributed outside of the spiral arms of the Galaxy. Component BI is cloudy and associated with Galactic arms. Component BII is extremely nonuniform and associated with HII regions and supernova remnants. The origin of the interstellar plasma turbulence is considered, and possible sources of turbulent energy are discussed. The contribution of supernova bursts in the interstellar gas ionization and generation of turbulence are analyzed among other factors.