Asymmetry function of interstellar scintillations of pulsars

A new method for separating intensity variations of a source’s radio emission having various physical natures is proposed. The method is based on the joint analysis of the structure function of intensity variations and the asymmetry function, which is a generalization of the asymmetry coefficient and which characterizes the asymmetry of the distribution function of intensity fluctuations on various scales for inhomogeneitiesin the diffractive scintillation pattern. Relationships for the asymmetry function in the cases of a logarithmic normal distribution of the intensity fluctuations and a normal distribution of the field fluctuations are derived. Theoretical relationships and observational data on interstellar scintillations of pulsars (refractive, diffractive, and weak scintillations) are compared. The data for PSR B0329+54, B1133+16, B1642-03, and B1933+16 pulsars were used for comparison. Pulsar scintillations match the behavior expected for a normal distribution of field fluctuations (diffractive scintillation) or logarithmic normal distribution of intensity fluctuations (refractive and weak scintillation). Analysis of the asymmetry function is a good test for distinguishing scintillations against the background of variations that have different origins.     

Phase and intensity distributions of individual pulses of PSR B0950+08

The distribution of the intensities of individual pulses of PSR B0950+08 as a function of the longitudes at which they appear is analyzed. The flux density of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of 13) due to the passage of the radiation through the interstellar plasma (interstellar scintillation). The intensities of individual pulses can exceed the amplitude of the mean pulse profile, obtained by accumulating 770 pulses, by more than an order of magnitude. The intensity distribution along the mean profile is very different for weak and strong pulses. The differential distribution function for the intensities is a power law with index n = ?1.1 ± 0.06 up to peak flux densities for individual pulses of the order of 160 Jy.     

The outer turbulence scale in the interstellar plasma

The structure function for phase fluctuations on spatial scales from 10⁶ to 10¹⁷ m is constructed using data on diffractive and refractive scintillation of pulsars, scattering angles, variations in pulse arrival times, and differences in dispersion measures observed for close pairs of pulsars in globular clusters. For distances R>1 kpc (a sample of pulsars with DM≥30 pc/cm³), the fluctuations in the interstellar electron density on scales from 10⁶ to 10¹⁴ m are well described by a Kolmogorov spectrum with index 11/3. Analysis of variations in the dispersion measures for close pairs of pulsars in globular clusters indicates an outer turbulence scale of L ₀=10¹⁵ m. The relative level of turbulent fluctuations is determined for the interstellar plasma, and the important role of turbulence in the energy balance is demonstrated.     

Analysis of Oscillatory Modes of the Magnetic Field of Solar Facular Formations

Geomagnetism and Aeronomy - Quasi-periodical variations in the magnetic fields of long-living, small-scale magnetic structures, solar facular formations (FFs), are analyzed. We used the method of...     

Numerical Simulation of Sub-Terahertz Thermal Emission: RADYN Code

Geomagnetism and Aeronomy - The temporal evolution of thermal bremsstrahlung in the sub-terahertz range is calculated for F-CHROMA models of the flare chromosphere and transition region (...     

Simulation of Microwave Emission from the Magnetic Arch with Growing Millimeter Spectrum

A three-dimensional simulation of the microwave emission of nonthermal electrons within a flare magnetic loop that takes into account the influence of the chromosphere has been carried out. The paper investigates the possibility of the generation of a microwave spectrum (observed for some solar flares) with a maximum in the centimeter wavelength range and a positive slope in the millimeter one under the some distribution of the magnetic field strength and the parameters of the anisotropic nonthermal electrons along the loop. By the example of the event on July 5, 2012, it is shown that nonthermal electrons can be responsible not only for the centimeter bell-shaped emission spectrum generated in the coronal part of the loop but also for the increasing millimeter spectrum generated in the chromosphere.     

The Use of NDVI in Digital Mapping of the Content of Available Lithium in the Arable Horizon of Soils in Southwestern Siberia

Izvestiya, Atmospheric and Oceanic Physics - We have determined the informational value of the Normalized Difference Vegetation Index (NDVI) for predictive mapping of the content of available...     

Long-term oscillations of sunspots and a special class of artifacts in SOHO/MDI and SDO/HMI data

A specific type of artifacts (named as “p2p”), that originate due to displacement of the image of a moving object along the digital (pixel) matrix of receiver are analyzed in detail. The criteria of appearance and the influence of these artifacts on the study of long-term oscillations of sunspots are deduced. The obtained criteria suggest us methods for reduction or even elimination of these artifacts. It is shown that the use of integral parameters can be very effective against the “p2p” artifact distortions. The simultaneous observations of sunspot magnetic field and ultraviolet intensity of the umbra have given the same periods for the long-term oscillations. In this way the real physical nature of the oscillatory process, which is independent of the artifacts have been confirmed again. A number of examples considered here confirm the dependence between the periods of main mode of the sunspot magnetic field long-term oscillations and its strength. The dependence was derived earlier from both the observations and the theoretical model of the shallow sunspot. The anti-phase behavior of time variations of sunspot umbra area and magnetic field of the sunspot demonstrates that the umbra of sunspot moves in long-term oscillations as a whole: all its points oscillate with the same phase.