The interpretation of non-linear radio spectra of discrete radio sources by a general mechanism

The analysis of discrete radio sources spectra in the range 10–5000 MHz reveals that deviations from a power law in the low-frequency region may be due to distortion of differential energy spectra of relativistic electrons at low energies. An empirical expression for an energy-spectrum law was found to be in a good agreement with most of the radio spectra measured. The main physical parameters of 92 sources are evaluated. It is concluded that a low-energy electron excess exists with respect to the lawE ^– in most of the discrete sources which radiate non-linear low-frequency spectra.The forms of radio and energy spectra are further considered in a logarithmic scale.     

The spectra of some discrete radio sources in 10–5000 MHz frequency range

On the basis of the absolute measurements in the 12.6–25 MHz frequency range and the relative measurements at frequencies 750, 1400, 2695 and 5000 MHz (NRAO) and 408, 1410 and 2650 MHz (Parkes), 57 standard spectra were obtained which are linear (on a log-log scale) in the range 12.6–5000 MHz. The comparison of the flux densities presented in the surveys at 10.03, 22.25, 26.3, 38, 86 and 178 MHz and the standard spectra was carried out and thus the correction coefficient was calculated. It was shown that the scale of absolute fluxes CKL on the frequencies 38 and 178 MHz is lowered on 28% and 8% respectively. The possible sources of divergences of the results of measurements in decametric wavelength is discussed. Making use of the corrected data at 38 MHz and 178 MHz, of the results at higher frequencies mentioned above and of the original results of measurements in the 12.6–25 MHz range, the spectra of 55 discrete sources were constructed. The spectra of 149 sources are also obtained on the basis of the surveys at 10.03, 22.25, 26.3, 38 and 178 MHz corrected according to standard spectra.     

Decametric survey of discrete sources in the northern sky

This paper presents results and describes the improved data processing algorithm of the low frequency sky survey of discrete sources carried out with the UTR-2 radio telescope. The measurements were conducted within the frequency range 10 to25 MHz. Coordinates and flux densities of the sources detected were obtained. Identification with sources from the 4C survey has been done. The resulting catalogue contains parameter estimates for 483 sources on a set of frequencies within the UTR-2 range. This revised version was published online in July 2006 with corrections to the Cover Date. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the effect of the distribution function of the injected or formed relativistic particles on the frequency spectra of the radio sources

In the present paper a model of the cosmic radio source with plasma, relativistic electrons and chaotic magnetic fields is considered. It is assumed that the energy changes of relativistic electrons which are due to spontaneous scattering on the transverse and Langmuir plasmons take place in this radio source. For such a radio source the kinetic equation has been solved in the presence of the injected or formed secondary electrons and the frequency spectrum has been obtained.     

Measurements of radio emission from the compact source in the Crab nebula with the uran-1 interferometer at 16.7, 20 and 25 MHz

This paper presents the results of measurements of the Crab nebula in the decametre range with an interferometer whose baseline is 2.4–3.5×10³ of the wavelength. Visibility function values, which in these observations determine the contribution by the compact source to the total nebula flux, have been measured at frequencies 16.7, 20 and 25 MHz to be 0.64±0.07, 0.43±0.04 and 0.31±0.03, respectively. The spectral index of the spectrum obtained for the compact source in the range 16.7–122 MHz is 2.09±0.04. Flattening of the nebula spectrum without the compact source has been confirmed for the decametre range.     

Decametric survey of discrete sources in the northern sky

The region of the celestial sphere between declinations =52°.3 and =59° and right ascensions =1^h and =19^h has been surveyed with the UTR-2 radiotelescope. The results of the survey are presented.The catalogue contains the positions and flux densities of 313 radio-sources detected at 10, 12.6, 14.7, 16.7, 20, and 25 MHz.     

Observational studies of the angular structure of the radio galaxy 3C 234 at decameter wavelengths

An analysis of the angular structure of the radio galaxy 3C 234 at decameter wavelengths based on data obtained on the URAN-1 and URAN-2 interferometers is presented. Four of the five model components that describe the radio-brightness distribution at centimeter wavelengths are observed at decameter wavelengths: two compact components and two neighboring extended components. The fifth, undetected, component is the most extended, and encompasses the central region of the radio source, including the nucleus of the galaxy. Self-absorption is detected in the compact components, whose angular sizes are determined to be 0.27±0.03″ (northeast component) and 0.55±0.05″ (southwest component), in agreement with direct measurements at centimeter wavelengths. Most of the decameter emission of the radio galaxy is associated with its extended components.     

A small-size (less than 1 min of ARC) decametric radio source in the Perseus cluster

Results of observations of decametric readio emission from the Perseus cluster with the aid of URAN-1 interferometer are presented. The 42.2 km baseline of the interferometer is oriented along the parallel. The object is shown to contain a radio source with dimensions which do not exceed 60 and whose flux is not less than 95 Jy over the frequency range from 16.7 to 25 MHz. Several source models are considered and a comparison with higher-frequency measurements is carried out. It seems possible that the source is a component of 3C84A which was reportedly observed earlier by the interferometry technique at 408 and 1415 MHz.     

Interferometric observations of 4C 21.53 and PSR 1937+214 at decameter wavelengths

Preliminary resuts of interferometric observations of 4C 21.53 and PSR 1937+214 at 25 and 20 MHz are presented. The observations were obtained using the URAN-1 and URAN-2 interferometers, with baselines of 42.4 and 152.3 km. In addition to the pulsar radiation, which provides about 70% of the total flux of the object, radio emission from extended components with dimensions of several tens arcseconds has been detected for the first time. The angular size of the pulsar is 3″ at 25 MHz and 4″.8 at 20 MHz. The pulsar’s low-frequency spectrum deviates appreciably from the power law derived at higher frequencies.     

Decametric survey of discrete sources in the northern Sky

The latest data obtained in the course of the UTR-2 Very Low-Frequency Sky Survey within the declination zone 41° to 52° together with the data from a number of higher frequency surveys have been used to determine radio spectra for 194 radio sources in the frequency range 12.6 to 1400 MHz. The spectrum plots and parameters of the sources are presented.