Radio Brightness Distribution Research Articles

Time-dependent radio fine structure of the quasar 3C 345

Results are reported for VLBI observations of 3C 345 at a wavelength of 3.8 cm with left circular polarization. Sixteen sets of correlated flux densities and three sets of closure phases were obtained from observations made over a three-year period with six independent interferometers formed from up to four antennas. The mathematical models employed to represent the radio brightness distribution of the source are described, and the data are analyzed on the basis of a two-component model. The results show that the compact source in 3C 345 consists of two components whose separation increased by about 0.3 milliarcsec over the observational period, that the smaller and weaker component is to the east and south of the larger and stronger one, and that the apparent expansion velocity would be about 2.5c for a redshift of 0.6, a Hubble constant of 60 km/sec per Mpc, and a deceleration parameter of unity. It is concluded that these findings are difficult to reconcile with the 'Christmas tree' model for the apparent change of separation with time over any given series of observations.

The radio brightness distribution of eight Markarian galaxies

The radio brightness distribution of eight Markarian galaxies

Radio brightness distribution of 3C273

THE radio source 3C273 was one of the first to be identified1 with a QSO. The main features of the brightness distribution have been established from lunar occupation studies2–5, which show that the source is double, with one component coincident with a 13 mag QSO or redshift 0.158. This component, 3C273B, is variable, and has an inverted radio spectrum. The component is compact, and details of its structure have been investigated with inter-continental (VLBI) interferometers6–8. The other component, 3C273A, has a normal radio spectrum and is identified with a faint optical jet lying in position angle 223° with respect to the QSO. Component A has extended radio structure, and is not detected in VLBI observations8. The colours of the jet indicate that the optical emission, like the radio emission from component A, is non-thermal9,10. The optical jet of 3C273 is an extremely unusual feature, and it would be interesting to make a detailed comparison of the optical and radio structure associated with the component. We provide here detailed information of the radio brightness distribution.

Solar limb brightening at millimeter wavelengths

The radio brightness distribution at λ9 mm, λ3.5 mm and λ1.2 mm is calculated employing a statistical technique to account for the presence of spicules randomly occurring along the ray path. The results indicate limb brightening at each wavelength when the Avery and House (1969) spicule model is employed. This contradicts the results of Lantos and Kundu (1972) whose method of computation is shown to be inadequate.

Observations of Cygnus a with the 5-km Radio Telescope

Maps of the distribution of radio brightness and polarization in Cygnus A at 5 GHz have been made with an angular resolution of |$2^".0\times3^".1$| arc. These show details of the structure of the compact features in the parts of the source most distant from the optical galaxy, as well as the structure and particularly the strong polarization in parts of the extensive tails. Some limited observations at 15 GHz with a resolution of 0″.4 arc have been used to define more closely the shape of the compact components. A weak central source < 1.5 kpc in diameter has been found which lies between the two optical ‘nuclei’ in photographs of the central region of the galaxy. On the assumption of equipartition between relativistic electrons and magnetic field, and from a study of the spectral distribution, it is concluded that there must be a continuous replenishment of energetic electrons within each of the two main compact components of the source, representing an energy supply of ∼ 1045 erg s−1. These electrons must diffuse out into the extensive tail regions on a time scale ≲ 4 × 104 yr and probably provide the entire energy requirements of these regions; the subsequent radiation losses provide an explanation of the change in the spectral index of the integrated emission at ∼ 1 GHz. The evidence now available is inconsistent with several of the physical models which have been proposed. The inertial and de Young & Axford models are incompatible with the upper limits on the masses of the components, as derived from the measurements of polarization, and do not account for the detailed shape of the components. Models based on a high temperature, high density ambient gas to provide the pressure needed to contain the compact components do not explain the physical alignment of the components with the central nucleus. The models most likely to provide a satisfactory explanation of the details observed seem to be those in which energy is continually transported to the components from the nucleus in the form of energetic particles or low frequency waves.

The problem of reconstructing the solar radiobrightness distribution

The problem of reconstructing the solar radiobrightness distribution

The darkening ring in the solar radiobrightness distribution at the ?=3 cm wavelength (polar region)

The darkening ring in the solar radiobrightness distribution at the ?=3 cm wavelength (polar region)

Radio-brightness distribution in the Crab Nebula at wavelengths in the centimeter and millimeter ranges

Radio-brightness distribution in the Crab Nebula at wavelengths in the centimeter and millimeter ranges

Numerical realization of the algorithm for restoration of radio images using the example of the radio-brightness distributions of the Crab Nebula (the one-dimensional case)

Numerical realization of the algorithm for restoration of radio images using the example of the radio-brightness distributions of the Crab Nebula (the one-dimensional case)

Determination of the radio brightness distribution over a source using a radio interferometer with independent heterodynes

Determination of the radio brightness distribution over a source using a radio interferometer with independent heterodynes

An electronic-optical processor for correlation arrays

A hybrid electronic-optical signal-processing system which can be applied to the recording and the reconstruction of one-and two-dimensional images of a radio-brightness distribution is described.

Electrons magnetic fields and background radio emission in the galaxy

Extensive data now available on the non-thermal background radio emission from different celestial directions, and recent measurements on the energy spectrum of cosmic ray electrons in the vicinity of the earth permit one to deduce information on the mean magnetic fields and cosmic electron spectra needed to exist in different regions of the Galaxy. It is found that in order to explain quantitatively the background radio brightness distributions from the Galaxy one needs (i) the same or nearly same electron spectrum that exists in the near interstellar space, to exist in almost all regions of Galactic space, (ii) a mean magnetic field close to 6×10−6 Gauss in the Disc in the direction of the Anti-centre, (iii) a mean magnetic field close to 2·5×10−6 Gauss in the radio Halo and (iv) a mean magnetic field probably close to 9·5×10−6 Gauss towards the Galactic Ridge in the direction of the Centre. Some inferences are also drawn on the confinement of cosmic rays in the Galaxy.

Techniques for Decimetre Wavelength Observations of Radio Plages and Bursts

The first daily maps showing the two-dimensional radio brightness distribution over the Sun were produced at Fleurs ten years ago when the 64-antenna grating cross was completed. The maps had a resolution of 3′ arc at λ = 21 cm.When the Fleurs field station was given to the University by CSIRO in 1963 it was decided to use the antennas of the grating cross and add to them four or more larger antennas (45 ft diameter) to produce a pair of high resolving-power compound interferometers.

Radio frequency synchrotron radiation from the Van Allen belts

Consider the case of Figure 1 in which an observer in space observes the earth at radio frequencies. In particular, consider the radio brightness distribution in one dimension; i.e. let the observer look at the earth such that he looks in the equatorial plane of the centered dipole model for the geomagnetic field. The question to be considered is how does the radio brightness b vary with the direction and frequency of observation. An estimate of b(R, ƒ) is made below assuming that the electrons in the Van Allen belts radiate in the synchrotron mode.

Measurements of lunar radio brightness distribution and certain properties of its surface layer

The construction of high resolution telescopes, including the 22 m radio telescope RT 22, developed at the P. N. Lebedev Physical Institute, made it possible to investigate the distribution of lunar radio brightness in the millimetre and centimetre wavelength ranges. Such research provides information which makes it possible to deduce certain properties of the surface layer which is responsible for radiation emission. During the first stage of the studies, which were carried out at the wavelengths of 4 mm, 8 mm, 2 cm and 3·2 cm, we observed the law of the decrease of the surface temperature from the equator to the poles, which turned out to be close to √cos ψ . The average effective dielectric constant was esti­mated as ∊ = 1·5. The measured phase dependence of the brightness temperature in the centre of the lunar disk, measured at the indicated wavelengths, is in good agreement with the results of calculations in terms of the one-layer model. With values of the material dielectric constant and density taken equal to those of terrestrial rock materials, the obtained measurements lead to a value of effective density of the surface layer of approximately ρ = 0·6 g/cm 3 . Using γ = ( kpc ) –½ = 400–600 (which follows from the phase dependence curves of the brightness temperature for the centre of lunar disk) and c = 0·2 cal./g, we obtain k ≃ 2 x 10 –5 cal cm –1 deg –1 s –1 . The penetration depth of the thermal wave under these conditions is close to 10 cm. A method of relative measurements has been developed for the detection of brightness temperature distinctions (‘radio contrasts’) of ‘sea’ and ‘continental’ regions on the Moon, using the new known averaged data characteristics of lunar radio emission. It was shown that the radio contrasts may depend mainly upon the differences among night surface temperatures connected with different values of the δ parameter, as well as upon the difference between the values of variable component of the brightness temperature, connected with different values of the δ parameter, which expresses the ratio of the depths of penetration of electromagnetic and thermal waves. The comparative measurements which were carried out in the 4 and 8 mm wavelength ranges showed relatively small contrasts between the brightness temperatures of ‘sea’ and ‘continental’ regions. The average excess temperature of the ‘sea’ region during a period of lunation was 1·5 ± 0·5 %. We came to the conclusion, which is in agreement with the results of measurements in 8 to 13 μ m interval, that the difference in night surface temperatures in the regions compared is about 8 degK. The difference in the values of the parameter γ corresponding to this difference is not more than 25 %. This indicates a high degree of homo­geneity of the material in the compared regions. The results of analogous measurements, carried out by B. Ya. Losovsky in the 16 mm wavelength range confirms this conclusion.

Small Diameter Components in the Crab Nebula at 1,422 Mc/s

PREVIOUS radio surveys of the Crab nebula at frequencies greater than 80 Mc/s show a generally smooth and slightly asymmetrical distribution of radio brightness with an angular extent of about 5 min of arc. The spectral index of this radiation is quite uniform over the source (approximately − 0.25 to −0.35) and can be explained as synchrotron emission. Recently, considerable interest has been aroused by the detection at Cambridge1,2 of a small diameter source which comprised 30–50 per cent of the radiation at 26.5 Mc/s. This source was found to have an extraordinarily high spectral index (− 1.2), so that at 408 Mc/s it contributes only about 2.5 per cent of the total flux. Subsequently, observers at Parkes3 reported the results of a lunar occultation at 404 and 1,420 Mc/s. In addition to the large scale structure, smaller components of size less than 1 min of arc were also detected at both frequencies. These were found to correspond to regions of intense optical emission, and are labelled A, B and C in Fig. 1.

The Maximum Resolution of a Radio Telescope Imposed by Corona Scattering

The scattering of radio waves in the solar corona will eradicate the fine structure of radio source brightness distributions. The magnitude of this effect is estimated for observations in various directions by a radio telescope situated at the earth. Even for observation in the antisolar direction, this effect may limit the resolution attainable by radio telescopes that would be otherwise technically feasible.

Some aspects of the problem of determining the true radio brightness distribution over the sky

Some aspects of the problem of determining the true radio brightness distribution over the sky

Measurements of lunar radio brightness distribution and certain properties of its surface layer

The construction of high resolution telescopes, including the 22 m radio telescope RT 22, developed at the P. N. Lebedev Physical Institute, made it possible to investigate the distribution of lunar radio brightness in the millimetre and centimetre wavelength ranges. Such research provides information which makes it possible to deduce certain properties of the surface layer which is responsible for radiation emission. During the first stage of the studies, which were carried out at the wavelengths of 4 mm, 8 mm, 2 cm and 3·2 cm, we observed the law of the decrease of the surface temperature from the equator to the poles, which turned out to be close to √cos ψ . The average effective dielectric constant was esti­mated as ∊ = 1·5. The measured phase dependence of the brightness temperature in the centre of the lunar disk, measured at the indicated wavelengths, is in good agreement with the results of calculations in terms of the one-layer model. With values of the material dielectric constant and density taken equal to those of terrestrial rock materials, the obtained measurements lead to a value of effective density of the surface layer of approximately ρ = 0·6 g/cm 3 . Using γ = ( kpc ) –½ = 400–600 (which follows from the phase dependence curves of the brightness temperature for the centre of lunar disk) and c = 0·2 cal./g, we obtain k ≃ 2 x 10 –5 cal cm –1 deg –1 s –1 . The penetration depth of the thermal wave under these conditions is close to 10 cm. A method of relative measurements has been developed for the detection of brightness temperature distinctions (‘radio contrasts’) of ‘sea’ and ‘continental’ regions on the Moon, using the new known averaged data characteristics of lunar radio emission. It was shown that the radio contrasts may depend mainly upon the differences among night surface temperatures connected with different values of the δ parameter, as well as upon the difference between the values of variable component of the brightness temperature, connected with different values of the δ parameter, which expresses the ratio of the depths of penetration of electromagnetic and thermal waves. The comparative measurements which were carried out in the 4 and 8 mm wavelength ranges showed relatively small contrasts between the brightness temperatures of ‘sea’ and ‘continental’ regions. The average excess temperature of the ‘sea’ region during a period of lunation was 1·5 ± 0·5 %. We came to the conclusion, which is in agreement with the results of measurements in 8 to 13 μ m interval, that the difference in night surface temperatures in the regions compared is about 8 degK. The difference in the values of the parameter γ corresponding to this difference is not more than 25 %. This indicates a high degree of homo­geneity of the material in the compared regions. The results of analogous measurements, carried out by B. Ya. Losovsky in the 16 mm wavelength range confirms this conclusion.

Detection of Fine Structure in the Crab Nebula at 38 Mc/s

SEVERAL observations of the distribution of radio brightness across the Crab Nebula have been reported over a wide range of frequencies1,2,4–6. The results indicate that the distribution, while slightly elongated, has an approximately Gaussian profile. There is some evidence that the angular diameter increases at the lowest frequencies1, but no fine structure has been detected. Kuz'min and Salamonovich6, observing at a wave-length of 8 mm, noted a small source slightly displaced from the centre of the nebula which they ascribed to an independent source of thermal origin.