Short Centimeter Research Articles

Galactic synchrotron emission according to the data of the RZF survey conducted at the RATAN-600 radio telescope

Deep 1–49 cm surveys of the circumzenithal sky area performed using the RATAN-600 radio telescope allowed the spectral index of Galactic synchrotron emission in the 7.6–49 cm wavelength interval to be refined. The data obtained are inconsistent with the model of synchrotron emission adopted to interpret the results of the first year of the WMAP mission, which led to the hypothesis of the early secondary ionization of the Universe at redshifts Z > 10–30. New observations made with the RATAN-600 demonstrated the possibility of deep studies of the intensity and polarization of the microwave background (the E component) in ground-based experiments at short centimeter wavelengths. Galactic synchrotron emission may as well limit the possibilities of space- and ground-based studies of the polarization of cosmic microwave background radiation arising as a result of scattering induced by relic gravitational waves (the B component). The sky area studied with the RATAN-600 is intended to be used to interpret the PLANCK mission data in order to ensure a more detailed account of the role of the Galactic synchrotron emission.

Synthesis of magnetospheric radio emissions during and after the Jupiter/SL-9 collision

A worldwide network of ground-based and spaced-based radiotelescopes monitored the continuum emission of Jupiter from millimetric to kilometric wavelengths throughout the SL-9 impacts in July 1994. Within 2 days of the first impact, an increase of flux density was detected and confirmed by many observatories at wavelengths from 3 to 90 cm. The increase involved only the synchrotron emission from the energetic electrons trapped in the Jovian radiation belts. At decameter and kilometer wavelengths, normally from radio sources located in the polar regions, no abnormal emission can be associated with certainty with the impacts. At short centimeter and millimeter wavelengths a search was made for impact-associated changes in Jupiter's deep atmosphere, but no detections have been reported and confirmed. The present knowledge of the synchrotron radio emission from the Jovian radiation belts is reviewed and the changes which occurred during and after the collision are commented on. During the week of cometary impacts, the synchrotron flux density increased, depending on the wavelength, by 10–40% and the radio spectrum hardened. Following the week of impacts, the flux density decreased at all wavelengths, more rapidly at 36–90 cm than at 6–22 cm. The observed decline was not a simple exponential decay, and the timescale was more than 100 days at 6–20 cm and less than 30 days at 36–90 cm. The beaming curve was flattened and distorted during and after the impacts, with long-lasting enhancements localized in longitude. Two-dimensional images show that the belts became brighter than before the impacts, and they remained bright at least one week after the first impact. The increase of brightness at the magnetic equator was concentrated in a limited range of longitude, from ≈80 to ≈300°. The radial distance of the peak intensity decreased over that week. Images in 3-D, constructed from observations with the Australia Telescope Compact Array, reveal distinct brightenings confined in longitude that can be attributed to the longitudes of individual impacts or group of impacts.

Dual pulsations in solar radio bursts at short centimeter wavelengths

It is well known that the oscillating MHD waves drive periodic variations in the magnetic field. But how the MHD waves can be triggered in the flaring loops is not yet well known. It seems to us that this problem should be connected with the physical processes occurring in the flare loop during a solar flare. A peculiar solar flare event at 04:00–04:51 UT on May 23, 1990 was observed simultaneously with time resolutions 1 s and 10 ms by Nanjing University Observatory and Beijing Normal University Observatory, which are about 1000 km apart, at 3.2 cm and 2 cm wavelengths, respectively. Two kinds of pulsations with quasi-periods 1.5 s and 40 s were found in radio bursts at the two short centimeter waves; however, the shorter quasi-periodic pulsations were superimposed upon the longer ones. From the data analysis of the above-mentioned quasi-periodic pulsations and associated phenomena in radio and soft X-ray emissions during this flare event published in Solar Geophysical Data (SGD), the authors suggest that the sudden increase in plasma pressure inside (or underlying) the flare kernel due to the upward moving chromospheric evaporated gas, which is caused by the explosive collision heating of strong non-thermal electrons injected downwards from the microwave burst source, plays the important role of triggering agents for MHD oscillations (fast magneto-acoustic mode and Alfven mode) of the flare loop. These physical processes occurring in the flare loop during the impulsive phase of the solar flare may be used to account for the origin and observational characteristics of quasi-periodic pulsations in solar radio bursts at the two short centimeter wavelengths during the flare event of 1990 May 23. In addition, the average physical parameters N, T, B inside or underlying the flare kernel can be also evaluated.

A statistical research for solar radio pulsation at short centimeter band: AAnS 34/2 (1993)189–197

A statistical research for solar radio pulsation at short centimeter band: AAnS 34/2 (1993)189–197

A non-linear modulation model for the fine structures in the solar short centimeter wave radio bursts

A theoretical model is presented here for the fine structures in the solar short centimeter radio bursts discovered recently. The three waves resonance interaction can occur when this radio emission, on its way outward through the corona, interacts with a MHD wave in the corona. In this way, a non-linear modulation in the emission flux can be induced. This model can satisfactorily interpret the inverse proportion relation between the emission flux and repetition rates of the fine structures. Moreover, this theoretical model anticipates that the period of modulation is related to the emission frequency, and the modulated amplitude of the fine structures is independent of the radio flux.

Multifrequency radio observations of coronal holes, filaments and cavities on RATAN–600

AbstractOn the basis of multifrequency solar radio observations made on RATAN–600 radiotelescope with high spatial resolution at nine wavelengths in the 2–32–wavelength range is shown that filaments and cavities are well detected on the solar scans at short centimeter wavelengths as the regions of low radio brightness with angular dimensions of 25′–80′ in E—W direction. The tendency of decreasing radio sizes for cavities and filaments from 2.0 to 8.0 cm is observed. The coronal hole (CH) is more contrast in the range of 8–32 cm. The radio size of CH in E—N direction increases from 2′ (at 8.2) to 5′.0 (at 31.6 cm). The spectra of the brightness temperature of CH and the quiet Sun are obtained. The brightness temperature of CH is twice lower than that of the quiet Sun at wavelength of 31.6 cm.

The Nucleus of NGC1275

The bright radio nucleus 3C84 of the peculiar galaxy NGC1275 was among the first sources studied by VLBI techniques sixteen years ago (Clark et al., 1968). Early observations at short centimeter wavelengths using arrays of up to four telescopes (Schilizzi et al., 1975, and references therein) demonstrated the presence of structure significantly more complex than that seen in other strong compact objects, but were insufficient to determine the brightness distribution with the relatively primitive methods then in use. By the time of the most recent international VLBI symposium (Aug. 1978, in Heidelberg, FRG), Pauliny-Toth et al. (1976) had succeeded in modelling the structure seen by a 4-station transatlantic array, revealing three distinct bright emission regions aligned in position angle −9°, and connected by non-colinear, more diffuse features. Further observations and a reanalysis of earlier data by Preuss et al. (1979) confirmed previous inferences that the three major condensations remained stationary but varied in brightness.

31.4-GHz flux density measurements of a complete sample of sources from the 5-GHz S5 survey

Measurements at 31.4-GHz (9.5-mm) are presented for the complete sample of 66 radio sources with declinations greater than +70/sup 0/ and 5-GHz flux densities greater than 0.5 Jy. About half the sources have the flat radio spectra characteristic of objects with compact components radiating most strongly in the mid-centimeter wavelength range, and about one third show evidence of very compact components (theta< or approx. =0.//0001) radiating at short centimeter wavelengths regardless of morphological type. The median spectral index of all the sources, the quasars alone, and the galaxies alone tends to flatten with increasing frequency for steep spectrum sources, whereas a steepening was found with increasing frequency for the flat spectrum sources.

Evidence for the depletion of ammonia in the Uranus atmosphere

The theoretical disk brightness temperature spectra for Uranus are computed and compared with the observed microwave spectrum. It is shown that the emission observed at short centimeter wavelengths originates deep below the region where ammonia would ordinarily begin to condense. We demonstrate that this result is inconsistent with a wide range of atmospheric models in which the partial pressure of NH 3 is given by the vapor-pressure equation in the upper atmosphere. It is estimated that the ammonia mixing ratio must be less than 10 −6 in the 150 to 200°K temperature range. This is two orders of magnitude less than the expected mixing ratio based on solar abundances. The evidence for this depletion and a possible explanation are discussed.

Avalanche Diode Noise Sources at Short Centimeter and Millimeter Wavelengths (Short Papers)

Semiconductor noise sources for microwave frequencies have been constructed using commercial avalanche diodes in waveguide mounts. For the diodes and waveguide configurations reported here the upper usable frequency is approximately 40 GHz. The measurements are in limited agreement with previous predictions. It is possible that a reduction in package and diode parasitic would improve this agreement, and raise appreciably the upper usable frequency of such noise sources.

Lunar microwave brightness temperature observations reevaluated in the light of Apollo program findings

Remote observations of the lunar radiowave emission are reexamined in the light of physical property data accumulated through the Apollo program. It is found that thermal and electrical properties determined for a number of different landing sites yield theoretical results in good agreement with remote observations for millimeter and short centimeter wavelengths. Theoretical models incorporating reflecting layers of rock and physical property data from the Apollo program are compared to the longer wavelength (5–500 cm) observational data to estimate a disk average steady state heat flow and a mean depth of the lunar regolith. It is found that a high heat flow, comparable to the heat flows measured at the Apollo 15 and 17 sites, is required to fit the available 5–20 cm wavelength remote data, and that a lunar surface layer relatively free of large boulders within the upper 10–30 m best fits the observations of a decreasing brightness temperature with wavelength for wavelengths greater than ∼ 50 cm.

Observations of the Radio Sources 3c 84, 3c 273, 3c 274, and 3c 279 AT Short Centimeter Wavelengths

Radio flux and linear polarization of various radio sources at short centimeter wavelengths in quasars study

Radio observations of Venus and the interpretations

The radio observations of Venus are reviewed and compared with theoretical microwave spectra computed for a variety of models of the Venusian environment. The models considered are (a) a CO2-N2 atmosphere, (b) an atmosphere of dust (the aeolosphere model), and (c) a cloud model with various loss mechanisms in the cloud. The effect of polarization on the surface emissivity has been included in all the computations. It is shown how the radio observations place limits upon the acceptable models, for example, the density and size of dust particles required in the aeolosphere model. It is shown how some models place severe restrictions on radar observations at short centimeter wavelengths, thereby emphasizing the importance of such experiments. These same models show that the Mariner II observations can not be interpreted in terms of surface phenomena and provide a new interpretation for the microwave phase effect.

A Broad-Band Microwave Source Comparison Radiometer for Advanced Research in Radio Astronomy

A sensitive microwave radiometer system operating at short centimeter wavelengths has been developed which will allow large extensions of the known spectra of a large number of radio sources; facilitate the measurement of source polarization; give information on galactic structure and the sources of galactic radio emission; provide new data on the physical structure of planetary nebulas; and provide a means of measuring more accurately planetary temperatures, and the precise position of the brighter radio sources. A traveling-wave tube radiometer operating at 8000 mc with a bandwidth of 1000 mc and sensitivities of the order of 0.01°K is described. The radiometer is more than one order of magnitude more sensitive than other existing radiometers operating at 8000 mc. The very serious effects of gain fluctuations, acting on small residual signals, when trying to achieve very high sensitivities, are discussed. A means of eliminating such effects by introducing compensating noise has been found successful. Radio observations with this radiometer in conjunction with a 28-foot parabolic reflector have shown that: 1) The predicted sensitivity is achieved. 2) Zero-level stability is extremely high. 3) It has been possible to detect in detail the distribution of radio brightness at this wavelength in the vicinity of the galactic plane. 4) Radiation from the planets Jupiter and Saturn has been detected, this being the first detection of Saturn as a radio source. 5) Radiation from two planetary nebulas has been detected, this being the first detection of these objects as radio sources.