scholarly journals Galactic and extra-galactic radio frequency radiation due to sources other than the thermal and 21-cm emission of the interstellar gas

1958 ◽  
Vol 5 ◽  
pp. 37-43
Author(s):  
R. Hanbury Brown
Keyword(s):  
Thermal Emission ◽  
Wave Length ◽  
Black Body ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Radio Frequency Radiation ◽  
The Galaxy ◽  
Image Position ◽  
Galactic Radio ◽  
Frequency Radiation

At wave-lengths greater than about one metre the majority of the radio emission which is observed from the Galaxy cannot be explained in terms of thermal emission from ionized interstellar gas. This conclusion is widely accepted and is based on observations of the equivalent temperature of the sky and the spectrum of the radiation. The spectrum at metre wave-lengths is of the general form: where TA is the equivalent black-body temperature of a region of sky and A is the wave-length. The exponent n varies with direction but lies between about 2·5 and 2·8, and is thus significantly greater than the value of 2·0 which is the maximum to be expected for thermal emission from an ionized gas. Furthermore the value of TA is about 1050 K at 15 m and thus greatly exceeds the electron temperature expected in H 11 regions.At centimetre wave-lengths it is likely that the majority of the radiation observed originates in thermal emission from ionized gas; however, the present discussion is limited to a range of wave-lengths from about 1 m to 10 m where the ionized gas in the Galaxy is believed to be substantially transparent and where the origin of most of the radiation is believed to be non-thermal.

scholarly journals 37. Galactic radio emission and the distribution of discrete sources: Introductory Lecture

1957 ◽  
Vol 4 ◽  
pp. 211-217
Author(s):  
R. Hanbury Brown
Keyword(s):  
Radio Emission ◽  
Thermal Emission ◽  
Wave Length ◽  
Black Body ◽  
Interstellar Gas ◽  
Ionized Gas ◽  
Introductory Lecture ◽  
The Galaxy ◽  
Image Position ◽  
Galactic Radio

At wave-lengths greater than about 1 metre the majority of the radio emission which is observed from the Galaxy cannot be explained in terms of thermal emission from ionized interstellar gas. This conclusion is widely accepted and is based on observations of the equivalent temperature of the sky and the spectrum of the radiation. The spectrum at metre wave-lengths is of the general form: where TA is the equivalent black-body temperature of a region of sky and λ is the wave-length. The exponent n varies with direction but lies between about 2·5 and 2·8, and is thus significantly greater than the value of 2·0 which is the maximum to be expected for thermal emission from an ionized gas. Furthermore, the value of TA is about 1050K. at 15 metres and thus greatly exceeds the electron temperature expected in H 11 regions.At centimetre wave-lengths it is likely that the majority of the radiation observed originates in thermal emission from ionized gas; however, the present discussion is limited to a range of wave-lengths from about 1 to 10 metres where the ionized gas in the Galaxy is believed to be substantially transparent and where the origin of most of the radiation is believed to be non-thermal.

Radio-Frequency Radiation from the Constellation of Cygnus

1952 ◽  
Vol 5 (1) ◽  
pp. 17 ◽  
Author(s):  
JH Piddington ◽  
HC Minnett
Keyword(s):  
Thermal Emission ◽  
Limited Extent ◽  
Interstellar Gas ◽  
Radio Frequency Radiation ◽  
Diffuse Source ◽  
Cygnus A ◽  
The Galaxy ◽  
New Evidence ◽  
Spiral Arm ◽  
Frequency Radiation

Observations are described of the radiation from portion of the constellation of Cygnus at frequencies of 1210 and 3000 Mc/s. Two sources of radiation were observed at the lower frequency, one being the well-known "radio star ", Cygnus-A. The other was a diffuse source of limited extent which might be called a " radio nebula ". Neither source could be observed at the higher frequency. The properties of both sources, particularly their spectra, are discussed and it is shown that earlier discrepancies in observations of the Cygnus region may be explained. The diffuse source coincides in position with the secondary maximum in the lower frequency galactic contours, which Bolton and Westfold (1950a, 1950b) have interpreted as a spiral arm of the Galaxy. The new evidence suggests that the source is probably due to thermal emission from clouds of ionized interstellar gas, possibly in the region of γ Cygni and having a temperature and electron density of the order of 104 �K, and 10 cm-3 respectively.

scholarly journals The generation of radio-frequency radiation in the sun

1948 ◽  
Vol 195 (1040) ◽  
pp. 82-97 ◽  
Keyword(s):  
Radio Frequency ◽  
Electron Temperature ◽  
Electric Fields ◽  
Solar Atmosphere ◽  
Solar Disk ◽  
Black Body ◽  
The Sun ◽  
Radio Frequency Radiation ◽  
Circularly Polarized ◽  
Frequency Radiation

Measurements of the radiation emitted by the sun at radio-frequencies have shown that the intensity greatly exceeds the value associated with a surface temperature of 6000° K. Under normal conditions the radiation, which appears to be randomly polarized, has an intensity which corresponds to the radiation from a black-body source subtending the same solid angle as the solar disk and at a temperature of about 10 6 °K. During the presence of sunspots very much more intense radiation is emitted by small areas of the solar disk; the intensity at these times corresponds to radiation from a source at a temperature of 10 9 to 10 10 °K, and the radiation is circularly polarized. The experimental results are considered theoretically in this paper, and it is concluded that the radiation in both cases arises from the acceleration of electrons in the solar atmosphere. It is suggested that by the action of the permanent magnetic field of the sun and the non-uniform rotation of the surface matter, a high potential difference is developed between the poles and the equator. Under normal conditions this potential can only produce small discharge currents through the solar atmosphere, although the electric field produced may be sufficient to maintain a mean electron temperature of 10 6 to 10 8 °K in the levels likely to emit radio-frequency radiation. During the presence of sunspots much more intense electric fields can be made available in the solar atmosphere, and in the neighbourhood of the sunspots electron temperatures of the order of 1010 °K should be maintained. A high-temperature electron gas can only radiate appreciably at those frequencies at which it absorbs well. An application of the magneto-ionic theory to the solar atmosphere above a sunspot shows that there are several regions capable of absorbing radiation at each frequency. For one of these regions the absorption (and therefore the radiating power) is very great, but radiation emitted by the region can only be propagated towards the centre of the sun. This region cannot therefore be responsible for the high-intensity radiation associated with sunspots, although the asymmetrical flow of energy from the region must produce an outward radiation pressure; this pressure may be of importance in accounting for the elevation of matter in the solar atmosphere above sunspots. Two other regions have a high absorption (each region absorbing one of the two circularly polarized components) and radiation from both regions can escape from the sun. Owing to the differences of radiating power and electron temperature in the two regions, it is likely that the intensities of the two emitted waves will be different. The radiation which is observed on the earth will therefore appear circularly polarized, the sense of the polarization corresponding to that of the most intense wave.

Solar Radio-Frequency Radiation of Thermal Origin

1949 ◽  
Vol 2 (2) ◽  
pp. 198 ◽  
Author(s):  
JL Pawsey ◽  
DE Yabsley
Keyword(s):  
Thermal Radiation ◽  
Wavelength Range ◽  
Black Body ◽  
Black Body Radiation ◽  
Kinetic Temperature ◽  
Radio Frequency Radiation ◽  
Thermal Origin ◽  
Outer Atmosphere ◽  
Frequency Radiation ◽  
Direct Confirmation

Observations of solar radiation in the wavelength range from one centimetre to four metres are studied in relation to expected thermal radiation. The data are derived partly from published and partly from unpublished observations. It is found that a relatively constant component can be identified throughout the whole of this wavelength range despite the complication introduced on the longer wavelengths by the presence of highly variable components. This steady component has the properties expected of thermal radiation and it is concluded that it is, in fact, thermal radiation from the ionized gases of the outer atmosphere of the sun. The intensity of radiation is found to increase fairly uniformly from that corresponding to black-body radiation at about 104 �K . at 1.25 cm. to about 106 �K. at 1.5 m. The results yield direct confirmation of the hypothesis that the corona has a kinetic temperature of about a million degrees.

scholarly journals An investigation of radio-frequency radiation from the sun

1948 ◽  
Vol 193 (1032) ◽  
pp. 98-120 ◽  
Keyword(s):  
Solar Radiation ◽  
Radio Frequency ◽  
Random Noise ◽  
Internal Noise ◽  
Black Body ◽  
Local Source ◽  
The Sun ◽  
Radio Frequency Radiation ◽  
Absolute Measurements ◽  
Frequency Radiation

It has been known for some time that the sun emits radio-frequency radiation whose intensity greatly exceeds the value expected from a black-body at 6000°K. In the present paper, experiments are described in which measurements have been made of the solar radiation at frequencies of 175 and 80 Mcyc. /sec. Measurement of the small powers which can be abstracted from practical aerial systems requires special types of receiving equipment if absolute measurements are to be recorded automatically over long periods of time. An apparatus has been developed in which the output power of a local source of random ‘noise’ is automatically and continuously adjusted so as to be equal to the aerial power; in this way the receiver is used only as an indicator of balance, and errors due to variation of its gain or internal noise are eliminated. A special type of aerial has been devised which enables the solar radiation to be recorded separately from the galactic radiation, and so enables continuous observation of the sun to be made with aerials of comparatively low directivity. The results obtained on these two frequencies show that the sun normally emits radiation whose intensity corresponds to a surface temperature of the order of 10 6 °K. Large fluctuations in the intensity occur, however, and during the passage of large sunspots, equivalent temperatures as high as 10 8 to 10 9 °K have been observed. In addition to these day-to-day variations the radiation is subject to sudden brief increases of intensity lasting only for a few seconds. Measurements of the diameter of the source, by a method analogous to Michelson’s stellar interferometer, have shown that during periods of very great intensity the radiation originates in an area of the sun of the same order of size as a sunspot. This result means that equivalent temperatures of 10 9 to 10 10 °K must exist. Measurements of the polarization of the radiation have shown that during periods of increased activity the radiation is mainly circularly polarized. The present account covers the experimental methods and the results obtained up to the present time. It is hoped to consider these results theoretically in a future paper.

scholarly journals Solar radiation in the radio spectrum - I. Radiation from the quiet sun

1948 ◽  
Vol 193 (1032) ◽  
pp. 44-59 ◽  
Keyword(s):  
Effective Temperature ◽  
Collision Frequency ◽  
Wave Length ◽  
Radio Spectrum ◽  
Quantum Mechanical ◽  
Ionized Gas ◽  
M Wave ◽  
Lorentz Theory ◽  
Mechanical Expression ◽  
Galactic Radio

The theory of the emission of thermal radiation from the solar envelope at radio-frequencies is worked out in detail. The Lorentz theory of absorption is used in conjunction with Kirchhoff’s law to derive the effective temperature of the various regions of the solar disk over the radio spectrum. A maximum effective temperature approaching 10 6 °C is found in the vicinity of 1 m. wave-length. Limb brightening occurs at centimetre wave-lengths. It is shown that Gaunt’s quantum mechanical expression for free-free emission yields results almost identical with the classical treatment, provided Chapman and Cowling’s expression for the collision frequency in a fully ionized gas is used in the latter treatment. It is suggested that it may be preferable to treat problems of solar and galactic radio noise by classical methods, particularly when the refractive index of the medium departs appreciably from unity.

Solar Radio-Frequency Emission from Localized Regions at Very High Temperatures

1951 ◽  
Vol 4 (2) ◽  
pp. 131
Author(s):  
JH Piddington ◽  
HC Minnett
Keyword(s):  
Radio Frequency ◽  
Solar Radio ◽  
Thermal Emission ◽  
Thermionic Emission ◽  
Magnetic Data ◽  
Radio Frequency Radiation ◽  
Sunspot Data ◽  
Polarization Characteristics ◽  
Frequency Radiation ◽  
Three Components

Solar radio-frequency radiation is analysed into three components ; a basic steady component B, a slowly varying component S, and various forms of more or less rapid fluctuations called the X component. The spectra of all three components are drawn between 600 and 24,000 Mc/s., and suggested extensions to lower frequencies are discussed. The properties of the S component are described in some detail ; these include correlation with sunspot data, polarization, and the location of the sources of origin. Evidence is presented in favour of generation by thermal processes. It is suggested that the S component is due to thermal emission from localized regions at temperatures of about 107 �K., often in the vicinity of sunspots. The radiation from a model hot region is examined in detail and the emission spectrum and polarization characteristics are derived. The results are found to compare reasonably with observation. Thermionic emission of electrons and protons would probably occur from the hot regions. These particles would travel to the Earth with average velocities of a few hundred kilometres per second and may be identical with the slow corpuscular radiation whose presence is deduced from terrestrial magnetic data.

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