The Spectra of Galactic and Extragalactic Radio Sources

Citation

Kellermann, Kenneth Irwin (1963) The Spectra of Galactic and Extragalactic Radio Sources. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/2CYZ-PE61. https://resolver.caltech.edu/CaltechETD:etd-04122004-164144

Abstract

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Observations have been made of the flux density of a number of discrete radio sources at 475, 710, 958, 1420, 2841, and 3200 Mc, using the two-element interferometer of the California Institute of Technology Radio Observatory. These have been combined with similar measurements at other frequencies made by different observers, to determine the spectral distribution for 242 sources where data is available over a wide range of frequencies.

It is shown that the spectra of most sources can be closely approximated by a simple power law of the form [...], at least between 38 and 1420 Mc. For these sources, the distribution of spectral indices is sharply peaked about a mean value of -0.77 with 50 per cent of the sources having an index between -0.70 and -0.85. No sources were found with an index steeper than -1.23. In most cases, the spectral index is a function of frequency over the observed range from 38 to 3200 Mc. For these sources, which generally have a high surface brightness, the typical change in spectral index is about 0.5 in the sense that the spectrum is flatter at longer wavelength.

The observed spectral distributions are interpreted in terms of synchrotron radiation and it is postulated that the bright sources having a curved spectrum are relatively young and rapidly evolving toward a power law spectrum.

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