The Continuous Spectra of Radio Sources with Particular Reference to Non-Thermal Galactic Sources

Citation

Harris, Daniel Everett (1961) The Continuous Spectra of Radio Sources with Particular Reference to Non-Thermal Galactic Sources. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/N09S-3J04. https://resolver.caltech.edu/CaltechETD:etd-03232006-111338

Abstract

960 Mc observations of over 400 sources are reported in two parts. Part I contains position and intensity measurements of 106 sources (chiefly taken from the recent Cambridge surveys), and the results of 376 intensity measurements of sources previously observed at Sydney. Spectral indices are derived from the intensity measurements and the previous investigator's observations. The resulting spectral index distribution has a median value of -0.65 ± 0.10 and a dispersion such that 75% of the values lie within 0.25 of the median. Galactic sources show a larger dispersion of spectral index than do the sources assumed to be external galaxies.

Part II is based on 960 Mc observations of extended galactic nebulae, usually identified with supernova remnants. Contour diagrams of antenna temperature are presented for four of the larger objects. A detailed study of the Cygnus Loop shows that the radio emission is chiefly non-thermal, with a spectral index of -0.1 ± 0.1. An attempt to detect linear polarization places an upper limit of 30% for selected regions of the Cygnus Loop. Spectral indices ranging from -0.8 to +0.5 are derived for 12 other sources. Calculations show that the occurrence of optical synchrotron radiation is not ruled out by existing observations. An empirical relation between spectral index and physical size of supernova remnants suggests that the energy spectrum of relativistic particles flattens with age. A possible mechanism for this behavior is considered.

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