The correlation function of Galactic synchrotron radiation

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Abstract
A key problem in contemporary astrophysics is to determine the fluctuations in the cosmic microwave background, insofar as these fluctuations carry crucial cosmological information about the early universe at z approximately 1000 when the decoupling of matter and radiation took plane. However, for frequencies below about 30 GHz at least, these fluctuations are seen against a foreground due to the Galactic synchrotron radiation (GSR) and the fine structure of this radiation is not well understood. The authors examine the fluctuations in the GSR in some detail. The reason for the study is not only the cosmological aspect-the fluctuations also have relevance to the cosmic ray origin problem. It is argued that the fluctuations should depend largely on the fluctuations of the Galactic magnetic field along the line of sight when measured over limited regions of the sky. The correlation functions have been derived for different assumptions about the magnetic field irregularity spectrum using an 'object' model, in which the interpretation of the correlation function has a simple meaning. It is shown that the correlation functions are not very sensitive to the magnetic spectrum, apart from the case where most of the magnetic energy resides in small structures. The results are compared with the data, although the comparison is not straightforward and the conclusion about the magnetic spectrum parameters is somewhat uncertain.

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