A determination of the Spectral Index of Galactic Synchrotron Emission in the 1-10 GHz range

We present an analysis of simultaneous multifrequency measurements of the Galactic emission in the 1-10 GHz range with 18 degrees angular resolution taken from a high-altitude site. Our data yield a determination of the synchrotron spectral index between 1.4 and 7.5 GHz of beta(syn) = 2.81 +/- 0.16. Combining our data with maps made by Haslam et al. and Reich & Reich, we find beta(syn) = 2.76 +/- 0.11 in the 0.4-7.5 GHz range. These results are in agreement with the few previously published measurements. The variation of beta(syn) with frequency based on our results and compared with other data found in the literature suggests a steepening of the synchrotron spectrum toward high frequencies, as expected from theory because of the steepening of the parent cosmic-ray electron energy spectrum. Comparison between the Haslam data and the 19 GHz map of Cottingham also indicates a spatial variation of the spectral index on large angular scales. Additional high-quality data are necessary to provide a serious study of these effects.