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° 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 β_syn = 2.81 ± 0.16. Combining our data with maps made by Haslam et al. and Reich & Reich, we find β_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 β_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.