Spectral index

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The spectral index of a radio source can hint at its physical properties. The spectral index is calculated from $S\propto\nu^\alpha$ where $S$ is flux and $ν$ is frequency. A more direct formula for $α$ : $\alpha=\frac{\log(S_1/S_2)}{\log(\nu_1/\nu_2)}$

A spectral index of -.1 typically indicates thermal, or free-free, bremsstrahlung emission, while a steep spectral index of -.7 indicates synchrotron emission.