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Therefore, the spectral index (S ν ∝ ν −α ) is around α ' 0.7.
Thus, we can now explain the observed positive spectral indices of the
spectra of the non–thermal sources such as Crab Nebula, Cygnus A, 3C273,
the disturbed Sun, etc. (Figure 30).

Figure 30: Spectra of continuum radio sources, including non–thermal
sources with positive spectral indices (Kraus, 1986; left), and the Crab Neb-
ula supernova remnant, a typical synchrotron radiation source.

References

Einstein, A., 1916, Zur Quantentheorie der Strahlung, Mitt. Phys.
Ges. (Z¨urich), 18, 47–62. (This paper was also published in
Physikalishe Zeitschrift, 1917, 18, 121.)
Kaifu, N., Suzuki, H., Ohishi, M., Morimoto, M., and Miyaji, T.,
1985, NRO Graphic Report No.1 (Nobeyama, Japan).
Kraus, J.D., 1986, Radio Astronomy, 2nd Edition, Cygnus–Quasar
Books (Powell, Ohio, U.S.A.).
Rohlfs, K., and Wilson, T.L., 2000, Tools of Radio Astronomy,
3rd Edition, Springer–Verlag (Germany).

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