Break in the Spectra

Since the energy loss due of synchrotron radiation $\propto$ $E^2$, the power law distribution of electron will change with time as the higher energy electron lose energy faster than the low energy electrons. The power law radio spectrum develops a break with different spectral indices on either side of the break and the break moves to lower frequencies as the synchrotron source ages. This break frequency can be used to make estimate about the age of the electron and magnetic field in the source. The figure 5.4 shows the synchrotron spectrum with a break around 150 MHz.

Figure 5.4: Synchrotron spectrum with a break around 150 MHz.

Power law spectra and breaks are usually seen in what are generally referred to as steep spectrum radio sources $\alpha > 0.5$. These sources are usually large and diffuse ($>$ few kilo-parsecs) and are usually optically thin.