A Multifrequency Study of Double-Double Radio Galaxies
  One of the striking examples of episodic activity in active galactic nuclei
are the double-double radio galaxies (DDRGs) with two pairs of
oppositely-directed radio lobes from two different cycles of activity. We
illustrate, using the DDRG J1453+3308 as an example, that observations over a
wide range of frequencies using both the GMRT and the VLA can be used to
determine the spectra of the inner and outer lobes, estimate their spectral
ages, estimate the time scales of episodic activity, and examine any difference
in the injection spectra in the two cycles of activity. Low-frequency GMRT
observations also suggest that DDRGs and triple-double radio galaxies are
rather rare.
