J1216+0709 : A radio galaxy with three episodes of AGN jet activity
  We report the discovery of a `Triple-Double Radio Galaxy (TDRG)' J1216+0709
detected in deep low-frequency Giant Metrewave Radio Telescope (GMRT)
observations. J1216+0709 is only the third radio galaxy, after B0925+420 and
Speca, with three pairs of lobes resulting from three different episodes of AGN
jet activity. The 610 MHz GMRT image clearly displays an inner pair of lobes, a
nearly co-axial middle pair of lobes and a pair of outer lobes that is bent
w.r.t. the axis of inner pair of lobes. The total end-to-end projected sizes of
the inner, middle, and outer lobes are 40$^{{\prime}{\prime}}$ ($\sim$ 95 kpc),
1$^{\prime}$.65 ($\sim$ 235 kpc) and 5$^{\prime}$.7 ($\sim$ 814 kpc),
respectively. Unlike the outer pair of lobes both the inner and middle pairs of
lobes exhibit asymmetries in arm-lengths and flux densities, but in opposite
sense, i.e., the eastern sides are farther and also brighter that the western
sides, thus suggesting the possibility of jet being intrinsically asymmetric
rather than due to relativistic beaming effect. The host galaxy is a bright
elliptical (m$_{\rm r}$ $\sim$ 16.56) with M$_{\rm SMBH}$ $\sim$ 3.9 $\times$
10$^{9}$ M$\odot$ and star-formation rate of $\sim$ 4.66$_{\rm -1.61}^{\rm
+4.65}$ M$_{\odot}$ yr$^{-1}$. The host galaxy resides is a small group of
three galaxies (m$_{\rm r}$ $\leq$ 17.77) and is possibly going through the
interaction with faint, dwarf galaxies in the neighbourhood, which may have
triggered the recent episodes of AGN activity.
