A diffuse bubble-like radio-halo source MRC 0116+111: imprint of AGN
  feedback in a low-mass cluster of galaxies
  We present detailed observations of MRC 0116+111, revealing a luminous, mini
radio-halo of ~240 kpc diameter located at the centre of a cluster of galaxies
at redshift z = 0.131. Our optical and multi-wavelength GMRT and VLA radio
observations reveal a highly unusual radio source: showing a pair of giant
(~100 kpc diameter) bubble-like diffuse structures, that are about three times
larger than the analogous extended radio emission observed in M87 - the
dominant central radio galaxy in the Virgo Cluster. However, in MRC 0116+111 we
do not detect any ongoing Active Galactic Nucleus (AGN) activity, such as a
compact core or active radio jets feeding the plasma bubbles. The radio
emitting relativistic particles and magnetic fields were probably seeded in the
past by a pair of radio-jets originating in the AGN of the central cD galaxy.
The extremely steep high-frequency radio spectrum of the north-western bubble,
located ~100 kpc from cluster centre, indicates radiation losses, possibly
because having detached, it is rising buoyantly and moving away into the
putative hot intra-cluster medium. The other bubble, closer to the cluster
centre, shows signs of ongoing particle re-acceleration. We estimate that the
radio jets which inflated these two bubbles might have also fed enough energy
into the intra-cluster medium to create an enormous system of cavities and
shock fronts, and to drive a massive outflow from the AGN, which could
counter-balance and even quench a cooling flow. Therefore, this source presents
an excellent opportunity to understand the energetics and the dynamical
evolution of radio-jet inflated plasma bubbles in the hot cluster atmosphere.
