  MS 0735.6+7421 ($z = 0.216$) is a massive cool core galaxy cluster hosting
one of the most powerful active galactic nuclei (AGN) outbursts known. The
radio jets of the AGN have carved out an unusually large pair of X-ray
cavities, each reaching a diameter of $200$ kpc. This makes MS 0735.6+7421 a
unique case to investigate active galactic nuclei feedback processes, as well
as other cluster astrophysics at radio wavelengths. We present new
low-radio-frequency observations of MS 0735.6+7421 taken with the Karl G.
Jansky Very Large Array (VLA): 5 hours of P-band ($224-480$ MHz) and 5 hours of
L-band ($1-2$ GHz) observations, both in C configuration. Our VLA P-band
($224-480$ MHz) observations reveal the presence of a new diffuse radio
component reaching a scale of $\sim$ $900$ kpc in the direction of the jets and
of $\sim$ $500$ kpc in the direction perpendicular to the jets. This component
is centered on the cluster core and has a radio power scaled at $1.4$ GHz of
$P_{1.4\text{ GHz}} = (4\pm2)\times 10^{24}$ WHz$^{-1}$. Its properties are
consistent with those expected from a radio mini-halo as seen in other massive
cool core clusters, although it may also be associated with radio plasma that
has diffused out of the X-ray cavities. Observations at higher spatial
resolution are needed to fully characterize the properties and nature of this
component. We also suggest that if radio mini-halos originate from jetted
activity, we may be witnessing the early stages of this process.

Astrophysics of Galaxies;High Energy Astrophysical Phenomena