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 ∼ 900 kpc in the direction of the jets and of ∼ 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 GHz = (4 ± 2) × 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.

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 diffuse radio component reaching a scale of ≈ 900 kpc in the direction of the jets and of ≈ 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 P1.4GHz = (4 ± 2) × 1024 W Hz−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, or to a combination of these two hypotheses. 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.