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In this work, we analysed new LOw Frequency ARray observations of the minihalo in the cluster RBS797, together with archival Very Large Arrayobservations and the recent Chandra results. This cluster is known to host apowerful active galactic nucleus (AGN) at its centre, with two pairs of jetspropagating in orthogonal directions. Recent X-ray observations have detectedthree pairs of shock fronts, connected with the activity of the central AGN.Our aim is to investigate the connection between the mini halo emission and theactivity of the central source. We find that the diffuse radio emission iselongated in different directions at 144 MHz (east-west) with respect to 1.4GHz (north-south), tracing the orientation of the two pairs of jets. The minihalo emission is characterised by an average spectral index $\alpha=-1.02\pm0.05$. The spectral index profile of the mini halo shows a gradual flatteningfrom the centre to the periphery. Such a trend is unique among the mini halosstudied to date, and resembles the spectral index trend typical of particlesre-accelerated by shocks. However, the estimated contribution to the radiobrightness profile coming from shock re-acceleration is found to beinsufficient to account for the radial brightness profile of the mini halo. Wepropose three scenarios that could explain the observed trend: (i) theAGN-driven shocks are propagating onto an already existing mini halo,re-energising the electrons. We estimate that the polarisation induced by theshocks could be detected at 6 GHz and above; (ii) we could be witnessingturbulent re-acceleration in a high magnetic field cluster; and (iii) the minihalo could have a hadronic origin, in which the particles are injected byFuture observations in polarisation would be fundamental to understand the roleof shocks and the magnetic field.

Shock imprints on the radio mini halo in RBS797