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Merging galaxy clusters produce low Mach number shocks in the intraclustermedium. These shocks can accelerate electrons to relativistic energies that aredetectable at radio frequencies. MACS J0744.9+3927 is a massive ($M_{500} =(11.8 \pm 2.8) \times 10^{14} M_{\odot}$), high-redshift ($z=0.6976$) clusterwhere a Bullet-type merger is presumed to have taken place. Sunyaev-Zel'dovichmaps from MUSTANG indicate that a shock, with Mach number $\mathcal{M} =1.0-2.9$ and an extension of $\sim 200$ kpc, sits near the centre of thecluster. The shock is also detected as a brightness and temperaturediscontinuity in X-ray observations. To search for diffuse radio emissionassociated with the merger, we have imaged the cluster with the LOw FrequencyARray (LOFAR) at 120-165 MHz. Our LOFAR radio images reveal previouslyundetected AGN emission, but do not show clear cluster-scale diffuse emissionin the form of a radio relic nor a radio halo. The region of the shock is onthe western edge of AGN lobe emission from the brightest cluster galaxy.Correlating the flux of known shock-induced radio relics versus their size, wefind that the radio emission overlapping the shocked region in MACSJ0744.9+3927 is likely of AGN origin. We argue against the presence of a reliccaused by diffusive shock acceleration and suggest that the shock is too weakto accelerate electrons from the intracluster medium.

Search for low-frequency diffuse radio emission around a shock in the massive galaxy cluster MACS J0744.9+3927