The largest galaxy clusters are observed still to be forming through major cluster-cluster mergers , often showing observational signatures such as radio relics and giant radio haloes .
Using LOFAR Two-meter Sky Survey data , we present new detections of both a radio halo ( with a spectral index of \alpha _ { 143 } ^ { 1400 } = 1.48 ^ { +0.06 } _ { -0.23 } ) and a likely radio relic in Abell 959 , a massive cluster at a redshift of z = 0.288 .
Using a sample of clusters with giant radio haloes from the literature ( 80 in total ) , we show that the radio halo in A959 lies reasonably well on the scaling relations between the thermal and non-thermal power of the system .
Additionally , we find evidence that steep-spectrum haloes tend to reside in clusters with high X-ray luminosities relative to those expected from cluster LM scaling relations , indicating that such systems may preferentially lie at an earlier stage of the merger , consistent with the theory that some steep-spectrum haloes result from low-turbulence mergers .
Lastly , we find that halo systems containing radio relics tend to lie at lower X-ray luminosities , relative to those expected from cluster LM scaling relations , for a given halo radio power than those without relics , suggesting that the presence of relics indicates a later stage of the merger , in line with simulations .