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We report on the detection of a giant radio halo in the cluster Abell 3404 aswell as confirmation of the radio halo observed in Abell 141 (with linearextents $\sim 770$ kpc and $\sim 850$ kpc, respectively). We use the MurchisonWidefield Array (MWA) in conjunction with the Australian Square Kilometre ArrayPathfinder (ASKAP) and the Australia Telescope Compact Array (ATCA) tocharacterise the emission and intervening radio sources from $\sim100$-$1000$MHz; power law models are fit to the spectral energy distributions withspectral indices $\alpha_{88}^{1110} = -1.66 \pm 0.07$ and $\alpha_{88}^{944} =-1.06 \pm 0.09$ for the radio halos in Abell 3404 and Abell 141, respectively.We find strong correlation between radio and X-ray surface brightness forAbell~3404 but little correlation for Abell~141. We note each cluster has anatypical morphology for a radio-halo--hosting cluster, with Abell 141 havingbeen previously reported to be in a pre-merging state, and Abell 3404 islargely relaxed with only minor evidence for a disturbed morphology. We findthat the radio halo power is consistent with the current radio halo sample and$P_\nu$-$M$ scaling relations, but note that the radio halo in Abell 3404 is anultra-steep-spectrum radio halo (USSRH) and, as with other USSRHs lies slightlybelow the best-fit $P_{1.4}$-$M$ relation. We find that an updated scalingrelation is consistent with previous results and shifting the frequency to 150MHz does not significantly alter the best-fit relations with a sample of 86radio halos. We suggest that the USSRH halo in Abell 3404 represents the faintclass of radio halos that will be found in clusters undergoing weak mergers.

MWA and ASKAP observations of atypical radio-halo-hosting galaxy clusters: Abell 141 and Abell 3404