We report on the detection of a giant radio halo in the cluster Abell 3404 as well as confirmation of the radio halo observed in Abell 141 (with linear extents $\sim\!770$ and $\sim\!850$ kpc, respectively). We use the Murchison Widefield Array, the Australian Square Kilometre Array Pathfinder, and the Australia Telescope Compact Array to characterise the emission and intervening radio sources from $\sim100$ to 1 000 MHz; power law models are fit to the spectral energy distributions with spectral indices $\alpha_{88}^{1\,110} = -1.66 \pm 0.07$ and $\alpha_{88}^{943} = -1.06 \pm 0.09$ for the radio halos in Abell 3404 and Abell 141, respectively. We find strong correlation between radio and X-ray surface brightness for Abell 3404 but little correlation for Abell 141. We note that each cluster has an atypical morphology for a radio-halo-hosting cluster, with Abell 141 having been previously reported to be in a pre-merging state, and Abell 3404 is largely relaxed with only minor evidence for a disturbed morphology. We find that the radio halo powers are consistent with the current radio halo sample and $P_\nu$ –M scaling relations, but note that the radio halo in Abell 3404 is an ultra-steep–spectrum radio halo (USSRH) and, as with other USSRHs lies slightly below the best-fit $P_{1.4}$ –M relation. We find that an updated scaling relation is consistent with previous results and shifting the frequency to 150 MHz does not significantly alter the best-fit relations with a sample of 86 radio halos. We suggest that the USSRH halo in Abell 3404 represents the faint class of radio halos that will be found in clusters undergoing weak mergers.

中文翻译：

---

MWA 和 ASKAP 对非典型无线电晕托管星系团的观测：Abell 141 和 Abell 3404

我们报告了在 Abell 3404 星团中检测到一个巨大的无线电晕，并确认了在 Abell 141 中观察到的无线电晕（线性范围 $\sim\!770$ 和 $\sim\!850$ kpc，分别）。我们使用默奇森宽场阵列、澳大利亚平方公里阵列探路者和澳大利亚望远镜紧凑型阵列来表征来自 $\sim100$ 至 1 000 MHz；幂律模型适合具有光谱指数的光谱能量分布 $\alpha_{88}^{1\,110} = -1.66 \pm 0.07$ 和 $\alpha_{88}^{943} = -1.06 \pm 0.09$ 分别为 Abell 3404 和 Abell 141 中的无线电晕。我们发现 Abell 3404 的射电和 X 射线表面亮度之间有很强的相关性，但 Abell 141 的相关性很小。我们注意到，每个星团都具有非典型的射电晕托管星团形态，此前有报道称 Abell 141 在合并前的状态，Abell 3404 在很大程度上放松了，只有少量证据表明其形态受到干扰。我们发现射电晕功率与当前的射电晕样本一致，并且 $P_\nu$ –米比例关系，但请注意，Abell 3404 中的无线电晕是一个超陡频谱无线电晕 (USSRH)，并且与其他 USSRH 一样，略低于最佳拟合 $P_{1.4}$ –米关系。我们发现更新后的比例关系与之前的结果一致，将频率移至 150 MHz 不会显着改变与 86 个无线电晕样本的最佳拟合关系。我们认为 Abell 3404 中的 USSRH 晕代表了在经历弱合并的星团中会发现的一类微弱的射电晕。