# A study of halo and relic radio emission in merging clusters using the Murchison Widefield Array

## TL;DR

This study used the Murchison Widefield Array to analyze radio haloes and relics in merging galaxy clusters, estimating their spectra at low frequencies and providing new insights into their properties and classifications.

## Contribution

It is the first to estimate the low-frequency spectra of cluster haloes and relics, reclassify some sources, and set unprecedented upper limits on halo radio powers.

## Key findings

- Diffuse radio emission detected in 8 clusters.
- Spectral indices follow a power law with mean values around -1.1.
- Upper limits on halo powers are 2-20 times lower than expected.

## Abstract

We have studied radio haloes and relics in nine merging galaxy clusters using the Murchison Widefield Array (MWA). The images used for this study were obtained from the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey which was carried out at 5 frequencies, viz. 88, 118, 154, 188 and 215 MHz. We detect diffuse radio emission in 8 of these clusters. We have estimated the spectra of haloes and relics in these clusters over the frequency range 80-1400 MHz; the first such attempt to estimate their spectra at low frequencies. The spectra follow a power law with a mean value of $\alpha = -1.13\pm0.21$ for haloes and $\alpha = -1.2\pm0.19$ for relics where, $S \propto \nu^{\alpha}$. We reclassify two of the cluster sources as radio galaxies. The low frequency spectra are thus an independent means of confirming the nature of cluster sources. Five of the nine clusters host radio haloes. For the remaining four clusters, we place upper limits on the radio powers of possible haloes in them. These upper limits are a factor of 2-20 below those expected from the $L_{\rm X}-P_{\rm 1.4}$ relation. These limits are the lowest ever obtained and the implications of these limits to the hadronic model of halo emission are discussed.