MNRAS 000, 1–13 (2015) Preprint 19 February 2016 Compiled using MNRAS L A T E X style file v3.0 A Newly-Discovered Radio Halo in Merging Cluster MACS J2243.3-0935 T. M. Cantwell 1⋆ , A. M. M. Scaife 1 , N. Oozeer 2,3,4 , Z. L. Wen 5 , J. L. Han 5 1 Jodrell Bank Centre for Astrophysics, Alan Turing Building, Oxford Road, Manchester M13 9PL, UK. 2 SKA South Africa, The Park, Park Road, Pinelands, Cape Town 7405, South Africa. 3 African Institute for Mathematical Sciences, 6-8 Melrose Road, Muizenberg 7945, South Africa 4 Centre for Space Research, North-West University, Potchefstroom 2520, South Africa. 5 National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, China. Accepted XXX. Received YYY; in original form ZZZ ABSTRACT We report the discovery of a radio halo in the massive merging cluster MACSJ2243.3- 0935, as well as a new radio relic candidate, using the Giant Meterwave Radio Tele- scope and the KAT-7 telescope. The radio halo is coincident with the cluster X-ray emission and has a largest linear scale of approximately 0.9 Mpc. We measure a flux density of 10.0 ± 2.0 mJy at 610 MHz for the radio halo. We discuss equipartition esti- mates of the cluster magnetic field and constrain the value to be of the order of 1 µG. The relic candidate is detected at the cluster virial radius where a filament meets the cluster. The relic candidate has a flux density of 5.2 ± 0.8 mJy at 610 MHz. We discuss possible origins of the relic candidate emission and conclude that the candidate is consistent with an infall relic. Key words: galaxies: clusters: intracluster medium 1 INTRODUCTION Galaxy Clusters are the largest viralised structures in the Universe with typical masses of order 10 15 M ⊙ . Most of this mass is composed of dark matter. The other 10-20% is con- tained in baryonic matter, with the mass in the hot intra- cluster medium (ICM) being about 10 times larger than the mass contained in galaxies (Kravtsov & Borgani 2012; Brunetti & Jones 2014). The ICM was first detected in the X-ray band, emitting via thermal Bremsstrahlung, indicat- ing that the ICM is a thermalised plasma (Voit 2005). How- ever the detection of Mpc scale diffuse emission in the radio band provides evidence that cosmic ray electrons (CRe) are also present in the ICM, as are cluster-scale magnetic fields (Brunetti & Jones 2014; Feretti et al. 2012). As such, ra- dio observations of clusters provide a unique opportunity to study the non-thermal populations of the ICM. The dynamics and evolution of galaxy clusters can also be indirectly probed using radio observations. Diffuse ra- dio emission in clusters is divided into three morphologi- cal classes: radio relics; giant radio halos; mini halos. Radio relics are normally elongated structures found at the periph- ery of clusters and can be highly polarised. Giant radio halos are usually found at the center of clusters and typically have a more rounded morphology than radio relics. Giant radio ⋆ E-mail: therese.cantwell@postgrad.manchester.ac.uk halos tend to be largely unpolarised due to a high degree of either beam or internal depolarisation. Both giant radio halos and radio relics have typical physical sizes of 1 Mpc. Both radio halos and radio relics are thought to be linked to cluster mergers where shocks and turbulence are expected to accelerate electrons to relativistic energies. See Feretti et al. (2012) and references therein for a review on diffuse radio emission in clusters. Since their discovery, a number of empirical scaling rela- tions have been found between the radio power of giant radio halos and the properties of the host cluster such as clus- ter mass, temperature and X-ray luminosity (Colafrancesco 1999; Govoni et al. 2001; Feretti 2002; Enßlin & R¨ ottgering 2002; Feretti 2003; Brunetti et al. 2009; Cassano et al. 2013; Yuan et al. 2015). The most well studied scaling relationship is between the radio power at 1.4 GHz, P 1.4 , and the X-ray luminosity, L x , of the ICM. When both clusters with a ra- dio halo and radio quiet clusters are examined, a bimodality is found in the distribution on the radio-X-ray plane, with radio loud clusters exhibiting a correlation and radio quiet clusters showing none (Cassano et al. 2013). This bimodal- ity is also found to correspond to the dynamical state of the cluster, further linking radio halos to cluster mergers. More recently a correlation between the radio power of halos at 1.4 GHz and the integrated Sunyaev-Zel’dovich (SZ) effect measurements, Y 500 was reported by Basu (2012). No bimodality in the cluster distribution was seen in the c  2015 The Authors arXiv:1602.05923v1 [astro-ph.CO] 18 Feb 2016