We report the discovery of extended radio emission in the Phoenix cluster (SPT-CL J2344-4243, z=0.596) with the GMRT at 610 MHz. The diffuse emission extends over a region of at least 400-500 kpc and surrounds the central radio source of the Brightest Cluster Galaxy, but does not appear to be directly associated with it. We classify the diffuse emission as a radio mini-halo, making it the currently most distant mini-halo known. Radio mini-halos have been explained by synchrotron emitting particles re-accelerated via turbulence, possibly induced by gas sloshing generated from a minor merger event. Chandra observations show a non-concentric X-ray surface brightness distribution, which is consistent with this sloshing interpretation. The mini-halo has a flux density of 17±5 mJy, resulting in a 1.4 GHz radio power of (10.4±3.5)×1024 W Hz−1. The combined cluster emission, which includes the central compact radio source, is also detected in a shallow GMRT 156 MHz observation and together with the 610 MHz data we compute a spectral index of −0.84±0.12 for the overall cluster radio emission. Given that mini-halos typically have steeper radio spectra than cluster radio galaxies, this spectral index should be taken as an upper limit for the mini-halo.
@article{arxiv.1404.3718,
title = {A distant radio mini-halo in the Phoenix galaxy cluster},
author = {R. J. van Weeren and H. T. Intema and D. V. Lal and F. Andrade-Santos and M. Brüggen and F. de Gasperin and W. R. Forman and M. Hoeft and C. Jones and S. E. Nuza and H. J. A. Röttgering and A. Stroe},
journal= {arXiv preprint arXiv:1404.3718},
year = {2015}
}
Comments
5 pages, 2 figures, 1 table. Accepted for publication in ApJL