Electron Transport in the Coma Cluster

Abstract

The inner regions of the Coma cluster of galaxies contain a source of diffuse synchrotron emission (‘Coma C’) which has a linear dimension of at least 500 kpc. There has been interest in the question of where the relativistic electrons responsible for this emission originate, and how they are transported through the intracluster medium (Tribble, 1993). It is widely thought that one or more of the radio galaxies in the centre of the cluster provides a likely source for particles which then diffuse out into the halo (Giovannini et al., 1993); a process which depends critically on the structure of this field in the intra-cluster medium. Recent observations of the emission from NGC4869 (Feretti et al., 1995), which occupies a central position in the Coma cluster, indicate the presence of a magnetic field which is both stronger (B ≈ 8µ G) and tangled on much shorter scales ≲ 1 kpc than had been thought previously (Kim et al., 1990). These new results suggest not only a shorter cooling time for energetic electrons, but also a slower rate of diffusive transport. In this paper we show the constraints that the new observations place on transport theories of the relativistic electrons.