THE MAGNETIC-FIELD IN THE COMA CLUSTER

The polarization data of the radio galaxy NGC 4869, belonging to the C oma cluster and located in its central region, allow us to obtain info rmation on the structure of magnetic field associated with the cluster itself. A magnetic field of less than or equal to 8.3h(100)(1/2) mu G , tangled on scales of the order of less than 1 kpc, is required to ex plain the observed fluctuations of the rotation measure. This magnetic field is more than one order of magnitude stronger than the equiparti tion value obtained for Coma C. This implies that the halo source Coma C may not be at the equipartition. Moreover, the need of efficient re acceleration mechanisms for the electrons radiating in Coma C is stron ger. The energy supply to the Coma C radiating electrons is probably p rovided by the cluster merger process.