<i>XMM-NEWTON</i>OBSERVATION OF THE NORTHWEST RADIO RELIC REGION IN A3667

Abstract

Abell 3667 is the archetype of a merging cluster with radio relics. The NW\nradio relic is the brightest cluster relic or halo known, and is believed to be\ndue to a strong merger shock. We have observed the NW relic for 40 ksec of net\nXMM time. We observe a global decline of temperature across the relic from 6 to\n1 keV, similar to the Suzaku results. Our new observations reveal a sharp\nchange of both temperature and surface brightness near the position of the\nrelic. The increased X-ray emission on the relic can be equivalently well\ndescribed by either a thermal or nonthermal spectral model. The parameters of\nthe thermal model are consistent with a Mach number M~2 shock and a shock speed\nof ~1200 km s^-1. The energy content of the relativistic particles in the radio\nrelic can be explained if they are (re)-accelerated by the shock with an\nefficiency of ~0.2%. Comparing the limit on the inverse Compton X-ray emission\nwith the measured radio synchrotron emission, we set a lower limit to the\nmagnetic field in the relic of 3 muG. If the emission from the relic is\nnon-thermal, this lower limit is in fact the required magnetic field.\n