XMM-Newton and INTEGRAL analysis of the Ophiuchus cluster of galaxies

¹ Observatory, University of Helsinki, Finland e-mail: Jukka.H.Nevalainen@helsinki.fi
² ISDC Data Centre for Astrophysics, Geneva Observatory, University of Geneva, Switzerland
³ SRON Netherlands Institute for Space Research, The Netherlands
⁴ University of Alabama in Huntsville, Huntsville, USA; NASA National Space and Technology Center, Huntsville, USA

Received: 20 May 2009
Accepted: 7 October 2009

Abstract

Aims. We investigated the non-thermal hard X-ray emission in the Ophiuchus cluster of galaxies. Our aim is to characterise the physical properties of the non-thermal component and its interaction with the cosmic microwave background.

Methods. We performed spatially resolved spectroscopy and imaging using XMM-Newton data to model the thermal emission. Combining this with INTEGRAL ISGRI data, we modelled the 0.6-140 keV band total emission in the central 7 arcmin region.

Results. The models that best describe both PN and ISGRI data contain a power-law component with a photon index in a range 2.2-2.5. This component produces ~10% of the total flux in the 1-10 keV band. The pressure of the non-thermal electrons is ~1% of that of the thermal electrons. Our results support the scenario whereby a relativistic electron population, which produces the recently detected radio mini-halo in Ophiuchus, also produces the hard X-rays via inverse compton scattering of the CMB photons. The best-fit models imply a differential momentum spectrum of the relativistic electrons with a slope of 3.4-4.0 and a magnetic field strength  μG. The lack of evidence for a recent major merger in the Ophiuchus centre allows the possibility that the relativistic electrons are produced by turbulence or hadronic collisions.