XMM-Newton and INTEGRAL analysis of the Ophiuchuscluster of galaxies

摘要

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 B 0.05-0.15 pG. 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.