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

TL;DR

This study analyzes the non-thermal hard X-ray emission in the Ophiuchus galaxy cluster, revealing a relativistic electron population likely responsible for observed radio and X-ray phenomena, with implications for cluster physics.

Contribution

First combined XMM-Newton and INTEGRAL data to characterize the non-thermal emission in the Ophiuchus cluster, providing new insights into electron populations and magnetic fields.

Findings

Non-thermal X-ray component accounts for ~10% of flux in 1-10 keV.

Relativistic electrons produce hard X-rays via inverse Compton scattering.

Magnetic field strength estimated at 0.05-0.15 microG.

Abstract

We investigated the non-thermal hard X-ray emission in the Ophiuchus cluster of galaxies. Our aim was to characterise the physical properties of the non-thermal component and its interaction with the cosmic microwave background. We performed spatially resolved spectroscopy and imaging using XMM-Newton data to model the thermal emission. Combining this with INTEGRAL ISGRI data, we modeled the 0.6-140 keV band total emission in the central 7 arcmin region. 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 microG. The lack of evidence for a recent major merger in the Ophiuchus center allows the possibility that the relativistic electrons are produced by turbulence or hadronic collisions.