Chandra measurements of non-thermal X-ray emission from massive, merging, radio-halo clusters
Nov, 2008Citations per year
Abstract: (arXiv)
We report the discovery of spatially-extended, non-thermal or hot, quasi-thermal emission components in Chandra X-ray spectra for five of a sample of seven massive, merging galaxy clusters with powerful radio halos: Abell 665, 2163, 2255, 2319, and 1E0657-56. The emission components can be fitted by power-law models with mean photon indices in the range 1.4 < Gamma < 2.0, or by bremsstrahlung emission from hot gas with kT > 20 keV. A control sample of regular, dynamically relaxed clusters without radio halos but with comparable thermal temperatures and luminosities shows no evidence for similar components in their Chandra spectra. Detailed X-ray spectral mapping reveals the complex thermodynamic states of the radio halo clusters. We report the discovery of a clear, large-scale shock front in Abell 2219. Our deepest observations, of the Bullet Cluster 1E0657-56, demonstrate a spatial correlation between the strongest power law X-ray emission, highest thermal pressure, and brightest 1.34GHz radio halo emission in this cluster. The integrated flux and mean spectral index of the power law X-ray emission from 1E0657-56 are in good agreement with constraints at harder X-ray energies from the Rossi X-ray Timing Explorer. We explore possible origins for the power law X-ray components which include inverse Compton scattering of cosmic microwave background photons by relativistic electrons in the clusters/ quasi-thermal bremsstrahlung from supra-thermal electrons energized by Coulomb collisions with an energetic, non-thermal proton population/ synchrotron emission associated with ultra-relativistic electrons/ and spatially unresolved temperature structure e.g. due to hot gas associated with shocks driven by the ongoing merger activity.References(97)
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