Iron K-line analysis of clusters of galaxies with the resonance scattering effect

Abstract

The spectral analysis was carried out in the central core and outer envelope region of each of 50 galaxy clusters observed with ASCA. Among them, we investigated iron K-lines of 8 targets which have large iron line intensities. Iron K-lines were separately observed as He-like K α, H-like K α by SIS and their blend and K β blended with nickel K α lines by GIS. Their energies and intensities were derived from spectral fittings of continuum and Gaussian lines in the energy range of 3 10keV. The intensity ratio of He-like K α to H-like K α has the tendency to be smaller than that estimated from a thin hot plasma model. The intensity ratio of K α to K β has the same tendency as well, and seems to be increasing from the core to the envelope for some clusters. These discrepancies would be due to the reduction of K α, especially He-like K α intensity. The optical depth of He-like iron K α is estimated to be around unity in the core, so that the line would be suppressed in the core and enhanced in the envelope by the resonance scattering effect. This observational evidence of the resonance scattering is critically important to determine the abundance and to investigate the origin of heavy elements in an intra-cluster medium (ICM).