Fumie Akimoto, Y. Tawara, A. Furuzawa, A. Kumada and K. Yamashita

Abstract

Two famous cooling flow clusters of galaxies, Virgo Cluster (16Mpc)(a giant elliptical galaxy M87 at the center) and Perseus Cluster (73Mpc) are observed with ASCA satellite, which is capable for imaging spectroscopy. The X-ray brightness distribution seems to be almost in spherical symmetry. Line features are outstanding from highly ionized ion (O,Si,S,Ar,Ca,Fe,Ni,etc.). At first, from the thermal continuum the temperature of each cluster of galaxies is confirmed to be cool at the center and become hot at outer part (1.8keV-2.7keV at M87 /4keV-7keV at Perseus). Secondly, based on the line features, the abundance of each cluster of galaxies is found to be enhanced at the center. The observed abundance of M87 ranges from 0.7 to 0.3 of solar and is 0.5 of solar on the average at the whole view of 30' . That of Perseus Cluster changes from 0.5 to 0.4 of solar. Among the observed lines, He-like iron K-alpha lines are found together with K-beta lines. The ratio of equivalent width between K-alpha and K-beta line is about 1.5 at the center of M87, while it is expected to be 9 in an ideal case of optically thin plasmas. The ratio gradually increases as the radial distance becomes larger. In order to understand these phenomena, we considered the effect of resonance scattering. The optical depth(=ta) of He-like iron K-alpha line is 6 times larger than that of K-beta line(=tb). Then K-alpha line is scattered largely in comparison with K-beta line. (In M87 ta=2.7, tb=0.45 and in Perseus Cluster ta=4, tb=0.7) We considering the resonance scattering, K-alpha line appears to be suppressed in a spectra at the center and be increased at outer part. This effect can explain the ratio of 3 in Perseus Cluster. In M87, introducing the effect is qualitatively favorable but cannot yet explain quantitatively such small ratio obtained by ASCA observation. It is needed to consider some more effects such as temperature, abundance, the size of cluster and characteristics of a giant elliptical galaxy M87.