Detection of iron emission line from the galaxy cluster including the distant radio galaxy 3C220.1

We detected an emission line feature at 4 keV in the X-ray spectrum of a sky region including the distant radio galaxy 3C220.1(z = 0.62) obtained with ASCA. The line energy is 6.1 - 7.0 keV (90% confidence) in the rest frame of 3C220.1. Within the present statistics, the observed spectra are consistent with two different models; a non-thermal model consisting of a power-law continuum plus a 6.4 keV iron emission line, and a Raymond-Smith thin-thermal emission model of kT ∼ 6 keV with a metal abundance of ∼ 0.5 solar. However, the large (∼ 500 eV) equivalent width of the line indicates that a significant fraction of the X-ray emission is likely to arise from the hot intracluster gas associating the galaxy cluster including 3C220.1. The spectral parameters of the thermal emission are consistent with the luminosity-temperature relation of nearby clusters and the mass estimates from the giant luminous arc.