Detection of iron emission lines from the galaxy cluster including the radio galaxy 3C 220.1 at z=0.62

We have detected an emission-line feature at 4 keV in the X-ray emission fr om a sky region including the distant radio galaxy 3C 220.1 (z = 0.62) obta ined with ASCA. The line energy is 6.1-7.0 keV (90% confidence) in the rest frame of 3C 220.1. Within the present statistics, the observed spectra are consistent with two different models: a nonthermal model consisting of a p ower-law continuum plus a 6.4 keV iron emission line and a Raymond-Smith th in thermal emission model of kT similar to 6 keV with a metal abundance of similar to 0.5 solar. However, because of the large (similar to 500 eV) equ ivalent width of the line, a significant fraction of the X-ray emission is likely to arise from the hot intracluster gas associated with the galaxy cl uster that includes 3C 220.1. The spectral parameters of the thermal emissi on are consistent with the luminosity-temperature relation of nearby cluste rs.