An X-ray spectroscopic determination of the Hubble constant

We propose to observe the Perseus cluster, in order to accurately constrain the spatial distribution of the Fe XXV n31 to n21 fluxes. The n21 resonance line is known to be optically thick to scattering, the n31 lines are not. The ratio map therefore provides a direct measure of the resonance scattering depth, which, when combined with the volume emission measure and the angular size of the cluster, produces an estimate of the absolute distance in a manner entirely analogous to the SunyaevZeldovich effect. Together with the redshift, this gives the Hubble constant directly, just from spatially resolved Xray spectroscopy. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]