A new X‐ray mission to measure the power spectrum of fluctuations in the Universe

We propose a new, simple, dedicated X-ray mission to measure the power spectrum of density fluctuations in the Universe, by accurately mapping the X-ray background on the whole sky on scales of ∽ 1 deg2. Since the method relies on the detection of excess fluctuations produced by the clustering of X-ray sources at intermediate redshifts above the confusion noise produced by bright foreground sources, counting noise and systematic noise need to be kept to a minimum. We propose a proportional counter with collimated fields of view of various sizes as the optimal instrument for this mission.