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 mappi ng the X-ray background on the whole sky on scales of similar to 1 deg (2). Since the method relies on the detection of excess fluctuations p roduced by the clustering of X-ray sources at intermediate redshifts a bove the confusion noise produced by bright foreground sources, counti ng noise and systematic noise need to be kept to a minimum. We propose a proportional counter with collimated fields of view of various size s as the optimal instrument for this mission.