BOLTZMANN APPROACH TO THE LARGE-ANGLE COSMIC X-RAY-BACKGROUND FLUCTUATIONS

Large-angle fluctuations in the cosmic X-ray background are investigat ed by a new formalism with a simple model of the X-ray sources. Our me thod is formulated from the Boltzmann equation and a simple extension of the work by Lahav et al. to be applicable to a hyperbolic (open) un iverse. The low multipole fluctuations due to the source clustering ar e analysed in various cosmological models in both numerical and analyt ic ways. The fluctuations strongly depend on the X-ray source evolutio n model, as pointed out previously. It turns out that the nearby (z le ss than or similar to 0.1) sources are the dominant contributors to th e large-angle fluctuations. If these nearby sources are removed in an observed X-ray map, the dipole (low multipole) moment of the fluctuati on drastically decreases. In this case the Compton-Getting effect of a n observer's motion can be a dominant contribution to the dipole fluct uation. This feature of fluctuation, relating to the matter power spec trum, is discussed.