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D. R. MacDonald (JPL), D. E. Gruber (UCSD)
The diffuse x-ray background (XRB) is widely held to originate largely from distant active galaxies. This view is supported by the recent resolution of the XRB into sources in the 2-10 keV band with CHANDRA. However, most of the x-ray background occurs in the 10-60 keV hard x-ray band and sensitive studies in this band are only now possible.
We have measured the fluctuations in the XRB from 15-40 keV using differences between adjacent HEXTE background fields. The measured fractional fluctuations increase with energy, which implies that the effective number of contributing sources is decreasing with energy. The fluctuation level and decrease are consistent with HEAO-1 results to 80 keV.