ASCA OBSERVATIONS OF THE SPECTRUM OF THE X-RAY-BACKGROUND

We present initial results from ASCA on the spectrum of the Cosmic X-r ay Background from 0.4 to 10 keV. About 250 ks of deep survey data has been collected from the performance verification phase of ASCA. About 110 ks of dark-earth data are used to assess the internal background. A single power-law describes the X-ray background very well in the 1 to 10 keV with no evidence for a steepening in the 1 to 3 keV range. A t 1 keV, the intensity of the X-ray background is 9.6 keV s(-1) cm(-2) sr-l keV(-1). Our data clearly show an excess above the extrapolation of the single power law model below 1 keV. At least part of this exce ss can be accounted for with a thermal component as there is evidence for O VII and O VIII emission.