K. C. Gendreau, R. Mushotzky, A. C. Fabian, S. S. Holt, T. Kii, P. J. Serlemitsos, Y. Ogasaka, Y. Tanaka, M. W. Bautz, Y. Fukazawa, Y. Ishisaki, Y. Kohmura, K. Makishima, M. Tashiro, Y. Tsusaka, H. Kunieda, G. R. Ricker, R. K. Vanderspek

Abstract

We present initial results from ASCA on the spectrum of the Cosmic X-ray 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. At 1 keV, the intensity of the X-ray background is 9.6 keV s(-1) cm(-2) sr(-1) 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 excess can be accounted for with a thermal component as there is evidence for OVII and OVIII emission.