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Session 36 - Extragalactic X-Ray Sources.
Display session, Tuesday, January 14
Metropolitan Ballroom,

[36.05] Observing the Granularity in the X-ray Background with RXTE

D. R. MacDonald, A. D. Zych (UCR), D. E. Gruber, P. R. Blanco, W. A. Heindl, D. Marsden, R. E. Rothschild (UCSD), E. Boldt, R. F. Mushotzky (LHEA/GSFC), A. C. Fabian (IoA, Cambridge), A. Antunes, E. Smith (Hughes STX)

The X-ray diffuse background (XRB) is widely held to originate largely from distant active galaxies. Counts of sources in survey missions and from fluctuation studies have given support to this view, but no deep studies have been performed in the 10-60 keV band where most of the emission occurs.

During normal observations, the HEXTE instrument on RXTE makes nearly simultaneous observations of two pairs of background fields separated by 3.0 degrees. Differences in fluxes from these pairs of background fields can be used to detect a source population much deeper, a distance of z=0.3, than can be studied from individual detections. Using the ensemble of all long RXTE pointings, a measurement of the fluctuations in the XRB in wide energy bands above 15 keV can be made. Tails of the distribution of differences between pairs of fields are dominated by sources that occur at a spatial density of one source per field of view. For the HEXTE instrument this is one per square degree. A number density and spectrum inferred from these data will constrain virtually all the current models of the origin of the X-ray background, provided that the limit of counting errors can be approached. We present here the result of a number of tests for systematics which have been performed on the 2-4 million seconds of data so far obtained, which is 10-20 percent of the expected total.

Program listing for Tuesday