X-ray background measurements with XMM-Newton EPIC

Abstract

We discuss the methods used to compile a high signal-to-noise dataset representative of both the instrumental and cosmic background signal measured at high galactic latitude by the XMM-Newton EPIC cameras. The characteristics of the EPIC background are described and the potential applications of the derived dataset in general science analysis are outlined. In the case of the cosmic X-ray background, the transition between a hard power-law spectrum (due to the integrated emission of unresolved, largely extragalactic, point sources) and a softer thermal spectrum (produced by hot plasma associated with the Galactic plane and halo) is unambiguously detected around ∼1 keV. We derive a value for the intensity of the power-law component of 2.15 ± 0.26 × 10-11 erg cm-2 s-1 deg-2 in the 2-10 keV band (normalisation at 1 keV of 11.1 photons cm-2 s-1 sr-1 keV-1. The implication is that recent, very deep Chandra observations have resolved ∼70-90% of the 2-10 keV background into discrete sources. Our measurement is towards the higher end of the range of quoted background normalisations.