X-ray background measurements with XMM-Newton EPIC

¹ Science Payload Technology Divn., Research and Science Support Dept. of ESA, ESTEC, 2200 AG Noordwijk, The Netherlands
² X-ray Astronomy Group, University of Leicester, Leicester LE1 7RH, UK
³ Mullard Space Science Lab, University College London, Holmbury St Mary, UK
⁴ Istituto di Fisica Cosmica “G Occhialini”, CNR, via Bassini 15, 20133 Milano Italy
⁵ Universita' di Milano Bicocca, Dipartimento di Fisica, Piazza della Scienza 3, 20126 Milano, Italy

Corresponding author: D. Lumb, dlumb@rssd.esa.int

Received: 18 February 2002
Accepted: 5 April 2002

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  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.