When is pile-up important in the XMM-Newton EPIC cameras?

¹ European Space Astronomy Centre of ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
² Institute of Astronomy, Madingley Rd, Cambridge, CB3 0HA, UK
e-mail: pj253@ast.cam.ac.uk

Received: 23 December 2014
Accepted: 23 June 2015

Abstract

Context. Pile-up in X-ray charged couple device (CCD) detectors is defined as the reconstruction of independent events in the same detection cell as a single event during a read-out cycle. Pile-up can seriously compromise the spectral performance, modifying both the flux and the spectral shape of celestial sources.

Aims. In this paper we define rigorous metrics to characterise the effect of pile-up in terms of flux loss and spectral distortion.

Methods. We extend analytical formulae derived for pile-up on CCD detectors with the inclusion of the calibrated energy-dependence of the point spread function. We validated our analytical results through both Monte-Carlo simulations of the EPIC cameras on-board XMM-Newton and comparison with pile-up diagnostics in observed data.

Results. We estimate new count rate levels corresponding to a given degree of flux loss and spectral distortion for each EPIC imaging acquisition mode and provide guidance to observers wishing to estimate these values in their own observations.

Conclusions. We strongly recommend using these thresholds in planning future observations with the EPIC cameras.