A new comprehensive 2D model of the point spread functions of the XMM-Newton EPIC telescopes: spurious source suppression and improved positional accuracy

¹ Dept. of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
e-mail: amr30@star.le.ac.uk
² XMM SOC, ESAC, Apartado 78, 28691 Villanueva de la Cañada, Madrid, Spain
³ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany

Received: 20 June 2011
Accepted: 23 August 2011

Abstract

Aims. We describe here a new full 2D parameterization of the PSFs of the three XMM-Newton EPIC telescopes as a function of instrument, energy, off-axis angle and azimuthal angle, covering the whole field-of-view (FoV) of the three EPIC detectors. It models the general PSF envelopes, the primary and secondary spokes, their radial dependencies, and the large-scale azimuthal variations.

Methods. This PSF model has been constructed via the stacking and centering of a large number of bright, but not significantly piled-up point sources from the full FoV of each EPIC detector, and azimuthally filtering the resultant PSF envelopes to form the spoke structures and the gross azimuthal shapes observed.

Results. This PSF model is available for use within the XMM-Newton science analysis system via the usage of current calibration files XRTi_XPSF_0011.CCF and later versions. Initial source-searching tests showed substantial reductions in the numbers of spurious sources being detected in the wings of bright point sources. Furthermore, we have uncovered a systematic error in the previous PSF system, affecting the entire mission to date, whereby returned source RA and Dec values are seen to vary sinusoidally about the true position (amplitude  ≈0.8″) with source azimuthal position.

Conclusions. The new PSF system is now available and is seen as a major improvement with regard to the detection of spurious sources. The new PSF also largely removes the discovered astrometry error and is seen to improve the positional accuracy of EPIC. The modular nature of the PSF system allows for further refinements in the future.