Properties of the background of EPIC-pn onboard XMM-Newton

¹ Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, 560-0043 Osaka, Japan e-mail: hkatayam@ess.sci.osaka-u.ac.jp
² Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo, Japan
³ Max-Planck-Institut für Extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

Corresponding author: K. Matsushita, matsushita@rs.kagu.tus.ac.jp

Received: 30 September 2002
Accepted: 29 July 2003

Abstract

We have investigated the background properties of EPIC-pn onboard XMM-Newton to establish the background subtraction method. Count rates of the background vary violently by two orders of magnitude at the maximum, while during the most quiet period, these are stable within 8% at a 1σ level. The overall spectrum is dominated by particle events above 5 keV, and its spatial variation is also found. The long-term variation of the background is also investigated with CAL CLOSED data, where the filter wheel was in closed position with the internal calibration source illuminating the sensitive area. The average background count rate decreased by 20% from March 2000 to January 2001, but it regained in February 2001. For the modeling of the background spectrum, we investigate relations between the 2.0–7.0 keV count rate and some characteristic parameters. The 2.0–7.0 keV background count rate shows a good correlation with the count rate of events outside the field of view. This correlation is usable for the modeling of the background.