BeppoSAX Low-Energy Concentrator Spectrometer background subtraction techniques

¹ Astrophysics Division, Space Science Department of ESA, ESTEC, Postbus 299, 2200 AG Noordwijk, The Netherlands
² Pembroke College, University of Oxford, St Aldates, Oxford, OX1 1DW, UK
³ Max-Planck-Institut für Extraterrestrische Physik, D-85740 Garching bei München, Germany
⁴ BeppoSAX Science Data Center, Nuova Telespazio, via Corcolle 19, I-00131 Roma, Italy
⁵ Department of Physics and Astronomy, Southampton University, SO17 1BJ, UK

Send offprint request to: A.N. Parmar

Received: 17 November 1998
Accepted: 2 February 1999

Abstract

We present 3 methods for the subtraction of non-cosmic and unresolved cosmic backgrounds observed by the Low-Energy Concentrator Spectrometer (LECS) on-board BeppoSAX. Removal of these backgrounds allows a more accurate modeling of the spectral data from point and small-scale extended sources. At high (> ) galactic latitudes, subtraction using a standard background spectrum works well. At low galactic latitudes, or in complex regions of the X-ray sky, two alternative methods are presented. The first uses counts obtained from two semi-annuli near the outside of the LECS field of view to estimate the background at the source location. The second method uses ROSAT Position Sensitive Proportional Counter (PSPC) all-sky survey data to estimate the LECS background spectrum for a given pointing position. A comparison of the results from these methods provides an estimate of the systematic uncertainties. For high galactic latitude fields, all 3 methods give 3σ confidence uncertainties of <  count s^-1 (0.1-10 keV), or <  count s^-1 (0.1-2 keV). These correspond to 0.1-2.0 keV fluxes of 0.7-1.8 and  erg cm^-2 s^-1 for a power-law spectrum with a photon index of 2 and photoelectric absorption of and  atom cm^-2, respectively. At low galactic latitudes, or in complex regions of the X-ray sky, the uncertainties are a factor ~2.5 higher.