BeppoSAX low-energy concentrator spectrometer background subtraction techniques

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 (>|25|°) 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 LEGS 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 <0.9 10-3 count s-1 (0.1 - 10 keV), or <1.5 10-3 count s-1 (0.1 - 2 keV). These correspond to 0.1 - 2.0 keV fluxes of 0.7 - 1.8 and 0.5 - 1.1 10-13 erg cm-2 s-1 for a power-law spectrum with a photon index of 2 and photoelectric absorption of 3 1020 and 3 1021 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.