BeppoSAX Low-Energy Concentrator Spectrometer background subtraction techniques

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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.

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