Astron. Astrophys. Suppl. Ser. 136, 407-418

BeppoSAX Low-Energy Concentrator Spectrometer background subtraction techniques

A.N. Parmar¹ - T. Oosterbroek¹ - A. Orr¹ - M. Guainazzi¹ - N. Shane^1,2 - M.J. Freyberg³ - D. Ricci⁴ - A. Malizia^4,5

Send offprint request: A.N. Parmar (aparmar@astro.estec. esa.nl)

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

Received November 17, 1998; accepted February 2, 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 (>$\vert 25 \vert ^\circ$) 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 3$\sigma$ 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 ${\rm 3 \ 10^{20}}$ and ${\rm 3 \ 10^{21}}$ atom cm^-2, respectively. At low galactic latitudes, or in complex regions of the X-ray sky, the uncertainties are a factor $\sim$2.5 higher.

Key words: instrumentation: detectors -- methods: data analysis -- diffuse radiation -- X-rays: general