The wide field cameras onboard the BeppoSAX X-ray astronomy satellite

Abstract

The two Wide Field Cameras (WFCs) currently flying on the Italian/Dutch X-ray satellite BeppoSAX, image the X-ray sky in the energy range of 1.8-28 keV. The field of view is 20°, the angular resolution is 5 arcmin and the energy resolution is 20% at 6 keV, while the source location accuracy will generally be better than one arcmin. All values are at Full Width Half Maximum. The design is based on the coded mask principle where mask and detector both have sizes of about 25.6 × 25.6 cm2. The detector is a Multi Wire Proportional Counter with a position resolution which is better than 0.5 mm for energies below 10 keV. The mask pattern is based on a so called triadic residue set with elements of 1 mm2 of which 33% are transparent for X-rays. The limiting sensitivity of the WFCs is a few mCrab in 105 s. The design and performance of the instrument is described here along with some calibration results and the principle of the image reconstruction. The WFCs represent the latest generation of coded mask X-ray cameras. Their unrivalled field of view, combined with appropriate spatial and temporal resolution and modest energy resolution make the instruments very well suited to perform extensive studies of large areas of the sky and to study transient X-ray phenomena.