We have independently analyzed sky images of the four BeppoSAX X-ray telescopes (LECS, MECS1, MECS2 and MECS3) using event files processed at the ASI Science Data Center (ASDC).
We have restricted our analysis to observations performed after May 6th 1998, since before this date various calibration problems have affected the absolute spacecraft attitude reconstruction (see the Appendix for a detailed discussion on this topic).
This time selection has not been possible for MECS1, since this unit
failed on May 6th 1997. We have therefore considered MECS1 observations
from the beginning of the mission (May 1996) until the failure of the unit.
Due to the worse spacecraft attitude reconstruction during this time interval,
the MECS1 data are affected by larger systematic errors on the absolute
sky position reconstruction.
LECS and MECS fields have been selected according to the following criteria:
Source detection of the targets has been performed using the DETECT routine of the XIMAGE package (Version 2.66a).
Images were accumulated in the 2-10 keV energy band (channels 44-220) for the MECS and in the 0.1-10 keV (channels 10-950) for the LECS.
Special attention has been devoted to the quality of the detections. For each source different sizes of the slide-cell of the DETECT routine have been attempted and all detections have been checked interactively.