  We present a study of the source positioning accuracy of the LECS and MECS
instruments on-board BeppoSAX. From the analysis of a sample of archival images
we find that a systematic error, which depends on the spacecraft roll angle and
has an amplitude of ~17'' for the LECS and ~27'' for the MECS, affects the sky
coordinates derived from both instruments. The error is due to a residual
misalignment of the two instruments with respect to the spacecraft Z axis
arisen from the presence of attitude inaccuracies in the observations used to
calibrate the pointing direction of LECS and MECS optical axes. Analytical
formulae to correct LECS and MECS sky coordinates are derived. After the
coordinate correction the 90% confidence level error radii are 16'' and 17''
for LECS and MECS respectively, improving by a factor of ~2 the source location
accuracy of the two instruments. The positioning accuracy improvement presented
here can significantly enhance the follow-up studies at other wavelengths of
the X-ray sources observed with LECS and MECS instruments.

Astrophysics