EDP Sciences
Free Access
Volume 396, Number 2, December III 2002
Page(s) 753 - 759
Section Instruments, observational techniques and data processing
DOI https://doi.org/10.1051/0004-6361:20021448

A&A 396, 753-759 (2002)
DOI: 10.1051/0004-6361:20021448

An improvement of the ${\vec Beppo}$SAX LECS and MECS positioning accuracy

M. Perri1, 2 and M. Capalbi1

1  ASI Science Data Center, c/o ESA-ESRIN, via Galileo Galilei, 00044 Frascati, Italy
    e-mail: perri@asdc.asi.it, capalbi@asdc.asi.it
2  Dipartimento di Fisica, Università "La Sapienza", Piazzale A. Moro 2, 00185 Roma, Italy

(Received 5 August 2002 / Accepted 3 October 2002 )

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.

Key words: instrumentation: miscellaneous -- X-rays: general

Offprint request: M. Perri, perri@asdc.asi.it

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