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A&A 411, L179-L183 (2003)
DOI: 10.1051/0004-6361:20031584

Letter

The INTEGRAL IBIS/ISGRI System Point Spread Function and Source Location Accuracy

A. Gros¹, A. Goldwurm¹, M. Cadolle-Bel¹, P. Goldoni¹, J. Rodriguez^{1, 2}, L. Foschini³, M. Del Santo⁴ and P. Blay<sup>5

1</sup>  CEA Saclay, DSM/DAPNIA/SAp, 91191 Gif-sur-Yvette Cedex, France
²  Integral Science Data Center, Chemin d'Écogia 16, 1290 Versoix, Switzerland
³  IASF/CNR, sezione di Bologna, via Gobetti 101, 40129 Bologna, Italy
⁴  IASF/CNR, sezione di Roma, via del Fosso del Cavaliere 100, 00133 Roma, Italy
⁵  GACE, Instituto de Ciencia de los Materiales, Universidad de Valencia, PO Box 22085, 46071 Valencia, Spain

(Received 18 July 2003 / Accepted 9 October 2003)

Abstract
The imager on board INTEGRAL (IBIS) presently provides the most detailed sky images ever obtained at energies above 30 keV. The telescope is based on a coded aperture imaging system which allows to obtain sky images in a large field of view (29    29 ) with an angular resolution of 12 '. The System Point Spread Function of the telescope and its detailed characteristics are here described along with the specific analysis algorithms used to derive the accurate point-like source locations. The derived location accuracy is studied using the first in-flight calibration data on strong sources for the IBIS/ISGRI system. The dependence of the calibrated location accuracy with the signal to noise ratio of the sources is presented. These preliminary studies demonstrate that the IBIS/ISGRI telescope and the standard scientific analysis software allow source localizations with accuracy at 90% confidence level better than 1 ' for sources with signal to noise ratios >30 over the whole field of view, in agreement with the expected performances of the instrument.

Key words: methods: data analysis -- techniques: image processing -- techniques: high angular resolution

Offprint request: A. Gros, Aleksandra.Gros@cea.fr

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