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Issue A&A
Volume 418, Number 3, May II 2004
Page(s) 1187 - 1200
Section Instruments, observational techniques, and data processing
DOI http://dx.doi.org/10.1051/0004-6361:20034026



A&A 418, 1187-1200 (2004)
DOI: 10.1051/0004-6361:20034026

Gamma-ray all-sky imaging with the Burst and Transient Source Experiment

S. E. Shaw1, M. J. Westmore1, A. B. Hill1, A. J. Bird1, A. J. Dean1, C. Ferguson1, J. Knödlseder2, J. J. Lockley1 and D. R. Willis1

1  School of Physics and Astronomy, University of Southampton, SO17 1BJ, UK
2  Centre d'Étude Spatiale des Rayonnements, 9 avenue Colonel-Roche, BP 4346, 31028 Toulouse Cedex 4, France

(Received 30 June 2003 / Accepted 21 December 2003 )

Abstract
The BATSE mission aboard CGRO monitored the whole sky in the 20 keV-1 MeV energy band continuously from April 1991 until June 2000. Although BATSE had very poor intrinsic angular resolution, the data can be used to survey the entire soft gamma-ray sky with  < $1^{\circ}$ angular resolution and ~mCrab sensitivity by using the Earth occultation method. This method determines flux by measuring the step in the count rate profile in each BATSE detector as a source rises above or sets below the Earth's limb. A maximum likelihood imaging technique can then be used to build up all-sky maps from the images of the Earth's limb produced by occulting sources. However, since the Earth seen from BATSE has a radius of ~70 $^{\circ}$, the limb images that intersect at the positions of bright point sources have a significant effect over the area of the all-sky map. A method for performing image cleaning on likelihood data has also been developed and is used to effectively remove artefacts from the all-sky maps. This paper describes the "LIMBO" imaging technique and presents preliminary all-sky maps of 25-160 keV emission, the first to be made since the HEAO1-A4 mission of 1978-79.


Key words: gamma-rays: observations -- methods: data analysis -- surveys

Offprint request: S. E. Shaw, simon.shaw@obs.unige.ch




© ESO 2004


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