Letter to the Editor

SPI/INTEGRAL in-flight performance

¹ Centre d'Étude Spatiale des Rayonnements, CNRS/UPS, BP 4346, 31028 Toulouse, France
² DSM/DAPNIA/SAp, CEA-Saclay, 91191 Gif-sur-Yvette, France
³ Max-Planck-Institut für extraterrestrische Physik, Postfach 1603, 85740 Garching, Germany
⁴ CNES/CST, 18 avenue Édouard Belin, 31401 Toulouse Cedex 4, France
⁵ Space Science Laboratory, University of California, Berkeley, CA 94720, USA
⁶ IASF, via Bassini 15, 20133 Milano, Italy
⁷ Institut de Physique Nucléaire, Université catholique de Louvain, 1348 Louvain-La Neuve, Belgium
⁸ UCSD/CASS, 9500 Gilman Drive, La Jolla, CA 92093-0111, USA
⁹ IFIC, University of Valencia, 50 avenida Dr. Moliner, 46100 Burjassot, Spain
¹⁰ Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA

Corresponding author: J. P. Roques, roques@cesr.fr

Received: 31 July 2003
Accepted: 23 September 2003

Abstract

The SPI instrument has been launched on-board the INTEGRAL observatory on October 17, 2002. SPI is a spectrometer devoted to the sky observation in the 20 keV–8 MeV energy range using 19 germanium detectors. The performance of the cryogenic system is nominal and allows to cool the 19 kg of germanium down to 85 K with a comfortable margin. The energy resolution of the whole camera is 2.5 keV at 1.1 MeV. This resolution degrades with time due to particle irradiation in space. We show that the annealing process allows the recovery of the initial performance. The anticoincidence shield works as expected, with a low threshold at 75 keV, reducing the GeD background by a factor of 20. The digital front-end electronics system allows the perfect alignement in time of all the signals as well as the optimisation of the dead time (12%). We demonstrate that SPI is able to map regions as complex as the galactic plane. The obtained spectrum of the Crab nebula validates the present version of our response matrix. The 3σ sensitivity of the instrument at 1 MeV is  ph cm^-2 s^-1 keV^-1 for the continuum and  ph cm^-2 s^-1 for narrow lines.