30TH INTERNATIONAL COSMIC RAY CONFERENCE The trigger unit of the space borne gamma-ray burst telescope ECLAIRs

schanne @ hep.saclay.cea.fr Preliminary version prior to conference Abstract: Gamma-ray bursts (GRB) sign energetic explosions in the Universe, occurring at cosmo-logical distances. Multi-wavelength observations of GRB allow to study their properties and to use them as cosmological tools. In 2012 the space borne gamma-ray telescope ECLAIRs is expected to provide accurate GRB localizations on the sky in near real-time, necessary for ground-based follow-up observations. Led by CEA Saclay, France, the project is currently in its technical design phase. ECLAIRs is optimized to detect highly red-shifted GRB thanks to a 4 keV low energy threshold. A coded mask telescope with a 1024 cm2 detection plane of 80×80 CdTe pixels permanently observes a 2 sr sky field. The on-board trigger detects GRB using count-rate increase monitors on multiple time-scales and cyclic images. It computes sky images in the 4-50 keV energy range by de-convolving de-tector plane images with the mask pattern and localizes newly detected sources with <10 arcmin accu-racy. While individual GRB photons are available hours later, GRB alerts are transmitted over a VHF network within seconds to ground, in particular to robotic follow-up telescopes, which refine GRB lo-calizations to the level needed by large spectroscopic telescopes. This paper describes the ECLAIRs concept, with emphasis on the GRB triggering scheme