Realisation of Events Trigger System for Space-borne Gamma-Ray Burst Polarimeter, POLAR
Le résumé fourni par la source
POLAR experiment is a novel compact space-borne Compton polarimeter conceived for a precise measurement of hard X-ray polarization and optimized for the detection of the prompt emission of Gamma-Ray Bursts (GRB) in the energy range 50-500 keV. The detector consists of an array of 1600 low-Z plastic scintillator bars. The incoming photons undergo Compton scattering in the bars and produce a modulation pattern; simulations and experiments have shown that the polarization degree and angle can be retrieved from this pattern with the accuracy necessary for pinning down the GRB mechanisms. The scintillating bars are divided into the groups of 64 and constitute 25 frontend readout modules. Each module comprises the flat-panel multi-anode photomultiplier, voltage divider circuit, ASIC chip, analog discriminators block and FPGA device. The ASIC chip, manufactured by IDEAS (Norway), performs amplification, shaping and discrimination of 64 signals from one photomultiplier, bringing out the information about number of triggered channels, as well as their position. The analog data can be also sampled by ADC and read out by FPGA. Besides the ASIC trigger signals, frontend module utilizes supplementary set of analog discriminators, that allows to distinguish the level of the energy deposited in the detector. Detection of the polarization signal requires measurements of the coincidence signals between at least two channels, not necessarily from the same frontend module. All trigger signals are then aggregated in the Central Task Processing Unit, so called Central Trigger. This subsystem allows for unique and uninhibited identification of the transient signal as well as rejection of possible sources of background. The article presents the principles of operation of events triggering system on the local (frontend module) and central levels. The qualification model of POLAR has been constructed and currently undergoes all required examinations, in view of a flight on the Chinese spacelab TG-2 expected for 2014.
Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.