INVESTIGATING THE NATURE OF VERY SHORT BURSTS DETECTED IN THE ANTI-COINCIDENCE SHIELD OF INTEGRAL/SPI

摘要

Since the launch of INTEGRAL in October 2002, the anti-coincidence shield (ACS) of the spectrometer SPI is contributing significantly to the study of Gamma-Ray Bursts (GRBs). The ACS is not only useful to detect particles, but it is also an almost omnidirectional GRB detector with a very high sensitivity. The ACS is showing very good capabilities in the detection of GRBs with on average one GRB candidate detected per day. The ACS bursts population, as the classical GRBs, is composed of two main classes: long (duration> 2s) and short (duration< 2s) bursts. In addition, the ACS counter exhibits very short spikes with a duration less than 150 ms. Their origin (electronics, instrumental or physical) is still unknown which has motivated our study. Our various investigations on the nature of very short ACS bursts show that they are best explained by electronic ringing, excited by the large energy deposit of a cosmic-ray particle, which was hitting one or more of the detectors.