BACKGROUND IN THE MULTIPLE EVENTS (ME) OF INTEGRAL/SPI

摘要

Above 100 keV, a significant fraction of the total events in SPI (Vedrenne et al. 2003) is due to the coincident two-detector events ("M"ultiple "E" vents, ME). Including ME in the scientific analysis not only improves the efficiency and sensitivity at high energies (more than 30% above IMeV, Roques et al. 2003; Attie et al. 2003), it also allows polarization measurements which cannot be done with single detector events (see the accompanying proceeding by E. Kalemci on measuring polarization with SPI and its scientific significance). The relative contribution of different background components (localized and non-localized beta decays, prompt emission, etc.) to the ME is different from that to the single-detector events. These differences may produce distributions of line and continuum background rates in pairs of detectors (ME-detectors) that vary from the distribution in individual detectors. Systematic variations in the distribution of background multiple events must be understood in order to perform polarization studies. In this proceeding, we summarize our efforts to understand the nature of the ME variations around the detector plane and their time dependence to enhance the analysis of the ME data for spectral, imaging and polarization studies with SPI.