Abstract. PICsIT (Pixellated Imaging CaeSium Iodide Telescope) is the high energy detector of the IBIS telescope on-board the INTEGRAL satellite. PICsIT operates in the gamma-ray energy range between 175 keV and 10 MeV, with a typical energy resolution of 10% at 1 MeV, and an angular resolution of 12 arcmin within a ∼100 square degree field of view, with the possibility to locate intense point sources in the MeV region at the few arcmin level. PICsIT is based upon a modular array of 4096 independent CsI(Tl) pixels, ∼0.70 cm 2 in cross-section and 3 cm thick. In this work, the PICsIT on-board data handling and science operative modes are described. This work presents the in-flight performances in terms of background count spectra, sensitivity limit, and imaging capabilities.

Abstract. Since the first in orbit activation of the PICsIT detector, frequent spikes have been noticed in its count rate. Tracks in the detector images, corresponding to the spikes, indicate that these events are generated by interaction of cosmic rays with the detector plane. Since these events constitute a significant fraction of the instrument background, a dedicated study has been performed and it has been clarified that the mechanism that leads to spikes and track formation is related to the presence in the CsI crystals of phosphorescence states having decay times of the order of 100 ms. We have also shown that these events, thanks to their temporal characteristics, can be removed from the PICsIT data when the instrument is in Photon by Photon mode. Moreover, thanks to the pixellated structure of the PICsIT detector, we have also obtained evidence of the presence of numerous electromagnetic and hadronic showers generated by the primary cosmic rays.

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