The oriented scintillation spectrometer experiment on GRO

Abstract The Oriented Scintillation Spectrometer Experiment (OSSE) uses four actively shielded NaI(Tl)-CsI(Na) phoswich detectors to undertake gamma-ray line and continuum observations in the 0.05 – 10 MeV energy range. There is also a capability to observe gamma rays and neutrons above 10 MeV, primarily for solar flare objectives. Each detector has a 3.8° × 11.4° (FWHM) field-of-view defined by tungsten collimators. OSSE will undertake a broad range of scientific objectives and will provide a line sensitivity of 2–5 × 10 −5 photons/cm 2 -s for a 10 6 -second observation and a corresponding continuum sensitivity of −3 Crab. The planned OSSE observation program during the first fifteen months of the mission is described. During this period, GRO will undertake a sequence of 2-week pointings which will permit the EGRET and COMPTEL to complete sky surveys. The scientific objectives and capabilities of OSSE are presented, and the opportunities for participation in Guest Investigations are discussed.