Mark D. Leising

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.

Gamma‐ray lines from classical novae

There is now a wealth of evidence supporting the idea that classical novae are thermonuclear runaways on white dwarfs. Explosive hydrogen burning produces substantial quantities of unstable nuclei. These nuclei emit γ‐rays and β+’s which might be detectable to present and future γ‐ray spectrometers. Here we describe the production and observability of several unstable nuclei, review the observations made to date, evaluate the prospects for future observations, and discuss the importance of detection of γ‐rays for improving our understanding of the nova phenomenon.

Gamma‐ray line diagnostics of Novae

The nuclear processing thought to power classical nova outbursts produces substantial quantities of unstable nuclei. These nuclei emit γ‐rays and β+’s which might be detectable to present and future γ‐ray spectrometers. We discuss the importance of detection of γ‐rays for improving our understanding of the nova phenomenon and we review the observations made to date.

The OSSE Data Analysis System

The Oriented Scintillation Spectrometer Experiment (OSSE) on board the Gamma Ray Observatory (GRO) spacecraft has a wide variety of operating modes, each of which produces its own type of data. Each operating mode has various adjustable parameters that effect the availability and interpretation of the various data types. OSSE, its modes and data products, have been described in detail elsewhere [1].

Supernova 1987A from 1 keV to 10 MeV: The status as of 1990

Satellite, rocket, and balloon borne instruments have obtained a wealth of high-energy data from SN 1987A. These have added significantly to our understanding of Type II supernovae. Besides the exciting direct detection of just-synthesized radioactivity via γ-ray line observations, the light curves of the lines and the extremely hard continuum which results from them have provided clues to the structure of the newly disrupted star. Mysteries still remain. We do not yet understand how the radioactive matter reached low depths in the envelope at such early times. We have not yet identified the mechanism which produced the softest observed X-ray emission. We do not know how much of other radioactive species were produced. This could help us begin to understand in detail the nuclear burning and mass ejection processes. We have not yet seen the signature of the compact remnant of the collapse. At this point we have great hope that some of these questions will be answered with the state-of-the-art experiments already flying and scheduled for launch soon.

Gamma-Ray Lines from Supernova 1987A

We review the observations of γ-ray lines from SN 1987A and place them in the context of theoretical expectations and related observations, including the optical light curve and hard X-ray detections.