Terrence John O'Neill

Coded-aperture x-ray/gamma-ray telescope for arc- minute localization of gamma-ray bursts

MARGIE will be a large-area, wide field-of-view, hard x- ray/gamma-ray imaging telescope capable of providing accurate positions for faint gamma-ray bursts in near-real- time and of performing a sensitive survey of both steady and transient cosmic sources. The instrument is designed to image faint bursts at the low-intensity end of the log N - log S distribution. MARGIE was recently selected by NASA for a mission-concept study for an Ultra Long Duration Balloon flight. We describe a program to develop an instrument based on the new detector technology of either cadmium zinc telluride room-temperature semiconductors or pixelated cesium iodide scintillators viewed by fast timing charge- coupled devices.

Compton telescope observations of gamma rays from SN 1987A

Results are reported of observations of a significant excess of gamma rays at energies of 1.0-2.5 MeV from the direction of SN 1987A, 418 days after detonation. Two features at 1.21 and 1.88 MeV are attributed to the 1.238 MeV and the combined 1.771, 2.015, and 2.035 MeV line emissions from the decay of Co-56 in the expanding ejecta with respective fluxes of (4.6 +/-1.4 +/-1.2) x 10 exp -4 and (3.5 +/-0.9 +/-0.9) x 10 exp -4 gamma/sq cm s, where the first error is statistical and the second systematic. The obtained energy resolution of 11 percent did not permit a definite separation of the 1.771-MeV line from the two other lines at 2.015 and 2.035 MeV that form the group at 1.88 MeV. The line fluxes were obtained after correcting for the north-south effect and the continuum.

A search for gamma rays of 1. 5-20. 0 MeV from Centaurus A

A search for a gamma-ray continuum and lines from Centaurus A is reported. No measurable gamma rays are found in the 1.5-20.0 MeV and 3 sigma upper limits are reported for various energies which are about a factor of two lower than the results reported by von Ballmoos et al. (1987). These upper limits, along with those of SAS 2 and COS B, suggest that the energy distribution turns over in the energy range of 500 keV to a few MeV. A high source temperature of 5 MeV or synchrotron self-Compton models for producing an excess of gamma rays of a few MeV do not appear necessary. 16 refs.

Improved Analysis of COMPTEL Solar Neutron Data, with Application to the 15 June 1991 Flare

Direct solar flare neutrons are a valuable diagnostic of high- energy ion acceleration in these events, and COMPTEL improves over all previous cosmic neutron detectors in its capacity for neutron energy measurement. Previous studies of COMPTEL neutron data have worked with an incomplete model of the instrumental response, applying energy-by-energy detection efficiencies. Here we employ statistical regularisation techniques with the full (Monte Carlo simulation derived) response matrix to produce improved estimates of neutron numbers and energy distribution. These techniques are applied to data from the well-observed 15 June 1991 flare. Our improved treatment of the instrumental response results in a reduction of 73% in total neutron numbers, compared with previously deduced values. Implications for the picture of primary ion acceleration in this flare are briefly discussed.