CGRO-COMPTEL All-Sky Survey at 2.223 MeV

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Session 5 -- Gamma Ray Astronomy
Display presentation, Monday, June 12, 1995, 9:20am - 6:30pm

[5.04] CGRO-COMPTEL All-Sky Survey at 2.223 MeV

S. J. Fletcher, M. McConnell, J. Ryan (UNH), W. Collmar, V. Sch\"onfelder, H. Steinle, A. Strong (MPE), R. van Dijk, W. Hermsen (SRON-Utrecht), K. Bennett, R. Much (SSD/ESA)

The COMPTEL instrument, on the Compton Gamma Ray Observatory, is a Compton imaging telescope operating in the energy range 0.75 - 30 MeV. With its large ($\sim 1$ steradian) field-of-view, it surveyed the entire sky during its first 15 months of operation (which began in April 1991). Since completing this survey, it made additional observations of selected regions of the sky. Within the energy range of COMPTEL, the neutron capture line at 2.223 MeV is of particular interest. Various scenarios of accretion onto compact objects predict potentially observable fluxes resulting from neutron capture in the atmosphere of the compact object's companion star. COMPTEL provides the best opportunity to test such models. Despite the presence of a strong internal background line at 2.223 MeV, COMPTEL provides an unprecedented sensitivity at this energy. The available data (accumulated over all phases of the CGRO misssion) now provides a COMPTEL narrow-line sensitivity approaching $\sim 1 \times 10^{-5} {\rm cm}^{-2} {\rm s}^{-1}$ over much of the sky. Predicted fluxes for the unshifted 2.223 MeV line from Cyg X-1 range from $\ 10^{-6}$ to $\ 10^{-5} {\rm cm}^{-2} {\rm s}^{-1}$ (Guessoum and Dermer, 1988) and from Cyg X-3 of $\sim 10^{-5}{\rm cm}^{-2}{\rm s}^{-1}$ (Vestrand, 1990). Upper limits from SMM are approximately an order of magnitude above that which can be achieved with COMPTEL. We review the status of our work and present the preliminary results.

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