OSSE Observations of the Soft Gamma-Ray Continuum from the Galactic Plane at Longitude 95°

We present the results of OSSE observations of the soft gamma ray continuumemission from the Galactic plane at longitude 95 degrees. Emission is detectedbetween 50 and 600 keV where the spectrum is fit well by a power law withphoton index -2.6+-0.3 and flux (4.0+-0.5) 10^{-2} photons/s/cm^2/rad/MeV at100 keV. This spectral shape in this range is similar to that found for thecontinuum emission from the inner Galaxy but the amplitude is lower by a factorof four. This emission is either due to unresolved and previously unknown pointsources or it is of diffuse origin, or a combination of the two. Simultaneousobservations with OSSE and smaller field of view instruments operating in thesoft gamma ray energy band, such as XTE or SAX, would help resolve this issue.If it is primarily diffuse emission due to nonthermal electron bremsstrahlung,as is the >1 MeV Galactic ridge continuum, then the power in low energy cosmicray electrons exceeds that of the nuclear component of the cosmic rays by anorder of magnitude. This would have profound implications for the origin ofcosmic rays and the energetics of the interstellar medium. Alternatively, ifthe emission is diffuse and thermal, then there must be a component of theinterstellar medium at temperatures near 10^9 K.Comment: 11 pages, Latex, requires AASTEX macros and psfig.tex, 2 postscript figures, Accepted for publication in the Astrophysical Journal Letter