OSSE OBSERVATIONS OF NGC-4151

We report results of a 2 week observation of the Seyfert galaxy NGC 4151 with the Oriented Scintillation Spectrometer Experiment (OSSE) instrument on the Compton Gamma Ray Observatory (GRO). The source had a very soft spectrum which is best represented by a broken power law or Sunyaev-Titarchuk thermal Comptonization model. It can be characterized by an exponential shape with an e-folding energy of 39 +/- 2 keV in the energy range 65-300 keV, and an intensity at 100 keV of (2.33 +/- 0.05) x 10(-5) photons cm-2 s-1 keV-1. Source intensity variability of approximately 25% was observed during the 14 days of our observations; no significant change in spectral shape was detected for this period. The steepness and shape of the spectrum above 100 keV rule out (chi2 probability -7 x 10(-4)) simple pair cascade models in a compact source which have been suggested for Seyfert galaxies.