The Canonical Seyfert Spectrum: The Implications of OSSE Observations
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
Pagination or Media Count:
In its first two years of operation, the Oriented Scintillation Spectrometer Experiment OSSE on the Compton Gamma Ray Observatory CGRO observed 26 active galaxies classified as Seyferts. These objects were selected for their historical X-ray characteristics as identified by HEAO-1, EXOSAT and Ginga and include three of the gamma-ray emitting AGN detected prior to the launch of CGRO. OSSE detects approximately half of these objects at a significance of 5 or greater. The OSSE observations in the 50 keV - 500 keV range indicate spectra which, on average, are significantly softer than the typical photon power law index, alpha 1.7, observed in x-rays. In case of NGC 4151, the brightest Seyfert 1 detected by OSSE, a distinctly thermal spectrum is observed during both 1991 and 1993 observations. An average Seyfert AGN spectrum is formed by a weighted summation of the individual observations excluding the brightest detections. This average photon spectrum from 26 observations of 15 AGNs is well described by a simple exponential function with an e-folding energy of 45 keV. We summarize the OSSE observation of Seyfert AGN and present the average spectrum above 50 keV.