OSSE Observations of Centaurus A Over 18 Months
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
Pagination or Media Count:
OSSE observed Centaurus A at energies between 0.05 and 10 MeV in 1991, 1992, and in 1993. During each observation, this AGN was found to be at relatively low intensities compared to previous observations. It exhibited roughly constant average intensity intervals of a few 5 to 8 days with abrupt 12 to 24-hour intensity changes about the mean of as much as 60. The spectral shape at low intensities can be represented by a single power-law up to about one MeV 1992 the more intense 1991 spectrum is best characterized by a broken power-law with a half-power steepening near 150 keV. Extrapolations to high energy, when compared with the EGRET upper limit for emission above 100 MeV, suggest a need for an additional spectral break above one MeV. The spectral behavior of the AGN in Cen A at energies below one MeV appears to be intermediate between that of flat-spectrum quasars such as 3C273 and of steep-spectrum Seyferts such as NGC 4151.