OSSE Observations of 3C 273
NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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We report results of multiple observations of the quasar 3C 273 with the Oriented Scintillation Spectrometer Experiment OSSE instrument on the Compton Gamma Ray Observatory. These observations span the period from 1991 June through 1993 January and represent the most sensitive observations to date in low-energy gamma rays. The source was detected at historically weak 100 keV fluxes compared with previous measurements. Variability by factors of 3 on time scales of approximately equal 2 months was observed in the energy band 50 keV - 150 keV. The data are well described by a single power law with a photon number index, 1.7 plus or minus 0.1. No significant change of , was observed during changes in intensity. Thermal models do not provide acceptable fits to the data. When the OSSE data are combined with contemporaneous measurements by COMPTEL and EGRET, the spectrum is seen to break at an energy of 1.0 sup 0.9, sub -0.4 MeV to a softer power law with Delta, 0.7 sup 0.06, sub -0.11, forming a power law with, 2.4 between 1 MeV and several GeV.