Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...445..182j&link_type=abstract
The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 445, no. 1, p. 182-188
Astronomy and Astrophysics
Astrophysics
24
Active Galactic Nuclei, Energy Distribution, Gamma Ray Spectra, Quasars, Variability, X Ray Spectra, Flux Density, Gamma Ray Observatory, Red Shift, Spectral Energy Distribution, Spectrum Analysis
Scientific paper
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 approximately 3 on timescales of approximately equal 2 months was observed in the energy band 50-150 keV. The data are well described by a single power law with a proton number index Gamma = 1.7 +/- 0.1. No significant change of Gamma 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(+0.9, -0.4) MeV to a softer power law with Delta Gamma = 0.7(+0.06, -0.11), forming a power law with Gamma = 2.4 between approximately 1 MeV and several GeV.
Dermer Carles D.
Grabelsky David Andrew
Johnson Neil W.
Jourdain Elisabeth
Jung Gregory V.
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