OSSE observations of 3C 273

W. N. Johnson*, C. D. Dermer, R. L. Kinzer, J. D. Kurfess, M. S. Strickman, K. Mcnaron-Brown, E. Jourdain, G. V. Jung, D. A. Grabelsky, W. R. Purcell, M. P. Ulmer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


We report results of multiple observations of the quasar 3C 273 with the Oriented Scintillation Spectrometer Experiment (OSSE) instrument on the Campton 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 timescales of ≈2 months was observed in the energy band 50-150 keV. The data are well described by a single power law with a photon number index Γ = 1.7 ± 0.1. No significant change of Γ 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 1.0-0.4+0.9 MeV to a softer power law with ΔΓ = 0.7-0.11+0.06, forming a power law with Γ = 2.4 between ∼1 MeV and several GeV.

Original languageEnglish (US)
Pages (from-to)182-188
Number of pages7
JournalAstrophysical Journal
Issue number1
StatePublished - May 20 1995


  • Gamma rays: observations
  • Quasars: individual (3C 273)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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