W. N. Johnson
United States Department of Defense
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Featured researches published by W. N. Johnson.
The Astrophysical Journal | 1993
A. C. Fabian; K. Nandra; A. Celotti; Martin J. Rees; J. E. Grove; W. N. Johnson
We present the first hard X-ray/soft γ-ray observations from the Oriented Scintillation Spectrometer Experiment (OSSE) of a bright Seyfert 1 galaxy, IC 4329A. Significant variability was seen over the 3 week observing period. The 50-200 keV spectrum is steep and can be characterized by a power-law spectrum of photon index 2.84±0.36, at 90% confidence. This is significantly steeper than the X-ray spectrum found from Ginga data of the source. Joint fits of the Ginga and OSSE data are well modeled by a thermal model represented by an exponential spectral break with an e-folding energy at about 130 keV. Good fits are also obtained if a reflection component is included. We constrain possible nonthermal continuum models involving photon-photon pair production
The Astrophysical Journal | 1994
A. C. Fabian; K. Nandra; A. Celotti; Martin J. Rees; J. E. Grove; W. N. Johnson
