Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...438l..63z&link_type=abstract
Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 438, no. 2, p. L63-L66
Astronomy and Astrophysics
Astronomy
186
Cosmology, Diffuse Radiation, Galactic Evolution, Radio Astronomy, Seyfert Galaxies, Spectrum Analysis, Stellar Coronas, X Ray Spectra, Compton Effect, Continuum Mechanics, Gamma Ray Observatory, Ginga Satellite, Power Series, Stellar Models
Scientific paper
We have obtained the first average 2-500 keV spectra of Seyfert galaxies, using the data from Ginga and Compton Gamma-Ray Observatory's (CGRO) Oriented Scintillation Spectrometer Experiment (OSSE). Our sample contains three classes of objects with markedly different spectra: radio-quiet Seyfert 1's and 2's, and radio-loud Seyfert 1's. The average radio-quiet Seyfert 1 spectrum is well-fitted by a power law continuum with the energy spectral index alpha approximately equals 0.9, a Compton reflection component corresponding to a approximately 2 pi covering solid angle, and ionized absorption. There is a high-energy cutoff in the incident power law continuum: the e-folding energy is Ec approximately equals 0.6+0.8-0.3 MeV. The simplest model that describes this spectrum is Comptonization in a relativistic optically-thin thermal corona above the surface of an accretion disk. Radio-quiet Seyfert 2's show strong netural absorption, and there is an indication that their X-ray power laws are intrinsically harder. Finally, the radio-loud Seyfert spectrum has alpha approximately equals 0.7, moderate neutral absorption EC = 0.4+0.7-0.2 MeV, and no or little Compton reflection. This is incompatible with the radio-quiet Seyfert 1 spectrum, and probably indicating that the X-rays are beamed away from the accretion disk in these objects. The average spectra of Seyferts integrated over redshift with a power-law evolution can explain the hard X-ray spectrum of the cosmic background.
Done Chris
Johnson Neil W.
McNaron-Brown Kellie
Smith David
Zdziarski Andrzej A.
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