Aa. Zdziarski et al., THE AVERAGE X-RAY GAMMA-RAY SPECTRA OF SEYFERT-GALAXIES FROM GINGA AND OSSE AND THE ORIGIN OF THE COSMIC X-RAY-BACKGROUND, The Astrophysical journal, 438(2), 1995, pp. 63-66
We have obtained the first average 2-500 keV spectra of Seyfert galaxi
es, using the data from Ginga and Compton Gamma-Ray Observatory's 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 almost-equal-to 0.9
, a Compton reflection component corresponding to a approximately 2pi
covering solid angle, and ionized absorption. There is a high-energy c
utoff in the incident power law continuum: the e-folding energy is E(c
) almost-equal-to 0.6(-0.3)+0.8 MeV. The simplest model that describes
this spectrum is Comptonization in a relativistic optically-thin ther
mal corona above the surface of an accretion disk. Radio-quiet Seyfert
2's show strong neutral absorption, and there is an indication that t
heir X-ray power laws are intrinsically harder, although the Seyfert 1
spectrum with alpha = 0.9 and strong reflection cannot be ruled out b
y the data. Finally, the radio-loud Seyfert spectrum has alpha almost-
equal-to 0.7, moderate neutral absorption, E(c) = 0.4(-0.2)+0.7 MeV, a
nd no or little Compton reflection. This is incompatible with the radi
o-quiet Seyfert 1 spectrum, and probably indicating that the X-rays ar
e beamed away from the accretion disk in these objects. The average sp
ectra of Seyferts integrated over redshift with a power-law evolution
can explain the hard X-ray spectrum of the cosmic background. The hump
at approximately 30 keV in that spectrum is due to the dominant contr
ibution of Seyfert 2's.