Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000mnras.312..177m&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 312, Issue 1, pp. 177-193.
Astronomy and Astrophysics
Astronomy
75
Galaxies: Active, Quasars: General, Diffuse Radiation, Gamma-Rays: Theory
Scientific paper
We present a calculation of the blazar contribution to the extragalactic diffuse γ-ray background (EGRB) in the EGRET energy range. Our model is based on inverse-Compton scattering as the dominant γ-ray production process in the jets of flat spectrum radio quasars (FSRQs) and BL Lac objects, and on the unification scheme of radio-loud AGN. According to this picture, blazars represent the beamed fraction of the Fanaroff-Riley radio galaxies (FR galaxies). The observed logN-logS distribution and redshift distribution of both FSRQs and BL Lacs constrain our model. Depending slightly on the evolutionary behaviour of blazars, we find that unresolved AGN underproduce the intensity of the extragalactic background radiation. With our model only 20-40per cent of the extragalactic background emission can be explained by unresolved blazars if we integrate to a maximum redshift of Zmax=3. For Zmax=5, blazars could account for 40-80per cent of the EGRB. Roughly 70-90per cent of the AGN contribution to the EGRB would result from BL Lacs. While the systematic uncertainties in our estimate for the FSRQ contribution appear small, in the case of BL Lacs our model parameters are not consistent with the results from studies in other wavelength regimes, and therefore may have larger systematic uncertainties. Thus we end up with two possibilities, depending on whether we underpredict or overpredict the BL Lac contribution: either unresolved AGN cannot account for the entire EGRB, or unresolved BL Lacs produce the observed background. We predict a significant flattening of the γ-ray logN-logS function in the next two decades of flux below the EGRET threshold.
Mücke Anita
Pohl Mario
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