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Register a new userA Unifying View of the Spectral Energy Distributions of Blazars
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G. Fossati
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We collect data from the radio to the gamma-ray range for three complete samples of blazars: the Slew Survey and the 1Jy samples of BL Lacs and the 2Jy sample of Flat Spectrum Radio-Loud Quasars (FSRQs). The fraction of objects detected in gamma-rays (E > 100 MeV) is 17%, 26% and 40% in the three samples respectively. Except for the Slew Survey sample, gamma-ray detected sources do not differ either from other sources in each sample, nor from all the gamma-ray detected sources, in terms of the distributions of redshift, radio and X-ray luminosities and of the broad band spectral indices (radio to optical and radio to X-ray). We compute average Spectral Energy Distributions (SEDs) from radio to gamma rays for groups of blazars binned according to radio luminosity, irrespective of the original classification as BL Lac or FSRQ. The resulting SEDs show a remarkable continuity in that: i) the first peak occurs in different frequency ranges for different luminosity classes, with most luminous sources peaking at lower frequencies; ii) the peak frequency of the gamma-ray component correlates with the peak frequency of the lower energy one; iii) the luminosity ratio between the high and low frequency components increases with bolometric luminosity. The continuity of properties among different classes of blazars and the systematic trends of the SEDs as a function of luminosity favor a unified view of the blazar phenomenon: a single parameter, related to luminosity, seems to govern the physical properties and radiation mechanisms in the relativistic jets present in BL Lac objects as well as in FSRQ. The general implications of this unified scheme are discussed.
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We consider archival ROSAT and HST observations of five FRI radio galaxies and isolate their nuclear emission from that of the host galaxy. This enable us to determine the Spectral Energy Distributions (SED) of their nuclei spanning from the radio to the X-ray band. They cannot be described as single power-laws but require the presence of an emission peak located between the IR and soft X-ray band. We found consistency between the SED peak position and the values of the broad band spectral indices of radio galaxies with those of BL Lac, once the effects of beaming are properly taken into account. FRI SED are thus qualitatively similar to those of BL Lacs supporting the identification of FRI sources as their mis-oriented counterparts. No dependence of the shape of the SED on the FR~I orientation is found.
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