G. Ghisellini, F. Tavecchio, L. Foschini, T. Sbarrato, G. Ghirlanda, L. Maraschi
Optical-UV photometry of blazars detected by the Fermi satellite and classified as BL Lacs allowed to determine the redshift for a handful of objects and redshift upper limits for the great majority. A few of these are candidates to be "blue quasars", namely FSRQs whose broad emission lines are hidden by an overwhelming synchrotron emission peaking in the UV. This implies that the emitting electrons have high energies, which in turn requires relatively weak radiative cooling, a condition that can be met if the main radiative dissipation of the jet power occurs outside the broad line region. We confirm this hypothesis by studying and modelling their spectral energy distributions and argue that these objects are a minority within the blazar populations.
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http://arxiv.org/abs/1205.0808
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