Blue quasars and blazar unification

Abstract

Blue quasars (BQ) are sources with strong broad emission lines and flat hard X-ray spectra, properties that characterize classical flat spectrum radio quasars (FSRQs), and high peak frequencies and steep soft X-ray spectra, properties that characterize intermediate or high peak frequency BL Lacerate objects. Blue quasars challenge our understanding of blazar properties in terms of a luminosity sequence, which makes their incorporation into current blazar unification schemes problematic. We argue that this situation can be remedied if, in addition to the intrinsic luminosity, the orientation of the blazar jet is explicitly considered. We show that the recently studied blue quasars are relatively misaligned blazars, and we argue that the aligned sources are similar to FSRQs. We point out that intermediate BLs are more aligned and less powerful than blue quasars and we address the very different emission line properties of these sources which display similar peak frequency and apparent luminosity.