Blue Quasars and Blazar Unification Schemes

Abstract

Blue quasars (BQs) are sources with strong broad emission lines and flat hard X-ray spectra, properties that resemble classical flat spectrum radio quasars (FSRQs), and high peak frequencies and steep soft X-ray spectra, properties that resemble intermediate or high peak frequency BL Lacertae objects(IBLs and HBLs respectively). BQs challenge our understanding of blazar properties in terms of a luminosity sequence, which makes their incorporation into current blazar unification schemes problematic. In this work we show that this situation can be remedied if, in addition to the intrinsic luminosity, the orientation of the blazar jet is explicitly considered. We show, using published data, that the recently studied BQs are relatively misaligned blazars, and we examine the predicted aligned population. We examine both possible cases, sources with pure synchrotron spectra and sources with an optical--UV thermal contribution, for both constant velocity and accelerating jets. We show that the aligned sources are similar to FSRQs, and we suggest ways to distinguish between constant velocity and accelerating flows. We point out that IBLs are more aligned and less powerful than BQs and we address the very different emission line properties of these sources which display similar spectral energy distributions.