Markos Georganopoulos

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

By including Klein-Nishina effects, we generalize previous calculations of the beaming pattern of photons produced by inverse Compton scattering. For an isotropic distribution of soft photons upscattered by nonthermal electrons with a power-law density distribution embedded in a plasma moving with relativistic bulk speed we show that the observed radiation intensity is proportional to D^(3+p), where D is the Doppler boosting factor, and p the electron distribution index. This agrees with previous computations performed in the Thomson limit, where the observed spectral index is a=(p-1)/2 and the beaming pattern D^(4+2a). Independent of D, Klein-Nishina effects limit the location of the peak energy of the observed spectral energy distribution such that e_{peak} less than 1/e_0, where e_0 is the energy of the seed photons in units of mc^2. Assuming that the seed photons originate in the broad line region, we demonstrate that the GeV emission of blazars is significantly modified by Klein-Nishina effects, the spectrum being softer than that calculated in the Thomson limit. We further show that the change in spectral index of the inverse Compton emission across the peak energy can exceed the value of 0.5 predicted by computations performed in the Thomson limit. The model spectra agree with OSSE and COMPTEL limits on this break without invoking the effects of differential absorption at the edge of a gamma-ray photosphere

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. 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 to 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 intermediate-frequency BL Lac objects are more aligned and less powerful than BQs, and we address the very different emission-line properties of these sources that display similar spectral energy distributions.

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.