Blue Fermi Flat Spectrum Radio Quasars

TL;DR

This paper investigates 'blue quasars', a subset of flat spectrum radio quasars with hidden emission lines, by analyzing their spectral energy distributions and discussing their place within the broader blazar population.

Contribution

It provides the first detailed spectral energy distribution models for 'blue quasars' and discusses their rarity among Fermi-detected blazars.

Findings

'Blue quasars' have high-energy electrons with weak radiative cooling.

Their jet dissipation likely occurs outside the broad line region.

'Blue quasars' are a minority within the blazar population.

Abstract

Many blazars detected by the Fermi satellite, observed spectroscopically in the optical, are line-less, and have been classified as BL Lac objects. Optical-UV photometry of nearly one hundred of them 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 flat spectrum radio quasars whose broad emission lines are hidden by an overwhelming synchrotron emission peaking in the UV. This implies that the emitting electrons have high energies. In turn, this 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 the spectral energy distributions of the 4 "blue quasars" recently discovered. Furthermore, we discuss the distribution of Fermi blazars in the gamma-ray spectral index -- gamma-ray luminosity plane, and argue that "blue quasars" objects are a minority within the blazar populations.