How many radio-loud quasars can be detected by the Gamma-Ray Large Area Space Telescope?

TL;DR

This paper estimates the number of radio-loud quasars detectable by GLAST using Comptonization models, concluding that most detections will be FSRQs and they contribute significantly to the gamma-ray background.

Contribution

It provides the first detailed estimate of radio quasar detections by GLAST based on luminosity functions and Comptonization models, distinguishing between external and synchrotron self-Compton processes.

Findings

Approximately 1200 radio quasars will be detected by GLAST.

Most detected radio AGNs will be FSRQs (~99%).

Radio quasars contribute about 30% to the extragalactic gamma-ray background.

Abstract

In the unification scheme, radio quasars and FR II radio galaxies come from the same parent population, but viewed at different angles. Based on the Comptonization models for the gamma-ray emission from active galactic nuclei (AGNs), we estimate the number of radio quasars and FR II radio galaxies to be detected by the Gamma-Ray Large Area Space Telescope (GLAST) using the luminosity function (LF) of their parent population derived from the flat-spectrum radio quasar (FSRQ) LF. We find that ~1200 radio quasars will be detected by GLAST, if the soft seed photons for Comptonization come from the regions outside the jets. We also consider the synchrotron self-Comptonization (SSC) model, and find it unlikely to be responsible for gamma-ray emission from radio quasars. We find that no FR II radio galaxies will be detected by GLAST. Our results show that most radio AGNs to be detected by GLAST will be FSRQs (~99 % for the external Comptonization model, EC model), while the remainder (~1 %) will be steep-spectrum radio quasars (SSRQs). This implies that FSRQs will still be good candidates for identifying gamma-ray AGNs even for the GLAST sources. The contribution of all radio quasars and FR II radio galaxies to the extragalactic gamma-ray background (EGRB) is calculated, which accounts for ~30 % of the EGRB.