Statistics of Cosmological Black Hole Jet Sources: Blazar Predictions for the Gamma-Ray Large Area Space Telescope

Abstract

A study of the statistics of cosmological black hole jet sources is applied to EGRET blazar data and predictions are made for GLAST. Black hole jet sources are modeled as collimated relativistic plasma outflows with radiation beamed along the jet axis due to strong Doppler boosting. The comoving rate density of blazar flares is assumed to follow a blazar formation rate (BFR), modeled by analytic functions based on astronomical observations and fits to EGRET data. The redshift and size distributions of γ-ray blazars observed with EGRET, separated into BL Lac objects (BLs) and flat spectrum radio quasar (FSRQ) distributions, are fit with monoparametric functions for the distributions of the jet Lorentz factor Γ, comoving directional power l′e, and spectral slope. A BFR factor ≈10× greater at z ≳ 1 than at present is found to fit the FSRQ data. A smaller comoving rate density and greater luminosity of BL flares at early times compared to the present epoch fits the BL data. Based on the EGRET observations, ≈1000 blazars consisting of ≈800 FSRQs and FR 2 radio galaxies and ≈200 BL Lac objects and FR 1 radio galaxies will be detected with GLAST during the first year of the mission. Additional AGN classes, such as hard-spectrum BL Lac objects that were mostly missed with EGRET, could add more GLAST sources. The FSRQ and BL contributions to the EGRET γ-ray background at 1 GeV are estimated at the level of ≈10%-15% and ≈2%-4%, respectively. EGRET and GLAST sensitivities to blazar flares are considered in the optimal case, and a GLAST analysis method for blazar detection is outlined.