Chasing the heaviest black holes of jetted Active Galactic Nuclei

TL;DR

This paper studies the most powerful high-redshift blazars with massive black holes and strong jets, highlighting their detectability in hard X-ray surveys and implications for future missions.

Contribution

It provides the first detailed comparison of high-redshift BAT-detected blazars with LAT blazars, emphasizing their extreme properties and detection prospects in hard X-ray bands.

Findings

BAT blazars have more powerful jets than LAT blazars.

Black hole masses in these blazars exceed billions of solar masses.

Hard X-ray surveys are more effective for detecting the most extreme blazars.

Abstract

We investigate the physical properties of the 10 blazars at redshift greater than 2 detected in the 3-years all sky survey performed by the Burst Alert Telescope (BAT) onboard the Swift satellite. We find that the jets of these blazars are among the most powerful known. Furthermore, the mass of their central black hole, inferred from the optical-UV bump, exceeds a few billions of solar masses, with accretion luminosities being a large fraction of the Eddington one. We compare their properties with those of the brightest blazars of the 3-months survey performed by the Large Area Telescope (LAT) onboard the Fermi satellite. We find that the BAT blazars have more powerful jets, more luminous accretion disks and larger black hole masses than LAT blazars. These findings can be simply understood on the basis of the blazar sequence, that suggests that the most powerful blazars have a spectral energy distribution with a high energy peak at MeV (or even sub-MeV) energies. This implies that the most extreme blazars can be found more efficiently in hard X-rays, rather than in the high energy gamma-ray band. We then discuss the implications of our findings for future missions, such as the New Hard X-ray Mission (NHXM) and especially the Energetic X-ray Imaging Survey Telescope (EXIST) mission which, during its planned 2 years all sky survey, is expected to detect thousands of blazars, with a few of them at z greater than 6.