Synoptic studies of seventeen blazars detected in very high-energy gamma-rays

TL;DR

This study analyzes 17 blazars emitting very high-energy gamma rays, examining their spectra, luminosities, and correlations with other wavelengths and black hole masses, revealing spectral hardening with luminosity and no strong BH mass influence.

Contribution

It provides the first comprehensive comparison of intrinsic spectra and multi-wavelength correlations for a sizable sample of VHE blazars, including constraints on redshift and spectral behaviors.

Findings

Gamma-ray and X-ray fluxes are correlated at 3.6-sigma significance.

Spectral hardening correlates with increasing gamma-ray luminosity.

No correlation between black hole mass and spectral index or luminosity.

Abstract

Since 2002, the number of detected blazars at gamma-ray energies above 100 GeV has more than doubled. I study 17 blazars currently known to emit E>100 GeV gamma rays. Their intrinsic energy spectra are reconstructed by removing extragalactic background light attenuation effects. Luminosity and spectral slope in the E>100 GeV region are then compared and correlated among each other, with X-ray, optical and radio data, and with the estimated black hole (BH) masses of the respective host galaxies. According to expectations from synchrotron self-Compton emission models, a correlation on the 3.6-sigma significance level between gamma-ray and X-ray fluxes is found, while correlations between gamma-ray and optical/radio fluxes are less pronounced. Further, a general hardening of the E>100 GeV spectra with increasing gamma-ray luminosity is observed. This goes in line with a correlation of the gamma-ray luminosity and the synchrotron peak frequency, which is also seen. Tests for possible selection effects reveal a hardening of the spectra with increasing redshift. The gamma-ray emission might depend on the mass of the central BH. The studied blazars show no correlation of the BH masses with the spectral index and the luminosity in the E>100 GeV region. Also temporal properties of the X-ray and E>100 GeV gamma-ray flux are considered. No general trends are found, except that the blazars with the most massive BHs do not show particularly high duty cycles. In general, VHE flare time-scales are not found to scale with the BH mass. As a specific application of the luminosity study, a constraint for the still undetermined redshift of the blazar PG 1553+113 is discussed.