2008MNRAS.385..119W

Since 2002, the number of detected blazars at γ-ray energies above 100 GeV has more than doubled. I study 17 blazars currently known to emit E > 100 GeV γ-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 3.6σ significance level between γ-ray and X-ray fluxes is found, while correlations between γ-ray and optical/radio fluxes are less pronounced. Further, a general hardening of the blazar spectra in the E > 100 GeV region with increasing γ-ray luminosity is observed, both for the full 17-source sample and for those sources which have been detected at distinct flux levels. This goes in line with a correlation of the γ-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 blazar γ-ray emission might depend on the mass of the central BH. The blazars under study do, however, show no correlation of the BH masses with the spectral index and the luminosity in the E > 100 GeV region.

I also consider temporal properties of the X-ray and E > 100 GeV γ-ray flux. No general trends are found, except for the observation that the blazars with the most massive BHs do not show particularly high duty cycles. These blazars include Mkn501 and PKS2155-304, for which recently very fast flares have been reported. In general, very high-energy 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 PG1553+113 is discussed.