Relations between variability indexes and beaming effects for Fermi blazars

Abstract

Since the Fermi Large Area Telescope launch, a large sample of blazars has been detected in the \(\gamma \)-ray band. One of the important parameters, the variability index (VI), is adopted to quantify the \(\gamma \)-ray blazar variability. The variability of blazars can be affected by the geometric jet structure, accretions, source sizes, or evolutions of particles. In this paper, we compiled a sample of 2250 blazars (792 flat spectrum radio quasars, 1458 BL Lacertae objects) with some physical parameters to investigate the correlations between the VI and beaming effects. The VI shows positive correlations with the Doppler factors, \(\gamma \)-ray luminosities, core dominances, and superluminal motions for both FSRQs and BL Lacs but only holds a positive correlation on polarizations for BL Lacs. The close correlations between VI and the beaming indicators reinforced the previous results that the \(\gamma \)-ray variability is related to the jet, and the VI can be regarded as an effective indicator for the jet beaming effects of Fermi blazars.