Unusual long-term low-activity states of EGRET blazars in the Fermi era

Abstract

We examine the long-term (∼10 years) γ-ray variability of blazars observed by the Energetic Gamma Ray Experiment Telescope (EGRET) and Fermi and find that 10 EGRET-detected flat-spectrum radio quasars (FSRQs) were not present in any part of the Fermi catalogue (during the first four years of Fermi observations). Six of these 10 EGRET sources show possible Fermi counterparts, based on overlap with error circles given in the third Fermi catalogue. A seventh EGRET source is positionally consistent with a newly discovered Fermi source from our analysis. Unlike the high luminosity state exhibited during 1991–1995, our analysis using seven years of Fermi data showed that five of these sources are in a low luminosity state in the GeV band. This result indicates that FSRQs exhibit a long-term quiescent state (lasting more than seven years). In addition, 37 new γ-ray sources are also detected during the course of this analysis. On the basis of active galactic nuclei (AGNs) being the most dominant source class in γ-rays, many of these new sources could be associated with AGNs and may exhibit long-term variabilities in γ-rays.