On the unified view of gamma-ray energy distribution of BL Lac objects and flat spectrum radio quasars

Abstract

We study the distributions of $$\gamma $$ -ray properties of a sample of $$\gamma $$ -ray loud blazars taken from the third catalogue of blazars detected by Fermi-Large Area Telescope (Fermi-LAT). We compute the $$\gamma $$ -ray dominance ( $$D_{\mathrm {g}}$$ ) of the sample which includes 415 flat spectrum radio quasars (FSRQs) and 535 BL Lacertae objects (BL Lacs). We find that BL Lacs and FSRQs are highly dominated by $$\gamma $$ -ray emission, which is consistent with diffuse high-energy neutrino flux associated with $$\gamma $$ -ray loud blazars. The $$\gamma $$ -ray dominance fairly scales with $$\gamma $$ -ray luminosity ( $$r \sim + 0.5$$ ) in both BL Lacs and FSRQs, but shows little or no correlation ( $$r \le 0.2$$ ) with radio luminosity in either sample. BL Lacs and FSRQs occupy separate and parallel regions on the $$D_{\mathrm {g}}$$ - luminosity plane. There is a fairly significant correlation ( $$r \sim 0.5$$ ) between $$\gamma $$ -ray dominance and frequency at synchrotron peak ( $$\nu _{\mathrm {pk}}$$ ) in BL Lacs, which disappears in FSRQs. On the other hand, there is a tight correlation ( $$r \ge +0.8$$ ) between $$\gamma $$ -ray and radio luminosity with a smooth transition from BL Lacs at low luminosities to FSRQs at high luminosities. Nevertheless, the presence of few BL Lac-like FSRQs is noted. These results suggest that while there may be intrinsic differences between BL Lacs and FSRQs, some form of a unified scheme can also be relevant.