The Two-Color Diagram: The "Double-Hump" Behavior at the Radio Band and the Evolution of Blazars

Abstract

We compiled a sample of 29 flat-spectrum radio quasars (FSRQs) and 48 BL Lac objects for which both B - V and U - B are available. The two-color (U - B, B - V) stellar evolution diagram of FSRQs and BL Lac objects in this sample shows that FSRQs and BL Lac objects can be considered to be in the same family, but they occupy different extreme regions in the diagram. The result of the two- color diagram of FSRQs and BL Lac objects in this paper is consistent with the intrinsic accretion rate - luminosity relation for FSRQs and BL Lac objects that was obtained in a previous paper. In addition, based on the quasi-simultaneous spectral properties of core-dominated radio sources observed by Punsly, we compiled another sample of FSRQs and BL Lac objects for which the quantities Delta log [(F-nu)(cm)/(F-nu)(mm)] have been well obtained. We found that there is a significant correlation between the intrinsic bolometric luminosity log L-bol(in) and the quantity Delta. We also found that FSRQs have a relatively higher bolometric luminosity and larger Delta than BL Lac objects. This result is also consistent with the intrinsic accretion rate - luminosity relation because the physical parameters Delta are strongly correlated with the accretion rates (M) and nuclear gas densities.