An extensive study of blazar broad emission line: Changing-look blazars and Baldwin effect

TL;DR

This study investigates the relationship between accretion disk emission lines and jet gamma-ray flux in blazars, revealing a Baldwin effect and identifying changing-look blazars with implications for their accretion states and emission mechanisms.

Contribution

It provides the first large-scale analysis linking emission line properties with gamma-ray flux and identifies new changing-look blazars, enhancing understanding of blazar emission dynamics.

Findings

Identified 52 changing-look blazars, 45 of which are newly confirmed.

Confirmed the Baldwin effect in blazars, showing an anti-correlation between EW and continuum.

Suggested LSP blazars are the main source of changing-look blazars.

Abstract

It is known that the blazar jet emissions are dominated by non-thermal radiation while the accretion disk jets are normally dominated by thermal emission. In this work, our aim is to study the connection between the two types of emission by investigating the correlation between the blazar emission line intensity property, which embodies the nature of accretion disk, and the $\gamma$-ray flux property, which is the representative of jet emission. We compiled a sample of 656 blazars with available emission line equivalent widths ($EW$), the GeV $\gamma$-ray flux, and the SED information from the literature. In this work, we found 55 previous BCUs are now identified as FSRQs, and found 52 Changing-look blazars based on their $EW$ and 45 of them are newly confirmed. These Changing-look blazars have a larger accretion ratio (${\dot M}/{\dot M}_{\rm Edd}$) than BL Lac objects. In addition, we suggest that the lower synchrotron peak blazars (LSPs) could be the source of Changing-look blazars because 90.7\% of the Changing-look blazars in this work are confirmed as LSPs. An anti-correlation between $EW$ and continuum intensity, the so-called global Baldwin effect (BEff) has been confirmed. We suggest the steeper global BEff observed for blazar than for radio-quiet active galactic nuclei (RQ-AGNs) is caused by the inverse Compton scattering of broad-emission-line photons. This interpretation is further supported by the positive correlation between the emission line $EW$ and intrinsic inverse Compton luminosity.