A Study of Broad Emission Line and Doppler Factor Estimation for Fermi Blazars

Abstract

In this work, we obtained a sample of 979 Fermi blazars with broad emission lines, including 701 objects collected from published works and 278 objects developed in this work. For the 278 objects, we made a crossmatch from three catalogs, the Fermi Large Area Telescope Fourth Source Catalog (4FGL), the Sloan Digital Sky Survey, and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope, and calculated the broad-line region (BLR) luminosity. Then, we estimated the Doppler factor and studied the correlations between the BLR luminosities and the γ-ray luminosities, the synchrotron peak frequency (ν p ), and Doppler factor (δ) for the whole sample. Our analyses and discussions came to the following main conclusions: For the 278 blazars, their BLR luminosity (log L BLR) ranges from 40.44 to 45.45 erg s−1, with a mean value of 43.39 erg s−1. The Doppler factor ranges from δ = 0.45 to δ = 88.52, with a mean value of 12.99 for the 979 Fermi blazars, which is consistent with the results in the literature. Both the BLR luminosity and the Doppler factor exhibit positive correlations with the γ-ray luminosity. The BLR luminosity is anticorrelated with synchrotron peak frequency, implying a Compton cooling. A line of log L BLR = 1.58 log ν p − 19.46 separating BL Lacertae objects and flat-spectrum radio quasars was obtained in the diagram of log L BLR against log ν p using a machine-learning method. Based on the analysis of the equivalent width and the Doppler factors, we proposed five changing-look blazar candidates.

Cluster Analysis of the Roma-BZCAT Blazars

“…Following works based on various multiband data just confirmed that the emissions in blazars is strongly beamed and affects the observational phenomenon known as "blazar sequence" (e.g., Fan et al 2017;Ouyang et al 2023;Wan et al 2024). In our study we did not apply the Doppler factor as one of the parameters because it is estimated for a limited number of blazars, e.g., for 979 Fermi blazars in one of the recent studies (Chen et al 2024). Therefore, we cannot test the intrinsic nature of the blazar sequence.…”

Jet Mechanism and γ-Ray-emitting Region for Fermi Flat-spectrum Radio Quasars with Broad-line Emissions

“…Second, a collection from Zhang et al (2020Zhang et al ( , 2022 and their respective references (briefly denoted as Z22), was employed. Lastly, new extensions from our preliminary work cited from Chen et al (2024) (marked as C24) were added. These expanded FSRQs collected from C24 had their full width at half maximum (FWHM) and continuum luminosities related to emission lines derived with the available software PyQSOFit (Guo et al 2018).…”

“…) ); column (10): the references for black hole mass. The references in columns (6) and (10) correspond to the literature such as Zhang et al (2020Zhang et al ( , 2022, Paliya et al (2021), andChen et al (2024). The symbol "TW" signifies that we calculate the black hole mass in this study.…”

“…Where is the γ-ray-emitting region located, inside or outside the BLR? We rely on black hole masses derived from the broad-line emissions collected from the literature (Zhang et al 2020;Paliya et al 2021;Zhang et al 2022;Chen et al 2024). Moreover, we determine the jet power based on a broadband fit accounting for the synchrotron and IC components.…”