An Empirical “High-confidence” Candidate Zone for Fermi BL Lacertae Objects

Shi-Ju Kang,Qingwen Wu,Fei-Fei Wang,Tian-Yuan Zheng,Yue Yin,Bin-Bin Zhang,Yu Liu,Kerui Zhu,Jianchao Feng

doi:10.3847/1538-4357/ab722d

Abstract

Abstract In the third catalog of active galactic nuclei detected by the Fermi Large Area Telescope Clean (3LAC) sample, there are 402 blazar candidates of uncertain type (BCU). The proposed analysis will help to evaluate the potential optical classification flat spectrum radio quasars (FSRQs) versus BL Lacertae (BL Lac) objects of BCUs, which can help to understand which is the most elusive class of blazar hidden in the Fermi sample. By studying the 3LAC sample, we found some critical values of γ-ray photon spectral index (Γph), variability index (VI), and radio flux ( ) of the sources separate known FSRQs and BL Lac objects. We further utilize those values to defined an empirical “high-confidence” candidate zone that can be classified as BCUs. Within such a zone (Γph < 2.187, log F R < 2.258, and log VI < 1.702), we found that 120 BCUs can be classified as BL Lac object candidates with a higher degree of confidence (with a misjudged rate <1%). Our results suggest that an empirical “high-confidence” diagnosis is possible to distinguish the BL Lac objects from the Fermi observations based on only the direct observational data of Γph, VI, and F R.

Highlights

Blazars are a particular class of radio-loud active galactic nuclei (AGNs) with a relativistic jet pointing toward the Earth
We find that there are no flat spectrum radio quasars (FSRQs) falling in a range γ-ray photon spectral index (Γph) < a1, logFR < a2 and logVI < a3, while some BL Lacerate objects (BL Lacs) lie in the zone, where ai (i=1,2,3) is set as the boundary value
We study the distributions of the FSRQs and BL Lacs based on the scatterplots of these 3 parameters

Summary

INTRODUCTION

Blazars are a particular class of radio-loud active galactic nuclei (AGNs) with a relativistic jet pointing toward the Earth. BCUs are those sources without a confirmed classifications due to the missing representative features on optical spectrum (BCU I), synchrotron peak frequencies of SED (BCU II), and/or their broadband emissions (BCU III) (see Ackermann et al 2015; Acero et al 2015 for the details and references therein) Studying such a large sample of BCUs is crucial to understand of the physics of γ-ray emission of blazars (e.g., Singal et al 2012; Singal 2015; Fan et al 2016; Kang et al 2018, 2019a,b; Zhu et al 2020).

DATA SELECTION AND ANALYSIS

COMPARISON WITH LITERATURE RESULTS

DISCUSSIONS

Findings

SUMMARY