Hunting for Candidates of Changing-look Blazars Using Mclust Clustering Analysis

Abstract

Changing-look blazars (CLBs) are blazars whose optical spectral lines at different epochs show significant changes and present a clear transition between standard FSRQ and BL Lacertae (BL Lac). Changing-look phenomena in blazars are highly significant for enhancing our understanding of certain physical problems of active galactic nuclei (AGNs), such as the potential mechanism of state transition in the accretion process of supermassive black holes in the central engine of AGNs, the possible intrinsic variation of the jet, and the connection between the accretion disk and the jet. Currently, the CLBs reported in the literature are still rare astronomical objects. In our previous work, we found that there are eight physical property parameters of CLBs located between those of FSRQs and BL Lacs. In order to search for more CLB candidates (CLBCs), we employed the mclust Gaussian mixture modeling clustering algorithm to perform clustering analysis for 255 subsets of the eight physical property parameters with 2250 blazars from 4FGL data release 3. We find that there are 29 subsets with three groups (corresponding to bl lacs, fsrqs, and CLBCs), in which there are four subsets with an adjusted Rand index greater than 0.610. The combined clustering results from the four subsets report that there are 111 CLBCs, which include 44 CLBs reported in previous literature and 67 new CLBCs, of which 11 are labeled as BL Lacs and 56 are labeled as FSRQs in the 4FGL catalog.