Evaluating Optical Classification for {\em Fermi} Blazar Candidates with a Statistical method using Broadband Spectral Indices

TL;DR

This study uses broadband spectral indices to statistically classify uncertain Fermi blazar candidates as BL Lac objects or FSRQs, demonstrating good agreement with spectroscopic identifications and highlighting selection effects.

Contribution

The paper introduces a statistical method based on broadband spectral indices for classifying Fermi blazar candidates, validated against spectroscopic data.

Findings

34% of radio-selected BCUs are BL Lac-like

77.3% of X-ray selected BCUs are BL Lac-like

High consistency with optical spectroscopic classifications

Abstract

We aim to test if a blazar candidate of uncertain-type (BCU) in the third Fermi active galactic nuclei catalog (3LAC) can be potentially classified as a BL Lac object or a flat spectrum radio quasar (FSRQ) by performing a statistical analysis of its broadband spectral properties. We find that 34% of the radio-selected BCUs (583 BCUs) are BL Lac-like and 20% of them are FSRQ-like, which maybe within 90% level of confidence. Similarly, 77.3% of the X-ray selected BCUs (176 BCUs) are evaluated as BL Lac-like and 6.8% of them may be FSRQ-like sources. And 88.7% of the BL Lac-like BCUs that have synchrotron peak frequencies available are high synchrotron peaked BL Lacs in the X-ray selected BCUs. The percentages are accordingly 62% and 7.3% in the sample of 124 optical-selected BCUs. The high ratio of source numbers of the BL Lac-like to the FSRQ-like BCUs in the X-ray and optically selected BCU samples is due to the selection effect. Examining the consistency between our evaluation and spectroscopic identification case by case with a sample of 78 radio-selected BCUs, it is found that the statistical analysis and its resulting classifications agree with the results of the optical follow-up spectroscopic observations. Our observation campaign for high-|\rho_{s}| BCUs , i.e., |\rho_{s}|>0.8, selected with our method is ongoing.