X-ray Spectra and Multiwavelength Machine Learning Classification for Likely Counterparts to Fermi 3FGL Unassociated Sources

TL;DR

This study uses X-ray spectral analysis and machine learning to classify unassociated Fermi-LAT sources, identifying likely blazar and pulsar candidates with high accuracy, enhancing understanding of high-energy astrophysical populations.

Contribution

The paper introduces a robust multiwavelength classification method combining X-ray spectral fitting with machine learning, improving source categorization accuracy for unassociated gamma-ray sources.

Findings

Achieved 98.6% classification accuracy with random forest.

Identified 126 likely blazar and 5 likely pulsar candidates.

Most X-ray spectra fit by absorbed power law, consistent with blazar and pulsar populations.

Abstract

We conduct X-ray spectral fits on 184 likely counterparts to Fermi-LAT 3FGL unassociated sources. Characterization and classification of these sources allows for more complete population studies of the high-energy sky. Most of these X-ray spectra are well fit by an absorbed power law model, as expected for a population dominated by blazars and pulsars. A small subset of 7 X-ray sources have spectra unlike the power law expected from a blazar or pulsar and may be linked to coincident stars or background emission. We develop a multiwavelength machine learning classifier to categorize unassociated sources into pulsars and blazars using gamma- and X-ray observations. Training a random forest procedure with known pulsars and blazars, we achieve a cross-validated classification accuracy of 98.6%. Applying the random forest routine to the unassociated sources returned 126 likely blazar candidates (defined as $ P_{bzr} > 90 \% $) and 5 likely pulsar candidates ($ P_{bzr} < 10 \% $). Our new X-ray spectral analysis does not drastically alter the random forest classifications of these sources compared to previous works, but it builds a more robust classification scheme and highlights the importance of X-ray spectral fitting. Our procedure can be further expanded with UV, visual, or radio spectral parameters or by measuring flux variability.