Feature selection for classification of blazars

Uemura, M., Abe, T., Yamada, Y., and Ikeda, S., “Feature selection for classification of blazars based on optical photometric and polarimetric time-series data”, PASJ, 72, 74, 2020

We investigated the differences of two sub-types of blazars, FSRQs, and BL Lac objects, in the variability. We characterize the variability using the Ornstein–Uhlenbeck (OU) process, and search for the features that are discriminative for the two subtypes. We used optical photometric and polarimetric data obtained with the 1.5 m Kanata telescope for 2008–2014. We found that four features, namely the variation amplitude, characteristic timescale, and non-stationarity of the variability obtained from the light curves and the median of the degree of polarization (PD), are essential for distinguishing between FSRQs and BL Lac objects. The characteristics of the variability imply that the nature of the variation in the jets is common in FSRQs and BL Lac objects. We found that BL Lac objects tend to have high PD medians, which suggests that they have a stable polarization component. FSRQs have no such component, possibly because of a strong Compton cooling effect in sub-parsec-scale jets.