Optical quasi-periodic oscillation and color behavior of blazar PKS 2155-304

TL;DR

This study analyzes 35 years of optical data of blazar PKS 2155-304, revealing a 317-day quasi-periodic oscillation, long-term variability, and a bluer-when-brighter spectral trend.

Contribution

It provides a comprehensive long-term optical analysis of PKS 2155-304, identifying a significant quasi-periodic oscillation and spectral behavior patterns.

Findings

Detected a 317-day periodic component in optical light curve

Observed a long-term trend with large amplitude variation

Found the source exhibits a bluer-when-brighter spectral trend

Abstract

PKS 2155-304 is a well studied BL Lac object in the southern sky. The historical optical data during different period have been collected and compiled. Light curves with a time span of 35 years have been constructed. The R-band light curve has been analyzed by means of three methods: epoch folding method, Jurkevich method and discrete correlation function (DCF) method. It is derived that there is an evident periodic component of 317 days (i.e. 0.87 yr) superposed on a long-term trend with large-amplitude variation in the light curve. The variability of this source is accompanied by a slight color variation, and the brightness and color index are correlated with each other. On the long time-scale, PKS 2155-304 exhibits a tendency of bluer-when-brighter, which means the spectrum becomes flatter when the source brightens.