Spectral Energy Distribution Variability of the Blazar OJ 287 during 2009-2021

TL;DR

This study analyzes the spectral energy distribution variability of blazar OJ 287 from 2009 to 2021, revealing differences between flare and quiescent states, and exploring the underlying physical mechanisms influencing its emission properties.

Contribution

It provides a comprehensive analysis of multi-wavelength SEDs of OJ 287 over a decade, highlighting the spectral behavior during different activity states and testing acceleration models.

Findings

Flare segments show higher peak flux than quiescent segments.

A bluer-when-brighter trend is confirmed, especially during flares.

An anti-correlation between peak frequency and curvature parameter is observed.

Abstract

Using nearly simultaneous radio, near-infrared, optical, and ultraviolet data collected since 2009, we constructed 106 spectral energy distributions (SEDs) of the blazar OJ 287. These SEDs were well-fitted by a log-parabolic model. By classifying the data into `flare' and `quiescent' segments, we found that the median flux at peak frequency of the SEDs during flare segments was 0.37$\pm$0.22 dex higher compared to quiescent segments, while no significant differences were observed in the median values of the curvature parameter $b$ or the peak frequency $\log \nu_{\mathrm{p}}$. A significant bluer-when-brighter trend was confirmed through a relation between $V$ magnitude and $B-V$ color index, with this trend being stronger in the flare segments. Additionally, a significant anti-correlation was detected between $\log \nu_{\mathrm{p}}$ and $b$, with a slope of 5.79 in the relation between $1/b$ and $\log \nu_{\mathrm{p}}$, closer to the prediction from a statistical acceleration model other than a stochastic acceleration interpretation, though a notable discrepancy persists. This discrepancy indicates that additional factors, such as deviations from idealized conditions or radiative contributions-such as thermal emission from the accretion disk in the optical-UV range during quiescent states-may play a role in producing the observed steeper slope. Within the framework of statistical acceleration mechanism, lack of correlation between change in peak intensity and change in peak frequency suggests that change in electron energy distribution is unlikely to be responsible for the time-dependent SED changes. Instead, changes in Doppler boosting or magnetic fields may have a greater influence.