Simultaneous Optical to X-ray Spectra of OJ 287: Insights into X-ray spectral changes and particle spectra

TL;DR

This study analyzes simultaneous optical to X-ray data of OJ 287, revealing how spectral changes reflect particle energy distributions and providing insights into blazar emission mechanisms during low X-ray flux states.

Contribution

It presents a detailed investigation of optical to X-ray spectral variations in OJ 287, highlighting the role of particle spectra in X-ray spectral changes during low flux states.

Findings

Optical-UV spectrum follows a power-law with index 2.71.

X-ray spectrum can be explained by extending the optical-UV power-law.

Spectral variations suggest changes in particle energy distribution.

Abstract

OJ 287 is one of the most dynamic BL Lacertae objects that has exhibited behaviour representative of the entire blazar class and is also one of the best sources with simultaneous multi-wavelength coordinated data. Motivated by strong X-ray variability exhibited by the source, we systematically investigated the simultaneous optical to X-ray emission of the source with a focus on the spectral state of the lowest recorded X-ray flux state to understand the X-ray spectral changes. The optical-UV emission being synchrotron, the associated spectral variation is a direct reflection of the high-energy end of the underlying particle spectrum and its power-law continuation to X-rays can drastically affect the X-ray spectrum without much change in optical flux. Thus the combined optical to X-ray provides a potential tool to investigate and explore particle spectrum as well as highest particle energies. We report the finding of a power-law optical-UV spectrum with a photon spectral index of 2.71 $\pm$ 0.03 continuing to X-ray energies and accounting for this contribution at X-ray results in a photon spectral index of 1.15-1.3. We discuss the possible implications of this on X-ray spectral variations and the particle spectrum.