The New Variability Phase of OJ 287 and Emergence of New Components in NIR to X-ray Region

TL;DR

This study analyzes the recent multi-wavelength activity of the super-massive binary black hole system OJ 287, revealing new spectral components and complex variability patterns across NIR to X-ray energies, with implications for understanding its emission zones.

Contribution

It presents the first detailed multi-wavelength spectral and temporal analysis of OJ 287's recent activity, identifying new emission components and variability behaviors across different energy bands.

Findings

Detection of new NIR-optical and optical-UV spectral components.

Observation of a shift in gamma-ray SED peak explained by inverse Compton scattering.

Identification of two emission zones at different scales contributing to the SED.

Abstract

We present a multi-wavelength (MW) spectral and temporal study of the recent activity of the claimed super-massive binary black hole system OJ 287 since December 2015. The overall MW activity can be divided into two durations: December 2015 - April 2016 (MJD: 57360 - 57500), showing strong activity from near-infrared (NIR) to $\gamma$-rays and September 2016 - June 2017 (MJD: 57650 - 57930), showing intense NIR to X-ray variability concurrent with detection at very high energies (VHE) by VERITAS, but without any signatures of variability in the Fermi-LAT band. In the first duration, the variations are almost simultaneous and the SEDs show new components in NIR-optical and optical-UV region. The NIR-optical bump is consistent with standard accretion-disk (AD) description while the optical-UV appears consistent with contributions from the broad-line region. The extracted broadband SEDs also show a clear shift in gamma-ray SED peak and can be explained with inverse Compton scattering of photons from broad line region. In the second period, the variations are also simultaneous except for one duration during which X-ray leads the optical/UV by $\sim$ 5-6 day. The broadband SEDs, on the other hand, show mixture of a typical OJ 287 SED and an HBL SED, consistent with an origin from two different zones, one located at sub-parsec scales and other at parsec scales.