Gamma-ray emission region located in the parsec scale jet of OJ287

TL;DR

This study localizes gamma-ray emission in the jet of OJ287 to over 14 parsecs from the black hole, using multi-spectral data and high-resolution imaging, revealing correlations with optical and radio flares.

Contribution

It provides the first direct evidence that gamma-ray emission in OJ287 occurs far from the central black hole, at over 14 parsecs in the jet, based on multi-wavelength correlation analysis.

Findings

Gamma-ray and mm flares are correlated and occur >14pc from the black hole.

Gamma-ray flares coincide with optical flares, suggesting a common origin.

Gamma-ray emission is likely produced by synchrotron self-Compton scattering.

Abstract

We report on the location of the gamma-ray emission region in flares of the BL Lacertae object OJ287 at >14pc from the central supermassive black hole. We employ data from multi-spectral range (total flux and linear polarization) monitoring programs combined with sequences of ultra-high-resolution 7mm VLBA images. The correlation between the brightest gamma-ray and mm flares is found to be statistically significant. The two gamma-ray peaks, detected by Fermi-LAT, that we report here happened at the rising phase of two exceptionally bright mm flares accompanied by sharp linear polarization peaks. The VLBA images show that these mm flares in total flux and polarization degree occurred in a jet region at >14pc from the innermost jet region. The time coincidence of the brighter gamma-ray flare and its corresponding mm linear polarization peak evidences that both the gamma-ray and mm outbursts occur >14pc from the central black hole. We find two sharp optical flares occurring at the peak times of the two reported gamma-ray flares. This is interpreted as the gamma-ray flares being produced by synchrotron self-Compton scattering of optical photons from the flares triggered by the interaction of moving knots with a stationary conical shock in the jet.