The Structure of the Strongly Lensed Gamma-ray Source B2 0218+35

TL;DR

This paper uses gravitational lensing combined with multi-wavelength data to spatially resolve gamma-ray flaring regions in a distant blazar, revealing they are offset from the radio core by about 51 parsecs.

Contribution

It presents a novel method combining Fermi-LAT, radio, and Planck data to achieve milliarcsecond resolution of gamma-ray source locations in a strongly lensed system.

Findings

Gamma-ray flares are offset from the radio core by 51±8 parsecs.

Achieved 1 milliarcsecond spatial resolution at gamma-ray energies.

First source where gamma-ray emission region is spatially resolved relative to radio core.

Abstract

Strong gravitational lensing is a powerful tool for resolving the high energy universe. We combine the temporal resolution of Fermi-LAT, the angular resolution of radio telescopes, and the independently and precisely known Hubble constant from Planck, to resolve the spatial origin of gamma-ray flares in the strongly lensed source B2 0218+35. The lensing model achieves 1 milliarcsecond spatial resolution of the source at gamma-ray energies. The data imply that the gamma-ray flaring sites are separate from the radio core: the bright gamma-ray flare (MJD: 56160 - 56280) occurred $51\pm8$ pc from the 15 GHz radio core, toward the central engine. This displacement is significant at the $\sim3\sigma$ level, and is limited primarily by the precision of the Hubble constant. B2 0218+35 is the first source where the position of the gamma-ray emitting region relative to the radio core can be resolved. We discuss the potential of an ensemble of strongly lensed high energy sources for elucidating the physics of distant variable sources based on data from Chandra and SKA.