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

Understand

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.