Exploring Gravitational Lensing
with High Energy Gamma Rays

Anna Barnacka (CfA-OIR)

The observation of gravitational lensing is challenging at high energies as only the most powerful sources can be detected. At these energies, the Fermi Gamma-ray Space Telescope has continuously monitored the whole sky since 2008, detecting photons from the most luminous objects in the Universe (e.g. blazars and gamma-ray bursts). I will present the lensing phenomena observed so far with the Fermi satellite, including the first evidence for strong gravitational lensing in high energy gamma-rays. The evidence comes from the observation of a gravitational-lens induced echo in the light curve of the distant blazar PKS 1830-211. The second phenomenon, called femtolensing, enabled the derivation of limits on the abundance of primordial black holes abundance. Here gamma-ray bursts, with known redshifts, detected by the Fermi Gamma-ray Burst Monitor (GBM) were used to search for the femtolensing effects caused by compact objects.