Potential of EBL and cosmology studies with the Cherenkov Telescope Array

Understand

Very high energy (VHE, E >100 GeV) gamma-rays are absorbed via interaction with low-energy photons from the extragalactic background light (EBL) if the involved photon energies are above the threshold for electron-positron pair creation.

• The VHE gamma-ray absorption, which is energy dependent and increases strongly with redshift, distorts the VHE spectra observed from distant objects.
• The observed energy spectra of the AGNs carry, therefore, an imprint of the EBL.
• The detection of VHE gamma-ray spectra of distant sources (z = 0.11 - 0.54) by current generation Imaging Atmospheric Cherenkov Telescopes (IACTs) enabled to set strong upper limits on the EBL density, using certain basic assumptions about blazar physics.