Non-vanishing parity-odd correlators of gamma-ray arrival directions observed by Fermi-LAT indicate the existence of a helical intergalactic magnetic field with strength B ~ 10-14 G on ~10 Mpc scales. We successfully test this hypothesis using more stringent cuts of the data, Monte Carlo simulations with Fermi-LAT time exposure information, separate analyses for the Northern and Southern galactic hemispheres, and confirm predictions made in Tashiro & Vachaspati. With some further technical assumptions, we show how to reconstruct the magnetic helicity spectrum from the parity-odd correlators.
- Cosmology: observations
- Early universe
- Gamma-rays: diffuse background