Have Cherenkov telescopes detected a new light boson?

Abstract

Recent observations by H.E.S.S. and MAGIC strongly suggest that the Universe is more transparent to very-high-energy gamma rays than previously thought. We show that this fact can be reconciled with standard blazar emission models provided that photon oscillations into a very light Axion-Like Particle occur in extragalactic magnetic fields. A quantitative estimate of this effect indeed explains the observed data and in particular the spectrum of blazar 3C279.

3 pages, 1 figure, Proceeding of the "Eleventh International Workshop on Topics in Astroparticle and Underground Physics" (TAUP), Roma, Italy, 1 - 5 July 2009 (to be published in the Proceedings)