* Astronomy

Title: Evidence for an axion-like particle from PKS 1222+216? 
Authors: F. Tavecchio, M. Roncadelli, G. Galanti, G. Bonnoli 

The surprising discovery by MAGIC of an intense, rapidly varying very high energy (E>50 GeV) emission from the flat spectrum radio quasar PKS 1222+216 represents a challenge for all interpretative scenarios. Indeed, in order to avoid absorption of gamma rays in the dense ultraviolet radiation field of the broad line region (BLR), one is forced to invoke the existence of a very compact (r~10^14 cm) emitting region at a large distance (R>10^18 cm) from the jet base. We present a scenario based on the standard blazar model for PKS 1222+216 where gamma rays are produced close to the central engine, but we add the new assumption that inside the source photons can oscillate into axion-like particles, which are a generic prediction of many extensions of the Standard Model of elementary particle interactions. As a result, a considerable fraction of photons can escape absorption from the BLR much in the same way as they largely avoid absorption from extragalactic background light when propagating over cosmic distances. We show that observations can be explained in this way for reasonable values of the model parameters, and in particular we find it quite remarkable that the most favourable value of photon-ALP coupling happens to be the same in both situations. An independent laboratory check of our proposal can be performed by the planned upgrade of the ALPS experiment at DESY. 

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Position (J2000):  R.A. 12 24 54.4 |  Dec. +21° 22' 46", z=0.43