Photons to axion-like particles conversion in Active Galactic Nuclei

Journal
Date Issued
2015
Author(s)
•
•
DOI
Description
Acknowledgements We thank Alessandro De Angelis, Luigina Feretti and Marcello Giroletti for useful discussions. F.T. acknowledges contribution from a grant PRIN-INAF-2011. The work of M.R. is supported by INFN TAsP and CTA grants.
Abstract
The idea that photons can convert to axion-like particles (ALPs) γ → a in or around an AGN and reconvert back to photons a → γ in the Milky Way magnetic field has been put forward in 2008 and has recently attracted growing interest. Yet, so far nobody has estimated the conversion probability γ → a as carefully as allowed by present-day knowledge. Our aim is to fill this gap. We first remark that AGN which can be detected above 100 GeV are blazars, namely AGN with jets, with one of them pointing towards us. Moreover, blazars fall into two well defined classes: BL Lac objects (BL Lacs) and Flat Spectrum Radio Quasars (FSRQs), with drastically different properties. In this Letter we report a preliminary evaluation of the γ → a conversion probability inside these two classes of blazars. Our findings are surprising. Indeed, while in the case of BL Lacs the conversion probability turns out to be totally unpredictable due to the strong dependence on the values of the somewhat uncertain position of the emission region along the jet and strength of the magnetic field therein, for FSRQs we are able to make a clear-cut prediction. Our results are of paramount importance in view of the planned very-high-energy photon detectors like the CTA, HAWK, GAMMA-400 and HISCORE.

Volume
744
Start page
375
Uri
Url
Issn Identifier
0370-2693
Ads BibCode
2015PhLB..744..375T
Rights
open.access
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