Hints for an axion-like particle from PKS 1222+216

Abstract

Flat spectrum radio quasars (FSRQs) are a particular class of blazars rich of optical/ultraviolet photons inside the broad line region (BLR), necessarily implying a huge optical depth for γ rays above 20 GeV. As a consequence, photons with energy above such a threshold should not be emitted. However, photons in the energy range 70 − 400 GeV have been observed by MAGIC from the FSRQ PKS 1222+216. Several astrophysical explanations exist in the literature, but they are all ad hoc, namely devised only for that specific purpose. We show that such a surprising discovery can be explained within standard blazar models by adding the new possibility that photons oscillate into axion-like particles (ALPs) and vice-versa inside the source. Through the photon-ALP oscillation mechanism a sizable fraction of very-high energy (VHE) photons can escape absorption from the BLR in a similar fashion as they largely avoid absorption from the extragalactic background light (EBL) in the intergalactic space. Actually, we show that not only are VHE photon indeed emitted, but also that their spectral energy distribution (SED) is such that they lie on the same Compton peak to which also lower energy photons simultaneously detected by Fermi/LAT belong.

Search for EeV photon-induced events at the Telescope Array

“…Bergman 3 , S.A. Blake 3 , I. Buckland 3 , B.G. Cheon 5 , M. Chikawa 6 , A. Fedynitch 6,7 , T. Fujii 4,8 , K. Fujisue 6 , K. Fujita 6 , R. Fujiwara 4 , M. Fukushima 6 , G. Furlich 3 , Z. Gerber 3 , N. Globus 9 , W. Hanlon 3 , N. Hayashida 10 , H. He 9 , R. Hibi 2 , K. Hibino 10 , R. Higuchi 9 , K. Honda 11 , D. Ikeda 10 , N. Inoue 12 , T. Ishii 11 , H. Ito 9 , D. Ivanov 3 , A. Iwasaki 4 , H.M. Jeong 13 , S. Jeong 13 , C.C.H. Jui 3 , K. Kadota 14 , F. Kakimoto 10 , O. Kalashev 15 , K. Kasahara 16 , S. Kasami 17 , S. Kawakami 4 , K. Kawata 6 , I. Kharuk 15 , E. Kido 9 , H.B.…”

“…Kim 3 , S.W. Kim 13 , Y. Kimura 4 , I. Komae 4 , K. Komori 17 , Y. Kusumori 17 , M. Kuznetsov 15,18 , Y.J. Kwon 19 , K.H.…”

“…Recently, several experiments reported evidence for the detection of ultra-high-energy photon-induced events from GRB 221009A [7][8][9][10][11]. How such photon-like particles have reached the Earth is yet unknown, and this observation may point to physics beyond the standard model [12][13][14]. This motivates for a search for photon-like-induced events in the Telescope Array's data.…”