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arXiv · 2306.04786

Propagation of very-high-energy $γ$-rays from distant blazars

L. J. Dong·Y. G. Zheng·S. J. Kang
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Abstract

We re-derive the possible dependence of the redshift with very high energy (VHE) $γ$-ray photon index. The results suggest that the universe to VHE $γ$-rays is becoming more transparent than usually expected. We introduce the extragalactic background light (EBL) plus the photon to axion-like particle (ALP) oscillations to explain this phenomenon. We concentrate our analysis on 70 blazars up to redshift $z \simeq 1$. Assuming this correlation is solely the result of photon-photon absorption of VHE photons with the EBL, which finds the deviations between the predictions and observations, especially at redshifts $0.2 < z < 1$. We then discuss the implications of photon-ALP oscillations for the VHE $γ$-ray spectra of blazars. A strong evidence shows that: 1) the EBL attenuation results that the VHE $γ$-ray photon index increases non-linearly at the ranges of redshift, $0.03 < z < 0.2$; 2) the photon-ALP oscillation results in a attractive characteristic in the VHE $γ$-ray photon index at the ranges of redshift, $0.2 < z < 1$. We suggest that both the EBL absorption and photon-ALP oscillation can influence on the propagation of VHE $γ$-rays from distant blazars.

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L. J. Dong, Y. G. Zheng, S. J. Kang. 2023-06-07. Propagation of very-high-energy $γ$-rays from distant blazars. https://doi.org/10.3847/1538-4357%2Facdc19

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