Detailed simulations of Fermi-LAT constraints on UHECR production scenarios
August 16, 2017
August 03, 2018
We have performed high-resolution simulations of the flux and spectrum of gammas detectable by Fermi-LAT, coming from UHECR-induced cascades, using the state-of-the-art (Gilmore) model of extragalactic background light, ELMAG to simulate the EM cascade (modified to work correctly for the Gilmore EBL) and CRPropa3 to simulate the production of EM secondaries from UHECR propagation. We examine the validity and limitations of the Liu et al. (2016) constraints, which found that we live in a local UHECR over-density. We also examine whether a model such as that of Unger, Farrar, and Anchordoqui (2015) -- which explains the full extragalactic CR spectrum and composition including the ankle, based on nuclear photodisintegration in the neighborhood surrounding the source -- satisfies the Fermi-LAT constraints, or requires Earth to be in an atypical position in the Universe as claimed by Liu et al. for pure proton primaries. We conclude that a mixed-composition scenario, like that of Unger, Farrar, and Anchordoqui, satisfies Fermi-LAT constraints evading any need for Earth to be in an atypical position in the Universe.
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