English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The Fermi Large Area Telescope (Fermi LAT) collaboration has recentlyreported on 50 months of measurements of the isotropic Extragalactic Gamma RayBackground (EGRB) spectrum between $100\mbox{MeV}$ and $820\mbox{GeV}$.Ultrahigh Energy Cosmic Ray (UHECR) protons interact with the Cosmic MicrowaveBackground (CMB) photons and produce cascade photons of energies$10\mbox{MeV}\mbox{-}1\mbox{TeV}$ that contribute to the EGRB flux. We examineseven possible evolution models for UHECRs and find that UHECR sources thatevolve as the Star Formation Rate (SFR), medium low luminosity active galacticnuclei type-1 ($L = 10^{43.5}\mbox{erg sec}^{-1}$ in the$[0.5\mbox{-}2]\mbox{KeV}$ band), and BL Lacertae objects (BL Lacs) are themost acceptable given the constraints imposed by the observed EGRB. Otherpossibilities produce too much secondary $\gamma$-radiation. In all cases, thedecaying dark matter contribution improves the fit at high energy, but thecontribution of still unresolved blazars, which would leave the smallest rolefor decaying dark matter, may yet provide an alternative improvement.  The possibility that the entire EGRB can be fitted with resolvable butnot-yet-resolved blazars, as recently claimed by Ajello et al. (2015), wouldleave little room in the EGRB to accommodate $\gamma$-rays from extragalacticUHECR production, even for many source evolution rates that would otherwise beacceptable. We find that, under the assumption of UHECRs being mostly protons,there is not enough room for producing extragalactic UHECRs with AGN, GRB, oreven SFR source evolution. Sources that evolve as BL Lacs on the other hand,would produce much less secondary $\gamma$-radiation and would remain a viablesource of UHECRs, provided that they dominate.

On ultra high energy cosmic rays and their resultant gamma rays