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 Tools annual

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 monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Recent data from the \emph{Fermi} Large Area Telescope have revealed about adozen distant hard-spectrum blazars that have very-high-energy (VHE; $\gtrsim100$ GeV) photons associated with them, but most of them have not yet beendetected by imaging atmospheric Cherenkov telescopes. Most of these high-energygamma-ray spectra, like those of other extreme high-frequency peaked BL Lacobjects, can be well explained either by gamma rays emitted at the source or bycascades induced by ultra-high-energy cosmic rays, as we show specifically forKUV 00311$-$1938. We consider the prospects for detection of the VHE sources bythe planned Cherenkov Telescope Array (CTA) and show how it can distinguish thetwo scenarios by measuring the integrated flux above $\sim 500$ GeV (dependingon source redshift) for several luminous sources with $z \lesssim 1$ in thesample. Strong evidence for the origin of ultra-high-energy cosmic rays couldbe obtained from VHE observations with CTA. Depending on redshift, if the oftenquoted redshift of KUV 00311-1938 ($z = 0.61$) is believed, preliminaryH.E.S.S. data favor cascades induced by ultra-high-energy cosmic rays. Accurateredshift measurements of hard-spectrum blazars are essential for this study.

Disentangling Hadronic and Leptonic Cascade Scenarios from the Very-High-Energy Gamma-Ray Emission of Distant Hard-Spectrum Blazars