High-Energy Emission Induced by Ultra-High-Energy Photons as a Probe of Ultra-High-Energy Cosmic-Ray Accelerators Embedded in the Cosmic Web

TL;DR

This paper explores how ultra-high-energy gamma-ray emissions, produced by cosmic-ray accelerators like gamma-ray bursts and active galaxies, can be used to probe the magnetic fields and properties of these distant sources.

Contribution

It demonstrates that UHE pair production and associated synchrotron emission are inevitable in structured regions, offering a new method to study UHECR sources and magnetic fields.

Findings

UHE pair production leads to detectable synchrotron emission.

Synchrotron pair echoes could be observed by future CTA.

Detection would inform on extragalactic magnetic fields and source properties.

Abstract

The photomeson production in ultra-high-energy cosmic-ray (UHECR) accelerators such as gamma-ray bursts and active galaxies may lead to ultra-high-energy (UHE) gamma-ray emission. We show that generation of UHE pairs in magnetized structured regions embedding the sources is inevitable, and accompanied >0.1 TeV synchrotron emission provides an important probe of UHECR acceleration. It would especially be relevant for powerful transient sources, and synchrotron pair echoes may be detected by future CTA via coordinated search for transients of duration ~0.1-1 yr for the structured regions with ~Mpc. Detections will be useful for knowing structured extragalactic magnetic fields as well as properties of the sources.