UHECR Echoes from the Council of Giants

TL;DR

This paper proposes that local extragalactic structures, specifically the Council of Giants, create 'echoes' of ultra-high-energy cosmic rays (UHECRs) from a recent outburst of Centaurus A, explaining observed anisotropies and offering new ways to study cosmic ray propagation.

Contribution

It introduces a novel echo model where local structures influence UHECR arrival directions, providing a new framework to interpret anisotropy data and cosmic ray composition.

Findings

Echoes of UHECRs are consistent with local structure effects.

The strongest echo lag is about 20 million years.

Light nuclei composition can be tested with future observatories.

Abstract

Recent anisotropy studies of UHECR data at energies $\gtrsim$ 40 EeV, have disclosed a correlation of their angular distribution with the extragalactic local structure, specifically with either local starburst galaxies or AGN. Using Monte Carlo simulations taking into account photo-disintegration processes, we further explore a framework in which these UHECRs were accelerated by Centaurus A in a recent powerful outburst before being scattered by magnetic fields associated with local, Council of Giant, extragalactic structure. We find that the observed intermediate scale anisotropies can be accounted for by the Council of Giant structure imposing a response function on the initial outburst of UHECRs from a single source located at Centaurus A's position. The presence of these local structures creates `echoes' of UHECRs after the initial impulse, and focusing effects. The strongest echo wave has a lag of $\sim$ 20 Myr, comparable to the age of synchrotron-emitting electrons in the giant Centaurus A lobes. Through consideration of the composition of both the direct and echo wave components, we find that the distribution of the light (1$<\ln A<$1.5) component across the sky offers exciting prospects for testing the echo model using future facilities such as Auger prime. Our results demonstrate the potential that UHECR nuclei offer, as "composition clocks", for probing propagation scenarios from local sources.