On Acceleration of Highest-Energy Cosmic Rays in a Novel Scenario of Magnetar Transients

TL;DR

This paper proposes a novel magnetar transient scenario involving a sudden axis flip and crust fracture, which can accelerate ions to ultra-high energies (~1 ZeV) and produce observable cosmic-ray and neutrino signatures.

Contribution

It introduces a new mechanism for magnetar transients that enables acceleration of ions to ZeV energies and predicts correlated cosmic-ray and neutrino signals.

Findings

Ion acceleration to ~1 ZeV within ~1 ps due to electric fields.

Pair plasma formation explains magnetar burst emissions.

High-energy neutrons and neutrinos are predicted as observational signatures.

Abstract

Transient phenomena in magnetars have been considered as possible acceleration sites of ultrahigh-energy cosmic-rays (CRs), whose energy reaches ~200 EeV, such as the Amaterasu particle. However, the process of CR acceleration and the trigger mechanism of magnetar transients remains unclear. A recently suggested scenario for the activity predicts that the magnetar's rotation axis suddenly flips due to the `Dzhanibekov effect,' resulting in a sudden rise of the Euler force. The material in the outer layer plastically flows due to the force and finally fractures in this scenario. We study the possibilities of ion acceleration along with this scenario. If the degenerate electrons burst open from the fractured region like a balloon burst, the pair plasma formation can be ignited inside the crust. We find that such pair plasma can emit photons similar to the observed bursts from magnetars. We also find that the electron stream at the beginning of the burst phenomenon possibly induces a strong electric field for a moment, resulting in the acceleration of ~1 ZeV ion within a timescale of ~1 ps. The nuclear spallation reactions limit this timescale, and therefore, high-energy CR `neutrons' from the parenteral nuclei become proper observational predictions of this scenario: their arrival time and direction will be correlated with the bursting photon emissions of the host magnetars. The nuclear spallation of ~ZeV nuclei is preferred to explain $\gtrsim$10 PeV neutrino events observed by IceCube and KM3Net.