Binary Neutron Star Merger Remnants as Sources of Cosmic Rays Below the "Ankle"

TL;DR

This study explores binary neutron star merger remnants as potential sources of cosmic rays below the ankle, constraining magnetic fields and particle interactions through multi-messenger observations.

Contribution

It provides new constraints on magnetic field strengths in merger remnants and demonstrates their potential to produce cosmic rays below the ankle.

Findings

Magnetic field at mG level is consistent with observed synchrotron emission.

Gamma-ray emission constrains magnetic field strength further.

Strong G-level magnetic fields could support cosmic ray acceleration.

Abstract

We investigate non-thermal electron and nuclei energy losses within the binary neutron star merger remnant produced by the event GW170817. The lack of a cooling feature within the detected synchrotron emission from the source is used to constrain the magnetic field at the mG level, assuming that this emission is electron synchrotron in origin, and that the accelerated spectrum in the electrons follows the form $dN/dE_e \propto E_e^{-2}$. The level of subsequent gamma-ray emission from the source is demonstrated to provide a further constraint on the source magnetic field strength. We also put forward alternative strong ($\sim$G) magnetic field scenarios able to support this emission. For such stronger fields, the photo-disintegration of non-thermal nuclei within the source is considered, and a bottleneck period of $\sim$5-30 days is found when this process peaks. We find that this class of source is in principle able to support the population of cosmic rays detected at Earth below the "ankle".