# $^{60}$Fe in core-collapse supernovae and prospects for X-ray and $\gamma$-ray detection in supernova remnants

## TL;DR

This paper studies $^{60}$Fe production in supernovae, its detection prospects in gamma-ray and X-ray spectra, and implications for understanding supernova remnants and solar system formation.

## Contribution

It provides new insights into $^{60}$Fe yields dependence on nuclear reaction rates and explores detection strategies for supernova remnants via gamma-ray and X-ray observations.

## Key findings

- $^{60}$Fe yield increases with $^{59}$Fe$(n, extgamma)^{60}$Fe cross section.
- Most models cannot explain Solar System $^{60}$Fe origin.
- Next-generation gamma-ray telescopes could detect up to 100 old SNRs.

## Abstract

We investigate $^{60}$Fe in massive stars and core-collapse supernovae focussing on uncertainties that influence its production in 15, 20 and 25 $M_\odot$ stars at solar metallicity. We find that the $^{60}$Fe yield is a monotonic increasing function of the uncertain $^{59}$Fe$(n,\gamma)^{60}$Fe cross section and that a factor of 10 reduction in the reaction rate results in a factor 8-10 reduction in the $^{60}$Fe yield; while a factor of 10 increase in the rate increases the yield by a factor 4-7. We find that none of the 189 simulations we have performed are consistent with a core-collapse supernova triggering the formation of the Solar System, and that only models using $^{59}$Fe$(n,\gamma)^{60}$Fe cross section that is less than or equal to that from NON-SMOKER can reproduce the observed $^{60}$Fe/$^{26}$Al line flux ratio in the diffuse ISM. We examine the prospects of detecting old core-collapse supernova remnants (SNRs) in the Milky Way from their $\gamma$-ray emission from the decay of $^{60}$Fe, finding that the next generation of gamma-ray missions could be able to discover up to $\sim100$ such old SNRs as well as measure the $^{60}$Fe yields of a handful of known Galactic SNRs. We also predict the X-ray spectrum that is produced by atomic transitions in $^{60}$Co following its ionization by internal conversion and give theoretical X-ray line fluxes as a function of remnant age as well as the Doppler and fine-structure line broadening effects. The X-ray emission presents an interesting prospect for addressing the missing SNR problem with future X-ray missions.