# A new delay time distribution for merging neutron stars tested against Galactic and cosmic data

## TL;DR

This paper introduces a new delay time distribution for merging neutron stars, tested against gamma-ray burst data and Galactic chemical evolution, providing insights into their role in element production and cosmic events.

## Contribution

The paper derives a novel delay time distribution for neutron star mergers and tests it against multiple observational constraints, improving understanding of their timing and contribution to element synthesis.

## Key findings

- SGRB distribution fits with 300-500 Myr delay times
- Eu production timescale must be <30 Myr if MNS are sole Eu sources
- Metallicity dependence and core-collapse SNe contribute to Eu production

## Abstract

The merging of two neutron stars (MNS) is thought to be the source of short gamma-ray bursts (SGRB) and gravitational wave transients, as well as the main production site of r-process elements like Eu. We have derived a new delay time distribution (DTD) for MNS systems from theoretical considerations and we have tested it against (i) the SGRB redshift distribution and (ii) the Galactic evolution of Eu and Fe, in particular the [Eu/Fe] vs [Fe/H] relation. For comparison, we also tested other DTDs, as proposed in the literature. To address the first item, we have convolved the DTD with the cosmic star formation rate, while for the second we have employed a detailed chemical evolution model of the Milky Way. We have also varied the DTD of Type Ia SNe (the main Fe producers), the contribution to Eu production from core-collapse SNe, as well as explored the effect of a dependence on the metallicity of the occurrence probability of MNS. Our main results can be summarized as follows: (i) the SGRB redshift distribution can be fitted using DTDs for MNS that produce average timescales of 300-500 Myr; (ii) if the MNS are the sole producers of the Galactic Eu and the occurrence probability of MNS is constant the Eu production timescale must be on the order of <30 Myr; (iii) allowing for the Eu production in core-collapse SNe, or adopting a metallicity-dependent occurrence probability, allow us to reproduce both observational constraints, but many uncertainties are still present in both assumptions.