# Neutrino pair annihilation above merger remnants: implications of a long-lived massive neutron star

**Authors:** Albino Perego, Hannah Yasin, Almudena Arcones  
**arXiv:** [1701.02017](https://arxiv.org/abs/1701.02017)  
**Date:** 2017-01-08  
**Summary page:** https://www.summarizepaper.com/en/paper/1701.02017v1/

## Key points

- Short gamma-ray bursts (GRBs) are poorly understood, but binary neutron star mergers are considered plausible progenitor candidates.
- Neutrino pair annihilation is a possible powering mechanism for short GRBs.
- A study presents calculations of the energy and momentum deposition from neutrino pair annihilation above merger remnants using a detailed, three-dimensional simulation of a binary neutron star merger aftermath.
- The presence of a long-lived massive neutron star increases the energy deposition rate by approximately two-fold due to radiation annihilation between it and the disk.
- Extrapolating cumulative deposited energy to one second yields approximately $2.2 \times 10^{49} \, {\rm erg}$, which is insufficient for most observed short GRBs even when assuming small jet opening angles and long-lived MNSs.
- Significantly more intense neutrino luminosities (a factor ~5-10 larger) are required to explain most observed short GRBs fully.
- It is unlikely that neutrino pair annihilation alone can explain the central engine of short GRBs without additional sources of energy or different mechanisms altogether.

## Summary

The central engine of short gamma-ray bursts (GRBs) remains poorly understood, but binary neutron star mergers are considered plausible progenitor candidates. One possible powering mechanism is the annihilation of neutrino pairs, and this study presents calculations of the energy and momentum deposition from such annihilation above merger remnants. Using a detailed, three-dimensional simulation of a binary neutron star merger aftermath, the authors compute deposition rates over a timescale comparable to the disk's lifetime (approximately 0.4 seconds), assuming a long-lived massive neutron star (MNS). Neutrino emission is modeled using a spectral leakage scheme, and neutrino annihilation rates are computed using a ray-tracing algorithm. The presence of the MNS increases the energy deposition rate by approximately two-fold due to radiation annihilation between it and the disk. Relativistic effects have only marginal impact on volume-integrated results despite significantly changing local rate intensity. Extrapolating cumulative deposited energy to one second yields approximately $2.2 \times 10^{49} \, {\rm erg}$; however, this energy is insufficient for most observed short GRBs even when assuming small jet opening angles and long-lived MNSs. Therefore, significantly more intense neutrino luminosities (a factor ~5-10 larger) are required to explain most observed short GRBs fully. Consequently, it is unlikely that neutrino pair annihilation alone can explain the central engine of short GRBs without additional sources of energy or different mechanisms altogether.