# Long gamma ray burst rate in the binary merger progenitor model

## TL;DR

This paper investigates the long gamma-ray burst rate within the binary merger progenitor model, showing that low metallicity binary systems can account for observed GRB rates and their redshift evolution.

## Contribution

It introduces a binary merger scenario with high spin helium stars as GRB progenitors, incorporating metallicity evolution to explain observed GRB rates.

## Key findings

- Long GRB rate aligns with observations.
- Low metallicity binaries are more likely to produce GRBs.
- GRB rate evolution matches observed redshift trends.

## Abstract

The long gamma ray bursts (GRBs) may arise from the core collapse of massive stars. However, the long GRB rate does not follow the star formation rate (SFR) at high redshifts. In this Letter, we focus on the binary merger model and consider the high spin helium stars after the merger as the progenitor of long GRBs. With this scenario, we estimate the GRB rate by the population synthesis method with the metallicity evolution. Low metallicity binaries are easier to become long GRB progenitors than those for solar metallicity due to the weak wind mass loss and the difference in the stellar evolution. In our results, the long GRB rate roughly agrees with the observed rate, and shows a similar behavior to the observed redshift evolution.