An Evolving Stellar Initial Mass Function and the Gamma-Ray Burst Redshift Distribution

TL;DR

This paper demonstrates that an evolving stellar initial mass function (IMF) can explain the observed redshift distribution of Swift gamma-ray bursts, aligning GRB rates with star formation history by increasing the proportion of massive stars at high redshifts.

Contribution

It introduces an evolving IMF model that accounts for the high-redshift GRB rate increase, providing a better fit to observations than static IMFs.

Findings

Evolving IMF explains high-redshift GRB rate increase.

The model fits the Swift GRB redshift distribution well.

Supports the idea of a non-constant stellar IMF over cosmic time.

Abstract

Recent studies suggest that Swift gamma-ray bursts (GRBs) may not trace an ordinary star formation history. Here we show that the GRB rate turns out to be consistent with the star formation history with an evolving stellar initial mass function (IMF). We first show that the latest Swift sample of GRBs reveals an increasing evolution in the GRB rate relative to the ordinary star formation rate at high redshifts. We then assume only massive stars with masses greater than the critical value to produce GRBs, and use an evolving stellar IMF suggested by Dav\'{e} (2010) to fit the latest GRB redshift distribution. This evolving IMF would increase the relative number of massive stars, which could lead to more GRB explosions at high redshifts. We find that the evolving IMF can well reproduce the observed redshift distribution of Swift GRBs.