Massive Be and Oe stars at low metallicity and long gamma ray bursts

TL;DR

This study links low metallicity massive Be/Oe stars, which are rapid rotators, to long gamma-ray burst progenitors, supported by observational data and rate calculations matching observed LGRB occurrences.

Contribution

It identifies low metallicity Be/Oe stars as potential LGRB progenitors and supports this with observational and theoretical evidence, including rate comparisons.

Findings

Be/Oe stars are 3-5 times more common in the SMC than in the Galaxy.

Low metallicity Be/Oe stars can reach the conditions needed for LGRB progenitors.

Calculated LGRB rates align with observed occurrences in the local universe.

Abstract

According to recent theoretical studies, the progenitors of Long Gamma Ray Bursts should be very fast rotating stars, massive enough but not so for collapsing into a black hole. In addition, recent observations seem to show that stars of about 20 solar masses could be at the origin of LGRBs. At low metallicity B-type stars rotate faster than at higher metallicity. We found with the ESO-WFI an occurrence of Be/Oe stars, that are quasi critical rotators, 3 to 5 times larger in the SMC than in the Galaxy. According to our results, and using observational clues on the SMC WR stars, as well as the theoretical predictions of the characteristics must have the LGRB progenitors, we have identified the low metallicity massive Be/Oe stars as potential LGRB progenitors. To support this identification, the expected rates and the numbers of LGRB were then calculated and compared to the observed ones: 3 to 6 LGRBs were found in the local universe in 11 years while 8 were actually observed.