Abstract
We have obtained deep spectroscopic observations of several nearby gamma-ray burst (GRB) host galaxies revealing for the first time the presence of Wolf-Rayet (WR) stars and numerous O stars located in rich and compact clusters or star forming regions. Surprisingly, high spatial resolution imaging shows that the GRBs and the associated supernovae did not occur in these regions, but several hundreds of parsec away. Considering various scenarios for GRB progenitors, we do not find any simple explanation of why they should be preferentially born in regions with low stellar densities. All the examined GRBs and associated SNe have occurred 400 to 800 pc from very high density stellar environments including large numbers of WR stars. Such distances can be travelled through at velocities of 100 km s-1 or larger, assuming the travel time to be the typical life time of WR stars. It leads us to suggest that GRB progenitors may be runaway massive stars ejected from compact massive star clusters. The ejection from such super star clusters may lead to a spin-up of these stars, producing the loss of the hydrogen and/or helium envelopes leading to the origin of the type Ibc supernovae associated with GRBs. If this scenario applies to all GRBs, it provides a natural explanation of the very small fraction of massive stars that emit a GRB at the end of their life. An alternative to this scenario could be a binary origin for GRBs, but this still requires an explanation of why it would preferentially occur in low stellar density regions.
Highlights
Gamma-Ray Bursts (GRBs) are believed to trace the death of massive, short lived stars, providing the most energetic events in the Universe
Are WR stars found in all GRB host galaxies? We have investigated archival data from ESO telescopes, to acquire good spectra of the most nearby GRB host galaxies, i.e. those for which 8 meter class telescopes are able to detect the faint signature of this stellar population
In the case of the very massive and compact super star clusters observed in the GRB host galaxies, the dynamical conditions, ejection probabilities, and the resulting properties of runaway stars may be quite different from the less dense and less populated associations and clusters typically found in our Galaxy
Summary
Gamma-Ray Bursts (GRBs) are believed to trace the death of massive, short lived stars, providing the most energetic events in the Universe. There is growing evidence that the majority of GRB host galaxies are Lyα emitters with star formation rates (SFRs) between 1 to 11 M /yr (Fynbo et al 2003; Jakobsson et al 2005) All this is indicative of low metallicity environments, as confirmed by direct abundance measurements (Prochaska et al 2004; Sollerman et al 2005; Hammer et al, in preparation). As a result, it leads to some controversy, since GRB hosts were formerly believed to be associated with galaxies with strong star formation rates averaging 100 M /yr from radio and sub-mm observations (Berger et al 2003).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
