Long [gamma]-ray bursts and core-collapse supernovae have different environments

When massive stars exhaust their fuel, they collapse and often produce the extraordinarily bright explosions known as core-collapse supernovae. On occasion, this stellar collapse also powers an even more brilliant relativistic explosion known as a long-duration [gamma]-ray burst. One would then expect that these long [gamma]-ray bursts and core-collapse supernovae should be found in similar galactic environments. Here we show that this expectation is wrong. We find that the [gamma]-ray bursts are far more concentrated in the very brightest regions of their host galaxies than are the core-collapse supernovae. Furthermore, the host galaxies of the long [gamma]-ray bursts are significantly fainter and more irregular than the hosts of the core-collapse supernovae. Together these results suggest that long-duration [gamma]-ray bursts are associated with the most extremely massive stars and may be restricted to galaxies of limited chemical evolution. Our results directly imply that long [gamma]-ray bursts are relatively rare in galaxies such as our own Milky Way. Not in our back yard In their death throes massive stars often produce supernovae, and occasionally a long-duration [gamma]-ray burst (GRB). That suggests that GRBs and supernovae should be found in similar environments, but work based on more than a thousand hours of Hubble Space Telescope observation time shows that expectation to be wrong. Most long GRBs are found in small, faint, irregular galaxies. Supernovae appear equally divided between spiral and irregular galaxies. GRBs are concentrated in the brightest regions of their host galaxies whereas supernovae occur throughout their host galaxies. A happy conclusion of this finding is that GRBs, which would cause havoc here on Earth if exploding nearby, should be relatively rare in the Milky Way. [gamma]-ray bursts are more concentrated in the very brightest regions of their host galaxies than are supernovae -- in addition, the host galaxies of the [gamma]-ray bursts are significantly fainter and more irregular than the hosts of the supernovae.
Author(s): A. S. Fruchter [sup.1] , A. J. Levan [sup.1] [sup.2] [sup.3] , L. Strolger [sup.1] [sup.4] [sup.23] , P. M. Vreeswijk [sup.5] , S. E. Thorsett [sup.6] , D. [...]