Gamma-ray Bursts - what kind of stars do they come from?

Long GRBs are the most luminous objects in the universe and mark the collapse of a very massive star, usually accompanied by a relativistic supernova. Their large distances do not allow us to directly identify the progenitor star as we were able to do with some type of supernova. We therefore rely on indirect methods to derive some information on the kind of progenitor star or system and what makes a massive star to explode in a supernova or a GRB. Integral field spectroscopy of some nearby GRB host galaxies allows us to study the properties of the star-forming region the GRB or SN exploded in. Emission line diagnostics show that metallicity might play an important role in the destiny of a massive star. To study the closer environment of a GRB is tricky due to the strong ionizing radiation from the GRB. However, one fortuante case allowed us to observe highly ionized material less than 100pc from the GRB site via absorption lines. An even closer look to the direct environment of the GRB was possible with another recent event. This very strange object possibly had a binary progenitor with a common envelope phase that expelled a thick shell of material before the explosion which was then illuminated by the actual GRB. A very weak supernova was observed later possibly making this object a kind of transition event between a supernova and a GRB.