The collapsar model has proved highly successful in explaining the properties of long \gamma -ray bursts ( GRBs ) , with the most direct confirmation being the detection of a supernova ( SN ) coincident with the majority of nearby long GRBs .
Within this model , a long GRB is produced by the core-collapse of a metal-poor , rapidly rotating , massive star .
The detection of some long GRBs in metal-rich environments , and more fundamentally the three examples of long GRBs ( GRB 060505 , GRB 060614 and GRB 111005A ) with no coincident SN detection down to very deep limits is in strong contention with theoretical expectations .
In this paper we present MUSE observations of the host galaxy of GRB 111005A , which is the most recent and compelling example yet of a SN-less , long GRB .
At z = 0.01326 , GRB 111005A is the third closest GRB ever detected , and second closest long duration GRB , enabling the nearby environment to be studied at a resolution of 270 pc at z = 0.01326 .
From the analysis of the MUSE data cube , we find GRB 111005A to have occurred within a metal-rich environment with little signs of ongoing star formation .
Spectral analysis at the position of the GRB indicates the presence of an old stellar population ( \tau \geq 10 Myr ) , which limits the mass of the GRB progenitor to M _ { ZAMS } < 15 M _ { \odot } , in direct conflict with the collapsar model .
Our deep limits on the presence of any SN emission combined with the environmental conditions at the position of GRB 111005A necessitate the exploration of a novel long GRB formation mechanism that is unrelated to massive stars .