The long-duration gamma-ray burst ( GRB ) 030329 , associated with supernova ( SN ) 2003dh , occurred inside a star-forming dwarf galaxy at redshift z = 0.1685 .
The low redshift , and a rich set of archival Hubble Space Telescope ( HST ) images , makes this GRB well-suited for a detailed study of the stellar population in the immediate vicinity of the explosion .
Since the lifetime of a star is directly tied to its mass , the age of the stellar population can be used to put constraints on the GRB and SN progenitor mass .
From the HST images we extract the colours of the precise site from which the GRB originated , and find that the colours are significantly different from those of the overall host galaxy and the surrounding starburst environment .

We have used spectral evolutionary models , including nebular emission , to carefully constrain the age of the stellar population , and hence the progenitor , at the very explosion site .
For instantaneous burst models we find that a population age of \sim 5 Myr best matches the data , suggesting a very massive ( M _ { \mathrm { ZAMS } } > 50 M _ { \odot } ) star as the progenitor , with an upper limit of 8 Myr ( M _ { \mathrm { ZAMS } } > 25 M _ { \odot } ) .
For more extended star formation scenarios , the inferred progenitor age is in most cases still very young ( < 7 Myr , implying M _ { \mathrm { ZAMS } } > 25 M _ { \odot } ) , with an upper limit of 20 Myr ( M _ { \mathrm { ZAMS } } > 12 M _ { \odot } ) .

These age estimates are an order of magnitude lower than the ages inferred from the overall host galaxy colours , indicating that progenitor mass estimates based on data for spatially unresolved GRB host galaxies will in general be of limited use .
Our results are consistent with the collapsar scenario .