Journal Article

Constraining the mass of the GRB 030329 progenitor*

Göran Östlin, Erik Zackrisson, Jesper Sollerman, Seppo Mattila and Matthew Hayes

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 387, issue 3, pages 1227-1236
Published in print July 2008 | ISSN: 0035-8711
Published online May 2008 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.13319.x
Constraining the mass of the GRB 030329 progenitor*

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The long-duration gamma-ray burst (GRB) GRB 030329, associated with the supernova (SN) 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 ∼5 Myr best matches the data, suggesting a very massive (MZAMS > 50 M) star as the progenitor, with an upper limit of 8 Myr (MZAMS > 25 M). For more extended star formation scenarios, the inferred progenitor age is in most cases still very young (<7 Myr, implying MZAMS > 25 M), with an upper limit of 20 Myr (MZAMS > 12 M).

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.

Keywords: stars: evolution; stars: individual: GRB 030329; stars: individual: SN 2003dh; galaxies: starburst; galaxies: stellar content; gamma-rays: bursts

Journal Article.  7715 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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