While the broad-lined Type Ic supernovae (SN Ic-bl) associated with long-duration gamma-ray bursts (GRBs) have been studied, we do not fully understand the conditions that lead to each kind of explosion in a massive star. Here we show clues as to the production mechanism of GRBs by comparing the chemical abundances at the sites of 5 nearby (z < 0.25) broad-lined SN Ic that accompany nearby GRBs with those of 12 nearby (z < 0.14) broad-lined SN Ic that have no observed GRBs. We show that the oxygen abundances at the GRB sites are systematically lower than those found near ordinary broad-lined SN Ic. A unique feature of this analysis is that we present new spectra of the host galaxies and analyze the measurements of both samples in the same set of ways, using 3 independent metallicity diagnostics. We demonstrate that neither SN selection effects (SN found via targeted vs. non-targeted surveys) nor the choice of strong-line metallicity diagnostic can cause the observed trend. Though our sample size is small, the observations are consistent with the hypothesis that low metal abundance is the cause of some massive stars becoming SN-GRB. We derive a cut-off metallicity of 0.2-0.6 Z⊙, with the exact value depending on the adopted metallicity scale and solar abundance value.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the International Astronomical Union|
|State||Published - Dec 2007|
Bibliographical noteFunding Information:
properties of five nearby SN-GRB hosts, for which we derived chemical abundances using the same three metallicity diagnostics as for SN without observed GRBs. Broad-lined SN Ic without GRBs tend to consistently inhabit more metal-rich environments, and their host galaxies, for the same luminosity range (−17 < MB < −21 mag), are systematically more metal-rich than corresponding GRB host galaxies. The trend is independent of the choice of diagnostic and cannot be due to selection effects as we include six SN found in a similar non-targeted manner as GRB-SN.The boundary between broad-lined SN Ic that have a GRB accompanying them and broad-lined SN Ic without a GRB lies at an oxygen abundance of ∼ 12+log(O/H)KD02 ∼ 8.5, which corresponds to 0.2−0.6 Z⊙ depending on the adopted metallicity scale and solar abundance value. M.M. acknowledges support from the Miller Foundation for the time during which part of this study was conducted and thanks the organizers of IAUS 250 for an enjoyable and enlightening conference. Supernova research at Harvard University has been supported in part by the National Science Foundation grant AST06-06772.
- Galaxies: abundances
- Gamma rays: bursts
- Supernovae: individual