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GRBs 070429B and 070714B: The High End of the Short-Duration Gamma-Ray Burst Redshift Distribution

Research paper by S. Bradley Cenko, Edo Berger, Ehud Nakar, Mansi M. Kasliwal, Antonio Cucchiara, Shri R. Kulkarni, Eran Ofek, Derek B. Fox, Fiona A. Harrison, Arne Rau, Paul A. Price, Avishay Gal-Yam, Michael A. Dopita, Bryan E. Penprase

Indexed on: 06 Feb '08Published on: 06 Feb '08Published in: Astrophysics



Abstract

We present optical spectra of the host galaxies of the short-duration gamma-ray burst GRB 070429B and the likely short-duration with extended emission GRB 070714B. In both cases, we find a single emission line that we identify as O II lambda 3727 at z ~ 0.9. Both events are more distant than any previous short-duration GRB with a secure host association from the sub-arcsecond position of an optical afterglow. GRBs 070429B and 070714B provide strong evidence in support of our previous claims in Berger et al. that a significant fraction of short-duration hosts (>~ 33%) reside at z > 0.7. We discuss the implications of the existence this population on the energetics of short-duration GRBs, as well as on progenitor models. In the context of the degenerate binary merger scenario, such events require progenitor systems with a range of lifetimes and disfavor progenitor models with a long, narrow lifetime distribution.