1. Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, California 91125, USA
2. Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, Pennsylvania 16802, USA
3. Institute of Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822-1897, USA
4. Department of Astronomy, San Diego State University, San Diego, California 92182, USA
5. Research School of Astronomy and Astrophysics, Australian National University, Mt Stromlo Observatory, via Cotter Road, Weston Creek, Australian Capital Territory 2611, Australia
6. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, California 91101, USA
7. Princeton University Observatory, Peyton Hall, Ivy Lane, Princeton, New Jersey 08544, USA
8. Department of Astrophysics, Tel Aviv University, 69978 Tel Aviv, Israel
9. National Radio Astronomy Observatory, PO Box 0, Socorro, New Mexico 87801, USA
10. Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel
11. Department of Physics & Astronomy, Pomona College, 610 N. College Avenue, Claremont, California 91711, USA
12. Department of Astronomy, University of Virginia, PO Box 400325, Charlottesville, Virginia 22904, USA
13. Institute for Advanced Study, Einstein Drive, Princeton, New Jersey 08540, USA
14. Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, New York 10003, USA

Correspondence to: A. Gal-Yam¹ Correspondence and requests for materials should be addressed to A.G. (Email: avishay@astro.caltech.edu).

Abstract

Over the past decade, our physical understanding of -ray bursts (GRBs) has progressed rapidly, thanks to the discovery and observation of their long-lived afterglow emission. Long-duration (>2 s) GRBs are associated with the explosive deaths of massive stars ('collapsars', ref. 1), which produce accompanying supernovae^{2, 3, 4, 5}; the short-duration (2 s) GRBs have a different origin, which has been argued to be the merger of two compact objects^{6, 7, 8, 9}. Here we report optical observations of GRB 060614 (duration 100 s, ref. 10) that rule out the presence of an associated supernova. This would seem to require a new explosive process: either a massive collapsar that powers a GRB without any associated supernova, or a new type of 'engine', as long-lived as the collapsar but without a massive star. We also show that the properties of the host galaxy (redshift z = 0.125) distinguish it from other long-duration GRB hosts and suggest that an entirely new type of GRB progenitor may be required.

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