title: No supernovae associated with two long-duration gamma-ray bursts.
abstract: It is now accepted that long-duration gamma-ray bursts (GRBs) are produced during the collapse of a massive star. The standard 'collapsar' model predicts that a broad-lined and luminous type Ic core-collapse supernova accompanies every long-duration GRB. This association has been confirmed in observations of several nearby GRBs. Here we report that GRB 060505 (ref. 10) and GRB 060614 (ref. 11) were not accompanied by supernova emission down to limits hundreds of times fainter than the archetypal supernova SN 1998bw that accompanied GRB 980425, and fainter than any type Ic supernova ever observed. Multi-band observations of the early afterglows, as well as spectroscopy of the host galaxies, exclude the possibility of significant dust obscuration and show that the bursts originated in actively star-forming regions. The absence of a supernova to such deep limits is qualitatively different from all previous nearby long-duration GRBs and suggests a new phenomenological type of massive stellar death.
authors.affiliation: Dark Cosmology Centre, University of Copenhagen, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark. jfynbo@dark-cosmology.dk
authors.forename: Johan P U
authors.initials: JP
authors.lastname: Fynbo
authors.forename: Darach
authors.initials: D
authors.lastname: Watson
authors.forename: Christina C
authors.initials: CC
authors.lastname: Thöne
authors.forename: Jesper
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authors.lastname: Sollerman
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Bloom
authors.forename: Tamara M
authors.initials: TM
authors.lastname: Davis
authors.forename: Jens
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authors.lastname: Hjorth
authors.forename: Páll
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authors.lastname: Jakobsson
authors.forename: Uffe G
authors.initials: UG
authors.lastname: Jørgensen
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authors.initials: JF
authors.lastname: Graham
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Fruchter
authors.forename: David
authors.initials: D
authors.lastname: Bersier
authors.forename: Lisa
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authors.lastname: Kewley
authors.forename: Arnaud
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authors.lastname: Cassan
authors.forename: José María Castro
authors.initials: JM
authors.lastname: Cerón
authors.forename: Suzanne
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authors.lastname: Foley
authors.forename: Javier
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authors.lastname: Gorosabel
authors.forename: Tobias C
authors.initials: TC
authors.lastname: Hinse
authors.forename: Keith D
authors.initials: KD
authors.lastname: Horne
authors.forename: Brian L
authors.initials: BL
authors.lastname: Jensen
authors.forename: Sylvio
authors.initials: S
authors.lastname: Klose
authors.forename: Daniel
authors.initials: D
authors.lastname: Kocevski
authors.forename: Jean-Baptiste
authors.initials: JB
authors.lastname: Marquette
authors.forename: Daniel
authors.initials: D
authors.lastname: Perley
authors.forename: Enrico
authors.initials: E
authors.lastname: Ramirez-Ruiz
authors.forename: Maximilian D
authors.initials: MD
authors.lastname: Stritzinger
authors.forename: Paul M
authors.initials: PM
authors.lastname: Vreeswijk
authors.forename: Ralph A M
authors.initials: RA
authors.lastname: Wijers
authors.forename: Kristian G
authors.initials: KG
authors.lastname: Woller
authors.forename: Dong
authors.initials: D
authors.lastname: Xu
authors.forename: Marta
authors.initials: M
authors.lastname: Zub