Astrophysics, abstract
astro-ph/0608322

From: Daniele Malesani [view email]

Date (v1): Tue, 15 Aug 2006 19:38:20 GMT (26kb)
Date (revised v2): Tue, 15 Aug 2006 22:32:22 GMT (26kb)

GRB 060614: an enigmatic long-duration gamma-ray burst not due to a hypernova

Authors: M. Della Valle, G. Chincarini, N. Panagia, G. Tagliaferri, D. Malesani, V. Testa, D. Fugazza, S. Campana, S. Covino, S. T. Holland, V. Mangano, L. A. Antonelli, P. D'Avanzo, F. Fiore, K. Hurley, I. F. Mirabel, S. Piranomonte, L. Stella

Comments: 13 pages, 3 figure. Submitted to Nature on 2006 Aug 9

Gamma-ray bursts (GRBs) are short, intense flashes of soft gamma radiation coming from the distant Universe. There is now convincing evidence that long-duration GRBs (those lasting more than ~2 s) originate from the deaths of massive stars. This conclusion is mostly based on a handful of outstanding associations between GRBs and supernovae (SNe) of type Ib/c. In particular, the GRB-associated SNe belong to a peculiar subclass, characterized by high luminosity at maximum light (M_V ~ -19, with a dispersion of ~1 mag) and high expansion velocity of the ejecta (v_max ~ 30000 km/s). Such SNe are often labelled "hypernovae". Here we report deep optical observations of GRB 060614 showing no emerging SN brighter than M_V = -13.9, up to 50 days after the burst. Any SN associated with this GRB was therefore at least 100 times fainter at optical wavelengths than the other SNe associated with GRBs. This fact allows us to set a stringent upper limit to the expansion velocity of the SN ejecta v < 3500 km/s. This is exceptionally low, about an order of magnitude smaller than all GRB-associated SNe discovered so far.

This is the first clear evidence that long-duration GRBs can be either associated with SNe which do not have hypernova properties or they can be produced by different phenomena.

http://arxiv.org/abs/astro-ph/0608322