The class of type Ic supernovae have drawn increasing attention since 1998 owing to their sparse association (only four so far) with long duration γ-ray bursts (GRBs)^{1, 2, 3, 4}. Although both phenomena originate from the core collapse of a massive star, supernovae emit mostly at optical wavelengths, whereas GRBs emit mostly in soft γ-rays or hard X-rays. Though the GRB central engine generates ultra-relativistic jets, which beam the early emission into a narrow cone, no relativistic outflows have hitherto been found in type Ib/c supernovae explosions, despite theoretical expectations^{5, 6, 7} and searches⁸. Here we report radio (interferometric) observations that reveal a mildly relativistic expansion in a nearby type Ic supernova, SN 2007gr. Using two observational epochs 60 days apart, we detect expansion of the source and establish a conservative lower limit for the average apparent expansion velocity of 0.6c. Independently, a second mildly relativistic supernova has been reported⁹. Contrary to the radio data, optical observations^{10, 11, 12, 13} of SN 2007gr indicate a typical type Ic supernova with ejecta velocities ~6,000 km s^-1, much lower than in GRB-associated supernovae. We conclude that in SN 2007gr a small fraction of the ejecta produced a low-energy mildly relativistic bipolar radio jet, while the bulk of the ejecta were slower and, as shown by optical spectropolarimetry¹⁴, mildly aspherical.

Item Type:	Refereed Article
Research Division:	Physical Sciences
Research Group:	Astronomical sciences
Research Field:	Stellar astronomy and planetary systems
Objective Division:	Expanding Knowledge
Objective Group:	Expanding knowledge
Objective Field:	Expanding knowledge in the physical sciences
UTAS Author:	Pidopryhora, Y (Dr Yurii Pidopryhora)
ID Code:	95781
Year Published:	2010
Web of Science® Times Cited:	45
Deposited By:	Mathematics and Physics
Deposited On:	2014-10-08
Last Modified:	2014-12-02
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