Journal Article

A relativistic type Ibc supernova without a detected γ-ray burst

Copete, A., Chugai, N., Chevalier, R. A., Ray, A., Barthelmy, S. D., Chakraborti, S., Challis, P., Connaughton, V., Fox, O., Chandra, P., Hamuy, M., Fransson, C., Foley, R. J., Pignata, G., Milne, P. A., Grindlay, J. E., Kirshner, R. P., Torres, M. A. P., Stritzinger, M. D., Chaplin, V., Bietenholz, M. F., Levesque, E. M., Soderberg, A. M., Wieringa, M. H.

2010

Overview

Supernovae with a difference Two groups working independently report the observation of mildly relativistic outflows from seemingly ordinary type Ibc and type Ic supernovae. Soderberg et al . detected luminous radio emission from the type Ibc supernova SN 2009bb, implying an expansion velocity of 0.85 times the speed of light, and a minimum energy comparable to those of the radio afterglows of nearby γ-ray bursts. Paragi et al . observed mildly relativistic expansion (at 0.6 times the speed of light or more) for a small fraction of the ejecta from the type Ic supernova SN2007gr. These discoveries are relevant to the long-standing question of what makes a small fraction of supernova explosions eject material at relativistic speeds, producing the γ-ray bursts characteristic of the explosion of a massive star. Soderberg et al . conclude that only about 1% of type Ibc supernovae harbour central engines and Paragi et al . that most or all type Ic supernovae produce mildly relativistic jets, but as they account for only a small fraction of the total energy, they are very hard to detect. Long duration γ-ray bursts mark the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. To date, central-engine-driven supernovae have been discovered exclusively through their γ-ray emission, yet it is expected that a larger population goes undetected. The discovery of luminous radio emission from the seemingly ordinary type Ibc supernova SN 2009bb, which requires a substantial relativistic outflow powered by a central engine, is now reported. Long duration γ-ray bursts (GRBs) mark 1 the explosive death of some massive stars and are a rare sub-class of type Ibc supernovae. They are distinguished by the production of an energetic and collimated relativistic outflow powered 2 by a central engine (an accreting black hole or neutron star). Observationally, this outflow is manifested 3 in the pulse of γ-rays and a long-lived radio afterglow. Until now, central-engine-driven supernovae have been discovered exclusively through their γ-ray emission, yet it is expected 4 that a larger population goes undetected because of limited satellite sensitivity or beaming of the collimated emission away from our line of sight. In this framework, the recovery of undetected GRBs may be possible through radio searches 5 , 6 for type Ibc supernovae with relativistic outflows. Here we report the discovery of luminous radio emission from the seemingly ordinary type Ibc SN 2009bb, which requires a substantial relativistic outflow powered by a central engine. A comparison with our radio survey of type Ibc supernovae reveals that the fraction harbouring central engines is low, about one per cent, measured independently from, but consistent with, the inferred 7 rate of nearby GRBs. Independently, a second mildly relativistic supernova has been reported 8 .

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/33/34/864 / 639/33/34/867 / Discovery and exploration / Humanities and Social Sciences / letter / multidisciplinary / NATURAL SCIENCES / NATURVETENSKAP / Observations / Science / Supernovae