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A rare star explosion preceded by a luminous flash

A team of European, Japanese and Chinese astrophysicists, in which of the laboratories of CNRS (KNOWLEDGE took part) (1) and from the ECA (Dapnia/SAp) comes to discover one of the strangest star explosions ever observed. The star which disintegrated was a massive star, from 15 to 25 times the mass of the Sun, undoubtedly only made up of carbon and oxygen. This rare cataclysm was preceded, two years before, by a short luminous flash. Observed for the first time, this signal forerunner offers to the astronomers the hope “to predict” the explosions and to observe stars right before the all last moments of their existence. These results are published in the Nature review of June 14, 2007
Two years after the observation of a luminous flash in galaxy UGC4904 in the constellation of the Lynx by an astronomer Japanese amateur, the appearance of an object ten times more luminous at the same place alerts a European consortium which mobilizes a battery of telescopes (2). The first observations obtained at the Observatory of Palma (Spain) reveal an exceptional explosion: in the emitted light, there is not any helium or hydrogen trace, the most abundant elements of stars. It is only one ten days later that, in the spectrum of the star (the distribution of the light according to energy), finally the first helium traces appear.
Observations on nearly three months will confirm these characteristics. The baptized supernova SN2006jc (according to its sequence number of discovered in the year (3), reached a maximum luminosity characteristic of the strongest star explosions, more than one billion times that of the Sun. The astronomers are accustomed to classifying these explosions in two main categories, the supernovas of the type I or II, which cover two types of completely different phenomena. Types I announce the disintegration of a small compact star, dwarf white, made unstable by an accumulation of matter coming from a companion. Types II mark on the contrary the explosion of a massive star. In the first case, one observes in the explosion very little hydrogen and helium, in the second, on the contrary, these two elements dominate. SN2006jc does not correspond to any of these cases: it was thus catalogued in another subcategory, Ic. These very rare cases were discovered very recently. Their scarcity is undoubtedly due to the high mass of star, probably a star from 60 to 100 solar masses, which lost a great quantity of mass before. It is then only the central part, a heart of carbon and oxygen from 15 to 25 solar masses which explodes. The majority of the elements of the explosion comes thus from the heart of star while helium observed is present only around, coming from the envelope of star ejected before.
The observation of the luminous flash in 2004 leaves many questions in addition outstanding. As for the earthquakes, the scientists know very few events forerunners able to indicate the imminence of a star explosion to them. The SN2006jc supernova is a single case of a star explosion preceded by a luminous flash two years before. It thus opens new horizons to predict the massive star explosions. The star Eta-Carina could be an example similar to SN2006jc close to our galaxy. It also knew a start of luminosity which made it most brilliant the second star of the sky in 1843. A forthcoming luminous start could then announce an imminent explosion.
A regular monitoring such objects should make it possible to locate these events in time. It would be an excellent use of the small telescopes and a beautiful programme of collaboration between astronomers amateurs and professionals.


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Notes-
1) French collaboration: Institute of Astrophysics of Paris (CNRS/UPMC/UMR7095), Observatory of High-Provence (CNRS/USR2207), Service of Astrophysics of CEA/Dapnia (CNRS/UMR 7158)

2) The observations were obtained at the Observatory of High-Provence (Telescope 1.93m, CNRS, France), the Observatory Asiago (Telescope Copernico 1,82m Italy), the National Astronomical Observatory (Telescope 2.16m, BAO, Xinglong Observatory, Beijing, China) and the Observatory of Palma (Telescopio Nationale Galileo 3.58m, Nordic Optical Telescope 2.56m, Liverpool Telescope 2.0m and William Herschell Telescope 4.2m, the Canaries, Spain).

3) Several hundreds of supernovas are discovered each year. The name of the supernova corresponds to the year of its discovery followed by letters indicating its row in the year. “SN2007a” is the first supernova discovered in 2007, “SN2007aa” the 27e.

Contacts:
Researchers: CEA/SAp: Jean-Marc Bonnet-Bidaud 01 69 08 92 59 IAP: Michel Dennefeld 01 44 32 81 16

Press: ECA Delphine Kaczmarek 01 64 50 20 97 delphine.kaczmarek@cea.fr

CNRS Martine Hasler 01 44 96 46 35 martine.hasler@cnrs-dir.fr

In The Images-
Galaxy UGC4904 at three different times photographs. In October 2004, a luminous object makes its appearance in the hardly visible part external of the galaxy during a few days then disparait. In September 2006, it misses always. On October 9, 2006, it becomes as luminous as the center of the galaxy, emitting more light as a billion stars. The supernova, baptized SN2006jc, will reach a maximum apparent magnitude of 14 before decreasing slowly. On the image of October 29, it is still 15.65.

For more details see-
http://www.cnrs.fr/