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Massive Star Burps, Then ExplodesUniv. of California, at Berkeley ReleaseContacts: Robert Naeye, NASA Goddard 1-301-286-4453 Robert Sanders, UC Berkeley 1-510-643-6998 For Release: April 4, 2007
On Oct. 20, 2004, Japanese amateur astronomer Koichi Itagaki saw the star let loose an outburst so bright that it was initially mistaken for a supernova. The star survived, but for only two years. On Oct. 11, 2006, professional and amateur astronomers witnessed the star actually blowing itself to smithereens as Supernova 2006jc.
"The beautiful aspect of our SN 2006jc observations is that although they were obtained in different parts of the electromagnetic spectrum, in the optical and in X-rays, they lead to the same conclusions," says Immler. "This event was a complete surprise," added Alex Filippenko, leader of the UC Berkeley/Keck supernova group and a member of NASA'S Swift team. "It opens up a fascinating new window on how some kinds of stars die." All the observations suggest that the supernova's blast wave took only a few weeks to reach the shell of material ejected two years earlier, which did not have time to drift very far from the star. As the wave smashed into the ejecta, it heated the gas to millions of degrees, hot enough to emit copious X-rays. The Swift satellite saw the supernova continue to brighten in X-rays for 100 days, something that has never been seen before in a supernova. All supernovae previously observed in X-rays have started off bright and then quickly faded to invisibility. "You don't need a lot of mass in the ejecta to produce a lot of X-rays," notes Immler. Swift's ability to monitor the supernova's X-ray rise and decline over six months was crucial to his team's mass determination. But he adds that Chandra's sharp resolution enabled his group to resolve the supernova from a bright X-ray source that appears in the field of view of Swift's X-ray Telescope. "We could not have made this measurement without Chandra," says Immler, who will submit his team's paper next week to the Astrophysical Journal. "The synergy between Swift's fast response and its ability to observe a supernova every day for a long period, and Chandra's high spatial resolution, is leading to a lot of interesting results." Foley and his colleagues, whose paper appears in the March 10 Astrophysical Journal Letters, propose that the star recently transitioned from a Luminous Blue Variable (LBV) star to a Wolf-Rayet star. An LBV is a massive star in a brief but unstable phase of stellar evolution. Similar to the 2004 eruption, LBVs are prone to blow off large amounts of mass in outbursts so extreme that they are frequently mistaken for supernovae, events dubbed "supernova impostors." Wolf-Rayet stars are hot, highly evolved stars that have shed their outer envelopes.
"It challenges some aspects of our current model of stellar evolution," says Foley. "We really don't know what caused this star to have such a large eruption so soon before it went supernova." "SN 2006jc provides us with an important clue that LBV-style eruptions may be related to the deaths of massive stars, perhaps more closely than we used to think," adds coauthor and UC Berkeley astronomer Nathan Smith. "The fact that we have no well-established theory for what actually causes these outbursts is the elephant in the living room that nobody is talking about." SN 2006jc occurred in galaxy UGC 4904, located 77 million light years from Earth in the constellation Lynx. The supernova explosion, a peculiar variant of a Type Ib, was first sighted by Itagaki, American amateur astronomer Tim Puckett and Italian amateur astronomer Roberto Gorelli. See also NASA Goddard press release at: http://www.nasa.gov/centers/goddard/news/topstory/ 2007/supernova_imposter.html [Press Index] [Press Releases] [Supernovas & Supernova Remnants] |
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Revised: September 14, 2007
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