"This extends the GRB-supernova connection to X-ray flashes and fainter supernovae, implying a common origin," said Elena Pian of Italy's National Institute for Astrophysics in Trieste and the lead author of one of four research papers about the event in the journal Nature on Wednesday.

It is the second-closest gamma-ray burst ever detected and the first view of a supernova in the act of exploding, according to the astronomers.

Pian and her group confirmed that the explosion was tied to a supernova called SN2006aj a few days after the outburst, which lasted 100 times longer than a typical gamma-ray burst but was much dimmer.

Alicia Soderberg and her colleagues at the California Institute of Technology in Pasadena used radio and X-ray wavelengths to calculate that GRB060218 was about 100 times less energetic than ordinary GRBs but similar events are probably more common.

In another report in the journal, Sergio Campana and scientists at the National Institute for Astrophysics observatory in Merate, Italy also said the collapsing star was associated with a supernova.

X-ray flashes appear to signal an explosion that leaves behind a neutron star while gamma-ray bursts are thought to mark the birth of a black hole, a region of space from which nothing can escape.

Scientists led by Paolo Mazzali, of the Max Planck Institute of Astrophysics in Garching, Germany found that the star had a smaller mass than those estimated for the normal GRB-supernova.

"The properties of GRB060218 suggest the existence of a population of events less luminous than classical GRBs, but possibly more numerous," Mazzali said in a statement.

In a commentary in the journal, Timothy Young of the University of North Dakota in the United States said the research has shown that at least some GRBs are warnings of the imminent explosion of massive stars.

"All four papers make clear that the exploding object sent out both a slightly aspherical shockwave, typical of a supernova, and a jet-like stream of material characteristic of a GRB," he said.

The scientist reports that the TCB was a comet, containing organic matter, which was heated after entering Earth's atmosphere, and organic matter started decomposing intensively and emitting carbon dioxide.

The scientist also showed the results of chemical analysis of particles found in wood and soil - their composition reminded that of the Halley's comet, studied by means of "Vega" spaceship.

The scientists are still unable to perform total identification of the TCB chemical composition, but they are sure that some high-temperature process (an explosion) had definitely taken place.

The scientists pinpointed the timing of the last subglacial flood by dating volcanic ash preserved on bedrock surfaces, said Laura Webb, a professor of earth sciences at Syracuse who took part in the study.

The Labyrinth is a network of ice-free bedrock channels and scoured terrain emerging from beneath the East Antarctic Ice Sheet. It is one of a series of large channel networks that cross the Transantarctic Mountains. Some of the chasms are up to 800 feet deep and thousands of feet wide. Scientists have long speculated that the volume of water required to create the channels was far more than that produced by melting glaciers.

Webb said it appeared the subglacial flooding was not continuous but episodic, and likely lasted days or months at a time.

In an article on the study that appeared last month in the journal "Geology," Webb and her colleagues estimated the flood raged with approximately 1,000 times the volume of water flowing over Niagara Falls. At that rate, it would take Lake Ontario, for instance, about a month to drain, she said.

Suzanne Baldwin, another Syracuse professor who was one of the study's principal researchers, warned that the ancient episode has implications for global climate change today.

Subglacial lakes in Antarctica were first identified in the 1960s, some sealed beneath up to 2 1/2 miles of ice. Since then, more than 150 have been discovered. But it is thought thousands may exist. The largest is Lake Vostok, similar in size to Lake Ontario. Another is the size of Rhode Island.

Baldwin and her colleagues believe there must be a more complete investigation of how a similar catastrophic release might alter the present-day environment.

Such a massive release of fresh water from the subglacial lakes would affect the stability of the East Antarctic ice sheet, the circulation of water in the Southern Ocean, and global weather patterns, all of which could change the balance of the Earth's ecosystems, she said.

Dominic Hodgson, a geologist at the British Antarctic Survey, said formation of the Labyrinth has been attributed to subglacial meltwater since at least 1993, but the Syracuse study provided a "better estimate" of the timing of its creation.

Hodgson, who has written extensively about global warming and its impact on Antarctica, said some lake water discharges are contemporary. One such rapid discharge occurred in 1997-1998 when a one-mile-square lake emptied into two other downstream lakes under the ice sheet over a period of 16 months.

"It is very unlikely that the volume of these discharges would equal those of the Miocene (epoch), when the Labyrinth formed, because the ice sheet then was much more dynamic and temperate and therefore likely contained - and discharged - substantially greater volumes of subglacial meltwater," Hodgson said.

The British scientist said that present day global warming has not had any measured effects on the volume or movement of subglacial meltwater beneath the Antarctic ice sheet "so it is premature to predict a new era of flooding as a result of global warming."