Paris, April 4 : A meticulous analysis of data has allowed astronomers to investigate the initial phases of a giant stellar explosion, which led to the ejection of matter at velocities close to the speed of light.

On 19 December 2004, the blast from an exploding star arrived at Earth.

ESA's (European Space Agency's) Integral satellite, an orbiting gamma-ray observatory, recorded the entire event, providing information for what may prove to be one of the most important gamma-ray bursts (GRBs) seen in recent years.

As the data was collected, astronomers saw the 500-second-long burst rise to extraordinary brilliance.

"It is in the top 1 percent of the brightest GRBs we have seen," said Diego Gotz, CEA Saclay, France, who headed the investigation.

The brightness of the event, known as GRB 041219A, has allowed the team to perform a painstaking investigation to extract a property known as the polarization of the gamma rays.

The team has shown that the gamma rays were highly polarized and varied tremendously in level and orientation.

Polarization refers to the preferred direction in which the radiation wave oscillates.

Polaroid sunglasses work with visible light by letting through only a single direction of polarization, blocking most of the light from entering our eyes.

The blast from a GRB is thought to be produced by a jet of fast-moving gas bursting from near the central engine; probably a black hole created by the collapse of the massive star.

The polarization is directly related to the structure of the magnetic field in the jet. So, it is one of the best ways for astronomers to investigate how the central engine produces the jet.

There are a number of ways this might happen.

In the first scenario, the jet carries a portion of the central engine's magnetic field into space. A second involves the jet generating the magnetic field far from the central engine.

A third concerns the extreme case in which the jet contains no gas just magnetic energy, and a fourth scenario entails the jet moving through an existing field of radiation.

According to Gotz, the Integral results favour a synchrotron model and, of those three, the most likely scenario is the first, in which the jet lifts the central engine's magnetic field into space.

"It is the only simple way to do it," he said.

What Gotz would most like to do is measure the polarisation for every GRB, to see whether the same mechanism applies to all. (ANI)