Belle Dumas, Physics Web
The gamma-ray burst GRB 031203 on the upper right. The image was taken with the help of the IBIS device on the Integral satellite. Credit: S. Sazonov
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Astronomers believe they have discovered a new type of gamma ray burst. The new type is more energetic than supernovae but much weaker, and also more common, than most of the "normal" gamma ray bursts discovered so far. The claim was made by two separate groups of researchers, who used the INTEGRAL satellite to study the gamma ray burst, which was observed on December 3, 2003. The results of the studies raise the possibility that there is a sequence of cosmic explosions in terms of the amount of energy released, beginning with supernovae and ending with gamma ray bursts.
Gamma Ray Bursts are the most powerful explosions in the universe. They have continued to baffle scientists for over 30 years, since the first discovery of gamma ray bursts. Most gamma-ray bursts are brighter than even the most massive supernova explosions, which occur when a star ends its life and collapses to form a black hole. However, there are astronomers who believe that there is a connection between the phenomenon of gamma ray bursts and supernovae. Although most supernova explosions do not have enough energy to produce gamma rays, the extra energy may come from material falling into the black hole.
Now new evidence supports the possibility of a connection between gamma-ray bursts and supernovae. On December 3, 2003, the Integral satellite of the European Space Agency detected a burst of gamma rays, which lasted about 30 seconds, in a small galaxy about 1.6 billion light years away from us. Just 18 seconds after the start of the burst, named GRB 031203, its position in the sky was sent by Integral's automatic burst detection system. Although at first glance the burst looked like a normal gamma ray burst, astronomers later discovered that an energy of about 0.6-1.4 times 10 to the 34 Joule power was released, a thousand times less than the amount released in a normal gamma ray burst.
These findings are even more puzzling given the fact that GRB 031203 is only the second closest burst ever discovered. The previous close eruption, discovered in 1998, was also very weak. Astronomers then thought that this was some unusual eruption. Now, however, the two teams of researchers, one from the United States and the other from Germany and Russia, think that these two bursts belong to an entirely new type of gamma-ray bursts, whose energy is somewhere between supernovae and other gamma-ray bursts.
"The discovery of GRB 031203 raises the possibility that there is a serious group of lower-energy gamma-ray bursts that we don't normally see because they are below our detection threshold," says Alicia Soderberg of the California Institute of Technology, a member of the American team and lead author of One of the articles in Nature. “GRB 031203 was only discovered because it was so close. "Its discovery raises the possibility that less energetic gamma-ray bursts may actually be more common than the energetic bursts," she said. Also, the findings rule out the possibility that all gamma ray bursts have the same energy.
Future missions to detect gamma ray bursts, such as Swift, which should be launched by NASA in October this year, may discover many more events of this type. "It will be interesting to find out whether lower-energy bursts are more common than the usual energetic bursts, and whether there is a continuous continuum of energy in gamma-ray bursts," added Sergey Sazonov, a member of the Russian-German team from the Moscow Institute of Space Research and the Max Planck Institute in Gerching.