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The Gamma-ray burst enigma

The X-ray astronomy satellite BeppoSAX (Satellite per Astronomia X, "Beppo" in honour of the Italian astronomer Giuseppe "Beppo" Occhialini, a pioneer in the study of cosmic rays), was a project of the Italian Space Agency (ASI) with participation of the Netherlands Agency for Aerospace Programs (NIVR). It was devoted to the study of X-ray emissions from space (which cannot be performed from Earth due to the presence of the atmosphere) and was launched on April 30, 1996. Originally planned to work for two years, it remained in operation for seven years until it was deorbited and fell into the Pacific Ocean on April 29, 2003.

Its goal was the study of the spectral behaviour of celestial sources over a wide range of energies, which is of primary importance in understanding comprehensively the emission mechanisms that, in several instances, produce spectral features localized in different regions of the electromagnetic spectrum.

The main scientific characteristic of the BeppoSAX mission was the wide spectral coverage, ranging from 0.1 to over 200 keV. BeppoSAX was the first X-ray mission with the capability of observing sources over more than tree decades of energy with a relatively large area, a good energy resolution, associated with imaging capabilities (resolution of about 1').

SAX could provide a significant contribution (and unique contribution for science involving the exploitation of the wide band) in several areas of X-ray astronomy such as: compact galactic sources; active galactic nuclei, clusters of galaxies, supernova remnants, normal galaxies, stars, gamma-ray bursts.

The most outstanding successes of the mission came from the study of gamma ray bursts, high energy emissions that had hitherto been an absolute mistery for astrophysics. By revealing the X-ray emission that follows the burst, BeppoSAX provided some fundamental pieces of this scientific jigsaw. During its lifetime, Beppo SAX observed more than 30 bursts, and was able to alert immediately other space or ground instruments at the time of their appearance. Guided by BeppoSAX, astronomers have discovered that this mysterious bursts come from extremely remote galaxies, and that their energy is comparable to what would be obtained annihilating the whole mass of our Sun in a few moments. They are, in other words, the biggest explosions occurring in the Universe after the Big Bang.