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The Double Firing Burst

Brightest gamma-ray burst provides wealth of information on how stars explode

10 september 2008

Astronomers from around the world combined data from ground- and space-based telescopes to paint a detailed portrait of the brightest explosion ever seen. The observations reveal that the jets of the gamma-ray burst called GRB 080319B were aimed almost directly at the Earth.

GRB 080319B was so intense that, despite happening halfway across the Universe, it could have been seen briefly with the unaided eye (ESO Press Release eso0808). In a paper to appear in the 11 September issue of Nature, Judith Racusin of Penn State University, Pennsylvania (USA), and a team of 92 co-authors report observations across the electromagnetic spectrum that began 30 minutes before the explosion and followed it for months afterwards.

"We conclude that the burst's extraordinary brightness arose from a jet that shot material almost directly towards Earth at almost the speed of light - the difference is only 1 part in 20 000," says Guido Chincarini, a member of the team.

Gamma-ray bursts are the Universe's most luminous explosions. Most occur when massive stars run out of fuel. As a star collapses, it creates a black hole or neutron star that, through processes not fully understood, drives powerful gas jets outward. As the jets shoot into space, they strike gas previously shed by the star and heat it, thereby generating bright afterglows.

The team believes the jet directed toward Earth contained an ultra-fast component just 0.4 degrees across (this is slightly smaller than the apparent size of the Full Moon). This jet is contained within another slightly less energetic jet about 20 times wider.

The broad component is more typical of other bursts. "Perhaps every gamma-ray burst has a narrow jet, but astronomers miss it most of the time," says team member Stefano Covino. "We happened to view this monster down the barrel of the very narrow and energetic jet, and the chance for this nearly head-on alignment to occur is only about once a decade," added his colleague Cristiano Guidorzi.

GRB 080319B was detected by the NASA/STFC/ASI Swift satellite towards the constellation of Boötes, the "Herdsman". A host of ground-based telescopes reacted promptly to study this new object in the sky, including ESO's Very Large Telescope, which was the first to provide the distance of the object, 7.5 billion light-years. The visible light from the burst was detected by a handful of wide-field cameras worldwide that are mounted on telescopes constantly monitoring a large fraction of the sky. One of these was the TORTORA camera mounted on the 0.6-m REM telescope at ESO's La Silla Observatory (eso0726).

TORTORA's rapid imaging provides the most detailed look yet at the visible light associated with the initial blast of a gamma-ray burst. "We've been waiting a long time for this one," says TORTORA senior scientist Grigory Beskin of Russia's Special Astrophysical Observatory. The data collected simultaneously by TORTORA and the Swift satellite allowed astronomers to explain the properties of this burst.

Noter

Read more on this illuminating blast in the additional PDF file.

Racusin, J. L. et al. 2008, Broadband observations of the naked-eye gamma-ray burst GRB 080319B, Nature, 11 September 2008.
The TORTORA camera is mounted on the Italian REM telescope at ESO's La Silla Observatory in Chile. It was built and is being operated by a collaboration between Italy's Bologna State University and Brera Observatory and Russia's Special Astrophysical Observatory and Institute of Precise Instrumentation. The REM team is composed of G. Chincarini, E. Molinari, F.M. Zerbi, L.A. Antonelli, S. Covino, P. Conconi, L. Nicastro, E. Palazzi, M. Stefanon, V. Testa, G. Tosti, F. Vitali, A. Monfardini, F. D'Alessio, P. D'Avanzo, D. Fugazza, G. Malaspina, S.D. Vergani, S. Campana, P. Goldoni, D. Guetta, N. Masetti, E.J.A. Meurs, L. Norci, E. Pian, A. Fernandez-Soto, L. Stella, G. Tagliaferri, G. Ihle, L. Gonzalez, A. Pizarro, P. Sinclair, and J. Valenzuela.
The TORTORA team comprises G. Beskin, S. Karpov, S. Bondar, A Guarnieri (TORTORA Italian PI), C. Bartolini, G. Greco, A. Piccioni, D. Nanni, F. Terra, and E. Molinari.

Swift is managed by NASA's Goddard Space Flight Center. It was built and is being operated in collaboration with Penn State, the Los Alamos National Laboratory, and General Dynamics in the U.S.; Brera Observatory and the Italian Space Agency in Italy; the University of Leicester and Mullard Space Science Laboratory in the United Kingdom; plus partners in Germany and Japan.

Kontakter

Guido Chincarini
University of Miliano Bicocca and INAF-Brera
Miliano Bicocca, Italy
Tel: +39 039 597 10 74
Mobil: +39 340 280 36 12
E-post: guido.chincarini@brera.inaf.it

Stefano Covino
University of Miliano Bicocca and INAF-Brera
Miliano Bicocca, Italy

Cristiano Guidorzi
University of Miliano Bicocca and INAF-Brera
Miliano Bicocca, Italy

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