William Herschel Telescope Takes the First Optical Image of a Gamma-Ray Burst

Press Release: ING 3/97

Contacts:

Dr. Rene G. M. Rutten
Isaac Newton Group of Telescopes
Roque de Los Muchachos Observatory, La Palma, Spain
Phone: +34-22-425441

Dr. John H. Telting
Isaac Newton Group of Telescopes
Roque de Los Muchachos Observatory, La Palma, Spain
Phone: +34-22-425463

Issued by:

Javier Méndez
ING Public Relations Officer
Phone: +34-22-425464
Fax: +34-22-425401
E-mail: jma@ing.iac.es

Santa Cruz de La Palma, the 16th of April 1997.- One of the big unresolved mysteries in the Universe is the origin of the enigmatic gamma-ray bursts (GRB), intense bursts of the highest energy radiation that have been detected by gamma-ray telescopes in space. Until recently these bursts were never seen in the visible light, which hampered further progress in finding an explanation for the GRBs for more than two decades. This situation changed dramatically on February 28 when a team of astronomers led by Jan van Paradijs of the University of Amsterdam and the University of Alabama in Huntsville pointed the 4.2-meter William Herschel Telescope on La Palma to the part of the sky where shortly before a new GRB had been detected.

The original GRB had been detected by the Gamma-Ray Burst Monitor onboard the Italian-Dutch BeppoSAX satellite. The same satellite later determined the coordinates of the source more accurately using its X-ray imaging instrument. In visible light the bursts are very faint, and fade beyond the detection limit of even the largest telescopes within a few days. As the position in the sky of gamma-ray bursts is often poorly known, a detection in visible light of such a source is very difficult, and had never before been achieved.

Less than one day after the first detection of the GRB, the William Herschel Telescope saw a faint optical source at the position on the sky determined by the X-ray satellite. This discovery was quickly followed up by observations with the Isaac Newton Telescope and other telescopes on La Palma and elsewhere, which showed that the source was fading. Also the Hubble Space Telescope was pointed at this newly discovered source and confirmed what was found by ground-based telescopes.

The accompanying picture, Press Photo ING 2/97, shows the optical counterpart as it was first seen by the William Herschel Telescope. When a few days later the Isaac Newton Telescope was trained on the same position on the sky the mysterious source had already faded beyond the detection limit of this telescope.

The current set of observations suggest that the GRBs find their origin in far-away galaxies where some yet unknown catastrophic event takes place, triggering a bright pulse of very high energy gamma radiation. The optical source discovered on La Palma is probably the result of the cooling fireball following from the main cataclysm.

Scientists around the world are highly excited about this discovery as it is an important step in unveiling the nature of these very energetic gamma-ray bursts. They now hope to study more of these events with powerful telescopes such as the ones of the UK-Dutch Isaac Newton Group (ING) on La Palma to further unreveal the cause these exotic bursts.