PLANET team observations GRB 990510: The Light of 10 Million Billion Suns

PLANET team observations GRB 990510
The Light of 10 Million Billion Suns

First posted: 18-May-1999

Seizing the moment

Reacting quickly to an international alert, astronomers from the PLANET collaboration have imaged the fading glow of a `gamma ray burst,' the most powerful type of explosion known in the Universe. It began just after dinner on Monday 10th May, as Karen Pollard (University of Canterbury) and John Menzies (South African Astronomical Observatory, SAAO) were about to begin the nights observing at the the 1.0-m telescope at SAAO Sutherland, South Africa looking for evidence of planets around other stars. At 20 minutes to six o'clock, Paul Vreeswijk of the Amsterdam/Huntsville GRB follow-up team (and a former member of PLANET) phoned with the news that the Italian-Dutch satellite, BeppoSAX, had detected tell-tale gamma rays and X-rays from an explosion in a distant galaxy near the South Celestial Pole. Phone calls were exchanged through the night as the PLANET observers obtained images of the region where the X-rays had been detected, then shipped them off electronically to Amsterdam. Working in the Netherlands, Vreeswijk and his colleagues Titus Galama and Evert Rol noticed that one of the dim star-like objects in the region was not seen in much old achival images of this sky region an announcement of the probable optical counterpart was issued immediately to colleagues around the world. Comparison of images taken at SAAO with a first one taken at the 2.2m telescope of ESO in Chile showed that this optical emission was fading fast, but with the precise position now available, the giant 8-m VLT telescope in Chile operated by the European Southern Observatory (ESO) was able to obtain a spectrum so that the power and distance of the outburst could be measured. The distance to the `afterglow' of the gamma-ray burst was determined to be about a staggering 10 billion light years. Since then, many teams around the world have interrupted their usual observing programs to collect data on this rare and transient event. (See for example the ESO press release which contains more of the continuing story.)

Far and Few

Gamma ray bursts are common - observing them optically so that their distances can be measured is not. In the 27 months since the detection of the first optical counterpart, only 11 more have been found. The extreme distance and extreme brightness of these mysterious explosions is telling us something we don't understand yet. Every clue is vital, and early measurements crucial.

What Are Gamma Ray Bursts?

BATSE (Burst and Transient Source Experiment) on the orbiting Compton Gamma Ray Observatory (NASA) picks up about one of these brief flashes of high-energy radiation (gamma rays being the most energetic radiation known) per day. Thousands have been detected since they were discovered in the late 1960s. But nobody knew what they were, although BATSE did at least establish that they were so evenly spread over the sky that they must be very distant (and hence very powerful) outbursts of some kind. The breakthrough came two years ago, when for the first time the fading `afterglow' of one of these explosions was detected in visible light by the Amsterdam/Huntsville GRB and BeppoSax teams, thanks to the more accurate positions available from the BeppoSAX satellite. Three months later, another optical afterglow was detected - this time in a faint galaxy whose distance could be measured. A year ago an article in Nature announced the detection of the optical detection of a gamma ray burst in a galaxy more than 12 billion light years away. Even the most exotic ideas proposed for these explosions (supergiant stars collapsing to black holes, black holes merging with each other, and other weird and wonderful notions) have trouble accounting for explosions with the power of ten million billion suns.

Further information

Amsterdam/Huntsville GRB team page
ESO Press Release

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