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
Back to the PLANET homepage