A team in Dublin used a telescope in South Africa to photograph an explosion from 11 billion years in the past, writes Dick Ahlstrom
Last May 26th an Irish-owned and operated telescope became the first on earth to catch the intense light signal coming from a massive collapsing star. Remarkably, the telescope responded robotically, opening its protective roof, aiming the instrument and then taking the pictures before relaying them back to Dublin and the world.
The robotic telescope, one of about 20 or so now operating at sites around the globe, are there to respond to one of the universe's biggest light shows, a gamma-ray burst (GRB). Ireland participates in this international effort via a GRB research group based at University College Dublin and Cork Institute of Technology (CIT).
When it comes to spotting and imaging GRBs it is all about being first, says senior lecturer in UCD's school of physics, Dr Lorraine Hanlon. "The gamma-ray burst community is extremely competitive," she suggests.
The goal is to be the first to record and distribute the signals, but GRB researchers readily share all their data and combine observational efforts to study these immensely powerful explosions. Taking a cooperative view has helped theorists develop good explanations for what takes place when a star collapses to unleash a GRB.
They take their name from the fact that a jump in the flux of incoming gamma-rays from space usually heralds the event. This radiation is quickly followed by the arrival of X-rays and light, and what a light it is.
For the brief moments the collapse takes, a GRB becomes brighter than the combined brightness of all the stars in the universe, explains Hanlon.
The fireworks end very quickly however, making it a real challenge to watch one occurring. The gamma-ray flux can be as short as 30 thousandths of a second or as long as 15 to 20 seconds, with most lasting no more than two seconds. "We want to observe the burst while the gamma-ray emission is still occurring," says Hanlon, but this is a tall order.
One or two GRBs occur each day somewhere out in space, but for years scientists could only observe the visual afterglow of these powerful events. It was too difficult to identify the distant point source of the gamma-rays and then swing telescopes into line to capture the pictures.
Then Nasa's Swift and Esa's Integral satellites were launched, carrying into orbit gamma-ray, x-ray and optical telescopes dedicated to the location and imaging of GRBs.
The GRB Co-ordinates Network was formed, a network of astronomers who wait for Swift and Integral to detect a GRB and then relay down its coordinates through the network so others can observe.
This is what happened when network member UCD's "Watcher" telescope at the Boyden Observatory near Bloemfontein in South Africa automatically responded on May 26th. The satellites detected the GRB and Watcher was making the first earthbound observations of GRB050626 just 36 seconds later.
Watcher had only become fully operational the week before, but happened to be sitting in the right place at the right time, explains Hanlon, who is involved in GRB research at UCD with Prof Brian McBreen.
"Very luckily, the sky was just dark enough in South Africa and the source was just above the local horizon and the weather was clear. Even more luckily, my PhD student John French was sitting at his computer in UCD when all this started happening, so he immediately began downloading the images as they were taken."
He and fellow student Martin Jelinek then distributed the first notification of the optical element of the GRB. Pictures from the next telescope to report didn't arrive for another 45 seconds.
The afterglow can last for weeks and observations continue during this time. The follow-up showed that the explosion was extremely distant and ancient, occurring 11 billion light years away when the universe was only about two billion years old.
Watcher only has a 40cm mirror but it and its ilk are valuable for this work because they are small and fully automated, Hanlon explains. It only took Watcher 19 seconds to align itself once it had the GRB coordinates. Large telescopes can see further but can't move as quickly.
Despite its sophistication Watcher comes at a surprisingly low cost. The Irish Research Council for Science, Engineering and Technology provided the €140,000 needed to buy the instrument, set up the communications links, install it in a building in South Africa and pay staff.
Watcher is used for other observations and its level of automation is astounding. "It operates autonomously in that it checks the weather to decide if it can observe and if it can it opens the roof, aligns itself and begins making observations. If it receives a message that a gamma-ray burst has occurred it suspends all other observations and moves to that position," she explains.
Hanlon points out that having a niche instrument like Watcher doesn't in any way diminish the need for Ireland to have access to facilities provided by the European Southern Observatory. "If anything, it just makes us hungrier for that access and better poised to use those facilities," she says.
Ironically, just as Watcher has entered its operational phase, the project funding has run out. "We are desperately looking for support to keep the project alive," she adds.