Revenge of the Magnetar

"The best way to pinpoint a magnetar," says Woods, "is to catch it when it's bursting - but that's not easy because the bursts are unpredictable and brief. Oftentimes they come and go in less than one-tenth of a second." To date only ten of these stars are known. Many more await discovery, he believes.

Image credit: Rob Duncan The distribution of magnetar candidates along the Milky Way. The red dot below the plane of the galaxy is located in the Large Magellanic cloud.

Finding them is the job of the Interplanetary Network (IPN) - a flotilla of spacecraft scattered around the solar system. Members include Ulysses, 2001 Mars Odyssey, RHESSI and others. None of these missions are dedicated to magnetar research, but each one carries a gamma-ray or x-ray detector - usually for some unrelated purpose. The detector on 2001 Mars Odyssey, for instance, is used to hunt for subsurface ice on Mars. Catching magnetars is a bonus.

Here's how it works: When a wave of radiation sweeps through the solar system, it hits the different spacecraft at slightly different times. Astronomers can figure out where the burst came from by comparing the arrival times. "It's simple triangulation," says Kevin Hurley of UC Berkeley who leads the effort. "The Ulysses spacecraft is particularly important because of its long looping orbit around the Sun. Ulysses' great distance from the other spacecraft makes the triangulation precise."

"Each year we pinpoint dozens of magnetar outbursts this way," he says. Most are from already-known objects like SGR 1900+14, but sometimes a new magnetar reveals itself. (Note: the majority of the bursts detected by the IPN are faint; only the strongest few ionize Earth's atmosphere.)

As soon as the Interplanetary Network locates a burster, the coordinates are emailed to astronomers around the world so they can observe the magnetar using their own telescopes on the ground. NASA missions such as the Chandra X-ray observatory and the Rossi X-ray Timing Explorer sometimes join the effort, too. Magnetar candidates attract the attention of dozens of observatories.

That's understandable. "From a physics point of view," notes Woods, "the energy reservoir in the magnetosphere and crusts of magnetars is 10 to 100 times bigger than the energy released during the August 27, 1998, outburst. So there is the potential for much higher-energy events. It's a good idea to keep an eye on these things."

And an ear. The next time you're driving home in the middle of the night and, unexpectedly, a country tune blares out of your radio, you might wonder ... did a magnetar do that? The cosmos is full of the strangest surprises.