Gamma-ray Flare Star
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February 10, 2009: NASA's Swift and Fermi spacecraft are monitoring a neutron star 30,000 light years from Earth that is drawing attention to itself with a series of powerful gamma-ray flares.
"At times, this remarkable object has erupted with more than a hundred flares in as little as 20 minutes," said Loredana Vetere, who is coordinating the Swift observations at Pennsylvania State University. "The most intense flares emitted more total energy than the sun does in 20 years."
Right: An artist's concept of the flare star in action. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab. [more]
The star, known as SGR J1550-5418, lies in the southern constellation Norma. It began a series of modest eruptions on Oct. 3, 2008, settled down for a while, then roared back to life on Jan. 22, 2009, with an intense episode.
Because of its rapid-fire outbursts and gamma-ray spectrum, astronomers classify the object as a "soft-gamma-ray repeater" -- only the sixth known. In 2004, a giant flare from another soft-gamma-ray repeater was so intense it ionized Earth's upper atmosphere from 50,000 light-years away: more.
Using data from an X-ray telescope onboard Swift, Jules Halpern at Columbia University captured the first "light echoes" ever seen from a soft-gamma-ray repeater. Images acquired when the latest flaring episode began show what appear to be expanding halos around the source. Multiple rings form as X-rays interact with dust clouds at different distances. Click on the image to play a 6-day movie:
Above: Swift's X-Ray Telescope (XRT) captured an apparent expanding halo around the flaring neutron star SGR J1550-5418. The halo formed as X-rays from the brightest flares scattered off of intervening dust clouds. Credit: NASA/Swift/Jules Halpern, Columbia Univ. [more]
Scientists think the source of the flares is a spinning neutron star--the superdense, city-sized remains of a supernova. Although only about 12 miles across, a neutron star contains more mass than the sun. This particular neutron star is believed to be a "magnetar," a neutron star with an incredibly intense magnetic field.
A popular theory of soft-gamma-ray repeaters holds that flares are caused by "starquakes" in the outer rigid crust of the magnetar. As a magnetar's colossal magnetic field shifts, it strains the crust with monstrous magnetic forces, often breaking it. When the crust snaps, it vibrates with seismic waves like in an earthquake and emits a flash of gamma-rays.
NASA's Fermi Gamma-ray Space Telescope, launched in June 2008, is ideal for this work. "The ability of Fermi's gamma-ray burst monitor to resolve the fine structure within these events will help us better understand how magnetars unleash their energy," said Chryssa Kouveliotou, an astrophysicist at NASA's Marshall Space Flight Center in Huntsville, Ala. The object has triggered Fermi's gamma-ray burst monitor more than 95 times since Jan. 22nd.
NASA's Wind satellite, the joint NASA-Japan Suzaku mission, and the European Space Agency's INTEGRAL satellite also have detected flares from SGR J1550-5418.
The flashes continue! Stay tuned to Science@NASA for updates.
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Credits: NASA's Goddard Space Flight Center in Greenbelt, Md., manages the Swift satellite. It is being operated in collaboration with partners in the U.S., the United Kingdom, Italy, Germany and Japan. NASA's Fermi Gamma-ray Space Telescope is an astrophysics and particle physics observatory developed in collaboration with the U.S. Department of Energy and with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the U.S.
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