Astronomers using NASA's Swift satellite and Fermi
Gamma-ray Space Telescope are seeing frequent blasts from a stellar
remnant 30, 000 light-years away. The high-energy fireworks arise from
a rare type of neutron star known as a soft-gamma-ray repeater. Such
objects unpredictably send out a series of X-ray and 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."
The object, which has long been known as an X-ray source, lies in the
southern constellation Norma. During the past two years, astronomers
have identified pulsing radio and X-ray signals from it. The object
began a series of modest eruptions on Oct. 3, 2008, then settled
down. It roared back to life Jan. 22 with an intense episode.
Because of the recent outbursts, astronomers will 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
measurably affected Earth's upper atmosphere from 50, 000 light-years
away.
Scientists think the source is a spinning neutron star, which is the
superdense, city-sized remains of an exploded star. Although only
about 12 miles across, a neutron star contains more mass than the
sun. The object has been cataloged as SGR J1550-5418.
While neutron stars typically possess intense magnetic fields, a
subgroup displays fields 1, 000 times stronger. These so-called
magnetars have the strongest magnetic fields of any known object in
the universe. SGR J1550-5418, which rotates once every 2.07 seconds,
holds the record for the fastest-spinning magnetar. Astronomers think
magnetars power their flares by tapping into the tremendous energy of
their magnetic fields.
"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 the instrument more than 95 times since
Jan. 22.
Using data from Swift's X-ray telescope, 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, with closer clouds producing larger rings. Both
the rings and their apparent expansion are an illusion caused by the
finite speed of light and the longer path the scattered light must
travel.
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.
"X-rays from the brightest bursts scatter off of dust clouds between
us and the star, " Halpern said. "As a result, we don't really know
the distance to this object as well as we would like. These images
will help us make a more precise measurement and also determine the
distance to the dust clouds."
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.
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.
To see the related images, visit:
http://www.nasa.gov/mission_pages/swift/bursts/gammaray_fireworks.html
For more information about the Swift satellite, visit: http://www.nasa.gov/swift
For more information about the Fermi mission, visit: http://www.nasa.gov/fermi
US $24.50
In what sounds like a one of a kind murder mystery, a dying star has fallen into a black hole and been ripped apart. The event, which was observed on March 28, was originally thought to be a gamma ray burst from a collapsing star, but researchers suspected something more sinister was at play. Their findings appear in a pair of papers published...
