Magnetars, the most magnetic stars known, more common than previouslythought (Forwarded)

Steve Roy
Media Relations Dept.
Marshall Space Flight Center, Huntsville, AL

(256) 544-0034

For release: 01/06/04

Release No.: N04-001

Magnetars, the most magnetic stars known, more common than previously thought

An investigation led by a NASA Marshall Center scientist at the National Space
Science and Technology Center (NSSTC) in Huntsville has shed new insight into
magnetars, the most magnetic stars known. New research suggests that these
exotic objects -- capable of stripping a credit card clean 100,000 miles away --
are far more common than previously thought. The NSSTC is a partnership with the
Marshall Center, industry and Alabama universities.

Observations of explosions from an ultra-powerful magnetic neutron star playing
hide-and-seek with astronomers suggest that these exotic objects called
magnetars -- capable of stripping a credit card clean 100,000 miles away -- are
far more common than previously thought.

Scientists from the United States and Canada present this result today at the
meeting of the American Astronomical Society in Atlanta. The work is based on
observations with the European Space Agency's XMM-Newton observatory and NASA's
Rossi X-ray Timing Explorer.

"We only know of about ten magnetars in the Milky Way galaxy," said the
investigation's leader, Dr. Peter Woods of NASA's Marshall Space Flight Center
in Huntsville, Ala., based at the National Space Science and Technology in
Huntsville. "If the antics of the magnetar we are studying now are typical,
turning on and off but never getting exceptionally bright, then there very well
could be hundreds more out there."

Wood's colleagues a Dr. Vicky Kaspi and Mr. Fotis Gavriil of McGill
University in Montreal; Dr. Christopher Thompson of the Canadian Institute for
Theoretical Astrophysics; Drs. Herman Marshall, Deepto Chakrabarty and Kathy
Flanagan at the Massachusetts Institute of Technology; and Drs. Jeremy Heyl and
Lars Hernquist at the Harvard-Smithsonian Center for Astrophysics.

The source in question is a magnetar "candidate" named 1E 2259+586 in the
constellation Cassiopeia, approximately 18,000 light years from Earth. A
magnetar is a special neutron star. A neutron star is a compact sphere
approximately 15 kilometers (10 miles) in diameter, the core remains of a
collapsed star roughly ten times more massive than the Sun. Magnetars, for
reasons poorly understood, have magnetic fields a thousand times stronger than
ordinary neutron stars, measuring 10**14 to 10**15 Gauss (or about a
hundred-trillion refrigerator magnets; the Sun's magnetic field is about 5 Gauss.)

Not all scientists are convinced that neutron stars can be so magnetic. As such,
magnetar candidates are often referred to in the scientific literature as either
Soft Gamma-ray Repeaters (SRGs) or Anomalous X-ray Pulsars (AXPs), depending on
their bursting characteristics. Members of this observation team helped
established the connection between SRGs and AXPs in 2002. The source 1E 2259 is
sometimes called an AXP.

For all their power, magnetars are not always majestic beacons. The opportunity
to study them comes when they erupt for hours to months, without warning,
emitting visible light and other wavelengths before growing dim once more.
Magnetar 1E 2259 suddenly began bursting in June 2002. Scientists collected data
on over 80 bursts recorded within a 4-hour window. No other bursts have been
detected since.

These same changes in emissions happened 12 years ago and remained a mystery
until this study. "Knowing what we know now, we realize that the earlier burst
activity was too dim to observe," said Woods.

The cumulative properties of the outburst in 1E 2259+586 led the team to make
several conclusions: First, the star suffered some major event lasting several
days with two distinct components, one on the surface of the star (perhaps a
fracture in the crust) and the other beneath the surface.

According to Kaspi, "The changes in persistent emission properties suggest that
the star underwent a plastic deformation of the crust that simultaneously
impacted the superfluid interior and the magnetosphere." (A neutron star's
interior is thought to be a superfluid of neutrons. The magnetosphere refers to
the region in which the neutron star's magnetic field controls the behavior of
the charged particles.)

The emission after the bursting was similar to that of an SGR, further blurring
the distinction between these two exotic species, Kaspi said. Also, from the
changes in emission, the scientists could infer previous burst active episodes
from this and other magnetar candidates.

"This sort of behavior could be happening all the time in other sources like it
throughout the Galaxy and we would never know it because our gamma-ray 'eyes'
are not sensitive enough," said Woods.

Thus, the non-detection of such outbursts by telescopes scanning the entire sky
for X-ray and gamma-ray sources suggests that the number of magnetar candidates
in our Galaxy is larger than previously thought but that they are in a prolonged
dim phase. The team plans to calculate this number. Helping them will be the
NASA Swift Gamma-Ray Burst Explorer, scheduled for launch in mid-2004. Swift
will be about 20 times more sensitive to magnetar bursts than anything that has
flown before. "If there is a big population of these objects out there, Swift
should find them," Woods said.

"Magnetars are not just the most magnetic stars known but they are stars not
powered by a conventional mechanism such as nuclear fusion, rotation or
accretion," Kaspi said. "Magnetars represent a new way for a star to shine,
which makes this a fascinating field."

ESA's XMM-Newton was launched in December 1999. NASA helped fund mission
development and supports guest observer time. The Rossi Explorer was launched in
December 1995. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the
day-to-day operation of the satellite and maintains its data archive.

Peter Woods joins the National Space Science and Technology Center through the
Universities Space Research Association. Fotis Gavriil is a graduate student in
the Physics Department of McGill University.

The NSSTC is a cooperative venture of NASA's Marshall Space Flight Center,
Alabama A & M University, Auburn University, Tuskegee University, The University
of Alabama, The University of Alabama at Birmingham, The University of Alabama
in Huntsville, and The University of South Alabama.