archive: SETI FW: [ASTRO] Ulysses Captures Gamma-Ray Flare From Shattered Star

SETI FW: [ASTRO] Ulysses Captures Gamma-Ray Flare From Shattered Star

Larry Klaes ( )
Fri, 2 Oct 1998 17:17:08 -0400

From: Ron Baalke
Sent: Friday, October 02, 1998 12:41 PM
Subject: [ASTRO] Ulysses Captures Gamma-Ray Flare From Shattered Star

PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011

Contact: Diane Ainsworth



The signal of a cataclysmic magnetic flare emanating from a star that
cracked apart halfway across the galaxy has been captured by NASA's Ulysses
spacecraft and is providing important clues about some of the most unusual
stars in the universe.

The magnetic burst from the star SGR1900+14, located in the
constellation Aquila 20,000 light-years away, was observed by Ulysses and
other spacecraft with high-energy radiation detectors in space on August 27,
1998, as its heavy metal crust fractured and released the most powerful wave
of gamma radiation yet observed from this type of star.

"Soft gamma repeaters (SRGs) emit magnetic radiation sporadically,
every few years, unlike gamma ray bursts, which explode and disappear," said
Dr. Edward J. Smith, Ulysses project scientist at NASA's Jet Propulsion
Laboratory, Pasadena, CA. "This was the fourth soft gamma repeater to be
observed, but unlike the others we have studied, this one emitted an
exceedingly intense burst of radiation. We estimate that it released as much
energy in a few seconds as the Sun emits in 300 years." Ulysses is a joint
mission of NASA and the European Space Agency.

SGR1900+14 is a newly discovered type of star called a "magnetar" - a
dense ball of super-heavy matter about the size of a city, but weighing more
than the Sun. Objects in this class have the greatest magnetic fields known
in the universe. A magnetar is so intense that it powers a steady glow of
X-rays from the star's surface, often punctuated by brief, intense gamma-ray
flashes and, occasionally, by catastrophic flares like the one observed on
August 27. Astronomers think that all these effects are caused by an
out-of-control magnetic field -- one capable of heating, mixing and
sometimes cracking the star's rigid surface.

Using several spacecraft detectors, including the Ulysses gamma ray
burst instrument, scientists were able to measure this extremely rare event
and pinpoint the precise source of the explosion with unprecedented clarity.

"The star, which has an extremely strong magnetic field, appears to
have experienced a 'star quake' so powerful that it created a temporary
ionosphere on the night side of Earth and sent two spacecraft into
protective safe modes," Smith said.

Data from the Ulysses experiment, showed radiation counts that
rocketed from background (near zero) levels to several thousand electrons
per second. Dr. Kevin Hurley of the University of California, Berkeley, who
is principal investigator of the gamma ray burst experiment on Ulysses,
reported that energy measurements were two times greater than any other
recorded burst.

"The radiation, as seen by the gamma ray burst detector, spiked
quickly and soon settled into a series of ever-smaller spikes that clearly
revealed the neutron star's rotational period," Hurley reported at a NASA
science press briefing on September 29. "The star reminded us of a dying
lighthouse. It kept rotating, but the lamp steadily faded away."

Hurley, who had been part of a team observing the star, recorded
pulses or flashes of magnetic radiation emanating from the star every 5.16
seconds using another satellite, known as the Japanese/NASA Advanced
Satellite for Cosmology and Astrophysics (ASCA). Comparisons of the ASCA
data and measurements from other satellites showed that the X-ray pulses
were gradually slowing down after the radiation burst subsided.

From its intensity and rotational slowing, scientists calculated that
SGR1900+14 has a magnetic field about a thousand trillion times stronger
than Earth's magnetic field and about one thousand times stronger than any
found elsewhere in the universe, Smith said. During the flashing episode,
Dr. Chryssa Kouveliotou of NASA's Marshall Space Flight Center in
Huntsville, AL, who led another team observing the star with sensitive X-ray
detectors aboard NASA's Rossi X-ray Timing Explorer satellite, found faint
X-rays coming from the star, similar to what they had observed in another
soft gamma repeater which turned out to be a magnetar.

Three of the four confirmed soft gamma repeaters - designated
1900+14, 1806-20 and 0526-66 -- have localized X-ray emissions; 1806-20 and
1900+14 have regular pulsations and 0526- 66 had an eight-second period
during its magnetic explosion observed in 1979. It is by comparing the
change in the rotational period of these stars across several observations
that scientists can measure their magnetic fields.

"Magnetars seem to answer several mysteries about the structure and
evolution of stars," said Kouveliotou. "We think magnetars spend their first
10,000 years as soft gamma repeaters. As they weaken with age and slow their
rotation, they become anomalous X-ray pulsars -- stars that do not have
enough 'juice' to flash anymore, but which emit a steady flow of X-rays for
perhaps another 30,000 years. After that, they fade to black and drift for
eternity through the heavens. The absence of observable pulsars in some
supernova remnants just means that the pulsar's lights have gone out sooner
than we expected."

Additional information on magnetars or the August 27 burst is
available on the Internet at and

The Ulysses mission to study the poles of the Sun is managed jointly
by NASA and the European Space Agency. The Jet Propulsion Laboratory manages
the U.S. portion of the mission for NASA's Office of Space Science,
Washington, DC. JPL is a division of the California Institute of Technology,
Pasadena, CA.