Don Savage
Headquarters, Washington, DC              September 29, 1997
(Phone: 202/358-1547)

Helen Worth
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone:  301/953-5113)

RELEASE:  97-220

NEAR SPACECRAFT GETS UNEXPECTED VIEW OF MYSTERIOUS GAMMA-RAY BURST

       A significant step toward revealing the mysteries of gamma-
ray bursts was taken this week by The Johns Hopkins University
Applied Physics Laboratory (APL), Laurel, MD, when NASA's Near
Earth Asteroid Rendezvous (NEAR) spacecraft sent back unexpected
data showing a major gamma-ray burst.  APL manages the NEAR
mission for NASA.

       The observation came after researchers reconfigured the
gamma-ray spectrometer to make more frequent data returns as NEAR
travels to a rendezvous with the asteroid Eros in February 1999.
If as distant as new evidence suggests, gamma-ray bursts are the
most violent explosions known, emitting in one second as much
energy as the Sun will emit in its lifetime.

       The gamma-ray spectrometer was not originally planned to
begin its work until the spacecraft reached Eros.  But while en
route a simple software change was added that gave a new
astrophysics capability to this planetary spectrometer, which
resulted in detection of a gamma-ray burst on Sept. 15, that
lasted for about 10 seconds.  Since then six more bursts have been
detected.  Several of the bursts have been confirmed by the
European Space Agency/NASA Ulysses spacecraft, now in a polar
orbit around the sun and by two detectors on NASA's Wind
spacecraft near the Earth.  These three spacecraft, along with
other Earth-orbiting spacecraft, form a 3-dimensional
interplanetary network for observing gamma-ray bursts that has not
been possible since the loss of the Mars Observer in 1993.

        "Seeing this burst validates that the NEAR detector can be
a true working partner in the interplanetary network for gamma-ray
burst detection," says APL's lead gamma-ray instrument engineer
John Goldsten, who was the first to see the gamma-ray burst data.

        Jacob Trombka, NASA's Science Team Leader for the gamma-
ray instrument, says, "NEAR's instrument is more sensitive than we
believed it would be.  It's seeing bursts that other spacecraft
aren't seeing." The success of the instrument is the result of a
good design, he says.  "Originally we didn't have time to include
a burst mode on the instrument, but the system was so well
designed that we were able to upload such a system a few weeks ago."

       Gamma-ray bursts remain one of the great mysteries of
astrophysics since their discovery more than 30 years ago.  They
tend to be randomly distributed over the sky and occur with a
frequency of about one per day for the most sensitive detectors.
If they are of cosmological origin, they represent the most
powerful events that are known in the universe.  The debate as to
their local or cosmological origin will most likely be resolved by
locating sources of gamma-ray bursts and then identifying them
with optical and radio telescopes.  NASA's Hubble Space Telescope
made the first observation of a fuzzy object associated with a
burst that was detected last Feb. 28 by the Italian BeppoSAX satellite.

       The sources of gamma-ray bursts can be located in the sky
by timing the arrival of the gamma-rays at three well-separated
spacecraft.  Since 1993, the spacecraft instrumented to observe
such bursts have been the Ulysses spacecraft plus several
spacecraft near the Earth: the BeppoSAX and Wind as well as NASA's
Compton Gamma-Ray Observatory (CGRO) and Rossi X-ray Timing
Explorer.  The near-Earth spacecraft are too close to each other
to allow a unique determination of the location of the bursts.

       The addition of the Near Earth Asteroid Rendezvous
spacecraft to the interplanetary network will provide 3-
dimensional triangulation of source locations and should greatly
increase the probability of associating a gamma-ray source with a
particular source from optical and radio telescopes.

       The new capability on NEAR will expand the network and
enable it to obtain the locations of moderate and stronger bursts,
which occur at least several times per month, to a position in the
sky accurate to about a minute of arc (about a thirtieth of the
size of the moon).

        NEAR, the first mission of NASA's Discovery Program for
"faster, better, cheaper" planetary exploration, will be the first
spacecraft to orbit an asteroid.  On June 27 NEAR sent back
spectacular images of 253 Mathilde as it flew past the asteroid.
In February 1999, NEAR will reach Eros and begin the first long-
term, close-up look at an asteroid's surface composition and
physical properties.

       NEAR was designed and built by The Johns Hopkins University
Applied Physics Laboratory, in Laurel, MD, which also manages the
program for NASA.

                             - end -

EDITOR'S NOTE:    Information and images on the NEAR mission can
be obtained on APL's NEAR homepage at URL:  http://sd-www.jhuapl.edu/NEAR/