Newsgroup: it.scienza.astronomia
Titolo: esplosione raggi gamma (la notizia e' del 27 gennaio)


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Donald Savage
Headquarters, Washington, DC                    January 27, 1999
(Phone:  
202/358-1727
)
Tim Tyson
Marshall Space Flight Center, Huntsville, AL
(Phone:  
256/544-0994
)
Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone:  
301/286-5017
)
RELEASE:  99-8
GAMMA RAY BURST IMAGED FOR FIRST TIME
       Astronomers racing the clock managed to take the first-ever
optical images of one of the most powerful explosions in the
Universe -- a gamma ray burst -- as it was occurring on Saturday,
Jan. 23, 1999.  Gamma ray bursts produce more energy in a very
short period than the rest of the entire Universe combined.
       Because such bursts occur with no warning and typically
last for just a few seconds, quick detection by orbiting
spacecraft and instant notification to astronomers are critical in
order to catch the bursts in the act.
       The gamma-ray-burst detectors of the Burst and Transient
Source Experiment (BATSE) onboard NASA's orbiting Compton Gamma
Ray Observatory detected the beginning of a bright gamma ray
burst.  As the burst was still in progress, computers determined a
rough location and radioed the position to the Gamma Ray Burst
Coordinates Network (GCN), based at NASA's Goddard Space Flight
Center, Greenbelt, MD.  The position was immediately forwarded via
the GCN to astronomers at ground based observatories throughout
the world.
       Just 22 seconds later the Robotic Optical Transient Search
Experiment (ROTSE) in Los Alamos, NM, operated by a team led by
Dr. Carl Akerlof of the University of Michigan, was in position
and took images of the patch of sky where the burst was reported.
Their equipment is assembled from 35 mm camera lenses and parts
culled from the amateur astronomy market.  The first picture
showed a brightening new star within the sky region where the
burst was reported.
       Five seconds later, the burst achieved peak brightness,
reaching 9th magnitude, about 16 times fainter than the human eye
can see, but easily visible in an amateur telescope.  Within eight
minutes of the initial detection, the burst had faded by a factor
of 100 below its maximum brightness.  "I was amazed," Akerlov
said.  "At best, we expected something really dim optically, at
the limit of our sensitivity.  Instead we found a whopper."
       "If this burst had originated in the Milky Way Galaxy, it
would have lit up the night sky," said Dr. Alan Bunner, Director
of NASA's Structure and Evolution of the Universe science theme at
NASA Headquarters.
       The event was also recorded by instruments aboard the
Italian-Dutch BeppoSAX satellite, which obtained a much more
accurate position for the burst within a few hours of its onset.
It was this more precise location information that the ROTSE team
used to find the burst in their images.
       "This is the Holy Grail for the Gamma Ray Burst Coordinates
Network," said Dr. Scott Barthelmy, the astronomer at Goddard, who
developed and runs the network.  "Optical telescopes had seen the
afterglow of a burst, but never the burst itself.  This
observation will help us understand the physical processes behind
the bursting."
       Within three hours of the gamma ray burst, a team of
astronomers led by Dr. Stephan Odewahn, and Profs. Shri Kulkarni
and George Djorgovski of the California Institute of Technology
used the 60-inch Mt. Palomar telescope to find a fading optical
counterpart to this gamma ray burst, helped by the precise
localization provided by BeppoSAX.
       The next night, a joint team led by Dr. D. Kelson of the
Carnegie Institution of Washington, using the Keck II 10-meter
telescope located at Mauna Kea, HI, found that the distance to the
burst is about nine billion light years, more than half way to the
edge of the observable Universe.
       Astronomers are not certain what produces gamma ray bursts,
but possible causes include the mergers of two neutron stars, two
black holes, or a neutron star and a black hole, or the explosion
of a so-called hypernova.  A hypernova is a theorized type of
supernova or exploding star.
       "The optical emission was about 10,000 times brighter than
ever observed, something you could see with a pair of good
binoculars," said Dr. Neil Gehrels, Project Scientist of the
Compton Observatory.  "Theorists will have a field day trying to
explain this phenomenon."
       Dr. Gehrels said the simultaneous observation of the burst
in optical and gamma ray energies might open the door to a whole
new generation of instruments like ROTSE, which is a fully
automated telescope that can respond to information about
transient celestial sources instantly.  Orbiting telescopes detect
several hundred gamma ray bursts each year.
       The ROTSE project is designed and operated by a
collaboration of astrophysicists from the University of Michigan
and the Department of Energy's Los Alamos and Lawrence Livermore
National Laboratories.  The Principal Investigator for BATSE is
Dr. Gerald Fishman at NASA's Marshall Space Flight Center,
Huntsville, AL.  The National Science Foundation provided funding
for observations at Keck II.
                              - end -

:)
Ma devi essere sempre cosi' acido? Capisco (ma non approvo) con gli
ufologi, ma lo devi essere anche con i tuoi colleghi astrofili?
^__^
Saluti scettici,
Roberto

non vedo quale sia il motivo di tanta meraviglia.
Caro tre e quattordici,
Riconosco di essere poco aggiornato. Mi consolo con il fatto che sono in
buona compagnia, in quanto la CNN ha riportato la notizia il 25 marzo, la
University of Michigan l'ha rilasciata il 24 e la Nature News Service ha
fatto lo stesso il 26 sempre del mese corrente. Evidentemente o sono un po'
distratti anche loro, oppure hanno ritenuto che valesse la pena di
riproporre la notizia.
Saluti
Antonio Zanardo

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 wrote in message 7doe11$si5$1...@hermes.iol.it...
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