archiv~1.txt: SETI [ASTRO] Caltech Observers Brightest Gamma-Ray Burst So Far

SETI [ASTRO] Caltech Observers Brightest Gamma-Ray Burst So Far

Larry Klaes ( )
Wed, 31 Mar 1999 10:37:56 -0500

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>Date: Mon, 29 Mar 1999 20:45:44 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] Caltech Observers Brightest Gamma-Ray Burst So Far
>Reply-To: Ron Baalke <>
>Media Relations
>Caltech Media Relations: Robert Tindol, (626) 395-3631,
>W. M. Keck Observatory: Andy Perala, (808) 885-7887,
>Embargoed for release at 3 p.m. EST, Thursday, March 25, 1999
>Caltech observes brightest gamma-ray burst so far
>PASADENA -- An extraordinarily bright cosmic gamma-ray flash turns out to be
>the most energetic one measured so far, according to a team of astronomers
>from the California Institute of Technology.
>"The burst appeared to be more luminous than the whole rest of the universe,
>and that would be very hard to explain by most current theories,"said Caltech
>professor of astronomy and planetary science Shrinivas Kulkarni, one of the
>principal investigators on the team.
>"It was ten times more luminous than the brightest burst seen so far, and
>that was quite unexpected."
>"If the gamma rays were emitted equally in all directions, their energy would
>correspond to ten thousand times the energy emitted by our sun over its
>lifetime so far, which is about 5 billion years," said Caltech professor of
>astronomy S. George Djorgovski, another of the principal investigators on the
>team. "Yet the burst lasted only a few tens of seconds."
>Gamma-ray bursts are mysterious flashes of high-energy radiation that appear
>from random directions in space and typically last a few seconds. They were
>first discovered by U.S. military Vela satellites in the 1960s. Since then,
>over a hundred theories of their origins have been proposed, but the causes
>of gamma-ray bursts remain unknown. Some theorists believe that the bursts
>originate during the formation of black holes.
>NASA's Compton Gamma-Ray Observatory satellite has detected several thousand
>bursts so far. The chief difficulty in studying these puzzling flashes is in
>locating them precisely enough and quickly enough to follow up with ground-
>based telescopes.
>A breakthrough in this field was made in early 1997 by the Italian/Dutch
>satellite BeppoSAX, which can locate the bursts with a sufficient accuracy.
>A team of Caltech astronomers was then able to establish that the bursts
>originate in the very distant universe. Since then, about a dozen bursts
>have been studied in detail by astronomers using ground-based telescopes.
>The bursts may last only a few seconds in gamma rays, but leave more long-
>lived but rapidly fading afterglows in X-rays, visible light, and radio
>waves, which can be studied further.
>This burst, called GRB 990123, was discovered by the BeppoSAX satellite
>on January 23. It was the brightest burst seen so far by this satellite,
>and one of the brightest ever seen by NASA's Compton Gamma-Ray Observatory.
>Within three hours of the burst, members of the Caltech team, including
>senior postdoctoral scholar in astronomy Stephen Odewahn and graduate
>students Joshua Bloom and Roy Gal, used Palomar Observatory's 60-inch
>telescope to discover a rapidly fading visible-light afterglow associated
>with the burst.
>"This adventure began at 5 a.m. with a wake-up call from our Italian friends
>alerting us about their burst detection," said Bloom, "But it was certainly
>worth it. We got to watch a remarkable fireworks show!"
>Following the Caltech team's announcement, several hours later a team of
>astronomers known as the ROTSE collaboration, led by Professor Carl
>Akerloff of the University of Michigan, reported that the visible light
>counterpart of the burst was also seen in the images taken with a small,
>robotic telescope operated by their team, starting only 22 seconds after
>the burst. This was the first time that such rapid measurement of a burst
>afterglow was made, and its extreme brightness was unexpected.
>Meanwhile, a new radio source, coincident with the visible-light afterglow
>discovered at Palomar, was found at the National Radio Astronomy
>Observatory's Very Large Array radio telescope, near Socorro, New Mexico,
>by Dale Frail and Kulkarni.
>Such a radio flash was predicted by Dr. Re'em Sari, a theorist at Caltech,
>and Dr. Tsvi Piran (now at Columbia University), and it provides an important
>input for theories of gamma-ray bursts.
>At the prompting of the Caltech team, a group of astronomers led by Professor
>Garth Illingworth of the University of California at Santa Cruz, used the
>W. M. Keck Observatory's 10-meter Keck-II telescope at Mauna Kea, Hawaii,
>to obtain a spectrum of the burst afterglow.
>A distance to the burst was determined from its spectrum, and the burst was
>found to be about 9 billion light-years from Earth.
>The Keck measurement of the distance was crucial. "We were stunned," said
>Djorgovski. "This was much further than we expected, and together with the
>observed brightness of the burst it implied an incredible luminosity.
>"The peak brightness of the visible light afterglow alone would be millions
>of times greater than the luminosity of an entire galaxy, and thousands of
>times brighter than the most luminous quasars known."
>This remarkable light flash contained only a small fraction of the total
>burst energy in the gamma rays. Caltech astronomers note that even more
>energy was likely emitted in forms that are difficult to observe, such as
>gravitational waves or neutrinos, elusive particles that can penetrate
>the entire planet Earth without stopping.
>As the burst's afterglow faded, the Caltech team discovered a faint galaxy
>adjacent to it in the sky, in infrared images obtained with the W. M. Keck
>Observatory's 10-meter Keck-I telescope at Mauna Kea.
>This is almost certainly the galaxy in which the burst originated. The galaxy
>is about as faint as an ordinary 100-watt lightbulb would be if seen from a
>distance of half a million miles, about twice the distance to the moon.
>Subsequently, following a proposal by the Caltech team and others, the Hubble
>Space Telescope obtained visible-light images of this galaxy and the burst's
>afterglow. The analysis of these images by the Caltech team indicates that
>the galaxy is not unusual in its properties, compared to other normal
>galaxies at comparable distances from Earth.
>A detailed follow-up study of the burst's afterglow by the Caltech team
>revealed a change in its brightness that could be interpreted as a sign of
>a jet of energy, moving close to the speed of light, and pointing nearly
>toward Earth.
>"This was the first time that such behavior was seen in a gamma-ray burst,"
>emphasized Kulkarni, "and it may help explain in part its enormous apparent
>Scientists are still debating whether such a powerful beaming of energy
>occurs in gamma-ray bursts.
>The team's findings appear in the April 1 issue of the scientific journal
>Nature, and in a forthcoming issue of the Astrophysical Journal Letters.
>In addition to Kulkarni, Djorgovski, Odewahn, Sari, Bloom, and Gal, the
>Caltech team also includes Professors Fiona Harrison and Gerry Neugebauer,
>Drs. Chris Koresko and Lee Armus, and several others.
>Images of the burst are available at:
>For further information, please contact:
>Prof. George Djorgovski, Caltech
>(626) 395-4415,
>Prof. Shrinivas Kulkarni Caltech
>(626) 395-4010,
>[Image 1]
>A section of the Hubble Space Telescope image of the field of GRB 990123,
>showing the afterglow and its host galaxy, taken about 16 days after the
>burst. The images were processed at Caltech by Dr. Stephen Odewahn, a member
>of the Caltech team.
>Image Credit: The Caltech GRB Team/Space Telecsope Science Institute
>[Image 2]
>A comparison of images of the field of GRB 990123, obtained at Palomar
>Observatory. The image on the top is from the Palomar Observatory's digital
>sky survey (DPOSS). The arrow points to the location of the burst. The image
>on the bottom is the discovery image obtained by S. C. Odewahn and J. S.
>Bloom within a couple of hours from the burst. It shows the burst afterglow
>source at the location marked with the arrow. Other objects are random
>foreground stars and galaxies.
>Related Links
>Djorgovski's research interests
>Kulkarni's research interests
>Caltech's Observatories
>The BeppoSAX spacecraft
>The Compton Gamma Ray Observatory