Distant Gamma Ray Burster Nailed

Robin Hanson (hanson@hss.caltech.edu)
Wed, 14 May 1997 17:50:13 -0700 (PDT)

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From: Robert Finn <finn@nasw.org>
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Date: Wed, 14 May 1997 17:01:11 -0700
Subject: fx-discuss: GRBr: New Caltech news release

This news release, which was issued minutes ago by Caltech, bears directly
on claim GRBr. It reports results that argue strongly for a very distant
origin for at least one gamma-ray burster.

Bob Finn

>For Immediate Release May 14, 1997
>Caltech Astronomers Crack the Puzzle of Cosmic Gamma-Ray Bursts
>PASADENA-A team of Caltech astronomers has pinpointed a gamma-ray burst
>several billion light-years away from the Milky Way. The team was following
>up on a discovery made by the Italian/Dutch satellite BeppoSAX.
>The results demonstrate for the first time that at least some of the
>enigmatic gamma-ray bursts that have puzzled astronomers for decades are
>extragalactic in origin.
>The team has announced the results in the International Astronomical Union
>Circular, which is the primary means by which astronomers alert their
>colleagues of transient phenomena. The results will be published in
>scientific journals at a later date.
>Mark Metzger, a Caltech astronomy professor , said he was thrilled by the
>result. "When I finished analyzing the spectrum and saw features, I knew we
>had finally caught it. It was a stunning moment of revelation. Such events
>happen only a few times in the life of a scientist."
>According to Dr. Shri Kulkarni, an astronomy professor at Caltech and another
>team member, gamma-ray bursts occur a couple of times a day. These
>brilliant flashes seem to appear from random directions in space and
>typically last a few seconds.
>"After hunting clues to these bursts for so many years, we now know that the
>bursts are in fact incredibly energetic events," said Kulkarni.
>For team member and astronomy professor George Djorgovski, "Gamma-ray bursts
>are one of the great mysteries of science. It is wonderful to contribute to
>its unraveling."
>The bursts of high-energy radiation were first discovered by military
>satellites almost 30 years ago, but so far their origin has remained a
>mystery. New information came in recent years from NASA's Compton Gamma-Ray
>Observatory satellite, which has so far detected several thousand bursts.
>Nonetheless, the fundamental question of where the bursts came from remained
>Competing theories on gamma-ray bursts generally fall into two types: one,
>which supposes the bursts to originate from some as-yet unknown population of
>objects within our own Milky Way galaxy, and another, which proposes that the
>bursts originate in distant galaxies, several billion light-years away. If
>the latter (as was indirectly supported by the Compton Observatory's
>observations), then the bursts are among the most violent and brilliant
>events in the universe.
>Progress in understanding the nature of the bursts was stymied by the fact
>that until recently the bursts were detected as very high-energy gamma rays.
>It is difficult to focus gamma rays, and thus the positional accuracy of the
>bursts was quite crude, leaving astronomers with thousands of faints stars
>and galaxies as potential "hosts."
>An important recent development was the deployment of BeppoSAX, a joint
>Italian/Dutch satellite launched in late 1996 by the Italian space agency.
>This satellite, for the first time, provided a rapid and accurate position in
>the sky for strong gamma-ray bursts. This enabled astronomers to search for
>possible visible and radio counterparts using telescopes on the ground. The
>first such counterpart was detected at the beginning of May, but faded away
>before its nature could be established.
>The satellite detected another burst on May 8, and Caltech astronomers were
>able to bring telescopes at Palomar Observatory to bear within a few hours.
>The Caltech team noticed a starlike object that was changing brightness in an
>unusual fashion at the position of the burst . Dr. Howard Bond of the Space
>Telescope Science Institute initially reported the object based on his
>measurements at Kitt Peak National Observatory.
>The crucial piece to the puzzle was finally found by the Caltech team on May
>11 using one of the two W.M. Keck 10-meter telescopes, the world's largest,
>on Mauna Kea, Hawaii. The variable object showed characteristic features in
>its spectrum, known to originate in intergalactic clouds. By measuring the
>wavelengths of these features, the Caltech astronomers were able to measure
>the distance to a gamma-ray burst for the first time. Their measurements
>place the burst at a distance of several billion light-years, over one half
>the size of the observable universe.
>Recent observations from the telescopes at Palomar show that this star-like
>object is fading away. As such rapid fading had been seen with the burst in
>March, the Caltech astronomers had to make an extra effort to identify this
>counterpart quickly so that the Keck observations could be carried out when
>the object was bright.
>The discovery is a major step to help scientists understand the nature of the
>burst's origin. We now know that for a few seconds the burst was over a
>million times brighter than an entire galaxy. No other phenomena are known
>that produce this much energy in such a short time. Thus, while the
>observations have settled the question of whether the bursts come from
>cosmological distances, their physical mechanism remains shrouded in mystery.
>The Caltech team, in addition to Metzger, Kulkarni, and Djorgovski, consists
>of professor Charles Steidel, postdoctoral scholars Steven Odewahn and Debra
>Shepherd, and graduate students Kurt Adelberger, Roy Gal, and Michael Pahre.
>The team also includes Dr. Dale Frail of the National Radio Astronomy
>Observatory in Socorro, New Mexico.
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