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BeppoSAX U.S. Coordination Facility

  Date: Tue, 1 Apr 1997 15:05:57 -0500 (EST)
  Subject:  Hubble Tracks the Fading Optical Counterpart of 
            a Gamma-Ray Burst
  Douglas Isbell
  Headquarters, Washington, DC                April 1, 1997
  (Phone:  202/358-1547)
  Ray Villard
  Space Telescope Science Institute, Baltimore, MD
  (Phone:  410/338-4514)
  Dave Drachlis
  Marshall Space Flight Center, Huntsville, AL
  (Phone: 205/544-0034)
  RELEASE:  97-63
      NASA's refurbished Hubble Space Telescope has made an 
  important contribution toward solving one of astronomy's 
  greatest enigmas by allowing astronomers to continue watching 
  the fading visible-light counterpart of a gamma-ray burst 
  (GRB), one of the most energetic and mysterious events in the 
      The so-called optical counterpart is presumably a cooling 
  fireball from the catastrophic event that triggered the massive 
  burst of invisible gamma rays -- the highest-energy radiation 
  in the universe.  This event may have unleashed as much energy 
  in a few seconds as the Sun does in ten billion years.
      The burst was detected by several space-based, high-energy 
  astrophysics observatories on Feb. 28. The visible GRB 
  counterpart, the first ever detected, was then discovered in a 
  pair of ground-based telescopic images of the region where the 
  burst occurred. Taken a week apart, the later picture showed 
  that an object that could be seen in the first image had 
  disappeared in the field, suggesting it was the decaying 
  fireball from the event. A week after that discovery, 
  astronomers at the New Technology Telescope and the Keck 
  telescope identified an extended source at the location of the 
  suspected GRB.
      Hubble's high resolution and sensitivity were brought in to 
  hunt down the rapidly dimming fireball -- plunging from 21st to 
  below 23rd magnitude in eight days -- after it had grown so 
  faint that it could not be resolved by ground-based telescopes 
  by March 13. On March 26, Hubble allowed astronomers to 
  reacquire the lost remnant and continue following the behavior 
  of the fading source. The Hubble observation clearly shows that 
  the visible GRB source has two components: a point-like object 
  and an extended feature.
      This observation demonstrates Hubble's unique capability 
  for monitoring the aftermath of gamma-ray bursts, long after 
  they have faded from the view of Earth-based telescopes. And 
  there will be no shortage of targets: once a day, a gamma-ray 
  burst occurs somewhere in the universe.
      "Now we know that, at least in some cases, we can follow 
  the aftermath of GRBs for several weeks, using a coordinated 
  effort between ground-based telescopes, Hubble and other 
  spacecraft," said Kailash Sahu, leader of a team of scientists 
  at The Space Telescope Science Institute, Baltimore, MD, who 
  used Hubble to resolve the fading GRB remnant. "The fact that 
  we were able to resolve the extended feature and measure its 
  brightness separately provides us with an unprecedented 
  opportunity to solve the mystery of these enigmatic objects," 
  added team member Mario Livio.  A scientific paper on the 
  team's findings has been submitted to the journal Nature.
      A much anticipated second observation with Hubble, 
  scheduled for April 7, should help clarify the nature of the 
  extended feature and place meaningful constraints on theories 
  about the mechanism behind these extraordinary detonations. 
  Hubble also may provide an answer to the question of whether 
  GRBs originate in our Milky Way galaxy, or come from far more 
  energetic events scattered at cosmological distances across the 
  far reaches of the universe. 
      If Hubble's follow-up observations show the extended object 
  adjoining the GRB has not  faded, it is probably related to a 
  host galaxy. This would confirm the notion that GRBs are 
  cosmological in origin, far removed from Earth in space and 
  time. Any measurable fading would present the startling 
  alternative that the extended object is a cloud of gas 
  illuminated by a GRB source within our own Milky Way.
      "This opens up a whole new era in gamma-ray burst research. 
  We now know that it is possible to see the fading optical 
  emission by rapid follow-up observations with powerful 
  telescopes. With several more of these, we should be able to 
  narrow the models of what could be causing these gigantic 
  outbursts," said Gerald Fishman of the Marshall Space Flight 
  Center, Huntsville, AL, a principal investigator on NASA's 
  Compton Gamma Ray Observatory.
      Hubble's contribution to solving the GRB mystery is the 
  latest in a series of extraordinary ground- and spacecraft-
  based observations, across the electromagnetic spectrum, that 
  has carried astronomers on a fast-paced detective hunt for the 
  mechanism powering the most energetic and elusive events in the 
      "Hubble's unmatched ability to see the faintest traces of 
  the universe is helping solve one of astronomy's most 
  perplexing unsolved problems," said Robert Williams, director 
  of The Space Telescope Science Institute, who provided some of 
  his discretionary time for the observation. "This has been a 
  textbook example of the importance of coordinated telescope 
  observations," he said.
      Although more than 2,000 separate GRBs have been catalogued 
  as they randomly occur across the sky, the outbursts have 
  perplexed astronomers for more than two decades. This is 
  because the source of a GRB had never been seen until a team of 
  astronomers led by Jan van Paradijs of the University of 
  Alabama in Huntsville, and the University of Amsterdam, found a 
  diffuse object at the location of a gamma ray burst using a 
  4.2-meter telescope at La Palma Observatory in the Canary Islands. 
      The burst had been detected by the Gamma-Ray Burst Monitor 
  aboard the  Italian-Dutch BeppoSAX  satellite. 
  Within eight hours after the burst was detected, the BeppoSAX 
  spacecraft was maneuvered to point its more precise X-ray imaging 
  instruments at the location. Hubble observing time was then set aside
  to allow astronomers to take images with Hubble's Wide Field Planetary 
  Camera 2 which clearly show a point-like source, at 25.7 magnitude, 
  and the extended object.
      The raw data from the Hubble image has been posted to the 
  Internet at the following URL: 

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This file was last modified on Monday, 19-Mar-2001 17:26:25 EST