Gamma-ray Bursts

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Gamma-ray Bursts

• Presentation by Aung Sis Naing

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A little bit about gamma-rays
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How do you make gamma-rays?
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What is GRB ?

• are short-lived bursts of gamma-ray photons
• last from a few milliseconds to several minutes
• shine hundreds of times brighter than a typical
  supernova
• they are (briefly) the brightest source of
  cosmic gamma-ray photons in the observable
  universe

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History

• In the early 1960s, the United States began
  launching a series of top-secret satellites
  designed to look for gamma rays emitted by
  nuclear bomb tests (on the look out for Soviet
  nuclear testing in violation of the atmospheric
  nuclear test ban treaty).
• Late 1960s -gtdetected bursts of gamma-rays
• Several years -gt gamma-ray bursts are coming from
  space
• They publicized the discovery in 1973.

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Vela Satellites

• Launched by the US Air Force to verify the
  Nuclear Test Ban Treaty of 1963.
• Sensitive to Gamma-Rays
• No test ban violations were identified, but
  mysterious flashes of gamma-rays were detected
  outside the solar system.

The Vela 5A Satellite
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Mystery

• Origin unknown -gt Astronomers didnt know if
  these bursts originated at the edge of our solar
  system, somewhere in our Milky Way Galaxy, or
  very far away.
• Most astronomers assumed that GRBS, like X-ray
  bursts, came from explosive events associated
  with neutron stars.

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Compton Gamma-Ray Observatory

• NASA launched Compton in 1991.
• Carried an array of 8 detectors
• Could determine the direction of a gamma-ray
  burst within about 1 deg.
• Recorded about 1 per day
• Even distribution across the sky -gtruled out the
  possibility that they come from anywhere in the
  Milky Way Galaxy.

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GRB Distribution detected by BATSE
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Afterglow

• X-ray afterglow detected by an Italian satellite
  in 1997
• Visual afterglow
• Very bright

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Theoretical Explanation

• Come from unusually powerful supernovae
• An ordinary supernova that forms a neutron star
  does not release enough energy to power the
  luminosity of the brightest GRBS.
• A supernova that forms a black hole-gtmore matter
  into smaller region-gtmore energy
• Hypernova

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Suggestions

• A lot of literature related to GRB
• http//imagine.gsfc.nasa.gov/docs/science/know_l1/
  grbs.html

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GRB Clip

• http//imagine.gsfc.nasa.gov/Videos/news/GRBstar2.
  mov

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• Thank you!
• Special Thanks to Online resources and The Cosmic
  Perspective by Bennett, et al.
• Q A