Gamma Ray Bursts (GRB)

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Gamma Ray Bursts (GRB)
Compton Gamma Ray Observatory (CGRO)
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Gamma Ray Bursts (GRB)
Gamma Rays the highest energy photons in the
electromagnetic spectrum
Gamma-ray bursts - short-lived bursts of gamma
ray photons, the most energetic form of light. At
least some of them are associated with a special
type of supernova, the explosions marking the
deaths of especially massive stars.
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Gamma Ray Bursts (GRB)
Lasting anywhere from a few milliseconds to
several minutes, gamma-ray bursts shine hundreds
of times brighter than a typical supernova and
about a million trillion times as bright as the
Sun, making them briefly the brightest source of
cosmic gamma-ray photons in the observable
universe. GRBs are detected roughly once per day
from wholly random directions of the sky.
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Gamma Ray Bursts (GRB)
No two gamma-ray bursts are the same, as can be
seen from this sample of light curves.
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Gamma Ray Bursts (GRB) An Interesting Start
Gamma Ray bursts were discovered serendipitously
in the late 1960s by U.S. military satellites
which were on the look out for Soviet nuclear
testing in violation of the atmospheric nuclear
test ban treaty. These satellites carried gamma
ray detectors since a nuclear explosion produces
gamma rays.
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Gamma Ray Bursts (GRB)
As recently as the early 1990s, astronomers
didn't even know if GRBs originated at the edge
of our solar system, in our Milky Way Galaxy or
incredibly far away near the edge of the
observable Universe.
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Gamma Ray Bursts (GRB)
Once discovered, GRBs were observed to be
distributed uniformly over the sky. If they
occurred within the galaxy, they should primarily
occur in the Milky Way disk (where most of the
stars in our galaxy are found). Either GRBs
occurred outside of the galaxy or there is a
halo around the Milky Way.
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Gamma Ray Bursts (GRB)
If the GRBs were far away, they would have large
Doppler shifts. However, with a Gamma Ray
wavelength of on the order of 10-15, shifts are
too small to measure Then
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Gamma Ray Bursts (GRB)
In 1997 the Dutch-Italian gamma-ray satellite
Bepposax monitored a gamma-ray burst. Soon after,
scientists could look with the Keck-telescope at
the found spot. And thus the first spectrum of a
fast-fading optical counterpart was obtained.
The redshift of this spectrum places the
gamma-ray burst at a distance of a few
Gigaparsecs. This is in galaxies far, far away.

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Gamma Ray Bursts (GRB)
The first optical images, taken with the
Herschel-telescope, of the gamma-ray burst that
was discovered at february 28 of 1997. At the top
picture one can see the gamma-ray burst. At the
bottom picture, taken eight days later, one can
see the burst is fading away. (Gamma-ray bursts
G.J.Fishman D.H.Hartmann Scientific American
March 1998)
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Gamma Ray Bursts (GRB)
Long or Short Duration? Gamma Ray Bursts are
separated into two classes long-duration bursts
and short-duration bursts. Long duration bursts
Gamma Ray Bursts that last more than 2
seconds. Short-duration bursts Gamma Ray Bursts
that last less than 2 seconds. Short duration
bursts range from a few milliseconds to 2 seconds
with an average duration time of about 0.3
seconds (300 milliseconds). The long-duration
bursts last anywhere from 2 seconds to a few
hundreds of seconds (several minutes) with an
average duration time of about 30
seconds. Astronomers think that long and short
duration GRBs are created by fundamentally
different physical properties. And whereas they
now are fairly confident of what drives the long
GRBs, there are only theories when it comes to
what drives short-duration bursts.
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Gamma Ray Bursts (GRB)
Model for Long Duration Bursts Collapsar Model
The core of a massive star rapidly collapses into
a black hole. In doing so, a shock wave is
created in the same way as in a supernova, but
the amount of gravitational energy is very large
near the event horizon. An especially violent
supernova occurs, shedding high energy photons
(gamma rays). Hypernova the especially violent
supernova associated with gamma bursts.
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Gamma Ray Bursts (GRB)
Model for Short Duration Bursts Binary Neutron
Star Model Gamma bursts created by the
collision and coalescence of two neutron stars.
Energy in the form of gamma rays is created for
relatively short time periods in the collision
process.
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Gamma Ray Bursts (GRB) Swift GRB Mission
Latest NASA mission launched in November 2004.
It is studying GRBs with more sensitivity than
other instruments.
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Gamma Ray Bursts Sprites Curious (non
astronomical gamma rays)
Sprites are created during lightning storms on
earth. The are vertical ejections from the
atmosphere, and have been detected by satellites.
Sprites are generators or gamma rays
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Gamma Ray Bursts (GRB)
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Gamma Ray Bursts (GRB)