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Offline DoctorBeaver

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Sunglasses wouldn't help with these
« on: 08/02/2008 17:16:55 »
from http://imagine.gsfc.nasa.gov/docs/science/know_l1/bursts.html

Gamma-ray bursts are 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 supernovae, the explosions marking the deaths of especially massive stars.

Lasting anywhere from a few milliseconds to several minutes, gamma-ray bursts (GRBs) 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.

Until recently, GRBs were arguably the biggest mystery in high-energy astronomy. They 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. 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. (That is, they didn't know how far away GRBs were to within a factor of a few billion light years!) But now a slew of satellite observations, follow-up ground-based observations, and theoretical work have allowed astronomers to link GRBs to supernovae in distant galaxies.


I don't think I'd like to be around if 1 of these happened near us. There wouldn't be a lot left on our poor, wee planet.


 

Offline JimBob

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« Reply #1 on: 09/02/2008 00:17:47 »
Actually, wouldn't there be part of one side of the earth left in tact, that area directly opposite the event?
 

Offline JP

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« Reply #2 on: 09/02/2008 00:23:22 »
There's a nice summary of what might happen if the Earth got hit by one of these here: http://www.exitmundi.nl/Gamma.htm

It's humbling to think that for all we humans have accomplished on Earth, there are phenomena like this out there that could wipe us out in seconds.
 

Offline DoctorBeaver

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« Reply #3 on: 09/02/2008 08:11:17 »
Actually, wouldn't there be part of one side of the earth left in tact, that area directly opposite the event?

Nope...

(from http://www.exitmundi.nl/Gamma.htm)
And you won't be safe on the other side of the planet.  A massive shockwave, much like the aftershock of a nuclear explosion, will sweep across the globe. A wall of fire will roast every living thing on Earth -- well, except a few fish, that is. The Gamma Ray Burst will reset evolution.
 

Offline lightarrow

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« Reply #4 on: 09/02/2008 15:59:15 »
Until recently, GRBs were arguably the biggest mystery in high-energy astronomy. They 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.

I wonder how can a satellite's detector aimed at the earth detect something coming from outer space.  ???
 

Offline DoctorBeaver

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« Reply #5 on: 09/02/2008 16:18:10 »
Until recently, GRBs were arguably the biggest mystery in high-energy astronomy. They 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.

I wonder how can a satellite's detector aimed at the earth detect something coming from outer space.  ???

 

another_someone

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« Reply #6 on: 09/02/2008 16:37:15 »
Until recently, GRBs were arguably the biggest mystery in high-energy astronomy. They 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.

I wonder how can a satellite's detector aimed at the earth detect something coming from outer space.  ???

Gamma rays are not easy to focus, so possibly the detectors are fairly omnidirectional, and multiple satellites to were used to refine their readings.

Again, was it actually looking for gamma rays, or Čerenkov radiation created in the atmosphere as the gamma rays hit it?
 

Offline DoctorBeaver

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« Reply #7 on: 09/02/2008 16:39:51 »
They could have come in from the side.
 

Offline JimBob

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lyner

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« Reply #9 on: 09/02/2008 19:26:20 »
Quote
Čerenkov radiation created in the atmosphere as the gamma rays hit it?
I think Cherenkov radiation is what is produced when a very fast particle hits a medium in which the velocity of light is  less than its speed i.e it signifies the presence of fast particles, not gamma rays.
 

another_someone

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« Reply #10 on: 09/02/2008 21:49:13 »
Quote
Čerenkov radiation created in the atmosphere as the gamma rays hit it?
I think Cherenkov radiation is what is produced when a very fast particle hits a medium in which the velocity of light is  less than its speed i.e it signifies the presence of fast particles, not gamma rays.

http://en.wikipedia.org/wiki/%C4%8Cerenkov_radiation#Astrophysics_experiments
Quote
When a high-energy cosmic ray interacts with the Earth's atmosphere, it may produce an electron-positron pair with enormous velocities. The Čerenkov radiation from these charged particles is used to determine the source and intensity of the cosmic ray, which is used for example in the Imaging Atmospheric Čerenkov Technique (IACT), by experiments such as VERITAS, H.E.S.S., and MAGIC. Similar methods are used in very large neutrino detectors, such as the Super-Kamiokande, the Sudbury Neutrino Observatory (SNO) and IceCube.

Čerenkov radiation can also be used to determine properties of high-energy astronomical objects that emit gamma rays, such as supernova remnants and blazars. This is done by projects such as STACEE, a gamma ray detector in New Mexico.

This does not explicitly say that it detect gamma ray, or whether it is looking at particles associated with gamma emitters, but not the gamma itself.  I am assuming (but maybe erroneously) that it is detecting gamma rays that are creating charged particles that hit the atmosphere, and these charged particles create Čerenkov radiation in the visible spectrum.
 

lyner

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« Reply #11 on: 09/02/2008 23:30:46 »
Quote
I am assuming (but maybe erroneously) that it is detecting gamma rays that are creating charged particles that hit the atmosphere, and these charged particles create Čerenkov radiation in the visible spectrum.
A sort of 'indirect' method? Could be.

btw  They do make X ray telescopes based on very oblique reflections from multiple layers of steel(?) paraboloids. They  might be suitable for detecting lower energy gamma radiation ; dunno the energy of the stuff in question, though (there is a fair 'overlap' in the frequency ranges of what is called X ray and what is called gamma). The advantage is that, with such a short wavelength, a moderately small aperture telescope can have quite good resolving power.
X ray astronomy produces some fine structured pictures of sources under study, I believe.
http://swift.sonoma.edu/about_swift/instruments/xrt.html
 

Offline DoctorBeaver

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« Reply #12 on: 10/02/2008 08:37:55 »
The technical pages of the MAGIC project give a lot of detail http://wwwmagic.mppmu.mpg.de/introduction/techdetails.html
http://wwwmagic.mppmu.mpg.de/introduction/factsheet/

In brief:-

satellite gamma ray detectors - 10GeV
Earth-based Cherenkov telescopes - 100GeV
MAGIC - 50-70GeV


« Last Edit: 10/02/2008 08:40:19 by DoctorBeaver »
 

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