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Gamma Ray Bursts

  1. Nov 22, 2013 #1
    I recently read the following article:
    It was not very long, and it did not contain much information. However, after a little searching I discovered the article was referring to GRB 130427A.

    The key features of this GRB are its strength at 94 GeV, and its duration at "better part of a day." Also its distance of 3.6 billion light years puts it relatively close by for a typical GRB.

    While searching for more information on this particular event I also encountered this paper:

    They were detecting gamma ray pulses in the 200 to 400 GeV range. Furthermore, these GRB had to be at least 10 solar radii from the surface of the pulsar. Granted, pulsars are neutron stars with a radius of maybe a dozen miles. So at 10 solar radii we are not talking about a large distance. Also, the Crab Nebula is only 6,500 ± 1600 light years, which is considerably closer than 3.6 billion light years.

    Is it the strength and the distance of the GRB that determines its power? In other words, if GRB 130427A were measured from a distance of 6,500 ± 1600 light years, instead of 3.6 billion light years, would the power of the GRB be significantly larger than the gamma ray pulses of 400 GeV being detected in the Crab Nebula?
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  3. Nov 22, 2013 #2


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    I'm not sure. At 3.6 billion light years the gamma rays have probably been stretched somewhat by expansion but I'm not sure how far, nor do I know whether the 94 GeV was before or after the effects of expansion.

    Also, note that the given energies are per photon, not the power output of the event.
  4. Nov 23, 2013 #3
    I guess that is what I am asking. They are saying not only was it the biggest GRB by more than a factor of three, but also incredibly long, lasting several hours. Could even the largest, most massive stars, like R136a, produce such an event?

    As you say, the energies per photon they are receiving was measuring 94 GeV. Yet we are also detecting gamma rays from the Crab Pulsar measuring 200 to 400 GeV. Granted, they are two completely different mechanisms, and the Crab Pulsar are short GRBs, only miliseconds in duration. But three times stronger than the biggest recorded GRB? You can understand my confusion.

    The only way I could figure out the discrepancy was due to distance.
  5. Nov 23, 2013 #4


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    I can definitely tell you that the total energy output from GRB 130427A was MUCH more than anything from the Crab Nebula. Had it been 6,000 light years away instead of 3.6 billion it would have been unimaginably bright.

    Note that the 200 - 400 GeV gamma rays from the Crab Nebula were not detected by the LAT aboard the Fermi Space Telescope. The "3 times greater" refers to the energy of the gamma rays detected by the LAT. One of the gamma rays it detected had an energy 3 times higher than the previous record for the LAT, not three times higher than ever detected.
  6. Nov 26, 2013 #5
    There is more information about this particular event.
    I was under the impression that all long-duration (more than two seconds) gamma-ray bursts were the result of either a hypernovae or a pair-instability supernovae. While the result of a hypernovae results in a black-hole, the result of a pair-instability supernovae leaves no black hole, or remnants of any kind.

    GRB 130427A lasted 80 seconds, with an after-glow that lasted for hours ("better part of a day"). Therefore, how can they make a definitive statement about the birth of a black hole? Why would this long-duration GRB produce a black hole and not all the other long-duration GRBs we have previously detected, making it a "watershed moment?"

    Furthermore, since GRB 130427A was one of the five closest GRBs detected (at ~3.6 billion light years distant), would they not also be able to detect the remnants of a hypernovae or a pair-instability supernovae that caused the GRB?

    One of the things that does make GRB 130427A unique is the number of instruments we had observing the event:

    • Los Alamos' RAPTOR (RAPid Telescopes for Optical Response)
    • NASA's Fermi Gamma-Ray Space Telescope
    • NASA's NuSTAR Space Telescope
    • NASA's Swift Gamma-Ray Burst Space Telescope

    tAxpDWZX-yw[/youtube] [url="http:/...ash From GRB 130427A by the RAPTOR Telescopes
  7. Nov 26, 2013 #6


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    I wish the author(a "writer" with a BSc in Molecular Biology?) had listed some references.

    The comments regarding the article are quite entertaining.

    ps. I know nothing of Cosmology, but saw a headline about GRB 130427A the other day, that made it sound like an exciting event.

    Headlines also tune me in to current events, which generally lead me to ask; "What the hell is a Raptor"?, which leads to googling, which leads to articles:

    Which gave references.....


    So then, this layman wants to know the expert's opinions on whether or not our robotic eyes witnessed the birth of a black hole back on April 27th.
    Last edited: Nov 26, 2013
  8. Nov 26, 2013 #7


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  9. Nov 27, 2013 #8
    I have read that before. Some have speculated that the Ordovician-Silurian extinction was caused by such an event. There is also evidence to suggest Earth was hit by a gamma-ray burst from within the Milky Way much more recently.

    Earth Was Hit by a Massive Gamma-Ray Burst in the Year 775
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