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Most distant gamma ray.

  1. Sep 22, 2008 #1


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    "This is the most amazing burst Swift has seen," said the mission's lead scientist Neil Gehrels at NASA's Goddard Space Flight Center in Greenbelt, Md. "It's coming to us from near the edge of the visible universe."

    Because light moves at finite speed, looking farther into the universe means looking back in time. GRB 080913's "lookback time" reveals that the burst occurred less than 825 million years after the universe began.

    The star that caused this "shot seen across the cosmos" died when the universe was less than one-seventh its present age. "This burst accompanies the death of a star from one of the universe's early generations," says Patricia Schady of the Mullard Space Science Laboratory at University College London, who is organizing Swift observations of the event

    So could this be a pop 111 star, could the spectrum tell us any thing?
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  3. Sep 22, 2008 #2


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    ==quote Wolram==
    http://www.sciencedaily.com/releases/2008/09/080919185809.htm ...

    Great find! Thanks for catching it.
    there's quite a mass of information just in this one Sciencedaily article that we can try to tease apart. this is the most distant GRB observed so far (not the most distant object).
    The estimated redshift is 6.7

    The earlier record for a GRB was 6.29.

    Just for comparisons, Ned Wright calculator says redshift 6.7 means
    the expansion age was 0.823 Gyr.
    the light travel time was 12.842 Gyr.
    the distance TODAY of the remnants from that event is 28.397 Gly.
    the distance THEN when the event happened was 3.6877 Gly.
    (I just quote: it doesnt round its answers off so we round to suit ourselves)

    to help look up papers about the event, here are some names
    Neil Gehrel, lead scientist for the Swift satellite
    Patricia Schady, coordinator for the GRB0809013 event
    Jochen Greiner, at the ESO, which got ground-based exposures within 3 minutes after the alert.

    The coordination of instruments is interesting. Swift satellite has a Burst Alert telescope as well as its main X-ray telescope. The main X-ray telescope had the thing targeted within 2 minutes of the smaller Burst Alert seeing it. Information was sent to ground and the ESO telescope started slewing automatically. Within 3 minutes after the alert the ESO telescope was on it.

    These high energy, short wavelength events are obviously very brief and they have to respond quickly to see them.

    Just a few years ago, my idea of a brief event was the optical flash of a supernova, but that actually takes DAYS to build up. The optical part of a supernova show is caused by the decay of a huge cloud of radioactive isotope that is puffed out into space around the exploded star. The real supernova explosion event is an X-ray flash when the explosion shockwave coming out from the core first breaks thru the surface of the star----that typically does not show up optically---the optical part comes many hours, or days, later. So what astronomers are now studying, and where the new information is about what they want to know, requires very quick reflexes to record the data---a different sense about timing.

    The Sciencedaily journalist got the expansion age at event-time right. He said the age then was less than 825 million years, and the calculator said 823 million years. As usual with journalists, he converted the light travel time into a phony distance figure. The calculator gives the real distances then and now. The travel time estimate was 12.8 billion years.

    Wolram, you ask could it be population III. We should look for something by Gehrels et al on arxiv. Or by that ESO guy, Greimer. I think the ESO took a spectrum, and they should be able to confirm any hypothetical classification. So far I only know what you told us, namely what is in the Sciencedaily piece.
    Last edited: Sep 22, 2008
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