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Thread: Discussion: Cosmic Rays Cause the Brightest ...

  1. #1
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    SUMMARY: When high-energy cosmic ray particles crash into the Earth's atmosphere, they produce some of the brightest radio flashes ever seen in the sky. And they had largely gone unnoticed until now. A new detector called LOPES uses prototype antennas which will eventually be built into the largest radio telescope in the world to watch the sky for these radio flashes. By studying these flashes, astronomers may gain some insights into the nature and origin of these cosmic rays.

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    I wish the story had said something about whether this equipment was giving more precise results than the optical systems like HESS, for information about direction, energy, and composition of the UHECR.

    If SKA and LOFAR can be used to passively collect this data while also doing their intended work, we could get a much better picture of the UHECR map of the sky within a few decades from now.
    Forming opinions as we speak

  3. #3
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    Well, it should have one advantage over HESS or the optical components of the Auger observatory: It is independent of daytime and should be able to observe at any weather. That means you can put the telescope at a site that is not feasible for optical astronomy (HESS is in Namibia, one of the premier astrophysics sites in the world).

    While they can obviously derive an energy spectrum, I'd like to know who good the positional accuracy is and if they can distiguish between differnt primary particles.

    I'm really looking forward to LOFAR and especially SKA!

  4. #4
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    The prototype has been running for some time: http://arxiv.org/abs/astro-ph/0409641 . Frequency range 40-80 MHz.

    I really like the notion of forming a background spectral energy distribution on the ultra-cheap, with a bigger 'sky' than other detection systems. Present positional accuracy will probably improve with more extended arrays (still cheap). Identification of primary particles will probably require supplemental equipment, unless some clever devil can work out a correlation amongst total energy, zenith angle, and waveform shape (IMHO). Given that the data are plentiful and cheap, the analysis should be forthcoming as soon as the statistical universe is large enough, and the model can be directly compared to detections by other means.

    Correlations with (say) Ice Cube detections in the next decade should help us figure out what's up in the more energetic parts of the sky! I love it. S

  5. #5
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    I wish the story had said something about whether this equipment was giving more precise results than the optical systems like HESS, for information about direction, energy, and composition of the UHECR.
    It would indeed be nice to have such information.

    Let's note, however, that HESS, CANGAROO, etc detect TeV (+/- and OOM or two) gammas; LOFAR detects anything (well, that's the implication from the report).

    My guess is that that the best from LOFAR is related to the number of antennae and the software used to analyse the signals.
    If SKA and LOFAR can be used to passively collect this data while also doing their intended work, we could get a much better picture of the UHECR map of the sky within a few decades from now.
    As only the gammas and (occasional? essentially zero??) neutrons among the 'UHECR' are uncharged, these are very likely the only ones whose direction will tell us anything useful - the many magnetic fields the UHECRs will have crossed to get to the Earth will have hopelessly scrambled any info about the direction of their origin.

  6. #6
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    Steady intragalactic point sources (of sufficient flux) and SN flashes of neutrinos should be within range of Ice Cube and Baikal detection-- Amanda synched with one GRB both in angular location and in time, but two excess detections in 60 days was statistically too small to assign any meaning to. It'll be interesting, one day soon, to observe the timing relationship between gamma bursts, neutrino bursts, UHECR's and optical afterglows linked to the same events. The neutrinos may precede the gamma burst, allowing earlier targeting of the source. S

  7. #7
    Heino Falcke Guest
    Just to very briefly answer one question raised: the radio technique has an excellent accuracy when it comes to determining positions as this is a radio interferometer which is very sensitive to directions (we keep the phase of the photons). We get sub-degree accuracy already now and this should improve linearly with separation of antennas (now ~100m, later perhaps 1km).

    This has to be compared to standard particle arrays such as Auger which at the moment delivers a few degrees but is expected to get to the degree scale in the end.

    HESS is indeed not a good comparison as this is an even lower energy scale where radio is probably not very useful.

    (Please note that I am not a regular visitor of this forum, so will likely not get around to make further comments).

  8. #8
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    Originally posted by wstevenbrown@May 20 2005, 05:38 AM
    The neutrinos may precede the gamma burst, allowing earlier targeting of the source.
    That's counter intuitive. Neutrinos have a little bit of mass. Wouldn't their slowness compared to light show up in a ten billion light-year journey?
    Forming opinions as we speak

  9. #9
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    Originally posted by antoniseb+May 20 2005, 12:50 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb @ May 20 2005, 12:50 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-wstevenbrown@May 20 2005, 05:38 AM
    The neutrinos may precede the gamma burst, allowing earlier targeting of the source.
    That&#39;s counter intuitive. Neutrinos have a little bit of mass. Wouldn&#39;t their slowness compared to light show up in a ten billion light-year journey? [/b][/quote]
    It depends on the detailed mechanism behind the burst ... while there will be a transit time delay for neutrinos (cf photons emitted at the same time), it&#39;s not at all clear yet how long it takes whatever is bursting forth from the unfortunate star that&#39;s going out with a bang - and that we see as the initial gamma pulse - to rip through the star. In &#39;normal&#39; core collapse SN, the neutrino burst is expected to preceed the &#39;light&#39; (gammas to radio) by quite some time (up to hours?) - the collapsing core becomes &#39;transparent&#39; to neutrinos &#39;long before&#39; the rebounding shock wave can make to the surface (and dump the remaining few percent of the energy of the collapse).

    I doubt that anyone can yet make a good case for a &#39;no loose ends&#39; model of long duration GRBs. :P

  10. #10
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    Originally posted by Heino Falcke@May 20 2005, 09:25 AM
    Just to very briefly answer one question raised: the radio technique has an excellent accuracy when it comes to determining positions as this is a radio interferometer which is very sensitive to directions (we keep the phase of the photons). We get sub-degree accuracy already now and this should improve linearly with separation of antennas (now ~100m, later perhaps 1km).

    This has to be compared to standard particle arrays such as Auger which at the moment delivers a few degrees but is expected to get to the degree scale in the end.

    HESS is indeed not a good comparison as this is an even lower energy scale where radio is probably not very useful.

    (Please note that I am not a regular visitor of this forum, so will likely not get around to make further comments).
    Thanks a lot Prof. Falcke for the input&#33;

  11. #11
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    Thanks, Nereid-- I should have been more explicit. You said it better than I would have. S

  12. #12
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    Afterthought: It occurred to me that the software involved must be able to distinguish the sferics caused by ordinary sorts of lightning, from the more rapidly-developing waveforms of CR&#39;s.

    In pursuing that thought, it seemed reasonable that this kind of gear would be of assistance to those who research extraordinary forms of lightning, such as sprites. I have elsewhere speculated that sprites may be precipitated by CR&#39;s and ultrahigh energy neutrinos, as the counterstrike along the ionization path caused by the CR/neutrino. Whether the connection exists or not, both sets of researchers could be of assistance to each other, at least from the standpoint of monitoring/maintenance-- and my model is falsifiable. S

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