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The recently published LIGO signal was extremely strong, this was detected using the upgraded, more sensitive version of the previous LIGO setup. Since the signal of a black hole merger is described by only a few parameters, this begs the question of why one couldn't have extracted information about the probability distribution over the parameters that describe the mergers from the noise, without necessarily being able to identify any individual events.

Count Iblis
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    There is in fact a plan for this, and I've already seen the perfect figure describing it in a talk (short answer: this is really hard, and only the next generation of sensitivity might help a little bit). Now the question is where can I find this figure and discussion in a paper. –  Feb 13 '16 at 19:11
  • @ChrisWhite that would be terrific. – Floris Feb 13 '16 at 19:12
  • Different black hole merger events will show up as signals of different amplitudes, frequencies, and phases, so I'm not sure if what you're talking about is possible. IF all black hole merger events showed up as signals of, say, the same frequency then there would obviously be bandpass filtering techniques one could apply to greatly increase the signal-to-noise and get meaningful statistical data. –  Feb 13 '16 at 21:39
  • Black hole mergers are not continuous event so it's not very useful to use statistical methods. These are definitely used, however, in detecting GWs from continuous-wave sources, such as pulsars. Is this your question? – hsnee Apr 05 '16 at 08:06
  • @hsnee What I'm getting at is that these irregular signals will contribute to the noise, making the noise to be have statistically differently compared to if that source of noise had been completely absent. Compare e.g. taking a picture of the blue sky around dusk. I cannot identify stars, but in every direction of a bright star a bit more light has been detected on average, but this swamped due to the read noise. In the direction of each star the probability distribution of the pixel gray values are slightly shifted. – Count Iblis Apr 05 '16 at 16:52
  • What can then be detected is not these individual shifts, but that spread out over the sky there are these shifts that are each individually swamped in the noise. So, one can say that one has detected the presence of stars without having detected even a single one. – Count Iblis Apr 05 '16 at 16:53
  • Your analogy actually makes me think of LIGO's all-sky searches: http://arxiv.org/abs/1202.2788 – hsnee Apr 05 '16 at 18:11
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    It's not only few parameters, but 16, which include 6x spin, 2x chirp mass, 2x symmetric mass ratios, 3x sky position, 2x binary orbital orientation, and one more which I can't remember right now.

    Marginalizing over these parameters yields much less sensitive results. Having said this, there are plans to search for sub-threshold events.

     – OTH Nov 25 '17 at 01:31

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For very small signals, the ones produced from heavier binaries, there is not enough information to do what you suggest. But, if you see the same event in 2 or more detectors you can be confident about your observation. While it is entirely possible if signal lasts for a long time. The sensitivity of the detector is not the primary concern. Its the sensitivity at low frequency. The time to merge depends on the frequency from where you start observing. If you strt at 1Hz, the time to merge is almost a full day. With signal lasting for such long duration there is no need for another detector (there is if you want to improve localization of the signal). However, pushing detectors sensitivity to 1 Hz is a far cry right now. Current detectors become insensitive to any frequency below 25 Hz.

user2555272
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