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Review Committee Meeting Monday 6 February 2006 09:00 PST / 12:00 EST

Minutes: Monday 6 February 2006 09:00 PST / 12:00 EST


  1. Continue the review of the GRB GWB search


We continued to go through Isabel's technical document.
  1. In response to last week's requests, Isabel has posted data conditioning sanity checks
    1. Consider spectral leakage. Certainly some of these plots show low frequency structure, e.g., Plot 9. However, it is not so clear if there is spectral leakage of low frequency content in, e.g., Plot 2.
      • The fact that 4-second DFT and 1-second DFT look similar is encouraging but not yet conclusive. It would be nice to have smoother spectra to compare to or perhaps calibrated spectra so they can be compared to official noise curves (to see if low frequency structure is correct).
      • Also, will need similar plots for H1, H2, L1, for representative S2, S3, and S4 data (nature of ASQ changes from run to run and IFO to IFO).
      • ACTION Jolien will figure out exactly what should be plotted.
    2. Consider time series continuity. Most of these plots, e.g., Plot 4 seem quite continuous. However, a couple, e.g., Plot 8 and Plot 9 show what appears to be a discontinuity on the transition boundaries.
      • ACTION Need to examine these transitions more. Perhaps there is significant fluctuations in the spectra near these transitions that is causing the whitening of one segment to be significantly different from other segments.
      • Idea: when making plots like these, it may be useful to overlay two time series that are processed similarly but on slightly shifted data so that the transitions occur at different places. Then discontinuities would be more distinct.
  2. Several issues for future analyses were raised. These include:
    1. Overwhitening: would naturally suppress lines and focus analysis to the most sensitive bands while rejecting noisy bands.
    2. Why cross-correlation? Another possibility would be to take the minimum of the two IFO's autocorrelation. Which is better? Jolien has posted his GWDAW-2000 presentation which argues that the minimum-method might be better for sufficiently non-Gaussian noise distributions [ PDF ].
    3. More time-domain filtering. Why is the band-passing done in the frequency domain?
    4. Is there a better way to do the whitening? E.g., power spectrum averaging (either time average or frequency bin average) to get a more stable spectral estimation.
  3. Calibration: are the most recent version of S4 (V04) calibration used?
    • No: at the moment V03 calibration is being used.
    • How much difference? Only seems to be a couple degrees in phase.
    • Amplitude error (15% in Livingston) is unimportant for the search algorithm but it is important for determining sensitivity.
    • Options: Either re-run analysis using V04 calibration for S4 or at least redo the simulations to re-evaluate sensitivity. (I.e., inject with V04 calibration, search with V03 calibration.)
  4. Calibration: is DARMERR or ASQ being used? A: ASQ. Should move to DARMERR in future.
  5. Calibration: are there any sign errors between H1 and H2 (note: search is insensitive to sign flips between H and L)? Almost certainly not. ACTION Need to double check with Mike Landry that the calibrations that were used for S2, S3, and S4 had correct relative sign between H1 and H2.
  6. Why was the frequency band 40 Hz to 2000 Hz used? A: 40 Hz is pretty arbitrary. 2000 Hz is the same as with the untriggered search.
  7. Why does the "whitened" spectrum look bad below 70 Hz? Not clear. (Not sure what data set the plot is from.) ACTION Isabel will investigate a bit.
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