4
$\begingroup$

I download LIGO data on GW150914 (gravitational waves) via the code in Mathematica

H1url = "https://losc.ligo.org/s/events/GW150914/H-H1_LOSC_4_V1-\
1126259446-32.hdf5";
strainH1 = Import[H1url, {"Datasets", "/strain/Strain"}];
attrsH1 = Import[H1url, {"Attributes", "/strain/Strain"}]

To my understanding, the data are those of 4096 seconds with a sample rate of 4 kHz. I plot the full data range to get Figure 1. Fig. 1. Ligo data, time in seconds on horizontal axis. Vertical axis shows strain

I zoom in on a portion of the plot. The result is shown in Fig. 2 same as Fig. 1 but zoomed in around 1900 secs

My first question is, what causes that sinusoidal pattern of period $T\approx 20 ~\text{s}$? Same as Fig. 2 but zoomed in even more

$\endgroup$
  • 1
    $\begingroup$ I suspect you'll have to ask someone at LIGO. If this is not a gravitational wave detection, it could be a host of other things that really nobody outside of LIGO would be able to know. $\endgroup$ – enumaris Mar 24 '18 at 2:17
3
$\begingroup$

Have a look at the LIGO data analysis tutorial, and in particular at this page.

There isn't really a 20Hz signal. It appears because the noise rises rapidly with decreasing frequency below 100Hz and the data you've downloaded is filtered below 20Hz. This causes the noise to peak at 20Hz, but really it's a continuous spectrum.

$\endgroup$
  • $\begingroup$ Yes, I see now that they comment on those 20 cycles explicitly :-) That probably explains it. $\endgroup$ – Your Majesty Mar 24 '18 at 14:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.