Gravitational Wave Open Science Center

Notes on the Binary Black Hole Events Tutorial

The Binary Black Hole Events tutorial may be found on the tutorials page.

Technical notes

This tutorial is intended for educational purposes. Results obtained here may not precisely match results in published papers. For analysis software packages, see the software page.

This tutorial has only been tested with the first four published gravitational wave discoveries (GW150914, LVT151012, GW151226, and GW170104), all of which are short-duration BBH events. Other types of events may require some edits to produce comparable results.

The templates used in this tutorial are generated using the model SEOBNRv2, using the median parameters as described in the paper Binary Black Hole Mergers in the first Advanced LIGO Observing Run. These templates are NOT best-fit waveforms, which would instead be obtained by selecting a maximum likelihood waveform. The choice to use median parameter waveforms allows a demonstration of how the 1-D marginalized parameters reported in published results correspond to the data, but they are not an optimal choice for SNR calculation or to seek "residual" signal.

In this tutorial, we make use of only one template, with a simple ASD estimate. The full parameter estimation analysis instead produces a Bayesian posterior result using many nearby templates. It does a more careful job estimating the ASD, and includes effects of uncertain calibration. As a result, results in the tutorial (SNR, masses, spins, D_eff) are somewhat different from what you will see in published papers.

The tutorial computes an "effective distance" D_eff. Is is NOT an estimate of the actual (luminosity) distance, which depends also on the source location and orbit orientation.

These distances are at non-zero redshift, so cosmological effects must be taken into account (neglected here). Since we estimate the BH masses using the phase evolution of the waveform, which has been redshifted, our masses are themselves "redshifted". The true source masses must be corrected for this effect; they are smaller by a factor (1+z).

Notes on updates

Sept 11, 2017
version 1.63
Changes:
- Edits to note regarding BNS range uses SNR 8 as nominal threshold

Sept 6, 2017
version 1.62
Changes:
- Changed note at top to explicitly say the "software" page has
packages used for LSC and Virgo Collaboration results papers

Aug 25, 2017
version 1.61
Changes:
-Added output for CSV files
-Point at json file v3 instead of v2


Aug 10, 2017
version 1.60
Changes:

- The json file (BBH_events_v2.json) contains the name of the V1
data files, which include an incorrect phase shift.  I will correct this
for GW150914, LVT151012, and GW151226

- Updated warning at top to say:
This tutorial is intended for educational purposes. Results obtained here
may not precisely match results in published papers. For analysis
software packages, see https://gw-openscience.org/software/

- Added audio players for the whitened template, whitened data, freq. shifted template, and freq. shifted data.

- Fixed outdated link at top of tutorial to GW150914 tutorial.

- Fixed problem of using same PSD to whiten both projections of template
 - phase shift and roll, and then whiten, as Ian suggested
 - Removed print statements from whiten function

- SNR and range have changed by about 1%.  Most liklely due to move to
C02 of calibration

- Adjusted normalization of whitened data to account for effect of
band-passing.