Preface - Important!

NOTE: This is an EXAMPLE of the data products that the LIGO Scientific Collaboration and Virgo Collaboration might release for their first gravitational wave transient detections. This particular event was not a real detection; it was a "blind injection". For more detail and background, see the GW100916 news release.

This page, and all the documents and information linked therein, are intended for release to interested scientific colleagues. We welcome your comments on what is useful to have on a page such as this. Please send your feedback to datainfo@ligo.org.

Information about GW100916

This page has been prepared by the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration to inform the broader community about an interesting event observed in the gravitational-wave detectors, and to make the data around that time available for others to analyze.

Summary of Observation

Data from the gravitational-wave detector network is analyzed in several ways. This page concerns an event identified by multiple analysis pipelines which search for gravitational wave events at all times in the available gravitational-wave data. The event time is 968654557.955 GPS == Sep 16, 2010 06:42:22.955 UTC, and thus it has been assigned the name "GW100916". At that time, the 4-km LIGO Hanford and LIGO Livingston detectors, the 3-km Virgo detector, and the GEO 600-m detector were all collecting data in "science mode" as part of the LIGO-GEO S6 and Virgo VSR3 science runs. Analysis revealed a highly significant event consistent with the coalescence (inspiral and merger) of two black holes or a black hole and a neutron star.

Analysis Results

Significance of the event

The event was found to be highly significant, with an estimated false alarm rate of less than 1 in 7000 years. For more details, please email datainfo@ligo.org.

Sky position probability maps

See skymap, zoomed skymap, and ascii file of skymap pixels. This information was sent to telescope partners by the LIGO/Virgo low-latency EM follow-up pipeline. The skymap plot is in equatorial coordinates (RA, DEC). The color represents the source location probability distribution across the sky (with a threshold). The zoom also includes the locations of nearby galaxies, indicated with black circles. The list of skymap pixels has RA and DEC in decimal degrees, and pixel size (typically 0.4x0.4 degrees); the last two columns give the probability and cumulative probability (truncated) for finding the source in that direction.
See skymap and zoomed skymap, and ascii file of skymap pixels, from full 15-parameter estimation produced by the SpinSpiral Markov chain Monte Carlo code with the SpinTaylor 3.5 PN waveform model. The skymap plot is in equatorial coordinates, with right ascension and declination in degrees. The color represents the source location probability distribution across the sky (with a threshold). The list of skymap pixels has RA in decimal hours and DEC in decimal degrees, and pixel size (typically 0.5x0.5 degrees); the last two columns give the probability and cumulative probability (truncated) for finding the source in that direction.

Parameter estimation

We performed coherent Bayesian analyses of the data using models of both spinning and non-spinning compact binary objects. Parameter estimates vary significantly depending on the exact model used for the gravitational waveform, particularly when we include spin effects. However, all models support the presence of a compact binary system in which the more massive component has a mass m₁ in the range 5.4 - 10.5 Msun, while the less massive component has a mass m₂ in the range 2.7 - 5.6 Msun.
The analysis also shows clear evidence that (at least) the more massive object has a dimensionless spin parameter S/M² above 0.67.
The accuracy with which the source location can be determined is limited by SNR, parameter degeneracies, and low relative sensitivity in the Virgo detector. We find that the source lies at a luminosity distance between 7 - 60 Mpc. The sky positions, estimated by different coherent reconstruction methods including a model-independent analysis, are mutually consistent. The three-site observation allows only a few probable source locations described by the sky map given above.
For more details, please email datainfo@ligo.org.

Documents

Normally this section would list (and provide links to) published papers and preprints about this event as they become available.

Although a paper draft was produced by the LSC and Virgo Collaboration, since this particular event is actually a "blind injection", that draft will not be published. For more details, please email datainfo@ligo.org.

More information on the analysis methods used to identify this event are here:

Gravitational-Wave Detector Data

Calibrated data from the LIGO and Virgo detectors is provided here for scientists who wish to do their own analysis. Any publication making use of such data must properly credit the LIGO Scientific Collaboration and the Virgo Collaboration. We request that anyone interested in publishing anything using these data please first consult with us at datainfo@ligo.org.
Note that proper analysis and interpretation of this data requires careful consideration of the detector noise -- which is non-white and non-stationary -- as well as the response of the detectors, which depends on the arrival direction and polarization content of the incoming gravitational wave.
Calibration uncertainties are estimated at 9.4% in magnitude and 2.5 degrees in phase for the LIGO Hanford data; 18% in magnitude, 2.8 degrees in phase and 10 us in timing for the LIGO Livingston data; and 8.5% in magnitude and 4.9 degrees in phase for the Virgo data.
Here we provide raw data on the locations and orientations of the detectors, excerpted from the file LALDetectors.h contained in the LALSuite analysis library, as well as some further notes and illustrations of the detector geometry.

Strain data h(t)

Strain time series from the LIGO Hanford, LIGO Livingston, and Virgo detectors, sampled at 16384 Hz and high-pass filtered to remove the dominant noise below 30 Hz for the LIGO detector data and 10 Hz for the Virgo data.

For 10 sec starting at GPS 968654552: Table with strain time series of all detectors
Time series for individual detectors, starting at GPS 968654552, duration 10 sec: LIGO Hanford, LIGO Livingston, Virgo.

The data provided here is in ASCII format. The format for routine and more extensive data releases is under discussion and may well differ from this.

Noise Spectrum

Plot and ASCII dump of the one-sided detector strain noise amplitude spectra around the time of the observed event: LIGO Hanford in red, LIGO Livingston in green, Virgo in magenta, and GEO 600 in gray. The vertical scale is strain per sqrt Hz. At these noise levels, an optimally located and oriented (5,5) Msun binary is expected to give a matched-filter signal-to-noise ratio (SNR) of 8 at distances of 120, 130 and 30 Mpc in LIGO Hanford, LIGO Livingston and Virgo respectively. The diagonal lines show the expected strength of binary coalescence signals observed in the LIGO Hanford (solid) and LIGO Livingston (dashed) detectors with SNRs of 15 and 10, respectively.

Plot (Figure 1 from the draft publication)
LIGO Hanford noise spectrum (ASCII data)
LIGO Livingston noise spectrum (ASCII data)
Virgo noise spectrum (ASCII data)

Audio files

With a decent pair of earbuds or headphones, the "whoop" or "chirp" that is GW100916 can be heard around 17 seconds into the recording. In the Livingston data you can also hear a short glitch (unrelated to the GW100916 signal) around 8 seconds into the recording. Each is whitened and bandpassed h(t). Caution: This can be loud if you are not careful, so start playing the file and adjust the sound level before putting on the earbuds/headphones.

Spectrograms

Spectrograms are time-frequency plots of the sort shown above. See their definitions and further plots.

About the Instruments and Collaborations

The LIGO Observatory

The Laser Interferometer Gravitational-Wave Observatory (LIGO) consists of two widely separated installations within the United States -- one in Hanford Washington and the other in Livingston, Louisiana -- operated in unison as a single observatory. LIGO is operated by the LIGO Laboratory, a consortim of the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT). Funded by the National Science Foundation, LIGO is an international resource for both physics and astrophysics.

The GEO600 Detector

The GEO600 project aims at the direct detection of gravitational waves by means of a laser interferometer of 600 m armlength located near Hannover, Germany. Besides collecting data for gravitational wave searches, the GEO600 detector has been used to develop and test advanced instrumentation for gravitational wave detection.

The LIGO Scientific Collaboration

The LIGO Scientific Collaboration (LSC) is a group of scientists seeking to make the first direct detection of gravitational waves, use them to explore the fundamental physics of gravity, and develop the emerging field of gravitational wave science as a tool of astronomical discovery. The LSC works toward this goal through research on, and development of techniques for, gravitational wave detection; and the development, commissioning and exploitation of gravitational wave detectors. The LSC carries out the science of the LIGO and GEO600 Observatories. Participation in the LSC is open to all interested scientists and engineers from educational and research institutions.

The Virgo Detector

The Virgo detector is located in the countryside near Pisa, in the Comune of Cascina. The construction of Virgo was completed in 2003. Virgo is a Michelson interferometer with two orthogonal Fabry-Perot arms of length 3 km, and a power recycling cavity. Virgo is presently being updated to give a new instrument called "Advanced Virgo" in the same infrastructure. It is planned to increase the sensitivity by one order of magnitude hopefully on the same schedule as Advanced LIGO.

The Virgo Collaboration

The Virgo detector is now operated by the Virgo Collaboration which involves groups coming from 19 European laboratories (8 Italian, 7 French, 1 of Hungary, 1 of Netherlands, 1 of Poland and an EGO (see below) team). The relevant institutions are CNRS (France), INFN (Italy), NIKHEF (The Netherlands), RMKI (Hungary), and PAN (Poland). The collaboration is organized by the Virgo Steering Committee (VSC), composed of representatives (or leaders) of all 19 groups. The collaboration is represented by the Spokesperson, elected by the VSC for three years.

The European Gravitational Observatory

The European Gravitational Observatory (EGO) is a consortium created jointly by CNRS for France and INFN for Italy in order to insure technically the operation of the Virgo detector, and to manage the funding by these two institutions. EGO is in charge of the maintenance of the detector, of a part of the R&D and will assist the construction of Advanced Virgo. Its governing body is the EGO Council, composed of members nominated by the funding institutions. The Council appoints a Director who is the representative and chief executive of EGO.

Note: This event was a "blind injection", i.e. a simulated signal inserted into the data streams of the detectors. This page is provided as an example of how a real gravitational wave event may be presented in the future.