GWTC-2 Data Release Documentation

Description

This data release is described in: GWTC-2: Compact Binary Coalescences Observed by LIGO and Virgo During the First Half of the Third Observing Run.

NOTE: O3a and O3A are used interchangeably.

Strain Data

Strain data for O3A events are available through the Event Portal, reflecting events observed by Advanced LIGO and Advanced Virgo between 1 April 2019 15:00 UTC and 1 October 2019 15:00 UTC.

These events are also included in a cumulative list of all GWTC events published to date.

Click on any event, and then select a GWF, HDF, or TXT file to download strain data.

Parameter Estimation

Values for 90% credible intervals for some parameters are displayed in the Event Portal, as described in the associated paper (See Tables IV, VI, and VIII). Credible intervals are recorded for:

  • The 1st release of posterior samples, released with the first posting to the arXiv. This is now deprecated.
  • The 2nd release, following comments from the journal referees. See "Notes and Changes" in DCC.

Parameter names are defined using standard PESummary parameter names. Note that parameter estimation results reported in this catalog may differ from results reported in previous publications. Displayed in the "Event List View" are the lowest false alarm rate and highest P_astro value taken across all search pipelines. The SNR value displayed is taken from the default PE result, or in the cases where no PE results are provided, the highest SNR from the search pipelines. Additional results can be found by clicking each event. See Event Portal Usage Notes for more details.

Updated Parameter Estimation Results

The parameter estimation results have been updated as part of the reanalysis of the O3a Science Run, see: documentation for details. Three events identified in GWTC-2 were not found by with high enough significance in the GWTC-2.1 reanalysis to be included in the GWTC-2.1 parameter estimation update, but have new search results reported in the GWTC-2.1-marginal table for GW190426_152155, and in the GWTC-2.1-auxiliary table for GW190909_114149 and GW190424_180648.

Low-Latency Alerts

Some events in the release triggered low-latency alerts, and were advertised through GCN. Any available low-latency information is linked from each event page. However, for events that did not trigger low-latency alerts, these links will yield "page not found." See the O3 Public Alerts Page for a complete list.

Data Products and Publications

Special Cases

GW190814

The H1 interferometer was out of observation mode at the time of GW190814, but was collecting strain data. A careful analysis by the detector characterization team identified useful time intervals for strain data from H1. These are included for this event.

GW190915_235702

As documented on the main event page for GW190915_235702, the Virgo frame type and channel were V1O3Repro1A and V1:Hrec_hoft_V1O3ARepro1A_16384Hz for the original strain data source. This data source had additional cleaning over that available for the standard online Virgo strain data source.

GW190924_021846

As documented on the main event page for GW190924_021846, the Virgo frame type and channel were V1O3Repro1A and V1:Hrec_hoft_V1O3ARepro1A_16384Hz for the original strain data source. This data source had additional cleaning over that available for the standard online Virgo strain data source.

GW190929_012149

As documented on the main event page for GW190929_012149, the Virgo frame type and channel were V1O3Repro1A and V1:Hrec_hoft_V1O3ARepro1A_16384Hz for the original strain data source. This data source had additional cleaning over that available for the standard online Virgo strain data source.

GW190424_180648

This event has been reanalysed as part of GWTC-2.1 and was recovered with a smaller SNR that caused it to fall out of significance. It is not among the GWTC-2.1-confident or GWTC-2.1-marginal event lists. The new search results obtained in the GWTC-2.1 reanalysis are available on the GWTC-2 main event page for GW190424_180648. (see the gstlal Search Pipeline GWTC-2.1 dark gray box). The new results were taken from the search data found in Zenodo.

GW190909_114149

This event has been reanalysed as part of GWTC-2.1 and experienced a down-ranking that caused it to fall out of significance. It is not among the GWTC-2.1-confident or GWTC-2.1-marginal event lists. The new search results obtained in the GWTC-2.1 reanalysis are updated on the GWTC-2 main event page for GW190909_114149. (see the gstlal, mbta, pycbc and pycbc_bbh Search Pipeline GWTC-2.1 dark gray box). The new results were taken from the search data found in Zenodo.

Notes on Strain Data

Data files containing calibrated strain are available for 4096 seconds centered on each event. Note that LIGO and Virgo data contain a number of instrumental artifacts, many of which are noted on the strain data notes page. Data are a calibrated strain time series sampled at 16384 Hz. Also provided is a copy of these data down-sampled to 4096 Hz. The down-sampled data were obtained using the scipy 'decimate' method. The anti-aliasing filter introduces errors up to a few percent in magnitude and a few milli-radians across the band, with larger errors close to the Nyquist frequency. Advanced LIGO and Virgo strain data are not calibrated below 10 Hz, as noted on the strain data notes page. 

from scipy.signal import decimate
data4seg = decimate(data16seg, 4, zero_phase=True)

Event Names

GWTC-2 event names are formatted as UTC date and time when the event appears in the data (GWYYMMDD_HHMMSS). Exceptions include events that have been previously published with a different name (GW190814, GW190521, GW190425, and GW190412). These events retain the names used in their discovery publications. Note that the GWTC-2 catalog paper uses additional naming conventions for brevity in some places.

Reading Files

Channel names found inside GWF files
4096 Hz Sampling Rate 16386 Hz Sampling Rate
{ifo}:GWOSC-4KHZ_R1_STRAIN {ifo}:GWOSC-16KHZ_R1_STRAIN
{ifo}:GWOSC-4KHZ_R1_DQMASK {ifo}:GWOSC-16KHZ_R1_DQMASK
{ifo}:GWOSC-4KHZ_R1_INJMASK {ifo}:GWOSC-16KHZ_R1_INJMASK

Where {ifo} = H1, L1, V1, or G1

Older releases of O3A data

Strain data for some of these events have been previously released as:

Data products for the same time period from different releases may have small differences due to different versions of calibration, data cleaning, and/or differences in how the down-sampling was applied to produce 4096 Hz files. Data quality segment information has also been updated, including times when low amplitude continuous wave injections were active.

Segments / Data Quality

Data quality categories are as defined in the event technical notes page. Continuous Wave injections (CW) are present during most events at a very low amplitude, and do not interfere with transient detection.

Data availability, data quality, and hardware injection segments are available:

  • In the data files, through bit masks with these bitmask definition. This definition is consistent across all events in this catalog.
  • Segment information for each event is available on individual event pages. Select an event from the first column on the GWTC-2 Event List page, then click on "Timeline: Query for Segments" found in the top left hand box.

Hardware Injections

In some cases, simulated signals known as hardware injections may be present in data files. Segment lists of hardware injections are available for each event.

Calibration Versions

The following channels and frame types were used from the original GWF frame files to package GWOSC public strain data. The 16 kHz strain vector exactly matches the source channels for times where DATA are available: 

For GW190915A, GW190924A, and GW190929A:
{   'H1':('H1:DCS-CALIB_STRAIN_CLEAN_C01', 'H1_HOFT_C01'), 
    'L1':('L1:DCS-CALIB_STRAIN_CLEAN_C01', 'L1_HOFT_C01'), 
    'V1':('V1:Hrec_hoft_V1O3ARepro1A_16384Hz', 'V1O3Repro1A'), 

All other events in GWTC-2:
{   'H1':('H1:DCS-CALIB_STRAIN_CLEAN_C01', 'H1_HOFT_C01'), 
    'L1':('L1:DCS-CALIB_STRAIN_CLEAN_C01', 'L1_HOFT_C01'), 
    'V1':('V1:Hrec_hoft_16384Hz', 'V1Online),

The DOI for this page is https://doi.org/10.7935/99gf-ax93

Release Notes

  • Added notes about 2nd PE release: March 9, 2021
  • First release: October 28, 2020
  • Added brief documentation of reanalysis of PE results by GWTC-2.1: January 19, 2022
  • Updated SNR, FAR and P_astro selections in Event List View: August 16, 2022