Gravitational Wave Open Science Center

GWTC-2.1 Data Release Documentation


Description

This data release is described in: GWTC-2.1: Deep Extended Catalog of Compact Binary Coalescences Observered by LIGO and VIRGO in the First Half of the Third Observing Run. GWTC-2.1 is a cumulative catalog describing all the gravitational-wave transients found in observing runs O1, O2 and O3a. This page provides documentation for the confident and marginal events found in a reanalysis of O3a using newer calibration of the strain data, and newer codes for searches and parameter estimations. Comparable information for earlier event releases may be found by following the links for GWTC-1 and GWTC-2 (where the latest information for O1, O2, and O3a may be found).

Here we provide newly calibrated strain and data quality for the 44 confident events from O3a with a probability of astrophysical origin (P_astro) greater than 0.5 in GWTC-2.1-confident, as well as 2 marginal candidates with a P_astro less than 0.5 that meet the previous GWTC-2 FAR ceiling of 2 per year in GWTC-2-marginal. FAR, SNR and P_astro search results are provided for all of the confident events and marginal candidates.

There are 8 new confident events reported in GWTC-2.1-confident that were not identified in the original GWTC-2 publication. These 8 new confident events include associated parameter estimation values found in Table V of the catalog paper.

In addition, the catalog paper identifies 1201 subthreshold candidates with a FAR less than 2 per day in any search pipeline. Data products associated with these subthreshold candidates are listed in the Data Products and Publications section below and directly at this Zenodo link.

Displayed in the "Event List Views" for both the GWTC-2.1-confident and GWTC-2.1-marginal 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 updated (May 10th, 2022) version of the catalog paper recomputes the parameters associated with each confident candidate from all previous catalog papers (GWTC-1-confident and GWTC-2) with the exception of GW170817 (see catalog paper for details).

The updated values for GWTC-1-confident appear under each event within the event's gray box with heading "GWTC-2.1 PE for GWyymmdd (update)", where the "GWTC-2.1" distinguishes the results from the original GWTC-1-confident results that used the same strain data. These new values are the result of updated analysis methods.

The updated values for GWTC-2 are found among the events listed in the GWTC-2.1-confident catalog, again within each individual event's gray box with heading "GWTC-2.1 PE for GWyymmdd (update)", where the "(update)" is to distinguish the result as being an update to the original results found in the GWTC-2 catalog. They are located under the GWTC-2.1-confident catalog and not under the GWTC-2 catalog as these updates used newer strain data calibration and newer analysis methods.

Also, the eight new events reported in GWTC-2.1-confident have also been updated and appear within the gray box with heading "GWTC-2.1 PE for GWyymmdd (update)", with the original results first appearing in the arXiv.org version of the catalog paper.

The updated parameter estimation results for the following four events included Virgo strain data that was previously excluded. The associated strain data and data quality information for these events is available in through the O3a Data Release.
Skymaps for event are available in the PE section where the link to skymaps for all events in a compressed tarfile on the Zenodo data products webpage is found. The individual skymap for each event can be found as separate FITS files within the compressed tarfile.

Strain Data

New calibration strain data for Confident O3A events and Marginal O3A events are available through the Event Portal, and cover the Advanced LIGO and Advanced Virgo O3a observing run 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

Parameter estimation values with 90% confidence intervals for some parameters are displayed in the Event Portal. The samples used to produce these values for each event in GWTC-2.1-confident are available in Zenodo.

Parameter names are defined using standard PE Summary parameter names. Note that parameter estimation results reported in this catalog may differ from results reported in previous publications.

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


These Zenodo links reference the latest version (Concept DOI) of the data set listed. All previous versions of the dataset are listed on the Zenodo page.

Parameter estimation values provided in this link are associated with the most recent (Version 2) sample release. The original Zenodo (Version 1) samples can be found directly at 10.5281/zenodo.5117703

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 after 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 after 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 after the standard online Virgo strain data source.

GW190424_180648

This event, previously found in the GWTC-2 event list, was recovered with a smaller SNR in the GWTC-2.1 reanalysis of O3a. 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, previously found in the GWTC-2 event list, experienced a down-ranking that caused it to fall out of significance in the GWTC-2.1 reanalysis of O3a. 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 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.
from scipy.signal import decimate
data4seg = decimate(data16seg, 4, zero_phase=True)

Advanced LIGO and Virgo strain data are not calibrated below 10 Hz, as noted on the strain data notes page.

Event Names

GWTC-2.1 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 (i.e., GW190814, GW190521, i GW190425, and GW190412). These events retain the names used in their discovery publications. Note that the GWTC-2.1 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, or V1



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 either the GWTC-2.1-confident Event List or the GWTC-2.1-confident 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 O3 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 events 'GW190915_235702, GW190916_200658, GW190917_114630, GW190924_021846, GW190925_232845, GW190926_050336, GW190929_012149 and 'GW190930_133541'
{   'H1':('H1:DCS-CALIB_STRAIN_CLEAN_SUB60HZ_C01', 'H1_HOFT_CLEAN_SUB60HZ_C01'), 
    'L1':('L1:DCS-CALIB_STRAIN_CLEAN_SUB60HZ_C01', 'L1_HOFT_CLEAN_SUB60HZ_C01'), 
    'V1':('V1:Hrec_hoft_V1O3ARepro1A_16384Hz', 'V1O3Repro1A'), 

All other events in GWTC-2.1:
{   'H1':('H1:DCS-CALIB_STRAIN_CLEAN_SUB60HZ_C01', 'H1_HOFT_CLEAN_SUB60HZ_C01'), 
    'L1':('L1:DCS-CALIB_STRAIN_CLEAN_SUB60HZ_C01', 'L1_HOFT_CLEAN_SUB60HZ_C01'), 
    'V1':('V1:Hrec_hoft_16384Hz', 'V1Online), 



The DOI for this page is https://doi.org/10.7935/qf3a-3z67



Release Notes

  • First release: Nov 5, 2021
  • Documentation updated PE results found in updated version of GWTC-2.1 catalog paper: Jan 27, 2022
  • Edited to fix typos and make default Zenodo links point to version 2 results: Aug 4, 2022
  • Updated SNR, FAR and P_astro selections in Event List View: August 16, 2022