GWTC-4.1 Data Release Documentation

Description

This data release is described in: GWTC-5.0: Updating the Gravitational-Wave Transient Catalog with Observations from the Second Part of the Fourth LIGO-Virgo-KAGRA Observing Run. GWTC-4.1 is an update based on the latest search results to the GWTC-4.0 gravitational-wave catalog describing the gravitational-wave transients found in observing run O4a satisfying:

  • P_astro > 0.5 (more likely to be of astrophysical origin than terrestrial origin),
  • have parameter estimation (PE) results triggered by having a FAR < 1 per year.

This page provides documentation for the probable events found in O4a after a new analysis of the data. Comparable information for earlier releases, including GWTC-4.0, may be found by following the link for all previous GWOSC releases where the latest information for observing runs O1, O2, O3a, O3b and O4a may be found.

Strain and data quality are provided for GWTC-4.1 events with search results described in Table 6 of GWTC-5.0: Appendix A. The parameter estimation values and associated credible intervals are provided for events described in Table 7 of GWTC-5.0: Appendix A.

Reported in the Event List Table for the GWTC-4.1 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.

Strain Data

Strain data for GWTC-4.1 events are available through the Event Portal. These events are also included in a cumulative list of all confident 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% credible intervals for some parameters are displayed in the Event Portal. The samples for each event used to produce these values for each event in GWTC-4.1 are available in Zenodo.

Parameter names are defined using standard PESummary parameter names.

This data release contains new parameter estimation posterior samples for O4a candidates associated with a re-analysis of the data.

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 O4 Public Alerts Page for a complete list.

Data Products and Publications

Notes on Strain Data

Data files containing calibrated strain are available for 4096 seconds for each event. Note that LIGO and Virgo data contain a number of instrumental artifacts, many of which are mentioned on the strain data notes page.

Calibrated strain time series are 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-4.1 event names are formatted as UTC date and time when the event appears in the data (GWYYMMDD_HHMMSS). The GW prefix is omitted when there is an identified plausible instrumental origin.

Reading Files

Channel names found inside GWF files
4096 Hz Sampling Rate 16384 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

Other releases of GWTC-4.1 strain data and results

  • Data for the events GW230529_181500 and GW231123_135430, were previously released in the O4 Discovery Papers.
  • The GWTC-4.1 catalog was previously released as GWTC-4.0 and available on GWOSC at GWTC-4.0.

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 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 definitions. The bitmask definitions are 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 either the GWTC-4.1 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: 

All events in GWTC-4.1:
{   'H1':('H1:H1_HOFT_C00_AR', 'GDS-CALIB_STRAIN_CLEAN_AR'), 
    'L1':('L1:L1_HOFT_C00_AR', 'GDS-CALIB_STRAIN_CLEAN_AR'),

The DOI for this page is https://doi.org/10.7935/6xqf-ba54

Release Notes

  • Initial Draft: April 3rd, 2026