Glossary¶
- background¶
The accidental coincidence rate—how often noise fluctuations produce triggers at a given ranking statistic. Estimated from non-zero lag data where real signals are broken by time-shifting one detector.
- burst¶
A short-duration gravitational-wave signal without a precise waveform model. Sources include supernovae, gamma-ray bursts, and neutron star mergers.
- CBC-PE¶
Compact-binary-coalescence parameter estimation. In public GWTC comparisons, cWB burst reconstructions are often compared with waveform-model-based CBC parameter-estimation results.
- cc¶
Network correlation — normalized cross-correlation between detectors measuring how well data matches the expected signal model. Threshold:
netCC(default 0.5).- CED¶
Coherent Event Display — a cWB event report page with plots, reconstructed waveforms, sky information, and diagnostic views for a candidate or public event.
- chi2¶
(\(\chi^2\)) — goodness-of-fit statistic. \(\chi^2 \sim 1\) for well-modeled signals, \(\chi^2 > 1\) for glitches.
- cluster¶
A group of time-frequency pixels with excess coherent power, selected before likelihood evaluation. Multiple clusters are merged into superclusters.
- coherent¶
Appearing consistently across all detectors after accounting for time-of-flight delays. Real GW signals are coherent; instrumental noise generally is not.
- config¶
Short for
user_parameters.yaml— the single YAML file controlling all aspects of a pycWB search.- cWB¶
Coherent Wave Burst — the core algorithm that pycWB implements. Uses wavelet transforms and network coherence to detect unmodeled bursts.
- cWB-2G¶
The standard second-generation coherent WaveBurst pipeline used for many LVK burst analyses and public GWTC waveform reconstructions.
- cWB-XP¶
A separate cWB branch described in the legacy public pages. It keeps the ROOT/C++ framework but uses a WaveScan-style multi-resolution transform and a cross-power statistic rather than being part of pycWB.
- DPF¶
Dominant Polarization Frame — the optimal polarization basis for a given sky direction. Maximizes the signal projected onto the \(+\) polarization, simplifying likelihood to single-polarization detection.
- DQ¶
Data Quality — flags indicating whether detector data is suitable for science analysis. CAT0 = science mode, CAT1 = bad data (vetoed), CAT2 = marginal data (applied as veto windows).
- event¶
A candidate gravitational-wave trigger produced by the likelihood pipeline. Includes time, frequency, sky position, SNR, and ranking statistic.
- FAR¶
False Alarm Rate — expected rate of background triggers at or above a given ranking statistic. \(FAR(\rho^*) = N_{bkg}(\rho \ge \rho^*) / T_{bkg}\). Units: yr-1.
- GWTC¶
Gravitational-Wave Transient Catalog — the LVK public catalog series of gravitational-wave detections. Public cWB pages provide waveform reconstruction and CED references for selected GWTC events.
- HEALPix¶
Hierarchical Equal Area isoLatitude Pixelation — a scheme for pixelizing the sphere.
healpixparameter controls sky resolution: \(N_{pix} = 12 \times 4^{healpix}\).- hrss¶
(\(h_{rss}\)) — root-sum-squared strain amplitude of a signal. Used as the amplitude measure for burst injections and efficiency.
- hrss50 / hrss90¶
The \(h_{rss}\) at which 50% / 90% of injected signals are recovered. Standard figures of merit for search sensitivity.
- injection¶
A simulated gravitational-wave signal added to detector data to measure search sensitivity. Defined by waveform parameters and sky location.
- job¶
One unit of computation: a specific segment processed at a specific lag for a specific injection trial. Submitted to a cluster as an independent task.
- job segment¶
A GPS time window containing detector data. A search is split into many segments that can run in parallel. Controlled by
segLen,segMLS,segEdge.- lag¶
A time-shift applied to one detector’s data relative to others. Used to estimate the background: non-zero lags break real signal coincidences, producing only accidental triggers. Controlled by
lagSize,lagStep,lagOff,lagMax.- lagOff¶
Offset for the first lag index.
lagOff = 0includes the zero-lag (physical coincidence).lagOff > 0skips the first N lags.- LALInference¶
A legacy LIGO/Virgo Bayesian parameter-estimation toolkit used in older GWTC comparisons. Public cWB pages compare wavelet-based cWB reconstructions with LALInference modeled waveform reconstructions for some catalogs.
- likelihood¶
The mathematical framework that evaluates how likely a cluster of pixels is to be a real GW signal rather than noise. Produces SNR, network correlation, and sky localization.
- livetime¶
Total analyzed time used for background estimation. \(T_{bkg} = N_{jobs} \times (N_{lags} - 1) \times T_{seg}\).
- MRA¶
Multi-Resolution Analysis — using wavelet transforms at multiple frequency resolutions to capture signals of different durations.
- network¶
The set of gravitational-wave detectors used in a search. Common networks: LH (LIGO Hanford + Livingston), LHV (LIGO + Virgo).
- pixel¶
A single time-frequency cell in the wavelet transform output. Excess power pixels are selected above a threshold and grouped into clusters.
- postproduction¶
The pipeline that runs after all search jobs finish. Produces background estimates, XGBoost ranking, detection efficiency curves, and HTML reports.
- progress¶
Per-job metadata (Parquet format) tracking which jobs/lags ran, how long each took, and whether they succeeded. Used by postproduction.
- ranking statistic¶
The final score assigned to each event, combining multiple features (SNR, \(\chi^2\), correlation, etc.) via XGBoost. Used for FAR assignment and sensitivity.
- rho¶
(\(\rho\)) — coherent network SNR. \(\rho = \sqrt{E_c - N_n}\) where \(E_c\) is coherent energy and \(N_n\) is null energy.
- rho0¶
(\(\rho_0\)) — unsubtracted SNR: \(\rho_0 = \sqrt{E_c}\). Used when
xgb_rho_mode: true.- segment¶
See job segment.
- simulation¶
An injection study measuring how efficiently the search recovers signals. Requires matched injection truth tables.
- sky mask¶
A restricted sky region for the likelihood scan. Used in targeted searches (e.g., GRB follow-up). Types: UniformAllSky, Patch, Fixed, Custom.
- slag¶
Super lag — a segment-level time shift for multi-detector networks. Increases total jobs by factor of
slagSize. Controlled byslagSize,slagMin,slagMax,slagOff.- SNR¶
Signal-to-Noise Ratio — measure of signal strength relative to background noise. See rho.
- subnetwork cut¶
Per-sky-direction threshold cuts that remove pixel clusters unlikely to be astrophysical. Controlled by
subnet,subcut,subrho.- supercluster¶
A merged group of nearby pixel clusters. The superclustering step determines which pixel groups are treated as a single candidate. Controlled by
TFgap,Tgap,Fgap.- time-frequency map¶
The output of the wavelet transform: a 2D representation of signal power vs. time and frequency. Excess pixels are selected from this map.
- trial / trial_idx¶
A group of injections sharing the same noise background within a job segment.
trial_idxidentifies which trial an injection belongs to.- WDM¶
Wilson-Daubechies-Meyer wavelet — the specific wavelet family used by cWB for time-frequency decomposition.
- whitening¶
Normalizing the detector noise to have flat (white) frequency spectrum. Methods:
wavelet,mesa, ormixed.- XGBoost¶
eXtreme Gradient Boosting — the machine-learning classifier used to combine multiple event features into a single ranking statistic.
- XTalk¶
Cross-talk — coherent instrumental artifacts that mimic GW signals. pycWB includes XTalk identification and subtraction.
- zero-lag¶
The unshifted (physical) coincidence between detectors where a real GW signal would appear. Excluded from background estimation.