Development and Application of the Spherical Harmonic Veto Definer for Gravitational-Wave Transient Search

The rapid analysis of gravitational-wave data is not trivial for many reasons, such as the non-Gaussian non-stationary nature of LIGO detector noise and the lack of exhaustive waveform models. Non-Gaussian non-stationary noise and instrumental artifacts are known as ’glitches’.
X-Pipeline Spherical Radiometer (X-SphRad) is a software package designed for performing autonomous searches for un-modelled gravitational- wave bursts. X-SphRad has an approach based on spherical radiometry, that transforms time-series data streams into the spherical harmonic domain. Spherical harmonic coefficients show potential in discriminating glitches from signals.
For my Ph.D. thesis, I evaluated and implemented a tool for glitch rejection called Spherical Harmonic Veto Definer (SHaVeD). SHaVeD is a Matlab script that loads spherical harmonic coefficients computed by X-SphRad, and performs statistics that computes a threshold to apply. The threshold is used to identify every glitch’s GPS time and create a cut of one second around it. SHaVeD saves this information in a two-column file where the first column is the GPS starting time of the cut and the second is the final time. X-SphRad can include SHaVeD as a data quality to veto glitches.
The tool is tested with X-SphRad and the coherent WaveBurst (cWB) pipeline over the O2 observation run. Results have shown how the inclusion of SHaVeD in the analysis could allow a lowering of some thresholds used in this type of research. Tests show how SHaVeD has reduced the amplitude of the loudest false event by a factor of 3, meaning that it rejected false events in a volume 9 times greater than usual.