cWB-space: A time-frequency unmodelled transient-search pipeline for LISA

Abstract

The Laser Interferometer Space Antenna (LISA) will observe massive-black-hole mergers and other transient phenomena alongside many long-lived gravitational-wave signals. Some transients may be incompletely modeled or have waveforms that have not been anticipated. We present \texttt{cWB-space}, a pipeline that combines an unmodeled transient search, waveform reconstruction, and a time-frequency glitch classifier. The search identifies concentrations of signal power in time and frequency and reconstructs candidate waveforms without requiring a source template. The glitch classifier compares how candidates appear in different combinations of LISA's laser measurements, with the background estimated from the observed data. We test the pipeline with simulated black-hole binaries with aligned and precessing spins, burst signals with different shapes, and instrumental glitches. The response comparisons help assess a candidate's astrophysical or instrumental origin, while also revealing correlated glitches that can resemble gravitational waves. In the Sangria simulated LISA data, the search recovers all six injected massive-black-hole binaries as its six highest-ranked candidates. Their local reconstructions recover the main features of the injected waveforms over the intervals studied. These results demonstrate how an unmodeled search can connect transient identification with investigation of a candidate's origin and waveform recovery.