Detecting gravitational wave bursts with LISA in the presence of instrumental glitches

The Laser Interferometer Space Antenna (LISA) will open a rich discovery space in the millihertz gravitational wave band. In addition to the anticipated signals from many millions of binary systems, this band may contain new and previously unimagined sources for which we currently have no models. To detect unmodeled and unexpected signals we need to be able to separate them from instrumental noise artifacts, or glitches. Glitches are a regular feature in the data from ground-based laser interferometers, and they were also seen in data from the LISA Pathfinder mission. In contrast to the situation on the ground, we will not have the luxury of having multiple independent detectors to help separate unmodeled signals from glitches, and new techniques have to be developed. Here we show that unmodeled gravitational wave bursts can be detected with LISA by leveraging the different way in which instrument glitches and gravitational wave bursts imprint themselves in the time-delay interferometry data channels. We show that for signals with periods longer than the light travel time between the spacecraft, the breathing mode or Sagnac data combination is key to detection. Conversely, for short-period signals it is the time of arrival at each spacecraft that aids separation. We investigate the conditions under which we can distinguish the origin of signals and glitches consisting of a single sine-Gaussian wavelet and determine how well we can characterize the signal. We find that gravitational wave bursts can be unambiguously detected and characterized with just a single data channel (four functioning laser links), though the signal separation and parameter estimation improve significantly when all six laser links are operational.