  The Laser Interferometer Space Antenna (LISA) will open a rich discovery
space in the milli-Hertz gravitational wave band. In addition to the
anticipated signals from many millions of binary systems, this band may contain
new and previously un-imagined 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 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
interferometery 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 waves 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.
