Time-Delay Interferometry (TDI) is the data processing technique needed for
generating interferometric combinations of data measured by the multiple
Doppler readouts available onboard the three LISA spacecraft. Within the space
of all possible interferometric combinations TDI can generate, we have derived
a specific combination that has zero-response to the gravitational wave signal,
and called it the {\it Zero-Signal Solution} (ZSS). This is a two-parameter
family of linear combinations of the generators of the TDI space, and its
response to a gravitational wave becomes null when these two parameters
coincide with the values of the angles of the source location in the sky.
Remarkably, the ZSS does not rely on any assumptions about the gravitational
waveform, and in fact it works for waveforms of any kind. Our approach is
analogous to the data analysis method introduced by G\"ursel & Tinto in the
context of networks of Earth-based, wide-band, interferometric gravitational
wave detectors observing in coincidence a gravitational wave burst. The ZSS
should be regarded as an application of the G\"ursel & Tinto method to the LISA
data.Comment: 29 pages, 17 Figure
