Fast detection and reconstruction of merging Massive Black Hole Binary signals

The Laser Interferometer Space Antenna (LISA) will detect gravitational waves from the population of merging massive black holes binaries (MBHBs) throughout the Universe. The LISA data stream will feature many superposed signals from different astrophysical sources, requiring a global fit procedure. Most of the MBHB signals will be loud enough to be detected days or even weeks before the merger; and for those sources LISA will be able to predict the time of the merger well in advance of the coalescence, as well as an approximate position in the sky. In this paper, we present a fast detection and signal reconstruction scheme for massive black hole binaries in the LISA observation band. We propose: (i) a detection scheme for MBHB mergers allowing a first subtraction of these signals for the purpose of a global fit, and (ii) an efficient early detection scheme providing a time-of-merger estimate for a pre-merger signal, that will allow to trigger a protection period, placing LISA in ``do not disturb'' mode and enabling more detailed analysis that will facilitate multi-messenger observations. We highlight the effect of confusion of several overlapping in time MBHB signals in the pre-merger detection.