A new type of hierarchical search algorithm for LISA sources

The LISA observatory will be capable of detecting black hole mergers during the early inspiral phase. This is true for the intermediate mass black hole binaries (IMBHs), extreme mass ratio inspirals (EMRIs), and stellar-mass black hole binaries (SBHBs). The challenge is that the signal builds up slowly during the inspiral, and coherently matching the phase evolution for extended periods is computationally costly. We present a new type of semi-coherent hierarchical search that multiplies modified posterior distributions found from analyses using short time segments (days or weeks). A key aspect of the method is using parallel tempering (replica exchange) with temperatures below unity, which allows the search to lock onto weak signals. The method is illustrated using simulated signals from stellar origin black hole binaries.