Event Rate for Extreme Mass Ratio Burst Signals in the Laser Interferometer Space Antenna Band

Stellar mass compact objects in short-period (P ≲ 10³ s) orbits about a 10^4.5-10^7.5 M_☉ massive black hole (MBH) are thought to be a significant continuous-wave source of gravitational radiation for the ESA/NASA Laser Interferometer Space Antenna (LISA) gravitational wave detector. These extreme mass ratio inspiral sources began in long-period, nearly parabolic orbits that have multiple close encounters with the MBH. The gravitational radiation emitted during the close encounters may be detectable by LISA as a gravitational wave burst if the characteristic passage timescale is less than 10⁵ s. Scaling a static, spherical model to the size and mass of the Milky Way bulge, we estimate an event rate of ~15 yr^-1 for such burst signals, detectable by LISA with signal-to-noise ratio greater than 5, originating in our Galaxy. When extended to include Virgo Cluster galaxies, our estimate increases to a gravitational wave burst rate of ~18 yr^-1. We conclude that these extreme mass ratio burst sources may be a steady and significant source of gravitational radiation in the LISA data streams.