Event Rate for Extreme Mass Ratio Burst Signals in the Lisa Band

Stellar mass compact objects in short period (P . 10 s) orbits about a 10–10M⊙ 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 10 s. Scaling a static, spherical model to the size and mass of the Milky Way bulge we estimate an event rate of ∼ 15 yr for such burst signals, detectable by LISA with signal-to-noise greater than five, originating in our galaxy. When extended to include Virgo cluster galaxies our estimate increases to a gravitational wave burst rate of ∼ 18 yr. We conclude that these extreme mass-ratio burst sources may be a steady and significant source of gravitational radiation in the LISA data streams. Subject headings: black hole physics — Galaxy: nucleus — gravitational waves — stellar dynamics