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Confusion Noise from LISA’s Capture Sources

Confusion Noise from LISA’s Capture Sources. Leor Barack (Southampton) Curt Cutler (AEI). LISA’s “Capture” sources. LISA should detect 100s-1000s Captures, mainly ~10 M  black holes, out to cosmological distances (Gair et al ., 2004). Confusion from unresolvable Captures.

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Confusion Noise from LISA’s Capture Sources

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  1. Confusion Noise from LISA’s Capture Sources Leor Barack (Southampton) Curt Cutler (AEI)

  2. LISA’s “Capture” sources • LISA should detect 100s-1000s Captures, mainly ~10 M black holes, out to cosmological distances (Gair et al., 2004)

  3. Confusion from unresolvable Captures Many Captures will not be individually resolvable: • Too far away • Unfavourable orbital orientation • Too many years to go before plunge when LISA observes • Sources to plunge in LISA band hundreds of years from now are already “in band” today, through weak high-harmonic radiation

  4. (for each of A=WDs, NSs, BHs ) Energy output from a single (“inclination averaged”) capture 0.05 < a < 0.07 depending on spin Spectral energy density for a single “eccentricity averaged” capture From analytic model (quadropole emission + post-Newtonian evolution) Space density of MBHs Capture rate per galaxy With flat space/no evolution model agrees to within 15% with a variety of cosmological/evolutionary models  (1 mHz  f  20 mHz) Noise spectral density from all Captures • Lump captured objects as 0.6 M WDs, 1.4 M NSs , 10 M BHs • Assume GWs from each class constitute an isotropic stochastic background:

  5. From Captures of 0.6 M WDs From Captures of 10 M BHs Confusion background from Captures(before subtraction of resolvable sources)

  6. Relative contribution to confusion energy from sources within detection distance, as function of “time to plunge”, t Relative contribution to confusion energy from detectable sources Approximate waveform model WD: ~ 97% NS: ~ 94% BH: ~ 30-100% • Estimate of irreducible confusion noise: Subtraction problem • “Chicken-and-egg” problem: To determine which sources are detectable need noise level; To determine noise level need to know which sources are detectable and hence subtractable • Ignoring this (can do for WDs, NSs), may roughly estimate subtractable portion for each WD, NS, BH, using

  7. From Captures of 0.6 M WDs From Captures of 10 M BHs Total LISA Noise, inc. Capture Confusion (after subtraction of resolvable sources)

  8. Sinst dominates Sconf dominates Detection rate, D Actual rate for BH Captures are near here Event rate density, R We seem to be lucky…

  9. References • Long paper: L. Barack and C. Cutler, PRD 2004 (gr-qc/0409010) • Summary in • L. Barack and C. Cutler, Proceedings of the 5th LISA symposium

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