Optimizing LISA for cost and science

1. Optimizing LISA for cost and science Sean T. McWilliams stmcwill@princeton.edu Princeton University LISA 9 Symposium, Paris, France May 24, 2012

2. Overview • Sensitivities and rates of NGO/SGO, Omega, and GADFLI for MBHBs, EMRIs, and GBs • MBHB parameter estimation, or why you should pay very close attention to GADFLI • Mission details, comparisons of designs • NB: very similar concept to GADFLI, GEOGRAWI by Tinto et al • Cost: speculative comparison • Conclusions: GADFLI wins on MBHB science (hands down), performs on EMRIs and GBs, uses LPF heritage, and may be the cheapest option. So… Sean T. McWilliams LISA 9 Symposium, Paris

3. MBHB Sensitivities and Rates • Total SNR for GADFLI for MBHBs is less than for NGO/SGO and OMEGA • HOWEVER, late inspiral SNR for low mass systems is largest for GADFLI • Detection rate good for all Sean T. McWilliams LISA 9 Symposium, Paris

4. EMRI and GB Rates • EMRI rate a conservative variant of Gair et al., Class. Quant. Grav. 21 (2004) S1595-S1606 • Extreme uncertainty in EMRI event rates • All options should see GBs, based on Nelemans catalog • EMRI and GB parameter estimation generally obey 1/SNR expectations, so GADFLI should worse as N1/3, or a factor of ~4 for EMRIs, < 2 for GBs Sean T. McWilliams LISA 9 Symposium, Paris

5. How does LISA measure MBHB parameters? • Independent waveform channels, with different frequency and spatial dependencies (aka TDI observables) • Frequency dependence of response function • Intrinsic parameter dependence of waveforms (for MBHBs, q, S1, S2, e) • Doppler modulation: annual (all) and shorter periods (geocentric) • Intrinsic parameter dependence of waveforms (for MBHBs, q, S1, S2, e) • Independent waveform channels, with different frequency and spatial dependencies (aka TDI observables) • Doppler modulation: annual (all) and shorter periods (geocentric) • Frequency dependence of response function Sean T. McWilliams LISA 9 Symposium, Paris

6. How to assess science performance Waveform Model • Use a parametrized model that encodes parameter information • Extrinsic parameters can easily be scaled/shifted, result is robust • Intrinsic parameters are more subtle (1+z)Mtot, DL, tc, φorb, θsky ,θsys q, S1 , S2, e • Instrument Modeling • Realistic orbit model • Instrumental noises • Full response function • Calculating uncertainties • Use the Fisher matrix formalism to estimate uncertainties • MCMC too costly, unnecessary with high SNR Sean T. McWilliams LISA 9 Symposium, Paris

7. MBHB Parameter Estimation: SGO vs. NGO • SGO (6 links) and NGO (4 links) were compared as part of the science performance task force • Relatively poor sky localization and distance determination with NGO Sean T. McWilliams LISA 9 Symposium, Paris

8. MBHB Parameter Estimation Without Spin • GADFLI makes up for lost SNR with diurnal modulation – there is more (sometimes much more) to PE than SNR • HOWEVER, at December’s workshop, I said “There is good reason to believe GADFLI could outperform other designs for estimating MBHB source parameters when spin is included, due to its sensitivity at higher frequencies, and its daily orbital modulation of signals.”… Sean T. McWilliams LISA 9 Symposium, Paris

9. MBHB Parameter Estimation With Spin • Spin makes a HUGE difference for parameter accuracy • Given the greater complexity in including intrinsic parameters, PE studies with spin were not completed until after the Team X selection • courtesy of Neil Cornish Sean T. McWilliams LISA 9 Symposium, Paris

10. MBHB Parameter Estimation With Spin See talk by Neil Cornish tomorrow morning for more details Sean T. McWilliams LISA 9 Symposium, Paris

11. Design comparison • GADFLI has a far more stable orbit than SGO/NGO or Omega, mission lifetime was limited solely to decrease cost • GADFLI much less expensive for orbit insertion, does not need a propulsion module • GADFLI and Omega must deal with eclipses and sunlight in the telescope. Without mitigation, GADFLI would need to drop out of science mode for ~40 days/yr. • All data provided by Gary Welter for Mission Concept Workshop Sean T. McWilliams LISA 9 Symposium, Paris

12. GADFLI pros/cons pros • seems to outperform even original LISA in MBHB science • no need for propulsion module • low launch mass • uses LPF GRS, space-qualified laser, highest TRL level overall • lower shot noise requirements • most stable, cheapest orbit of any conceivable option • … naively, should be less expensive than other options cons • GADFLI less sensitive to EMRIs and GBs by a factor of a few • Thermal issues must be understood • Eclipses, sun pointing, can leave science mode in worst case • Different face to the sun and changing Earth albedo – is thermal variability an issue? Sean T. McWilliams LISA 9 Symposium, Paris

13. Conclusions • GADFLI measures EVERY parameter 1-2 orders of magnitude better than SGO (another 10x better than NGO for key parameters) • sky localization of O(1 arcmin) for most sources, down to O(1 arcsec) – pinpoint individual galaxy! • These results use Cornish and Lang code, should be checked independently • Since GADFLI has lighter/smaller components on the most stable and cheapest orbits, using as much or more LPF heritage than any other option, it should be the cheapest possibility. • If we are “revolutionaries” and “risk-takers”, we should be willing to change our proposal if new information DRASTICALLY changes the science picture • NB: Geostationarity and precise dimensions are NOT set in stone. Have a lot of room to increase orbit to mitigate thermal issues, make decommissioning less of an issue. • If limitation is launch on 2 Soyez, shrink components if necessary (eg less strict shot noise req, can shrink mirror)… if budget improves, prospects with a longer mission and a fourth satellite are tantalizing Sean T. McWilliams LISA 9 Symposium, Paris 11 August 2008 Sean T. McWilliams NRDA 2008 – Syracuse, NY 13

14. Questions? GADFLI -- Geocentric Antenna for Drag-Free Laser Interferometry Wikipedia defines a gadfly as “a person who upsets the status quo by posing upsetting or novel questions, or just being an irritant.” Hopefully this concept is the right balance of novel question and irritant. Sean T. McWilliams LISA 9 Symposium, Paris 11 August 2008 Sean T. McWilliams NRDA 2008 – Syracuse, NY 14