GW Constraints In The Presence Of Solar-system Ephemeris Uncertainties

Presentation at International Pulsar Timing Array 2017 meeting in Sevres, France.

Transcript

1. GW CONSTRAINTS IN THE PRESENCE OF SOLAR-SYSTEM EPHEMERIS UNCERTAINTIES Stephen Taylor JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY © 2017 California Institute of Technology. Government sponsorship acknowledged 1
2. 2 1 2 3 4 the solar-system ephemeris JPL ephemerides modeling ephemeris uncertainties impact on GW constraints (with NANOGrav 11yr results) Overview
3. 3 THE SOLAR-SYSTEM EPHEMERIS
4. 4 Tracing a TOA back from an observatory to the emission time at the pulsar involves a chain of corrections The Solar-System Ephemeris tpsr e = tobs a IS B tpsr e tobs a IS B
5. 5 1 2 3 4 all TOAs are referenced to the quasi-inertial frame of the SSB (need Roemer delay) Roemer delay dependent on masses & orbits of all important dynamical objects don’t need SSB to navigate probes to planets (accurate SSB is not a big priority) the Roemer is not fit for in Tempo2, it is subtracted from pre-fit JPL solutions The Solar-System Ephemeris
6. 6 The Solar-System Ephemeris = ~ robs · ~ RBB c Barycenter position dependent on masses & orbits of all important dynamical objects ~ r obs = ~ r SSB EB + ~ r EB obs = ~ e(t) · ~ RBB c Roemer delay Observatory position Small error in barycenter position
7. 7 JPL EPHEMERIDES
8. 8 JPL Ephemerides Credit: M. Vallisneri J1713+0747 (quadratic subtracted)
9. 9 upper limits and detection statistics are sensitive to our choice of ephemeris model 1 2 not obvious that most recent is “best” 3 what are the big differences between all of these DE- versions?
10. 10 the ephemeris where no red noise appears in PPTA timing of J1909-3744 JPL Ephemerides DE418 DE421 DE430 DE435 DE436 includes updates to Saturn’s orbit. Dominant uncertainty likely to be Jupiter includes updates to Mercury’s orbit. Dominant uncertainty still likely to be Jupiter created in Jan 2016 for Cassini, this is an incremental improvement to Saturn incremental improvement to DE435
11. 11 MODELING EPHEMERIS UNCERTAINTIES
12. 12 Modeling Ephemeris Uncertainties timing model white noise intrinsic red noise common red noise (or GWB) Current Bayesian Model ephemeris uncertainty term Expanded Model marginalize over ephemeris differences to isolate GW signal from choice of DE— GOAL
13. 13 Modeling Ephemeris Uncertainties ephemeris uncertainty term physically motivated • Fourier expansion of barycenter error vector [Lentati, Taylor, Mingarelli et al. (2015)] • planet mass perturbation [Champion et al. (2010)] • dipolar spatially-correlated red process phenomenological • Roemer mixture model • PCA of Roemer delays from DE421, DE430, etc. to construct empirical basis • [maybe] PCA of Roemer delays from many, many perturbed ephemerides
14. Power-law red process for {x,y,z} ephemeris error time-series 14 Modeling Ephemeris Uncertainties • Simulate 36 pulsars (IPTA MDC), with 11.4 yr baseline (same as NANOGrav 11yr dataset). • 500 ns precision. No other processes in data. • Create dataset with DE436. Analyze with others. dashed = original solid = with ephemeris uncertainty
15. Perturbing the planet masses in Roemer delay correction. 14 Modeling Ephemeris Uncertainties • Simulate 36 pulsars (IPTA MDC), with 11.4 yr baseline (same as NANOGrav 11yr dataset). • 500 ns precision. No other processes in data. • Create dataset with DE436. Analyze with others. dashed = original solid = with ephemeris uncertainty
16. Roemer mixture model 14 Modeling Ephemeris Uncertainties • Simulate 36 pulsars (IPTA MDC), with 11.4 yr baseline (same as NANOGrav 11yr dataset). • 500 ns precision. No other processes in data. • Create dataset with DE436. Analyze with others. dashed = original solid = with ephemeris uncertainty
17. Roemer mixture model 14 Modeling Ephemeris Uncertainties • Simulate 36 pulsars (IPTA MDC), with 11.4 yr baseline (same as NANOGrav 11yr dataset). • 500 ns precision. No other processes in data. • Create dataset with DE436. Analyze with others. dashed = original solid = with ephemeris uncertainty Roemer mixture model (no DE436)
18. 15 IMPACT ON GW CONSTRAINTS
19. 16 Impact On GW Constraints (preliminary NANOGrav 11yr results) • Bayes factor for a common red process (i.e. leaving out H&D correlations) versus noise range from ~1 (DE435) to ~10 (DE430). • It is crucial to marginalize over the difference in the ephemeris uncertainties for robust GW statistics. PRELIMINARY BF ~ 2.5 UL ~ 1.5e-15
20. 16 Impact On GW Constraints (preliminary NANOGrav 11yr results) • Bayes factor for a common red process (i.e. leaving out H&D correlations) versus noise range from ~1 (DE435) to ~10 (DE430). • It is crucial to marginalize over the difference in the ephemeris uncertainties for robust GW statistics. PRELIMINARY
21. 17 1 2 3 4 choice of solar-system ephemeris affects GW upper limits and detection statistics our models attempt to perturb the Roemer delay and marginalize over differences our models (Roemer mixture, planet-mass perturbations, Roemer GP) can not yet “connect” all ephemerides JPL can provide partials to perturb away from DE436, or even provide many perturbed ephemerides to construct an empirical basis Summary & Outlook