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G1500523
Scorpius X-1 and other LMXBsdirected and all-sky searches for continuous gravitational waves
Grant David Meadors1 (for the LIGO-Virgo Collaboration)
1. Albert-Einstein-Institute Hannover
2015 June, Osaka GWPAW
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Neutron stars in binary systemsGravitational-wave sources?Low Mass X-ray Binaries (LMXBs)55% (225/405) of pulsars >10 Hz in binary systems (2015 ATNF)
Longer life as ms pulsars than isolated sources (recycling)Ellipticity & accretion hot spotsTorque-balance (Papaloizou & Pringle 1978, Wagoner 1984):
h0 = 5× 10−27(300Hzν
)1/2 ( F×10−8erg cm−2s−1
)1/2
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Scorpius X-1: parameters and possibilities
Example (Scorpius X-1 torque-balance limit, 50 to 1500 Hz)
h0 = 3.5× 10−26(600Hz
f
)1/2
→ 2.2× 10−26 < h0 < 1.2× 10−25
2.8 kpc (9000 light-years)ε < 3× 10−3
α=16h19m55.1s, δ=-15d38m24.9s60000 LSol (2.3 ×1031 W)
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Scorpius X-1: overview
LIGO searches to date:S2, F-stat, LSC: Phys Rev D 76 (2007) 082001S4, stoch-radiometer, LSC: Phys Rev D 76 (2007) 082003S5, stoch-radiometer, LVC: Phys Rev Lett 76 (2011) 271102S6 & VSR2/3, TwoSpect, LVC: Phys Rev D 90 (2014) 062010S5, sideband, LVC: Phys Rev D 91 (2015) 062008
Today: directed search in latest (S6) science data:based on TwoSpect, (methods: Goetz & Riles 2011)and previous all-sky results (above).Also! See Chris Messenger’s talk,comparing methods with the Sco X-1 mock data challengeWhy a directed S6 search?→ Mock data challenge hinted at better h0 upper limitsO(1/
√2) in SIMULATED DATA than all-sky
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TwoSpect algorithm for CW binary searchesSignal model (GW phase Φ for binary system)Orbital freq. Ω = 2π/P , mod. depth ∆fobs = 2πf (a sin i)/(cP):
Φ(t) = Φ0 + 2π[f0(t − tref) + ∆fobs sin(Ω[t − tasc])/Ω]
FFT over spectrogram time [fixed f ]: (t, f ) (LEFT) → (f ′, f ) (RIGHT) 5 / 15
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TwoSpect algorithm for CW binary searches
R-statistic (weighted sum of 2nd Fourier-plane pixels)
R =ΣM−1i=0 w(mi )[Z (mi )− λ(mi )]
ΣM−1i=0 [w(mi )]2
w : template weighti : index in M-pixel template structureZ : spectral power after barycentering & antenna patternλ: background noise power (χ2-distributed)
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Directed TwoSpect: cost for fully-templated searchSpeed – Tobs = 1 yr → 3 s/template
All-sky vs directed: O(1018) vs O(108) templatesAll-sky: hierarchical; incoherent harmonic sum of pixels,then templates to test interesting outliersDirected: purely-templated search for full sensitivity,search at one IFO over ±3σ around a sin i :
Ntemplate = 2(Tsft +
1fbw
)× . . .[
1 +4πTsft
P(6σa sin i )(fmax + fmin + fbw )
](fmax − fmin)
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Directed TwoSpect: cost for fully-templated search
Scorpius X-1 (P ≈ 68023.7 s, a sin i ≈ 1.44± 0.18s)P and a sin i require Tsft ↓ as f ↑ (to prevent spectral leakage)
S6 search computational cost2 IFOs× (2000 Hz ⊆ [40, 2040] Hz)Ntemplate = 4.6× 108 →∼ 540 core-months
Processing2 kHz, ±3σa sin i search over all S6 data from H1 & L1Completed
Post-processingUnderway: upper limit validation, follow-up, review
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Detection efficiency (simulated noise, simulated signal)
Detection efficiency of 500 injections, threshold log10 p = −7.75[no real data: demonstration of technique in simulation]
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h0 recovered vs injected (simulated noise, simulated signal)
‘h0’ (uncalibrated R1/4) & tentative 95% conf. UL w/ 500 inj.[no real data: demonstration of technique in simulation]
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S6: Scorpius X-1 search summary
S6 production search 100% done in 30 days, 2 kHz per H1, L1
1 Upper limit validation with injections:a priori noise floor → h0 distribution,a posteriori peaks of bands → h0 distribution,
2 Outlier followupTwoSpect can estimate f , a sin i of candidates
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S6: J1751-305 search
Fastest-orbiting XTE(P ≈ 2545.3 s, a sin i ≈ 0.010± 0.003s):Quick search (< 105 templates), debate about r -modesyet estimated d > 7 kpc near galactic center
ν0: 435.31799 Hzr -mode: (2-0.5727597)*(435.31799 Hz) = 621.3034 Hz
Search frequencies [434.5,436.5], [620.5,622.5] & [869.5,871.5] Hz
→ ν0, r -mode, 2ν0: analysis done; upper limits forthcoming
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Future directed search improvementsCoherently summing SFTs from multiple detectors:sum SFTs from N seperate detectorswith data taken in coincidence(forthcoming methods paper)Elliptical polarization:search over cos ι, ψ termsOrbital phase:redesign statistic to account for complex 2nd FFT phase,could recover Tasc
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Summary
Scorpius X-1 search summaryScorpius X-1 & J1751-305 processing done in S6Post-processing of TwoSpect output underwayAnalysis and results awaiting internal LVC reviewGoal DIRECTED S6 observational paper by next run
AcknowledgmentsDomo arigato gozaimasu to our hostshere in Osaka for GWPAW (and the Kagra tour)!
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Bibliography
References
E. A. Goetz, Ph.D. thesis, University of Michigan (2010).
E. Goetz and K. Riles, Class. Quant. Grav. 28 (2011).
J. Aasi et al., Phys. Rev. D 90 (2014).
D. Chakrabarty et al., Nature 424, 42 (2003).
R. Manchester, G. Hobbs, A. Teoh, and M. Hobbs, Astronom.J. 129 (2005).
C. Markwardt et al., Astrophys. J 575, L21 (2002).
J. Papaloizou and J. Pringle, M.N.R.A.S. 184 (1978).
R. Wagoner, Ap. J. 278 (1984).
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