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

1 / 15

G1500523

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

2 / 15

G1500523

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)

3 / 15

G1500523

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

4 / 15

G1500523

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

G1500523

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)

6 / 15

G1500523

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)

7 / 15

G1500523

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

8 / 15

G1500523

Detection efficiency (simulated noise, simulated signal)

Detection efficiency of 500 injections, threshold log10 p = −7.75[no real data: demonstration of technique in simulation]

9 / 15

G1500523

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]

10 / 15

G1500523

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

11 / 15

G1500523

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

12 / 15

G1500523

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

13 / 15

G1500523

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)!

14 / 15

G1500523

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).

15 / 15