Photo credit: NASA/CXC/SAO

1. Results from LIGO’s second science run: a search for continuous gravitational wavesMichael LandryLIGO Hanford ObservatoryCalifornia Institute of Technologyon behalf of the LIGO Scientific Collaborationhttp://www.ligo.orgCAP CongressJune 16, 2004Winnipeg, Canada Photo credit: NASA/CXC/SAO

2. Talk overview • Laser Interferometer Gravitational Wave Observatory (LIGO) overview • The what and how of gravitational radiation • Search for continuous waves (CW) • Source model • Time-domain Analysis method • Limit our search (for the analysis presented here, only)to gravitational waves from a triaxial neutron star emitted at twice its rotational frequency, 2*frot • Signal would be frequency modulated by relative motion of detector and source, plus amplitude modulated by the motion of the antenna pattern of the detector • Validation by hardware injection of fake pulsars • Results

3. Example: Ring of test masses responding to wave propagating along z What are Gravitational Waves? • Gravitational Waves = “Ripples in space-time” • Perturbation propagation similar to light (obeys same wave equation!) • Propagation speed = c • Two transverse polarizations - quadrupolar: +andx Amplitude parameterized by (tiny) dimensionless strain h: DL ~ h(t) x L

4. What makes Gravitational Waves? • Compact binary inspiral: “chirps” • NS-NS waveforms are well described • BH-BH need better waveforms • Supernovae / GRBs: “bursts” • burst signals in coincidence with signals in electromagnetic radiation / neutrinos • all-sky untriggered searches too • Cosmological Signal: “stochastic background” • Pulsars in our galaxy:“periodic” • search for observed neutron stars (this talk) • all-sky search (computing challenge)

5. Gravitational Wave Detection • Suspended Interferometers • Suspended mirrors in “free-fall” • Michelson IFO is “natural” GW detector • Broad-band response (~50 Hz to few kHz) • Waveform information (e.g., chirp reconstruction)

6. LIGO Observatories Hanford (H1=4km, H2=2km) Observation of nearly simultaneous signals 3000 km apart rules out terrestrial artifacts Livingston (L1=4km)

7. Strain noise comparison: science runs S1 (L1) 1st Science Run end Sept. 2002 17 days • With GEO: • Phys Rev D • 69, 082004 • (2004) S2 (L1) 2nd Science Run end Apr. 2003 59 days Initial LIGO Design S3 (H1) 3rd Science Run end Jan. 2004 70 days

8. S2 expectations • Coloured spectra: average amplitude detectable in time T (1% false alarm, 10% false dismissal rates): • Solid black lines: LIGO and GEO science requirement, for T=1 year • Circles: upper limits on gravitational waves from known EM pulsars, obtained from measured spindown (if spindown is entirely attributable to GW emission) • Only known, isolated targets shown here GEO LIGO

9. CW source model • F+ and Fx : strain antenna patterns of the detector to plus and cross polarization, bounded between -1 and 1 • Here, signal parameters are: • h0 – amplitude of the gravitational wave signal • y – polarization angle of signal • i – inclination angle of source with respect to line of sight • f0 – initial phase of pulsar; F(t=0), and F(t)= f(t) + f0 The expected signal has the form: PRD 58 063001 (1998) Heterodyne, i.e. multiply by: so that the expected demodulated signal is then: Here, a = a(h0, y, i, f0), a vector of the signal parameters.

10. Analysis summary Heterodyne, lowpass, average, calibrate: Bk Raw Data Compute likelihoods Model: yk uniform priors on h0(>0), cosi, j0, y Compute pdf for h0 1 PDF 0 h95 Compute upper limit “h95” strain

11. Injection of fake pulsars during S2 Parameters of P1: Two simulated pulsars, P1 and P2, were injected in the LIGO interferometers for a period of ~ 12 hours during S2 P1: Constant Intrinsic Frequency Sky position: 0.3766960246 latitude (radians) 5.1471621319 longitude (radians) Signal parameters are defined at SSB GPS time 733967667.026112310 which corresponds to a wavefront passing: LHO at GPS time 733967713.000000000 LLO at GPS time 733967713.007730720 In the SSB the signal is defined by f = 1279.123456789012 Hz fdot = 0 phi = 0 psi = 0 iota = p/2 h0 = 2.0 x 10-21

12. Preliminaryupper limits for 28 known pulsars Blue: pulsar timing checked by Michael Kramer, Jodrell Bank Purple: pulsar timing from ATNF catalogue

13. Equatorial Ellipticity • Results on h0 can be interpreted as upper limit on equatorial ellipticity • Ellipticity scales with the difference in radii along x and y axes • Distance r to pulsar is known, Izz is assumed to be typical, 1045 g cm2

14. Preliminaryellipticitylimits for 28 known pulsars Blue: timing checked by Jodrell Bank Purple: ATNF catalogue

15. Summary and future outlook • LIGO • Good progress towards design sensitivity • Initial results from first two data runs • S2 analyses • Time-domain analysis of 28 known pulsars complete • Broadband frequency-domain all-sky search underway • ScoX-1 LMXB frequency-domain search near completion • Incoherent searches reaching maturity, preliminary S2 results produced • S3 run • Time-domain analysis on more pulsars, including binaries • Improved sensitivity LIGO/GEO run • Oct 31 03 – Jan 9 04 • Approaching spindown limit for Crab pulsar

16. Why look for Gravitational Radiation? • Because it’s there! (presumably) • Test General Relativity: • Quadrupolar radiation? Travels at speed of light? • Unique probe of strong-field gravity • Gain different view of Universe: • Sources cannot be obscured by dust / stellar envelopes • Detectable sources some of the most interesting, least understood in the Universe • Opens up entirely new non-electromagnetic spectrum

17. Strong Indirect Evidence:Orbital Decay Emission of gravitational waves Neutron Binary System – Hulse & Taylor PSR 1913 + 16 -- Timing of pulsars 17 / sec · · ~ 8 hr • Neutron Binary System • separated by 106 miles • m1 = 1.4m; m2 = 1.36m; e = 0.617 • Prediction from general relativity • spiral in by 3 mm/orbit • rate of change orbital period

18. What Limits the Sensitivityof the Interferometers? • Seismic noise & vibration limit at low frequencies • Atomic vibrations (Thermal Noise) inside components limit at mid frequencies • Quantum nature of light (Shot Noise) limits at high frequencies • Myriad details of the lasers, electronics, etc., can make problems above these levels • Best design sensitivity: • ~ 3 x 10-23 Hz-1/2 @ 150 Hz

19. CW sources • Nearly-monochromatic continuous sources of gravitational waves include neutron stars with: • spin precession at ~frot • excited oscillatory modes such as the r-mode at 4/3 * frot • non-axisymmetric distortion of crystalline structure, at 2frot • Limit our search to gravitational waves from a triaxial neutron star emitted at twice its rotational frequency (for the analysis presented here, only) • Signal would be frequency modulated by relative motion of detector and source, plus amplitude modulated by the motion of the antenna pattern of the detector

20. Source model • F+ and Fx : strain antenna patterns of the detector to plus and cross polarization, bounded between -1 and 1 • Here, signal parameters are: • h0 – amplitude of the gravitational wave signal • y – polarization angle of signal • i – inclination angle of source with respect to line of sight • f0 – initial phase of pulsar; F(t=0), and F(t)= f(t) + f0 The expected signal has the form: PRD 58 063001 (1998) Heterodyne, i.e. multiply by: so that the expected demodulated signal is then: Here, a = a(h0, y, i, f0), a vector of the signal parameters.

21. Analysis summary Heterodyne, lowpass, average, calibrate: Bk Raw Data Compute likelihoods Model: yk uniform priors on h0(>0), cosi, j0, y Compute pdf for h0 1 PDF 0 h95 Compute upper limit “h95” strain