1. LIGO-G040276-00-Z Results from LIGO’s second science run: a search for continuous gravitational waves Michael Landry LIGO Hanford Observatory California Institute of Technology on behalf of the LIGO Scientific Collaboration http://www.ligo.org CAP Congress June 16, 2004 Winnipeg, Canada Photo credit: NASA/CXC/SAO

2. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 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*f rot –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. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 3 Gravitational Waves = “Ripples in space-time” Perturbation propagation similar to light (obeys same wave equation!) »Propagation speed = c »Two transverse polarizations - quadrupolar: + and x What are Gravitational Waves? Example: Ring of test masses responding to wave propagating along z Amplitude parameterized by (tiny) dimensionless strain h:  L ~ h(t) x L

4. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 4 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) What makes Gravitational Waves?

5. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 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-G040276-00-Z Landry - CAP Congress, 16 June 2004 6 LIGO Observatories Livingston (L1=4km) Hanford (H1=4km, H2=2km) Observation of nearly simultaneous signals 3000 km apart rules out terrestrial artifacts

7. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 7 Strain noise comparison: science runs Initial LIGO Design S1 (L1) 1 st Science Run end Sept. 2002 17 days S2 (L1) 2 nd Science Run end Apr. 2003 59 days S3 (H1) 3 rd Science Run end Jan. 2004 70 days With GEO: Phys Rev D 69, 082004 (2004)

8. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 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 LIGO GEO

9. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 9 CW source model F + and F x : strain antenna patterns of the detector to plus and cross polarization, bounded between -1 and 1 Here, signal parameters are: »h 0 – amplitude of the gravitational wave signal »  – polarization angle of signal »  – inclination angle of source with respect to line of sight »  0 – initial phase of pulsar;  (t=0), and  (t)=  t  0 so that the expected demodulated signal is then: The expected signal has the form: Heterodyne, i.e. multiply by: Here, a = a(h 0, , ,  0 ), a vector of the signal parameters. PRD 58 063001 (1998)

10. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 10 Compute likelihoods Analysis summary Heterodyne, lowpass, average, calibrate: B k Model: y k Compute pdf for h 0 Compute upper limit “h 95 ” Raw Data uniform priors on h 0 (>0), cos     h 95 1 PDF 0 strain

11. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 11 Injection of fake pulsars during S2 Parameters of P1: 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 =  /2 h 0 = 2.0 x 10 -21 Two simulated pulsars, P1 and P2, were injected in the LIGO interferometers for a period of ~ 12 hours during S2

12. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 12 Preliminary upper limits for 28 known pulsars h 0 UL rangePulsar 10 -23 -10 -22 J1939+2134, B1951+32, J1913+1011, B0531+21 10 -24 -10 -23 B0021-72C, B0021-72D, B0021-72F, B0021-72G, B0021- 72L, B0021-72M, B0021-72N, J0711-6830, B1820-30A, J1730-2304, J1721-2457, J1629-6902, J1910-5959E, J2124-3358, J1910-5959C, J0030+0451, J1024-0719, J1910-5959D, J2322+2057, B1516+02A, J1748-2446C, J1910-5959B, J1744-1134, B1821-24 Blue: pulsar timing checked by Michael Kramer, Jodrell Bank Purple: pulsar timing from ATNF catalogue

13. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 13 Equatorial Ellipticity Results on h 0 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, I zz is assumed to be typical, 10 45 g cm 2

14. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 14 Preliminary ellipticity  limits for 28 known pulsars  UL range Pulsar 10 -2 -10 -1 B1951+32, J1913+1011, B0531+21 10 -3 -10 -2 - 10 -4 -10 -3 B1821-24, B0021-72D, J1910-5959D, B1516+02A, J1748- 2446C, J1910-5959B 10 -5 -10 -4 J1939+2134, B0021-72C, B0021-72F, B0021-72L, B0021-72G, B0021-72M, B0021-72N, B1820-30A, J0711-6830, J1730-2304, J1721-2457, J1629-6902, J1910-5959E, J1910-5959C, J2322+2057 10 -6 -10 -5 J1024-0719, J2124-3358, J0030+0451, J1744-1134 Blue: timing checked by Jodrell Bank Purple: ATNF catalogue

15. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 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. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 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. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 17 Strong Indirect Evidence: Orbital Decay Neutron Binary System – Hulse & Taylor PSR 1913 + 16 -- Timing of pulsars   17 / sec Neutron Binary System separated by 10 6 miles m 1 = 1.4m  ; m 2 = 1.36m  ;  = 0.617 Prediction from general relativity spiral in by 3 mm/orbit rate of change orbital period ~ 8 hr Emission of gravitational waves

18. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 18 What Limits the Sensitivity of 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. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 19 CW sources Nearly-monochromatic continuous sources of gravitational waves include neutron stars with: »spin precession at ~f rot »excited oscillatory modes such as the r-mode at 4/3 * f rot »non-axisymmetric distortion of crystalline structure, at 2f rot 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. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 20 Source model F + and F x : strain antenna patterns of the detector to plus and cross polarization, bounded between -1 and 1 Here, signal parameters are: »h 0 – amplitude of the gravitational wave signal »  – polarization angle of signal »  – inclination angle of source with respect to line of sight »  0 – initial phase of pulsar;  (t=0), and  (t)=  t  0 so that the expected demodulated signal is then: The expected signal has the form: Heterodyne, i.e. multiply by: Here, a = a(h 0, , ,  0 ), a vector of the signal parameters. PRD 58 063001 (1998)

21. LIGO-G040276-00-Z Landry - CAP Congress, 16 June 2004 21 Compute likelihoods Analysis summary Heterodyne, lowpass, average, calibrate: B k Model: y k Compute pdf for h 0 Compute upper limit “h 95 ” Raw Data uniform priors on h 0 (>0), cos     h 95 1 PDF 0 strain