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Recent results on the search for continuous sources with LIGO

Recent results on the search for continuous sources with LIGO. A.M. Sintes for the LSC Universitat de les Illes Balears, Spain. TAUP, 10 September 2005 Zaragoza, Spain. Content. LIGO science runs Gravitational waves from pulsars Directed pulsar search All Sky search Coherent methods

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Recent results on the search for continuous sources with LIGO

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  1. Recent results on the search for continuous sources with LIGO A.M. Sintes for the LSC Universitat de les Illes Balears, Spain TAUP, 10 September 2005 Zaragoza, Spain

  2. Content • LIGO science runs • Gravitational waves from pulsars • Directed pulsar search • All Sky search • Coherent methods • Einstein at Home • Semi-coherent methods: The Hough transform • Current search efforts

  3. 2 2 2 2 4 4 4 4 1 1 1 1 3 3 3 3 10-22 10-21 E3 E7 E5 E9 E10 E8 Runs S1 S2 S3 S4 S5 Science First Science Data LIGO Time Line 1999 2000 2001 2002 2003 2004 2005 2006 2 4 2 4 4 1 3 1 3 2 4 3 1 3 Inauguration First Lock Full Lock all IFO Now 4K strain noise at 150 Hz [Hz-1/2] 10-17 10-18 10-20 E2 E11 Engineering

  4. LIGO Science Runs S1 1st Science Run Sept 02 (17 days) S2 2nd Science Run Feb - Apr 03 (59 days) LIGO Target Sensitivity S3 3rd Science Run Nov 03 – Jan 04 (70 days)

  5. LIGO S4 - Best Performance

  6. Low Mass X-Ray Binaries Wobbling Neutron Star Bumpy Neutron Star Young Neutron Stars Gravitational waves from pulsars • Pulsars (spinning neutron stars) are known to exist! • Emit gravitational waves if they are non-axisymmetric:

  7. Detection of periodic sources • But what is a pulsar? • Highly compact stars - as massive as Sun but only 10 km in size • Rapidly spinning stars - some pulsars spin about their axis once each second while others spin 100’s of times. • Pulsars in our galaxy:“periodic” • search for observed neutron stars • all sky search (computing challenge) • Our galaxy might contain ~109 NS, of which ~103 have been identified

  8. Neutron Stars Sources • Great interest in detecting radiation: physics of such stars is poorly understood. • After 35 years we still don’t know what makes pulsars pulse. • Interior properties not understood: equation of state, superfluidity, superconductivity, solid core, source of magnetic field. • May not even be neutron stars: could be made of strange matter!

  9. GWs from pulsars: The signal • The GW signal from a neutron star: • Nearly-monochromatic continuous signal • spin precession at ~frot • excited oscillatory modes such as the r-mode at 4/3* frot • non-axisymmetric distortion of crystalline structure, at 2frot (Signal-to-noise)2 ~

  10. R Signal received from a pulsar • A gravitational wave signal we detect from a pulsar will be: • Frequency modulated by relative motion of detector and source • Amplitude modulated by the motion of the antenna pattern of the detector

  11. Target known pulsars • For target searches only one search template (or a reduced parameter space) is required e.g. search for known radio pulsars with frequencies (2frot) in detector band . There are ~102 known radio pulsars fGW> 50 Hz • Known parameters: position, frequency and spin-down (or approximately) • Unknown parameters: amplitude, orientation, polarization and phase • Timing information provided from radio observations In the event of a glitch we would need to add an extra parameter for jump in GW phase • Coherent search methods can be used i.e. those that take into account amplitude and phase information

  12. Frequency domain Conceived as a module in a hierarchical search Best suited for large parameter space searches(when signal characteristics are uncertain) Straightforward implementation of standard matched filtering technique (maximum likelihood detection method): Cross-correlation of the signal with the template and inverse weights with the noise Frequentist approach used to cast upper limits. Time domain process signal to remove frequency variations due to Earth’s motion around Sun and spindown Best suited to target known objects, even if phase evolution is complicated Efficiently handless missing data Upper limits interpretation: Bayesian approach Two search methods

  13. Summary of directed pulsar search • S1 (LIGO and GEO: separate analyses) • Upper limit set for GWs from J1939+2134 (h0<1.4 x 10-22) • Phys. Rev. D 69, 082004 (2004) • S2 science run (LIGO: 3 ifos coherently, TDS) • End-to-end validation with 2 hardware injections • Upper limits set for GWs from 28 known isolated pulsars • Phys. Rev. Lett. 94, 181103 (2005) • S3 & S4 science runs (LIGO and GEO: up to 4 ifos coherently, TDS) • Additional hardware injections in both GEO and LIGO • Add known binary pulsars to targeted search • Full results with total of 93 (33 isolated, 60 binaries) pulsars

  14. Heterodyne, low-pass, average, calibrate: Bk Raw Data Model: yk Compute joint likelihood Compute posterior pdfs posterior  prior  likelihood uniform priors on h0(>0), cosi, j0, y Compute upper limits Time domain analysis method

  15. Directed Search in S1 NO DETECTION EXPECTED Detectable amplitudes with a 1% false alarm rate and 10% false dismissal rate Upper limits on from spin-down measurements of known radio pulsars Crab Pulsar Predicted signal for rotating neutron star with equatorial ellipticity e = d I/I: 10-3 , 10-4 , 10-5 @ 8.5 kpc. PSR J1939+2134 1283.86 Hz P’ = 1.0511 10-19 s/s D = 3.6 kpc

  16. S2 Directed Pulsar SearchFeb 14 – Apr 14, 2003 28 Radio Sources 95% upper limits • Performed joint coherent analysis for 28 pulsars using data from all IFOs • Most stringent UL is for pulsar J1910-5959D (~221 Hz) where 95% confident that h0 < 1.7x10-24 • 95% upper limit for Crab pulsar (~ 60 Hz) is h0 < 4.7 x 10-23 • 95% upper limit for J1939+2134 (~ 1284 Hz) is h0 < 1.3 x 10-23

  17. S2 Results Lowest 95% UL on h0 = 1.7 10-24 (J1910-5959D) Lowest bound on e = 4.5 10-6 (J2124-3358) NO gravitational waves → e < 10-5 – 10-6(no mountains > 10 cm) Crab pulsar: h0 = 4.1 10-23 , e = 2.1 10-2 (~30 times spin-down upper limit)

  18. New Results LIGO- S4 Preliminary • Searched for signals for all known pulsars with 2frot > 50 Hz for which data provided by Jodrell Bank or ATNF catalog was sufficiently accurate • Total of 93 pulsars (33 isolated and 60 binaries) • Model corrected for timing noise for the Crab pulsar. • Main change for S3/S4 has been to add code to account for extra Doppler shift in binary systems • Code uses the 5 known Keplerian parameters plus some relativistic corrections for a few pulsars Best upper limit is for J0537-6910 (fGW=124.1 Hz) with h095% < 4.2 x 10-25 Crab (J0534+2200)h095% < 4.6 x 10-24, ~3.2> spin-down limit

  19. ALL SKY SEARCH enormous computing challenge

  20. Einstein@Home • GEO-600 Hannover • LIGO Hanford • LIGO Livingston • Current search point • Current search coordinates • Known pulsars • Known supernovae remenants • User name • User’s total credits • Machine’s total credits • Team name • Current work % complete Einstein@Home LIGO Pulsar Search using home pc’s BRUCE ALLEN Project Leader Univ of Wisconsin Milwaukee LIGO, UWM, AEI, APS http://einstein.phys.uwm.edu }

  21. What is Einstein@home? • How does Einstein@home currently work? • Downloads data from Einstein@home servers • Searches the sky in a narrow range of frequencies • Uploads interesting candidates for further follow-up • Screensaver shows where you are currently searching in the sky • Launched on Feb 19, 2005. Testing since Summer 2004. • APS idea to make this a WYP activity, and organize publicity. • We currently have over 98,000 users and about 175,000 host machines. • Current growth rate is about 8000 participants/week. • Versions available for Windows, Mac, Linux. • S3 analysis completed using 22 million CPU hours (2 million jobs completed, each lasts about 11.1 CPU hours. Each work-unit runs up to 12 times until is validated)

  22. Frequency Time Alternative search strategies • The idea is to perform a search over the total observation time using an incoherent (sub-optimal) method: We propose to search for evidence of a signal whose frequency is changing over time in precisely the pattern expected for some one of the parameter sets • The methods used are • Radon transform (Stack and Slide) • Hough transform • Power-flux method Phase information is lost between data segments

  23. n d a Time-frequency pattern We use the Hough transform to find a pattern produced by the Doppler modulation & spin-down of a GW signal in the time-frequency plane of our data. For isolated NS the expected pattern depends on: {a,d, f0, fn}

  24. The second science run. Feb.14-Apr.14,2003Sensitivity of the Hough search Characteristic amplitude detectable from a known generic source with a 10% false dismissal and 1% false alarm rate using the Hough transform Astrophysics expectation h0 less than 4x10-24

  25. Input data & Parameter space • Input data: S2 (Feb 14- Apr 14, 2003) • Calibrated 30 minutes SFTs produced according to DQ segments • L1: N=687; H1: N=1761; H2: N=1384 • Search for isolated pulsars • frequency band 200 – 400 Hz (Δf = 1/1800 Hz = 5.55×10 – 4 Hz) • 1 spin-down parameter (11 values: Δf1= –1.1×10– 10 Hz s– 1) • Templates: • 1.5×105 sky locations for the whole sky @ 300 Hz • 1.9×109 @ 200-201 Hz • 7.5×109@ 399-400 Hz

  26. Number count distributionfrom L1, H1, H2 blue: 206-207 Hz green: 343-344 Hz asterisks: theoretical

  27. Known spectral disturbances: 200-400 Hz • Calibration lines • n*60 Hz power lines • n*16 Hz due to data acquisition • Mechanical resonances: violin modes • Comb ~37 Hz, with side lobes ~0.7Hz, due to synthesized oscillators • n*0.25 Hz

  28. L1 kk No evidence for a detection H1 H2

  29. Frequentist upper limit • Perform the Hough transform for a set of points in parameter space l={a,d,f0,fi}S , given the data: HT: S  N l n(l) • Determine the maximum number count n* n* = max (n(l)): lS • Determine the probability distribution p(n|h0) for a range of h0 • The 95% frequentist upper limit h095% is the value such that for repeated trials with a signal h0 h095%, we would obtain n  n* more than 95% of the time Compute p(n|h0) via Monte Carlo signal injections

  30. Hough S2: 95 % UL Summarygr-qc/0508065

  31. Major Search Efforts Currently Underway • TD-search • S3/S4 results with total of 93 pulsars (reviewing results) • Fstat Search • S2 data, 1 detection statistic, 1 pipeline, 2 searches: all-sky search for isolated pulsars, ~ 600 Hz bandwidth, Tobs: 10 hrs, 2 IFOs, search for signal from Sco-X1 (pulsar in a binary system), Tobs: 6 hrs. • Einstein @ home • S3 data: analysis complete. S4 analysis underway. Will continue until end of the year. • Power-flux, Stack-slide & Hough search • S4 data, all-sky, wide band search for isolated pulsars • Hough Search • Improvements to the method under way, expected sensitivity improvement. Next search will use Fstat. • Employ hierarchical schemes which alternate coherent and semi-coherent techniques

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