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The Search for GRAVITATIONAL WAVES using the LIGO INTERFEROMETERS

The Search for GRAVITATIONAL WAVES using the LIGO INTERFEROMETERS. Adrian Melissinos, University of Rochester On behalf of the LIGO Scientific Collaboration. In honor of Professor Piyare Lal Jain University of Buffalo, October 21, 2006. GRAVITATIONAL WAVES.

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The Search for GRAVITATIONAL WAVES using the LIGO INTERFEROMETERS

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  1. The Search for GRAVITATIONAL WAVES using the LIGO INTERFEROMETERS Adrian Melissinos, University of Rochester On behalf of the LIGO Scientific Collaboration In honor of Professor Piyare Lal Jain University of Buffalo, October 21, 2006 Lal Jain Fest

  2. Lal Jain Fest GRAVITATIONAL WAVES What are gravitational waves? A change in the space-time metric (in the weak field approximation) gμν= ημν – hμν hμν << 1 Where  hμν= − (16πG/c4) Tμν = 0 (in free space) Generated by catastrophic events such as SN collapse, binary star or black hole mergers; should be emitted by rotating astrophysical bodies (i.e. pulsars with Q ≠ 0). Possibly produced in the early universe and manifested today as a stochastic background. Estimates of the amplitude density of gravitational waves at the earth (strain density) h(f) ~ 10 -23/√Hz

  3. Lal Jain Fest DETECTION OF a G.W. 1. Direct coupling to matter: J.Weber’s resonant cylinders absorb energy from the wave and “ring”. They are narrow band devices and of limited sensitivity even when cooled to mK temeperatures. 2. Direct coupling to photons: In R.L.Forward’s and R.Weiss’ interferometers the GW interacts “elastically” with the optical field. SIDEBANDS AT ± ARE DUE TO ABSORPTION AND STIMULATED EMISSION OF A GRAVITON FROM/INTO THE FIELD  Ω  +   -    Usual interpretation: the distance between free-falling mirrors is modified resulting in a phase shift of the stored optical field.

  4. Lal Jain Fest Recycled Michelson Interferometer with Fabry-Perot arms • Want "optical" arm length ~ GW /4 for best antenna response • Adds complexity; now each arm needs to be held near L = k * LASER/2 • Add mirror to "recycle" photons (equivalent to more laser power) 4 km Fabry-Perot cavity recycling mirror 150 W LASER 15 kW 6W (0.2W) end test mass

  5. Lal Jain Fest THE HANFORD AND LIVINGSTON LIGO INTERFEROMETERS

  6. LIGOBeam Tube Lal Jain Fest

  7. Lal Jain Fest LIGO Vacuum Equipment

  8. Lal Jain Fest CORE OPTICS 10 kg Fused Silica, 25 cm diameter 10 cm thick

  9. Lal Jain Fest 2 2 2 2 4 4 4 4 1 1 1 1 3 3 3 3 10-22 10-21 S4 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 Runs S1 S2 S3 S5 Science First Science Data

  10. Lal Jain Fest S5 Science Run: Nov ‘05 -… June 2006 LIGO-G060293-01-Z hrms = 3x10-22 in 100Hz band

  11. Astrophysical Sources of Gravitational Waves • Compact binaries • Black holes & neutron stars • Inspiral and merger • Probe internal structure, populations, and spacetime geometry • Spinning neutron stars • Isolated neutron stars with mountains or wobbles • Low-mass x-ray binaries • Probe internal structure and populations Lal Jain Fest

  12. Gravitational-Wave Bursts • Catastrophic events involving solar-mass (1-100 Mo) compact objects. • core-collapse supernovae • accreting/merging black holes • gamma-ray burst engines • other … ??? • Sources typically not well understood, involving complicated (and interesting!) physics. • Dynamical gravity with event horizons • Behavior of matter at supra-nuclear densities • Lack of signal models makes GWBs more difficult to detect. SN 1987 A Lal Jain Fest

  13. Progress in Upper Limits S4 projected S5 projected • No GWBs detected through S4. • Set limits on GWB rate as a function of amplitude. S1 Lower rate limits from longer observation times Excluded 90% CL S2 Lower amplitude limits from lower detector noise Rate Limit (events/day) Lal Jain Fest

  14. Gravitational waves from compact binaries • LIGO is sensitive to gravitational waves from binary systems with neutron stars & black holes • Waveforms depend on masses and spins. • Binary neutron stars • Estimates give upper bound of 1/3 yr in LIGO S5 • Binary black holes • Estimates give upper bound of 1/yr in LIGO S5 Lal Jain Fest

  15. Binary Neutron Stars S2 Observational Result Phys. Rev. D. 72, 082001 (2005) • S3 search • Under internal review • 0.09 yr of data • ~3 Milky-Way like galaxies • S4 search complete • Under internal review • 0.05 yr of data • ~24 Milky-Way like galaxies cumulative number of events signal-to-noise ratio squared Lal Jain Fest

  16. Lal Jain Fest Bright bursts of gamma rays occur at cosmological distances seen at rate ~1/day. Long duration > 2s associated with “hypernovae” (core collapse to black hole) Hjorth et al, Nature 423 847 (2003). Leonor/Sannibale, Session W11 Short duration < 2 s Binary NS-NS or NS-BH coalescence? Gehrels et al., Nature 437, 851–854 (2005). Dietz, Session W11 Strongly relativistic - Interesting targets for LIGO!

  17. Lal Jain Fest Use triggers from satellites Swift, HETE-2, INTEGRAL, IPN, Konus-Wind Include both “short” and “long” GRBs Cross correlate data between pairs of detectors around time of event 25 – 100 ms target signal duration [-2,+1] min around GRB Compare largest measured CC to background distribution of CCs (from neighboring times with no GRB signal). Improbably large CC equals candidate GWB sample GRB lightcurve (BATSE) trigger time detector 2 detector 1

  18. No loud signals seen so far. • Look also for weak cumulative effect from population of GRBs. • Use binomial test to compare to uniform distribution. • No significant deviation from expected distribution. • Significance of deviation in plot at right ~50%. probabilities of observed cross-correlations expected distribution if no signal Leonor / Sannibale, Session W11 Lal Jain Fest

  19. Lal Jain Fest Continuous waves Accreting Neutron Stars Wobbling Neutron Stars Bumpy Neutron Star Low-mass x-ray binary Wobbling pulsars Credit: M. Kramer Credit: Dana Berry/NASA

  20. Lal Jain Fest Known pulsars S5 preliminary • 32 known isolated, 44 in binaries, 30 in globular clusters Gravitational-wave amplitude Lowest ellipticity upper limit: PSR J2124-3358 (fgw = 405.6Hz, r = 0.25kpc) ellipticity = 4.0x10-7 ~2x10-25 Frequency (Hz)

  21. To participate, sign up at http://www.physics2005.org Einstein@Home • Matched-filtering for continuous GWs • All-sky, all-frequency search • computationally limited • Aiming at detection, not upper limits • Public outreach distributed computing • S3 results: • No evidence of pulsars • S4 search • Underway Lal Jain Fest

  22. Stochastic Background • Cross-correlate two data streams x1 and x2 • For isotropic search optimal statistic is “Overlap Reduction Function” (determined by network geometry) Detector noise spectra g(f) frequency (Hz) Lal Jain Fest

  23. Technical Challenges 100 10-1 H1-L1 coherence 10-2 10-3 100 200 300 400 500 Simulated pulsar line frequency (Hz) • Example: • Correlations at harmonics of 1 Hz. • Due to GPS timing system. • Lose ~3% of the total bandwidth (1/32 Hz resolution). • Digging deep into instrumental noise looking for small correlations. • Need to be mindful of possible non-GW correlations • common environment (two Hanford detectors) • common equipment (could affect any detector pair!) Lal Jain Fest

  24. S4 Analysis Details S4: Sensitivity vs Frequency • Cross-correlate Hanford-Livingston • Hanford 4km – Livingston • Hanford 2km – Livingston • Weighted average of two cross-correlations (new in S4). • Do not cross-correlate the Hanford detectors. • Data quality: • Drop segments when noise changes quickly (non-stationary). • Drop frequency bins showing instrumental correlations (harmonics of 1 Hz, bins with pulsar injections). • Bayesian UL: Ω90% = 6.5 × 10-5 • Use S3 posterior distribution for S4 prior. • Marginalized over calibration uncertainty with Gaussian prior (5% for L1, 8% for H1 and H2). Lal Jain Fest

  25. Radiometer: Proof-of-Principle • Analysis of a simulated point source at the position of the Virgo galaxy cluster (12.5h,12.7). • simulated H1-L1 data Lal Jain Fest

  26. Predictions and Limits LIGO S1: Ω0< 44 PRD 69 122004 (2004) LIGO S3: Ω0< 8.4x10-4 PRL 95 221101 (2005) LIGO S4: Ω0< 6.5x10-5 (new) Initial LIGO, 1 yr data Expected Sensitivity ~4x10-6 CMB Adv. LIGO, 1 yr data Expected Sensitivity ~ 1x10-9 0 Pulsar Timing -2 CMB+galaxy+Ly-aadiabatichomogeneous BB Nucleo- synthesis -4 -6 (W0) -8 Cosmic strings Log -10 Pre-BB model -12 Inflation -14 Cyclic model Slow-roll EW or SUSY Phase transition -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 -18 10 Log (f [Hz]) Lal Jain Fest

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