LIGO-G Z Results from LIGO observations Stochastic Background & Continuous Wave Signals Nelson Christensen for the LIGO Scientific Collaboration

LIGO-G ZChristensen MG LIGO Science Goals l Direct verification of two dramatic predictions of Einstein’s general relativity »gravitational waves and black holes l Physics & Astronomy »Detailed tests of properties of gravitational waves including speed, polarization, graviton mass,..... »Probe strong field gravity around black holes and in the early universe »Probe the neutron star equation of state »Performing routine astronomical observations to understand compact binary populations, supernovae rates, test gamma-ray burst models,.... l LIGO provides a new window on the Universe

LIGO-G ZChristensen MG Astrophysical Sources of Gravitational Waves l Compact binaries »Black holes & neutron stars »Inspiral and merger »Probe internal structure, populations, and spacetime geometry l Spinning neutron stars »Isolated neutron stars with mountains or wobbles »Low-mass x-ray binaries »Probe internal structure and populations

LIGO-G ZChristensen MG Astrophysical Sources of Gravitational Waves l Bursts »Neutron star birth, tumbling and/or convection »Correlations with electro-magnetic observations l Stochastic background »Big bang & early universe »Background of gravitational wave bursts Burst and inspiral results See talk by S. Fairhurst. In this session, GW.1

LIGO-G ZChristensen MG Outline l Overview of gravitational-wave (GW) searches by the LIGO Scientific Collaboration: »Stochastic GW Background »Continuous Wave GW l This talk: hit some of the highlights. l No GW identified so far, but LIGO is now setting meaningful and physically important upper limits.

LIGO-G Z Stochastic Gravitational-Wave Backgrounds

LIGO-G ZChristensen MG Stochastic GW Backgrounds l Astrophysical backgrounds due to unresolved individual sources »E.g.: BH mergers, inspirals, supernovae WMAP 3-year data l Cosmological background from Big Bang (analog of CMB) GW spectrum due to cosmological BH ringdowns (Regimbau & Fotopoulos)

LIGO-G ZChristensen MG Signals from the Early Universe cosmic gravitational-wave background ( s) cosmic microwave background ( s) Cosmological GWs in the LIGO band (100 Hz) today were produced s after the big bang. Their detection would be very interesting!

LIGO-G ZChristensen MG Log(f [Hz]) Log (0)(0) Inflation Slow-roll Cosmic strings Pre-big bang model EW or SUSY Phase transition Cyclic model CMB Pulsar Timing BB Nucleo- synthesis LIGO S4: Ω 0 < 6.5x10 -5 (new) Initial LIGO, 1 yr data Expected Sensitivity ~ 4x10 -6 Advanced LIGO, 1 yr data Expected Sensitivity ~ 1x10 -9 LIGO S1: Ω 0 < 44 PRD (2004) LIGO S3: Ω 0 < 8.4x10 -4 PRL (2005) Predictions and Limits H 0 = 72 km/s/Mpc

LIGO-G ZChristensen MG Stochastic Searches Analysis of data from the first 4 science runs is complete. Publications (S1 & S3): 1. B. Abbott et al. (LSC), Analysis of First LIGO Science Data for Stochastic Gravitational Waves. Phys. Rev. D 69, (2004) 2. B. Abbott et al. (LSC), Upper Limits on a Stochastic Background of Gravitational Waves. Phys. Rev. Lett. 95, (2005) Science run 4: This talk. (Paper in preparation.)

LIGO-G ZChristensen MG Procedure detector noise spectra Test  GW (f) =   (f/100Hz) . l Most sensitivity from Hz band (LHO-LLO). “Overlap Reduction Function” (determined by network geometry) frequency (Hz)  (f) Search: cross-correlate data streams x 1, x 2. Optimal statistic Y for all-sky search is:

LIGO-G ZChristensen MG Technical Challenges l Example: »Correlations at harmonics of 1 Hz. »Due to GPS timing system. »Lose ~3% of the total bandwidth (1/32 Hz resolution). H1-L1 coherence frequency (Hz) Simulated pulsar line l Digging deep into instrumental noise looking for small correlations. l Need to be mindful of possible non-GW correlations »common environment (H1-H2) »common equipment (e.g. DAQ – could affect any IFO pair!)

LIGO-G ZChristensen MG Analysis Details l Study H1-L1, H2-L1 (not co- located H1-H2). l Analyze data in 192-sec chunks. »Estimate power spectrum, theoretical variance  i using neighboring segments (avoids bias). »Drop segments when  i changes quickly (non-stationary). »Construct weighted average of Y i. l Drop frequency bins showing instrumental correlations »Harmonics of 1 Hz, bins with pulsar injections. l Remaining Y i values Gaussian distributed. i-1 ii+1i+2 YiYi ii

LIGO-G ZChristensen MG Combined Results l Weighted average of H1-L1 and H2-L1 measurements (new in S4). »Weights: 1/variance(f). » Ω  σ Ω = (-0.8  4.3) × »h = 72 km/s/Mpc » Hz (includes 99% of inverse variance) l Bayesian 90% UL: »Use S3 posterior distribution for S4 prior. »Marginalized over calibration uncertainty with Gaussian prior (5% for L1, 8% for H1 and H2). Ω 90% = 6.5 × 10 -5

LIGO-G ZChristensen MG Other   (f) Expected from S5 Bayesian 90% upper limits Measured (S3, S4)

LIGO-G ZChristensen MG Signal Recovery hardware injections (moving mirrors) Demonstrated ability to estimate  GW accurately: theoretical errors software injections standard errors (10 trials)

LIGO-G ZChristensen MG Other Activities l Directional search (“GW Radiometer”) »Use cross-correlation kernel optimized for unpolarized point source »Ballmer, gr-qc/ l Search at LIGO Free Spectral Range (37.5 kHz). l Suppressing correlated noise for H1-H2 pair. »Fotopoulos [To appear in CQG / GWDAW Proc.] l S4 L1-ALLEGRO (bar detector) search at Hz »Results forthcoming -> See J. Whelan’s talk in session GW.4.

LIGO-G ZChristensen MG Radiometer: Proof-of-Principle l Analysis of a simulated point source at the position of the Virgo galaxy cluster (12.5h,12.7  ). »simulated H1-L1 data

LIGO-G ZChristensen MG Continuous waves Credit: Dana Berry/NASACredit: M. Kramer Accreting Neutron Stars Wobbling Neutron Stars Bumpy Neutron Star

LIGO-G ZChristensen MG Continuous wave searches: pulsars l Rotating stars produce GWs if they have asymmetries or if they wobble. l Observed spindown can be used to set strong indirect upper limits on GWs. l There are many known pulsars (rotating stars!) that produce GWs in the LIGO frequency band (40 Hz-2 kHz). »Targeted searches for 73 known (radio and x-ray) systems in S5: isolated pulsars, binary systems, pulsars in globular clusters… l There are likely to be many non-pulsar rotating stars producing GWs. »All-sky, unbiased searches; wide-area searches. l GWs (or lack thereof) can be used to measure (or set up upper limits on) the ellipticities of the stars. l Search for a sine wave, modulated by Earth’s motion, and possibly spinning down: easy, but computationally expensive! Crab pulsar (Chandra Telescope)

LIGO-G ZChristensen MG LSC periodic searches Finely tuned searches over a narrow parameter space (known pulsars, parameter estimation) Coherent searches: Bayesian time-domain (TDS) Isolated and binary pulsars Markov chain Monte Carlo F-statistic frequency domain Isolated all-sky over wide frequency range Binary x-ray with some unknown orbital parameters Directed for known x-ray sources Incoherent searches: Hough transform Stack-slide Powerflux Deep searches over a broad parameter space Fast, robust, wide-parameter searches

LIGO-G ZChristensen MG Search for waves from known pulsars S2 Results reported in Physical Review Letters (2005) l Pulsars for which the ephemeris is known from EM observations l In S2 »28 known isolated pulsars targeted l Spindown limit »assumes all loss of angular momentum radiated to GW

LIGO-G ZChristensen MG Coherent search for unknown isolated sources l Entire sky search l Fully coherent matched filtering l 160 to Hz l df/dt < 4 x Hz/s l 10 hours of S2 data; computationally intensive l 95% confidence upper limit on the GW strain amplitude range from 6.6x to 1.0x across the frequency band l More hierarchical searches to come with more sensitive data l Scorpius X-1 l Fully coherent matched filtering l 464 to 484 Hz, 604 to 624 Hz l df/dt < 1 x Hz/s l 6 hours of S2 data l 95% confidence upper limit on the GW strain amplitude range from 1.7x to 1.3x across the two 20 Hz wide frequency bands l See gr-qc/ See talk by R. Prix in session GW.4

LIGO-G ZChristensen MG Early S5 run l Used parameters provided by Pulsar Group, Jodrell Bank Observatory for S3 – checked for validity over the period of S5 l Analysed from 4 Nov - 31 Dec 2005 using data from the three LIGO observatories - Hanford 4k and 2k (H1, H2) and Livingston 4k (L1) Frequency (Hz) h/Hz 1/2

LIGO-G ZChristensen MG Search for waves from known pulsars l 32 known isolated, 41 in binaries, 29 in globular clusters Lowest ellipticity upper limit: PSR J (f gw = 405.6Hz, r = 0.25kpc) ellipticity = 4.0x10 -7 Crab pulsar

LIGO-G ZChristensen MG Progression of pulsars upper limits Crab pulsar Upper limits on GWs from targeted pulsars:

LIGO-G ZChristensen MG Preliminary S5 Results, 95% upper limits h0h0 Pulsars 1x < h 0 < 5x x < h 0 < 1x h 0 > 1x EllipticityPulsars  < 1x x10 -6 <  < 5x x10 -6 <  < 1x  > 1x All values assume I = kgm 2 and no error on distance Lowest h 0 upper limit: PSR J (f gw = Hz, r = 1.6kpc) h 0 = 1.6x Lowest ellipticity upper limit: PSR J (f gw = 405.6Hz, r = 0.25kpc)  = 4.0x10 -7

LIGO-G ZChristensen MG S5 Continues … l Results for first two months of S5 only. How will the rest of the run progress? l Will have more up-to-date pulsar timings for current pulsars and possibly more objects. l Should have amplitudes of < and ellipticities <10 -6 for many objects l Our most stringent ellipticities (4.0x10 -7 ) are starting to reach into the range of neutron star structures for some neutron-proton-electron models (B. Owen, PRL, 2005). l Crab pulsar is nearing the spin- down upper limit

LIGO-G ZChristensen MG l Matched-filtering for continuous GWs l All-sky, all-frequency search »computationally limited l Aiming at detection, not upper limits l Public outreach distributed computing To participate, sign up at

LIGO-G ZChristensen MG Public distributed computing project to look for isolated pulsars in LIGO/GEO data ~ 45 TFlops 24/7 Makes use of coherent F-statistic method S3 - no spindown No evidence of strong pulsar signals Outliers are consistent with instrumental artifacts or bad bands. None of the low significance remaining candidates showed up in follow-up on S4 data. S4 - one spindown parameter, up to f/fdot ~ 10,000 yr Using segment lenghts of 30 hours Analysis took ~ 6 months Currently in post-processing stage S5 - just started Faster more efficient application Estimated 6-12 months

LIGO-G ZChristensen MG

LIGO-G ZChristensen MG S5 incoherent searches preliminary l Place sky dependent upper limits by averaging power l Account for Doppler modulation in average l Also account for amplitude modulation See talks by A. Sintes in session GW.4

LIGO-G ZChristensen MG Conclusions l Analysis of LIGO data is in full swing, and results from LIGO searches from science runs 4, 5 are now appearing. »Significant improvements in interferometer sensitivity since S3. »In the process of accumulating 1 year of data (S5). l Stochastic search: further improvements »Latest result:  GW < 6.5x10 -5 (12 x better than S3). »Expect to surpass Big Bang nucleosynthesis limit in S5. »LLO-Allegro result at 900 Hz is forthcoming »Novel searches: directional, high-frequency, noise cancellation l Continuous-wave searches »Known pulsar searches are beginning to place interesting upper limits in S5 »All sky searches are under way and exploring large area of parameter space