Activities of the LIGO Scientific Collaboration’s Continuous Wave Group

1. Activities of the LIGO Scientific Collaboration’s Continuous Wave Group Xavier Siemens for the LSCUniversity of Wisconsin -- Milwaukee

2. The CW Group http://www.lsc-group.phys.uwm.edu/pulgroup/ • For the first science run (S1): set upper limit on a single known pulsar (J1939+2134) using two independent methods (Frequency domain, optimal for large parameter space searches, and Time domain, optimal for targeted searches). • For the second and third science runs (S2, S3) the group has been involved in a variety of activities, which include the coherent methods used for S1 as well as incoherent methods… (NASA/CXC/SAO)

3. The Signal • We search for gravitational waves generated by neutron star with deviations from axisymmetry. For example, isolated neutron star parameters: • Frequencyf of source in Solar System Barycenter (SSB) • Rate of change of frequency df/dt in SSB • Sky coordinates(, ) of source • Strain amplitudeh0 • Spin-axis inclination • Phase, Polarization,  Phase evolution Amplitude modulation

4. The Searches Coherent searches: • Time-domain: - Targeted - Markov Chain Monte Carlo - Frequency-domain: - Isolated - Binary, Sco X-1 Searches over narrow parameter space Searches over wide parameter space Ultimately, would like to combine these two in a hierarchical scheme Incoherent searches: • Hough transform - Stack-Slide - Powerflux Excess power searches

5. Time domain searches Targeted search: • Targeting radio pulsars with rotational frequencies > 25 Hz at known locations with phase inferred from radio data • Upper limits defined in terms of Bayesian posterior probability distributions for the pulsar parameters • For S2 looked at 28 known isolated pulsars (gr-qc/0410007) ; best strain upper limits were at the level of a few x 10^-24 • For S3 will soon extend search to known neutron stars in binaries and will benefit from much improved sensitivity. TALK:Matt Pitkin Markov Chain Monte Carlo: • Computational Bayesian technique • MCMC can both estimate parameters and generate summary statistics (pdfs, cross-correlations, etc) • Initial Applications: searches in restricted parameter space and SN1987a (location known but other parameters not known) POSTER: John Veitch

6. Isolated Search • The detection statistic is the so-called F-Statistic, which is the log of the likelihood maximized over the unknown parameters [Jaranowski, Krolak and Schutz, PRD58 063001; Jaranowski and Krolak, PRD59 063003] • For S2 we are doing a wide band (160 Hz-460 Hz) all-sky search for the 10 most sensitive hours of data for both the Livingston and the Hanford (4km) interferometers. • We are combining the results of the two searches incoherently using a coincidence scheme and setting upper limits on 1Hz bands using a frequentist scheme based on the loudest coincident event. • For S2 we expect upper limits in the strain to be in the range of several x 10^-23 for quiet bands and around 10^-22 for noisy bands TALK: Yousuke Itoh

7. Binary Search • S2 analysis: upper-limit on Sco X-1 using a one-stage coherent search over short integration time (Tobs = 6 hr). • Also uses the F-statistic and a coincidence scheme, and sets a frequentist upper limit based on the loudest coincident event TALK:Chris Messenger • In the future: search Sco X-1 and other known LMXBs (~20 targets) with a hierarchical scheme: • Coherent analysis over short data chunks • Add incoherently (stack-slide) chunks POSTER: Virginia Re (Artist’s impression: NASA)

8. Stack-Slide • An incoherent search method that stacks and slides normalised power to search for periodic sources. • Starting point is a set of Short Fourier Transforms (SFTs). Then we: • Stack the (normalised) power • Slide to correct for Doppler shifts and spin-down • Sum and search for significant peaks • Can be used as part of a hierarchical search with coherent & incoherent stages

9. Hough transform • An incoherent search method conceptually similar to stack-slide • Select a threshold for the normalised power and label frequency bins with a 1 if the threshold is exceeded or 0 otherwise • Slide to correct for Doppler shifts and spin-down • Compute the number count for a given frequency bin by summing the 0’s and 1’s • For S2: All-sky search using entire data set with one spin-down parameter for the Livingston and Hanford 4km interferometers. Set an frequentist upper limit using software injections • Can be used as part of a hierarchical search with coherent & incoherent stages TALK: Badri Krishnan

10. Powerflux • An incoherent search method, similar to stack-slide and Hough • The main differences are that for this search the sum of the power for each frequency bin is • weighted with the antenna pattern functions of the interferometer, and, • weighted by the noise, which is estimated from neighboring frequency bins. The weighting scheme is chosen to minimize the variance for the estimator of the gravitational wave amplitude • Can be used as part of a hierarchical search with coherent & incoherent stages

11. Einstein@home • Like SETI@home, but for LIGO/GEO data. When computer idle, screensaver does ‘real work’. • American Physical Society (APS) will publicize as part of World Year of Physics (WYP) 2005 activities, and will help with web site & graphics. • Use infrastructure/help from SETI@home developers for the distributed computing parts. • Goal: pulsar searches using ~1 million clients. Support for Windows, Mac OSX, Linux clients. • Why? • From our own clusters we can get ~ thousands of CPUs. From Einstein@home hope to get order(s) of magnitude more at low cost. • Great outreach and science education tool. It runs the coherent isolated F-statistic code. Still testing but… Read all about it and sign up at : http://einstein.phys.uwm.edu

12. Upcoming talks/posters Talks: 10:18 Badri Krishnan: The Hough transform search for gravitational waves from pulsars 10:55 Chris Messenger: Bounding the strength of gravitational radiation from SCO-X1 11:13 Mathew Pitkin: Searching for gravitational waves from known milisecond pulsars 11:31 Yousuke Itoh: All-sky broad band search for continuous waves using LIGO Posters: Reinhard Prix: Matched filtering properties of all-sky searches for continuous gravitational waves Virginia Re: Stack-slide hierarchical searches for gravitational waves from accreting neutron stars John Veitch: A time-domain MCMC search technique for gravitational radiation of uncertain frequency from a targeted neutron star.