Download Searching for Gravitational Waves from Binary Black Hole MACHOs

Activities of the LIGO Scientific
Collaboration’s Continuous Wave
Group
Xavier Siemens
for the LSC
University of Wisconsin -- Milwaukee
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The CW Group
http://www.lsc-group.phys.uwm.edu/pulgroup/
(NASA/CXC/SAO)
•
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…
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The Signal
• We search for gravitational waves generated by neutron
star with deviations from axisymmetry.
For example, isolated neutron star parameters:
• Frequency f of source in Solar System
Barycenter (SSB)
• Rate of change of frequency df/dt in SSB
• Sky coordinates (, ) of source
• Strain amplitude h0
• Spin-axis inclination 
• Phase, Polarization , 
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Phase evolution
Amplitude modulation
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The Searches
Coherent searches:
Searches over
narrow
parameter space
- Time-domain:
- Targeted
- Markov Chain Monte Carlo
- Frequency-domain:
- Isolated
- Binary, Sco X-1
Searches over
wide parameter
space
Ultimately,
would like to
combine these
two in a
hierarchical
scheme
Incoherent searches:
- Hough transform
Excess
power
searches
- Stack-Slide
- Powerflux
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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
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Markov Chain Monte Carlo:
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Computational Bayesian technique
MCMC can both estimate parameters and generate summary statistics (pdfs, crosscorrelations, etc)
Initial Applications: searches in restricted parameter space and SN1987a (location
known but other parameters not known)
POSTER: John Veitch
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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
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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
(Artist’s impression: NASA)
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
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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
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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
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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
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Einstein@home
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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
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Upcoming talks/posters
Talks:
10:18
10:55
11:13
11:31
Badri Krishnan: The Hough transform search for gravitational waves from pulsars
Chris Messenger: Bounding the strength of gravitational radiation from SCO-X1
Mathew Pitkin: Searching for gravitational waves from known milisecond pulsars
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.
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