ligo-g040276-00-z results from ligo’s second science run: a search for continuous gravitational...
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LIGO-G040276-00-Z
Results from LIGO’s second science run: a search for continuous gravitational waves Michael LandryLIGO Hanford ObservatoryCalifornia Institute of Technology
on behalf of the LIGO Scientific Collaborationhttp://www.ligo.org
CAP CongressJune 16, 2004Winnipeg, Canada
Photo credit: NASA/CXC/SAO
Landry - CAP Congress, 16 June 2004 2LIGO-G040276-00-Z
Talk overview
• Laser Interferometer Gravitational Wave Observatory (LIGO) overview» The what and how of gravitational radiation
• Search for continuous waves (CW)» Source model
» Time-domain Analysis method– Limit our search (for the analysis presented here, only)to gravitational
waves from a triaxial neutron star emitted at twice its rotational frequency, 2*frot
– Signal would be frequency modulated by relative motion of detector and source, plus amplitude modulated by the motion of the antenna pattern of the detector
» Validation by hardware injection of fake pulsars
» Results
Landry - CAP Congress, 16 June 2004 3LIGO-G040276-00-Z
• Gravitational Waves = “Ripples in space-time”
• Perturbation propagation similar to light (obeys same wave equation!)» Propagation speed = c
» Two transverse polarizations - quadrupolar: + and x
What are Gravitational Waves?
Example:
Ring of test masses
responding to wave
propagating along z
Amplitude parameterized by (tiny) dimensionless strain h: L ~ h(t) x L
Landry - CAP Congress, 16 June 2004 4LIGO-G040276-00-Z
• Compact binary inspiral: “chirps”» NS-NS waveforms are well described» BH-BH need better waveforms
• Supernovae / GRBs: “bursts” » burst signals in coincidence with signals in
electromagnetic radiation / neutrinos» all-sky untriggered searches too
• Cosmological Signal: “stochastic background”
• Pulsars in our galaxy: “periodic”» search for observed neutron stars (this talk)
» all-sky search (computing challenge)
What makes Gravitational Waves?
Landry - CAP Congress, 16 June 2004 5LIGO-G040276-00-Z
Gravitational Wave Detection
• Suspended Interferometers
» Suspended mirrors in “free-fall”
» Michelson IFO is
“natural” GW detector
» Broad-band response
(~50 Hz to few kHz)
» Waveform information
(e.g., chirp reconstruction)
Landry - CAP Congress, 16 June 2004 6LIGO-G040276-00-Z
LIGO Observatories
Livingston (L1=4km)
Hanford (H1=4km, H2=2km)Observation of nearly simultaneous signals 3000 km apart rules out terrestrial artifacts
Landry - CAP Congress, 16 June 2004 7LIGO-G040276-00-Z
Strain noise comparison: science runs
Initial LIGO Design
S1 (L1)1st Science Runend Sept. 2002
17 daysS2 (L1)2nd Science Runend Apr. 2003
59 days
S3 (H1)3rd Science Runend Jan. 2004
70 days
With GEO:Phys Rev D 69, 082004 (2004)
Landry - CAP Congress, 16 June 2004 8LIGO-G040276-00-Z
S2 expectations
• Coloured spectra: average amplitude detectable in time T (1% false alarm, 10% false dismissal rates):
0 11.4 ( ) /hh S f T• Solid black lines: LIGO and
GEO science requirement, for T=1 year
• Circles: upper limits on gravitational waves from known EM pulsars, obtained from measured spindown (if spindown is entirely attributable to GW emission)
• Only known, isolated targets shown here
LIGO
GEO
Landry - CAP Congress, 16 June 2004 9LIGO-G040276-00-Z
CW source model
• F+ and Fx : strain antenna patterns of the detector to plus and cross polarization, bounded between -1 and 1
• Here, signal parameters are:» h0 – amplitude of the gravitational wave signal
» – polarization angle of signal» – inclination angle of source with respect to line of sight
» 0 – initial phase of pulsar; (t=0), and (t)= t0
2
0 0
1 cost F t; h cos ( ) F t; h cos sin ( )
2h t t
so that the expected demodulated signal is then:
00 cosh;tF2
cos1h;tF4
1;ty 0k
20kk
ii eie a
The expected signal has the form:
Heterodyne, i.e. multiply by: ( )i te
Here, a = a(h0, , , 0), a vector of the signal parameters.
PRD 58 063001 (1998)
Landry - CAP Congress, 16 June 2004 10LIGO-G040276-00-Z
Compute likelihoods
Analysis summary
k2
k k
1p B a
B ynn
k
Heterodyne, lowpass,
average, calibrate: Bk
Model: yk
Compute pdf for h0
Compute upper limit “h95”
aBpap B|ap kk
Raw Data
uniform priorson h0(>0), cos
h95
1
0strain
Landry - CAP Congress, 16 June 2004 11LIGO-G040276-00-Z
Injection of fake pulsars during S2
Parameters of P1:P1: Constant Intrinsic FrequencySky position: 0.3766960246 latitude (radians)
5.1471621319 longitude (radians)Signal parameters are defined at SSB GPS time733967667.026112310 which corresponds to a wavefront passing:LHO at GPS time 733967713.000000000LLO at GPS time 733967713.007730720In the SSB the signal is defined byf = 1279.123456789012 Hzfdot = 0phi = 0psi = 0iota = /2h0 = 2.0 x 10-21
Two simulated pulsars, P1 and P2, were injected in the LIGO
interferometers for a period of ~ 12 hours during S2
Landry - CAP Congress, 16 June 2004 12LIGO-G040276-00-Z
Preliminary
upper limits for 28 known pulsars
h0 UL range Pulsar
10-23-10-22 J1939+2134, B1951+32, J1913+1011, B0531+21
10-24-10-23
B0021-72C, B0021-72D, B0021-72F, B0021-72G, B0021-72L, B0021-72M, B0021-72N, J0711-6830, B1820-30A, J1730-2304, J1721-2457, J1629-6902, J1910-5959E, J2124-3358, J1910-5959C, J0030+0451, J1024-0719,
J1910-5959D, J2322+2057, B1516+02A, J1748-2446C, J1910-5959B, J1744-1134, B1821-24
Blue: pulsar timing checked by Michael Kramer, Jodrell Bank
Purple: pulsar timing from ATNF catalogue
Landry - CAP Congress, 16 June 2004 13LIGO-G040276-00-Z
Equatorial Ellipticity
• Results on h0 can be interpreted as upper limit on equatorial ellipticity
• Ellipticity scales with the difference in radii along x and y axes
xx yy
zz
I I
I
40
2 24 gw zz
c r h
G f I
• Distance r to pulsar is known, Izz is assumed to be typical, 1045 g cm2
Landry - CAP Congress, 16 June 2004 14LIGO-G040276-00-Z
Preliminary ellipticitylimits for 28 known pulsars
UL range Pulsar
10-2-10-1 B1951+32, J1913+1011, B0531+21
10-3-10-2 -
10-4-10-3 B1821-24, B0021-72D, J1910-5959D, B1516+02A, J1748-2446C, J1910-5959B
10-5-10-4
J1939+2134, B0021-72C, B0021-72F, B0021-72L, B0021-72G, B0021-72M, B0021-72N, B1820-30A, J0711-6830, J1730-2304,
J1721-2457, J1629-6902, J1910-5959E, J1910-5959C, J2322+2057
10-6-10-5 J1024-0719, J2124-3358, J0030+0451, J1744-1134
Blue: timing checked by Jodrell Bank
Purple: ATNF catalogue
Landry - CAP Congress, 16 June 2004 15LIGO-G040276-00-Z
Summary and future outlook
• LIGO» Good progress towards design sensitivity
» Initial results from first two data runs
• S2 analyses» Time-domain analysis of 28 known pulsars complete
» Broadband frequency-domain all-sky search underway
» ScoX-1 LMXB frequency-domain search near completion
» Incoherent searches reaching maturity, preliminary S2 results produced
• S3 run» Time-domain analysis on more pulsars, including binaries
» Improved sensitivity LIGO/GEO run
» Oct 31 03 – Jan 9 04
» Approaching spindown limit for Crab pulsar
Landry - CAP Congress, 16 June 2004 16LIGO-G040276-00-Z
Why look for Gravitational Radiation?
• Because it’s there! (presumably)
• Test General Relativity:» Quadrupolar radiation? Travels at speed of light?
» Unique probe of strong-field gravity
• Gain different view of Universe:» Sources cannot be obscured by dust / stellar envelopes
» Detectable sources some of the most interesting,
least understood in the Universe
» Opens up entirely new non-electromagnetic spectrum
Landry - CAP Congress, 16 June 2004 17LIGO-G040276-00-Z
Strong Indirect Evidence: Orbital Decay
Neutron Binary System – Hulse & Taylor
PSR 1913 + 16 -- Timing of pulsars
17 / sec
Neutron Binary System• separated by 106 miles• m1 = 1.4m; m2 = 1.36m; = 0.617
Prediction from general relativity• spiral in by 3 mm/orbit• rate of change orbital period
~ 8 hr
Emission of gravitational waves
Landry - CAP Congress, 16 June 2004 18LIGO-G040276-00-Z
What Limits the Sensitivityof the Interferometers?
• Seismic noise & vibration limit at low frequencies
• Atomic vibrations (Thermal Noise) inside components limit at mid frequencies
• Quantum nature of light (Shot Noise) limits at high frequencies
• Myriad details of the lasers, electronics, etc., can make problems above these levels
Best design sensitivity:
~ 3 x 10-23 Hz-1/2 @ 150 Hz
Landry - CAP Congress, 16 June 2004 19LIGO-G040276-00-Z
CW sources
• Nearly-monochromatic continuous sources of gravitational waves include neutron stars with:
» spin precession at ~frot
» excited oscillatory modes such as the r-mode at 4/3 * frot
» non-axisymmetric distortion of crystalline structure, at 2frot
• Limit our search to gravitational waves from a triaxial neutron star emitted at twice its rotational frequency (for the analysis presented here, only)
• Signal would be frequency modulated by relative motion of detector and source, plus amplitude modulated by the motion of the antenna pattern of the detector
Landry - CAP Congress, 16 June 2004 20LIGO-G040276-00-Z
Source model
• F+ and Fx : strain antenna patterns of the detector to plus and cross polarization, bounded between -1 and 1
• Here, signal parameters are:» h0 – amplitude of the gravitational wave signal
» – polarization angle of signal» – inclination angle of source with respect to line of sight
» 0 – initial phase of pulsar; (t=0), and (t)= t0
2
0 0
1 cost F t; h cos ( ) F t; h cos sin ( )
2h t t
so that the expected demodulated signal is then:
00 cosh;tF2
cos1h;tF4
1;ty 0k
20kk
ii eie a
The expected signal has the form:
Heterodyne, i.e. multiply by: ( )i te
Here, a = a(h0, , , 0), a vector of the signal parameters.
PRD 58 063001 (1998)
Landry - CAP Congress, 16 June 2004 21LIGO-G040276-00-Z
Compute likelihoods
Analysis summary
k2
k k
1p B a
B ynn
k
Heterodyne, lowpass,
average, calibrate: Bk
Model: yk
Compute pdf for h0
Compute upper limit “h95”
aBpap B|ap kk
Raw Data
uniform priorson h0(>0), cos
h95
1
0strain