First results from the S1 Science Run Searches for Burst...
Transcript of First results from the S1 Science Run Searches for Burst...
G. Gonzalez, Lousiana State University 1LIGO-G030142-00-Z
First results from the S1 Science RunSearches for Burst and Inspiral
Gravitational Waves
Gabriela GonzálezLouisiana State University
On behalf of the LIGO Scientific Collaborationhttp://www.ligo.org
Moriond 2003Gravitational Waves and Experimental Gravity
Les Arcs , France (March 22-29, 2003)
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LIGO Sensitivity for S1LIGO Sensitivity for S1
LIGOS1 Run-----------“First
Upper Limit Run”
!Aug – Sept 2002!17 days
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InIn--Lock Data Summary from S1Lock Data Summary from S1Red lines: integrated up time Green bands (w/ black borders): epochs of lock
•August 23 – September 9, 2002: 408 hrs (17 days).•H1 (4km): duty cycle 57.6% ; Total Locked time: 235 hrs •H2 (2km): duty cycle 73.1% ; Total Locked time: 298 hrs •L1 (4km): duty cycle 41.7% ; Total Locked time: 170 hrs
•Double coincidences: •L1 && H1 : duty cycle 28.4%; Total coincident time: 116 hrs •L1 && H2 : duty cycle 32.1%; Total coincident time: 131 hrs •H1 && H2 : duty cycle 46.1%; Total coincident time: 188 hrs
•Triple Coincidence: L1, H1, and H2 : duty cycle 23.4% ;•Total coincident time: 95.7 hrs
H1: 235 hrs H2: 298 hrs L1: 170 hrs 3X: 95.7 hrs
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Non-Stationarity and Epoch Veto
Strategy:Veto certain epochs based on excessive BLRMS noise in some bandsCut: 10σ in 320-400Hz ; 3σ cut in 400-600, 600-1600, 1600-3000 Hz; σ=68-percentile
Band-Limited RMS(BLRMS)
(6 min segments)Non-stationary noiseHere shown for S1:Hanford-4km (H1)
Cut for 600-1600 Hz bandCut for 1600-3000 Hz band
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Big Glitches in H1
Found by inspiral searchcode with SNR=10.4
These occurred ~4 timesper hour during S1
REFL_I channel (frequency noise or common mode length) has a very clear transient
Use glitchMon to generate veto triggers
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Veto Safety
Have to be sure there aren’t couplings between channels which would cause a real gravitational wave to veto itself !
Look at large injections
No sign of signal in H1:LSC-REFL_I for inspiral injections; some signs for bursts injections. Burst group does not use REFL_I veto.
Best veto channel for L1 (AS_I) was disallowed because there was a small coupling: neither burst or inpiral groups used any vetos for L1.
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Gravitational wave burst searchesBurst Working Group
Elements of the analysis:
• Identification of detector events» Event Trigger Generation and coincidence → observed number of events Nobs
• Estimation of expected contribution from background» Time shift analysis → expected number of background events Nb
• Estimation of efficiency» Simulations → efficiency as a function of signal amplitude ε(h0)
• Determination of live-time T» Triple-time subject to vetos
• Result: Event Rate = I(Nobs,Nb,p)/ε(h0)T» I(Nobs,Nb,p): Interval in expected number of foreground events (Feldman & Cousins)
with confidence p.We expect an upper limit, but this method allows a detection.
Have to be careful with: • Systematic error estimation and propagation
» Calibrations, background estimation, efficiency• Parameter tuning: all done in playground dataset.
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Burst Analysis Pipeline
Dataqualitycheck
Candidate Event TriggersLDAS
(LIGO Data Analysis System)Burst Analysis Algorithms
Diagnostics TriggersDMT
(Data Monitor Tool)Glitch Analysis Algorithms
GW/VetoanticoincidenceEvent Analysis Tools
IFO1events
Multi-IFO coincidence
and clustering
IFO 1Strain Data
IFO 1 Auxiliary dataFrom diagnostics channels
(non GW)
Interpretation:Quantify Upper Limit
Quantify Efficiency (via simulations)
IFO3events
IFO2eventsImplemented in LIGO Science run 1 (S1)
3 interferometers: LLO-4k LHO-4k LHO-2k
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TFCLUSTERS: An Event Trigger Generator
Amplitude Spectrogram• 360 seconds of data• 16384 Hz sample rate• 8 Hz resolution• 125 ms time slice• Rectangular window• No overlap Thresholded Spectrogram
• Fit each frequency bin to a Rice distribution• Determine 99% amplitude threshold for each
frequency• “Black pixels” exceed the threshold
Black Pixel Clusters• Find contiguous clusters greater than or equal to 5
pixels• Apply set of rules to group nearby clusters• Report cluster properties:
start time durationfrequency bandwidthsize power
A different search was done with the SLOPE algorithm
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Data Quality
• Most dramatic non-stationarity is removed by the epoch veto.
• Single-ifo vetoes would have made remaining data from L1, H1 yield histograms that are close to Gaussian.
• Declining to use single-ifo vetoesleaves some obvious non-Gaussian tails. Still, the overall event rates are not dramatically affected.
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Efficiency
! Use Gaussians and Sine Gaussians
!Fit smooth sigmoid curves to efficiency measured above threshold.
TFCLUSTERS
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Preliminary results
• Identification of detector events» Event Trigger Generation and coincidence TF clusters: 1.9/day
• Estimation of expected contribution from background» Time shift analysis
• Estimation of efficiency
» Simulations : with 50% efficiency, 1 msec, 1 10-17 Gaussian burst (optimal polarization, arrival direction) . Better for 554 Hz sine gaussians: 3 10-18
» Determination of live-time T : 35.5 hours
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• Able to exclude gravitational wave bursts of peak strength h above rate r
• Upper limit in strain compared to prior (cryogenic bar) results:
» S1: h < 5 x 10-17 - this result» IGEC 20001 : h < 1 x 10-17
» Astone et al.2 2001: h ~ 2 x 10-18
• Upper limit in rate constrained by observation time:
» S1: 17d - this result» IGEC - 90d (2X coinc.), 260d (3X coinc.)» Astone - 90d
Excluded Regionat 90% upper
limit confidence bound
1Int.J.Mod.Phys. D9 (2000) 2372Class.Quant.Grav. 19 (2002) 5449
Result:Rate-strength diagram
Preliminary
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Coalescing BinariesInspiral Sources Working Group
Three source targets:
Neutron star binaries (1-3 Msun)Neutron star search
completeBlack hole binaries (> 3 Msun)
Black hole search will be done in next science run, S2
MACHO binaries (0.5-1 Msun)MACHO search under way
11994 data, Allen et al., Phys.Rev.Lett. 83 (1999) 1498
S1:
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Optimal Filtering Using FFTs
•Transform data to frequency domain : •Calculate template in frequency domain : •Combine, weighting by power spectral density of noise:
•Then inverse Fourier transform gives you the filter outputat all times:
•Find maxima of over arrival time and phase•Characterize event by signal-to-noise ratio, ρ
)(~ fh)(~ fs
|)(|)(~)(~ *
fSfhfs
h
dfefS
fhfstz tfi
h
π2
0
*
|)(|)(~)(~
4)( ∫∞
=
|)(| tz
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Template Bank
•Calculatedbased on L1noise curve
•Templatesplaced formaximummismatchof δ = 0.03
2110 templatesSecond-orderpost-Newtonian
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“Chi-Squared Veto”
•Any large glitch in the data can lead to a large filter output•The essence of a “chirp” is that the signal power is distributed over frequencies in a particular way•Divide template into sub-bands and calculate a χ2-like quantity:
•Correct for large signals which fall between points in the template bank:
•We use p = 8 and make the cut α2 ≤ 5
∑=
−=p
ll ptztztr
1
22 /)()()(
( )ptrt /1)()( 2222 δρα +=
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Effect of Vetoeson Playground Data
Disallo
wed Deadtime = 0.3%
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Analysis PipelineL1 triggers
Epoch veto
H1 triggers
Epoch vetoREFL_I veto
L1 distance <20 kpc?
Seen in H1 with consistent time and
total mass?
Event candidatesSNR from L1 SNR from H1
Only L1operating
Bothoperating Only H1
operating
Discard
Yes No
Yes No
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Statistical Method
•Expected rate in Milky Way is very low !•Philosophy: concentrate on getting best upper limit⇒ Use all four categories of event candidates
»Yields 289 hours of observation time,vs. 116 hours of simultaneous L1+H1 operation
•Add together SNR distributions from each category•Use the “maximum-SNR statistic”
»Because it’s hard to know a priori where one should set a threshold»Useful since candidate events are so sharply peaked at low SNR»Yields a frequentist upper limit, R(90%) < 2.3 / ( ε T )
Efficiency of analysis pipeline above observed max SNR Observation time
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Population Monte Carlo
• Mass distribution derived from population synthesis models
• Spatial distribution out to 200kpc including Milky Way, LMC and SMC
• LMC and SMC contribute about 12% of a Milky Way equivalent Galaxy
• Signals injected into data stream and used to determine efficiency of pipeline to detection of BNS population
H1
L1
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Inspiral Search: preliminary result
•Use triggers from H 4km and L 4km interferometers: » T = 295.3 hours
» Max SNR observed: 15.9 An event seen in L1 only, with effective distance = 95 kpcThere are no event candidates in the coincidence category
» Monte Carlo simulation efficiency for SNR=15.9: ε = 35%
» 90% confidence limit = 2.3 / (ε T)
•Limit on binary neutron star coalescence rate (preliminary!):»R90% (Milky Way) < 2.3 / (0.35 x 295.3 hr) = 170 /yr
•Compare with:»26X lower than best published observational limit -- 40m prototype at Caltech:
R90% (Milky Way) < 4400 /yr» Many orders of magnitude higher than expected galactic rate: ~10-6 - 10-5 /yr
(Kalogera et al)
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S2 run began 14 February• Will last through 14
April• Sensitivity is ~10x
better than S1• Duration will be ~ 4x
longer• Prospects:
» Bursts: 4X lower glitch rate, tighter coincidence testsbetter tuning to sweet spot
» Inspirals: reach will exceed 1Mpc --includes Andromeda, M33!
LIGO Science Has Started !