Paris, July 17, 2009

RECENT RESULTS OF THE IGEC2 COLLABORATION RECENT RESULTS OF THE IGEC2 COLLABORATION SEARCH FOR GRAVITATIONAL WAVE BURSTSEARCH FOR GRAVITATIONAL WAVE BURST

Massimo Visco

on behalf of the IGEC2 Collaboration

Paris, July 17, 2009

• IGEC2 collaboration detectors

• IGEC2 activity during past years

• Data analysis methods

• Results of second data exchange of IGEC2: 2005-2007

• Data quality

• Analysis parameters optimization

• Results

• Conclusion and perspectives of the IGEC2 observatory

OUTLINE OF THE TALK OUTLINE OF THE TALK

Paris, July 17, 2009

IGEC2IGEC2

International Gravitational Events Collaboration

ALLEGRO - AURIGA - ROG (EXPLORER-NAUTILUS)

Paris, July 17, 2009

SENSITIVITY OF IGEC DETECTORSSENSITIVITY OF IGEC DETECTORS

•The best sensitivity is reached around 900 Hz

Paris, July 17, 2009

First analysis- from May to November 2005 when no

other observatory was operating. Based on three-fold

coincidences. No detection

Second analysis – from November 16th, 2005 to April

14th, 2007 – Based on three and four-fold coincidences.

No detection

Future analysis - on April 14th 2007 ALLEGRO ceased

data taking. Since then the three European detectors

gathered new data yet to be analyzed.

IGEC2 – search for burst signals 2005- …IGEC2 – search for burst signals 2005- …

Paris, July 17, 2009

• The events selected by each group using filter matched to signals are characterized by Fourier amplitude H and arrival time ti:

h(t)= H · (t- ti)

• The data are exchanged after adding a “secret time shift” to arrival time ti.

• A statistical distribution of the accidental time coincidences number is calculated using lists of candidate events obtained from the original ones adding many different time shifts.

• The analysis parameters (search threshold, coincidence window) are fixed “a priori” using the accidental coincidences analysis.

• Finally the groups exchange the secret times and the search for real

coincidences is performed.

DATA ANALYSIS METHODS DATA ANALYSIS METHODS The analysis is based on time coincidence among candidate events selected

in each detector.

Paris, July 17, 2009

• The analysis is based on a composite search, an OR of five different configurations: four and three-fold coincidences.

• To our knowledge this is the longest reported period of fourfold coincidence observation.

• The background was fixed at 1 event/century equally divided in the four configurations (0.2 event/century each).

• The data of 2007 became available later, they were analyzed using slightly different SNR thresholds.

IGEC 2 IGEC 2 22ndnd period: Nov 16 period: Nov 16thth, 2005 – Apr 14, 2005 – Apr 14thth, 2007, 2007

Paris, July 17, 2009

OPERATION TIME – OPERATION TIME – NOV 16NOV 16thth 2005–APR 14 2005–APR 14thth, 2007, 2007

515 days

Number of detectors in coincidence

Exclusiveobservation

timeAnalyzed time

0 0 d −−−

1 1.6 d −−−

2 31.0 d −−−

3 188.8 d482.4 d

4 293.5 d57% of time with 4 detectors

94% of time useful for analysis

Full coverage

Paris, July 17, 2009

EVENTS AMPLITUDE DISTRIBUTIONSEVENTS AMPLITUDE DISTRIBUTIONS

• SNR > 4.5 for AURIGA• SNR > 4.0 for EXPLORER and NAUTILUS• H > 1.1· 10-21 Hz-1 for ALLEGRO

Paris, July 17, 2009

DATA QUALITY: DISTRIBUTIONS OF EVENTSDATA QUALITY: DISTRIBUTIONS OF EVENTS

•Few events/day with SNR>7

•Few very large events (SNR>30) on the whole period

Paris, July 17, 2009

Analysis target are: • a false alarm low enough to select significant candidate events (1 event /century)• a reasonable detection efficiency for the searched signals (to be evaluated by software injections)

The parameters to be tuned are:• events SNR selection threshold• time coincidence windows

TUNING OF ANALYSIS PARAMETERTUNING OF ANALYSIS PARAMETER

alarmfalse

sig

N

EfficiencyNR

The R factor must be maximized. It depends on shape and energy

of the different signals

Paris, July 17, 2009

TIME UNCERTAINTYTIME UNCERTAINTYThe time windows were chosen large enough to include not only -like signals.

By software injection we tested the response also to damped sinusoids:h(t)=h0 sin(2 f0 t) e-t/ (t)

Statistical uncertainty: 95% of coincidences retrieved with a 25 ms windows

Systematic biases: the time bias is within 15 ms for <30 ms

Paris, July 17, 2009

TIME COINCIDENCE WINDOWTIME COINCIDENCE WINDOW

The maximum light travel time between detectors is:

2 ms for European detectors 20 ms European - United States detectors

The chosen time windows were:

40 ms for European detectors coincidences60 ms for European - United States detectors coincidences

Paris, July 17, 2009

Example of threefold coincidence EX-NA-AU

SNR SELECTIONSNR SELECTION• Once the time windows were fixed, we tuned the SNR thresholds to the required false alarm.

• We used different thresholds for each configuration and for each detector: equal for ALLEGRO, EXPLORER, NAUTILUS and higher by a factor 1.5-1.8 for AURIGA

Selected threshold configuration to have

0.2 event/century

Paris, July 17, 2009

BACKGROUND EVALUATION BACKGROUND EVALUATION

• In order to highlight possible data correlation the background analysis was implemented using more than one time shift.

• We used 13 different time shifts from 0.12s to 3s. • For each shift value we performed about 12 million of time

lags.

Averaged false alarms with their

standard deviations

The experimental false alarm error is larger

than the statistical oneBut this does not effect

our analysis

Paris, July 17, 2009

BACKGROUND EVALUATION BACKGROUND EVALUATION

• A precise evaluation of errors, including systematic effects, was made possible by calculating false alarms with different time shifts.

Configuration P(N=0) P(N=1) P(N=2) P(N=3)

AL AU EX0.998049 ± 0.000046 (1.949±0.046) · 10-3 (2.02±0.49) · 10-6 <8·10-8

0.998049 ± 0.000047 (1.949± 0.047) · 10-3 (1.904± 0.091) · 10-6 (1.241±0.088) ·10-9

AL AU NA0.997840 ± 0.000102 (2.15±0.10) · 10-3 (2.23±0.35) · 10-6 <8· 10-8

0.997840 ± 0.000102 (2.19± 0.10) · 10-3 (2.34±0.22) · 10-6 (1.69±0.24) · 10-9

AL EX NA0.998299 ± 0.000057 (1.700±0.057) · 10-3 (1.49± 0.29) · 10-6 <8· 10-8

0.998299 ± 0.000057 (1.700±0.057) · 10-3 (1.448±0.097) · 10-6 (8.24±0.83) · 10-10

AU EX NA0.998325 ± 0.000034 (1.674±0.034) · 10-3 (1.51±0.26) · 10-6 <8 · 10-8

0.998325 ± 0.000034 (1.674±0.034) · 10-3 (1.40±0.057) · 10-6 (7.85±0.48) · 10-10

AL AU EX NA0.998402 ± 0.000024 (1.598±0.024) · 10-3 (2.1±3.9) · 10-7 <9 ·10-8

0.998403 ± 0.000024 (1.595±0.023) ·10-3 (1.275±0.038) · 10-6 (6.79±0.30) · 10-10

• Each first row contains experimental occurrence probability from time shifts

• Each second row contains Poisson probability using the experimental mean

• The two values are fully compatible

Paris, July 17, 2009

FINAL RESULTSFINAL RESULTS

NO COINCIDENCE given a false alarm of 1/century

• The collaboration established a priori to make available the coincidences found with no selection, at high false alarm, for further analysis with other experiments.

ConfigurationOperation time

(days) Accidental

numberCoincidences

number

AL AU EX 361.8 4.29±0.01 3

AL AU NA 390.6 5.15±0.01 5

AL EX NA 308.7 10.23±0.01 8

AU EX NA 308.7 2.34±0.01 4

AL AU EX NA 293.5 (7.66±0.01)·10-3 0

Paris, July 17, 2009

CONCLUSIONCONCLUSION

• Nowadays interferometric detectors have reached a sensitivity at least one order of magnitude better than bar detectors and no further upgrade is scheduled.

•The IGEC observatory is presently capable of unattended, low cost operations with high duty cycle and low false alarm.

•Interferometric detectors have scheduled up-grades in the near future and an important increase in sensitivity is expected.

• At present the role of bar detectors is to guarantee the coverage for rare but powerful events with specific attention to the periods not covered by interferometers.