1. Paris, July 17, 2009 RECENT RESULTS OF THE IGEC2 COLLABORATION SEARCH FOR GRAVITATIONAL WAVE BURST Massimo Visco on behalf of the IGEC2 Collaboration

2. 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

3. Paris, July 17, 2009 IGEC2 International Gravitational Events Collaboration ALLEGRO - AURIGA - ROG (EXPLORER-NAUTILUS)

4. Paris, July 17, 2009 A 4-ANTENNAE OBSERVATORY The four antennas see an identical signal, independently of the source and time

5. Paris, July 17, 2009 SENSITIVITY OF IGEC DETECTORS The best sensitivity is reached around 900 Hz

6. Paris, July 17, 2009 First experience using the data of 5 bar detectors: ALLEGRO, AURIGA, EXPLORER, NAUTILUS and NIOBE. In four years 29 days of four-fold coincidences- 178 days of three-fold coincidences - 713 days of two-fold coincidences After the last upgrades the resonant detectors have resumed the operations at different times: EXPLORER in 2000, AURIGA in 2003, NAUTILUS in 2003, ALLEGRO in 2004. NIOBE no longer in operation. IGEC 1 – search for burst signals – 1997÷2000

7. 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 16 th, 2005 to April 14 th, 2007 – Based on three and four-fold coincidences. No detection ­Future analysis - on April 14 th 2007 ALLEGRO ceased data taking. Since then the three European detectors gathered new data yet to be analyzed. IGEC2 – search for burst signals 2005- …

8. Paris, July 17, 2009 The events selected by each group using filter matched to  signals are characterized by Fourier amplitude H and arrival time t i : h(t)= H ·  (t- t i ) The data are exchanged after adding a “secret time shift” to arrival time t i. 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 The analysis is based on time coincidence among candidate events selected in each detector.

9. 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 2 nd period: Nov 16 th, 2005 – Apr 14 th, 2007

10. Paris, July 17, 2009 OPERATION TIME – NOV 16 th 2005–APR 14 th, 2007 515 days Number of detectors in coincidence Exclusive observation time Analyzed time 00 d−−− 11.6 d−−− 231.0 d−−− 3188.8 d 482.4 d 4293.5 d 57% of time with 4 detectors 94% of time useful for analysis Full coverage

11. Paris, July 17, 2009 AMPLITUDE OF THE EXCHANGED DATA in terms of Fourier amplitude H SNR > 4.5 for AURIGA SNR > 4.0 for EXPLORER and NAUTILUS H>1.1· 10 -21 Hz -1 for ALLEGRO

12. Paris, July 17, 2009 EVENTS AMPLITUDE DISTRIBUTIONS SNR > 4.5 for AURIGA SNR > 4.0 for EXPLORER and NAUTILUS H>1.1· 10 -21 Hz -1 for ALLEGRO

13. Paris, July 17, 2009 DATA QUALITY: DISTRIBUTIONS OF EVENTS Few events/day with SNR>7 Few very large events (SNR>30) on the whole period

14. 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 PARAMETER The R factor must be maximized. It depends on shape and energy of the different signals

15. Paris, July 17, 2009 TIME UNCERTAINTY The 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)=h 0 sin(2  f 0 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

16. Paris, July 17, 2009 TIME 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 coincidences 60 ms for European - United States detectors coincidences

17. Paris, July 17, 2009 Example of threefold coincidence EX-NA-AU SNR 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

18. Paris, July 17, 2009 SAMPLE DETECTION EFFICIENCY AU-EX-NA An efficiency of about 50% is reached with different signals at amplitudes hrss of (7·10 -20 - 5·10 -19 ) Efficiency Damped Sinusoid Galactic Center w=60ms

19. Paris, July 17, 2009 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 one But this does not effect our analysis

20. Paris, July 17, 2009 BACKGROUND EVALUATION A precise evaluation of errors, including systematic effects, was made possible by calculating false alarms with different time shifts. ConfigurationP(N=0)P(N=1)P(N=2)P(N=3) AL AU EX 0.998049 ± 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 NA 0.997840 ± 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 NA 0.998299 ± 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 NA 0.998325 ± 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 NA 0.998402 ± 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

21. Paris, July 17, 2009 FINAL 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. Configuration Operation time (days) Accidental number Coincidences number AL AU EX361.84.29±0.013 AL AU NA390.65.15±0.015 AL EX NA308.710.23±0.018 AU EX NA308.72.34±0.014 AL AU EX NA293.5(7.66±0.01)·10 -3 0

22. Paris, July 17, 2009 CONCLUSION 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.