Burst search results from C7 and WSR runs . F.Cavalier, LAL-Orsay for the Virgo burst group. LSC-Virgo meeting Baton Rouge, 17/03/2007. Outline. The data set: C7 run WSR data Comparison with LIGO The Data Quality Flags DQ Category 1 DQ Category 2
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for the Virgo burst group
Baton Rouge, 17/03/2007
Virgo sensitivity similar to H2 sensitivity starting from ~ 900 Hz
(at the level of S4 sensitivity above ~ 500 Hz)
Key numbers : ~ 10-22/sqrt(Hz) @ 500 Hz and ~ 2x10-22/sqrt(Hz) @ 1 kHz
Effect of DQ flags application on noise rejection
Estimation of the event rate at a fixed hrss for target signals
Cut @ 90% : rate ~3.8 mHz
Cut @ 50% : rate ~1.2 mHz
rate ~ 0.25 Hz <=> 50% detected events if
Mean ~ 0.25 Hz
s ~ 0.05 Hz
WSR1 event distribution is dominated by similar events characterized by a strong oscillation of the control signals (longitudinal and angular). This kind of events is easily vetoed using any optical channel. It appears that these events are present at a smaller rate in C7.
During C7, the events are not uniformly distributed in time but appear by bunch lasting few seconds. The spectrogram shows that the events are broadband contrary to most of events caused by external disturbance. This broadband spectral signature gave hints to identify the BoBs as local increases of the noise level due to an increase of the coupling factor between the frequency noise (which is dominant at high frequency for C7 and the dark fringe.
The presence of a peak around t=27s in the correlogram of the burst events gave strong indication that the residual angular motion of the mirrors could play a role.
Indeed 27s corresponds to the frequency of a mechanical resonance between the Filter 7 and the marionette of the
suspension that, if excited may induce mirror angular degrees of freedom excitation.
It has been noticed that when such events dominate the distribution, the rate clearly follows the weather conditions, confirming the explanation of the event source. In the latest WSRs, the correlation between weather conditions and trigger rate is still present but has decreased.
Clearly, for the last veto which is based on the same photodiode as the gravitational wave signal, the use of hardware injection is mandatory to insure that the decoupling between phase and quadrature signals is effective.
But dead time due to DQ + veto is huge: 24.6%
Time distribution of the triggers SNR
Correlogram after all cuts: rather flat
Only 0.5 and 0.6 Hz resonances remain
and upper limit vary
At high frequency the
efficiency is worsen due
to the ITF noise increase
hrss @ eff=50%
1.1 2.4 10-20/√(Hz)
PRELIMINARYUpper limits on the event rate
(Frequentist CL assuming no background)
UL on the rate of events/day: