AURIGA: results from run1 

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The first cryogenic run (run1) of the Auriga detector begun in June 1997. The detector operated until November 1999 when a vacuum leakage inside the cryostat forced the warming up and the stopping of the detector.

Follow this link for a step-by-step description of the Auriga detector in run1.

 

In the chart below we show the duty cycle of Auriga during run1: the different colors refer to different amplitude thresholds, as indicated in the legend. Here the thresholds are given in terms of the amplitude of the Fourier transform of the gravitational signal and have units of Hz-1

   
click for a larger picture

 

The recorded data cover a fraction of about 80% of the total elapsed time. After removal of periods when a veto is applied (either by the experimenter due to operation on the apparatus, either by the data analysis due to the presence of not modeled noise) the duty cycle (ie the time periods when the detector is sensible) is just 30% of the total time when AURIGA was running.

A sample of the AURIGA sensitivity is shown here: the data show the behavior of the detector over 24 hours. The top plot shows the effective temperature, which is a measure of the detector's sensitivity: it remained around 1mK during the whole day except when experimenter activity, consisting on cryogenic maintenance, disturbed the detector, thus causing a loss in sensitivity recovered after a few hours. The bottom plot shows the sensitivity in the frequency domain: this is actually the typical plot one uses to quote the sensitivity of a gravitational wave detector. The sensitivity Shh is maximum at the mechanical resonances (911Hz and 929Hz). 

In numbers, the sensitivity during RUN1 was:

During RUN1 the detector worked at a bar thermodynamic temperature of 0.24K with a minimum of 0.06K. Actually, a lower temperature could have been reached easily but this has not become a goal since the performance of the detector (both in terms of duty cycle and sensitivity) would have not improved. The cryogenic maintenance consisted into a one-per-week refill of liquid helium into the internal dewar (operation lasting about 5 hours with no much effect on the detector output) and a one-per-day refill of liquid helium in the 1K pot (operation lasting about 1 hour but blinding the detector output for about 2-3 hours).

The detector data were analyzed in coincidence with the other gw detectors operating worldwide (named IGEC): this is essential in order to reduce the false alarm rate and thus increase the confidence in the detection. We refer you to see the IGEC website for more details.. 

Unfortunately, the sensitivity of the IGEC observatory in the years 1997-2000 was not enough to allow the detection of a gravitational wave. So, gravitational waves are still an elusive signal, never detected by any instrument.

The reasons for the AURIGA run2 are in the expected sensitivity (and bandwidth) improvement and thus increased detection probability.

For more details on the IGEC data we refer you to the following paper:
IGEC, Methods and results of the IGEC search for burst gravitational waves in the years1997-2000, Phys. Rev. D 68 (2003) 022001, also on astro-ph/0302482


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