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Present status
NAUTILUS has been operating in the current configuration
since March 2003, after a
hardware upgrade. It is operating at the thermodynamic temperature of
about 3.5 K. In January 2004, after a tune-up period, the apparatus has
reached its best sensitivity of h = 3 · 10−19 for
short conventional burst of GWs. Presently the overall sensitivity of
NAUTILUS (figure 1) is limited by the thermal noise of the detector,
better performances can be obtained cooling down the antenna to 100 mK
temperatures.
The duty cycle of the detector is higher than 90%, limited only by the
periodic cryogenic operations necessary to keep the apparatus low
temperature. The experiment shows constant performances and the data are
not effected by human activity. The data quality is constant all over the
week and no night-day dependence is observed.
Data collected are stored on a RAID system for further analysis such as
search for short GW bursts with coincidence technique among two or more
GW antennae, stochastic background and monochromatic signals.
NAUTILUS is part of the international network of
resonant-mass detectors (IGEC2) which includes ALLEGRO at the Louisiana
State University, Baton Rouge, AURIGA at the INFN Legnaro Laboratories and
EXPLORER at CERN.
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Figure 1: Experimental strain sensitivity of NAUTILUS (input
noise spectral amplitude in units of Hz-1/2).
The peak sensitivity is about 2 10-21 Hz-1/2.
The spectral
amplitude is better than 1 10-20 Hz-1/2 over a band
of about 35 Hz. The peak at 1001 Hz is a calibration reference signal
fed into the d.c. SQUID amplifier to monitor the gain of the electronics.
Figure 2: Detector
sensitivity to bursts versus time, averaged every
hour,
over 2005. The average
minimum detectable amplitude h of a GW burst of duration 1 ms is h
= 3 10-19.
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