The sensitivity of Advanced Virgo during O3, its improvement over time and
a comparison with the sensitivity during O2.
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The top plot shows the Advanced Virgo
sensitivity to gravitational waves versus frequency. Here, the sensitivity
is given in terms of amplitude spectral density of the interferometer output
noise, expressed in units of gravitational wave strain. Thus the lower the
curve, the more sensitive the detector in that frequency range.
In the bottom plots the sensitivity is given
in terms of the 'BNS range', i.e. the average distance at which the merger of
a Binary Neutron Star system (BNS) gives a matched filter signal-to-noise
ratio (SNR) of 8 in Advanced Virgo with the current sensitivity; the distance
is averaged over all the possible sky localisations and binary orientations.
Each neutron star in the binary system is assumed to have a mass equal to 1.4
solar masses. The BNS range is given in units of megaparsecs (millions of
parsecs, in short Mpc): a parsec is equal to 3.26 light-years. The larger the
BNS range, the more sensitive the detector.
The bottom left plot refers to the 2nd
observation period (O2, August 2017 for Virgo); the bottom-right plot refers
to the 3rd observation period (O3, April 2019-March 2020). The steady
improvements are shown by the lowering of the sensitivity curve in the top
plot and the corresponding increase of the BNS range in the bottom plots.