Seismic glitchness at Sos Enattos site: impact on intermediate black hole binaries detection efficiency

Abstract

Third-generation gravitational wave observatories will extend the lower frequency limit of the observation band toward 2 Hz, where new sources of gravitational waves, in particular intermediate-mass black holes (IMBH), will be detected. In this frequency region, seismic noise will play an important role, mainly through the so-called Newtonian noise, i.e., the gravity-mediated coupling between ground motion and test mass displacements. The signal lifetime of such sources in the detector is of the order of tens of seconds. In order to determine whether a candidate site to host the Einstein Telescope observatory is particularly suitable to observe such sources, it is necessary to estimate the probability distributions that, in the characteristic time scale of the signal, the sensitivity of the detector is not perturbed by Newtonian noise. In this paper, a first analysis is presented, focused on the Sos Enattos site (Sardinia, Italy), a candidate to host the Einstein Telescope. Starting from a long data set of seismic noise, this distribution is evaluated considering both the presently designed triangular ET configuration and also the classical ”L” configuration.

A lower limit for Newtonian-noise models of the Einstein Telescope

“…The comparison indicates an inconsistency between the two results. The NN estimates for Sardinia published in[20] are shown as blue markers, which lie well above the median of the lower bound. This is to be expected when the model of the total NN predicts a significant contribution from seismic compression of the medium.…”

“…Modeling of NN has made significant progress over the past years driven by the development of a NN cancellation system as part of an upgrade of the Advanced Virgo detector and for the estimation of NN as part of the evaluation of ET candidate sites [17,19,20,18]. Models have been improving by incorporating an increasing amount of observed properties of seismic fields and by including more details in numerical simulations about the local geology and topography.…”

“…Test-mass location Coupling factor Spherical (as used in [20,18]) NN in the small-cavern approximation can be significantly smaller than 4π/3 depending on cavern shape and test-mass location. This however is only relevant for the lower seismic NN bound that relies entirely on the cavern-wall contribution.…”

“…This does not mean that these estimates are necessarily accurate. In fact, a very simple uniform geology was assumed to calculate the NN estimate in [20], and a conservative assumption was made concerning the mode content of the underground seismic field. However, despite the simplifying assumptions (or in this case rather because of the simplifying assumptions), the NN estimates are consistent with the lower bound.…”

Optimizing the third generation of gravitational-wave observatories for Galactic astrophysics

“…The azimuths are defined as counterclockwise relative to due east. The coordinates for Hanford, Livingston, Virgo, and Kagra are taken from LIGO Scientific Collaboration (2018); those for India are taken from Bilby (Ashton et al 2019); those for Einstein Telescope are taken from the locations of recent seismic studies (Bader et al 2021;Allocca et al 2021); and those for Cosmic Explorer are assumed to be the same as in Borhanian (2021) few kilohertz, which is the frequency range of interest for many Galactic science targets. In the case when one detector is significantly more sensitive than the others in a network, the overall network antenna pattern will be dominated by the single, most sensitive detector.…”