All-sky search of NAUTILUS data

TL;DR

This paper reports a comprehensive all-sky search for continuous gravitational waves from neutron stars using NAUTILUS data, setting upper limits on wave amplitude without detecting any signals.

Contribution

It introduces a coherent analysis method over half a year of data, establishing new upper limits on gravitational wave amplitudes in the targeted frequency band.

Findings

No gravitational-wave signals detected.

Upper limits on wave amplitude range from 3.4e-23 to 1.3e-22.

Analysis confirms the sensitivity and reliability of the search method.

Abstract

A search for periodic gravitational-wave signals from isolated neutron stars in the NAUTILUS detector data is presented. We have analyzed half a year of data over the frequency band $<922.2; 923.2>$ Hz, the spindown range $<-1.463\times10^{-8}; 0>$ Hz/s and over the entire sky. We have divided the data into 2 day stretches and we have analyzed each stretch coherently using matched filtering. We have imposed a low threshold for the optimal detection statistic to obtain a set of candidates that are further examined for coincidences among various data stretches. For some candidates we have also investigated the change of the signal-to-noise ratio when we increase the observation time from two to four days. Our analysis has not revealed any gravitational-wave signals. Therefore we have imposed upper limits on the dimensionless gravitational-wave amplitude over the parameter space that we have searched. Depending on frequency, our upper limit ranges from $3.4 \times 10^{-23}$ to $1.3 \times 10^{-22}$. We have attempted a statistical verification of the hypotheses leading to our conclusions. We estimate that our upper limit is accurate to within 18%.