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Authors: P.Astone, M.Bassan, P.Bonifazi, K.M.Borkowski, R.J.Budzyński, A.Chincarini, E.Coccia, S.D'Antonio, M.Di Paolo Emilio, V.Fafone, S.Frasca, S.Foffa, G.Giordano, P.Jaranowski, W.Kondracki, A.Królak, M.Maggiore, A.Marini, Y.Minenkov, I.Modena, G.Modestino, A.Moleti, G.V.Pallottino, C.Palomba, R.Parodi, M.Pietka, G.Pizzella, H.J.Pletsch, L.Quintieri, F.Ricci, A.Rocchi, F.Ronga, R.Sturani, R.Terenzi, R.Vaccarone, M.Visco

Date: 1 Sep 2008

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 $<-1.463\times10ˆ{-8}; 0>$ 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 $3.4 \times 10ˆ{-23}$ to $1.3 \times 10ˆ{-22}$. We have attempted a statistical verification of the hypotheses leading to our conclusions. We estimate that our upper limit is accurate to within 18%.

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