S. Frasca

A method for detection of known sources of continuous gravitational wave signals in non-stationary data

A method for searching continuous gravitational wave signals from isolated neutron stars whose position, frequency and frequency evolution are known is described in this paper. This method is applied to data of interferometric detectors such as Virgo. The method is based on the use of 5-vectors, which are the Fourier components of the signal and data at five frequencies around the source intrinsic frequency. The main characteristics of the method are its simplicity and the strong reduction of the computing time needed for the analysis and in particular for all the simulation procedures. We also introduce here the concept of coherence to state the reliability of a detection.

Adaptive Hough transform for the search of periodic sources

Real data produced by gravitational wave detectors are affected by non-stationarities which must be properly weighted in order to reduce their effect. In the incoherent step of the hierarchical method for the periodic sources search, based on the Hough transform, two kinds of non-stationarities must be taken into account: one connected to non-stationary disturbances and another, with a period of one sidereal day, due to the rotation of the Earth, which changes the orientation of the detector and therefore the signal amplitude. In this paper, we describe the adaptive Hough transform in which these two issues are suitably treated. We discuss its statistical properties and some implementative details.

Evaluation of sensitivity and computing power for the Virgo hierarchical search for periodic sources

In this paper we present the hierarchical search for periodic gravitational sources that we propose for the data analysis of the Virgo and Explorer and Nautilus resonant gravitational antennae. All the equations that can be used to tune the algorithm are presented.

Method for narrow-band search of continuous gravitational wave signals

Targeted searches of continuous waves from spinning neutron stars normally assume that the frequency of the gravitational wave signal is at a given known ratio with respect to the rotational frequency of the source, e.g. twice for an asymmetric neutron star rotating around a principal axis of inertia. In fact this assumption may well be invalid if, for instance, the gravitational wave signal is due to a solid core rotating at a slightly different rate with respect to the star crust. In this paper we present a method for {it narrow-band} searches of continuous gravitational wave signals from known pulsars in the data of interferometric detectors. This method assumes source position is known to high accuracy, while a small frequency and spin-down range around the electromagnetic-inferred values is explored. Barycentric and spin-down corrections are done with an efficient time-domain procedure. Sensitivity and computational efficiency estimates are given and results of tests done using simulated data are also discussed.

Detection of periodic gravitational wave sources by Hough transform in the frequency and spin down plane

In the hierarchical search for periodic sources of gravitational waves, the candidate selection, in the incoherent step, can be performed with Hough transform procedures. In this paper we analyze the problem of sensitivity loss due to discretization of the parameters space vs computing cost, comparing the properties of the sky Hough procedure with those of a new frequency Hough, which is based on a transformation from the time - observed frequency plane to the source frequency - spin down plane. Results on simulated peak maps suggest various advantages in favor of the use of the frequency Hough. The ones which show up to really make the difference are 1) the possibility to enhance the frequency resolution without relevantly affecting the computing cost. This reduces the digitization effects; 2) the excess of candidates due to local disturbances in some places of the sky map. They do not affect the new analysis because each map is constructed for only one position in the sky. Pacs. numbers: 04.80Nn,07.05Kf,97.60Jd 1.