Discrete resampling for semi-targeted continuous waves search in the Virgo interferometer

摘要

Pulsars, and more in general rotating neutron stars, are expected to permanently emit gravitational waves, mainly at the double of the rotational frequency. This type of signals requires long observation times in order to distinguish the peak at the emission frequency in the antenna signal spectrum from the incoherent noise floor. The energy of the signal spectral peak is smeared by the Doppler phase modulation due to the antenna motion with respect to the source and by the phase shift induced by the source rotational frequency slowing because of energy losses due to emissions. The correction to these effects requires, in general, the knowledge of the source emission frequency, of the spin-down and of the source sky position. We propose a very effective method to compensate for Doppler and spin-down. The technique is particularly useful for semi-targeted searches. It consists in a fast resampling of the antenna signal aimed to synchronize with a large accuracy the detector time with the source one. The applied correction is valid for all the emission frequencies, fixed a fractional spin-down. If the emission frequency and the spin-down are unknown, one can perform the peak energy recovery assuming different possible value of the fractional spin-down and search for a peak coming out from the spectral floor.