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In this paper we present the results of a coherent narrow-band search forcontinuous gravitational-wave signals from the Crab and Vela pulsars conductedon Virgo VSR4 data. In order to take into account a possible small mismatchbetween the gravitational wave frequency and two times the star rotationfrequency, inferred from measurement of the electromagnetic pulse rate, a rangeof 0.02 Hz around two times the star rotational frequency has been searched forboth the pulsars. No evidence for a signal has been found and 95$\%$ confidencelevel upper limits have been computed both assuming polarization parameters arecompletely unknown and that they are known with some uncertainty, as derivedfrom X-ray observations of the pulsar wind torii. For Vela the upper limits arecomparable to the spin-down limit, computed assuming that all the observedspin-down is due to the emission of gravitational waves. For Crab the upperlimits are about a factor of two below the spin-down limit, and represent asignificant improvement with respect to past analysis. This is the first timethe spin-down limit is significantly overcome in a narrow-band search.

Narrow-band search of continuous gravitational-wave signals from Crab and Vela pulsars in Virgo VSR4 data