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

TL;DR

This study conducted a focused search for continuous gravitational waves from Crab and Vela pulsars using Virgo VSR4 data, setting new upper limits that challenge previous constraints and surpass the spin-down limit for Crab.

Contribution

First narrow-band search to significantly exceed the spin-down limit for Crab pulsar, providing improved upper limits on gravitational wave emission from these pulsars.

Findings

No gravitational wave signals detected.

Upper limits for Vela are near the spin-down limit.

Crab upper limits are about twice below the spin-down limit.

Abstract

In this paper we present the results of a coherent narrow-band search for continuous gravitational-wave signals from the Crab and Vela pulsars conducted on Virgo VSR4 data. In order to take into account a possible small mismatch between the gravitational wave frequency and two times the star rotation frequency, inferred from measurement of the electromagnetic pulse rate, a range of 0.02 Hz around two times the star rotational frequency has been searched for both the pulsars. No evidence for a signal has been found and 95$\%$ confidence level upper limits have been computed both assuming polarization parameters are completely unknown and that they are known with some uncertainty, as derived from X-ray observations of the pulsar wind torii. For Vela the upper limits are comparable to the spin-down limit, computed assuming that all the observed spin-down is due to the emission of gravitational waves. For Crab the upper limits are about a factor of two below the spin-down limit, and represent a significant improvement with respect to past analysis. This is the first time the spin-down limit is significantly overcome in a narrow-band search.