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The Laser Interferometer Gravitational Observatory (LIGO) has recentlyreached the end of its fifth science run (S5), having collected more than ayear worth of data. Analysis of the data is still ongoing but a positivedetection of gravitational waves, while possible, is not realistically expectedfor most likely sources. This is particularly true for what concernsgravitational waves from known pulsars. In fact, even under the most optimistic(and not very realistic) assumption that all the pulsar's observed spin-down isdue to gravitational waves, the gravitational wave strain at earth from all theknown isolated pulsars (with the only notable exception of the Crab pulsar)would not be strong enough to be detectable by existing detectors. By August2006, LIGO had produced enough data for a coherent integration capable toextract signal from noise that was weaker than the one expected from the Crabpulsar's spin-down limit. No signal was detected, but beating the spin-downlimit is a considerable achievement for the LIGO Scientific Collaboration(LSC). It is customary to translate the upper limit on strain from a pulsarinto a more astrophysically significant upper limit on ellipticity. Once thespin-down limit has been beaten, it is possible to release the constraint thatall the spin-down is due to gravitational wave emission. A more complete modelwith diverse braking mechanisms can be used to set limits on severalastrophysical parameters of the pulsar. This paper shows possible values ofsuch parameters for the Crab pulsar given the current limit on gravitationalwaves from this neutron star.

Upper and lower limits on the Crab pulsar's astrophysical parameters set  from gravitational wave observations by LIGO: braking index and energy  considerations