| Abstract: | We present direct upper limits on continuous gravitational wave emission from
the Vela pulsar using data from the Virgo detector’s second science run. These
upper limits have been obtained using three independent methods that assume the
gravitational wave emission follows the radio timing. Two of the methods
produce frequentist upper limits for an assumed known orientation of the star’s
spin axis and value of the wave polarization angle of, respectively,
$1.9ee{-24}$ and $2.2ee{-24}$, with 95% confidence. The third method, under
the same hypothesis, produces a Bayesian upper limit of $2.1ee{-24}$, with 95%
degree of belief. These limits are below the indirect {it spin-down limit} of
$3.3ee{-24}$ for the Vela pulsar, defined by the energy loss rate inferred
from observed decrease in Vela’s spin frequency, and correspond to a limit on
the star ellipticity of $sim 10^{-3}$. Slightly less stringent results, but
still well below the spin-down limit, are obtained assuming the star’s spin
axis inclination and the wave polarization angles are unknown. |
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