# title
Diving below the Spin-down Limit: Constraints on Gravitational Waves from the Energetic Young Pulsar PSR J0537-6910

# abstract
<jats:title>Abstract</jats:title>                <jats:p>We present a search for quasi-monochromatic gravitational-wave signals from the young, energetic X-ray pulsar PSR J05376910 using data from the second and third observing runs of LIGO and Virgo. The search is enabled by a contemporaneous timing ephemeris obtained using Neutron star Interior Composition Explorer (NICER) data. The NICER ephemeris has also been extended through 2020 October and includes three new glitches. PSR J05376910 has the largest spin-down luminosity of any pulsar and exhibits fRequent and strong glitches. Analyses of its long-term and interglitch braking indices provide intriguing evidence that its spin-down energy budget may include gravitational-wave emission from a time-varying mass quadrupole moment. Its 62 Hz rotation frequency also puts its possible gravitational-wave emission in the most sensitive band of the LIGO/Virgo detectors. Motivated by these considerations, we search for gravitational-wave emission at both once and twice the rotation frequency from PSR J05376910. We find no signal, however, and report upper limits. Assuming a rigidly rotating triaxial star, our constraints reach below the gravitational-wave spin-down limit for this star for the first time by more than a factor of 2 and limit gravitational waves from the <jats:italic>l</jats:italic> = <jats:italic>m</jats:italic> = 2 mode to account for less than 14% of the spin-down energy budget. The fiducial equatorial ellipticity is constrained to less than about 3 10<jats:sup>5</jats:sup>, which is the third best constraint for any young pulsar.</jats:p>

# authorList[]
Abbott, R., Abbott, T. D., Abraham, S., Acernese, F., Ackley, K., Adams, A., ... Guillot, S.