Search for continuous gravitational waves from the pulsar J0435+3233

We perform a search for continuous gravitational waves from J0435+3233 using LIGO O4a public data. J0435+3233 is unique among millisecond pulsars as it exhibits an exceptionally large spin-down and marks the first pulsar observed to date with a spin-down larger than 10-12 Hz/s in the sub 10 ms spin period range, making it a potentially strong source of continuous gravitational waves. We target signals at exactly twice the rotation frequency, a narrow band around this frequency, and also signals corresponding to r-modes. Our results are consistent with a non-detection. Our most stringent upper limit on the intrinsic gravitational wave amplitude at 95% confidence is h 0=5.8 times10-27. With an estimated source distance of 1.2 kpc this upper limit constraints the ellipticity to be smaller greater than 1.6 times10-8. If the observed spin-down is all intrinsic, this is the first source for which the spin-down upper limit is beaten by over an order of magnitude and the ellipticity is constrained to the physically very interesting range of the low 10-8 region.