New searches for continuous gravitational waves from seven fast pulsars

TL;DR

This paper reports on targeted searches for continuous gravitational waves from seven pulsars using Advanced LIGO data, setting upper limits on gravitational wave amplitudes and constraining neutron star properties.

Contribution

First searches for continuous gravitational waves from these seven pulsars, exploring emission at twice the rotation frequency and nearby bands, with new upper limits and ellipticity constraints.

Findings

No gravitational wave signals detected.

Upper limits close to the spin-down limit for one pulsar.

Ellipticity constraints within neutron star crust support range.

Abstract

We conduct searches for continuous gravitational waves from seven pulsars, that have not been targeted in continuous wave searches of Advanced LIGO data before. We target emission at exactly twice the rotation frequency of the pulsars and in a small band around such frequency. The former search assumes that the gravitational wave quadrupole is changing phase-locked with the rotation of the pulsar. The search over a range of frequencies allows for differential rotation between the component emitting the radio signal and the component emitting the gravitational waves, for example the crust or magnetosphere versus the core. Timing solutions derived from the Arecibo 327-MHz Drift-Scan Pulsar Survey (AO327) observations are used. No evidence of a signal is found and upper limits are set on the gravitational wave amplitude. For one of the pulsars we probe gravitational wave intrinsic amplitudes just a factor of 3.8 higher than the spin-down limit, assuming a canonical moment of inertia of $10^{38}$ kg m$^2$. Our tightest ellipticity constraint is $1.5 \times 10^{-8}$, which is a value well within the range of what a neutron star crust could support.