Hierarchical follow-up of sub-threshold candidates of an all-sky Einstein@Home search for continuous gravitational waves on LIGO sixth science run data

TL;DR

This paper presents a deep all-sky search for continuous gravitational waves from neutron stars using a hierarchical approach supported by Einstein@Home, setting the most stringent upper limits to date on wave amplitudes.

Contribution

It introduces a new hierarchical multi-stage method for gravitational wave searches, enabling deeper probing of sub-threshold candidates with extensive computing support.

Findings

No candidates consistent with gravitational wave emission were found.

Set the most constraining upper limits on gravitational wave strain amplitudes to date.

Placed upper limits on neutron star ellipticity at 300 Hz less than 6x10^-7.

Abstract

We report results of an all-sky search for periodic gravitational waves with frequency between 50 and 510 Hz from isolated compact objects, i.e. neutron stars. A new hierarchical multi-stage approach is taken, supported by the computing power of the Einstein@Home project, allowing to probe more deeply than ever before. 16 million sub-threshold candidates from the initial search [LVC,arXiv:1606.09619] are followed up in three stages. None of those candidates is consistent with an isolated gravitational wave emitter, and 90% confidence level upper limits are placed on the amplitudes of continuous waves from the target population. Between 170.5 and 171 Hz we set the most constraining 90% confidence upper limit on the strain amplitude h0 at 4.3x10-25 , while at the high end of our frequency range we achieve an upper limit of 7.6x10-25. These are the most constraining all-sky upper limits to date and constrain the ellipticity of rotating compact objects emitting at 300 Hz at a distance D to less than 6x10-7 [d/100pc].