Abstract
We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 20-500 Hz range from neutron stars with ellipticity of 1e-8. This frequency region is particularly hard to probe because of the quadratic dependence of signal strength on frequency. The search employs the Falcon analysis pipeline on LIGO O2 public data. Compared to previous Falcon analyses the coherence length has been quadrupled, with a corresponding increase in sensitivity. This enables us to search for small ellipticity neutron stars in this low frequency region up to 44 pc away. The frequency derivative range is up to 3e-13 Hz/s easily accommodating sources with ellipticities of 1e-7 and a corresponding factor of 10 increase in reach. New outliers are found, many of which we are unable to associate with any instrumental cause.
Highlights
Detectable continuous gravitational waves are expected from fast rotating neutron stars if they present some sort of nonaxially symmetric deformation
We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 20–500 Hz range from neutron stars with ellipticity of ≈10−8
Just as in our previous papers [2,3], we have a number of interesting outliers
Summary
Detectable continuous gravitational waves are expected from fast rotating neutron stars if they present some sort of nonaxially symmetric deformation. In [6] the authors conclude that the most likely detection will happen in the frequency range covered by this search Their conclusions are somewhat pessimistic due in part to a number of simplifying assumptions. In [7] the authors favor higher frequencies and higher spin-down rates than we have searched This is due to the focus of paper [7] on “probing” neutron stars at a given ellipticity, without taking into account the frequency evolution of neutron stars. This approach is reasonable, because finding a high-ellipticity source would be very interesting, and it is important to know which parameter space to search. The improvements to the Falcon pipeline [11,12,13,14] in computing speed allow 2 days coherence length for the first analysis stage, a factor of 4 longer than used in our previous searches [2,3]
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