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].
Highlights
We report results of an all-sky search for periodic gravitational waves with frequency between 50 and 510 Hz from isolated compact objects, e.g., neutron stars
The beauty of continuous signals is that, even if a candidate is not significant enough to be recognized as a real signal after a first semicoherent search, it is still possible to improve its significance to the level necessary to claim a detection after a series of follow-up searches
We set frequentist upper limits on the maximum gravitational wave amplitude consistent with this null result in 0.5 Hz bands: h900%ðfÞ. h900%ðfÞ is the GW amplitude such that 90% of a population of signals with parameter values in our search range would have been detected by our search, i.e., would have survived the last 2F threshold at 15.0 at stage 4
Summary
The beauty of continuous signals is that, even if a candidate is not significant enough to be recognized as a real signal after a first semicoherent search, it is still possible to improve its significance to the level necessary to claim a detection after a series of follow-up searches. [1] and [2] detail a semicoherent search plus a three-stage follow-up of order 100 candidates; Refs. [3] and [4] detail a semicoherent search plus a series of vetoes and a final coherent follow-up of over 1000 candidates. The search detailed here follows up 16 million candidates and is the first large-scale hierarchical search ever done. A semicoherent search is performed, and the top ranking cells in parameter space ( referred to as “candidates”) are marked and are searched in the stage. In the first three stages, the thresholds that define the top ranking cells are low enough that many false alarms are expected over the large parameter space that was searched. V, we summarize the main findings and discuss prospects for this type of search
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