Search of the Orion spur for continuous gravitational waves using a loosely coherent algorithm on data from LIGO interferometers

We report results of a wideband search for periodic gravitational waves from isolated neutron stars within the Orion spur towards both the inner and outer regions of our Galaxy. As gravitational waves interact very weakly with matter, the search is unimpeded by dust and concentrations of stars. One search disk (A) is 6.87\ifmmode^\circ\else\textdegree\fi{} in diameter and centered on $2{0}^{\mathrm{h}}1{0}^{\mathrm{m}}54.7{1}^{\mathrm{s}}+33\ifmmode^\circ\else\textdegree\fi{}3{3}^{\ensuremath{'}}25.2{9}^{\ensuremath{'}\ensuremath{'}}$, and the other (B) is 7.45\ifmmode^\circ\else\textdegree\fi{} in diameter and centered on ${8}^{\mathrm{h}}3{5}^{\mathrm{m}}20.6{1}^{\mathrm{s}}\ensuremath{-}46\ifmmode^\circ\else\textdegree\fi{}4{9}^{\ensuremath{'}}25.15{1}^{\ensuremath{'}\ensuremath{'}}$. We explored the frequency range of 50--1500 Hz and frequency derivative from 0 to $\ensuremath{-}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{Hz}/\mathrm{s}$. A multistage, loosely coherent search program allowed probing more deeply than before in these two regions, while increasing coherence length with every stage. Rigorous follow-up parameters have winnowed the initial coincidence set to only 70 candidates, to be examined manually. None of those 70 candidates proved to be consistent with an isolated gravitational-wave emitter, and 95% confidence level upper limits were placed on continuous-wave strain amplitudes. Near 169 Hz we achieve our lowest 95% C.L. upper limit on the worst-case linearly polarized strain amplitude ${h}_{0}$ of $6.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}$, while at the high end of our frequency range we achieve a worst-case upper limit of $3.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}$ for all polarizations and sky locations.

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