Directed search for continuous gravitational-wave signals from the Galactic Center in the Advanced LIGO second observing run

In this work we present the results of a search for continuous gravitational waves from the Galactic Center using LIGO O2 data. The search uses the band-sampled-data directed search pipeline, which performs a semicoherent wide-parameter-space search, exploiting the robustness of the FrequencyHough transform algorithm. The search targets signals emitted by isolated asymmetric spinning neutron stars, located within 25--150 parsecs from the Galactic Center. The frequencies covered in this search range between 10 and 710 Hz with a spin-down range from $\ensuremath{-}1.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ to $3.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}\text{ }\text{ }\mathrm{Hz}/\mathrm{s}$. No continuous wave signal has been detected and upper limits on the gravitational wave amplitude are presented. The most stringent upper limit at 95% confidence level, for the Livingston detector, is $\ensuremath{\sim}1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}25}$ at frequencies near 160 Hz. To date, this is the most sensitive directed search for continuous gravitational-wave signals from the Galactic Center and the first search of this kind using the LIGO second observing run.