Up to now there has been no search for gravitational waves from the $r$-modes of neutron stars in spite of the theoretical interest in the subject. Several oddities of $r$-modes must be addressed to obtain an observational result: The gravitational radiation field is dominated by the mass current (gravitomagnetic) quadrupole rather than the usual mass quadrupole, and the consequent difference in polarization affects detection statistics and parameter estimation. To astrophysically interpret a detection or upper limit it is necessary to convert the gravitational-wave amplitude to an $r$-mode amplitude. Also, it is helpful to know indirect limits on gravitational-wave emission to gauge the interest of various searches. Here I address these issues, thereby providing the ingredients to adapt broad-band searches for continuous gravitational waves to obtain $r$-mode results. I also show that searches of existing data can already have interesting sensitivities to $r$-modes.

• Received 11 June 2010

DOI:https://doi.org/10.1103/PhysRevD.82.104002