Gravitational radiation and rotation of accreting neutron stars

Recent discoveries by the Rossi X-Ray Timing Explorer indicate that most of the rapidly accreting ((M) over dot 10(-11) M. yr(-1)) weakly magnetic (B << 10(11) G) neutron stars in the Galaxy are rotating at spin frequencies nu(s) greater than or similar to 250 Hz. Remarkably, they all rotate in a narrow range of frequencies (no more than a factor of 2, with many within 20% of 300 Hz). I suggest that these stars rotate fast enough so that, on average, the angular momentum added by accretion is lost to gravitational radiation. The strong nu(s)-dependence of the angular momentum loss rate from gravitational radiation then provides a natural reason for similar spin frequencies. Provided that the interior temperature has a large-scale asymmetry misaligned from the spin axis, then the temperature-sensitive electron captures in the deep crust can provide the quadrupole needed (similar to 10(-7) MR2) to reach this limiting situation at nu(s) approximate to 300 Hz. This quadrupole is only present during accretion and makes it difficult to form radio pulsars with nu(s) > (600-800) Hz by accreting at (M) over dot 10(-10) M. yr(-1). The gravity wave strength is h(c) similar to (0.5-1) x 10(-26) from many of these neutron stars and greater than 2 x 10(-26) for Sco X-l. Prior knowledge of the position, spin frequency, and orbital periods will allow for deep searches for these periodic signals with gravitational wave interferometers (LIGO, VIRGO, and the "dual-recycled" GEO 600 detector), and experimenters need to take such sources into account. Sco X-l will most likely be detected first.