Gravitational Radiation and Rotation of Accreting Neutron Stars

Abstract

Recent discoveries by the Rossi X-Ray Timing Explorer indicate that most of\nthe rapidly accreting and weakly magnetic neutron stars in the Galaxy are\nrotating at spin frequencies greater than 250 Hz. Remarkably, they all rotate\nin a narrow range of frequencies. I suggest that these stars rotate fast enough\nso that, on average, the angular momentum added by accretion is lost to\ngravitational radiation. The strong spin frequency dependence of the angular\nmomentum loss rate from gravitational radiation then provides a natural reason\nfor similar spin frequencies. Provided that the interior temperature has a\nlarge scale asymmetry misaligned from the spin axis, then the temperature\nsensitive electron captures in the deep crust can provide the quadrupole needed\nto reach this limiting situation at 300 Hz. This quadrupole is only present\nduring accretion and makes it difficult to form radio pulsars spinning more\nrapidly than 600-800 Hz via rapid accretion. The gravity wave strength is\n<10^{-26} from most neutron stars and >2 X 10^{-26} for Sco X-1. Prior\nknowledge of the position, spin frequency and orbital periods will allow for\ndeep searches for these periodic signals with gravitational wave\ninterferometers (LIGO, VIRGO and the dual-recycled GEO 600 detector) and\nexperimenters need to take such sources into account. Sco X-1 will most likely\nbe detected first.\n