Gravitational waves from a spinning particle scattered by a relativistic star: Axial mode case - art. no. 124012

We use a perturbation method to study gravitational waves from a spinning t est particle scattered by a relativistic star. The present analysis is rest ricted to axial modes. By calculating the energy spectrum, the wave forms, and the total energy and angular momentum of gravitational waves, we analyz e the dependence of the emitted gravitational waves on particle spin. For a normal neutron star, the energy spectrum has one broad peak whose characte ristic frequency corresponds to the angular velocity at the turning point ( a periastron). Since the turning point is determined by the orbital paramet er, there exists a dependence of the gravitational wave on particle spin. W e find that the total energy of l = 2 gravitational waves gets larger as th e spin increases in the antiparallel direction to the orbital angular momen tum. For an ultracompact star, in addition to such an orbital contribution, we find the quasinormal modes excited by a scattered particle, whose excit ation rate to gravitational waves depends on the particle spin. We also dis cuss the ratio of the total angular momentum to the total energy of gravita tional waves and explain its spin dependence.