Gravitational Waves from Inspiraling Compact Binaries with Magnetic Dipole Moments

We investigate the effects of magnetic dipole-dipole coupling and electromagnetic radiation on the frequency evolution of gravitational waves from inspiraling binary neutron stars with magnetic dipole moments. This study is motivated by the discovery of superstrongly magnetized neutron stars, i.e., magnetars. We derive the contributions of the magnetic fields to the accumulated cycles in gravitational waves as Nmag ~ 6 × 10-3(H/1016 G)2, where H denotes the strength of the polar magnetic fields of each neutron star in the binary system. It is found that the effects of the magnetic fields will be negligible for the detection and the parameter estimation of gravitational waves if the upper limit for the magnetic fields of neutron stars is less than ~1016 G, which is the maximum magnetic field observed in soft gamma repeaters and anomalous X-ray pulsars to date. We also discuss the implications of electromagnetic radiation from inspiraling binary neutron stars for the precursory X-ray emission prior to the gamma-ray burst observed by the Ginga satellite.