Magnetic fields of neutron stars in low mass X-ray binaries

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Abstract
We report detailed radiation transport calculations which show that the shape of the 1–30 keV continuum spectrum of a weakly magnetic accreting neutron star depends on the strength of its magnetic field. We use this dependence to estimate the magnetic fields of several accreting neutron stars in LMXBs. We demonstrate that the magnetic field strengths estimated in this way correlate strongly with the properties of the 15–60 Hz magnetospheric QPOs and the kilohertz QPOs observed in many Z and atoll sources. We also find that sources currently accreting at high rates have higher magnetic field strengths than sources currently accreting at lower rates. This is an important constraint on models of the evolution of the magnetic field strengths of accreting neutron stars.