Evidence for a 2:3 resonance in Sco X-1 kHz QPOs

Abstract

We find evidence that the two high frequency QPOs in Sco X-1 are, more often than not, approximately in the 2:3 frequency ratio familiar from studies of black hole candidates (e.g., XTE J1550-564, Remillard et al. 2002). This implies that the double kHz QPO phenomenon in neutron stars has its origin in properties of strong-field gravity and has little to do with the rotation of a stellar surface or any magnetic field structure anchored in the star. 1. The larger picture Recent X-ray observations showed that in some black holes, as in neutron stars, high frequency quasi-periodic oscillations (QPOs) come in pairs. This in itself suggests that the QPO phe- nomenon in black holes and in neutron stars may have the same origin. We think that the frequency ratios may be even more revealing.