The Duration of the Detached Phase in Low-Mass X-Ray Binaries in which the Neutron Star was Formed by Accretion-Induced Collapse of a White Dwarf

Abstract

The magnetic field strengths in the range 5x10⁸; G to 10¹⁰ G inferred from the presence of Quasi Periodic Oscillations (QPO’s) in the X-ray fluxes of GX 5-1, Cygnus X-2 and Sco X-1 (Van der Klis et al., 1985 a,b; Hasinger et al., 1985; Middleditch and Priedhorsky, 1985) suggest that the neutron stars in these systems are younger than ~ 10⁸ yrs. Since, on the other hand, these systems themselves have ages > 5x10⁹ yrs (see Van den Heuvel, this volume) these neutron stars must have been formed during the mass transfer process itself by the accretion-induced collapse (AIC) of a white dwarf (cf. Van der Klis et al., 1985a and Van den Heuvel, this volume).