ON THE NATURE OF THE FIRST TRANSIENT Z SOURCE XTE J1701–462: ITS ACCRETION DISK STRUCTURE, NEUTRON STAR MAGNETIC FIELD STRENGTH, AND HARD TAIL

Using data from the Rossi X-Ray Timing Explorer , we investigate the spectral evolution along a "Z" track and a "ν" track on the hardness–intensity diagrams of the first transient Z source XTE J1701−462. The spectral analyses suggest that the inner disk radius depends on the mass accretion rate, in agreement with the model prediction, , for a radiation-pressure-dominated accretion disk interacting with the magnetosphere of a neutron star (NS). The changes in the disk mass accretion rate are responsible for the evolution of the "Z" or "ν" track. Radiation pressure thickens the disk considerably and also produces significant outflows. The NS surface magnetic field strength, derived from the interaction between the magnetosphere and the radiation-pressure-dominated accretion disk, is ∼(1–3) × 10 9 G, which is possibly between normal atoll and Z sources. A significant hard tail is detected in the horizontal branches and we discuss several possible origins of the hard tail.