Determining the neutron star surface magnetic field strength of two Z sources

TL;DR

This paper estimates the surface magnetic field strengths of two Z-source neutron stars, GX 17+2 and Cyg X-2, using disk motion data, revealing fields comparable to millisecond pulsars and suggesting aligned magnetic and rotational axes.

Contribution

It provides the first estimates of magnetic field strengths for these Z sources based on disk motion analysis, highlighting their similarities to millisecond pulsars.

Findings

Magnetic fields are ~(1-5)×10^8 G and ~(1-3)×10^8 G for GX 17+2 and Cyg X-2.

Magnetic axes likely aligned with rotation axes, explaining lack of pulsations.

Magnetic field strengths are comparable to those in millisecond X-ray pulsars.

Abstract

From the extreme position of disk motion, we infer the neutron star (NS) surface magnetic field strength B_0 of Z-source GX 17+2 and Cyg X-2. The inferred B_0 of GX 17+2 and Cyg X-2 are ~(1-5)X10^8 G and ~(1--3)X10^8 G}, respectively, which are not inferior to that of millisecond X-ray pulsars or atoll sources. It is likely that the NS magnetic axis of Z sources is parallel to the axis of rotation, which could result in the lack of pulsations in these sources.