HBO and Periastron Precession around the X-ray Neutron Star Magnetosphere

TL;DR

This paper models the 15-60 Hz HBO QPOs in X-ray neutron stars as resulting from periastron precession at the magnetosphere-disk boundary, linking these oscillations to accretion rate and kHz QPOs.

Contribution

It extends the periastron precession model to explain HBO QPOs and derives theoretical relations consistent with empirical data for neutron star systems.

Findings

QPO frequencies increase with accretion rate

Theoretical relations match empirical formulas

Best-fit neutron star mass is about 1.9 solar masses

Abstract

Based on the periastron precession model to account for kHz QPO of the binary X-ray neutron star, proposed by Stella and Vietri, we ascribe the 15-60 Hz Quasi Periodic Oscillation (QPO) to the periastron precession frequency of the orbiting accreted matter at the boundary of magnetosphere-disk of X-ray neutron star (NS). The obtained conclusions include: all QPO frequencies increase with increasing the accretion rate. The theoretical relations between 15-60 Hz QPO (HBO) frequency and the twin kHz QPOs are similar to the measured empirical formula. Further, the better fitted NS mass by the proposed model is about 1.9 solar masses for the detected LMXBs.