Simplified Picture of Low Mass X-ray Binaries based on Data from Aql X-1 and 4U1608-52

TL;DR

This paper presents a simplified model of low mass X-ray binaries with neutron stars, identifying three states and transitions based on data from Aql X-1 and 4U1608-52, and discusses magnetic field estimation.

Contribution

It introduces a new simplified framework for understanding the states and transitions in NS-LMXBs, including a method to estimate magnetic field strength from state transitions.

Findings

Identified three distinct states in NS-LMXBs.

Mapped the state transition pathways and their physical conditions.

Proposed a way to estimate neutron star magnetic fields from transition data.

Abstract

We propose a simplified picture of low mass X-ray binaries containing a neutron star (NS-LMXBs) based on data obtained from AqlX-1 and 4U1608-52 which often produce outbursts. In this picture we propose at least three states and three state transitions; i.e., the states: (1) soft state, (2) hard-high state, and (3) hard-low state, and the state transitions: (i) hard-high state to soft state, (ii) soft state to hard-high state, and (iii) hard-high state to hard-low state or vice versa. Gases from the accretion disc of an NS-LMXB penetrate almost the entire magnetic field and accrete onto the neutron star in cases (1) and (2), whereas in case (3) some gases accrete around the magnetic poles in a manner resembling the behavior of an X-ray pulsar, and considerable gas is dispersed or ejected by the propeller effect. Transition (iii) occurs when the Alfv\'{e}n radius is equal to the co-rotation radius. Therefore, in this case, it is possible to estimate the strength of the neutron star's magnetic field by detecting transition (iii). We also discuss the no-accretion X-ray state or recycled pulsar state, in which the Alfv\'{e}n radius is larger than the light cylinder radius.