2.1 Neutron Star
The idea of neutron star was proposed just after the discovery of the neutron by Chadwick in 1932
(**** et al. ????). On November 28, 1967, Bell and Herwish were discovered a pulsation with 1.337
sec from PSR 1919+21. Such short term pulsation of ? 1.3 sec cannot be achieve with a low density
normal star. Herwish reached the possibilities of a white dwarf or neutron star, shortly. This is a ?rst
discovery of the neutron star. Herwish recieved the Novel prize for this discovery.
The neutron star birth as a remnant of a core-collapse supernova as suggested by Baade and
Zwicky (1934). Since the neutron star mainly sustained by degeneracy force of neutrons, its radius
and its mass are colculated to be 10 km and 1.4Msun, respectively. The neutron star has a density
about three times larger than the nuclear saturation density ( ? 2.8× 10 14 g/cm 3). In such a high
density condition, some exotic particles start to appear like pion condensates, lambda hyperons, etc.
Many theoretical studies suggest that the neutron star interior contains these strangeness particles,
and propose a lot of Equation of States (EoSs) of the nuclear matter REFERENCE. The EoS can
be constrained by measuring the neutron star mass and radii, directly. However, these neutron star
parameters are di?cult to determine, especially the neutron star radii; we only have few observational
determination. In recent study, neutron stars which have ? 2 Msun were discovered REFERENCE.
Neutron star is powerful tool to reveal the physics of the cold-dense matter.
Some of neutron stars are categorized as binary neutron star. The binary neutron stars consist
of two ob ject: a compact ob ject and a companion. They are also characterized as High Mass X-ray
Binary (HMXB) and Low Mass X-ray Binary (LMXB), depending on their companion mass. Each
properties are listed in Table 2.1. The most important di?erence of these two is the magnetic ?eld
strength. Since the neutron star which belongs to HMXB has strong magnetic ?eld of ? 10 12 G,
kinematics of accreting matters are controlled by the magnetic ?eld. In NS-HMXB, accreting matters
captured by the magnetic ?eld, and the accreting ?ow is channeled into an accretion along the magnetic
?eld. Finally the accreting matters fall onto the magnetic poles on the neutron star surface. Therefore,
this type of neutron star exhibits a pulsation synchronized with their rotation and hence is observed