Pulsars and neutron stars/Neutron star properties
Introduction
[edit | edit source]Neutron star masses
[edit | edit source]A catalogue of pulsar and companion masses is available. Below we list the pulsar masses for systems in which the mass is well determined:
| Pulsar | Mass (solar masses) |
|---|---|
| J0337+1715 | 1.4378(13) |
| J0348+0432 | 2.01(4) |
| J0437-4715 | 1.44(7) |
| J0453+1559 | 1.559(5) |
| J0621+1001 | 1.53 +0.10-0.20 |
| J0737-3039A | 1.3381(7) |
| J0737-3039B | 1.2489(7) |
| J0751+1807 | 1.26(14) |
| J1012+5307 | 1.64(22) |
| J1141-6545 | 1.27(1) |
| B1534+12 | 1.3330(4) |
| J1614-2230 | 1.97(4) |
| J1713+0747 | 1.31(11) |
| J1738+0333 | 1.47+0.07-0.06 |
| J1756-2251 | 1.341(7) |
| J1802-2124 | 1.24(11) |
| J1807-2500B | 1.3655(21) |
| B1855+09 | 1.58+10-13 |
| J1903+0327 | 1.667(21) |
| J1906+0746 | 1.291(11) |
| J1909-3744 | 1.47(3) |
| J1910-5958A | 1.3(2) |
| B1913+16 | 1.4398(2) |
| B2127+11C | 1.358(10) |
| J2222-0137 | 1.20(14) |
| B2303+46 | 1.24-1.44 |
Neutron star radii
[edit | edit source]It is very difficult to make a direct determination of a neutron star radius. One method is to study X-ray bursters - these are neutron stars that are still accreting material from a companion in a close orbit. It is thought that they can build up layers of material on their surface until it reaches a critical mass at which point it undergoes a thermonuclear explosion causing a burst of emission from the surface. From a knowledge of the distance to the neutron star it is possible to estimate the radius of the neutron star. Results are obtained of around 9.6 to 11km (see e.g., Fujimoto & Gottwald 1989). More recently model spectra of neutron star atmospheres is used to fit the thermal X-ray spectra of neutron stars. Suleimanov et al. (2015) obtain radii of around 12km.
The neutron star interior
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Types of neutron stars
[edit | edit source]There is a large zoology of different types of neutron star. They can be differentiated between radio loud and radio quiet sources. Some are rotationally-powered whilst others are accretion-powered. There are now sources that switch between the different types. For instance, Papitto et al. discuss a neutron star (IGR J18245-2452; PSR J1824-2452I located in the globular cluster M28) which accretes matter and angular momentum from its companion star (this system is a low-mass X-ray binary; LMXB). During this stage, bright X-ray emission is observed. However, the rate of mass transfer can decrease and a radio millisecond pulsar switches on - in this state the emission is powered by the neutron star's rotating magnetic field.
Types of neutron star include:
- radio pulsars
- recycled pulsars
- millisecond pulsars
- magnetar
- soft gamma ray repeater
- anomalous X-ray pulsar
- recycled pulsars
- Low-mass X-ray binaries (LMXB)
- Intermediate-mass X-ray binaries (IMXB)
- High-mass X-ray binaries (HMXB)
- Accretion powered pulsar