Study on Mass Distribution and Birth Mode of Neutron Star
Abstract
The measured masses of 72 neutron stars (NSs) in 63 pairs of binary systems are studied in this paper, including 18 X-ray binary systems (XBs), 9 double neutron star systems (DNSs), 4 neutron star-main sequence binary systems (NSMSs), and 32 neutron star-white dwarf binary systems (NSWDs). We use the method of Monte-Carlo random sampling to deal with the uncertainty of measured masses to increase the accuracies of statistical results. We find that the measured masses have a bimodal distribution, with the first peak around (1.328±0.220) M_{⊙}, and a much wider second peak at (1.773±0.416) M_{⊙}, respectively. It is worth noting that, even though the DNSs are excluded, the mass distribution is still bimodal and peaked respectively at (1.360±0.337) M_{⊙} and (1.854±0.322) M_{⊙}. The average mass of 18 DNSs is (1.330±0.0089) M_{⊙}. Through the above mass distribution, it can be clearly seen that DNS has a little influence on the mass distribution of NS, and the distribution of NS mass also implies that there are two birth modes of NSs. We think that they are the nuclear collapse supernova explosion and the electron capture supernova eruption. The single peak structure of DNS mass implies that the evolution mechanism of DNS may be different from other binary systems. In order to further study the characteristics of neutron star mass distribution, we divide the 53 NSs with measured mass into two groups, the millisecond neutron star (MSP, the spin period P_{s}≤20 ms) and normal neutron star (PSR, P_{s}>20 ms). We find that their mass distributions also show the bimodal structure, and the average mass of MSP is ∼0.22 M_{⊙} larger than the average mass of PSR. This indicates that the spin of NS will reach milliseconds after the accretion of about 0.22 M_{⊙}. According to the distribution of NS mass and period on the M-P_{s} diagram, the fitting results of the M-P_{s} relation is M = 1.4 + (P_{s}/{ms})^{-3/2} M_{⊙}.
- Publication:
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Acta Astronomica Sinica
- Pub Date:
- May 2018
- Bibcode:
- 2018AcASn..59...27L
- Keywords:
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- stars: neutron;
- binaries;
- mass;
- methods: statistical