Issue |
A&A
Volume 527, March 2011
|
|
---|---|---|
Article Number | A83 | |
Number of page(s) | 8 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361/201015532 | |
Published online | 28 January 2011 |
Study of measured pulsar masses and their possible conclusions
1
National Astronomical Observatories, Chinese Academy of
Sciences,
Beijing
100012,
PR China
e-mail: zhangcm@bao.ac.cn
2
School of Space Science and Physics, Shandong University at
Weihai, Weihai
264209, PR
China
3
Astronomical Institute, Institute of High Energy Physics, Chinese
Academy of Sciences, Beijing
100039, PR
China
4 Department de Física, CFM, Universidade Federal de Santa
Catarina Florianópolis, SC, CP. 476, CEP 88.040-900, Brazil
5
Mathematical Sciences Institute, The Australian National
University, Canberra
ACT
0200,
Australia
6
Lapth - Lapp, Université de Savoie, BP 110, 74941
Annecy-le-Vieux Cedex,
France
Received:
5
August
2010
Accepted:
2
October
2010
We study the statistics of 61 measured masses of neutron stars (NSs) in binary pulsar systems, including 18 double NS (DNS) systems, 26 radio pulsars (10 in our Galaxy) with white dwarf (WD) companions, 3 NSs with main-sequence companions, 13 NSs in X-ray binaries, and one undetermined system. We derive a mean value of M = 1.46 ± 0.30 M⊙. When the 46 NSs with measured spin periods are divided into two groups at 20 milliseconds, i.e., the millisecond pulsar (MSP) group and others, we find that their mass averages are, respectively, M = 1.57 ± 0.35 M⊙ and M = 1.37 ± 0.23 M⊙. In the framework of the pulsar recycling hypothesis, this suggests that an accretion of approximately ~0.2 M⊙ is sufficient to spin up a neutron star and place it in the millisecond pulsar group. Based on these estimates, an approximate empirical relation between the accreting mass (ΔM) of recycled pulsar and its spin period is proposed as ΔM = 0.43 (M⊙)(P/1 ms) − 2/3. If we focus only on the DNS, the mass average of all 18 DNSs is 1.32 ± 0.14 M⊙, and the mass averages of the recycled DNSs and the non-recycled NS companions are, respectively, 1.38 ± 0.12 M⊙ and 1.25 ± 0.13 M⊙. This is consistent with the hypothesis that the masses of both NSs in DNS system have been affected by accretion. The mass average of MSPs is higher than the Chandrasekhar limit 1.44 M⊙, which may imply that most of binary MSPs form via the standard scenario by accretion recycling. If we were to assume that the mass of a MSP formed by the accretion induced collapse (AIC) of a white dwarf must be less than 1.35 M⊙, then the portion of the binary MSPs involved in the AICs would not be higher than 20%, which imposes a constraint on the AIC origin of MSPs. With accreting mass from the companion, the nuclear matter composition of MSP may experience a transition from the “soft” equation of state (EOS) to a “stiff” EOS or even neutron to quark matter.
Key words: pulsars: general / stars: neutron
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.