SWIFT J1749.4-2807: A neutron or quark star?

作     者：Jun-Wei Yu Ren-Xin Xu 

作者机构：School of Physics and State Key Laboratory of Nuclear Physics and Technology Peking University Beijing 100871 China 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2010年第10卷第9期

页      面：815-820页

核心收录：

学科分类：07[理学] 08[工学] 070401[理学-天体物理] 0835[工学-软件工程] 0704[理学-天文学] 081202[工学-计算机软件与理论] 0812[工学-计算机科学与技术（可授工学、理学学位）] 

基　　金：supported by the National Natural Science Foundation of China (Grant Nos. 10778611 and 10973002) the National Basic Research Program of China(Grant No. 2009CB824800) 

主　　题：X-rays binaries i binaries eclipsing -- pulsars general -- pulsars individual SWIFT J1749.4-2807 

摘      要：We investigate a unique accreting millisecond pulsar with X-ray eclipses, SWIFT J1749.4-2807 （hereafter J1749）, and try to set limits on the binary system by various methods including use of the Roche lobe, the mass-radius relations of both main sequence （MS） and white dwarf （WD） companion stars, as well as the measured mass function of the pulsar. The calculations are based on the assumption that the radius of the companion star has reached its Roche radius （or is at 90%）, but the pulsar＇s mass has not been assumed to be a certain value. Our results are as follows. The companion star should be an MS one. For the case that the radius equals its Roche one, we have a companion star with mass M ≈ 0.51 Me and radius Rc ≈ 0.52 R⊙, and the inclination angle is i ≈ 76.5°; for the case that the radius reaches 90% of its Roche one, we have M ≈ 0.43M⊙, Rc ≈ 0.44R⊙ and i ≈ 75.7°. We also obtain the mass of J1749, Mp ≈ 1 M⊙, and conclude that the pulsar could be a quark star if the ratio of the critical frequency of rotation-mode instability to the Keplerian one is higher than - 0.3. The relatively low pulsar mass （about - M⊙） may also challenge the conventional recycling scenario for the origin and evolution of millisecond pulsars. The results presented in this paper are expected to be tested by future observations.