Ghosh & Lamb关系在X射线双星脉冲星4U 1626-67自旋上下运动中的应用
Application of the Ghosh & Lamb Relation to the Spin-up/down Behavior in the X-ray Binary Pulsar 4U 1626-67
摘要：
分析了2009年10月至2013年9月期间X射线脉冲双星4U 1626-67的MAXI/GSC连续观测数据，采用历元折叠法确定了每60 d的脉冲周期和脉冲周期导数。得到的周期与费米/GBM脉冲星计划提供的周期一致。在所有60天的时间间隔内，脉冲星都被观测到自旋上升，自旋上升速率与2-20 keV的通量呈正相关。我们将Ghosh & Lamb（1979，ApJ，234，296）提出的吸积力矩模型应用于MAXI/GSC数据，以及包括自旋上升和自旋下降阶段的过去数据。Ghosh & Lamb关系被证实成功地解释了所观察到的自旋上/下速率与通量之间的关系。通过比较模型预测的光度与观测的通量，将源距约束在5-13 kpc，这与Chakrabarty（1998，ApJ，492，342）的结果一致。相反，如果假设源距离，数据可以约束中子星的质量和半径，因为Ghosh & Lamb模型依赖于这些参数。我们尝试了这个想法，并发现假设的距离，例如，10 kpc给出的质量范围是1.81-1.90太阳质量，半径为11.4-11.5 km，尽管这些结果仍然受到除了距离之外的相当大的系统不确定性的影响。
英文摘要：
We analyzed continuous MAXI/GSC data of the X-ray binary pulsar 4U 1626-67 from 2009 October to 2013 September, and determined the pulse period and the pulse-period derivative for every 60-d interval by the epoch folding method. The obtained periods are consistent with those provided by the Fermi/GBM pulsar project. In all the 60-d intervals, the pulsar was observed to spin up, with the spin-up rate positively correlated with the 2-20 keV flux. We applied the accretion torque model proposed by Ghosh & Lamb (1979, ApJ, 234, 296) to the MAXI/GSC data, as well as the past data including both spin-up and spin-down phases. The Ghosh & Lamb relation was confirmed to successfully explain the observed relation between the spin-up/down rate and the flux. By comparing the model-predicted luminosity with the observed flux, the source distance was constrained as 5-13 kpc, which is consistent with that by Chakrabarty (1998, ApJ, 492, 342). Conversely, if the source distance is assumed, the data can constrain the mass and radius of the neutron star, because the Ghosh & Lamb model depends on these parameters. We attempted this idea, and found that an assumed distance of, e.g., 10 kpc gives a mass in the range of 1.81-1.90 solar mass, and a radius of 11.4-11.5 km, although these results are still subject to considerable systematic uncertainties other than that in the distance.
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