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arXiv 2004.05787astro-ph.HEastro-ph.SR
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SAX J1712中的高能热核爆发.6-3739

The energetic thermonuclear bursts in SAX J1712.6-3739

Jie Lin, Wenfei Yu

摘要:

中子星低质量X射线双星SAXJ1712.6 -3739在过去的X射线观测中以其非常长而坚硬的热核爆发而闻名。它的热核爆发非常活跃,在Swift/BAT的硬X射线观测中甚至可以持续数十分钟(E > 15 keV)。为了探索SAXJ1712.6 -3739及其热核爆发的性质,我们分析了Swift/BAT观测到的4次爆发。利用Swift/BAT和Swift/XRT的观测资料,计算了这些爆发的峰值通量和注量。根据雨燕观测到的峰值通量,SAXJ1712.6 -3739的距离估计为4.6千秒差距,这比BeppoSAX观测的估计要近得多。相应的绝对星等和平均吸积率与其超致密X射线双星性质一致。通过有效持续时间的测量,我们确定2010年爆发对应于正常X射线爆发,2011年爆发对应于中等持续时间爆发,2014年和2018年爆发的能量比普通中等持续时间爆发高,但比超级爆发低。由于SAXJ1712.6 -3739的平均质量吸积率仅为0.6%Eddington吸积率,并且目前的理论预测在很低的吸积率下在爆发器中不产生碳。因此,2014年和2018年的爆发很可能是深氦爆发。在雨燕的观测中,SAXJ1712.6 -3739显示了至少三种不同的热核爆发持续时间。它们可能是由可变的吸积速率引起的,因为它们的点火柱深度大致遵循相应吸积速率下纯氦爆发点火模型的预测。

英文摘要:

The neutron star low-mass X-ray binary SAX J1712.6-3739 is known for its very long and hard thermonuclear bursts in past X-ray observations. Its thermonuclear bursts are so energetic that they can even last for tens of minutes in the hard X-ray observations of Swift/BAT (E > 15 keV). For exploring the natures of SAX J1712.6-3739 and its thermonuclear bursts, we analyzed its four bursts which were all captured by Swift/BAT. The peak flux and fluence for these bursts are derived by applying the archive observation data of Swift/BAT and Swift/XRT. Based on the peak fluxes observed by Swift, the distance of SAX J1712.6-3739 is estimated as 4.6 kpc, which is much closer than the estimate by the BeppoSAX observations. The corresponding absolute magnitude and average accretion rate agree its ultra-compact X-ray binary nature. By the measurements of effective duration, we determined that the 2010 burst corresponds to a normal X-ray burst, the 2011 burst is consistent with an intermediate-duration burst while the 2014 and the 2018 bursts are more energetic than common intermediate-duration bursts but less energetic than superbursts. Since the average mass accretion rate of SAX J1712.6-3739 was only 0.6% Eddington accretion rate, and current theory predict no carbon production in the bursters under very low accretion rate. Therefore, the 2014 and the 2018 bursts are very likely to be deep helium bursts. In the Swift observations, SAX J1712.6-3739 has shown at least three different levels of duration in thermonuclear bursts. They were possibly induced by variable accretion rates, because their ignition column depths roughly follow the prediction of ignition models for pure helium bursts at corresponding accretion rates.

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