标题： 热核火焰在 SAX J1808.4-3658 中子星上的传播：一种观测工具 显示英文标题

标题： Spreading of thermonuclear flames on the neutron star in SAX J1808.4-3658: an observational tool

摘要： 我们分析了存储的 Rossi X 射线定时探测器（RXTE）比例计数组（PCA）数据，这些数据来自吸积毫秒脉冲星 SAX J1808.4-3658 在 2002 年爆发期间的热核 X 射线爆发。 我们提供了在爆发上升阶段振荡频率非单调变化的证据，并展示了振荡频率、幅度以及推断出的燃烧区域面积的时间演化之间的相关性。 我们还讨论了幅度和燃烧区域面积的变化与中子星表面热核火焰传播的一致性。 基于此讨论，我们推断，对于 2002 年 10 月 15 日的热核爆发，点火很可能发生在中纬度地区，燃烧区域大约用了 0.2 秒几乎环绕了中子星的赤道区域，之后较低幅度的振荡源于同一半球中爆发点燃处剩余的燃烧前沿不对称性。 我们的观测结果和理论讨论表明，研究爆发上升阶段爆发光振荡性质的演化可以为理解中子星表面在极端物理条件下热核火焰的传播提供有力工具。 显示英文摘要

摘要： We analyse archival Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) data of thermonuclear X-ray bursts from the 2002 outburst of the accreting millisecond pulsar SAX J1808.4-3658. We present evidence of nonmonotonic variations of oscillation frequency during burst rise, and correlations among the time evolution of the oscillation frequency, amplitude, and the inferred burning region area. We also discuss that the amplitude and burning region area evolutions are consistent with thermonuclear flame spreading on the neutron star surface. Based on this discussion, we infer that for the 2002 Oct. 15 thermonuclear burst, the ignition likely occured in the mid-latitudes, the burning region took ~ 0.2 s to nearly encircle the equatorial region of the neutron star, and after that the lower amplitude oscillation originated from the remaining asymmetry of the burning front in the same hemisphere where the burst ignited. Our observational findings and theoretical discussion indicate that studies of the evolution of burst oscillation properties during burst rise can provide a powerful tool to understand thermonuclear flame spreading on neutron star surfaces under extreme physical conditions.