磁星SGR 1830-0645爆发衰变期间的脉冲峰值迁移：地壳运动和磁层解扭
Pulse Peak Migration during the Outburst Decay of the Magnetar SGR 1830-0645: Crustal Motion and Magnetospheric Untwisting
摘要：
磁星，孤立的中子星的磁场强度通常为$\gtrsim10^{14}$ ~G，表现出独特的长达数月的爆发时期，在此期间，软X射线脉冲轮廓的强烈演变，以及非热磁层发射成分，经常被观察到。在最近一次爆发衰变的前37天，使用磁星SGR 1830-0645的近每日NICER观测，清楚地观察到脉冲峰值的相位迁移，将脉冲形状从最初的三峰转换为单峰轮廓。这样的峰合并以前从未在磁星上看到过。我们的高分辨率相位分辨光谱分析显示，尽管复杂的初始脉冲形状，温度没有显着的演变。然而，推测的地表热点在峰值迁移和爆发衰减期间收缩。我们提出了两个可能的起源，这种演变。对于地表内热，地壳构造运动可能是其根本原因。推测的地壳运动速度为$\lesssim100$ ~m~day $^{-1}$，驱动区的密度为$ρ\sim10^{10}$ ~g~cm $^{-3}$，深度为$\sim200$ ~m。或者，热点可能是由扭曲的磁层粒子轰击加热的，磁层拥有通量管或绳，有点类似于太阳日冕环，在30-40天的时间尺度上解开和消散。峰值迁移则可能是由于磁力线脚点运动（必然由地壳运动驱动）和不断变化的地表辐射束的组合。这些新的数据集生动地描绘了与磁星爆发相关的动态，但它也强调了需要一个更通用的理论图，其中磁层和地壳被认为是串联的。
英文摘要：
Magnetars, isolated neutron stars with magnetic field strengths typically $\gtrsim10^{14}$~G, exhibit distinctive months-long outburst epochs during which strong evolution of soft X-ray pulse profiles, along with nonthermal magnetospheric emission components, is often observed. Using near-daily NICER observations of the magnetar SGR 1830-0645 during the first 37 days of a recent outburst decay, a pulse peak migration in phase is clearly observed, transforming the pulse shape from an initially triple-peaked to a single-peaked profile. Such peak merging has not been seen before for a magnetar. Our high-resolution phase-resolved spectroscopic analysis reveals no significant evolution of temperature despite the complex initial pulse shape. Yet the inferred surface hot spots shrink during the peak migration and outburst decay. We suggest two possible origins for this evolution. For internal heating of the surface, tectonic motion of the crust may be its underlying cause. The inferred speed of this crustal motion is $\lesssim100$~m~day$^{-1}$, constraining the density of the driving region to $ρ\sim10^{10}$~g~cm$^{-3}$, at a depth of $\sim200$~m. Alternatively, the hot spots could be heated by particle bombardment from a twisted magnetosphere possessing flux tubes or ropes, somewhat resembling solar coronal loops, that untwist and dissipate on the 30-40~day timescale. The peak migration may then be due to a combination of field-line footpoint motion (necessarily driven by crustal motion) and evolving surface radiation beaming. These novel dataset paints a vivid picture of the dynamics associated with magnetar outbursts, yet it also highlights the need for a more generic theoretical picture where magnetosphere and crust are considered in tandem.
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