论文标题
GRB 180620a中具有强烈进动运动的新生磁铁的早期演变
Early Evolution of a Newborn Magnetar with Strong Precession Motion in GRB 180620A
论文作者
论文摘要
在某些伽马射线爆发（GRB）的余辉灯弯曲中观察到的早期X射线高原归因于新生儿磁盘的偶极辐射（DRS）。高原中的准周期振荡（QPO）信号将是磁性进液运动的有力证据。通过对GRB 180620a的X射线余泽灯曲线进行时频域分析，我们在其早期X射线高原中找到了$ \ sim650 $秒的QPO信号。我们通过采用马尔可夫链蒙特卡洛算法，使用磁性进动模型拟合灯曲线。观察到的灯曲线和QPO信号与我们的模型很好地表示。磁盘的衍生磁场强度为$ b _ {\ rm p} =（1.02^{+0.59} _ { - 0.61}）\ times10^{15} $ 〜g。它以$ω_{s} \ propto（1+t/τ_{\ rm sd}）^{ - 0.96} $而迅速旋转为$ω_{s} \ propto（1+t/τ_{\ rm sd}），其中$τ_{\ rm sd} = 9430 $ 〜s。它的进动速度的演变甚至快于$ω_s$，即$ω_{p} \ propto（1+t/τ_{p}）^{ - 2.18 \ pm0.11} $，其中$τ_{p} = 2239 \ pm pm206 $ 〜s。推断的制动指数为$ n = 2.04 $。我们认为，通过磁层过程额外的能量损失会导致其快速旋转，磁盘的低制动指数以及强烈的进动运动。
The observed early X-ray plateau in the afterglow lightcurves of some gamma-ray bursts (GRBs) is attributed to the dipole radiations (DRs) of a newborn magnetar. A quasi-periodic oscillation (QPO) signal in the plateau would be strong evidence of the magnetar precession motion. By making a time-frequency domain analysis for the X-ray afterglow lightcurve of GRB 180620A, we find a QPO signal of $\sim650$ seconds in its early X-ray plateau. We fit the lightcurve with a magnetar precession model by adopting the Markov chain Monte Carlo algorithm. The observed lightcurve and the QPO signal are well represented with our model. The derived magnetic field strength of the magnetar is $B_{\rm p}= (1.02^{+0.59}_{-0.61})\times10^{15}$~G. It rapidly spins down with angular velocity evolving as $Ω_{s} \propto(1+t/τ_{\rm sd})^{-0.96}$, where $τ_{\rm sd}=9430$~s. Its precession velocity evolution is even faster than $Ω_s$, i.e. $Ω_{ p}\propto (1+t/τ_{p})^{-2.18\pm0.11}$, where $τ_{p}=2239\pm206$~s. The inferred braking index is $n=2.04$. We argue that the extra energy loss via the magnetospheric processes results in its rapid spin-down, a low braking index of the magnetar, and the strong precession motion.
