标题： M82 X-2轨道衰减的另一种模型：Bp星的异常磁制动 显示英文标题

标题： An alternative model for the orbital decay of M82 X-2: the anomalous magnetic braking of a Bp star

摘要： 最近，第一个脉动的超亮X射线源M82 X-2被报告称以$\dot{P}=-(5.69\pm0.24)\times 10^{-8}~\rm s\,s^{-1}$的速率经历快速轨道衰减，这是基于七年\emph{NuSTAR}的数据。 为了说明观测到的轨道周期导数，需要从供体恒星向吸积中子星转移的质量速率为$\sim200\dot{M}_{\rm edd}$ ($\dot{M}_{\rm edd}$是爱丁顿吸积率)。 然而，其他潜在模型不能被完全排除。 在本工作中，我们提出一种异常磁制动（AMB）模型来解释检测到的M82 X-2轨道衰减。 如果供体恒星是一颗具有异常强磁场的Ap/Bp恒星，那么强表面磁场与供体恒星表面驱动的风之间的磁耦合可能导致有效的角动量损失，从而导致在M82 X-2中观测到的快速轨道衰减。 质量为$5.0-15.0~M_{\odot}$、表面磁场为$3000-4500~\rm G$的Ap/Bp恒星的AMB机制可以产生M82 X-2的观测值$\dot{P}$。 我们还讨论了其他替代模型的可能性，包括伴星膨胀和周围的环联星盘。 显示英文摘要

摘要： Recently, the first pulsating ultraluminous X-ray source M82 X-2 was reported to be experiencing a rapid orbital decay at a rate of $\dot{P}=-(5.69\pm0.24)\times 10^{-8}~\rm s\,s^{-1}$ based on seven years \emph{NuSTAR} data. To account for the observed orbital-period derivative, it requires a mass transfer rate of $\sim200\dot{M}_{\rm edd}$ ($\dot{M}_{\rm edd}$ is the Eddington accretion rate) from the donor star to the accreting neutron star. However, other potential models cannot be completely excluded. In this work, we propose an anomalous magnetic braking (AMB) model to interpret the detected orbital decay of M82 X-2. If the donor star is an Ap/Bp star with an anomalously strong magnetic field, the magnetic coupling between strong surface magnetic field and irradiation-driven wind from the surface of the donor star could cause an efficient angular-momentum loss, driving a rapid orbital decay observed in M82 X-2. The AMB mechanism of an Ap/Bp star with a mass of $5.0-15.0~M_{\odot}$ and a surface magnetic field of $3000-4500~\rm G$ could produce the observed $\dot{P}$ of M82 X-2. We also discuss the possibility of other alternative models including the companion star expansion and a surrounding circumbinary disk.