探索SFXTs的喷气发射条件
Exploring jet-launching conditions for SFXTs
摘要：
在喷流形成的磁离心机制中，假设吸积中子星只有在其表面磁场足够弱时才会产生相对论喷流（$B \sim 10^8$ G）。然而，中子星最常见的表现形式是中子星，其磁场分布在$B \sim 10^{12}$ G处达到峰值。如果中子星的磁场在诞生时至少有这个强度，那么在双星系统中发射出喷流之前，它必须有相当大的衰减。我们研究中子星的磁场演化，从一个高质量的恒星伴星的风吸积物质，以便我们可以限制吸积率和地壳中的杂质，这是必要的条件喷流形成。我们求解了中子星磁场在地壳中的扩散和对流的感应方程，假设球形吸积在一个简化的一维处理。我们结合了最先进的微观物理学，包括一致的热演化曲线，并根据核心的超流性条件假设了两种不同的中子星冷却方案。我们发现，在这种情况下，磁场衰减在长时间尺度主要是由吸积率，而杂质含量和热演化的中子星发挥次要作用。对于吸积率$\dot{M}\gtrsim10^{-10}$ M $_{\odot}$ yr $^{-1}$，表面磁场在$\sim$ 10 $^7$ yr中衰减达4个数量级，这是这些系统中高质量恒星伴星演化所施加的时间尺度。基于这些结果，我们讨论了在强风吸积的高质量双星系统中，如超巨星快速X射线瞬变，瞬时喷流发射的可能性。
英文摘要：
In the magneto-centrifugal mechanism for jet formation, accreting neutron stars are assumed to produce relativistic jets only if their surface magnetic field is weak enough ($B \sim 10^8$ G). However, the most common manifestation of neutron stars are pulsars, whose magnetic field distribution peaks at $B \sim 10^{12}$ G. If the neutron star magnetic field has at least this strength at birth, it must decay considerably before jets can be launched in binary systems. We study the magnetic field evolution of a neutron star that accretes matter from the wind of a high-mass stellar companion so that we can constrain the accretion rate and the impurities in the crust, which are necessary conditions for jet formation. We solved the induction equation for the diffusion and convection of the neutron star magnetic field confined to the crust, assuming spherical accretion in a simpliflied one-dimensional treatment. We incorporated state-of-the-art microphysics, including consistent thermal evolution profiles, and assumed two different neutron star cooling scenarios based on the superfluidity conditions at the core. We find that in this scenario, magnetic field decay at long timescales is governed mainly by the accretion rate, while the impurity content and thermal evolution of the neutron star play a secondary role. For accretion rates $\dot{M}\gtrsim10^{-10}$ M$_{\odot}$ yr$^{-1}$, surface magnetic fields can decay up to four orders of magnitude in $\sim$10$^7$ yr, which is the timescale imposed by the evolution of the high-mass stellar companion in these systems. Based on these results, we discuss the possibility of transient jet-launching in strong wind-accreting high-mass binary systems like supergiant fast X-ray transients.
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