Anomalous X-ray pulsars and soft gamma repeaters are slowly rotating, young, and isolated neutron stars exhibiting sporadic outbursts and high X-ray quiescent luminosities. They are believed to be powered by ultrastrong magnetic fields, B ∼ 10¹⁴−10¹⁵ G, associated with “magnetars.” In the peculiar case of SGR 0418+5729, timing parameters imply a dipolar B-field of 6.1 10¹² G. This discovery has challenged the traditional picture of magnetars in terms of B-field strengths, evolutionary stages, and ages. Here we provide a novel approach to estimate a magnetar’s age by considering the self-consistent time evolution of a plasma-filled oblique pulsar with the state-of-the-art magnetospheric particle acceleration gaps. The rotational period of magnetars increases over time due to angular momentum extraction by gravitational-wave radiations, magnetic dipole radiations, and particle winds. These torques also change the obliquity angle between the magnetic and rotation axes. For SGR 0418+5729, we obtain a dipolar B-field of 1.0 10¹⁴ G, and a realistic age of ∼18 kyr, consistent within the magnetar paradigm.

异常 X 射线脉冲星和软伽马中继器是缓慢旋转的、年轻的、孤立的中子星，表现出零星爆发和高 X 射线静态光度。它们被认为是由与“磁星”相关的超强磁场B ∼ 10 ¹⁴ -10 ¹⁵ G提供动力的。在 SGR 0418+5729 的特殊情况下，时序参数意味着6.1 10 ¹² G的偶极B 场。这一发现挑战了磁星在B方面的传统图片-场强、进化阶段和年龄。在这里，我们通过考虑具有最先进磁层粒子加速间隙的等离子体填充倾斜脉冲星的自洽时间演化，提供了一种估计磁星年龄的新方法。由于引力波辐射、磁偶极子辐射和粒子风的角动量提取，磁星的自转周期会随着时间的推移而增加。这些扭矩还会改变磁轴和旋转轴之间的倾斜角。对于 SGR 0418+5729，我们获得了1.0 10 ¹⁴ G的偶极B 场和 ∼18 kyr 的实际年龄，在磁星范式内是一致的。