标题： 磁星磁场演化的观测线索 显示英文标题

标题： Observational Clues to the Magnetic Evolution of Magnetars

摘要： 利用搭载于 Suzaku 卫星上的硬 X 射线探测器获取的四个存档 X 射线数据集，对三个磁星进行了定时研究，它们分别是：1E 1841-045（2006 年观测）、SGR 0501+4516（2008 年）和 1RXS J170849.0-400910（2009 年和 2010 年）。 它们的脉冲周期得到了重新确认，通常是在 12-50 keV 的能量范围内。1E 1841-045 的 11.783 秒脉冲以及 SGR 0501+4516 的 5.762 秒脉冲都表现出周期性的相位调制，分别具有约 23.4 ks 和约 16.4 ks 的长周期。对于 1RXS J170849.0-400910 的两个数据集，在 46.5 ks 处也观察到了脉冲相位调制现象。在这所有情况下，调制幅度为脉冲周期的 6% 到 16%。 包括之前确认的四个天体在内，这种特征性定时行为现在已经在总共七个磁星中被检测到，并被解释为中子星自由进动的结果，这些中子星的非球形变形程度约为 ~10^{-4}。 假设这种变形是由磁应力引起的，这些磁星被认为拥有 ~10^{16} G 的环向磁场。通过比较这些天体的估算环向磁场强度 Bt 与它们的偶极磁场强度 Bd，发现 Bt/Bd 比值随着它们的特征年龄而增加。因此，磁星的环向磁场可能比偶极磁场持续时间更长。 这解释了某些中子星类别的存在，这些中子星的偶极磁场相对较弱，但据推测内部隐藏着较强的环向磁场。 显示英文摘要

摘要： Utilizing four archival X-ray datasets taken with the Hard X-ray Detector onboard Suzaku, timing studies were performed on three magnetars, 1E 1841-045 (observed in 2006), SGR 0501+4516 (2008), and 1RXS J170849.0-400910 (2009 and 2010). Their pulsations were reconfirmed, typically in an energy range of 12-50 keV. The 11.783 s pulses of 1E 1841-045, and those of SGR 0501+4516 with 5.762 s were periodically phase modulated, with a long period of about 23.4 ks and about 16.4 ks, respectively. The pulse-phase modulation was also observed, at 46.5 ks, from two datasets of 1RXS J170849.0-400910. In all these cases, the modulation amplitude was 6 to 16 percent of the pulse cycle. Including previously confirmed four objects, this characteristic timing behavior is now detected from seven magnetars in total, and interpreted as a result of free precession of neutron stars that are deformed to an asphericity of ~10^{-4}. Assuming that the deformation is due to magnetic stress, these magnetars are inferred to harbor toroidal magnetic fields of Bt~10^{16} G. By comparing the estimated Bt of these objects with their poloidal dipole field Bd, the Bt/Bd ratio is found to increase with their characteristic age. Therefore, the toroidal fields of magnetars are likely to last longer than their dipole fields. This explains the presence of some classes of neutron stars that have relatively weak Bd but are suspected to hide strong Bt inside them.