[论文解读] SXP 1062, a young Be X-ray binary pulsar with long spin period; Implications for the neutron star birth spin

F. Haberl, R. Sturm+3 more|MPG.PuRe (Max Planck Society)|Dec 2, 2011

Astrophysical Phenomena and Observations参考文献 37被引用 32

一句话总结

本文报告在大麦哲伦云中发现一个年轻的超新星遗迹（SNR），中心为Be/X射线双星脉冲星SXP 1062，该脉冲星具有显著长的自转周期1062秒及较高的自转降速率−2.6 × 10⁻¹² Hz s⁻¹。作者推断，该中子星可能以至少0.5秒的自转周期诞生，挑战了传统认为中子星通常以数十毫秒的周期诞生的假设。

ABSTRACT

(shortened) The SMC is ideally suited to investigating the recent star formation history from X-ray source population studies. It harbours a large number of Be/X-ray binaries, and the supernova remnants can be easily resolved with imaging X-ray instruments. We search for new supernova remnants in the SMC and in particular for composite remnants with a central X-ray source. We study the morphology of newly found candidate supernova remnants using radio, optical and X-ray images and investigate their X-ray spectra. Here we report on the discovery of the new supernova remnant around the recently discovered Be/X-ray binary pulsar SXP 1062 in radio and X-ray images. The Be/X-ray binary system is found near the centre of the supernova remnant, which is located at the outer edge of the eastern wing of the SMC. The remnant is oxygen-rich, indicating that it developed from a type Ib event. From XMM-Newton observations we find that the neutron star with a spin period of 1062 s shows a very high average spin-down rate of 0.26 s per day over the observing period of 18 days. From the currently accepted models, our estimated age of around 10000-25000 years for the supernova remnant is not long enough to spin down the neutron star from a few 10 ms to its current value. Assuming an upper limit of 25000 years for the age of the neutron star and the extreme case that the neutron star was spun down by the accretion torque that we have measured during the XMM-Newton observations since its birth, a lower limit of 0.5 s for the birth spin period is inferred. For more realistic, smaller long-term average accretion torques our results suggest that the neutron star was born with a correspondingly longer spin period. This implies that neutron stars in Be/X-ray binaries with long spin periods can be much younger than currently anticipated.

研究动机与目标

• 调查大麦哲伦云（SMC）中Be/X射线双星脉冲星SXP 1062与新发现的超新星遗迹（SNR）之间的关联。
• 确定SNR的年龄并评估其对SXP 1062中子星自转演化的影响。
• 检验观测到的中子星高自转降速率是否足以解释其当前1062秒的长自转周期，假设其以典型短周期（约10 ms）诞生。
• 基于观测到的自转降速行为，评估Be/X射线双星中中子星诞生自转周期分布的含义。

提出的方法

• 利用XMM-Newton X射线观测、光学窄带成像（MCELS）和射电连续谱数据（ATCA）进行多波段分析，以识别并表征SNR及其中心源。
• 从XMM-Newton EPIC-pn和MOS仪器中提取光谱，分析SXP 1062及周围SNR的X射线辐射，包括背景减除和源区选择。
• 基于18天观测基线内的相干X射线脉动，测量脉冲星的自转周期及其自转降速率（ḟ）。
• 利用形态学和光谱特性（包括指示为Ib型超新星的富氧成分）估算SNR的年龄。
• 在吸积力矩主导的假设下，对中子星自转演化进行建模，利用测得的自转降速率推导其诞生自转周期的下限。
• 将观测到的自转降速率与Be/X射线双星中吸积力矩的理论模型进行比较，考虑时间平均与瞬时力矩行为。

实验结果

研究问题

• RQ1 Be/X射线双星脉冲星SXP 1062是否与大麦哲伦云中的超新星遗迹存在物理关联？
• RQ2 基于多波段观测，SXP 1062周围超新星遗迹的估计年龄是多少？
• RQ3 若中子星以典型短周期（约10 ms）诞生，观测到的自转降速率是否足以解释其当前1062秒的自转周期？
• RQ4 若中子星自诞生以来仅因吸积力矩而自转降速，观测到的自转降速率对其诞生自转周期施加了何种限制？
• RQ5 SXP 1062与一个年轻SNR的关联是否意味着Be/X射线双星中的中子星可能以远长于传统假设的自转周期诞生？

主要发现

• 在射电、光学和X射线波段均发现了以大麦哲伦云中Be/X射线双星脉冲星SXP 1062为中心的壳状超新星遗迹。
• 该SNR富含氧，表明其起源于Ib型超新星，估计年龄为10,000至25,000年。
• SXP 1062中的中子星在18天的XMM-Newton观测期内表现出高达−2.6 × 10⁻¹² Hz s⁻¹的平均自转降速率。
• 假设中子星自诞生以来一直以该速率自转降速，可推导出其诞生自转周期的下限为0.5秒。
• 对于更现实、更低的长期平均吸积力矩，推导出的诞生自转周期将更长，表明Be/X射线双星中的中子星可能以远长于经典~10 ms的周期诞生。
• SXP 1062与一个年轻SNR的关联意味着，若中子星以长自转周期诞生，则其在Be/X射线双星中的年龄可能远比以往认为的年轻。