河外球状星团中旋转最慢的X射线脉冲星
The slowest spinning X-ray pulsar in an extragalactic globular cluster
摘要：
中子星被认为是出生时快速旋转，然后表现出一个阶段的旋转动力脉动，因为他们放慢到1-10秒的周期。在我们的银河系中观测到的大量毫秒中子星可以用再循环概念来解释：在双星系统中，在一个施主星吸积的时期，中子星旋转到毫秒周期。然而，在这个回收过程中，只有少数几个旋转频率相对较高的恒星被观察到。本文报道了在仙女座星系球状星团B 091 D中用$P_{\rm spin} = 1.20$探测到的X射线脉冲星，它是在球状星团中发现的最慢的脉冲星。这颗明亮的（高达爱丁顿光度的30%）自旋脉冲星，持续了12年的观测，必须在不到100万年前开始吸积，还没有时间加速到数百赫兹。在这个独特的宽双星中的中子星，轨道周期为$P_{\rm orb} = 30.5$ h，位于一个12 Gyr的富含金属的星团中，它是从一个低质量的、稍微进化的后主序星伴星吸积而来的。我们认为，我们正在目睹一个双星形成在相对较近的时代，得到一个$\sim 0.8M_\odot$恒星在动力学相互作用-一个可行的方案，在一个巨大的密集球状星团像B 091 D与高全球和特定的恒星相遇率。因此，这种强烈吸积的非回收X射线脉冲星提供了标准脉冲星回收图片中长期寻找的缺失部分。
英文摘要：
Neutron stars are thought to be born rapidly rotating and then exhibit a phase of a rotation-powered pulsations as they slow down to 1-10 s periods. The significant population of millisecond pulsars observed in our Galaxy is explained by the recycling concept: during an epoch of accretion from a donor star in a binary system, the neutron star is spun up to millisecond periods. However, only a few pulsars are observed during this recycling process, with relatively high rotational frequencies. Here we report the detection of an X-ray pulsar with $P_{\rm spin} = 1.20$ s in the globular cluster B091D in the Andromeda galaxy, the slowest pulsar ever found in a globular cluster. This bright (up-to 30% of the Eddington luminosity) spinning-up pulsar, persistent over the 12 years of observations, must have started accreting less than 1 Myr ago and has not yet had time to accelerate to hundreds of Hz. The neutron star in this unique wide binary with an orbital period $P_{\rm orb} = 30.5$ h in a 12 Gyr old, metal rich star cluster, accretes from a low mass, slightly evolved post-main sequence companion. We argue that we are witnessing a binary formed at relatively recent epoch by getting a $\sim 0.8M_\odot$ star in a dynamical interaction -- a viable scenario in a massive dense globular cluster like B091D with high global and specific stellar encounter rates. This intensively accreting non-recycled X-ray pulsar provides therefore a long-sought missing piece in the standard pulsar recycling picture.
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