The Slowest Spinning X-Ray Pulsar in an Extragalactic Globular Cluster
Journal
Date Issued
2017
Author(s)
Abstract
Neutron stars are thought to be born rapidly rotating and then exhibit a phase of 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}{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 Hertz. The neutron star in this unique wide binary with an orbital period {P}{orb}=30.5 {hr} 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 a relatively recent epoch by getting a ∼0.8 {M}☉ 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 therefore provides a long-sought missing piece in the standard pulsar recycling picture.
Volume
839
Issue
2
Start page
125
Issn Identifier
0004-637X
Ads BibCode
2017ApJ...839..125Z
Rights
open.access
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