Affiliation:
1. Key Laboratory for Computational Astrophysics, National Astronomical Observatory, Chinese Academy of Sciences, Datun Road 20A, Beijing 100012, People’s Republic of China
2. School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
Abstract
ABSTRACT
In classical supergiant X-ray binaries (SgXBs), the Bondi–Hoyle–Lyttleton wind accretion was usually assumed, and the angular momentum transport to the accretors is inefficient. The observed spin-up/spin-down behaviour of the neutron star in SgXBs is not well understood. In this paper, we report an extended low state of Vela X-1 (at orbital phases 0.16–0.2), lasting for at least 30 ks, observed with Chandra during the onset of an unusual spin-up period. During this low state, the continuum fluxes dropped by a factor of 10 compared to the preceding flare period, and the continuum pulsation almost disappeared. Meanwhile, the Fe K α fluxes of the low state were similar to the preceding flare period, leading to an Fe K α equivalent width (EW) of 0.6 keV, as high as the Fe K α EW during the eclipse phase of Vela X-1. Both the pulsation cessation and the high Fe K α EW indicate an axisymmetric structure with a column density larger than 1024 cm−2 on a spatial scale of the accretion radius of Vela X-1. These phenomena are consistent with the existence of an accretion disc that leads to the following spin-up of Vela X-1. It indicates that disc accretion, although not always, does occur in classical wind-fed SgXBs.
Funder
National Natural Science Foundation of China
Chinese Academy of Sciences
Publisher
Oxford University Press (OUP)
Subject
Space and Planetary Science,Astronomy and Astrophysics
Cited by
16 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
1. High-Mass X-ray Binaries;Handbook of X-ray and Gamma-ray Astrophysics;2024
2. Stellar black holes and compact stellar remnants;Black Holes in the Era of Gravitational-Wave Astronomy;2024
3. High-Mass X-ray Binaries;Handbook of X-ray and Gamma-ray Astrophysics;2023-09-05
4. A NICER Viewing Angle on the Accretion Stream of Vela X-1;The Astrophysical Journal;2023-06-01
5. An Overview of Compact Star Populations and Some of Its Open Problems;Galaxies;2023-01-18