Orbital and superorbital periods in ULX pulsars, disc-fed HMXBs, Be/X-ray binaries, and double-periodic variables. (4th May 2020)

• Record Type: Journal Article
• Authors: Townsend, L J; Charles, P A
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 495:Number 1(2020)
• Page Start: L139
• Page End: L143
• Publication Date: 2020-05-04
• Subjects: pulsars: general -- X-rays: binaries -- binaries: close; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slaa078
• Languages: English
• ISSNs: 1745-3933

Abstract

ABSTRACT: We present evidence for a simple linear relationship between the orbital period and superorbital period in ultra-luminous X-ray (ULX) pulsars, akin to what is seen in the population of disc-fed neutron star supergiant X-ray binary and Be/X-ray binary systems. We argue that the most likely cause of this relationship is the modulation of precessing hotspots or density waves in an accretion or circumstellar disc by the binary motion of the system, implying a physical link between ULX pulsars and high-mass X-ray binary (HMXB) pulsars. This hypothesis is supported by recent studies of Galactic and Magellanic Cloud HMXBs accreting at super-Eddington rates, and the position of ULX pulsars on the spin period–orbital period diagram of HMXBs. An interesting secondary relationship discovered in this work is the apparent connection between disc-fed HMXBs, ULXs, and a seemingly unrelated group of early-type binaries showing so-called double-periodic variability. We suggest that these systems are good candidates to be the direct progenitors of Be/X-ray binaries.