The Great Pretenders Among the ULX Class. (May 2017)

• Record Type: Journal Article
• Authors: Christodoulou, Dimitris M.; Laycock, Silas G. T.; Kazanas, Demosthenes; Cappallo, Rigel; Contopoulos, Ioannis
• Is Part Of: Research in astronomy and astrophysics. Volume 17:Number 6(2017:Jun.)
• Publication Date: 2017-05
• Subjects: accretion, accretion disks -- stars: magnetic fields -- stars: neutron -- X-rays: binaries -- X-rays: individual (M82 X-2, NGC 7793 P13, NGC 5907 ULX-1); Astronomy -- Periodicals; Astrophysics -- Periodicals; 520.5
• DOI: 10.1088/1674-4527/17/6/63
• Languages: English
• ISSNs: 1674-4527

Abstract

Abstract: The recent discoveries of pulsed X-ray emission from three ultraluminous X-ray (ULX) sources have finally enabled us to recognize a subclass within the ULX class: the great pretenders, neutron stars (NSs) that appear to emit X-ray radiation at isotropic luminosities L X = 7 × 10 39 erg s − 1 − 1 × 10 41 erg s − 1 only because their emissions are strongly beamed toward our direction and our sight lines are offset by only a few degrees from their magnetic-dipole axes. The three known pretenders appear to be stronger emitters than the presumed black holes of the ULX class, such as Holmberg II & IX X-1, IC10 X-1 and NGC 300 X-1. For these three NSs, we have adopted a single reasonable assumption, that their brightest observed outbursts unfold at the Eddington rate, and we have calculated both their propeller states and their surface magnetic-field magnitudes. We find that the results are not at all different from those recently obtained for the Magellanic Be/X-ray pulsars: the three NSs reveal modest magnetic fields of about 0.3–0.4 TG and beamed propeller-line X-ray luminosities of ∼ 10 36 − 10 37 erg s − 1, substantially below the Eddington limit.