The Great Pretenders Among the ULX Class

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.

Formation of Double Neutron Star Systems

“…The recent discovery that a number of ultra-luminous X-ray sources (ULXs: M82 X-2, NGC 7793 P13 and NGC 5907) are pulsating NSs (Bachetti et al 2014;Israel et al 2017b;Fürst et al 2016;Israel et al 2017a) has lead to the suggestion that ULXs might be HMXBs (Ekşi et al 2015;Kluźniak & Lasota 2015;Shao & Li 2015;Mushtukov et al 2015), including BeHMXBs (Karino & Miller 2016;Christodoulou et al 2017), and which could therefore suggest that some ULXs might potentially lead to the production DNS systems.…”

Ultraluminous X‐ray sources: Three exciting years

“…Ekşi et al 2015;Dall'Osso et al 2015), and beaming (e.g. Christodoulou et al 2014). This source has also been proposed as an alternative path for the formation of millisecond pulsars (Kluźniak and Lasota 2015).…”

Bose-Einstein condensate strings

“…For a barotropic fluid, the limit n → ∞ must be taken before substituting the equation of state into the Poisson equation, leading to the separate (critical) case, for which ð1=ξÞdðξdðlnðτÞÞ=dτÞ=dξ þ τ ¼ 0. In this case, we have that Γ → 2, α → U 0 and ξ ¼ ½U 0 =ð4πGρ c Þ 1=2 r. This equation can also be generalized to include rotating fluids by adding a term of the form Ω 2 ξ, where Ω ¼ ΩðξÞ is a function of the rescaled radial coordinate ξ only, to the right-hand side [31][32][33].…”

“…Hence, all Bose-Einstein condensate forms of matter can generally be described as fluids satisfying a polytropic equation of state of index n and, importantly, this remains true relativistically, as well as in the nonrelativistic limit, which, in effect, has been thoroughly studied in [31][32][33], at least in the limit of the Fermi-Thomas approximation. The remainder of this study is therefore dedicated to determining the astrophysical and cosmological significance of stringlike (i.e.…”