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.
- Publication:
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Research in Astronomy and Astrophysics
- Pub Date:
- May 2017
- DOI:
- 10.1088/1674-4527/17/6/63
- arXiv:
- arXiv:1703.08476
- Bibcode:
- 2017RAA....17...63C
- Keywords:
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- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- To appear in Research in Astronomy and Astrophysics