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The Great Pretenders Among the ULX Class
Dimitris M Christodoulou1,2, Silas G T Laycock1,3, Demosthenes Kazanas4
1Lowell Center for Space Science and Technology, University of Massachusetts Lowell, Lowell, MA, 01854, USA.
Research in Astronomy and Astrophysics
|August 28, 2020
Summary
Great pretenders, a new subclass of ultraluminous X-ray (ULX) sources, are identified as neutron stars (NSs) with beamed emissions. These NSs mimic higher luminosities due to their orientation, revealing modest magnetic fields and lower intrinsic X-ray luminosities.
Area of Science:
- Astrophysics
- High-energy astrophysics
- X-ray astronomy
Background:
- Ultraluminous X-ray (ULX) sources challenge conventional understanding of X-ray binaries.
- Pulsed X-ray emission has been detected from three ULX sources, suggesting a new subclass.
Purpose of the Study:
- To identify and characterize a subclass of ULX sources, termed 'great pretenders'.
- To investigate the nature of these sources, specifically whether they are neutron stars (NSs) or black holes.
- To determine the magnetic field strengths and emission properties of these 'great pretender' NSs.
Main Methods:
- Analysis of pulsed X-ray emission data from three ULX sources.
- Modeling of X-ray emission assuming Eddington-limited outbursts.
- Calculation of propeller states and surface magnetic-field magnitudes for NSs.
Main Results:
- Three ULX sources identified as 'great pretenders' are likely neutron stars (NSs).
- These NSs exhibit beamed X-ray emission, mimicking higher isotropic luminosities.
- Calculated magnetic fields are modest (~0.3-0.4 TG), with intrinsic X-ray luminosities of ~10^36-10^37 erg s^-1.
Conclusions:
- The 'great pretender' subclass consists of neutron stars with beamed emission, not intrinsically more luminous objects.
- Their observed high luminosities are an observational artifact due to viewing angle.
- These findings align with properties of Magellanic Be/X-ray pulsars.
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