NATURE OF THE EXTREME ULTRALUMINOUS X-RAY SOURCES

ABSTRACT In this proof-of-concept study we demonstrate that in a binary system mass can be transferred toward an accreting compact object at an extremely high rate. If the transferred mass is efficiently converted to X-ray luminosity (with disregard of the classical Eddington limit) or if the X-rays...

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Bibliographic Details
Published in:The Astrophysical journal 2015-09, Vol.810 (1), p.1-8
Main Authors: Wiktorowicz, Grzegorz, Sobolewska, Ma gorzata, Sa dowski, Aleksander, Belczynski, Krzysztof
Format: Article
Language:English
Subjects:
Approximation
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BINARY STARS
Binary systems
Binary systems (materials)
BLACK HOLES
HELIUM
LUMINOSITY
MASS TRANSFER
NEUTRON STARS
NEUTRONS
ROCHE EQUIPOTENTIALS
stars: black holes
stars: neutron
X RADIATION
X-RAY SOURCES
X-rays
X-rays: binaries
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Summary:ABSTRACT In this proof-of-concept study we demonstrate that in a binary system mass can be transferred toward an accreting compact object at an extremely high rate. If the transferred mass is efficiently converted to X-ray luminosity (with disregard of the classical Eddington limit) or if the X-rays are focused into a narrow beam, then binaries can form extreme ultraluminous X-ray (ULX) sources with an X-ray luminosity of . For example, Lasota and King argued that the brightest known ULX (HLX-1) is a regular binary system with a rather low-mass compact object (a stellar-origin black hole (BH) or a neutron star (NS)). The predicted formation efficiencies and lifetimes of binaries with the very high mass transfer rates are large enough to explain all observed systems with extreme X-ray luminosities. These systems are not only limited to binaries with stellar-origin BH accretors. Notably, we have also identified such objects with NSs. Typically, a BH is fed by a massive ( ) Hertzsprung gap donor with Roche lobe overflow (RLOF) rate of ). For NS systems the typical donors are evolved low-mass ( ) helium stars with RLOF rate of . Our study does not prove that any particular extreme ULX is a regular binary system, but it demonstrates that any ULX, including the most luminous ones, may potentially be a short-lived phase in the life of a binary star.
ISSN:0004-637X
1538-4357
1538-4357
DOI:10.1088/0004-637X/810/1/20