Super-eddington accretion in the ultraluminous x-ray source NGC 1313 X-2: An ephemeral feast

Journal Article · Fri Jan 10 04:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/780/2/147· OSTI ID:22348244

Weng, Shan-Shan ^[1]; Zhang, Shuang-Nan; Zhao, Hai-Hui ^[2]

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1. Department of Physics, Xiangtan University, Xiangtan 411105 (China)
2. Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

We investigate the X-ray spectrum, variability, and the surrounding ionized bubble of NGC 1313 X-2 to explore the physics of super-Eddington accretion. Beyond the Eddington luminosity, the accretion disk of NGC 1313 X-2 is truncated at a large radius (∼50 times the innermost stable circular orbit), and displays the similar evolution track with both luminous Galactic black-hole and neutron star X-ray binaries (XRBs). In super-critical accretion, the speed of radiatively driven outflows from the inner disk is mildly relativistic. Such ultra-fast outflows would be overionized and might produce weak Fe K absorption lines, which may be detected by the coming X-ray mission Astro-H. If NGC 1313 X-2 is a massive stellar XRB, the high luminosity indicates that an ephemeral feast is held in the source. That is, the source must be accreting at a hyper-Eddington mass rate to give the super-Eddington emission over ∼10{sup 4}-10{sup 5} yr. The expansion of the surrounding bubble nebula with a velocity of ∼100 km s{sup –1} might indicate that it has existed over ∼10{sup 6} yr and is inflated by the radiatively driven outflows from the transient with a duty cycle of activity of ∼ a few percent. Alternatively, if the surrounding bubble nebula is produced by line-driven winds, less energy is required than the radiatively driven outflow scenario, and the radius of the Strömgren radius agrees with the nebula size. Our results are in favor of the line-driven winds scenario, which can avoid the conflict between the short accretion age and the apparently much longer bubble age inferred from the expansion velocity in the nebula.

• OSTI ID: 22348244
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 780; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BLACK HOLES
EMISSION
EVOLUTION
EXPANSION
K ABSORPTION
LUMINOSITY
MASS
NEBULAE
NEUTRON STARS
RELATIVISTIC RANGE
TRANSIENTS
VELOCITY
X RADIATION
X-RAY SOURCES
X-RAY SPECTRA