Accretion disk spectra of the ultra-luminous X-ray sources in nearby spiral galaxies and galactic superluminal jet sources

Ken Ebisawa, Piotr T. Zycki, Aya Kubota, Tsunefumi Mizuno, Ken Ya Watarai

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and Galactic superluminal jet sources share the common spectral characteristic that they have unusually high disk temperatures which cannot be explained in the framework of the standard optically thick accretion disk in the Schwarzschild metric. On the other hand, the standard accretion disk around the Kerr black hole might explain the observed high disk temperature, as the inner radius of the Kerr disk gets smaller and the disk temperature can be consequently higher. However, we point out that the observable Kerr disk spectra becomes significantly harder than Schwarzschild disk spectra only when the disk is highly inclined. This is because the emission from the innermost part of the accretion disk is Doppler-boosted for an edge-on Kerr disk, while hardly seen for a face-on disk. The Galactic superluminal jet sources are known to be highly inclined systems, thus their energy spectra may be explained with the standard Kerr disk with known black hole masses. For ULXs, on the other hand, the standard Kerr disk model seems implausible, since it is highly unlikely that their accretion disks are preferentially inclined, and, if edge-on Kerr disk model is applied, the black hole mass becomes unreasonably large (≳ 300 M). Instead, the slim disk (advection dominated optically thick disk) model is likely to explain the observed super-Eddington luminosities, hard energy spectra, and spectral variations of ULXs. We suggest that ULXs are accreting black holes with a few tens of solar mass, which is not unexpected from the standard stellar evolution scenario, and that their X-ray emission is from the slim disk shining at super-Eddington luminosities.

Original languageEnglish
Pages (from-to)67-70
Number of pages4
JournalProgress of Theoretical Physics Supplement
Volume155
Publication statusPublished - 2004
Externally publishedYes

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spiral galaxies
accretion disks
x rays
energy spectra
luminosity
Schwarzschild metric
stellar evolution
advection
temperature

ASJC Scopus subject areas

  • Physics and Astronomy(all)

Cite this

Accretion disk spectra of the ultra-luminous X-ray sources in nearby spiral galaxies and galactic superluminal jet sources. / Ebisawa, Ken; Zycki, Piotr T.; Kubota, Aya; Mizuno, Tsunefumi; Watarai, Ken Ya.

In: Progress of Theoretical Physics Supplement, Vol. 155, 2004, p. 67-70.

Research output: Contribution to journalArticle

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