Computer Science
Scientific paper
Apr 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007iaus..238..209m&link_type=abstract
Black Holes from Stars to Galaxies -- Across the Range of Masses. Edited by V. Karas and G. Matt. Proceedings of IAU Symposium #
Computer Science
8
Scientific paper
Ultra-luminous compact X-ray sources (ULXs; Makishima et al. 2000) are promising candidates for intermediate-mass black holes. This candidacy comes in the first place from their high X-ray luminosities reaching 10(39.5-40.5) erg/s, corresponding to the Eddington limits for 20-200 M[sun] black holes. Although ULXs could be normal stellar-mass black holes with highly super-Eddington and/ or anisotropic X-ray emission (e.g., King 2002), this possibility is considered rather low because of the absence of such abnormally luminous states among known Galactic and Magellanic black-hole binaries (BHB). Although ULXs exhibit rather complex spectral behavior, they are typically found in either multi-color-disk type spectral state, or in power-law type one. The former state of ULXs may be distinguished from the standard-disk state of Galactic/Magellanic BHBs, by the rather high disk temperature (Makishima et al. 200) of ULXs and apparent non-constancy of their inner-disk radii (Mizuno et al. 2001). Observations with the CCD camera (XIS) onboard Suzaku launched in 2005 July, as well as the XMM-Newton EPIC (e.g., Foschini et al. 2005; Tsunoda et al. 2006), suggest that the multi-color-disk type spectra are in reality emitted by slim disks (Watarai et al. 2001), which may form around black holes under super-critical accretion rate (but the luminosity remaining only slightly super-Eddington; Kubota and Makishima 2004; Abe et al. 2005). The Hard X-ray Detector onboard Suzaku is providing useful upper limits on the 15-50 keV emission from a few ULXs. It is intriguing that a fair fraction of ULXs are surrounded by optical line-emitting nebulae (Pakull 2004). In X-rays as well, some ULXs may be accompanied by thin-thermal spectral components (e.g., Miyaji et al. 2001). This possibility is reinforced by the Suzaku XIS data, and archival XMM-Newton data. These optical and X-ray results suggest that each ULX is surrounded by a gigantic hot plasma bubble, which could be interpreted as a remnant of the explosion which produced the IMBH.
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