Ultraluminous X-ray source 1E 0953.8+6918 (M81 X-9): an intermediate-mass black hole candidate and its environs |
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| Authors: | QDaniel Wang |
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| Institution: | Astronomy Department, University of Massachusetts, Amherst, MA 01003, USA |
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| Abstract: | We present a ROSAT and ASCA study of the Einstein source X-9 and its relation to a shock-heated shell-like optical nebula in a tidal arm of the M81 group of interacting galaxies. Our ASCA observation of the source shows a flat and featureless X-ray spectrum well described by a multicolour disc blackbody model. The source most likely represents an optically thick accretion disc around an intermediate-mass black hole ( M ～102 M⊙) in its high/soft state, similar to other variable ultraluminous X-ray sources observed in nearby disc galaxies. Using constraints derived from both the innermost stable orbit around a black hole and the Eddington luminosity, we find that the black hole is fast-rotating and that its mass is between ～80 M⊙–1.5×102 M⊙. The inferred bolometric luminosity of the accretion disc is ～(1.1×1040 erg s?1)/(cos i ). Furthermore, we find that the optical nebula is very energetic and may contain large amounts of hot gas, accounting for a soft X-ray component as indicated by archival ROSAT PSPC data. The nebula is apparently associated with X-9; the latter may be powering the former and/or they could be formed in the same event (e.g. a hypernova). Such a connection, if confirmed, could have strong implications for understanding both the birth of intermediate-mass black holes and the formation of energetic interstellar structures. |
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| Keywords: | binaries: general ISM: bubbles galaxies: individual: M81 X-rays: galaxies |
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