期刊
ASTROPHYSICAL JOURNAL
卷 737, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/737/2/81
关键词
accretion, accretion disks; black hole physics; galaxies: stellar content
资金
- National Natural Science Foundation of China [10903004, 10978001]
- 973 Program of China [2009CB824800]
- Foundation for the Author of National Excellent Doctoral Dissertation of China [200935]
- Tsinghua University
- Program for New Century Excellent Talents in University
- NASA [NNX08AJ26G]
- NASA [NNX08AJ26G, 101076] Funding Source: Federal RePORTER
Using archival Hubble Space Telescope (HST) imaging data, we report the multiband photometric properties of 13 ultraluminous X-ray sources (ULXs) that have a unique compact optical counterpart. Both magnitude and color variation are detected at timescales of days to years. The optical color, variability, and X-ray to optical flux ratio indicate that the optical emission of most ULXs is dominated by X-ray reprocessing on the disk, similar to that of low-mass X-ray binaries. For most sources, the optical spectrum is a power law, F-nu alpha nu(alpha) with alpha in the range 1.0-2.0 and the optically emitting region has a size on the order of 10(12) cm. Exceptions are NGC 2403 X-1 and M83 IXO 82, which show optical spectra consistent with direct emission from a standard thin disk, M101 ULX-1 and M81 ULS1, which have X-ray to optical flux ratios more similar to high-mass X-ray binaries, and IC 342 X-1, in which the optical light may be dominated by the companion star. Inconsistent extinction between the optical counterpart of NGC 5204 X-1 and the nearby optical nebulae suggests that they may be unrelated.
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