Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 712, Issue 2, Pages L169-L173Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/712/2/L169
Keywords
accretion, accretion disks; black hole physics; X-rays: binaries; X-rays: individual (CXOM82 J095550.2+694047=X41.4+60)
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Funding
- 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]
- Chandra [GO9-0034X]
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The thermal dominant state in black hole binaries (BHBs) is well understood but rarely seen in ultraluminous X-ray sources (ULXs). Using simultaneous observations of M82 with Chandra and XMM-Newton, we report the first likely identification of the thermal dominant state in a ULX based on the disappearance of X-ray oscillations, low timing noise, and a spectrum dominated by multicolor disk emission with luminosity varying to the fourth power of the disk temperature. This indicates that ULXs are similar to Galactic BHBs. The brightest X-ray spectrum can be fitted with a relativistic disk model with either a highly super-Eddington (L(disk)/L(Edd) = 160) non-rotating black hole (BH) or a close to Eddington (L(disk)/L(Edd) similar to 2) rapidly rotating BH. The latter interpretation is preferred, due to the absence of such highly super-Eddington states in Galactic BHs and active galactic nuclei, and suggests that the ULX in M82 contains a BH of 200-800 solar masses with nearly maximal spin. On long timescales, the source normally stays at a relatively low flux level with a regular 62-day orbital modulation and occasionally exhibits irregular flaring activity. These thermal dominant states are observed during outbursts.
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