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Identification of the X-Ray Thermal Dominant State in an Ultraluminous X-Ray Source in M82
Journal article   Open access   Peer reviewed

Identification of the X-Ray Thermal Dominant State in an Ultraluminous X-Ray Source in M82

Hua Feng and Philip Kaaret
Astrophysical journal. Letters, Vol.712(2), pp.L169-L173
03/01/2010
DOI: 10.1088/2041-8205/712/2/L169
url
https://doi.org/10.1088/2041-8205/712/2/L169View
Published (Version of record) Open Access

Abstract

Astrophys. J. 712: L169-L173, 2010 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 4th 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 or a close to Eddington (L_disk/L_Edd ~ 2) rapidly rotating black hole. The latter interpretation is preferred, due to the absence of such highly super-Eddington states in Galactic black holes and active galactic nuclei, and suggests that the ULX in M82 contains a black hole 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. The thermal dominant states are all found during outbursts.
 Physics - High Energy Astrophysical Phenomena

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