Accretion Disk Spectra of the Brightest Ultra - luminous X - ray Source in M 82

Emission spectra of hot accretion disks characteristic of advection dominated accretion flow (ADAF) models are investigated for comparison with the brightest ultra-luminous source, X-1, in the galaxy M82. If the spectral state of the source is similar to the low luminosity hard state of stellar mass black holes in our Galaxy, a fit to the Chandra X-ray spectrum and constraints from the radio and infrared upper limits, require a black hole mass in the range of 9×10−5×10 M⊙. Lower black hole masses (. 10 M⊙) are possible if M82 X-1 corresponds to the high luminosity hard state of Galactic black hole X-ray binary sources. Both of these spectrally degenerate hot accretion disk solutions lead to an intermediate mass black hole interpretation for M82 X-1. Since these solutions have different spectral variability with X-ray luminosity and predict different infrared emission, they can be distinguished by future off axis Chandra observations or simultaneous sensitive infrared detections. Subject headings: black hole physics galaxies: individual: M82: X-rays: galaxies X-rays: black holes Shanghai Astronomical Observatory, 80 Nandan Road, Shanghai 200030, China Joint Institute for Galaxy and Cosmology (JOINGC) of SHAO and USTC Northwestern University, Department of Physics and Astronomy, 2145 Sheridan Road, Evanston, IL 60208 ASIAA/National Tsing Hua University TIARA, Hsinchu, Taiwan Inter-University Center for Astronomy and Astrophyscs, Post Bag 4, Ganeshkhind, Pune 411 007, India Department of Astronomy, Peking University, Beijing 100871, China Department of Physics, Purdue University, West Lafayette, IN 47907