Submitted on October 6, 2005
Accepted on November 18, 2005
The Orbital Period of the Ultraluminous X-ray Source in M82
Philip Kaaret 1*,
Melanie G. Simet 1,
Cornelia C. Lang 1
1 Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA.
* To whom correspondence should be addressed.
Philip Kaaret , E-mail: philip-kaaret{at}uiowa.edu
The ultraluminous x-ray source (ULX) in M82 has been identified as a possible intermediate mass black hole formed in stellar collisions in the super star cluster MGG 11. We find that the x-ray flux from M82 is modulated with a peak to peak amplitude corresponding to an isotropic luminosity of 2.4 x 1040 erg s-1 in M82 and a period of 62.0 ± 2.5 days, which we interpret as the orbital period of the ULX binary. This orbital period implies that the mass donor star must be a giant or supergiant. Large mass transfer rates, sufficient to fuel the ULX, are expected for a giant phase mass donor in an x-ray binary. The giant phase has a short life time, indicating that we see the ULX in M82 in a brief and unusual period of its evolution.
