The Orbital Period of the Ultraluminous X-ray Source in M82
Philip Kaaret,*
Melanie G. Simet,
Cornelia C. Lang
The ultraluminous x-ray source (ULX) in the galaxy M82 has been
identified as a possible intermediate-mass black hole formed
in stellar collisions in the super star cluster MGG 11. The
x-ray flux from M82 is modulated, with a peak-to-peak amplitude
corresponding to an isotropic luminosity of 2.4 _ 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 lifetime, indicating that we see the ULX in M82
in a brief and unusual period of its evolution.
* To whom correspondence should be addressed. E-mail: philip-kaaret{at}uiowa.edu
