The Orbital Period of the Ultraluminous X-ray Source in M82

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Science  27 Jan 2006:
Vol. 311, Issue 5760, pp. 491
DOI: 10.1126/science.1121067

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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.

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