A 62 Day X-Ray Periodicity and an X-Ray Flare from the Ultraluminous X-Ray Source in M82

Abstract

In 240 days of X-ray monitoring of M82, we have discovered an X-ray periodicity at $62.0\pm 2.5$ days with a peak to peak amplitude corresponding to an isotropic luminosity of $2.4\times 10^{40}\mathrm{erg}{\mathrm{s}}^{-1}$ in M82 and an X-ray flare reaching a peak luminosity of $9.8\times 10^{40}\mathrm{erg}{\mathrm{s}}^{-1}$. The periodicity and flare likely originate from the ultraluminous X-ray source (ULX) in M82 which has been identified as a possible intermediate mass black hole. We suggest that the 62~day modulation is due to orbital motion within an X-ray binary with a Roche-lobe overflowing companion star which would imply that the average density of the companion star is near $5\times 10^{-5}\mathrm{gc}{\mathrm{m}}^{-3}$ and is therefore a giant or supergiant. Chandra observations just after the flare show an energy spectrum that is consistent with a power-law with no evidence of a thermal component or line emission. Radio observations made with the VLA during the flare allow us to rule out a blazar identification for the source and place strong constraints on relativistically beamed models of the X-ray emission. The Chandra observations reveal a second X-ray source reached a flux of $4.4\times 10^{-12}\mathrm{ergc}{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$ in the 0.3-7 keV band which is dramatically higher than any flux previously seen from this source and corresponds to an isotropic luminosity of $1.1\times 10^{40}\mathrm{erg}{\mathrm{s}}^{-1}$. This source is a second ultraluminous X-ray source in M82 and may give rise to the QPOs detected from the central region of M82.

15 pages, one color figure, to appear in ApJ

References in corpus (1)

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

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