Chandra High-Resolution Camera Observations of the Luminous X-Ray Source in the Starburst Galaxy M82

We have analyzed early Chandra High Resolution Camera observations of the starburst galaxy M82, concentrating on the most luminous x-ray source. We find a position for the source of $\rm R.A. = 09^h 55^m 50^s.2, decl. = +69^{\circ} 40\arcmin 46\arcsec.6$ (J2000) with a $1\sigma$ radial error of $0.7\arcsec$ and report detection of an x-ray oscillation with a period in the range 573-613 s. The accurate x-ray position shows that the luminous source is not at the dynamical centre of M82 or coincident with any suggested radio AGN candidate. The detection of $\sim 600$s oscillations excludes the possibility that the source is a supernova or remnant, suggests that the source is a compact object, and can be used to place an upper bound of $1.3 \times 10^{6} M_{\odot}$ on the mass of the compact object. The x-ray luminosity suggests a compact object mass of at least $500 M_{\odot}$. Thus, the luminous source in M82 likely represents a new class of compact object with a mass intermediate between those of stellar mass black hole candidates and supermassive black holes found in the centres of galaxies.