A DEEP CHANDRA X-RAY LIMIT ON THE PUTATIVE IMBH IN OMEGA CENTAURI

We report a sensitive X-ray search for the proposed intermediate-mass black hole (IMBH) in the massive Galactic cluster, omega Centauri (NGC 5139). Combining Chandra X-ray Observatory data from Cycles 1 and 13, we obtain a deep (~291 ks) exposure of the central regions of the cluster. We find no evidence for an X-ray point source near any of the cluster's proposed dynamical centers, and place an upper limit on the X-ray flux from a central source of [functionof] sub(X)(0.5-7.0 keV) [< or =, slant] 5.0 x 10 super(-16) erg cm super(-2) s super(-1) after correcting for absorption. This corresponds to an unabsorbed X-ray luminosity of L sub(X)(0.5-7.0 keV) [< or =, slant] 1.6 x 10 super(30) erg s super(-1), for a cluster distance of 5.2 kpc, Galactic column density N sub(H) = 1.2 x 10 super(21) cm super(-2), and power-law spectrum with [Gamma] = 2.3. If a ~10 super(4) M sub([middot in circle]) IMBH resides in the cluster's core, as suggested by some stellar dynamical studies, its Eddington luminosity would be L sub(Edd) ~ 10 super(42) erg s super(-1). The new X-ray limit would then establish an Eddington ratio of L sub(x)/L sub(Edd) [