  Chandra observations of the core of the nearby starburst galaxy NGC 253
reveal a heavily absorbed source of hard X-rays embedded within the nuclear
starburst region. The source has an unabsorbed, 2 to 10 keV luminosity of
>=10^39 erg/s and photoionizes the surrounding gas. We observe this source
through a dusty torus with a neutral absorbing column density of NH ~ 2x10^23
cm^-2. The torus is hundreds of pc across and collimates the starburst-driven
nuclear outflow. We suggest that the ionizing source is an intermediate-mass
black hole or a weakly accreting supermassive black hole, which may signal the
beginnings or endings of AGN activity.
