Chandra Observations of the Evolving Core of the Starburst Galaxy NGC 253

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, 2-10 keV luminosity of ≥1039 ergs s-1 and photoionizes the surrounding gas. We observe this source through a dusty torus with a neutral absorbing column density of NH ~ 2 × 1023 cm-2. The torus is hundreds of parsecs 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 active galactic nucleus activity.