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 to 10 keV luminosity of ≥ 10 erg s and photoionizes the surrounding gas. We observe this source through a dusty torus with a neutral absorbing column density of NH ∼ 2 × 10 23 cm. 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. Subject headings: galaxies: active — galaxies: individual (NGC 253) — galaxies: nuclei — galaxies: starburst — X-rays: galaxies also Johns Hopkins University Chandra Fellow