X-Ray Imaging of the Seyfert 2 Galaxy Circinus with [ITAL]Chandra[/ITAL]

Abstract

We present results from the zero-order imaging of a Chandra High-Energy Transmission Grating Spectrometer observation of the nearby Seyfert 2 galaxy Circinus. Twelve X-ray sources were detected in the Advanced CCD Imaging Spectrometer-S (ACIS-S) image of the galaxy, embedded in diffuse X-ray emission. The latter shows a prominent (~18'') soft "plume" in the northwest direction, coincident with the [O III] ionization cone. The radial profiles of the brightest X-ray source at various energies are consistent with an unresolved (FWHM ~ 08) component, which we identify as the active nucleus, plus two extended components with FWHM ~ 23 and 18'', respectively. In a radius of 3'', the nucleus contributes roughly the same flux as the extended components at the softest energies (2 keV). However, at harder energies (>2 keV), the contribution of the nucleus is dominant. The zero-order ACIS spectrum of the nucleus exhibits emission lines at both soft and hard X-rays, including a prominent Fe Kα line at 6.4 keV, showing that most of the X-ray lines previously detected with ASCA originate in a compact region (15 pc). Based on its X-ray spectrum, we argue that the 23 extended component is scattered nuclear radiation from nearby ionized gas. The large-scale extended component includes the emission from the northwest plume and possibly from the outer starburst ring.