The Detection of Circumnuclear X-ray Emission from the Seyfert Galaxy

We present the first high-resolution, X-ray image of the circumnuclear regions of the Seyfert 1 galaxy NGC 3516, using the Chandra X-ray Observatory (CXO). All three of the CXO observations reported were performed with one of the two grating assemblies in place, and here we restrict our analysis to undispersed photons (i.e. those detected in the zeroth-order). A previously-unknown X-ray source is detected ∼6 arcsec (1.1h 75 kpc) NNE of the nucleus (position angle ∼29 degrees) which we designate CXOU 110648.1+723412. Its spectrum can be characterized as a power law with a photon index Γ ∼1.8– 2.6, or as thermal emission with a temperature kT ∼0.7–3 keV. Assuming a location within NGC 3516, isotropic emission implies a luminosity L ∼2–8×1039h 75 erg s −1 in the 0.4–2 keV band. If due to a single point source, the object is super-Eddington for a 1.4M⊙ neutron star. However, multiple sources or a small, extended source cannot be excluded using the current data. Large-scale extended X-ray emission is also detected out to ∼ 10 arcsec (∼ 1.7h 75 kpc) from the nucleus to the NE and SW, and is approximately aligned with the morphologies of the radio emission and extended narrow emission line region (ENLR). The mean luminosity of this emission is 1–5×1037h 75 erg s −1 arcsec, in the 0.4–2 keV band. Unfortunately the current data cannot usefully constrain its spectrum. These results are consistent with earlier suggestions of circumnuclear X-ray emission in NGC 3516. If the extended emission is due to scattering of the nuclear X-ray continuum, then the pressure in the X-ray emitting gas is at least two orders of magnitude too small to provide the confining medium for the ENLR clouds. Subject headings: galaxies: active – galaxies: individual (NGC 3516) – galaxies: nuclei – galaxies: Seyfert – X-rays: galaxies