Tracing a Disk Wind in NGC 3516

TL;DR

This study investigates the complex absorption features in the X-ray spectra of NGC 3516, revealing a new circumnuclear gas zone and evidence of a disk wind, which clarify the source of spectral variability in this AGN.

Contribution

It uncovers a previously unknown high-ionization gas zone and demonstrates that absorption variations, including eclipses, are due to a disk wind in NGC 3516.

Findings

Discovery of a new high-ionization gas zone with log xi ~ 4.3

Identification of a lower-ionization layer with 50% covering fraction

Evidence of a disk wind with outflow velocities 1000-2000 km/s

Abstract

X-ray spectra of AGN often contain signatures indicative of absorption in multiple layers of gas whose ionization-state and covering fraction may vary with time. It has been unclear to date how much of the observed X-ray spectral and timing behavior in AGN can be attributed to variations in absorption, versus variations in the strengths of emission or reflection components. Diagnostics of the inner regions of AGN cannot be reliably performed until the origin of observed effects is understood. We investigate the role of the X-ray absorbers in the Seyfert 1 galaxy NGC 3516. Time-averaged and flux-selected spectroscopy is used to examine the behavior of NGC 3516 observed in Chandra HETG and XMM data from Oct 2006. New H-like and He-like emission and absorption features discovered in the Fe K regime reveal a previously unknown zone of circumnuclear gas in NGC 3516 with log xi ~ 4.3 and column density 1E23 cm^-2. A lower-ionization layer with log xi ~2 and of similar column density is confirmed from previous observations, this layer has a covering fraction around 50%, and changes in covering provide a simple explanation of a deep dip in the light curve that we interpret as an eclipse of the continuum due to passage of a cloud across the sight line within half a day. These inner zones of absorbing gas are detected to have outflow velocities in the range 1000-2000 km/s, this, and constraints on radial location are consistent with an origin as part of a disk wind in NGC 3516.