High-Resolution X-Ray and Ultraviolet Spectroscopy of the Complex Intrinsic Absorption in NGC 4051 with Chandra and the Hubble Space Telescope
Abstract
We present the results from simultaneous observations of the narrow-line Seyfert 1 galaxy NGC 4051 with the Chandra High Energy Transmission Grating Spectrometer and the Hubble Space Telescope Space Telescope Imaging Spectrograph. The X-ray grating spectrum reveals absorption and emission lines from hydrogen-like and helium-like ions of O, Ne, Mg, and Si. We resolve two distinct X-ray absorption systems: a high-velocity blueshifted system at -2340+/-130 km s-1 and a low-velocity blueshifted system at -600+/-130 km s-1. In the UV spectrum we detect strong absorption, mainly from C IV, N V, and Si IV, that is resolved into as many as nine different intrinsic absorption systems with velocities between -650 and 30 km s-1. Although the low-velocity X-ray absorption is consistent in velocity with many of the UV absorption systems, the high-velocity X-ray absorption seems to have no UV counterpart. In addition to the absorption and emission lines, we also observe rapid X-ray variability and a state of low X-ray flux during the last ~15 ks of the observation. NGC 4051 has a soft X-ray excess that we fit in both the high and low X-ray flux states. The high-resolution X-ray spectrum directly reveals that the soft excess is not composed of narrow emission lines and that it has significant spectral curvature. A power-law model fails to fit it, while a blackbody produces a nearly acceptable fit. We compare the observed spectral variability with the results of previous studies of NGC 4051.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2001
- DOI:
- 10.1086/321635
- arXiv:
- arXiv:astro-ph/0104125
- Bibcode:
- 2001ApJ...557....2C
- Keywords:
-
- Galaxies: Active;
- galaxies: individual (NGC 4051);
- Galaxies: Nuclei;
- Galaxies: Seyfert;
- Ultraviolet: Galaxies;
- X-Rays: Galaxies;
- Astrophysics
- E-Print:
- 16 pages, 13 figures included, LaTeX emulateapj5.sty, accepted for publication in The Astrophysical Journal (this version is the same as the first version)