2009/01/20 by K. C. Steenbrugge, M. Fenovcik, M. Feňovčík +3 · 2 citations
Physics and Astronomy · #Absorption (acoustics) #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Galaxy #Optics #Outflow #Physics #Radiative transfer #Spectral line #Spectroscopy #astro-ph.CO #astro-ph.HE
paper · pdf · doi:10.1051/0004-6361/200810416
Accepted by A&A, 14 pages, 9 figures
arxiv created 2009/01/20 · openalex publication_date 2009/01/30 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
<i>Context. <i/>With the new generation of high-resolution X-ray spectrometers the understanding of warm absorbers in active galactic nuclei has improved considerably. However, the important questions regarding the distance and structure of the photoionised wind remain unsolved.<i>Aims. <i/>To constrain the distance of the photoionised wind, we study the variability of the continuum, absorption, and, emission in one of the brightest and most variable low-luminosity AGN: the narrow-line Seyfert galaxy NGC 4051.<i>Methods. <i/>We analyse two observations taken with the Low Energy Transmission Grating Spectrometer of <i>Chandra<i/>. We investigated the spectral response to a sudden flux decrease by a factor of 5, which occurred during the second observation.<i>Results. <i/>We detect a highly ionised absorption component with an outflow velocity of -4670 km s<sup>-1<sup/>, one of the highest outflow velocity components observed in a Seyfert 1 galaxy. Furthermore, this is one of the only observations whereby the X-ray observed absorption component is unaccompanied by a corresponding UV absorption component with the same outflow velocity. The spectra contain a relativistic Ly<i>α<i/> line with properties similar to those determined for this source with XMM-<i>Newton<i/>, and four absorption components spanning a range in ionisation parameter <i>ξ<i/> between 0.07 and 3.19 (log values, and units of 10<sup>-9<sup/> W m). An emission component producing radiative recombination continua of and appears during the low state. The black body temperature decreases with the drop in flux observed in the second observation.<i>Conclusions. <i/>For all absorber components we exclude that the ionisation parameter linearly responded to the decrease in flux by a factor of 5. The variability of the absorber suggest that at least three out of four detected components are located in the range pc. For one component we only have a lower limit of 0.3 pc. These distances are different from earlier suggestions.