TY - JOUR
T1 - High-resolution X-ray spectroscopy of the low and high states of the Seyfert 1 galaxy NGC 4051 with Chandra LETGS
AU - Steenbrugge, K.C.
AU - Fenovcik, M.
AU - Kaastra, J.S.
AU - Costantini, E.
AU - Verbunt, F.W.M.
PY - 2009
Y1 - 2009
N2 - Context. 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.
Aims. 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.
Methods. We analyse two observations taken with the Low Energy Transmission Grating Spectrometer of Chandra. We investigated
the spectral response to a sudden flux decrease by a factor of 5, which occurred during the second observation.
Results. We detect a highly ionised absorption component with an outflow velocity of −4670 km s−1, 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 Oviii Lyα line with properties similar to those determined for this source with XMM-Newton, and four absorption
components spanning a range in ionisation parameter ξ between 0.07 and 3.19 (log values, and units of 10−9 W m). An emission
component producing radiative recombination continua of Cvi and C v appears during the low state. The black body temperature
decreases with the drop in flux observed in the second observation.
Conclusions. 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
0.02−1 pc. For one component we only have a lower limit of 0.3 pc. These distances are different from earlier suggestions.
AB - Context. 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.
Aims. 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.
Methods. We analyse two observations taken with the Low Energy Transmission Grating Spectrometer of Chandra. We investigated
the spectral response to a sudden flux decrease by a factor of 5, which occurred during the second observation.
Results. We detect a highly ionised absorption component with an outflow velocity of −4670 km s−1, 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 Oviii Lyα line with properties similar to those determined for this source with XMM-Newton, and four absorption
components spanning a range in ionisation parameter ξ between 0.07 and 3.19 (log values, and units of 10−9 W m). An emission
component producing radiative recombination continua of Cvi and C v appears during the low state. The black body temperature
decreases with the drop in flux observed in the second observation.
Conclusions. 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
0.02−1 pc. For one component we only have a lower limit of 0.3 pc. These distances are different from earlier suggestions.
M3 - Article
SN - 0004-6361
VL - 496
SP - 107
EP - 119
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
IS - 1
ER -