116 research outputs found
Photometric reverberation mapping of 3C120
We present the results of a five month monitoring campaign of the local
active galactic nuclei (AGN) 3C120. Observations with a median sampling of two
days were conducted with the robotic 15cm telescope VYSOS-6 located near Cerro
Armazones in Chile. Broad band (B,V) and narrow band (NB) filters were used in
order to measure fluxes of the AGN and the H_beta broad line region (BLR)
emission line. The NB flux is constituted by about 50% continuum and 50% H_beta
emission line. To disentangle line and continuum flux, a synthetic H_beta light
curve was created by subtracting a scaled V-band light curve from the NB light
curve. Here we show that the H_beta emission line responds to continuum
variations with a rest frame lag of 23.6 +/- 1.69 days. We estimate a virial
mass of the central black hole M_BH = 57 +/- 27 * 10^6 solar masses, by
combining the obtained lag with the velocity dispersion of a single
contemporaneous spectrum. Using the flux variation gradient (FVG) method, we
determined the host galaxy subtracted rest frame 5100A luminosity at the time
of our monitoring campaign with an uncertainty of 10% (L_AGN = 6.94 +/- 0.71*
10^43 ergs^-1). Compared with recent spectroscopic reverberation results, 3C120
shifts in the R_BLR - L_AGN diagram remarkably close to the theoretically
expected relation of R-L^0.5. Our results demonstrate the performance of
photometric AGN reverberation mapping, in particular for efficiently
determining the BLR size and the AGN luminosityComment: 11 pages, 11 figures, Published in Astronomy and Astrophysic
Modelling photometric reverberation data -- a disk-like broad-line region and a potentially larger black hole mass for 3C120
We consider photometric reverberation mapping, where the nuclear continuum
variations are monitored via a broad-band filter and the echo of emission line
clouds of the broad line region (BLR) is measured with a suitable narrow-band
(NB) filter. We investigate how an incomplete emission-line coverage by the NB
filter influences the BLR size determination. This includes two basic cases: 1)
a symmetric cut of the blue and red part of the line wings, and 2) the filter
positioned asymmetrically to the line centre so that essentially a complete
half of the emission line is contained in the NB filter. Under the assumption
that the BLR size is dominated by circular Keplerian orbits, we find that
symmetric cutting of line wings may lead to overestimating the BLR size by less
than 5%. The case of asymmetric half-line coverage, similar as for our data of
the Seyfert 1 galaxy 3C120, yields the BLR size with a bias of less than 1%.
Our results suggest that any BLR size bias due to narrow-band line cut in
photometric reverberation mapping is small and in most cases negligible. We
used well sampled photometric reverberation mapping light curves with sharp
variation features in both the continuum and the Hbeta light curves to
determine the geometry type of the Hbeta BLR for 3C120. Modelling of the light
curve, under the assumption that the BLR is essentially virialised, argues
against a spherical geometry and favours a nearly face-on disk-like geometry
with inclination i = 10 +/- 4 deg and extension from 22 to 28 light days. The
low inclination may lead to a larger black hole mass than the derived when
using the average geometry scaling factor f=5.5. We discuss deviations of
Seyfert 1 galaxies from the M_BH - sigma relation.Comment: 9 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Dust reverberation-mapping of the Seyfert 1 galaxy WPVS48
Using robotic telescopes of the Universitatssternwarte Bochum near Cerro
Armazones in Chile, we monitored the z=0.0377 Seyfert 1 galaxy WPVS48 (2MASX
J09594263-3112581) in the optical (B and R) and near-infrared (NIR, J and Ks)
with a cadence of two days. The light curves show unprecedented variability
details. The NIR variation features of WPVS48 are consistent with the
corresponding optical variations, but the features appear sharper in the NIR
than in the optical, suggesting that the optical photons undergo multiple
scatterings. The J and Ks emission, tracing the hot (1600 K) dust echo, lags
the B and R variations by on average 64 +/- 4 days and 71 +/- 5 days,
respectively (restframe). WPVS48 lies on the known tau-M_V relationship.
However, the observed lag is about three times shorter than expected from the
dust sublimation radius r_sub inferred from the optical-UV luminosity, and
explanations for this common discrepancy are searched for. The sharp NIR echos
argue for a face-on torus geometry and allow us to put forward two potential
scenarios: 1) as previously proposed, in the equatorial plane of the accretion
disk the inner region of the torus is flattened and may come closer to the
accretion disk. 2) The dust torus with inner radius r_sub is geometrically and
optically thick, so that the observer only sees the facing rim of the torus
wall, which lies closer to the observer than the torus equatorial plane and
therefore leads to an observed foreshortened lag. Both scenarios are able to
explain the factor three discrepancy between tau and r_sub. Longer-wavelength
dust reverberation data might enable one to distinguish between the scenarios.Comment: 4 pages, 6 figures, Published in Astronomy and Astrophysic
The warm absorber in NGC 5548: The lean years
We study the variability of the warm absorber and the gas responsible for the
emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the
location and physical properties of these components. Using X-ray spectra taken
with the \textit{Chandra}LETGS in 2002 and 2005, we study variability in the
ionic column densities and line intensities. We find a lower \ion{O}{vii}
forbidden emission line flux in 2005, while the Fe K line flux stays
constant. The warm absorber is less ionized in 2005, allowing us to constrain
its location to within 7 pc of the central source. Using both the observed
variability and the limit on the FWHM of the \ion{O}{vii} f line, we have
constrained the location of the narrow line region to a distance of 1 pc from
the central source. The apparent lack of variability of the Fe K line
flux does not allow for a unique explanation.Comment: 6 pages, 6 figures, accepted by A&
Chandra LETGS and XMM-Newton observations of NGC 4593
In this paper, we analyze spectra of the Seyfert 1 galaxy NGC 4593 obtained
with the Chandra Low Energy Transmission Grating Spectrometer (LETGS), the
Reflection Grating Spectrometer (RGS) and the European Photon Imaging Camera's
(EPIC) onboard of XMM-Newton. The two observations were separated by ~7 months.
In the LETGS spectrum we detect a highly ionized warm absorber corresponding to
an ionization state of 400x10^{-9} W m, visible as a depression at 10-18 \AA.
This depression is formed by multiple weak Fe and Ne lines. A much smaller
column density was found for the lowly ionized warm absorber, corresponding to
xi = 3x10^{-9} W m. However, an intermediate ionization warm absorber is not
detected. For the RGS data the ionization state is hard to constrain. The EPIC
results show a narrow Fe Kalpha line.Comment: 8 pages, 10 figures, accepted for publication in A&
High-resolution X-ray spectroscopy of the Narrow line Seyfert 1 galaxy NGC 4051 with Chandra LETGS
We study the absorption and emission properties of the photoionised gas near
one of the brightest and most variable AGN, the Seyfert galaxy NGC 4051, in
order to constrain the geometry, dynamics and ionisation structure of the
outflow. We analyse two observations taken with the Low Energy Transmission
Grating Spectrometer (LETGS) of Chandra. We study the spectra of both
observations and investigate the spectral response to a sudden, long-lasting
flux decrease of a factor of 5 that occurred during the second observation. We
confirm the preliminary detection of a highly ionised component with an outflow
velocity of -4500 km/s, one of the highest velocity outflow components seen in
a Seyfert 1 galaxy. The sudden drop in intensity by a factor of five during the
second observation causes a drop in ionisation parameter of a similar magnitude
in the strongest and main ionisation component (v = -610 km/s), allowing us for
the first time to determine the recombination time of this component and
thereby its distance in a robust way. We find an upper limit to the distance of
10^15 m, ruling out an origin in the narrow emission line region. In addition,
an emission component producing strong radiative recombination continua of C VI
and C V appears during the low state. This can be explained by emission from an
ionised skin of the accretion disk at a distance of only ~4x10^12 m from the
black hole. Finally, the spectra contain a broad relativistic O VIII line with
properties similar to what was found before in this source with XMM-Newton;
this line has disappeared during the low flux state, consistent with the
disappearance of the inner part of the accretion disk during that low flux
state. (abridged)Comment: 11 pages, 6 figures, submitted to Astronomy and Astrophysic
High-resolution X-ray spectroscopy of the low and high states of the Seyfert 1 galaxy NGC 4051 with Chandra LETGS
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, one of the highest outflow velocity components
observed in a Seyfert 1 galaxy. The spectra contain a relativistic O VIII Ly
alpha line, and four absorption components spanning a range in ionisation
parameter xi between 0.07 and 3.19. An emission component producing radiative
recombination continua of C VI 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. ABRIDGEDComment: Accepted by A&A, 14 pages, 9 figure
The broad-line region and dust torus size of the Seyfert 1 galaxy PGC50427
We present the results of a three years monitoring campaigns of the type-1 active galactic nucleus (AGN) PGC50427. Through the use of
Photometric Reverberation Mapping with broad and narrow band filters, we
determine the size of the broad-line emitting region by measuring the time
delay between the variability of the continuum and the H emission line.
The H emission line responds to blue continuum variations with an
average rest frame lag of days. Using single epoch spectroscopy
we determined a broad-line H velocity width of 1020 km s and in
combination with the rest frame lag and adoption a geometric scaling factor , we calculate a black hole mass of . Using the flux variation gradient method, we separate the host
galaxy contribution from that of the AGN to calculate the rest frame 5100\AA~
luminosity at the time of our monitoring campaign. The rest frame lag and the
host-subtracted luminosity permit us to derive the position of PGC50427 in the
BLR size -- AGN luminosity diagram, which is remarkably close to the
theoretically expected relation of . The simultaneous
optical and NIR ( and ) observations allow us to determine the size
of the dust torus through the use of dust reverberation mapping method. We find
that the hot dust emission () lags the optical variations with an
average rest frame lag of days. The dust reverberation radius
and the nuclear NIR luminosity permit us to derive the position of PGC50427 on
the known diagram. The simultaneus observations for the
broad-line region and dust thermal emission demonstrate that the innermost dust
torus is located outside the BLR in PGC50427, supporting the unified scheme for
AGNs. (Abstract shortened, see the manuscript.)Comment: 11 pages, 23 figures, accepted for publication in Astronomy and
Astrophysic
X-Ray/Ultraviolet Observing Campaign of the Markarian 279 Active Galactic Nucleus Outflow: a close look at the absorbing/emitting gas with Chandra-LETGS
We present a Chandra-LETGS observation of the Seyfert 1 galaxy Mrk 279. This
observation was carried out simultaneously with HST-STIS and FUSE, in the
context of a multiwavelength study of this source. The Chandra pointings were
spread over ten days for a total exposure time of ~360 ks. The spectrum of
Mrk279 shows evidence of broad emission features, especially at the wavelength
of the OVII triplet. We quantitatively explore the possibility that this
emission is produced in the broad line region (BLR). We modeled the broad UV
emission lines seen in the FUSE and HST-STIS spectra following the ``locally
optimally emitting cloud" approach. We find that the X-ray lines luminosity
derived from the best fit BLR model can match the X-ray features, suggesting
that the gas producing the UV lines is sufficient to account also for the X-ray
emission. The spectrum is absorbed by ionized gas whose total column density is
~5x10^{20} cm^{-2}. The absorption spectrum can be modeled by two distinct gas
components (log xi ~ 0.47 and 2.49, respectively) both showing a significant
outflow velocity. However, the data allow also the presence of intermediate
ionization components. The distribution of the column densities of such extra
components as a function of the ionization parameter is not consistent with a
continuous, power law-like, absorber, suggesting a complex structure for the
gas outflow for Mrk 279 (abridged).Comment: 16 pages, 12 figures. To appear in A&
- âŠ