154 research outputs found
Detection of a relic X-ray jet in Cygnus A
We present a 200 ks Chandra ACIS-I image of Cygnus A, and discuss a long
linear feature seen in its counterlobe. This feature has a non-thermal spectrum
and lies on the line connecting the brighter hotspot on the approaching side
and the nucleus. We therefore conclude that this feature is (or was) a jet.
However, the outer part of this X-ray jet does not trace the current counterjet
observed in radio. No X-ray counterpart is observed on the jet side. Using
light-travel time effects we conclude that this X-ray 50 kpc linear feature is
a relic jet that contains enough low-energy plasma (gamma ~ 10^3) to
inverse-Compton scatter cosmic microwave background photons, producing emission
in the X-rays.Comment: 4 pages. Proceedings of "High Energy Phenomena in Relativistic
Outflows", held in Dublin, Ireland, September 24-28, 200
Multiwavelength study of Cygnus A IV. Proper motion and location of the nucleus
Context. Cygnus A, as the nearest powerful FR II radio galaxy, plays an
important role in understanding jets and their impact on the surrounding
intracluster medium. Aims. To explain why the nucleus is observed superposed
onto the eastern lobe rather than in between the two lobes, and why the jet and
counterjet are non-colinear. Methods. We made a comparative study of the radio
images at different frequencies of Cygnus A, in combination with the published
results on the radial velocities in the Cygnus A cluster. Results. From the
morphology of the inner lobes we conclude that the lobes are not interacting
with one another, but are well separated, even at low radio frequencies. We
explain the location of the nucleus as the result of the proper motion of the
galaxy through the cluster. The required proper motion is of the same order of
magnitude as the radial velocity offset of Cygnus A with the sub-cluster it
belongs to. The proper motion of the galaxy through the cluster likely also
explains the non-co-linearity of the jet and counterjet.Comment: Accepted for publication in A&A, 8 pages, 4 figure
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
Radio and X-ray emission from disc winds in radio-quiet quasars
It has been proposed that the radio spectra of radio-quiet quasars is
produced by free-free emission in the optically thin part of an accretion disc
wind. An important observational constraint on this model is the observed X-ray
luminosity. We investigate this constraint using a sample of PG radio-quiet
quasars for which XMM-Newton EPIC spectra are available. Comparing the
predicted and measured luminosities for 0.5, 2 and 5 keV, we conclude that all
of the studied PG quasars require a large hydrogen column density absorber,
requiring these quasars to be close to or Compton-thick. Such a large column
density can be directly excluded for PG 0050+124, for which a high-resolution
RGS spectrum exists. Further constraint on the column density for a further 19
out of the 21 studied PG quasars comes from the EPIC spectrum characteristics
such as hard X-ray power-law photon index and the equivalent width of the Fe
Kalpha line; and the small equivalent width of the C IV absorber present in UV
spectra. For 2 sources: PG 1001+054 and PG 1411+442 we cannot exclude that they
are indeed Compton-thick, and the radio and X-ray luminosity are due to a wind
originating close to the super-massive black hole. We conclude that for 20 out
of 22 PG quasars studied free-free emission from a wind emanating from the
accretion disc cannot mutually explain the observed radio and X-ray luminosity.Comment: Accepted for publication in MNRAS, 10 pages, 5 figure
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
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
XMM-NEWTON High Resolution Spectroscopy of NGC 5548
We analyze a 137 ks exposure X-ray spectrum of the Seyfert 1 galaxy NGC 5548
obtained with the XMM-Newton Reflection Grating Spectrometer. Due to the long
exposure time, the spectrum is of higher statistical quality than the previous
observations of this AGN. Therefore, we detect for the first time in NGC 5548
inner-shell transitions from O III to O VI ions, and the Unresolved Transition
Array of M-shell iron. The warm absorber found from this X-ray observation
spans three orders of magnitude in ionization parameter. We detect O III, which
is as lowly ionized as the warm absorber detected in the UV band, to Fe XXIV.
For O VI the column density determined from our X-ray data is an order of
magnitude larger than the column density measured in previous UV observations.
We conclude that there is substantially more low ionized material than
previously deduced from UV observations. However, only a few percent of the
warm absorber detected in the X-rays is lowly ionized. A 99.9 % significant
increase in the derived absorbing column density with higher ionization states
is observed. The outflow velocities determined from the X-ray absorption lines
are consistent with those deduced from the UV lines, evidence, together with
the detection of O VI, that the X-ray and UV warm absorber are different
manifestations of the same phenomenon. From a simple mass conservation
argument, we indicate that our data set is consistent with an outflow with
small opening angle formed due to instabilities in the accretion disk. Possible
due to uncertainties in the radiative transport mechanism, an apparent deviant
iron to oxygen abundance is detected. No strong relativistically broadened
emission lines of O VIII, N VII and C VI were detected.Comment: 10 pages, 10 figures, to be published in A&
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