675 research outputs found
PCA of PCA: Principal Component Analysis of Partial Covering Absorption in NGC 1365
We analyse 400 ks of XMM-Newton data on the active galactic nucleus NGC 1365
using principal component analysis (PCA) to identify model independent spectral
components. We find two significant components and demonstrate that they are
qualitatively different from those found in MCG?6-30-15 using the same method.
As the variability in NGC 1365 is known to be due to changes in the parameters
of a partial covering neutral absorber, this shows that the same mechanism
cannot be the driver of variability in MCG-6-30-15. By examining intervals
where the spectrum shows relatively low absorption we separate the effects of
intrinsic source variability, including signatures of relativistic reflection,
from variations in the intervening absorption. We simulate the principal
components produced by different physical variations, and show that PCA
provides a clear distinction between absorption and reflection as the drivers
of variability in AGN spectra. The simulations are shown to reproduce the PCA
spectra of both NGC 1365 and MCG-6-30-15, and further demonstrate that the
dominant cause of spectral variability in these two sources requires a
qualitatively different mechanism.Comment: 8 pages, 10 figures. Accepted for publication in MNRA
Most Supermassive Black Holes must be Rapidly Rotating
We use the integrated spectrum of the X-ray background and quasars Spectral
Energy Distribution to derive the contribution of quasars to the energy output
of the Universe. We find a lower limit for the energy from accretion onto black
holes of 6%, of the total luminosity of the Universe and probably more, with
15% quite possible. Comparing these values with the masses of black holes in
the center of nearby galaxies we show that the accretion process must be on
average very efficient: at least 15% of the accreted mass must be transformed
into radiated energy. This further implies that most supermassive black holes
are rapidly rotating.Comment: 8 Pages, Astrophysical Journal Letters, in pres
Quasars as standard candles II
A tight non-linear relation between the X-ray and the optical-ultraviolet (UV) emission has been observed in active galactic nuclei (AGN) over a wide range of redshift and several orders of magnitude in luminosity, suggesting the existence of an ubiquitous physical mechanism regulating the energy transfer between the accretion disc and the X-ray emitting corona. Recently, our group developed a method to use this relation in observational cosmology, turning quasars into standardizable candles. This work mainly seeks to investigate the potential evolution of this correction at high redshifts. We thus studied the LXâ
ââ
LUV relation for a sample of quasars in the redshift range 4â< âzâ< â7, adopting the selection criteria proposed in our previous work regarding their spectral properties. The resulting sample consists of 53 type 1 (unobscured) quasars, observed either with Chandra or XMM-Newton, for which we performed a full spectral analysis, determining the rest-frame 2 keV flux density, as well as more general X-ray properties such as the estimate of photon index, and the soft (0.5â2 keV) and hard (2â10 keV) unabsorbed luminosities. We find that the relation shows no evidence for evolution with redshift. The intrinsic dispersion of the LXâLUV for a sample free of systematics/contaminants is of the order of 0.22 dex, which is consistent with previous estimates from our group on quasars at lower redshift
Nuclear X-ray properties of the peculiar radio-loud hidden AGN 4C+29.30
We present results from a study of a nuclear emission of a nearby radio
galaxy, 4C+29.30, over a broad 0.5-200 keV X-ray band. This study used new
XMM-Newton (~17 ksec) and Chandra (~300 ksec) data, and archival Swift/BAT data
from the 58-month catalog. The hard (>2 keV) X-ray spectrum of 4C+29.30 can be
decomposed into an intrinsic hard power-law (Gamma ~ 1.56) modified by a cold
absorber with an intrinsic column density N_{H,z} ~ 5x10^{23} cm^{-2}, and its
reflection (|Omega/2pi| ~ 0.3) from a neutral matter including a narrow iron
Kalpha emission line at the rest frame energy ~6.4 keV. The reflected component
is less absorbed than the intrinsic one with an upper limit on the absorbing
column of N^{refl}_{H,z} < 2.5x10^{22} cm^{-2}. The X-ray spectrum varied
between the XMM-Newton and Chandra observations. We show that a scenario
invoking variations of the normalization of the power-law is favored over a
model with variable intrinsic column density. X-rays in the 0.5-2 keV band are
dominated by diffuse emission modeled with a thermal bremsstrahlung component
with temperature ~0.7 keV, and contain only a marginal contribution from the
scattered power-law component. We hypothesize that 4C+29.30 belongs to a class
of `hidden' AGN containing a geometrically thick torus. However, unlike the
majority of them, 4C+29.30 is radio-loud. Correlations between the scattering
fraction and Eddington luminosity ratio, and the one between black hole mass
and stellar velocity dispersion, imply that 4C+29.30 hosts a black hole with
~10^8 M_{Sun} mass.Comment: 13 pages, 5 figures, ApJ in pres
XMM-Newton observations of ULIRGs I: A Compton-thick AGN in IRAS19254-7245
We present the XMM-Newton observation of the merging system IRAS 19254-7245,
also known as The Superantennae, whose southern nucleus is classified as a
Seyfert 2 galaxy. The XMM-Newton data have allowed us to perform a detailed
X-ray imaging and spectral analysis of this system. We clearly detect, for the
first time in this system, a strong EW ~ 1.4 keV Fe emission line at 6.49+/-0.1
keV (rest-frame). The X-ray spectrum requires a soft thermal component (kT~0.9
keV; L(0.5-2) ~ 4E41 cgs), likely associated with the starburst, and a hard
power-law continuum above 2 keV (observed L(2-10) ~ 4E42 cgs). We confirm the
flatness of this latter component, already noted in previous ASCA data. This
flatness, together with the detection of the strong Fe-Kalpha line and other
broad band indicators, suggest the presence of a Compton-thick AGN with
intrinsic luminosity > 1E44 cgs. We show that a Compton-thick model can
perfectly reproduce the X-ray spectral properties of this object.Comment: 6 pages, 4 figures, Latex manuscript, Accepted for publication in
Astronomy and Astrophysic
Revealing the X-ray Variability of AGN with Principal Component Analysis
We analyse a sample of 26 active galactic nuclei with deep XMM-Newton
observations, using principal component analysis (PCA) to find model
independent spectra of the different variable components. In total, we identify
at least 12 qualitatively different patterns of spectral variability, involving
several different mechanisms, including five sources which show evidence of
variable relativistic reflection (MCG-6-30-15, NGC 4051, 1H 0707-495, NGC 3516
and Mrk 766) and three which show evidence of varying partial covering neutral
absorption (NGC 4395, NGC 1365, and NGC 4151). In over half of the sources
studied, the variability is dominated by changes in a power law continuum, both
in terms of changes in flux and power law index, which could be produced by
propagating fluctuations within the corona. Simulations are used to find unique
predictions for different physical models, and we then attempt to qualitatively
match the results from the simulations to the behaviour observed in the real
data. We are able to explain a large proportion of the variability in these
sources using simple models of spectral variability, but more complex models
may be needed for the remainder. We have begun the process of building up a
library of different principal components, so that spectral variability in AGN
can quickly be matched to physical processes. We show that PCA can be an
extremely powerful tool for distinguishing different patterns of variability in
AGN, and that it can be used effectively on the large amounts of high-quality
archival data available from the current generation of X-ray telescopes.Comment: 25 pages, 27 figures, accepted to MNRAS. Analysis code available on
request to lead author. Edit: Rogue table remove
Disentangling the Complex Broadband X-ray Spectrum of IRAS 13197-1627 with NuSTAR, XMM-Newton and Suzaku
We present results from a coordinated -+ observation of
the type 1.8 Seyfert galaxy IRAS 13197-1627. This is a highly complex source,
with strong contributions from relativistic reflection from the inner accretion
disk, neutral absorption and further reprocessing by more distant material, and
ionised absorption from an outflow. We undertake a detailed spectral analysis
combining the broadband coverage provided by -+ with a
multi-epoch approach incorporating archival observations performed by
- and . Our focus is on characterising the reflection from
the inner accretion disk, which previous works have suggested may dominate the
AGN emission, and constraining the black hole spin. Using lamppost disk
reflection models, we find that the results for the inner disk are largely
insensitive to assumptions regarding the geometry of the distant reprocessor
and the precise form of the illuminating X-ray continuum. However, these
results do depend on the treatment of the iron abundance of the distant
absorber/reprocessor. The multi-epoch data favour a scenario in which the AGN
is chemically homogeneous, and we find that a rapidly rotating black hole is
preferred, with , but a slowly-rotating black hole is not
strongly excluded. In addition to the results for the inner disk, we also find
that both the neutral and ionised absorbers vary from epoch to epoch, implying
that both have some degree of inhomogeneity in their structure.Comment: 15 pages, 7 figures, accepted for publication in MNRA
Highly ionized iron absorption lines from outflowing gas in the X-ray spectrum of NGC 1365
We present the discovery of four absorption lines in the X-ray spectrum of
the Seyfert Galaxy NGC 1365, at energies between 6.7 and 8.3 keV. The lines are
detected with high statistical confidence (from >20sigma for the strongest to
\~4sigma for the weakest) in two XMM-Newton observations 60 ksec long. We also
detect the same lines, with lower signal-to-noise (but still >2sigma for each
line) in two previous shorter (~10 ksec) XMM observations. The spectral
analysis identifies these features as FeXXV and FeXXVI Kalpha and Kbeta lines,
outflowing with velocities varying between ~1000 to ~5000 km/s among the
observations. These are the highest quality detections of such lines so far.
The high equivalent widths (EW(Kalpha)~100 eV) and the Kalpha/Kbeta ratios
imply that the lines are due to absorption of the AGN continuum by a highly
ionized gas with column density N_H~5x10^23 cm^{-2}Comment: 15 pages, 4 figures. Accepted for publication in ApJ Letter
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