2,845 research outputs found
Compton reflection in AGN with Simbol-X
AGN exhibit complex hard X-ray spectra. Our current understanding is that the
emission is dominated by inverse Compton processes which take place in the
corona above the accretion disk, and that absorption and reflection in a
distant absorber play a major role. These processes can be directly observed
through the shape of the continuum, the Compton reflection hump around 30 keV,
and the iron fluorescence line at 6.4 keV. We demonstrate the capabilities of
Simbol-X to constrain complex models for cases like MCG-05-23-016, NGC 4151,
NGC 2110, and NGC 4051 in short (10 ksec) observations. We compare the
simulations with recent observations on these sources by INTEGRAL, Swift and
Suzaku. Constraining reflection models for AGN with Simbol-X will help us to
get a clear view of the processes and geometry near to the central engine in
AGN, and will give insight to which sources are responsible for the Cosmic
X-ray background at energies above 20 keV.Comment: 4 pages, 1 figure, to appear in the proceedings of the second
Simbol-X Symposium "Simbol-X - Focusing on the Hard X-ray Universe", AIP
Conf. Proc. Series, P. Ferrando and J. Rodriguez ed
The Second INTEGRAL AGN Catalogue
The INTEGRAL mission provides a large data set for studying the hard X-ray
properties of AGN and allows testing of the unified scheme for AGN. We present
analysis of INTEGRAL IBIS/ISGRI, JEM-X, and OMC data for 199 AGN supposedly
detected by INTEGRAL above 20 keV. The data analysed here allow a significant
spectral extraction on 148 objects and an optical variability study of 57 AGN.
The slopes of the hard X-ray spectra of Seyfert 1 and Seyfert~2 galaxies are
found to be consistent within the uncertainties, whereas higher cut-off
energies and lower luminosities are measured for the more absorbed / type 2
AGN. The intermediate Seyfert 1.5 objects exhibit hard X-ray spectra consistent
with those of Seyfert 1. When applying a Compton reflection model, the
underlying continua appear the same in Seyfert 1 and 2 with photon index 2, and
the reflection strength is about R = 1, when assuming different inclination
angles. A significant correlation is found between the hard X-ray and optical
luminosity and the mass of the central black hole in the sense that the more
luminous objects appear to be more massive. There is also a general trend
toward the absorbed sources and type 2 AGN having lower Eddington ratios. The
black holemass appears to form a fundamental plane together with the optical
and X-ray luminosity of the form Lv being proportional to Lx^0.6 M^0.2, similar
to that found between radio luminosity Lr, Lx, and M. The unified model for
Seyfert galaxies seems to hold, showing in hard X-rays that the central engine
is the same in Seyfert 1 and 2, but seen under different inclination angles and
absorption. (Abridged)Comment: 26 pages, 16 figures, accepted for publication in A&A. Corrections by
language editor included in version
AGN's UV and X-ray luminosities in clumpy accretion flows
We consider the fuelling of the central massive black hole in Active Galactic
Nuclei, through an inhomogeneous accretion flow. Performing simple analytical
treatments, we show that shocks between elements (clumps) forming the accretion
flow may account for the UV and X-ray emission in AGNs. In this picture, a
cascade of shocks is expected, where optically thick shocks give rise to
optical/UV emission, while optically thin shocks give rise to X-ray emission.
The resulting blue bump temperature is found to be quite similar in different
AGNs. We obtain that the ratio of X-ray luminosity to UV luminosity is smaller
than unity, and that this ratio is smaller in massive objects compared to less
massive sources. This is in agreement with the observed ratio
and suggests a possible interpretation of the
anticorrelation.Comment: 8 pages, 1 figure, accepted for publication in A&
X-ray power law spectra in active galactic nuclei
X-ray spectra of active galactic nuclei (AGN) are usually described as power
law spectra, characterized by the spectral slope or photon index
. Here we discuss the X-ray spectral properties within the framework of
clumpy accretion flows, and estimate the power law slope as a function of the
source parameters. We expect harder spectra in massive objects than in less
massive sources, and steeper spectra in higher accretion rate systems. The
predicted values of the photon index cover the range of spectral slopes
typically observed in Seyfert galaxies and quasars. The overall trends are
consistent with observations, and may account for the positive correlation of
the photon index with Eddington ratio (and the possible anticorrelation with
black hole mass) observed in different AGN samples. Spectral properties are
also closely related to variability properties. We obtain that shorter
characteristic time scales are associated with steeper spectra. This agrees
with the observed `spectral-timing' correlation.Comment: 6 pages, 1 figure, Astronomy and Astrophysics, accepte
S100A13 partecipates in the release of fibroblast growth factor 1 in response to heat shock in vitro
The efficient low-mass Seyfert MCG-05-23-016
The Seyfert 1.9 galaxy MCG-05-23-016 has been shown to exhibit a complex
X-ray spectrum. This source has moderate X-ray luminosity, hosts a comparably
low-mass black hole, but accretes at a high Eddington rate, and allows us to
study a super massive black hole in an early stage. Three observations of the
INTEGRAL satellite simultaneous with pointed Swift/XRT observations performed
from December 2006 to June 2007 are used in combination with public data from
the INTEGRAL archive to study the variability of the hard X-ray components and
to generate a high-quality spectrum from 1 to 150 keV. The AGN shows little
variability in the hard X-ray spectrum, with some indication of a variation in
the high-energy cut-off energy ranging from 50 keV to >>100 keV, with an
electron plasma temperature in the 10 - 90 keV range. The reflection component
is not evident and, if present, the reflected fraction can be constrained to R
< 0.3 for the combined data set. Comparison to previous observations shows that
the reflection component has to be variable. No variability in the UV and
optical range is observed on a time scale of 1.5 years. The hard X-ray spectrum
of MCG-05-23-016 appears to be stable with the luminosity and underlying power
law varying moderately and the optical/UV flux staying constant. The spectral
energy distribution appears to be similar to that of Galactic black hole
systems, e.g. XTE 1118+480 in the low state. The AGN exhibits a remarkably high
Eddington ratio of L(bol)/L(Edd)> 0.8 (or L(bol)/L(Edd) > 0.1, if we consider a
higher mass of the central engine) and, at the same time, a low cut-off energy
around 70 keV. Objects like MCG-05-23-016 might indicate the early stages of
super massive black holes, in which a strong accretion flow feeds the central
engine.Comment: 8 pages, 5 figures, accepted for publication in A&
Hard X-ray Variability of AGN
Aims: Active Galactic Nuclei are known to be variable throughout the
electromagnetic spectrum. An energy domain poorly studied in this respect is
the hard X-ray range above 20 keV.
Methods: The first 9 months of the Swift/BAT all-sky survey are used to study
the 14 - 195 keV variability of the 44 brightest AGN. The sources have been
selected due to their detection significance of >10 sigma. We tested the
variability using a maximum likelihood estimator and by analysing the structure
function.
Results: Probing different time scales, it appears that the absorbed AGN are
more variable than the unabsorbed ones. The same applies for the comparison of
Seyfert 2 and Seyfert 1 objects. As expected the blazars show stronger
variability. 15% of the non-blazar AGN show variability of >20% compared to the
average flux on time scales of 20 days, and 30% show at least 10% flux
variation. All the non-blazar AGN which show strong variability are
low-luminosity objects with L(14-195 keV) < 1E44 erg/sec.
Conclusions: Concerning the variability pattern, there is a tendency of
unabsorbed or type 1 galaxies being less variable than the absorbed or type 2
objects at hardest X-rays. A more solid anti-correlation is found between
variability and luminosity, which has been previously observed in soft X-rays,
in the UV, and in the optical domain.Comment: 9 pages, 7 figures, accepted for publication in A&
Altered redox status in the blood of psoriatic patients: involvement of NADPH oxidase and role of anti-TNF-α therapy
Extreme flux states of NGC 4151 observed with INTEGRAL
We present a comprehensive spectral analysis of all INTEGRAL data obtained so far for the X-ray-bright Seyfert galaxy NGC 4151. We also use all contemporaneous data from RXTE, XMM-Newton, Swift and Suzaku. We find a linear correlation between the medium- and hard-energy X-ray fluxes measured by INTEGRAL, which indicates an almost constant spectral index over 6 yr. The majority of INTEGRAL observations were made when the source was either at a very bright or very dim hard-X-ray state. We find that thermal Comptonization models applied to the bright state yields the plasma temperature of â50-70 keV and its optical depth of â1.3-2.6, depending on the assumed source geometry. For the dim state, these parameters are in the ranges of â180-230 keV and â0.3-0.7, respectively. The Compton parameter is for all the spectra, indicating a stable geometry. Using this result, we can determine the reflection effective solid angles associated with the close and distant reprocessing media as and , respectively. The plasma energy balance, the weak disc reflection and a comparison of the UV fluxes illuminating the plasma to the observed ones are all consistent with an inner hot accretion surrounded by an outer cold disc. The disc truncation radius can be determined from an approximate equipartition between the observed UV and X-ray emission, and from the fitted disc blackbody model, as âŒ15 gravitational radii. Alternatively, our results can be explained by a mildly relativistic coronal outflo
An active state of the BL Lac Object Markarian 421 detected by INTEGRAL in April 2013
Multiwavelength variability of blazars offers indirect insight into their
powerful engines and on the mechanisms through which energy is propagated from
the centre down the jet. The BL Lac object Mkn 421 is a TeV emitter, a bright
blazar at all wavelengths, and therefore an excellent target for variability
studies. Mkn 421 was observed by INTEGRAL and Fermi-LAT in an active state on
16-21 April 2013. Well sampled optical, soft, and hard X-ray light curves show
the presence of two flares. The average flux in the 20-100 keV range is 9.1e-11
erg/s/cm2 (~4.5 mCrab) and the nuclear average apparent magnitude, corrected
for Galactic extinction, is V ~12.2. In the time-resolved X-ray spectra (3.5-60
keV), which are described by broken power laws and, marginally better, by
log-parabolic laws, we see a hardening that correlates with flux increase, as
expected in refreshed energy injections in a population of electrons that later
cool via synchrotron radiation. The hardness ratios between the JEM-X fluxes in
two different bands and between the JEM-X and IBIS/ISGRI fluxes confirm this
trend. During the observation, the variability level increases monotonically
from the optical to the hard X-rays, while the large LAT errors do not allow a
significant assessment of the MeV-GeV variability. The cross-correlation
analysis during the onset of the most prominent flare suggests a monotonically
increasing delay of the lower frequency emission with respect to that at higher
frequency, with a maximum time-lag of about 70 minutes, that is however not
well constrained. The spectral energy distributions from the optical to the TeV
domain are satisfactorily described by homogeneous models of blazar emission
based on synchrotron radiation and synchrotron self-Compton scattering, except
in the state corresponding to the LAT softest spectrum and highest flux.Comment: 11 pages, 6 figures, in press in A&
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