180 research outputs found
The properties of the absorbing and line emitting material in IGR J16318-4848
We have performed a detailed analysis of the XMM-Newton observation of IGR
J16318-4848, to study the properties of the matter responsible for the
obscuration and for the emission of Fe and Ni lines. Even if the line of sight
material has a column density of about 2x10^24 cm^-2, from the Fe Kalpha line
EW and Compton Shoulder we argue that the matter should have an average column
density of a few x10^23 cm^-2, along with a covering factor of about 0.1-0.2.
The iron Kalpha line varies on time scales as short as 1000 s, implying a size
of the emitting region smaller than about 3x10^13 cm. The flux of the line
roughly follows the variations of the continuum, but not exactly, suggesting a
variation of the geometrical properties of the emitting region on similar time
scales.Comment: accepted for publication in MNRAS, pink page
Cosmological Evolution of the Central Engine in High-Luminosity, High-Accretion Rate AGN
In this paper I discuss the status of observational studies aiming at probing the cosmological evolution of the central engine in high-luminosity, high-accretion rate Active Galactic Nuclei (AGN). X-ray spectroscopic surveys, supported by extensive multi-wavelength coverage, indicate a remarkable invariance of the accretion disk plus corona system, and of their coupling up to redshifts z≈6. Furthermore, hard X-ray (E >10 keV) surveys show that nearby Seyfert Galaxies share the same central engine notwithstanding their optical classication. These results suggest that the high-luminosity, high accretion rate quasar phase of AGN evolution is homogeneous over cosmological times
AGN spectral states from simultaneous UV and X-ray observations by XMM-Newton
The supermassive black holes in active galactic nuclei (AGN) and stellar-mass
black holes in X-ray binaries (XRBs) are believed to work in a similar way.
While XRBs evolve rapidly and several sources have undergone a few complete
cycles from quiescence to an outburst and back, most AGN remain in the same
state over periods of decades, due to their longer characteristic timescale
proportional to their size. However, the study of the AGN spectral states is
still possible with a large sample of sources. Multi-wavelength observations
are needed for this purpose since the AGN thermal disc emission dominates in
the ultraviolet energy range, while the up-scattered hot-corona emission is
detected in X-rays. We compared simultaneous UV and X-ray measurements of AGN
obtained by the XMM-Newton satellite. The non-thermal flux was constrained from
the 2-12 keV X-ray luminosity, while the thermal disc component was estimated
from the UV flux at 2900A. The hardness (ratio between the X-ray and UV plus
X-ray luminosity) and the total luminosity were used to construct the AGN state
diagrams. For sources with reliable mass measurements, the Eddington ratio was
used instead of the total luminosity. The state diagrams show that the
radio-loud sources have on average higher hardness, due to the lack of the
thermal disc emission in the UV band, and have flatter intrinsic X-ray spectra.
In contrast, the sources with high luminosity and low hardness are radio-quiet
AGN. The hardness-Eddington ratio diagram reveals that the average
radio-loudness is stronger for low-accreting sources, while it decreases when
the accretion rate is close to the Eddington limit. Our results indicate that
the general properties of AGN accretion states are similar to those of X-ray
binaries. This suggests that the AGN radio dichotomy of radio-loud and
radio-quiet sources can be explained by the evolution of the accretion states.Comment: 13 pages, 12 figures, accepted in A&
XMM-NEWTON SCIENTIFIC HIGHLIGHTS: X-RAY SPECTROSCOPIC POPULATION STUDIES OF AGN
In this paper I review the contribution that the XMM-Newton ESA X-ray mission has given to our understanding of Active Galactic Nuclei, together with other operational, and complementary, X-ray facilities. I will focus on answering three basic questions: a) to which extent do AGN share the same engine?; b) to which extent are AGN “relativistic machines”?; c) to which extent do AGN affect their immediate environment
Spectral Variability and iron line emission in the ASCA Observations of the Seyfert 1 Galaxy NGC4051
We present the results of an extensive analysis of the ``ASCA'' AO2
observation of the Seyfert 1 galaxy NGC4051. The target exhibits broadband
[0.5--10 keV] variability by a factor on time scales ,
with a typical doubling time . The spectrum is characterized by a
strong emission excess over the extrapolated power law at energies . Absorption edges due to ionized oxygen species OVII and OVIII are
detected together with an emission-like feature at . The OVII
edge undergoes significant variability on a timescale as low as ,
whilst no contemporary variability of the OVIII feature is detected. Typical
variability time scales place constraints on the location and the density of
the absorbing matter. In the self-consistent hypothesis of a high energy () power law reflected by an infinite plane-parallel cold slab, a
photon index change () has also been observed; a natural
explanation can be found in the framework of non-thermal Comptonization models.
The iron line is redshifted (centroid energy ) and broad
(); multicomponent structure is suggestive of emission from a
relativistic accretion disk; however if the disk is not ionized a contribution
by a molecular torus or an iron overabundance by a factor are
required.Comment: 17 pages, latex, 12 figures. To be published in Publication of
Astronomical Society of Japa
The nature of the soft X-ray emission in obscured AGN
The origin of the soft X-ray emission in obscured AGN is still largely
unknown. However, important progresses have been made thanks to the high energy
and spatial resolution of XMM-Newton and Chandra. We review here the latest
results on this issue, focusing on the physical properties of the material
responsible for the soft X-ray emission and its relation to the circumnuclear
environment, putting them in the general context of our understanding of the
AGN structure and its feedback to the host galaxy.Comment: 8 pages, 12 figures, invited review talk at the Workshop "The
multicoloured landscape of compact objects and their explosive origin",
Cefalu' (Sicily), 11-24 June 2006, to be published by AI
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