1,539 research outputs found
X-ray Signatures of Circumnuclear Gas in AGN
X-ray spectra of AGN are complex. X-ray absorption and emission features
trace gas covering a wide range of column densities and ionization states. High
resolution spectra show the absorbing gas to be outflowing, perhaps in the form
of an accretion disk wind. The absorbing complex shapes the form of the X-ray
spectrum while X-ray reverberation and absorption changes explain the spectral
and timing behaviour of AGN. We discuss recent progress, highlighting some new
results and reviewing the implications that can be drawn from the data.Comment: Proceedings of the conference "Suzaku 2011, Exploring the X-ray
Universe: Suzaku and Beyond
The Global Implications of the Hard X-ray Excess in Type 1 AGN
Recent evidence for a strong 'hard excess' of flux at energies > 20 keV in
some Suzaku observations of type 1 Active Galactic Nuclei (AGN) has motivated
an exploratory study of the phenomenon in the local type 1 AGN population. We
have selected all type 1 AGN in the Swift Burst Alert Telescope (BAT) 58-month
catalog and cross-correlated them with the holdings of the Suzaku public
archive. We find the hard excess phenomenon to be a ubiquitous property of type
1 AGN. Taken together, the spectral hardness and equivalent width of Fe K alpha
emission are consistent with reprocessing by an ensemble of Compton-thick
clouds that partially cover the continuum source. In the context of such a
model, ~ 80 % of the sample has a hardness ratio consistent with > 50% covering
of the continuum by low-ionization, Compton-thick gas. More detailed study of
the three hardest X-ray spectra in our sample reveal a sharp Fe K absorption
edge at ~ 7 keV in each of them, indicating that blurred reflection is not
responsible for the very hard spectral forms. Simple considerations place the
distribution of Compton-thick clouds at or within the optical broad line
region.Comment: Accepted for publication in Ap
Wikipedia as Distributed Knowledge Laboratory: The Case of Neoliberalism
Merit, Expertise and Measuremen
An S2 Fluorescence Model for Interpreting High-Resolution Cometary Spectra. I. Model Description and Initial Results
A new versatile model providing S2 fluorescence spectrum as a function of
time is developed with the aim of interpreting high resolution cometary
spectra. For the S2 molecule, it is important to take into account both
chemical and dynamic processes because S2 has a short lifetime and is confined
in the inner coma where these processes are most important. The combination of
the fluorescence model with a global coma model allows for the comparison with
observations of column densities taken through an aperture and for the analysis
of S2 fluorescence in different parts of the coma. Moreover, the model includes
the rotational structure of the molecule. Such a model is needed for
interpreting recent high spectral resolution observations of cometary S2. A
systematic study of the vibrational-rotational spectrum of S2 is undertaken,
including relevant effects, such as non-equilibrium state superposition and the
number density profile within the coma due to dynamics and chemistry, to
investigate the importance of the above effects on the scale length and
abundance of S2 in comets.Comment: 20 pages, 7 figure
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