3,319 research outputs found
Resonant Absorption in the AGN spectra emerging from photoionized gas: differences between steep and flat ionizing continua
We present photoionization models accounting for both photoelectric and
resonant absorption. Resonance absorption lines from C, O, Ne, Mg, Si S and Fe
between 0.1 and 10 keV are treated. In particular we consider the complex of
almost 60 strong Fe L absorption lines around 1 keV. We calculate profiles,
intensities and equivalent widths of each line, considering both Doppler and
natural broadening mechanisms. Doppler broadening includes a term accounting
for turbulence of the gas along the line of sight. We computed spectra
transmitted by gas illuminated by drastically different ionizing continua and
compared them to spectra observed in flat X-ray spectrum, broad optical
emission line type 1 AGN, and steep X-ray spectrum, narrow optical emission
line type 1 AGN. We show that the keV absorption feature observed in
moderate resolution X-ray spectra of several Narrow Line Seyfert 1 galaxies can
be explained by photoionization models, taking into account for resonance
absorption, without requiring relativistic outflowing velocities of the gas, if
the physical properties of these absorbers are close to those found in flat
X-ray spectrum Seyfert 1 galaxies.Comment: 22 pages, 10 figures. Accepted for publication on Ap
The XMM-Newton/INTEGRAL monitoring campaign of IGR J16318-4848
IGR J16318-4848 is the prototype and one of the more extreme examples of the
new class of highly obscured Galactic X-ray sources discovered by INTEGRAL. A
monitoring campaign on this source has been carried out by XMM-Newton and
INTEGRAL, consisting in three simultaneous observations performed in February,
March and August 2004. The long-term variability of the Compton-thick
absorption and emission line complexes will be used to probe the properties of
the circumstellar matter. A detailed timing and spectral analysis of the three
observations is performed, along with the reanalysis of the XMM-Newton
observation performed in February 2003. The results are compared with
predictions from numerical radiative transfer simulations to derive the
parameters of the circumstellar matter. Despite the large flux dynamic range
observed (almost a factor 3 between observations performed a few months apart),
the source remained bright (suggesting it is a persistent source) and
Compton-thick (NH >1.2x10^24 cm-2). Large Equivalent Width (EW) emission lines
from Fe Kalpha, Fe Kbeta and Ni Kalpha were present in all spectra. The
addition of a Fe Kalpha Compton Shoulder improves the fits, especially in the
2004 observations. Sporadic occurrences of rapid X-ray flux risings were
observed in three of the four observations. The Fe Kalpha light curve followed
the continuum almost instantaneously, suggesting that the emission lines are
produced by illumination of small-scale optically-thick matter around the
high-energy continuum source. Using the iron line EW and Compton Shoulder as
diagnostic of the geometry of the matter, we suggest that the obscuring matter
is in a flattened configuration seen almost edge-on.Comment: accepted by Astronomy and Astrophysic
XMM-Newton view of the double-peaked Fe K-alpha complex in E1821+643
We present the results of the analysis of the hard band XMM-Newton spectra of
the luminous, L(2-10keV)~3.4E+45 erg/s, radio-quiet quasar, E1821+643. Two
emission features were observed in the 6-7 keV rest frame band, confirming
previous Chandra detection of these structures. We interpret these features as
two single emission lines, one consistent with the neutral Fe K-alpha line at
6.4 keV and the other most likely due to FeXXVI. If related to the quasar, the
high-energy emission line should originate in highly ionised matter, i.e. the
accretion disc or the clouds of the emission line regions. Alternatively, it
may be related to the intergalactic medium of the rich galaxy cluster in which
E1821+643 is embedded. A composite broad emission line in combination with an
absorption line model, however, also fits the data well. We discuss the
possible physical interpretations of the origin of these features.Comment: Accepted for publication in A&A, 7 pages and 7 figure
Suzaku Confirms NGC~3660 is an Unabsorbed Seyfert 2
An enigmatic group of objects, unabsorbed Seyfert 2s may have intrinsically
weak broad line regions, obscuration in the line of sight to the BLR but not to
the X-ray corona, or so much obscuration that the X-ray continuum is completely
suppressed and the observed spectrum is actually scattered into the line of
sight from nearby material. NGC 3660 has been shown to have weak broad
optical/near infrared lines, no obscuration in the soft X-ray band, and no
indication of "changing look" behavior. The only previous hard X-ray detection
of this source by Beppo-SAX seemed to indicate that the source might harbor a
heavily obscured nucleus. However, our analysis of a long-look Suzaku
observation of this source shows that this is not the case, and that this
source has a typical power law X-ray continuum with normal reflection and no
obscuration. We conclude that NGC 3660 is confirmed to have no unidentified
obscuration and that the anomolously high Beppo-SAX measurement must be due to
source confusion or similar, being inconsistent with our Suzaku measurements as
well as non-detections from Swift-BAT and RXTE.Comment: Accepted to PAS
Suzaku observation of the Phoenix Galaxy
In recent years, several Seyfert 2 galaxies have been discovered that change
state when observed in X-rays a few years apart, switching from Compton-thin to
reflection-dominated or viceversa. We observed a member of this class of
"Changing-look" sources, the Phoenix Galaxy, with Suzaku, with the aim of
better understanding the nature of the variations. The Suzaku spectrum was
analyzed, and the results compared with previous ASCA and XMM-Newton
observations. The source was caught in a Compton-thin state, as in XMM-Newton,
but differently from ASCA. Comparing the Suzaku and XMM-Newton observations, a
variation in the column density of the absorber on a time scale of years is
discovered. A similar change, but on much shorter time scales (i.e. ks) may
also explain the count-rate variations during the Suzaku observations. A soft
excess is also present, likely due to continuum and line emission from
photoionized circumnuclear matter.Comment: Accepted for publication in Astronomy & Astrophysic
X-ray observations of the Compton-thick Seyfert 2 galaxy, NGC 5643
We present results from a ~55 ks long XMM-Newton observation of the obscured
AGN, NGC 5643, performed in July 2009. A previous, shorter (about 10 ks)
XMM-Newton observation in February 2003 had left two major issues open, the
nature of the hard X-ray emission (Compton-thin vs Compton-thick) and of the
soft X-ray excess (photoionized vs collisionally ionized matter). The new
observation shows that the source is Compton-thick and that the dominant
contribution to the soft X-ray emission is by photoionized matter (even if it
is still unclear whether collisionally ionized matter may contribute as well).
We also studied three bright X-ray sources that are in the field of NGC 5643.
The ULX NGC 5643 X-1 was confirmed to be very luminous, even if more than a
factor 2 fainter than in 2003. We then provided the first high quality spectrum
of the cluster of galaxies Abell 3602. The last source, CXOJ143244.5-442020, is
likely an unobscured AGN, possibly belonging to Abell 3602.Comment: 6 pages. Accepted for publication in A&
Applying Lean to Healthcare Delivery Processes - a Case-based Research
The purpose of this paper is to demonstrate that Lean principles and methodology should be applied on a regular basis to the entire process flow of healthcare delivery systems. With reference to an actual case-based research, this article demonstrates how patient flows can be successfully optimized if Lean is not limited to single processes/contexts only, and it is applied to achieve holistic process improvement of an entire system. The complexity of healthcare delivery systems requires inclusive investigation from various points of view. This is why case-study-based research has been used to investigate dynamic, experiential and complex processes and areas, such as the ones featured by this article. The methodological basis for this research has been a twelve-step optimization approach outlined by the authors during a previous successful Lean programme. This same approach has been applied to optimize patient flows in the emergency departments of four different hospitals in Northern Italy. The research has involved teams composed of medical, nursing, technical and administrative staff.The results outlined in the article suggest that inclusive application of Lean tools leads to effective process optimization and a better working environment, when in connection with a systematic and holistic optimization approach. Feedback from participants was obtained through a satisfaction survey and a project assessment; it reported enthusiastic project acceptance and good teamwork climate. Among the results of the research performed in the four hospitals, several measures have been effectively implemented to reduce the lead-time for patients from registration to discharge. At the same time, patient-staff ratio and quality of care have been either maintained or even improved. However, lack of a definite conclusive evaluation can be explained by the research project still being implemented.The value of this paper lies in demonstrating how Lean contributes to achieve better process performance and high staff satisfaction, when implemented within the whole supply chain of a healthcare delivery system on a regular basis
The changing X-ray time lag in MCG-6-30-15
MCG-6-30-15 is one of the most observed Narrow Line Seyfert 1 galaxies in the
X-ray band. In this paper we examine the X-ray time lags in this source using a
total of 600 ks in observations (440 ks exposure) taken with the XMM-Newton
telescope (300 ks in 2001 and 300 ks in 2013). Both the old and new
observations show the usual hard lag that increases with energy, however, the
hard lag turns over to a soft lag at frequencies below ~1e-4 Hz. The highest
frequencies (~1e-3 Hz) in this source show a clear soft lag, as previously
presented for the first 300 ks observation, but no clear iron K lag is detected
in either the old or new observation. The soft lag is more significant in the
old observation than the new. The observations are consistent with a
reverberation interpretation, where the soft, reflected emission is delayed
with respect to the hard powerlaw component. These spectral timing results
suggest that two distinct variability mechanisms are important in this source:
intrinsic coronal variations (which lead to correlated variability in the
reprocessed emission), and geometrical changes in the corona. Variability due
to geometrical changes does not result in correlated variability in the
reflection, and therefore inhibits the clear detection of an iron K lag.Comment: Resubmitted to MNRAS after minor corrections. 11 pages, 10 figure
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