359 research outputs found
A characterization of the NGC 4051 soft X-ray spectrum as observed by XMM-Newton
Soft X-rays high resolution spectroscopy of obscured AGNs shows the existence
of a complex soft -ray spectrum dominated by emission lines of He and H-like
transitions of elements from Carbon to Neon, as well as L-shell transitions due
to iron ions. In this paper we characterize the XMM-Newton RGS spectrum of the
Seyfert 1 galaxy NGC 4051 observed during a low flux state and infer the
physical properties of the emitting and absorbing gas in the soft X-ray regime.
X-ray high-resolution spectroscopy offers a powerful diagnostic tool since the
observed spectral features strongly depend on the physical properties of matter
(ionization parameter U, electron density n_e, hydrogen column density N_H),
which in turn are tightly related to the location and size of the X-ray
emitting clouds. We carried out a phenomenological study to identify the atomic
transitions detected in the spectra. This study suggests that the spectrum is
dominated by emission from a photoionised plasma. Then, we used the
photoionization code Cloudy to produce synthetic models for the emission line
component and the warm absorber observed during phases of high intrinsic
luminosity. The low state spectrum cannot be described by a single
photoionization component. A multi-ionization phase gas with ionization
parameter in the range log U = 0.63-1.90 and column density log N_H =
22.10-22.72 cm^-2 is required, while the electron density n_e remains
unconstrained. A warm absorber medium is required by the fit with parameters
log U = 0.85, log N_H = 23.40 and log n_e \ut< 5. The model is consistent with
an X-ray emitting regions at a distance > 5 x 10^-2 pc from the central engine.Comment: Accepted for publication on section 4 "Extragalactic astronomy" of
Astronomy and Astrophysics, 2010, 12 pages, 8 Figures, 4 Tables, in printer
format. A few typos corrected
A USB3.0 FPGA Event-based Filtering and Tracking Framework for Dynamic Vision Sensors
Dynamic vision sensors (DVS) are frame-free sensors
with an asynchronous variable-rate output that is ideal for hard
real-time dynamic vision applications under power and latency
constraints. Post-processing of the digital sensor output can
reduce sensor noise, extract low level features, and track objects
using simple algorithms that have previously been implemented
in software. In this paper we present an FPGA-based framework
for event-based processing that allows uncorrelated-event noise
removal and real-time tracking of multiple objects, with dynamic
capabilities to adapt itself to fast or slow and large or small
objects. This framework uses a new hardware platform based on
a Lattice FPGA which filters the sensor output and which then
transmits the results through a super-speed Cypress FX3 USB
microcontroller interface to a host computer. The packets of
events and timestamps are transmitted to the host computer at
rates of 10 Mega events per second. Experimental results are
presented that demonstrate a low latency of 10us for tracking
and computing the center of mass of a detected object.Ministerio de Economía y Competitividad TEC2012-37868-C04-0
On the driver of relativistic effects strength in Seyfert galaxies
Spectroscopy of X-ray emission lines emitted in accretion discs around
supermassive black holes is one of the most powerful probes of the accretion
flow physics and geometry, while also providing in principle observational
constraints on the black hole spin.[...] We aim at determining the ultimate
physical driver of the strength of this relativistic reprocessing feature. We
first extend the hard X-ray flux-limited sample of Seyfert galaxies studied so
far (FERO, de la Calle Perez et al. 2010) to obscured objects up to a column
density N_H=6x10^23 atoms/cm/cm. We verify that none of the line properties
depends on the AGN optical classification, as expected from the Seyfert
unification scenarios. There is also no correlation between the accretion disc
inclination, as derived from formal fits of the line profiles, and the optical
type or host galaxy aspect angle, suggesting that the innermost regions of the
accretion disc and the host galaxy plane are not aligned. [...]. Data are not
sensitive enough to the detailed ionisation state of the line-emitting disc.
However, the lack of dependency of the line EW on either the luminosity or the
rest-frame centroid energy rules out that disc ionisation plays an important
role on the EW dynamical range in Seyferts. The dynamical range of the
relativistically broadened K-alpha iron line EW in nearby Seyferts appears to
be mainly determined by the properties of the innermost accretion flow. We
discuss several mechanisms (disc ionisation, disc truncation, aberration due to
a mildly relativistic outflowing corona) which can explain this. [...]
Observational data are still not in contradiction with scenarios invoking
different mechanisms for the spectral complexity around the iron line, most
notably the "partial covering" absorption scenario. (abridged).Comment: Accepted for publication on Astronomy & Astrophysics. 14 pages, 9
figure
Obscuring clouds playing hide-and-seek in the Active Nucleus H0557-385
This paper reports on two XMM-Newton observations of the Seyfert 1 Galaxy
H0557-385 obtained in 2006, which show the source at an historical low flux
state, more than a factor of 10 lower than a previous XMM-Newton look in 2002.
The low flux spectrum presents a strong Fe Kalpha line associated to a Compton
reflection continuum. An additional spectral line around 6.6 keV is required to
fit Kalpha emission from Fe XXV. The spectral curvature below 6 keV implies
obscuration by neutral gas with a column density of 8*10^{23}cm^{-2} partially
covering the primary emission, which still contributes for a few percent of the
soft X-ray emission. Absorption by ionised material on the line of sight is
required to fit the deep trough below 1 keV. The comparison of the two spectral
states shows that the flux transition is to be ascribed entirely to intervening
line-of-sight clouds with high column density.Comment: 5 pages, accepted for publication on MNRAS Letter
The rise of an ionized wind in the Narrow Line Seyfert 1 Galaxy Mrk 335 observed by XMM-Newton and HST
We present the discovery of an outflowing ionized wind in the Seyfert 1
Galaxy Mrk 335. Despite having been extensively observed by most of the largest
X-ray observatories in the last decade, this bright source was not known to
host warm absorber gas until recent XMM-Newton observations in combination with
a long-term Swift monitoring program have shown extreme flux and spectral
variability. High resolution spectra obtained by the XMM-Newton RGS detector
reveal that the wind consists of three distinct ionization components, all
outflowing at a velocity of 5000 km/s. This wind is clearly revealed when the
source is observed at an intermediate flux state (2-5e-12 ergs cm^-2 s^-1). The
analysis of multi-epoch RGS spectra allowed us to compare the absorber
properties at three very different flux states of the source. No correlation
between the warm absorber variability and the X-ray flux has been determined.
The two higher ionization components of the gas may be consistent with
photoionization equilibrium, but we can exclude this for the only ionization
component that is consistently present in all flux states (log(xi)~1.8). We
have included archival, non-simultaneous UV data from HST (FOS, STIS, COS) with
the aim of searching for any signature of absorption in this source that so far
was known for being absorption-free in the UV band. In the COS spectra obtained
a few months after the X-ray observations we found broad absorption in CIV
lines intrinsic to the AGN and blueshifted by a velocity roughly comparable to
the X-ray outflow. The global behavior of the gas in both bands can be
explained by variation of the covering factor and/or column density, possibly
due to transverse motion of absorbing clouds moving out of the line of sight at
Broad Line Region scale.Comment: 24 pages, 12 figures, ApJ accepte
Electrical conductances of Tetrabutylammonium and Decamethylferrocenium Hexafluorophosphate in organic solvents
The electrical conductances of tetrabutylammonium hexafluorophosphate in acetone and of decamethylferrocenium hexafluorophosphate in acetone, acetonitrile 1,2-dichloroethane, and dichloromethane have been measured at 25°C. The Walden product of the Bu4N+ cation and the PF-6 anion in acetone and other solvents is discussed in relation to the dielectric friction. The electric conductance at infinite dilution and the association constant of decamethylferrocenium hexafluorophosphate were determined in the four solvents investigated. The association constant of this electrolyte increases with decreasing reduced temperature, as expected in the framework of the association theory, within the primitive model of electrolytes.Fil: Goldfarb, Darío L.. Comisión Nacional de Energía Atómica; ArgentinaFil: Longinotti, María Paula. Comisión Nacional de Energía Atómica; ArgentinaFil: Corti, Horacio Roberto. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Relativistic inflow in the Seyfert 1 Mrk 335 revealed through X-ray absorption
The analysis of hard X-ray features in XMM-Newton data of the bright Sy 1 galaxy Mrk 335 is reported here. The presence of a broad, ionised iron K alpha emission line in the spectrum, first found by Gondoin et al.(2002), is confirmed. The broad line can be modeled successfully by relativistic accretion disc reflection models. Regardless of the underlying continuum we report, for the first time in this source, the detection of a narrow absorption feature at the rest frame energy of ~5.9 keV. If the feature is identified with a resonance absorption line of iron in a highly ionised medium, the redshift of the line corresponds to an inflow velocity of ~0.11-0.15 c. Preliminary results from a longer (100ks) exposure are also presented
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