22,161 research outputs found
Investigating the nature of narrow-line Seyfert 1 galaxies with high-energy spectral complexity
(abridged) With the commissioning of XMM came the discovery of 2.5-10 keV
spectral complexity in some narrow-line Seyfert 1 galaxies (NLS1). In this
work, we define two samples of NLS1: a complex sample whose members exhibit
high-energy complexity (C-sample), and a general sample of NLS1 whose 2.5-10
keV spectra do not strongly deviate from a simple power law (S-sample).
Considering historical light curves of each object we find that the C-sample is
representative of NLS1 in a low X-ray flux state, whereas the members of the
S-sample appear to be in a typical flux state. Moreover, from measurements of
alpha_ox with contemporaneous UV/X-ray data, we find that the C-sample of NLS1
appear X-ray weaker at the time of the observation. For two NLS1 in the
C-sample multi-epoch measurements of alpha_ox are available and suggest that
alpha_ox approaches more normal values as the complexity between 2.5-10 keV
diminishes. This implies that a source could transit from one sample to the
other as its X-ray flux varies. Secondly, there are indications that the
C-sample sources, on average, exhibit stronger optical FeII emission, with the
three most extreme (FeII/H_beta > 1.8) FeII emitters all displaying complexity
in the 2.5-10 keV band. However, it is not clear if the possible connection
between FeII strength and spectral complexity is due to the FeII producing
mechanism or because strong FeII emitters may exhibit the greatest variability
and consequently more likely to be caught in an extreme (low) flux state. Based
on the current analysis it we can not straightforwardly dismiss absorption or
reflection as the cause of the X-ray complexity.Comment: 8 pages, 3 figures. Accepted for publication in MNRA
X-rays from the radio-quiet quasar PG 1407+265: relativistic jet or accretion disc emission?
We present two XMM-Newton observations of the luminous (L_x > 10^46 erg/s),
radio-quiet quasar, PG 1407+265, separated by eleven months. The data indicate
two distinct states: a highly variable, bright state (first epoch); and a
quiescent, low-flux one (second epoch). During the low-flux state the spectrum
is consistent with a single, unabsorbed power law. However, during the brighter
state a highly variable, steep component is statistically required.
Contemporaneous UV data from the Optical Monitor allow an estimate of the
optical-to-X-ray spectral index (alpha_ox), which appears typical of
radio-quiet quasars during the low-flux state, but extremely flat during the
high-flux state. The XMM-Newton data can be described as originating from a
combination of jet and accretion disc processes, in which the (relativistic)
X-ray jet only works intermittently. The scenario could help describe some of
the complexities seen in the broadband spectral energy distribution of PG
1407+265, such as weak high-ionisation emission lines, strong Fe II, unbeamed
continuum, and the weak radio emission relative to the optical.Comment: 9 pages, 8 figures. Accepted for publication in MNRAS. Correction
made to reported aox value. No changes in conclusion
The origin of blue-shifted absorption features in the X-ray spectrum of PG 1211+143: Outflow or disc?
In some radio-quiet active galaxies (AGN), high-energy absorption features in
the x-ray spectra have been interpreted as Ultrafast Outflows (UFOs) -- highly
ionised material (e.g. Fe XXV and Fe XXVI) ejected at mildly relativistic
velocities. In some cases, these outflows can carry energy in excess of the
binding energy of the host galaxy. Needless to say, these features demand our
attention as they are strong signatures of AGN feedback and will influence
galaxy evolution. For the same reason, alternative models need to be discussed
and refuted or confirmed. Gallo & Fabian proposed that some of these features
could arise from resonance absorption of the reflected spectrum in a layer of
ionised material located above and corotating with the accretion disc.
Therefore, the absorbing medium would be subjected to similar blurring effects
as seen in the disc. A priori, the existence of such plasma above the disc is
as plausible as a fast wind. In this work, we highlight the ambiguity by
demonstrating that the absorption model can describe the ~7.6 keV absorption
feature (and possibly other features) in the quasar PG 1211+143, an AGN that is
often described as a classic example of an UFO. In this model, the 2-10 keV
spectrum would be largely reflection dominated (as opposed to power law
dominated in the wind models) and the resonance absorption would be originating
in a layer between about 6 and 60 gravitational radii. The studies of such
features constitutes a cornerstone for future X-ray observatories like Astro-H
and Athena+. Should our model prove correct, or at least important in some
cases, then absorption will provide another diagnostic tool with which to probe
the inner accretion flow with future missions.Comment: 4 pages. Accepted for publication in MNRAS Letter
How well can we measure supermassive black hole spin?
Being one of only two fundamental properties black holes possess, the spin of
supermassive black holes (SMBHs) is of great interest for understanding
accretion processes and galaxy evolution. However, in these early days of spin
measurements, consistency and reproducibility of spin constraints have been a
challenge. Here we focus on X-ray spectral modelling of active galactic nuclei
(AGN), examining how well we can truly return known reflection parameters such
as spin under standard conditions. We have created and fit over 4000 simulated
Seyfert 1 spectra each with 3751k counts. We assess the fits with
reflection fraction of = 1 as well as reflection-dominated AGN with =
5. We also examine the consequence of permitting fits to search for retrograde
spin. In general, we discover that most parameters are over-estimated when
spectroscopy is restricted to the 2.5 - 10.0 keV regime and that models are
insensitive to inner emissivity index and ionization. When the bandpass is
extended out to 70keV, parameters are more accurately estimated. Repeating the
process for = 5 reduces our ability to measure photon index (3 to 8
per cent error and overestimated), but increases precision in all other
parameters -- most notably ionization, which becomes better constrained
(45 erg cm ) for low ionization parameters (200 erg
cm ). In all cases, we find the spin parameter is only well
measured for the most rapidly rotating supermassive black holes (i.e.
0.8 to about 0.10) and that inner emissivity index is never well
constrained. Allowing our model to search for retrograde spin did not improve
the results.Comment: Accepted for publication in MNRAS. 13 pages, 7 figure
Deficient Reasoning for Dark Matter in Galaxies
Astronomers have been using the measured luminosity to estimate the {\em
luminous mass} of stars, based on empirically established mass-to-light ratio
which seems to be only applicable to a special class of stars---the
main-sequence stars---with still considerable uncertainties. Another basic tool
to determine the mass of a system of stars or galaxies comes from the study of
their motion, as Newton demonstrated with his law of gravitation, which yields
the {\em gravitational mass}. Because the luminous mass can at best only
represent a portion of the gravitational mass, finding the luminous mass to be
different or less than the gravitational mass should not be surprising. Using
such an apparent discrepancy as a compelling evidence for the so-called dark
matter, which has been believed to possess mysterious nonbaryonic properties
and present a dominant amount in galaxies and the universe, seems to be too far
a stretch when seriously examining the facts and uncertainties in the
measurement techniques. In our opinion, a galaxy with star type distribution
varying from its center to edge may have a mass-to-light ratio varying
accordingly. With the thin-disk model computations based on measured rotation
curves, we found that most galaxies have a typical mass density profile that
peaks at the galactic center and decreases rapidly within of the
cut-off radius, and then declines nearly exponentially toward the edge. The
predicted mass density in the Galactic disk is reasonably within the reported
range of that observed in interstellar medium. This leads us to believe that
ordinary baryonic matter can be sufficient for supporting the observed galactic
rotation curves; speculation of large amount of non-baryonic matter may be
based on an ill-conceived discrepancy between gravitational mass and luminous
mass which appears to be unjustified
Driving extreme variability: The evolving corona and evidence for jet launching in Markarian 335
Variations in the X-ray emission from the narrow line Seyfert 1 galaxy,
Markarian 335 (Mrk 335), are studied on both long and short timescales through
observations made between 2006 and 2013 with XMM-Newton, Suzaku and NuSTAR.
Changes in the geometry and energetics of the corona that give rise to this
variability are inferred through measurements of the relativistically blurred
reflection seen from the accretion disc. On long timescales, we find that
during the high flux epochs the corona has expanded, covering the inner regions
of the accretion disc out to a radius of 26(-7,+10)rg. The corona contracts to
within 12rg and 5rg in the intermediate and low flux epochs, respectively.
While the earlier high flux observation made in 2006 is consistent with a
corona extending over the inner part of the accretion disc, a later high flux
observation that year revealed that the X-ray source had become collimated into
a vertically-extended jet-like corona and suggested relativistic motion of
material upward. On short timescales, we find that an X-ray flare during a low
flux epoch in 2013 corresponded to a reconfiguration from a slightly extended
corona to one much more compact, within just 2~3rg of the black hole. There is
evidence that during the flare itself, the spectrum softened and the corona
became collimated and slightly extended vertically as if a jet-launching event
was aborted. Understanding the evolution of the X-ray emitting corona may
reveal the underlying mechanism by which the luminous X-ray sources in AGN are
powered.Comment: 21 pages, 9 figures. Accepted for publication in MNRA
An alternative method of analysis for base accelerated dynamic response in NASTRAN
An alternative method of analysis to determine the dynamic response of structures subjected to base accelerations is presented. The method is exact as opposed to the approximate technique of using unusually large masses and loads to enforce desired base accelerations. This paper presents the relevant equations to motion, ALTERs for direct and modal frequency-, random- and transient-response rigid formats, and illustrative examples
Acoustical modes of arbitrary volumes using NASTRAN transient heat transfer RF9
An equivalence between temperature and pressure, heat conduction and stiffness and heat capacity and mass is defined, enabling acoustical modal analysis of arbitrary three dimensional volumes. The transient heat transfer analysis rigid format in NASTRAN, RF9, has been altered providing the acoustical analysis capability. Examples and ALTERs are included
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