1,341 research outputs found
Rocks and Hard Places: Exploring Educational Psychologistsâ Perspectives on âOff-Rollingâ or Illegal Exclusionary Practices in Mainstream Secondary Schools in England
Research being undertaken by the Universities of Exeter and Plymouth is exploring educational psychologistsâ knowledge of, and perspectives on, exclusionary practices in schools in England, particularly illegal practices referred to as âoff-rollingâ. Preliminary findings from the survey element of a mixed methods research project are reported here. The role of business models in the provision of educational psychology services to schools is considered through the conceptual lens of Giroux, Agamben and Ball to highlight ambiguities around the client relationship and to recast individualised ethical dilemmas as systemic features that inhibit direct challenges to school practices relating to inclusion. It is suggested that traded and privatised services risk implicating educational psychologists in schoolsâ management of the (in)visibility of âoff-rollingâ and the manufactured legitimacy of varied exclusionary practices
The X-ray reflector in NGC 4945: a time and space resolved portrait
We present a time, spectral and imaging analysis of the X-ray reflector in
NGC 4945, which reveals its geometrical and physical structure with
unprecedented detail. NGC 4945 hosts one of the brightest AGN in the sky above
10 keV, but it is only visible through its reflected/scattered emission below
10 keV, due to absorption by a column density of ~4\times10^24 cm-2. A new
Suzaku campaign of 5 observations spanning ~6 months, together with past
XMM-Newton and Chandra observations, show a remarkable constancy (within <10%)
of the reflected component. Instead, Swift-BAT reveals strong intrinsic
variability on time scales longer than one year. Modeling the circumnuclear gas
as a thin cylinder with the axis on the plane of the sky, we show that the
reflector is at a distance >30-50 pc, well within the imaging capabilities of
Chandra at the distance of NGC 4945 (1"~18 pc). Accordingly, the Chandra
imaging reveals a resolved, flattened, ~150 pc-long clumpy structure, whose
spectrum is fully due to cold reflection of the primary AGN emission. The
clumpiness may explain the small covering factor derived from the spectral and
variability properties.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in MNRA
GRS 1915+105 : High-energy Insights with SPI/INTEGRAL
We report on results of two years of INTEGRAL/SPI monitoring of the Galactic
microquasar GRS 1915+105. From September 2004 to May 2006, the source has been
observed twenty times with long (approx 100 ks) exposures. We present an
analysis of the SPI data and focus on the description of the high-energy (> 20
keV) output of the source. We found that the 20 - 500 keV spectral emission of
GRS 1915+105 was bound between two states. It seems that these high-energy
states are not correlated with the temporal behavior of the source, suggesting
that there is no direct link between the macroscopic characteristics of the
coronal plasma and the the variability of the accretion flow. All spectra are
well fitted by a thermal comptonization component plus an extra high-energy
powerlaw. This confirms the presence of thermal and non-thermal electrons
around the black hole.Comment: 7 pages, 8 figures, 2 tables; accepted (09/11/2008) for publication
in A&
ON THE GEOMETRY OF THE X-RAY EMITTING REGION IN SEYFERT GALAXIES
For the first time, detailed radiative transfer calculations of Comptonized
X-ray and gamma-ray radiation in a hot pair plasma above a cold accretion disk
are performed using two independent codes and methods. The simulations include
both energy and pair balance as well as reprocessing of the X- and gamma-rays
by the cold disk. We study both plane-parallel coronae as well as active
dissipation regions having shapes of hemispheres and pill boxes located on the
disk surface. It is shown, contrary to earlier claims, that plane-parallel
coronae in pair balance have difficulties in selfconsistently reproducing the
ranges of 2-20 keV spectral slopes, high energy cutoffs, and compactnesses
inferred from observations of type 1 Seyfert galaxies. Instead, the
observations are consistent with the X-rays coming from a number of individual
active regions located on the surface of the disk.
A number of effects such as anisotropic Compton scattering, the reflection
hump, feedback to the soft photon source by reprocessing, and an active region
in pair equilibrium all conspire to produce the observed ranges of X-ray
slopes, high energy cutoffs, and compactnesses. The spread in spectral X-ray
slopes can be due to a spread in the properties of the active regions such as
their compactnesses and their elevations above the disk surface. Simplified
models invoking isotropic Comptonization in spherical clouds are no longer
sufficient when interpreting the data.Comment: 9 pages, 3 postscript figures, figures can be obtained from the
authors via e-mail: [email protected]
Balancing pressures for Special Educational Needs Coordinators as managers, leaders and advocates in the emerging context of the COVID-19 pandemic
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Hard X-ray spectral variability of the brightest Seyfert AGN in the Swift/BAT sample
Aims: We used data from the 58 month long, continuous Swift/Burst Alert
Telescope (BAT) observations of the five brightest Seyfert galaxies at hard
X-rays, to study their flux and spectral variability in the 20-100 keV energy
band. The column density in these objects is less than 10^24 cm-2, which
implies that the Swift/BAT data allow us to study the "true" variability of the
central source. Results: All objects show significant variations, with an
amplitude which is similar to the AGN variability amplitude at energies below
10 keV. We found evidence for an anti-correlation between variability amplitude
and black hole mass. The light curves in both bands are well correlated, with
no significant delays on time scales as short as 2 days. NGC 4151 and NGC 2110
do not show spectral variability, but we found a significant anti-correlation
between hardness ratios and source flux in NGC 4388 (and NGC 4945, IC 4329, to
a lesser extent). This "softer when brighter" behaviour is similar to what has
been observed at energies below 10 keV, and cannot be explained if the
continuum varies only in flux; the intrinsic shape should also steepen with
increasing flux. Conclusions: The presence of significant flux variations
indicate that the central source in these objects is intrinsically variable on
time scales as short as 1-2 days. The intrinsic slope of the continuum varies
with the flux (at least in NGC 4388). The positive "spectral slope-flux"
correlation can be explained if the temperature of the hot corona decreases
with increasing flux. The lack of spectral variations in two objects, could be
due to the fact that they may operate in a different "state", as their
accretion rate is less than 1% of the Eddington limit (significantly smaller
than the rate of the other three objects in the sample).Comment: Accepted (29/10/11) for publication in A&A (12 pages, containing 14
figures and 2 tables). (Abstract shortened --see link for the complete one
Hard X-ray colours of Neutron Star and Black Hole Low Mass X-ray Binaries with INTEGRAL
The X-ray spectra of Low Mass X-ray Binaries (LMXB) can change on short
time-scales, making it difficult to follow their spectral characteristics in
detail through model fitting. Colour-colour (C-C) diagrams are therefore often
used as alternative, model independent, tools to study the spectral variability
of these sources. The INTEGRAL mission, with its high sensitivity, large field
of view and good angular resolution, is well suited to study the hard X-ray
properties of LMXBs. In particular the ISGRI imager on board of INTEGRAL allows
the regular monitoring of the sources in the less frequently studied domain
above 20 keV. In this proceeding, C-C diagrams have been made with data from
the INTEGRAL public archive; a search is made for systematic differences in the
C-C diagrams between black hole candidates (BH) and neutron stars (NS) in LMXBs
using a moments analysis method.Comment: Paper from poster presentation at COSPAR meeting, Beijing, 2006. in
press: Advances in Space Research, Editor: Wynn H
The first outburst of the black hole candidate MAXI J1836-194 observed by INTEGRAL, Swift, and RXTE
MAXI J1836-194 is a transient black-hole candidate discovered in outburst by
MAXI on 30 August 2011. We report on the available INTEGRAL, Swift, and RXTE
observations performed in the direction of the source during this event before
55 864 MJD. Combining the broad band (0.6-200 keV) spectral and timing
information obtained from these data with the results of radio observations, we
show that the event displayed by MAXI J1836-194 is another example of "failed"
outburst. During the first ~20 days after the onset of the event, the source
underwent a transition from the canonical low/hard to the hard intermediate
state, while reaching the highest X-ray flux. In the ~40 days following the
peak of the outburst, the source displayed a progressive spectral hardening and
a decrease of the X-ray flux, thus it entered again the low/hard state and
began its return to quiescence.Comment: Accepted for A&A Letters on 22 Dec. 201
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