1,151 research outputs found
Rocks and Hard Places: Exploring Educational Psychologists’ Perspectives on “Off-Rolling” or Illegal Exclusionary Practices in Mainstream Secondary Schools in England
Research being undertaken by the Universities of Exeter and Plymouth is exploring educational psychologists’ knowledge of, and perspectives on, exclusionary practices in schools in England, particularly illegal practices referred to as “off-rolling”. 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 schools’ management of the (in)visibility of “off-rolling” and the manufactured legitimacy of varied exclusionary practices
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]
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
A burst from the direction of UZ Fornacis with XMM-Newton
The XMM-Newton pointing towards the magnetic cataclysmic variable UZ For
finds the source to be a factor > 10^3 fainter than previous EXOSAT and ROSAT
observations. The source was not detected for the majority of a 22 ksec
exposure with the EPIC cameras, suggesting that the accretion rate either
decreased, or stopped altogether. However a 1.1 ksec burst was detected from UZ
For during the observation. Spectral fits favour optically thin, kT = 4.4 keV
thermal emission. Detection of the burst by the on-board Optical Monitor
indicates that this was most probably an accretion event. The 0.1-10 keV
luminosity of 2.1 x 10^30 erg/s is typical for accretion shock emission from
high state polars and would result from the potential energy release of ~ 10^16
g of gas. There is no significant soft excess due to reprocessing in the white
dwarf atmosphere.Comment: 7 pages, 2 postscript figures, ApJL, in pres
Cyclotron modeling phase-resolved infrared spectroscopy of polars I: EF Eridani
We present phase-resolved low resolution infrared spectra of the polar EF
Eridani obtained over a period of 2 years with SPEX on the IRTF. The spectra,
covering the wavelength range 0.8 to 2.4 microns, are dominated by cyclotron
emission at all phases. We use a ``Constant Lambda'' prescription to attempt to
model the changing cyclotron features seen in the spectra. A single cyclotron
emission component with B = 12.6 MG, and a plasma temperature of kT = 5.0 keV,
does a reasonable job in matching the features seen in the H and K bands, but
fails to completely reproduce the morphology shortward of 1.6 microns. We find
that a two component model, where both components have similar properties, but
whose contributions differ with viewing geometry, provides an excellent fit to
the data. We discuss the implications of our models and compare them with
previously published results. In addition, we show that a cyclotron model with
similar properties to those used for modeling the infrared spectra, but with a
field strength of B = 115 MG, can explain the GALEX observations of EF Eri.Comment: 25 pages, 5 figures, to appear in Ap
High Energy Break and Reflection Features in the Seyfert Galaxy MCG+8-11-11
We present the results from ASCA and OSSE simultaneous observations of the
Seyfert 1.5 galaxy MCG+8-11-11 performed in August-September 1995. The ASCA
observations indicate a modest flux increase (20%) in 3 days, possibly
correlated to a softening of the 0.6-9 keV spectrum. The spectrum is well
described by a hard power law (Gamma=1.64) absorbed by a column density
slightly larger than the Galactic value, with an iron line at 6.4 keV of EW=400
eV. The simultaneous OSSE data are characterized by a much softer power law
with photon index Gamma=3.0, strongly suggesting the presence of a spectral
break in the hard X/soft gamma-ray band. A joint fit to OSSE and ASCA data
clearly shows an exponential cut-off at about 300 keV, and strong reflection
component. MCG+8-11-11 features a spectral break in the underlying continuum
unambiguously. This, together with the inferred low compactness of this source,
favours thermal or quasi-thermal electron Comptonization in a structured Corona
as the leading process of high energy radiation production.Comment: 13 pages, + 4 figure.ps AAS LateX [11pt,aasms4]{article} To be
published in ApJ, Main Journa
Intensive HST, RXTE and ASCA Monitoring of NGC 3516: Evidence Against Thermal Reprocessing
During 1998 April 13-16, NGC 3516 was monitored almost continuously with HST
for 10.3 hr in the UV and 2.8 d in the optical, and simultaneous RXTE and ASCA
monitoring covered the same period. The X-rays were strongly variable with the
soft (0.5-2 keV) showing stronger variations (~65% peak-to-peak) than the hard
(2-10 keV; ~50% peak-to-peak). The optical continuum showed much smaller but
highly significant variations: a slow ~2.5% rise followed by a faster ~3.5%
decline. The short UV observation did not show significant variability.
The soft and hard X-ray light curves were strongly correlated with no
significant lag. Likewise, the optical continuum bands (3590 and 5510 A) were
also strongly correlated with no measurable lag above limits of <0.15 d.
However no significant correlation or simple relationship could be found for
the optical and X-ray light curves. These results appear difficult to reconcile
with previous reports of correlations between X-ray and optical variations and
of measurable lags within the optical band for some other Seyfert 1s.
These results also present serious problems for "reprocessing" models in
which the X-ray source heats a stratified accretion disk which then reemits in
the optical/ultraviolet: the synchronous variations within the optical would
suggest that the emitting region is <0.3 lt-d across, while the lack of
correlation between X-ray and optical variations would indicate, in the context
of this model, that any reprocessing region must be >1 lt-d in size. It may be
possible to resolve this conflict by invoking anisotropic emission or special
geometry, but the most natural explanation appears to be that the bulk of the
optical luminosity is generated by some other mechanism than reprocessing.Comment: 23 pages including 6 figures, accepted for publication in Ap
Isotropic Mid-Infrared Emission from the Central 100 pc of Active Galaxies
Dust reprocesses the intrinsic radiation of active galactic nuclei (AGNs) to
emerge at longer wavelengths. The observed mid-infrared (MIR) luminosity
depends fundamentally on the luminosity of the central engine, but in detail it
also depends on the geometric distribution of the surrounding dust. To quantify
this relationship, we observe nearby normal AGNs in the MIR to achieve spatial
resolution better than 100 pc, and we use absorption-corrected X-ray luminosity
as a proxy for the intrinsic AGN emission. We find no significant difference
between optically classified Seyfert 1 and 2 galaxies. Spectroscopic
differences, both at optical and IR wavelengths, indicate that the immediate
surroundings of AGNs is not spherically symmetric, as in standard unified AGN
models. A quantitative analysis of clumpy torus radiative transfer models shows
that a clumpy local environment can account for this dependence on viewing
geometry while producing MIR continuum emission that remains nearly isotropic,
as we observe, although the material is not optically thin at these
wavelengths. We find some luminosity dependence on the X-ray/MIR correlation in
the smallest scale measurements, which may indicate enhanced dust emission
associated with star formation, even on these sub-100 pc scales.Comment: 10 pages, 5 figures; accepted for publication in Ap
Variability and spectral modeling of the hard X-ray emission of GX 339-4 in a bright low/hard state
We study the high-energy emission of the Galactic black hole candidate GX
339-4 using INTEGRAL/SPI and simultaneous RXTE/PCA data. By the end of January
2007, when it reached its peak luminosity in hard X-rays, the source was in a
bright hard state. The SPI data from this period show a good signal to noise
ratio, allowing a detailed study of the spectral energy distribution up to
several hundred keV. As a main result, we report on the detection of a variable
hard spectral feature (>150 keV) which represents a significant excess with
respect to the cutoff power law shape of the spectrum. The SPI data suggest
that the intensity of this feature is positively correlated with the 25 - 50
keV luminosity of the source and the associated variability time scale is
shorter than 7 hours. The simultaneous PCA data, however, show no significant
change in the spectral shape, indicating that the source is not undergoing a
canonical state transition. We analyzed the broad band spectra in the lights of
several physical models, assuming different heating mechanisms and properties
of the Comptonizing plasma. For the first time, we performed quantitative model
fitting with the new versatile Comptonization code BELM, accounting
self-consistently for the presence of a magnetic field. We show that a
magnetized medium subject to pure non-thermal electron acceleration provides a
framework for a physically consistent interpretation of the observed 4 - 500
keV emission. Moreover, we find that the spectral variability might be
triggered by the variations of only one physical parameter, namely the magnetic
field strength. Therefore, it appears that the magnetic field is likely to be a
key parameter in the production of the Comptonized hard X-ray emission.Comment: 14 pages, 9 figures, 3 tables, uses emulateApj.cls, accepted for
publication in Ap
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