713 research outputs found
Large Scale Fluctuations in the X-Ray Background
We present an attempt to measure the large angular scale fluctuations in the
X-Ray Background (XRB) from the HEAO1-A2 data, expressed in terms of spherical
harmonics. We model the harmonic coefficients assuming a power spectrum and an
epoch-dependent bias parameter, and using a phenomenological scenario
describing the evolution of the X-ray sources. From the few low-order
multipoles detected above shot noise, we estimate the power-spectrum
normalization on scales intermediate between those explored by local galaxy
redshift surveys (~ 100 Mpc) and by the COBE Microwave Background measurements
(~ 1000 Mpc). We find that the HEAO1 harmonics are consistent with present
epoch rms fluctuations of the X-ray sources bx(0)sigma8 ~ 1-2 in 8 Mpc spheres.
Therefore the observed fluctuations in the XRB are roughly as expected from
interpolating between the local galaxy surveys and the COBE CMB experiment. We
predict that an X-ray all-sky surface brightness survey resolving sources a
factor of 10 fainter than HEAO1, may reveal fluctuations to significantly
larger angular scales and therefore more strongly constrain the large scale
structure of the Universe on scales of hundreds of Mpcs.Comment: 14 pages, 3 Postscript figures, uses aaspp4.sty and psfig. Revised
following referee's report. Accepted for publication in Ap
Accurate Galactic 21-cm H I measurements with the NRAO Green Bank Telescope
Aims: We devise a data reduction and calibration system for producing
highly-accurate 21-cm H I spectra from the Green Bank Telescope (GBT) of the
NRAO.
Methods: A theoretical analysis of the all-sky response of the GBT at 21 cm
is made, augmented by extensive maps of the far sidelobes. Observations of
radio sources and the Moon are made to check the resulting aperture and main
beam efficiencies.
Results: The all-sky model made for the response of the GBT at 21 cm is used
to correct for "stray" 21-cm radiation reaching the receiver through the
sidelobes rather than the main beam. This reduces systematic errors in 21-cm
measurements by about an order of magnitude, allowing accurate 21-cm H I
spectra to be made at about 9' angular resolution with the GBT. At this
resolution the procedures discussed here allow for measurement of total
integrated Galactic H I line emission, W, with errors of 3 K km s^-1,
equivalent to errors in optically thin N_HI of 5 x 10^18 cm^-2.Comment: 49 pages, 25 figures; A&A, in pres
Study of the Fast X-Ray Transient XTE J1901+014 Based on INTEGRAL, RXTE and ROSAT Data
The source XTE J1901+014 discovered by the RXTE observatory during an intense
outburst of hard radiation and classified as a fast X-ray transient is studied.
The source's spectral characteristics in the quiescent state have been
investigated for the first time both in the soft X-ray energy range (0.6-20
keV) based on ROSAT and RXTE data and in the hard energy range (>20 keV) based
on INTEGRAL data. A timing analysis of the source's properties has revealed
weak nonperiodic bursts of activity on time scales of several tens of seconds
and two intense (0.5-1 Crab) outbursts more than several hundred seconds
in duration. Certain assumptions about the nature of the object under study are
made.Comment: 19 pages, 7 figure
The broad iron Kalpha line of Cygnus X-1 as seen by XMM-Newton in the EPIC-pn modified timing mode
We present the analysis of the broadened, flourescent iron Kalpha line in
simultaneous XMM-Newton and RXTE data from the black hole Cygnus X-1. The
XMM-Newton data were taken in a modified version of the timing mode of the
EPIC-pn camera. In this mode the lower energy threshold of the instrument is
increased to 2.8 keV to avoid telemetry drop outs due to the brightness of the
source, while at the same time preserving the signal-to-noise ratio in the Fe
Kalpha band. We find that the best-fit spectrum consists of the sum of an
exponentially cut off power-law and relativistically smeared, ionized
reflection. The shape of the broadened Fe Kalpha feature is due to strong
Compton broadening combined with relativistic broadening. Assuming a standard,
thin accretion disk, the black hole is close to rotating maximally.Comment: Astron. Astrophys., in pres
BeppoSAX and multiwavelength observations of BL Lacertae in 2000
We present two BeppoSAX observations of BL Lac (2200+420) as part of a
multiwavelength campaign performed in 2000. The source was in different states
of activity: in June, the X-ray spectrum was faint and hard (alpha sim 0.8),
with positive residuals towards low energies. In October we detected the
highest [2-10] keV flux ever measured for the source. During this observation,
the spectrum was soft (alpha sim 1.56) up to 10 keV, while above this energy a
hard component was dominating. The BeppoSAX data are confirmed by simultaneous
RXTE short observations. During the first observation the soft X-ray flux was
variable on timescales of a few hours, while the hard X-ray flux was almost
constant. During the second observation, instead, the soft spectrum displayed
an erratic behaviour with large variations (up to factors 3-4) on timescales
smaller than 2 hrs. The analysis of the multiwavelength SED of October
evidenced an intriguing feature: the optical and X-ray sections of the SED are
misaligned, while in the prevailing standard picture, they are both thought to
be produced via synchrotron emission. We suggested four scenarios to account
for this discrepancy: a higher than galactic dust-to-gas ratio towards the
source, the first detection of bulk Compton emission in the X-ray band, the
presence of two synchrotron emitting regions located at different distances
from the nucleus, the detection of a Klein-Nishina effect on the synchrotron
spectrum. We evidenced the favorable and critical points of each scenario, but,
at present, we cannot discriminate between them.Comment: 13 pages, 8 figures, accepted by A&
The Early Positive Approaches to Support (E-PAtS) study: study protocol for a feasibility cluster randomised controlled trial of a group programme (E-PAtS) for family caregivers of young children with intellectual disability
Background: Children with intellectual disability have an IQ < 70, associated deficits in adaptive skills and are at increased risk of having clinically concerning levels of behaviour problems. In addition, parents of children with intellectual disability are likely to report high levels of mental health and other psychological problems. The Early Positive Approaches to Support (E-PAtS) programme for family caregivers of young children (5 years and under) with intellectual and developmental disabilities is a group-based intervention which aims to enhance parental psychosocial wellbeing and service access and support positive development for children. The aim of this study is to assess the feasibility of delivering E-PAtS to family caregivers of children with intellectual disability by community parenting support service provider organisations. The study will inform a potential, definitive RCT of the effectiveness and cost-effectiveness of E-PAtS. /
Methods: This study is a feasibility cluster randomised controlled trial, with embedded process evaluation. Up to 2 family caregivers will be recruited from 64 families with a child (18 months to 5 years) with intellectual disability at research sites in the UK. Participating families will be allocated to intervention: control on a 1:1 basis; intervention families will be offered the E-PAtS programme immediately, continuing to receive usual practice, and control participants will be offered the opportunity to attend the E-PAtS programme at the end of the follow-up period and will continue to receive usual practice. Data will be collected at baseline, 3 months post-randomisation and 12 months post-randomisation. The primary aim is to assess feasibility via the assessment of: recruitment of service provider organisations; participant recruitment; randomisation; retention; intervention adherence; intervention fidelity and the views of participants, intervention facilitators and service provider organisations regarding intervention delivery and study processes. The secondary aim is preliminary evaluation of a range of established outcome measures for individual family members, subsystem relationships and overall family functioning, plus additional health economic outcomes for inclusion in a future definitive trial. /
Discussion: The results of this study will inform a potential future definitive trial, to evaluate the effectiveness and cost-effectiveness of the E-PAtS intervention to improve parental psychosocial wellbeing. Such a trial would have significant scientific impact internationally in the intellectual disability field. /
Trial registration: ISRCTN7041947
Pulsed Gamma Rays from the Original Millisecond and Black Widow Pulsars: a case for Caustic Radio Emission?
We report the detection of pulsed gamma-ray emission from the fast
millisecond pulsars (MSPs) B1937+21 (also known as J1939+2134) and B1957+20
(J1959+2048) using 18 months of survey data recorded by the \emph{Fermi} Large
Area Telescope (LAT) and timing solutions based on radio observations conducted
at the Westerbork and Nan\c{c}ay radio telescopes. In addition, we analyzed
archival \emph{RXTE} and \emph{XMM-Newton} X-ray data for the two MSPs,
confirming the X-ray emission properties of PSR B1937+21 and finding evidence
() for pulsed emission from PSR B1957+20 for the first time. In
both cases the gamma-ray emission profile is characterized by two peaks
separated by half a rotation and are in close alignment with components
observed in radio and X-rays. These two pulsars join PSRs J0034-0534 and
J2214+3000 to form an emerging class of gamma-ray MSPs with phase-aligned peaks
in different energy bands. The modeling of the radio and gamma-ray emission
profiles suggests co-located emission regions in the outer magnetosphere.Comment: Accepted for publication in the Astrophysical Journa
Early Positive Approaches to Support (E-PAtS) for Families of Young Children With Intellectual Disability: A Feasibility Randomised Controlled Trial
Background: Parents of children with intellectual disabilities are likely to experience poorer mental well-being and face challenges accessing support. Early Positive Approaches to Support (E-PAtS) is a group-based programme, co-produced with parents and professionals, based on existing research evidence and a developmental systems approach to support parental mental well-being. The aim of this study was to assess the feasibility of community service provider organisations delivering E-PAtS to parents/family caregivers of young children with intellectual disability, to inform a potential definitive randomised controlled trial of the effectiveness and cost-effectiveness of E-PAtS. Methods: This study was a feasibility cluster randomised controlled trial, with embedded process evaluation. Up to two parents/family caregivers of a child (18 months to <6 years old) with intellectual disability were recruited at research sites and allocated to intervention (E-PAtS and usual practise) or control (usual practise) on a 1:1 basis at cluster (family) level. Data were collected at baseline and 3 and 12 months' post-randomisation. The following feasibility outcomes were assessed: participant recruitment rates and effectiveness of recruitment pathways; retention rates; intervention adherence and fidelity; service provider recruitment rates and willingness to participate in a future trial; barriers and facilitating factors for recruitment, engagement, and intervention delivery; and feasibility of collecting outcome measures. Results: Seventy-four families were randomised to intervention or control (n = 37). Retention rates were 72% at 12 months post-randomisation, and completion of the proposed primary outcome measure (WEMWBS) was 51%. Recruitment of service provider organisations and facilitators was feasible and intervention implementation acceptable. Adherence to the intervention was 76% and the intervention was well-received by participants; exploratory analyses suggest that adherence and attendance may be associated with improved well-being. Health economic outcome measures were collected successfully and evidence indicates that linkage with routine data would be feasible in a future trial. Conclusions: The E-PAtS Feasibility RCT has demonstrated that the research design and methods of intervention implementation are generally feasible. Consideration of the limitations of this feasibility trial and any barriers to conducting a future definitive trial, do however, need to be considered by researchers. Clinical Trial Registration: https://www.isrctn.com, identifier: ISRCTN70419473
Crab: the standard X-ray candle with all (modern) X-ray satellites
Various X-ray satellites have used the Crab as a standard candle to perform
their calibrations in the past. The calibration of XMM-Newton, however, is
independent of the Crab nebula, because this object has not been used to adjust
spectral calibration issues. In 2004 a number of special observations were
performed to measure the spectral parameters and the absolute flux of the Crab
with XMM-Newtons EPIC-pn CCD camera. We describe the results of the campaign in
detail and compare them with data of four current missions (Integral, Swift,
Chandra, RXTE) and numerous previous missions (ROSAT, EXOSAT, Beppo-SAX, ASCA,
Ginga, Einstein, Mir-HEXE).Comment: 12 pages, 7 figure
RXTE Absolute Timing Results for the Pulsars B1821-24 and B1509-58
Observations with the Rossi X-ray Timing Explorer and the Jodrell Bank,
Parkes, and Green Bank telescopes have enabled us to determine the time delay
between radio and X-ray pulses in the two isolated pulsars B1821-24 and
B1509-58. For the former we find that the narrow X-ray and radio pulse
components are close to being coincident in time, with the radio peak leading
by 0.02 period (60 +/- 20 microsec), while the wide X-ray pulse component lags
the last of the two wider radio components by about 0.08 period. For the latter
pulsar we find, using the standard value for the dispersion measure, that the
X-ray pulse lags the radio by about 0.27 period, with no evidence for any
energy-dependence in the range 2-100 keV. However, uncertainties in the history
of the dispersion measure for this pulsar make a comparison with previous
results difficult. It is clear that there are no perceptable variations in
either the lag or the dispersion measure at time scales of a year or less.Comment: 20 pages including 6 figures, accepted by Astrophysical Journa
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