113 research outputs found
IGRJ16479-4514: the first eclipsing supergiant fast X-ray transient?
Supergiant fast X-ray transients are a new class of high mass X-ray binaries
recently discovered with INTEGRAL. Hours long outbursts from these sources have
been observed on numerous occasions at luminosities of ~1E36-1E37 erg/s,
whereas their low level activity at ~1E32-1E34 erg/s has not been deeply
investigated yet due to the paucity of long pointed observations with high
sensitivity X-ray telescopes. Here we report on the first long (~32 ks) pointed
XMM-Newton observation of IGR J16479-4514, a member of this new class. This
observation was carried out in March 2008, shortly after an outburst from this
source, with the main goal of investigating its low level emission and physical
mechanisms that drive the source activity. Results from the timing, spectral
and spatial analysis of the EPIC-PN XMM-Newton observation show that the X-ray
source IGRJ16479-4514 underwent an episode of sudden obscuration, possibly an
X-ray eclipse by the supergiant companion. We also found evidence for a soft
X-ray extended halo around the source that is most readily interpreted as due
to scattering by dust along the line of sight to IGRJ16479-4514. We discuss
this result in the context of the gated accretion scenarios that have been
proposed to interpret the behaviour of supergiant fast X-ray transient.Comment: Accepted for publication in MNRAS letter. 6 pages and 5 figures. We
updated one reference and the acknowledgment
Face-on, stream-fed intermediate polars: an alternative model for RX J1914.4+2456 and RX J0806.3+1527
RX J1914.4+2456 and RX J0806.3+1527 have been proposed as double degenerate binaries with orbital periods of 569 s and 321 s respectively. An alternative model, in which the periods are related to the spin of a magnetic white dwarf in an intermediate polar system, has been rejected by other authors. We show that a face-on, stream-fed intermediate polar model for the two systems is viable and preferable to the other models. In each case, the X-ray modulation periods then represent the rotation of the white dwarf in the binary reference frame. The model explains the fully modulated X-ray pulse profiles, the X-ray spectra, the antiphase between X-ray and optical/infrared modulation, the lack of longer period modulation, and the low level of polarization. The optical spectrum of RX J0806.3+1527 suggests that Balmer series lines are present, blended with HeII lines. This is unlike the spectra of any of the known AM CVn stars and suggests that the system is not a double degenerate binary. The optical spectrum of RX J1914.4+2456 has spectral features that are consistent with those of a K star, ruling out the double degenerate models in this case. The lack of optical/infrared emission lines in RX J1914.4+2456 may be attributed to a high mass accretion rate and its face-on orientation. Its reported period decrease may be a short term spin-up episode driven by the current high . Finally we suggest that there is an observational selection effect such that the face-on intermediate polars that are detected will all have a stream-fed component, and the purely stream-fed intermediate polars that are detected will all be face-on systems
The broad band spectral properties of binary X-ray pulsars
The X-ray telescopes on board BeppoSAX are an optimal set of instruments to
observe bright galactic binary pulsars. These sources emit very hard and quite
complex X-ray spectra that can be accurately measured with BeppoSAX between 0.1
and 200 keV. A prototype of this complexity, the source Her X-1, shows at least
seven different components in its spectrum. A broad band measure is therefore
of paramount importance to have a thorough insight into the physics of the
emitting region. Moreover the detection of cyclotron features, when present,
allows a direct and highly significant measure of the magnetic field intensity
in the emission region. In this paper we briefly report the results obtained
with BeppoSAX on this class of sources, with emphasis on the detection and on
the measured properties of the cyclotron lines.Comment: 10 Latex pages, 4 figures, uses psfig.sty. Accepted for publication
in Advances in Space Research, in Proceedings of 32nd Scientific Assembly of
COSPAR - Symposium E1.1: "Broad-Band X-ray Spectroscopy of Cosmic Sources
The optical counterparts of Accreting Millisecond X-Ray Pulsars during quiescence
Eight Accreting Millisecond X-ray Pulsars (AMXPs) are known to date. Optical
and NIR observations carried out during quiescence give a unique opportunity to
constrain the nature of the donor star and to investigate the origin of the
observed quiescent luminosity at long wavelengths. Using data obtained with the
ESO-Very Large Telescope, we performed a deep optical and NIR photometric study
of the fields of XTE J1814-338 and of the ultracompact systems XTE J0929-314
and XTE J1807-294 during quiescence in order to look for the presence of a
variable counterpart. If suitable candidates were found, we also carried out
optical spectroscopy. We present here the first multi-band (VR) detection of
the optical counterpart of XTE J1814-338 in quiescence together with its
optical spectrum. The optical light curve shows variability in both bands
consistent with a sinusoidal modulation at the known 4.3 hr orbital period and
presents a puzzling decrease of the V-band flux around superior conjunction
that may be interpreted as a partial eclipse. The marginal detection of the
very faint counterpart of XTE J0929-314 and deep upper limits for the
optical/NIR counterpart of XTE J1807-294 are also reported. We also briefly
discuss the results reported in the literature for the optical/NIR counterpart
of XTE J1751-305. Our findings are consistent with AMXPs being systems
containing an old, weakly magnetized neutron star, reactivated as a millisecond
radio pulsar during quiescence which irradiates the low-mass companion star.
The absence of type I X-ray bursts and of hydrogen and helium lines in outburst
spectra of ultracompact (P_orb < 1 hr) AMXPs suggests that the companion stars
are likely evolved dwarf stars.Comment: Accepted for publication by A&A; 12 pages, 12 figure
Participatory Action Research (PAR) in Middle School: Opportunities, Constraints, and Key Processes
Late childhood and early adolescence represent a critical transition in the developmental and academic trajectory of youth, a time in which there is an upsurge in academic disengagement and psychopathology. PAR projects that can promote youthâs sense of meaningful engagement in school and a sense of efficacy and mattering can be particularly powerful given the challenges of this developmental stage. In the present study, we draw on data from our own collaborative implementation of PAR projects in secondary schools to consider two central questions: (1) How do features of middle school settings and the developmental characteristics of the youth promote or inhibit the processes, outcomes, and sustainability of the PAR endeavor? and (2) How can the broad principles and concepts of PAR be effectively translated into specific intervention activities in schools, both within and outside of the classroom? In particular, we discuss a participatory research project conducted with 6th and 7th graders at an urban middle school as a means of highlighting the opportunities, constraints, and lessons learned in our efforts to contribute to the high-quality implementation and evaluation of PAR in diverse urban public schools
Evaluation of Changes in Individual Community-Related Empowerment in Community Health Promotion Interventions in Estonia
This study assessed changes in community membersâ ratings of the dimensions of individual community related empowerment (ICRE) before and two years after the implementation of an empowerment expansion framework in three community health promotion initiatives within the Estonian context. We employed a self-administered questionnaire, the adapted mobilisation scaleâindividual. As the first step, we investigated the multidimensional nature of the ICRE construct and explored the validity and reliability (internal consistency) of the ICRE scale. Two datasets were used. The first dataset comprised a cross-sectional random sample of 1,000 inhabitants of Rapla County selected in 2003 from the National Population Register, which was used to confirm the composition of the dimensions of the scale and to examine the reliability of the dimensions. The second dataset comprised two waves of data: 120 participants from three health promotion programs in 2003 (pre-test) and 115 participants in 2005 (post-test), and the dataset was used to compare participantsâ pre-test and post-test ratings of their levels of empowerment. The content validity ratio, determined using Lawsheâs formula, was high (0.98). Five dimensions of ICRE, self-efficacy, intention, participation, motivation and critical awareness, emerged from the factor analysis. The internal consistency (α) of the total empowerment scale was 0.86 (subscales self-efficacy α = 0.88, intention α = 0.83, participation α = 0.81 and motivation α = 0.69; critical awareness comprised only one item). The levels of ICRE dimensions measured after the application of the empowerment expansion framework were significantly more favourable for the dimensions self-efficacy, participation, intention and motivation to participate. We conclude that for Rapla community workgroups and networks, their ICRE was rendered more favourable after the implementation of the empowerment expansion framework
Measuring the Intrapersonal Component of Psychological Empowerment: Confirmatory Factor Analysis of the Sociopolitical Control Scale
The Sociopolitical Control Scale (SPCS) is a widely used measure of the intrapersonal component of psychological empowerment. Confirmatory factor analyses (CFA) were conducted with data from two samples to test the hypothesized structure of the SPCS, the potential effects of method bias on the measure's psychometric properties, and whether a revised version of the scale (SPCSâR) yielded improved model fit. Sample 1 included 316 randomly selected community residents of the Midwestern United States. Sample 2 included 750 community residents of the Northeastern U.S. Results indicated that method bias from the use of negatively worded items had a significant effect on the factor structure of the SPCS. CFA of the SPCSâR, in which negatively worded items were rephrased so that all statements were positively worded, supported the measure's hypothesized twoâfactor structure (i.e., leadership competence and policy control). Subscales of the SPCSâR were found reliable and related in expected ways with measures of community involvement. Implications of the study for empowermentâbased research and practice are described, and strategies to further develop the SPCS are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117223/1/ajcp9070.pd
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
INTEGRAL survey of the Cassiopeia region in hard X rays
We report on the results of a deep 1.6 Ms INTEGRAL observation of the
Cassiopeia region performed from December 2003 to February 2004. Eleven sources
were detected with the imager IBIS-ISGRI at energies above 20 keV, including
three new hard X-ray sources. Most remarkable is the discovery of hard X-ray
emission from the anomalous X-ray pulsar 4U 0142+61, which shows emission up to
\~150 keV with a very hard power-law spectrum with photon index Gamma = 0.73
+/- 0.17. We derived flux upper limits for energies between 0.75 MeV and 30 MeV
using archival data from the Compton telescope COMPTEL. In order to reconcile
the very hard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL
upper limits, the spectrum has to bend or break between ~75 keV and ~750 keV.
1E 2259+586, another anomalous X-ray pulsar in this region, was not detected.
INTEGRAL and COMPTEL upper limits are provided. The new INTEGRAL sources are
IGR J00370+6122 and IGR J00234+6144. IGR J00370+6122 is a new supergiant X-ray
binary with an orbital period of 15.665 +/- 0.006 days, derived from RXTE
All-Sky Monitor data. Archival BeppoSAX Wide-Field Camera data yielded four
more detections. IGR J00234+6144 still requires a proper identification. Other
sources for which INTEGRAL results are presented are high-mass X-ray binaries
2S 0114+650, Gamma~Cas, RX J0146.9+6121 and 4U 2206+54, intermediate polar V709
Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each of these sources the
hard X-ray spectra are fitted with different models and compared with earlier
published results.Comment: 16 pages, 13 figures, accepted for publication in A&
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