3,322 research outputs found
Energy-Dependent Harmonic Ratios of the Cyclotron Features of X0331+53 in the 2004-2005 Outburst
We report on changes of the cyclotron resonance energies of the recurrent
transient pulsar, X0331+53 (V0332+53). The whole RXTE data acquired in the
2004-2005 outburst were utilized. The 3-80 keV source luminosity varied between
1.7x10^36 and 3.5x10^38 ers/s, assuming a distance of 7 kpc. We confirmed that
the fundamental cyclotron resonance energy changed from ~22 to ~27 keV in a
clear anti-correlation to the source luminosity, and without any hysteresis
effects between the rising and declining phases of the outburst. In contrast,
the second harmonic energy changed from ~49 to ~54 keV, implying a weaker
fractional change as a function of the luminosity. As a result, the observed
resonance energy ratio between the second harmonic and the fundamental was ~2.2
when the source was most luminous, whereas the ratio decreased to the nominal
value of 2.0 at the least luminous state. Although the significance of this
effect is model dependent, these results suggest that the fundamental and
second harmonic resonances represent different heights in the accretion column,
depending on the mass accretion rate.Comment: 39 pages, 15 figures, 4 tables. Accepted for publication in
Astrophysical Journa
Buckling analysis of stiffened variable angle tow panels
Variable angle tow (VAT) laminates have previously shown enhanced buckling performance compared to conventional straight fibre laminates. In this study, an analytical method is developed for the buckling analysis of a novel blade stiffened VAT panel to allow this potential to be more fully exploited. The prebuckling and buckling analysis, performed on a representative section of a blade stiffened VAT panel, are based on a generalised Rayleigh–Ritz procedure. The buckling analysis includes a first order shear deformation theory by introducing additional shape functions for transverse shear and is therefore applicable to structures with thick skins relative to characteristic length. Modelling of the stiffener is achieved with two approaches; idealisation as a beam attached to the skin’s midplane and as a rigidly attached plate. Comparing results with finite element analysis (Abaqus) for selected case studies, local buckling errors for the beam model and plate model were found to be less than 3% and 2% respectively, whilst the beam model error for global buckling was between 3% and 10%. The analytical model provides an accurate alternative to the computationally expensive finite element analysis and is therefore suitable for future work on the design and optimisation of stiffened VAT panels
Multiple Cyclotron Lines in the Spectrum of 4U 0115+63
We report phase resolved spectroscopy of the transient accreting pulsar,
4U0115+63. For the first time, more than two cylotron resonance scattering
features are detected in the spectrum of an X-ray pulsar. The shape of the
fundamental line appears to be complex, and this is in agreement with
predictions of Monte-Carlo models. As in other pulsars, the line energies and
optical depths are strong functions of pulse phase. One possible model for this
is an offset of the dipole of the neutron star magnetic field.Comment: 5 pages. To appear in "Proceedings of the 5th Compton Symposium
INTEGRAL High Energy Observations of 2S 0114+65
We report the first INTEGRAL timing and spectral analysis of the high mass
X-ray binary source 2S 0114+65 at high energies (5-100 keV). The pulse period
was found at 2.668 hr with a high pulsed fraction, ~80% in both the 20-40 keV
and 40-80 keV energy bands. The spin-up trend over ~8 years was measured to be
-8.9 * 10^{-7}. The hard X-ray spectrum obtained with JEM-X/ISGRI is well
described by a high energy exponential cut-off power law model where the
estimated luminosity is 1.8 * 10^{36} erg/s in the 5-100 keV energy band, for a
source distance of 7.2 kpc. We tentatively identify a cyclotron resonance
scattering feature at ~22 keV with one harmonic, implying a magnetic field of
2.5 * 10^{12} G.Comment: 4 pages, 5 figures, accepted to A&A Letter
Discovery of a Transition to Global Spin-up in EXO 2030+375
EXO 2030+375, a 42-second transient X-ray pulsar with a Be star companion,
has been observed to undergo an outburst at nearly every periastron passage for
the last 13.5 years. From 1994 through 2002, the global trend in the pulsar
spin frequency was spin-down. Using RXTE data from 2003 September, we have
observed a transition to global spin-up in EXO 2030+375. Although the spin
frequency observations are sparse, the relative spin-up between 2002 June and
2003 September observations, along with an overall brightening of the outbursts
since mid 2002 observed with the RXTE ASM, accompanied by an increase in
density of the Be disk, indicated by infrared magnitudes, suggest that the
pattern observed with BATSE of a roughly constant spin frequency, followed by
spin-up, followed by spin-down is repeating. If so this pattern has
approximately an 11 year period, similar to the 15 +/- 3 year period derived by
Wilson et al. (2002) for the precession period of a one-armed oscillation in
the Be disk. If this pattern is indeed repeating, we predict a transition from
spin-up to spin-down in 2005.Comment: Accepted for publication in ApJ Letters, 4 pages, 5 figures, using
emulateapj.cl
Nonsolar astronomy with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is a NASA Small Explorer satellite designed to study hard x-ray and gamma-ray emission from solar flares. In addition, its high-resolution array of germanium detectors can see photons from high-energy sources throughout the Universe. Here we discuss the various algorithms necessary to extract spectra, lightcurves, and other information about cosmic gamma-ray bursts, pulsars, and other astrophysical phenomena using an unpointed, spinning array of detectors. We show some preliminary results and discuss our plans for future analyses. All RHESSI data are public, and scientists interested in participating should contact the principal author
Longitudinal study of local authority child and family social workers (wave 1) Findings from a 5 year study of local authority child and family social workers in England.
The longitudinal study investigates recruitment, retention and career progression in local authority child and family social work over 5 years. This is the first of 5 reports.
It provides workforce information for employers and policy makers.
Topics covered in this report include:
•entry routes into local authority child and family social work
•current employment and career history
•workplace wellbeing
•management, supervision and working environment
•job satisfaction
•career progression and future career plan
Insights into the development of Ixodes scapularis: a resource for research on a medically important tick species
Ticks (Acari: Ixodida) are arthropod ectoparasites dependent on a bloodmeal from a vertebrate host at each developmental stage for completion of their life cycle. This tick feeding cycle impacts animal health by causing damage to hides, secondary infections, immune reactions and diseases caused by transmission of pathogens. The genus Ixodes includes several medically important species that vector diseases, including granulocytic anaplasmosis and Lyme disease. I. scapularis, commonly called the black-legged or deer tick, is a medically-important tick species in North America and therefore was the first tick genome to be sequenced, thus serving as an important resource for tick research. This Primer focuses on the normal developmental cycle and laboratory rearing of I. scapularis. Definition of normal morphology, along with a consistent source of laboratory-reared I. scapularis, are fundamental for all aspects of future research, especially the effects of genetic manipulation and the evaluation of tick vaccine efficacy. Recent research important for the advancement of tick research, namely the development of tick cell culture systems for study of ticks and tick-borne pathogens, RNA interference for genetic manipulation of ticks and discovery of candidate antigens for development of tick vaccines, are briefly presented along with areas to target for future research.The preparation of this chapter was partially supported by the EU FP7 ANTIGONE project number 278976, and the Walter R. Sitlington Endowed Chair for Food Animal Research to K.M. Kocan.Peer Reviewe
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