8,043 research outputs found
Spectral and timing studies of 2S 1417-624 during a giant outburst
We present the results obtained from timing and spectral studies of the
accretion powered X-ray pulsar 2S~1417-624 during a giant outburst in 2009 by
using {\it Rossi X-ray Timing Explorer (RXTE)} observations. X-ray pulsations
were detected in the light curves obtained from all epochs of observations. The
pulsar was found to be spinning-up during the outburst. The pulse profiles were
observed to be strongly dependent on photon energy and luminosity. A double
peaked profile at lower luminosity evolved into a triple peaked profile at the
peak of the outburst which is further reverted back to a double peaked
structure during the decay of the outburst. An anti-correlation was also
observed between the pulse fraction and the source flux. The 3-70 keV energy
spectrum of pulsar was well described with a power law modified with high
energy cutoff model along with an iron fluorescence line at 6.4 keV. Based on
the evolution of pulse profile, pulse fraction and spectral parameters across
observed luminosity, we interpret our results in terms of changes in the pulsar
beam configuration from sub-critical to super-critical regimes.Comment: 9 pages,7 figures; Accepted for publication in Monthly Notices of the
Royal Astronomical Society journal on July 2, 201
Effects of T-tabs and large deflections in DCB specimen tests
A simple strength of materials analysis was developed for a double-cantilever beam (DCB) specimen to account for geometric nonlinearity effects due to large deflections and T-tabs. A new DCB data analysis procedure was developed to include the effects of these nonlinearities. The results of the analysis were evaluated by DCB tests performed for materials having a wide range of toughnesses. The materials used in the present study were T300/5208, IM7/8551-7, and AS4/PEEK. Based on the present analysis, for a typical deflection/crack length ratio of 0.3 (for AS4/PEEK), T-tabs and large deflections cause a 15 percent and 3 percent error, respectively, in the computer Mode 1 strain energy release rate. Design guidelines for DCB specimen thickness and T-tab height were also developed in order to keep errors due to these nonlinearities within 2 percent. Based on the test results, for both hinged and tabbed specimens, the effects of large deflection on the Mode 1 fracture toughness (G sub Ic) were almost negligible (less than 1 percent) in the case of T300/5208 and IM7/8551-7; however, AS4/PEEK showed a 2 to 3 percent effect. The effects of T-tabs G sub Ic were more significant for all the materials with T300/5208 showing a 5 percent error, IM7/8551-7 a 15 percent error, and, AS4/PEEK a 20 percent error
Near-infrared Observations of Be/X-ray Binary Pulsar A0535+262
We present results obtained from an extensive near-infrared spectroscopic and
photometric observations of the Be/X-ray binary A0535+262/HDE 245770 at
different phases of its ~111 day orbital period. This observation campaign is a
part of the monitoring programme of selective Be/X-ray binary systems aimed at
understanding the X-ray and near-IR properties at different orbital phases,
especially during the periastron passage of the neutron star. The near-IR
observations were carried out using the 1.2 m telescope at Mt. Abu IR
observatory. Though the source was relatively faint for spectroscopic
observations with 1.2 m telescope, we monitored the source during the 2011
February--March giant outburst to primarily investigate whether any drastic
changes in the near-IR JHK spectra take place at the periastron passage.
Changes of such a striking nature were expected to be detectable in our
spectra. Photometric observations of the Be star show a gradual and systematic
fading in the JHK light curves since the onset of the X-ray outburst that could
suggest a mild evacuation/truncation of the circumstellar disc of the Be
companion. Near-IR spectroscopy of the object shows that the JHK spectra are
dominated by the emission lines of hydrogen Brackett and Paschen series and HeI
lines at 1.0830, 1.7002 and 2.0585 micron. The presence of all hydrogen
emission lines in the JHK spectra, along with the absence of any significant
change in the continuum of the Be companion during X-ray quiescent and X-ray
outburst phases suggest that the near-IR line emitting regions of the disc are
not significantly affected during the X-ray outburst.Comment: 10 Pages, 5 Figures, Accepted for publication in Res. in Astronomy
and Astrophysic
Total cross sections for neutron-nucleus scattering
Systematics of neutron scattering cross sections on various materials for
neutron energies up to several hundred MeV are important for ADSS applications.
Ramsauer model is well known and widely applied to understand systematics of
neutron nucleus total cross sections. In this work, we examined the role of
nuclear effective radius parameter (r) on Ramsauer model fits of neutron
total cross sections. We performed Ramsauer model global analysis of the
experimental neutron total cross sections reported by W. P. Abfalterer, F. B.
Bateman, {\it et. al.,}, from 20MeV to 550MeV for nuclei ranging from Be to U .
The global fit functions which can fit total cross section data over periodic
table are provided along with the required global set of parameters. The global
fits predict within deviation to data, showing the scope for
improvement. It has been observed that a finer adjustment of r parameter
alone can give very good Ramsauer model description of neutron total scattering
data within deviation. The required r values for Ramsauer model
fits are shown as a function of nuclear mass number and an empirical formula is
suggested for r values as a function of mass number. In optical model
approach for neutron scattering, we have modified the real part of
Koning-Deleroche potentails to fit the neutron total cross sections using SCAT2
code. The modified potentails have a different energy dependence beyond 200MeV
of neutron energy and fit the total cross sections from Al to Pb.Comment: 9 pages, 20figures, Poster number ND-1457, ND2010 Conference in Kore
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