10,437 research outputs found
Detection of Cyclotron Resonance Scattering Feature in High Mass X-ray Binary Pulsar SMC X-2
We report broadband spectral properties of the high mass X-ray binary pulsar
SMC X-2 by using three simultaneous and /XRT observations
during its 2015 outburst. The pulsar was significantly bright, reaching a
luminosity up to as high as 5.510~ergs~s in 1-70
keV range. Spin period of the pulsar was estimated to be 2.37 s. Pulse profiles
were found to be strongly luminosity dependent. The 1-70 keV energy spectrum of
the pulsar was well described with three different continuum models such as (i)
negative and positive power-law with exponential cutoff, (ii) Fermi-Dirac
cutoff power-law and (iii) cutoff power-law models. Apart from the presence of
an iron line at 6.4 keV, a model independent absorption like feature at
27 keV was detected in the pulsar spectrum. This feature was identified
as a cyclotron absorption line and detected for the first time in this pulsar.
Corresponding magnetic field of the neutron star was estimated to be
2.310 G. The cyclotron line energy showed a marginal
negative dependence on the luminosity. The cyclotron line parameters were found
to be variable with pulse phase and interpreted as due to the effect of
emission geometry or complicated structure of the pulsar magnetic field.Comment: 5 Pages, 5 figures, 2016, MNRAS, 461, L97-L10
Class Transitions and Two Component Accretion Flow in GRS 1915+105
The light curve of the galactic micro-quasar GRS 1915+105 changes in at least
thirteen different ways which are called classes. We present examples of the
transitions from one class to another as observed by the IXAE instrument aboard
the Indian Satellite IRS-P3. We find that the transitions are associated with
changes in photon counts over a time-scale of only a few hours and they take
place through unknown classes. Assuming that the transitions are caused by
variation of the accretion rates, this implies that a significant fraction of
the matter must be nearly freely falling in order to have such dramatic changes
in such a short time.Comment: 9 pages, 6 figures, Astronomy and Astrophys. (in press
Implementation of multigrid methods for solving Navier-Stokes equations on a multiprocessor system
Presented are schemes for implementing multigrid algorithms on message based MIMD multiprocessor systems. To address the various issues involved, a nontrivial problem of solving the 2-D incompressible Navier-Stokes equations is considered as the model problem. Three different multigrid algorithms are considered. Results from implementing these algorithms on an Intel iPSC are presented
Effects of partitioning and scheduling sparse matrix factorization on communication and load balance
A block based, automatic partitioning and scheduling methodology is presented for sparse matrix factorization on distributed memory systems. Using experimental results, this technique is analyzed for communication and load imbalance overhead. To study the performance effects, these overheads were compared with those obtained from a straightforward 'wrap mapped' column assignment scheme. All experimental results were obtained using test sparse matrices from the Harwell-Boeing data set. The results show that there is a communication and load balance tradeoff. The block based method results in lower communication cost whereas the wrap mapped scheme gives better load balance
Understanding the spectral and timing behavior of a newly discovered transient X-ray pulsar Swift J0243.6+6124
We present the results obtained from timing and spectral studies of the newly
discovered accreting X-ray binary pulsar Swift J0243.6+6124 using a NuSTAR
observation in 2017 October at a flux level of ~280 mCrab. Pulsations at
9.85423(5) s were detected in the X-ray light curves of the pulsar. Pulse
profiles of the pulsar were found to be strongly energy dependent. A broad
profile at lower energies was found to evolve into a double peaked profile in
30keV. The 3-79 keV continuum spectrum of the pulsar was well described
with a negative and positive exponential cutoff or high energy cutoff power law
models modified with a hot blackbody at 3 keV. An iron emission line was
also detected at 6.4 keV in the source spectrum. We did not find any signature
of cyclotron absorption line in our study. Results obtained from phase-resolved
and time-resolved spectroscopy are discussed in the paper.Comment: 7 pages, 6 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Society Journa
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