14,265 research outputs found
Relativistic superluminal radio jets in microquasars in our galaxy
We discuss the origin of superluminal radio jets in Black hole X-ray binaries
with relativistic radio jets in our Galaxy popularly known as microquasars. We
classify the relativistic superluminal jet according to the radio emission in
black hole X-ray binaries (transient or persistent) rather than the mass of the
companion. The black hole X-ray binaries with transient radio emission (mostly
LMXBs) produce superluminal jets with 1 when the accretion
rate, is high and the bolometric luminosity L
approaches the Eddington Luminosity, L. On the other hand, the black
hole X-ray binaries with persistent radio emission (mostly HMXBs) produce
superluminal jets with 1 at relatively low . We
specially discuss the case of V4641 Sgr, a HMXB with transient radio emission
which produces superluminal radio jets like in LMXBs.Comment: 6 pages, 2 figures,VI Microquasar Workshop: Microquasars and Beyond,
September 18-22, 2006, Como, Ital
Book Reviews: The Yoga of the Christ in the Gospel According to St. John
Two book reviews for Ravi Ravindra\u27s The Yoga of the Christ in the Gospel According to St. John
Lead and uranium group abundances in cosmic rays
The importance of Lead and Uranium group abundances in cosmic rays is discussed in understanding their evolution and propagation. The electronic detectors can provide good charge resolution but poor data statistics. The plastic detectors can provide somewhat better statistics but charge resolution deteriorates. The extraterrestrial crystals can provide good statistics but with poor charge resolution. Recent studies of extraterrestrial crystals regarding their calibration to accelerated uranium ion beam and track etch kinetics are discussed. It is hoped that a charge resolution of two charge units can be achieved provided an additional parameter is taken into account. The prospects to study abundances of Lead group, Uranium group and superheavy element in extraterrestrial crystals are discussed, and usefulness of these studies in the light of studies with electronic and plastic detectors is assessed
Evidence of two unique variability classes from IGR J17091-3624
IGR J17091-3624 is the second black hole X-ray binary after GRS 1915+105,
which showed large and distinct variabilities. The study of these variability
classes can be useful to understand the accretion-ejection mechanisms of
accreting black holes, and hence to probe the strong gravity regime. We report
the discovery of two new variability classes (C1 and C2) from IGR J17091-3624
from the 2011 outburst Rossi X-ray Timing Explorer data. These unique classes
will be useful to have complete details about the source, and to learn new
aspects about variabilities. For examples, the C1 class shows that the
intensity and period of oscillations, energy spectrum and power spectrum can
clearly evolve in tens of seconds. Moreover, in such a small time scale,
soft-lag becomes hard-lag. The C2 class shows that the variability and the
nonvariability can occur at similar energy spectrum, and a soft state is not
required for variability to happen.Comment: 5 pages, 6 figures, accepted for publication in Monthly Notices of
the Royal Astronomical Society Letter
From solar-like to anti-solar differential rotation in cool stars
Stellar differential rotation can be separated into two main regimes:
solar-like when the equator rotates faster than the poles and anti-solar when
the polar regions rotate faster than the equator. We investigate the transition
between these two regimes with 3-D numerical simulations of rotating spherical
shells. We conduct a systematic parameter study which also includes models from
different research groups. We find that the direction of the differential
rotation is governed by the contribution of the Coriolis force in the force
balance, independently of the model setup (presence of a magnetic field,
thickness of the convective layer, density stratification). Rapidly-rotating
cases with a small Rossby number yield solar-like differential rotation, while
weakly-rotating models sustain anti-solar differential rotation. Close to the
transition, the two kinds of differential rotation are two possible bistable
states. This study provides theoretical support for the existence of anti-solar
differential rotation in cool stars with large Rossby numbers.Comment: 5 pages, 6 figures, accepted for publication in MNRA
Detector calibration of the Indian cosmic ray experiment (IONS) in Space-Shuttle Spacelab-13
In the Indian cosmic ray experiment (IONS) in Spacelab-3 the intention is to study nuclei up to iron in low energy cosmic rays, using CR-39 (DOP) detectors. CR-39 (DOP) was exposed to He4, C12, O16, Ne20, Si28, Ar40, Cr52 and Fe56 accelerated beams from various accelerator facilities available around the world. Different beam energies and exposure angles were used. From these exposures, the charge resolution and energy resolution for the detector in the region of interest were studied. The effect of pre-annealing and depth on the response of our detector was studied. For isotopic resolution, exposed the detector samples were exposed to Ne2O and Ne22 accelerated beams. Samples of CR-39 (DOP) exposed to different accelerated heavy ions were kept in the detector module to take into account the effect of ambient conditions on detector response during the flight
Relative abundances of sub-iron to iron nuclei in low energy (50-250 MeV/N) cosmic rays as observed in the Skylab experiment
A Lexan polycarbonate detector exposed on the exterior of Skylab-3 for 73 days during a solar quiet period was used to study the relative abundances of calcium to nickel ions in low energy cosmic rays of 50 to 250 MeV/N. The method of charge identification is based on the measurement of conelength (L) and residual range (R) of these particles in various Lexan sheets. Since more than one cone (sometimes as many as five) is observed and is measured, the charge accuracy becomes precise and accurate. The ratio of (calcium to manganese) to (iron and cobalt) obtained at three energy intervals of 50 to 80, 80 to 150, 150 to 250 and 50 to 250 MeV/N are 7.6 plus or minus 3.8, 2.7 plus or minus 0.8, 1.4 plus or minus 0.6 and 3.3 plus or minus 0.7 respectively. These data thus indicate a large increase of this ratio with decreasing energy. The origin of this strong energy dependence is not understood at present
Formation rates of Dark Matter Haloes
We derive an estimate of the rate of formation of dark matter halos per unit
volume as a function of the halo mass and redshift of formation. Analytical
estimates of the number density of dark matter halos are useful in modeling
several cosmological phenomena. We use the excursion set formalism for
computing the formation rate of dark matter halos. We use an approach that
allows us to differentiate between major and minor mergers, as this is a
pertinent issue for semi-analytic models of galaxy formation. We compute the
formation rate for the Press-Schechter and the Sheth-Tormen mass function. We
show that the formation rate computed in this manner is positive at all scales.
We comment on the Sasaki formalism where negative halo formation rates are
obtained. Our estimates compare very well with N-Body simulations for a variety
of models. We also discuss the halo survival probability and the formation
redshift distributions using our method.Comment: 30 pages, 9 figure
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