132 research outputs found
Non-Steady State Accretion Disks in X-Ray Novae: Outburst Models for Nova Monocerotis 1975 and Nova Muscae 1991
We fit outbursts of two X-ray novae (Nova Monocerotis 1975=A0620-00 and Nova
Muscae GS 1991=1124-683) using a time-dependent accretion disk model. The model
is based on a new solution for a diffusion-type equation for the
non-steady-state accretion and describes the evolution of a viscous alpha-disk
in a binary system after the peak of an outburst, when matter in the disk is
totally ionized. The accretion rate in the disk decreases according to a power
law. We derive formulas for the accretion rate and effective temperature of the
disk. The model has three free input parameters: the mass of the central object
M, the turbulence parameter alpha, and the normalization parameter delta t.
Results of the modeling are compared with the observed X-ray and optical B and
V light curves. The resulting estimates for the turbulence parameter
are similar: 0.2-0.4 for A 0620-00 and 0.45-0.65 for GS 1124-683, suggesting a
similar nature for the viscosity in the accretion disks around the compact
objects in these sources. We also derive the distances to these systems as
functions of the masses of their compact objects.Comment: 10 pages, 7 figures; style improve
Synthesis and sorption properties of filled fibrous sorbents with immobilized hetarylformazan groups
New sorbents were prepared by immobilization of structurally different sulfur-containing hetaryl-formazans on nonwoven polyacrylonitrile fiber tilled with AV-17 anion exchanger. Sorption of some heavy metals on these materials was studied as influenced by various factors. Sorbents for selective recovery of copper(II) in the presence of nickel(II), zinc(II), and cadmium(II) cations were found
Synthesis and catalytic properties of copper(II) 1-aryl-5-benzothiazolylformazanates
New copper(II) benzothiazolylformazane complexes were synthesized and immobilized on AN-18 anion exchanger. The influence of the composition of the coordination core of copper(II) benzthiazolylformazanates and temperature on their catalytic properties in decomposition of H2O2 and oxidation of Na2S in aqueous solution was studied
Ultra-High-Energy Cosmic Ray Acceleration by Magnetic Reconnection in Newborn Accretion Induced Collapse Pulsars
We here investigate the possibility that the ultra-high energy cosmic ray
(UHECR) events observed above the GZK limit are mostly protons accelerated in
reconnection sites just above the magnetosphere of newborn millisecond pulsars
which are originated by accretion induced collapse (AIC). We show that
AIC-pulsars with surface magnetic fields G and spin periods , are able to
accelerate particles to energies eV. Because the expected rate
of AIC sources in our Galaxy is very small (\sim 10^{-5} yr^{-1}), the
corresponding contribution to the flux of UHECRs is neglegible, and the total
flux is given by the integrated contribution from AIC sources produced by the
distribution of galaxies located within the distance which is unaffected by the
GZK cutoff ( Mpc). We find that the reconnection efficiency factor
needs to be in order to reproduce the observed flux of
UHECRs.Comment: Latex file, 16 pages, 2 figures, replaced with revised version
accepted for publication in the ApJ letter
Synthesis and spectroscopic features of iron(II) 1-aryl-5-benzothiazol-2- ylformazanates
New iron(II) coordination compounds with 1-aryl-5-(benzothiazol-2-yl) formazans were prepared. Their compositions and structures were determined by electronic spectroscopy, mass spectrometry, single crystal X-ray diffraction analysis, and magnetochemical measurements. © 2008 Pleiades Publishing, Ltd.Russian Foundation for Basic Researc
Analysis of accretion disc structure and stability using open code for vertical structure
Radial structure of accretion discs around compact objects is often described
using analytic approximations which are derived from averaging or integrating
vertical structure equations. For non-solar chemical composition, partial
ionization, or for supermassive black holes, this approach is not accurate.
Additionally, radial extension of `analytically-described' disc zones is not
evident in many cases. We calculate vertical structure of accretion discs
around compact objects, with and without external irradiation, with radiative
and convective energy transport taken into account. For this, we introduce a
new open Python code, allowing different equations of state (EoS) and opacity
laws, including tabular values. As a result, radial structure and stability
`S-curves' are calculated for specific disc parameters and chemical
composition. In particular, based on more accurate power-law approximations for
opacity in the disc, we supply new analytic formulas for the farthest regions
of the hot disc around stellar-mass object. On calculating vertical structure
of a self-irradiated disc, we calculate a self-consistent value of the
irradiation parameter for stationary -disc. We find that,
for a fixed shape of the X-ray spectrum, depends weakly on the
accretion rate but changes with radius, and the dependence is driven by the
conditions in the photosphere and disc opening angle. The hot zone extent
depends on the ratio between irradiating and intrinsic flux: corresponding
relation for is obtained.Comment: Accepted for publication in MNRAS, 15 pages, 15 figures, 3 appendi
The effect of thermal winds on the outbursts evolution of LMXB systems
Theoretical models of accretion discs and observational data indicate that
the X-ray emission from the inner parts of an accretion disc can irradiate its
outer regions and induce a thermal wind, which carries away the mass and
angular momentum from the disc. Our aim is to investigate the influence of the
thermal wind on the outburst light curves of black hole X-ray binary systems.
We carry out numerical simulations of a non-stationary disc accretion with wind
using upgraded open code freddi. We assume that the wind launches only from the
ionised part of the disc and may turn off if the latter shrinks fast enough.
Our estimates of the viscosity parameter are shifted downward compared
to a scenario without a wind. Generally, correction of depends on the
spectral hardness of central X-rays and the disc outer radius, but unlikely to
exceed a factor of 10 in the case of a black hole low-mass X-ray binary (BH
LMXB). We fit 2002 outburst of BH LMXB 4U 1543-47 taking into account the
thermal wind. The mass loss in the thermal wind is of order of the accretion
rate on the central object at the peak of the outburst. New estimate of the
viscosity parameter for the accretion disc in this system is about two
times lower than the previous one. Additionally, we calculate evolution of the
number of hydrogen atoms towards 4U 1543-47 due to the thermal wind from the
hot disc.Comment: 19 pages, 22 figures, accepted for publication in MNRA
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