670 research outputs found
Spin Accumulation in the Extrinsic Spin Hall Effect
The drift-diffusion formalism for spin-polarized carrier transport in
semiconductors is generalized to include spin-orbit coupling. The theory is
applied to treat the extrinsic spin Hall effect using realistic boundary
conditions. It is shown that carrier and spin diffusion lengths are modified by
the presence of spin-orbit coupling and that spin accumulation due to the
extrinsic spin Hall effect is strongly and qualitatively influenced by boundary
conditions. Analytical formulas for the spin-dependent carrier recombination
rates and inhomogeneous spin densities and currents are presented.Comment: 5 pages, 3 figure
Structure, Dynamics and Deuterium Fractionation of Massive Pre-Stellar Cores
High levels of deuterium fraction in NH are observed in some
pre-stellar cores. Single-zone chemical models find that the timescale required
to reach observed values () is longer than the free-fall
time, possibly ten times longer. Here, we explore the deuteration of turbulent,
magnetized cores with 3D magnetohydrodynamics simulations. We use an
approximate chemical model to follow the growth in abundances of NH and
ND. We then examine the dynamics of the core using each tracer for
comparison to observations. We find that the velocity dispersion of the core as
traced by ND appears slightly sub-virial compared to predictions of the
Turbulent Core Model of McKee & Tan, except at late times just before the onset
of protostar formation. By varying the initial mass surface density, the
magnetic energy, the chemical age, and the ortho-to-para ratio of H, we
also determine the physical and temporal properties required for high
deuteration. We find that low initial ortho-to-para ratios ()
and/or multiple free-fall times () of prior chemical evolution are
necessary to reach the observed values of deuterium fraction in pre-stellar
cores.Comment: 20 pages, 18 figures; accepted for publication in Ap
STRUCTURE, DYNAMICS, AND DEUTERIUM FRACTIONATION OF MASSIVE PRE-STELLAR CORES
High levels of deuterium fraction in NH are observed in some pre-stellar cores. Single-zone chemical models find that the timescale required to reach observed values () is longer than the free-fall time, possibly ten times longer. Here, we explore the deuteration of turbulent, magnetized cores with 3D magnetohydrodynamics simulations. We use an approximate chemical model to follow the growth in abundances of NH and ND. We then examine the dynamics of the core using each tracer for comparison to observations. We find that the velocity dispersion of the core as traced by ND appears slightly sub-virial compared to predictions of the Turbulent Core Model of McKee & Tan, except at late times just before the onset of protostar formation. By varying the initial mass surface density, the magnetic energy, the chemical age, and the ortho-to-para ratio of H, we also determine the physical and temporal properties required for high deuteration. We find that low initial ortho-to-para ratios () and/or multiple free-fall times () of prior chemical evolution are necessary to reach the observed values of deuterium fraction in pre-stellar cores
A systematic look at the Very High and Low/Hard state of GX 339-4: Constraining the black hole spin with a new reflection model
We present a systematic study of GX 339-4 in both its very high and low hard
states from simultaneous observations made with XMM-Newton and RXTE in 2002 and
2004. The X-ray spectra of both these extreme states exhibit strong reflection
signatures, with a broad, skewed Fe-Kalpha line clearly visible above the
continuum. Using a newly developed, self-consistent reflection model which
implicitly includes the blackbody radiation of the disc as well as the effect
of Comptonisation, blurred with a relativistic line function, we were able to
infer the spin parameter of GX 339-4 to be 0.935 +/- 0.01 (statistical) +/-
0.01 (systematic) at 90 per cent confidence. We find that both states are
consistent with an ionised thin accretion disc extending to the innermost
stable circular orbit around the rapidly spinning black hole.Comment: 10 pages, 10 figures, accepted for publication in MNRAS 17/04/0
High Resolution X-Ray Imaging of the Center of IC342
We presented the result of a high resolution (FWHM~0.5'') 12 ks Chandra HRC-I
observation of the starburst galaxy IC342 taken on 2 April 2006. We identified
23 X-ray sources within the central 30' x 30' region of IC342. Our HRC-I
observation resolved the historical Ultraluminous X-ray sources (ULX), X3, near
the nucleus into 2 sources, namely C12 and C13, for the first time. The
brighter source C12, with L(0.08-10keV)=(6.66\pm0.45)\times10^{38}ergs^-1, was
spatially extended (~82 pc x 127 pc). From the astrometric registration of the
X-ray image, C12 was at R.A.=03h:46m:48.43s, decl.=+68d05m47.45s, and was
closer to the nucleus than C13. Thus we concluded that source was not an ULX
and must instead be associated with the nucleus. The fainter source C13, with
L(0.08-10keV)=(5.1\pm1.4) x 10^{37}ergs^-1 was consistent with a point source
and located $6.51'' at P.A. 240 degree of C12.
We also analyzed astrometrically corrected optical Hubble Space Telescope and
radio Very Large Array images, a comparison with the X-ray image showed
similarities in their morphologies. Regions of star formation within the
central region of IC342 were clearly visible in HST H alpha image and this was
the region where 3 optical star clusters and correspondingly our detected X-ray
source C12 were observed. We found that a predicted X-ray emission from
starburst was very close to the observed X-ray luminosity of C12, suggesting
that nuclear X-ray emission in IC342 was dominated by starburst. Furthermore,
we discussed the possibility of AGN in the nucleus of IC342. Although our data
was not enough to give a firm existence of an AGN, it could not be discarded.Comment: 29 page, 8 figures, accepted by Ap
Jet-disc coupling through a common energy reservoir in the black hole XTE J1118+480
We interpret the rapid correlated UV/optical/ X-ray variability of XTE
J1118+480 as a signature of the coupling between the X-ray corona and a jet
emitting synchrotron radiation in the optical band. We propose a scenario in
which the jet and the X-ray corona are fed by the same energy reservoir where
large amounts of accretion power are stored before being channelled into either
the jet or the high energy radiation. This time dependent model reproduces the
main features of the rapid multi-wavelength variability of XTE J1118+480.
Assuming that the energy is stored in the form of magnetic field, we find that
the required values of the model parameters are compatible with both a patchy
corona atop a cold accretion disc and a hot thick inner disc geometry. The
range of variability timescales for the X-ray emitting plasma are consistent
with the dynamical times of an accretion flow between 10 and 100 Schwarzschild
radii. On the other hand, the derived range of timescales associated with the
dissipation in the jet extends to timescales more than 10 times larger,
confirming the suggestion that the generation of a powerful outflow requires
large scale coherent poloidal field structures. A strong requirement of the
model is that the total jet power should be at least a few times larger than
the observed X-ray luminosity. This would be consistent with the overall low
radiative efficiency of the source. We present independent arguments showing
that the jet probably dominates the energetic output of all accreting black
holes in the low-hard state.Comment: 14 pages, 2 figures, to appear in MNRA
Modeling the UBVRI time delays in Mrk 335
We develop a model of time delays between the continuum bands in the Narrow
Line Seyfert 1 galaxy Mrk 335 to explain the observed delays measured in this
source. We consider two geometries: an accretion disk with fully ionized warm
absorber of considerable optical depth, located close to the symmetry axis, and
an accretion disk with a hot corona. Both media lead to significant disk
irradiation but the disk/corona geometry gives lower values of the time delays.
Only the disk/corona models give results consistent with measurements of
Sergeev et al., and a low value of the disk inclination is favored. The
presence of an optically thick, fully ionized outflow is ruled out at the
2-sigma level.Comment: MNRAS (in press
Growth, Crystal Structure and Magnetic Characterization of Zn-Stabilized CePtIn4
The growth and characterization of CePtIn4, stabilized by 10% Zn substitution
for In, is reported. The new material is orthorhombic, space group Cmcm (No.
63), with lattice parameters a = 4.51751(4) {\AA}, b = 16.7570(2) {\AA}, and c
= 7.36682(8) {\AA}, and the refined crystal composition has 10% of Zn
substituted for In, i.e. the crystals are CePt(In3.6Zn0.1)4. Crystals were
grown using a self-flux method: only growths containing Zn yielded CePtIn4
crystals, while Ce3Pt4In13 crystals formed when Zn was not present. Anisotropic
temperature-dependent magnetic susceptibilities for single crystals show that
Zn-stabilized CePtIn4 orders magnetically at ~1.9 K. High-temperature
Curie-Weiss fits indicate an effective moment of ~2.30 muB/ Ce and a
directionally averaged Weiss-temperature of approximately - 9 K. Specific heat
data shows a peak consistent with the ordering temperature seen in the magnetic
susceptibility data. Zn-stabilized CePtIn4 is metallic and displays no
superconducting transition down to 0.14 K.Comment: 8 pages, 5 figures, 1 tabl
A bright off-nuclear X-ray source: A bright off-nuclear X-ray source: a type IIn supernova, a bright ULX or a recoiling super-massive black hole in CXO J122518.6+144545
In this Paper we report the discovery of CXO J122518.6+144545; a peculiar
X-ray source with a position 3.6+-0.2",off-nuclear from an SDSS DR7 z=0.0447
galaxy. The 3.6" offset corresponds to 3.2 kpc at the distance of the galaxy.
The 0.3-8 keV X-ray flux of this source is 5x10^-14 erg cm^-2 s^-1 and its
0.3-8 keV luminosity is 2.2x10^41 erg/s (2.7x10^41 erg/s; 0.5-10 keV) assuming
the source belongs to the associated galaxy. We find a candidate optical
counterpart in archival HST/ACS g'-band observations of the field containing
the galaxy obtained on June 16, 2003. The observed magnitude of g'=26.4+-0.1
corresponds to an absolute magnitude of -10.1. We discuss the possible nature
of the X-ray source and its associated candidate optical counterpart and
conclude that the source is either a very blue type IIn supernova, a ULX with a
very bright optical counterpart or a recoiling super-massive black hole.Comment: 6 pages, 3 figures, accepted for publication in MNRA
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