17,457 research outputs found
Black Hole Mass of the Ultraluminous X-ray source M82 X-1
We report the first clear evidence for the simultaneous presence of a low
frequency break and a QPO in the fluctuation power spectrum of a well known
ultraluminous X-ray source (ULX) in M82 using long XMM-Newton observations. The
break occurs at a frequency of 34.2_{-3}^{+6}mHz. The QPO has a centroid at
114.3\pm1.5mHz, a coherence Q~3.5 and an amplitude (rms) of 19% in the 2-10keV
band. The power spectrum is approximately flat below the break frequency and
then falls off above the break frequency as a power law with the QPO
superimposed. This form of the power spectrum is characteristic of the Galactic
X-ray binaries (XRBs) in their high or intermediate states. M82 X-1 was likely
in an intermediate state during the observation. The EPIC PN spectrum is well
described by a model comprising an absorbed power-law (Gamma~2) and an iron
line at ~6.6keV with a width sigma~0.2keV and an equivalent width of ~180eV.
Using the well established correlations between the power and energy spectral
parameters for XRBs, we estimate a black hole mass for M82 X-1 in the range of
25-520Msun including systematic errors that arise due to the uncertainty in the
calibration of the photon spectral index versus QPO frequency relation.Comment: Final version, accepted for publication in ApJ Letter
The angular spin current and its physical consequences
We find that in order to completely describe the spin transport, apart from
spin current (or linear spin current), one has to introduce the angular spin
current. The two spin currents respectively describe the translational and
rotational motion of a spin. The definitions of these spin current densities
are given and their physical properties are discussed. Both spin current
densities appear naturally in the spin continuity equation. Moreover we predict
that the angular spin current can also induce an electric field , and
in particular scales as at large distance , whereas the
field generated from the linear spin current goes as .Comment: 7 pages, 2 figure
The Top Ten List of Gravitational Lens Candidates from the HST Medium Deep Survey
A total of 10 good candidates for gravitational lensing have been discovered
in the WFPC2 images from the HST Medium Deep Survey (MDS) and archival primary
observations. These candidate lenses are unique HST discoveries, i.e. they are
faint systems with sub-arcsecond separations between the lensing objects and
the lensed source images. Most of them are difficult objects for ground-based
spectroscopic confirmation or for measurement of the lens and source redshifts.
Seven are ``strong lens'' candidates which appear to have multiple images of
the source. Three are cases where the single image of the source galaxy has
been significantly distorted into an arc. The first two quadruply lensed
candidates were reported in Ratnatunga et al 1995 (ApJL, 453, L5) We report on
the subsequent eight candidates and describe them with simple models based on
the assumption of singular isothermal potentials. Residuals from the simple
models for some of the candidates indicate that a more complex model for the
potential will probably be required to explain the full structural detail of
the observations once they are confirmed to be lenses. We also discuss the
effective survey area which was searched for these candidate lens objects.Comment: 26 pages including 12 figures and 10 tables. AJ Vol. 117, No.
P,T-Violating Nuclear Matrix Elements in the One-Meson Exchange Approximation
Expressions for the P,T-violating NN potentials are derived for ,
and exchange. The nuclear matrix elements for and
exchange are shown to be greatly suppressed, so that, under the assumption of
comparable coupling constants, exchange would dominate by two orders of
magnitude. The ratio of P,T-violating to P-violating matrix elements is found
to remain approximately constant across the nuclear mass table, thus
establishing the proportionality between time-reversal-violation and
parity-violation matrix elements. The calculated values of this ratio suggest a
need to obtain an accuracy of order for the ratio of the
PT-violating to P-violating asymmetries in neutron transmission experiments in
order to improve on the present limits on the isovector pion coupling constant.Comment: 17 pages, LaTeX, no figure
Exact solutions of a particle in a box with a delta function potential: The factorization method
We use the factorization method to find the exact eigenvalues and
eigenfunctions for a particle in a box with the delta function potential
. We show that the presence of the potential
results in the discontinuity of the corresponding ladder operators. The
presence of the delta function potential allows us to obtain the full spectrum
in the first step of the factorization procedure even in the weak coupling
limit .Comment: 8 pages, 2 figures, to appear in American Journal of Physic
Graviton mediated photon-photon scattering in general relativity
In this paper we consider photon-photon scattering due to self-induced
gravitational perturbations on a Minkowski background. We focus on four-wave
interaction between plane waves with weakly space and time dependent
amplitudes, since interaction involving a fewer number of waves is excluded by
energy-momentum conservation. The Einstein-Maxwell system is solved
perturbatively to third order in the field amplitudes and the coupling
coefficients are found for arbitrary polarizations in the center of mass
system. Comparisons with calculations based on quantum field theoretical
methods are made, and the small discrepances are explained.Comment: 5 pages, 3 figure
Emotional distress in infertile women and failure of assisted reproductive technologies: meta-analysis of prospective psychosocial studies
Objective To examine whether pretreatment emotional distress in women is associated with achievement of pregnancy after a cycle of assisted reproductive technology
- âŠ