11,683 research outputs found
Investigating slim disk solutions for HLX-1 in ESO 243-49
The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the
best intermediate mass black hole candidate, displays spectral transitions
similar to those observed in Galactic black hole binaries, but with a
luminosity 100-1000 times higher. We investigated the X-ray properties of this
unique source fitting multi-epoch data collected by Swift, XMM-Newton & Chandra
with a disk model computing spectra for a wide range of sub- and
super-Eddington accretion rates assuming a non-spinning black hole and a
face-on disk (i = 0 deg). Under these assumptions we find that the black hole
in HLX-1 is in the intermediate mass range (~2 x 10^4 M_odot) and the accretion
flow is in the sub-Eddington regime. The disk radiation efficiency is eta =
0.11 +/-0.03. We also show that the source does follow the L_X ~ T^4 relation
for our mass estimate. At the outburst peaks, the source radiates near the
Eddington limit. The accretion rate then stays constant around 4 x 10^(-4)
M_odot yr^(-1) for several days and then decreases exponentially. Such
"plateaus" in the accretion rate could be evidence that enhanced mass transfer
rate is the driving outburst mechanism in HLX-1. We also report on the new
outburst observed in August 2011 by the Swift-X-ray Telescope. The time of this
new outburst further strengthens the ~1 year recurrence timescale.Comment: 24 pages, 10 figures, accepted for publication in Ap
Orbital motion of the young brown dwarf companion TWA 5 B
With more adaptive optics images available, we aim at detecting orbital
motion for the first time in the system TWA 5 A+B. We measured separation and
position angle between TWA 5 A and B in each high-resolution image available
and followed their change in time, because B should orbit around A. The
astrometric measurement precision is about one milli arc sec. With ten year
difference in epoch, we can clearly detect orbital motion of B around A, a
decrease in separation by ~ 0.0054 arc sec per year and a decrease in position
angle by ~ 0.26 degrees per year. TWA 5 B is a brown dwarf with ~ 25 Jupiter
masses (Neuh\"auser et al. 2000), but having large error bars (4 to 145 Jupiter
masses, Neuh\"auser et al. 2009). Given its large projected separation from the
primary star, ~ 86 AU, and its young age ~ 10 Myrs), it has probably formed
star-like, and would then be a brown dwarf companion. Given the relatively
large changes in separation and position angle between TWA 5 A and B, we can
conclude that they orbit around each other on an eccentric orbit. Some evidence
is found for a curvature in the orbital motion of B around A - most consistent
with an elliptic (e=0.45) orbit. Residuals around the best-fit ellipse are
detected and show a small-amplitude (~ 18 mas) periodic sinusoid with ~ 5.7 yr
period, i.e., fully consistent with the orbit of the inner close pair TWA 5
Aa+b. Measuring these residuals caused by the photocenter wobble - even in
unresolved images - can yield the total mass of the inner pair, so can test
theoretical pre-main sequence models.Comment: 6 pages, 4 figures, accepted for publication in A&A; corrected typo
in amplitude below Fig.
Kinetic theory of age-structured stochastic birth-death processes
Classical age-structured mass-action models such as the McKendrick-von Foerster equation have been extensively studied but are unable to describe stochastic fluctuations or population-size-dependent birth and death rates. Stochastic theories that treat semi-Markov age-dependent processes using, e.g., the Bellman-Harris equation do not resolve a population's age structure and are unable to quantify population-size dependencies. Conversely, current theories that include size-dependent population dynamics (e.g., mathematical models that include carrying capacity such as the logistic equation) cannot be easily extended to take into account age-dependent birth and death rates. In this paper, we present a systematic derivation of a new, fully stochastic kinetic theory for interacting age-structured populations. By defining multiparticle probability density functions, we derive a hierarchy of kinetic equations for the stochastic evolution of an aging population undergoing birth and death. We show that the fully stochastic age-dependent birth-death process precludes factorization of the corresponding probability densities, which then must be solved by using a Bogoliubov-–Born–-Green–-Kirkwood-–Yvon-like hierarchy. Explicit solutions are derived in three limits: no birth, no death, and steady state. These are then compared with their corresponding mean-field results. Our results generalize both deterministic models and existing master equation approaches by providing an intuitive and efficient way to simultaneously model age- and population-dependent stochastic dynamics applicable to the study of demography, stem cell dynamics, and disease evolution
Origin of Middle-Infrared Peaks in Cerium Compounds
We have demonstrated that the middle-infrared (mid-IR) peaks in the optical
conductivity spectra of Ce ( = Pd, Sn, In) can be explained by
first-principle band structure calculation with the spin-orbit interaction. The
mid-IR peak shapes in these materials are not identical to one another:
CePd, CeSn, and CeIn have a triple-peak structure, double-peak
structure and broad single-peak structure, respectively. These peaks can be
theoretically explained by the optical transition from the occupied state to
the spin-orbit splitted Ce state. This result indicates that the mid-IR
peaks originate from the simple band picture with the Ce state near the
Fermi level, not from the conventional cf hybridization gap based on the
periodic Anderson model.Comment: 5 pages, 6 figures. To be published in J. Phys. Soc. Jpn. 78(1)
(2009
Comprehensive health assessments during de-institutionalization: An observational study
Background: People with intellectual disability (ID) leaving institutions pass through a transition stage that makes them vulnerable to inadequate health care. They enter into community care under general practitioners (GPs) who are often untrained and inexperienced in their needs. Specifically designed health reviews may be of assistance to both them and their new GPs as they go through that phase
Magnetic Flux of EUV Arcade and Dimming Regions as a Relevant Parameter for Early Diagnostics of Solar Eruptions - Sources of Non-Recurrent Geomagnetic Storms and Forbush Decreases
This study aims at the early diagnostics of geoeffectiveness of coronal mass
ejections (CMEs) from quantitative parameters of the accompanying EUV dimming
and arcade events. We study events of the 23th solar cycle, in which major
non-recurrent geomagnetic storms (GMS) with Dst <-100 nT are sufficiently
reliably identified with their solar sources in the central part of the disk.
Using the SOHO/EIT 195 A images and MDI magnetograms, we select significant
dimming and arcade areas and calculate summarized unsigned magnetic fluxes in
these regions at the photospheric level. The high relevance of this eruption
parameter is displayed by its pronounced correlation with the Forbush decrease
(FD) magnitude, which, unlike GMSs, does not depend on the sign of the Bz
component but is determined by global characteristics of ICMEs. Correlations
with the same magnetic flux in the solar source region are found for the GMS
intensity (at the first step, without taking into account factors determining
the Bz component near the Earth), as well as for the temporal intervals between
the solar eruptions and the GMS onset and peak times. The larger the magnetic
flux, the stronger the FD and GMS intensities are and the shorter the ICME
transit time is. The revealed correlations indicate that the main quantitative
characteristics of major non-recurrent space weather disturbances are largely
determined by measurable parameters of solar eruptions, in particular, by the
magnetic flux in dimming areas and arcades, and can be tentatively estimated in
advance with a lead time from 1 to 4 days. For GMS intensity, the revealed
dependencies allow one to estimate a possible value, which can be expected if
the Bz component is negative.Comment: 27 pages, 5 figures. Accepted for publication in Solar Physic
Large-scale structure in the Lyman-alpha forest II: analysis of a group of ten QSOs
The spatial distribution of Ly-alpha forest absorption systems towards ten
QSOs has been analysed to search for large-scale structure over the redshift
range 2.2 < z < 3.4. The QSOs form a closely spaced group on the sky and are
concentrated within a 1 deg^2 field. We have employed a technique based on the
first and second moments of the transmission probability density function which
is capable of identifying and assessing the significance of regions of over- or
underdense Ly-alpha absorption. We find evidence for large-scale structure in
the distribution of Ly-alpha forest absorption at the > 99 per cent confidence
level. In individual spectra we find overdense Ly-alpha absorption on scales of
up to 1200 km s^-1. There is also strong evidence for correlated absorption
across line of sight pairs separated by < 3 h^-1 proper Mpc (q_0 = 0.5). For
larger separations the cross-correlation signal becomes progressively less
significant.Comment: 15 pages, LaTeX, 6 Postscript figures, accepted for publication in
MNRA
A High Deuterium Abundance at z=0.7
Of the light elements, the primordial abundance of deuterium, (D/H)_p,
provides the most sensitive diagnostic for the cosmological mass density
parameter Omega_B. Recent high redshift (D/H) measurements are highly
discrepant, although this may reflect observational uncertainties. The larger
(D/H) values, which imply a low Omega_B and require the Universe to be
dominated by non-baryonic matter (dynamical studies indicate a higher total
density parameter), cause problems for galactic chemical evolution models since
they have difficulty in reproducing the large decline down to the lower
present-day (D/H). Conversely, low (D/H) values imply an Omega_B greater than
derived from ^7Li and ^4He abundance measurements, and may require a deuterium
abundance evolution that is too low to easily explain. Here we report the first
measurement at intermediate redshift, where the observational difficulties are
smaller, of a gas cloud with ideal characteristics for this experiment. Our
analysis of the z = 0.7010 absorber toward 1718+4807 indicates (D/H) = 2.0 +/-
0.5 x 10^{-4} which is in the high range. This and other independent
observations suggests there may be a cosmological inhomogeneity in (D/H)_p of
at least a factor of ten.Comment: 6 pages, 1 figur
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