9,425 research outputs found
A Double Outburst from IGR J00291+5934: Implications for Accretion Disk Instability Theory
The accretion-powered millisecond pulsar IGR J00291+5934 underwent two ~10 d
long outbursts during 2008, separated by 30 d in quiescence. Such a short
quiescent period between outbursts has never been seen before from a neutron
star X-ray transient. X-ray pulsations at the 599 Hz spin frequency are
detected throughout both outbursts. For the first time, we derive a pulse phase
model that connects two outbursts, providing a long baseline for spin frequency
measurement. Comparison with the frequency measured during the 2004 outburst of
this source gives a spin-down during quiescence of -4(1)x10^-15 Hz/s,
approximately an order of magnitude larger than the long-term spin-down
observed in the 401 Hz accretion-powered pulsar SAX J1808.4-3658. If this
spin-down is due to magnetic dipole radiation, it requires a 2x10^8 G field
strength, and its high spin-down luminosity may be detectable with the Fermi
Large Area Telescope. Alternatively, this large spin-down could be produced by
gravitational wave emission from a fractional mass quadrupole moment of Q/I =
1x10^{-9}. The rapid succession of the outbursts also provides a unique test of
models for accretion in low-mass X-ray binaries. Disk instability models
generally predict that an outburst will leave the accretion disk too depleted
to fuel a second outburst after such a brief quiescence. We suggest a
modification in which the outburst is shut off by the onset of a propeller
effect before the disk is depleted. This model can explain the short quiescence
and the unusually slow rise of the light curve of the second 2008 outburst.Comment: 17 pages, 8 figures; accepted by Ap
Investigating international new product diffusion speed: A semiparametric approach
Global marketing managers are interested in understanding the speed of the
new product diffusion process and how the speed has changed in our ever more
technologically advanced and global marketplace. Understanding the process
allows firms to forecast the expected rate of return on their new products and
develop effective marketing strategies. The most recent major study on this
topic [Marketing Science 21 (2002) 97--114] investigated new product diffusions
in the United States. We expand upon that study in three important ways. (1)
Van den Bulte notes that a similar study is needed in the international
context, especially in developing countries. Our study covers four new product
diffusions across 31 developed and developing nations from 1980--2004. Our
sample accounts for about 80% of the global economic output and 60% of the
global population, allowing us to examine more general phenomena. (2) His model
contains the implicit assumption that the diffusion speed parameter is constant
throughout the diffusion life cycle of a product. Recognizing the likely
effects on the speed parameter of recent changes in the marketplace, we model
the parameter as a semiparametric function, allowing it the flexibility to
change over time. (3) We perform a variable selection to determine that the
number of internet users and the consumer price index are strongly associated
with the speed of diffusion.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS519 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Extending Romanovski polynomials in quantum mechanics
Some extensions of the (third-class) Romanovski polynomials (also called
Romanovski/pseudo-Jacobi polynomials), which appear in bound-state
wavefunctions of rationally-extended Scarf II and Rosen-Morse I potentials, are
considered. For the former potentials, the generalized polynomials satisfy a
finite orthogonality relation, while for the latter an infinite set of
relations among polynomials with degree-dependent parameters is obtained. Both
types of relations are counterparts of those known for conventional
polynomials. In the absence of any direct information on the zeros of the
Romanovski polynomials present in denominators, the regularity of the
constructed potentials is checked by taking advantage of the disconjugacy
properties of second-order differential equations of Schr\"odinger type. It is
also shown that on going from Scarf I to Scarf II or from Rosen-Morse II to
Rosen-Morse I potentials, the variety of rational extensions is narrowed down
from types I, II, and III to type III only.Comment: 25 pages, no figure, small changes, 3 additional references,
published versio
[TiII] and [NiII] emission from the strontium filament of eta Carinae
We study the nature of the [TiII] and [NiII] emission from the so-called
strontium filament found in the ejecta of eta Carinae. To this purpose we
employ multilevel models of the TiII and NiII systems which are used to
investigate the physical condition of the filament and the excitation
mechanisms of the observed lines. For the TiII ion, for which no atomic data
was previously available, we carry out ab initio calculations of radiative
transition rates and electron impact excitation rate coefficients. It is found
that the observed spectrum is consistent with the lines being excited in a
mostly neutral region with an electron density of the order of cm
and a temperature around 6000 K. In analyzing three observations with different
slit orientations recorded between March~2000 and November~2001 we find line
ratios that change among various observations, in a way consistent with changes
of up to an order of magnitude in the strength of the continuum radiation
field. These changes result from different samplings of the extended filament,
due to the different slit orientations used for each observation, and yield
clues on the spatial extent and optical depth of the filament. The observed
emission indicates a large Ti/Ni abundance ratio relative to solar abundances.
It is suggested that the observed high Ti/Ni ratio in gas is caused by dust-gas
fractionation processes and does not reflect the absolute Ti/Ni ratio in the
ejecta of \etacar. We study the condensation chemistry of Ti, Ni and Fe within
the filament and suggest that the observed gas phase overabundance of TiComment: 14 paginas, 12 figure
Image Subtraction Reduction of Open Clusters M35 & NGC 2158 In The K2 Campaign-0 Super-Stamp
Observations were made of the open clusters M35 and NGC 2158 during the
initial K2 campaign (C0). Reducing these data to high-precision photometric
time-series is challenging due to the wide point spread function (PSF) and the
blending of stellar light in such dense regions. We developed an
image-subtraction-based K2 reduction pipeline that is applicable to both
crowded and sparse stellar fields. We applied our pipeline to the data-rich C0
K2 super-stamp, containing the two open clusters, as well as to the neighboring
postage stamps. In this paper, we present our image subtraction reduction
pipeline and demonstrate that this technique achieves ultra-high photometric
precision for sources in the C0 super-stamp. We extract the raw light curves of
3960 stars taken from the UCAC4 and EPIC catalogs and de-trend them for
systematic effects. We compare our photometric results with the prior
reductions published in the literature. For detrended, TFA-corrected sources in
the 12--12.25 magnitude range, we achieve a best 6.5 hour window
running rms of 35 ppm falling to 100 ppm for fainter stars in the 14--14.25 magnitude range. For stars with , our detrended and
6.5 hour binned light curves achieve the highest photometric precision.
Moreover, all our TFA-corrected sources have higher precision on all time
scales investigated. This work represents the first published image subtraction
analysis of a K2 super-stamp. This method will be particularly useful for
analyzing the Galactic bulge observations carried out during K2 campaign 9. The
raw light curves and the final results of our detrending processes are publicly
available at \url{http://k2.hatsurveys.org/archive/}.Comment: Accepted for publication in PASP. 14 pages, 5 figures, 2 tables.
Light curves available from http://k2.hatsurveys.org/archive
A near-NHEK/CFT correspondence
We consider excitations around the recently introduced near-NHEK metric
describing the near-horizon geometry of the near-extremal four-dimensional Kerr
black hole. This geometry has a U(1)_L x U(1)_R isometry group which can be
enhanced to a pair of commuting Virasoro algebras. We present boundary
conditions for which the conserved charges of the corresponding asymptotic
symmetries are well defined and non-vanishing and find the central charges
c_L=12J/hbar and c_R=0 where J is the angular momentum of the black hole.
Applying the Cardy formula reproduces the Bekenstein-Hawking entropy of the
black hole. This suggests that the near-extremal Kerr black hole is
holographically dual to a non-chiral two-dimensional conformal field theory.Comment: 11 pages, v2: references updated, adde
ets-2 is a target for an akt (Protein kinase B)/jun N-terminal kinase signaling pathway in macrophages of motheaten-viable mutant mice
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