257 research outputs found
On distributional and asymptotic results for exponential functional of renewal -- reward processes describing risk models
Inspired by the double-debt problem in Japan where the mortgagor has to pay the remaining loan even if their house was destroyed by a catastrophic event, we model the lender's cash flow, by an exponential functional of a renewal-reward process. We propose an insurance add-on to the loan repayments and analyse the asymptotic behavior of the distribution of the first hitting time, which represents the probability of full repayment. We show that the finite-time probability of full loan repayment converges exponentially fast to the infinite-time one. In a few concrete scenarios, we calculate the exact form of the infinite-time probability and the corresponding premiums
Properties of the cosmological filament between two clusters: A possible detection of a large-scale accretion shock by
We report on the results of a observation of the plasma in the
filament located between the two massive clusters of galaxies Abell 399 and
Abell 401. Abell 399 (=0.0724) and Abell 401 (=0.0737) are expected to be
in the initial phase of a cluster merger. In the region between the two
clusters, we find a clear enhancement in the temperature of the filament plasma
from 4 keV (expected value from a typical cluster temperature profile) to
6.5 keV. Our analysis also shows that filament plasma is present out to
a radial distance of 15' (1.3 Mpc) from a line connecting the two clusters. The
temperature profile is characterized by an almost flat radial shape with
6-7 keV within 10' or 0.8 Mpc. Across =8'~from the axis, the
temperature of the filament plasma shows a drop from 6.3 keV to 5.1 keV,
indicating the presence of a shock front. The Mach number based on the
temperature drop is estimated to be 1.3. We also successfully
determined the abundance profile up to 15' (1.3 Mpc), showing an almost
constant value (=0.3 solar) at the cluster outskirt. We estimated the
Compton -parameter to be 14.5, which is in
agreement with 's results (14-17 on the filament). The
line of sight depth of the filament is 1.1 Mpc, indicating that the
geometry of filament is likely a pancake shape rather than cylindrical. The
total mass of the filamentary structure is 7.7. We discuss a possible interpretation of the drop of X-ray emission
at the rim of the filament, which was pushed out by the merging activity and
formed by the accretion flow induced by the gravitational force of the
filament.Comment: 8 pages, 8 figures, accepted for publication in A&
Interacting Large-Scale Magnetic Fields and Ionised Gas in the W50/SS433 System
The W50/SS433 system is an unusual Galactic outflow-driven object of
debatable origin. We have used the Australia Telescope Compact Array (ATCA) to
observe a new 198 pointing mosaic, covering , and
present the highest-sensitivity full-Stokes data of W50 to date using
wide-field, wide-band imaging over a 2 GHz bandwidth centred at 2.1 GHz. We
also present a complementary H mosaic created using the Isaac Newton
Telescope Photometric H Survey of the Northern Galactic Plane (IPHAS).
The magnetic structure of W50 is found to be consistent with the prevailing
hypothesis that the nebula is a reanimated shell-like supernova remnant (SNR),
that has been re-energised by the jets from SS433. We observe strong
depolarization effects that correlate with diffuse H emission, likely
due to spatially-varying Faraday rotation measure (RM) fluctuations of
to 61 rad m on scales to 6 pc. We also report the discovery of
numerous, faint, H filaments that are unambiguously associated with the
central region of W50. These thin filaments are suggestive of a SNR's shock
emission, and almost all have a radio counterpart. Furthermore, an RM-gradient
is detected across the central region of W50, which we interpret as a loop
magnetic field with a symmetry axis offset by to the
east-west jet-alignment axis, and implying that the evolutionary processes of
both the jets and the SNR must be coupled. A separate RM-gradient is associated
with the termination shock in the Eastern ear, which we interpret as a
ring-like field located where the shock of the jet interacts with the
circumstellar medium. Future optical observations will be able to use the new
H filaments to probe the kinematics of the shell of W50, potentially
allowing for a definitive experiment on W50's formation history.Comment: Submitted to MNRA
Ion-by-ion Cooling efficiencies
We present ion-by-ion cooling efficiencies for low-density gas. We use Cloudy
(ver. 08.00) to estimate the cooling efficiencies for each ion of the first 30
elements (H-Zn) individually. We present results for gas temperatures between
1e4 and 1e8K, assuming low densities and optically thin conditions. When
nonequilibrium ionization plays a significant role the ionization states
deviate from those that obtain in collisional ionization equilibrium (CIE), and
the local cooling efficiency at any given temperature depends on specific
non-equilibrium ion fractions. The results presented here allow for an
efficient estimate of the total cooling efficiency for any ionic composition.
We also list the elemental cooling efficiencies assuming CIE conditions. These
can be used to construct CIE cooling efficiencies for non-solar abundance
ratios, or to estimate the cooling due to elements not explicitly included in
any nonequilibrium computation. All the computational results are listed in
convenient online tables.Comment: Submitted to ApJS. Electronic data available at
http://wise-obs.tau.ac.il/~orlyg/ion_by_ion
Stochastic integration based on simple, symmetric random walks
A new approach to stochastic integration is described, which is based on an
a.s. pathwise approximation of the integrator by simple, symmetric random
walks. Hopefully, this method is didactically more advantageous, more
transparent, and technically less demanding than other existing ones. In a
large part of the theory one has a.s. uniform convergence on compacts. In
particular, it gives a.s. convergence for the stochastic integral of a finite
variation function of the integrator, which is not c\`adl\`ag in general.Comment: 16 pages, some typos correcte
Why Do Only Some Galaxy Clusters Have Cool Cores?
Flux-limited X-ray samples indicate that about half of rich galaxy clusters
have cool cores. Why do only some clusters have cool cores while others do not?
In this paper, cosmological N-body + Eulerian hydrodynamic simulations,
including radiative cooling and heating, are used to address this question as
we examine the formation and evolution of cool core (CC) and non-cool core
(NCC) clusters. These adaptive mesh refinement simulations produce both CC and
NCC clusters in the same volume. They have a peak resolution of 15.6 h^{-1} kpc
within a (256 h^{-1} Mpc)^3 box. Our simulations suggest that there are
important evolutionary differences between CC clusters and their NCC
counterparts. Many of the numerical CC clusters accreted mass more slowly over
time and grew enhanced cool cores via hierarchical mergers; when late major
mergers occurred, the CC's survived the collisions. By contrast, NCC clusters
experienced major mergers early in their evolution that destroyed embryonic
cool cores and produced conditions that prevented CC re-formation. As a result,
our simulations predict observationally testable distinctions in the properties
of CC and NCC beyond the core regions in clusters. In particular, we find
differences between CC versus NCC clusters in the shapes of X-ray surface
brightness profiles, between the temperatures and hardness ratios beyond the
cores, between the distribution of masses, and between their supercluster
environs. It also appears that CC clusters are no closer to hydrostatic
equilibrium than NCC clusters, an issue important for precision cosmology
measurements.Comment: 17 emulateapj pages, 17 figures, replaced with version accepted to
Ap
Robust Digital Holography For Ultracold Atom Trapping
We have formulated and experimentally demonstrated an improved algorithm for
design of arbitrary two-dimensional holographic traps for ultracold atoms. Our
method builds on the best previously available algorithm, MRAF, and improves on
it in two ways. First, it allows for creation of holographic atom traps with a
well defined background potential. Second, we experimentally show that for
creating trapping potentials free of fringing artifacts it is important to go
beyond the Fourier approximation in modelling light propagation. To this end,
we incorporate full Helmholtz propagation into our calculations.Comment: 7 pages, 4 figure
A Parameter Space Exploration of Galaxy Cluster Mergers I: Gas Mixing and the Generation of Cluster Entropy
We present a high-resolution set of adiabatic binary galaxy cluster merger
simulations using FLASH. These are the highest-resolution simulations to date
of such mergers using an AMR grid-based code with Eulerian hydrodynamics. In
this first paper in a series we investigate the effects of merging on the
entropy of the hot intracluster gas, specifically with regard to the ability of
merging to heat and disrupt cluster "cool-cores." We find, in line with recent
works, that the effect of fluid instabilities that are well-resolved in
grid-based codes is to significantly mix the gases of the two clusters and to
significantly increase the entropy of the gas of the final merger remnant. This
result is characteristic of mergers over a range of initial mass ratio and
impact parameter. In line with this, we find that the kinetic energy associated
with random motions is higher in our merger remnants which have high entropy
floors, indicating the motions have efficiently mixed the gas and heated the
cluster core with gas of initially high entropy. We examine the implications of
this result for the maintenance of high entropy floors in the centers of galaxy
clusters and the derivation of the properties of dark matter from the thermal
properties of the X-ray emitting gas.Comment: 25 pages, 23 figures, Accepted to Ap
Galaxy clusters at z~1 imaged by ALMA with the Sunyaev-Zel'dovich effect
We present high angular-resolution measurements of the thermal
Sunyaev-Zel'dovich effect (SZE) toward two galaxy clusters, RCS J2319+0038 at
z=0.9 and HSC J0947-0119 at z=1.1, by the Atacama Large
Millimeter/submillimeter Array (ALMA) in Band 3. They are supplemented with
available Chandra X-ray data, optical data taken by Hyper Suprime-Cam on
Subaru, and millimeter-wave SZE data from the Atacama Cosmology Telescope.
Taking into account departures from spherical symmetry, we have reconstructed
non-parametrically the inner pressure profile of two clusters as well as
electron temperature and density profiles for RCS J2319+0038. This is one of
the first such measurements for an individual cluster at . We
find that the inner pressure profile of both clusters is much shallower than
that of local cool-core clusters. Our results consistently suggest that RCS
J2319+0038 hosts a weak cool core, where radiative cooling is less significant
than in local cool cores. On the other hand, HSC J0947-0119 exhibits an even
shallower pressure profile than RCS J2319+0038 and is more likely a
non-cool-core cluster. The SZE centroid position is offset by more than 140
kpc from the peaks of galaxy distribution in HSC J0947-0119,
suggesting a stronger influence of mergers in this cluster. We conclude that
these distant clusters are at a very early stage of developing the cool cores
typically found in clusters at lower redshifts.Comment: 26 pages, 13 figures, 8 tables, submitted to PAS
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