2,884 research outputs found
Decentralized credtor-led corporate restructuring - cross-country experience
Countries that have experienced banking crises have adopted oneof two distinct approaches toward the resolution of non-performing assets-a centralized or a decentralized solution. A centralized approach entails setting up a government agency-an asset management company-with the full responsibility for acquiring, restructuring, and selling of the assets. A decentralized approach relies on banks and other creditors to manage and resolve non-performing assets. The authors study banking crises where governments adopted a decentralized, creditor-led workout strategy following systemic crises. They use a case study approach and analyze seven banking crises in which governments mainly relied on banks to resolve non-performing assets. The study suggests that out of the seven cases, only Chile, Norway, and Poland successfully restructured their corporate sectors with companies attaining viable financial structures. The analysis underscores that as in the case of a centralized strategy the prerequisites for a successful decentralized restructuring strategy are manifold. The successful countries significantly improved the banking system's capital position, enabling banks to write down loan losses; banks as well as corporations had adequate incentives to engage in corporate restructuring; and ownership links between banks and corporations were limited or severed during crises.Financial Intermediation,Financial Crisis Management&Restructuring,Payment Systems&Infrastructure,Banks&Banking Reform,International Terrorism&Counterterrorism,Banks&Banking Reform,Financial Crisis Management&Restructuring,Financial Intermediation,International Terrorism&Counterterrorism,Banking Law
Sommerfeld Enhancements for Thermal Relic Dark Matter
The annihilation cross section of thermal relic dark matter determines both
its relic density and indirect detection signals. We determine how large
indirect signals may be in scenarios with Sommerfeld-enhanced annihilation,
subject to the constraint that the dark matter has the correct relic density.
This work refines our previous analysis through detailed treatments of resonant
Sommerfeld enhancement and the effect of Sommerfeld enhancement on freeze out.
Sommerfeld enhancements raise many interesting issues in the freeze out
calculation, and we find that the cutoff of resonant enhancement, the
equilibration of force carriers, the temperature of kinetic decoupling, and the
efficiency of self-interactions for preserving thermal velocity distributions
all play a role. These effects may have striking consequences; for example, for
resonantly-enhanced Sommerfeld annihilation, dark matter freezes out but may
then chemically recouple, implying highly suppressed indirect signals, in
contrast to naive expectations. In the minimal scenario with standard
astrophysical assumptions, and tuning all parameters to maximize the signal, we
find that, for force-carrier mass m_phi = 250 MeV and dark matter masses m_X =
0.1, 0.3, and 1 TeV, the maximal Sommerfeld enhancement factors are S_eff = 7,
30, and 90, respectively. Such boosts are too small to explain both the PAMELA
and Fermi excesses. Non-minimal models may require smaller boosts, but the
bounds on S_eff could also be more stringent, and dedicated freeze out analyses
are required. For concreteness, we focus on 4 mu final states, but we also
discuss 4 e and other modes, deviations from standard astrophysical assumptions
and non-minimal particle physics models, and we outline the steps required to
determine if such considerations may lead to a self-consistent explanation of
the PAMELA or Fermi excesses.Comment: 31 pages, published versio
Challenging GRB models through the broadband dataset of GRB060908
Context: Multiwavelength observations of gamma-ray burst prompt and afterglow
emission are a key tool to disentangle the various possible emission processes
and scenarios proposed to interpret the complex gamma-ray burst phenomenology.
Aims: We collected a large dataset on GRB060908 in order to carry out a
comprehensive analysis of the prompt emission as well as the early and late
afterglow. Methods: Data from Swift-BAT, -XRT and -UVOT together with data from
a number of different ground-based optical/NIR and millimeter telescopes
allowed us to follow the afterglow evolution from about a minute from the
high-energy event down to the host galaxy limit. We discuss the physical
parameters required to model these emissions. Results: The prompt emission of
GRB060908 was characterized by two main periods of activity, spaced by a few
seconds of low intensity, with a tight correlation between activity and
spectral hardness. Observations of the afterglow began less than one minute
after the high-energy event, when it was already in a decaying phase, and it
was characterized by a rather flat optical/NIR spectrum which can be
interpreted as due to a hard energy-distribution of the emitting electrons. On
the other hand, the X-ray spectrum of the afterglow could be fit by a rather
soft electron distribution. Conclusions: GRB060908 is a good example of a
gamma-ray burst with a rich multi-wavelength set of observations. The
availability of this dataset, built thanks to the joint efforts of many
different teams, allowed us to carry out stringent tests for various
interpretative scenarios showing that a satisfactorily modeling of this event
is challenging. In the future, similar efforts will enable us to obtain
optical/NIR coverage comparable in quality and quantity to the X-ray data for
more events, therefore opening new avenues to progress gamma-ray burst
research.Comment: A&A, in press. 11 pages, 5 figure
Supernovae in Helium Star--Compact Object Binaries: A Possible Gamma-ray Burst Mechanism
Helium star--compact object binaries, and helium star--neutron star binaries
in particular, are widely believed to be the progenitors of the observed double
neutron star systems. In these, the second neutron star is presumed to be the
compact remnant of the helium star supernova. Here, the observational
implications of such a supernova are discussed, and in particular are explored
as a candidate gamma-ray burst mechanism. In this scenario the supernova
results in a transient period of rapid accretion onto the compact object,
extracting via magnetic torques its rotational energy at highly super-Eddington
luminosities in the form of a narrowly beamed, strongly electromagnetically
dominated jet. Compton scattering of supernova photons advected within the
ejecta, and photons originating at shocks driven into the ejecta by the jet,
will cool the jet and can produce the observed prompt emission characteristics,
including the peak--inferred isotropic energy relation, X-ray flash
characteristics, subpulse light curves, energy dependent time lags and subpulse
broadening, and late time spectral softening. The duration of the burst is
limited by the rate of Compton cooling of the jet, eventually creating an
optically thick, moderately relativistically expanding fireball which can
produce the afterglow emission. If the black hole or neutron star stays bound
to a compact remnant, late term light curve variability may be observed as in
SN 2003dh.Comment: Published version (includes discussion of black hole binaries). 11
pages, 1 figur
Variable polarization in the optical afterglow of GRB 021004
We present polarimetric observations of the afterglow of gamma-ray burst
(GRB) 021004, obtained with the Nordic Optical Telescope (NOT) and the Very
Large Telescope (VLT) between 8 and 17 hours after the burst. Comparison among
the observations shows a 45 degree change in the position angle from 9 hours
after the burst to 16 hours after the burst, and comparison with published data
from later epochs even shows a 90 degree change between 9 and 89 hours after
the burst. The degree of linear polarization shows a marginal change, but is
also consistent with being constant in time. In the context of currently
available models for changes in the polarization of GRBs, a homogeneous jet
with an early break time of t_b ~ 1 day provides a good explanation of our
data. The break time is a factor 2 to 6 earlier than has been found from the
analysis of the optical light curve. The change in the position angle of the
polarization rules out a structured jet model for the GRB.Comment: 5 pages, 2 figures. Published in A&A letter
Effects of replacing soybean meal with xylose-treated soybean meal on performance of nursing Awassi ewes and fattening lambs
Two experiments were conducted to evaluate the effect of replacing soybean meal with xylose-treated soybean meal (soypass meal; SPM) on performance of nursing Awassi ewes and fattening lambs. In Experiment 1, lasting for eight weeks, 39 Awassi ewes and their lambs were randomly assigned to three diets. Diets were formulated by replacing soybean meal from the basal diet (CON-SBM; n=13) with 50% (50% SPM; n=13) and 100% (100% SPM; n=13) SPM. Initial and final weights of the ewes were not different (P>0.55) among diets. Total gain and average daily gain (ADG) of lambs were similar (P=0.44) among diets. Ewes fed the CON-SBM diet tended (P<0.09) to have lower milk yields than those fed the 50% SPM and 100% SPM diets. No differences (P>0.38) in milk component percentages among diets were observed. In Experiment 2, lasting for 63 days, twenty weaned lambs were used to determine the effects of replacing soybean meal with SPM on growth performance. Diets were either soybean meal (SBM; n=10) or SPM (SPM; n=10). Nutrient intake and digestibility were not different between diets. However, rumen undegradable protein intake was greater (P<0.05) for the SPM diet than for the SBM diet. Final body weight, ADG and the feed conversion ratio were similar (P>0.05) between the diets. Results suggest that replacement of soybean meal with soypass meal is not likely to produce any production benefits in nursing Awassi ewes and fattening lambs except for the slight improvement of milk yield
Two types of softening detected in X-ray afterglows of Swift bursts: internal and external shock origins?
The softening process observed in the steep decay phase of early X-ray
afterglows of Swift bursts has remained a puzzle since its discovery. The
softening process can also be observed in the later phase of the bursts and its
cause has also been unknown. Recently, it was suggested that, influenced by the
curvature effect, emission from high latitudes would shift the Band function
spectrum from higher energy band to lower band, and this would give rise to the
observed softening process accompanied by a steep decay of the flux density.
The curvature effect scenario predicts that the terminating time of the
softening process would be correlated with the duration of the process. In this
paper, based on the data from the UNLV GRB group web-site, we found an obvious
correlation between the two quantities. In addition, we found that the
softening process can be divided into two classes: the early type softening
() and the late type softening ().
The two types of softening show different behaviors in the duration vs.
terminating time plot. In the relation between the variation rates of the flux
density and spectral index during the softening process, a discrepancy between
the two types of softening is also observed. According to their time scales and
the discrepancy between them, we propose that the two types are of different
origins: the early type is of internal shock origin and the late type is of
external shock origin. The early softening is referred to the steep decay just
following the prompt emission, whereas the late decay typically conceives the
transition from flat decay to late afterglow decay. We suspect that there might
be a great difference of the Lorentz factor in two classes which is responsible
for the observed discrepancy.Comment: 20 pages, 5 figures, 2 tables, Accepted for Publication to Journal of
Cosmology and Astroparticle Physics (JCAP
Cannonballs in the context of Gamma Ray Bursts: Formation sites ?
We investigate possible formation sites of the cannonballs (in the gamma ray
bursts context) by calculating their physical parameters, such as density,
magnetic field and temperature close to the origin. Our results favor scenarios
where the cannonballs form as instabilities (knots) within magnetized jets from
hyperaccreting disks. These instabilities would most likely set in beyond the
light cylinder where flow velocity with Lorentz factors as high as 2000 can be
achieved. Our findings challenge the cannonball model of gamma ray bursts if
these indeed form inside core-collapse supernovae (SNe) as suggested in the
literature; unless hyperaccreting disks and the corresponding jets are common
occurrences in core-collapse SNe.Comment: 10 pages, 12 figure
The Spectrum of Electromagnetic Jets from Kerr Black Holes and Naked Singularities in the Teukolsky Perturbation Theory
We give a new theoretical basis for examination of the presence of the Kerr
black hole (KBH) or the Kerr naked singularity (KNS) in the central engine of
different astrophysical objects around which astrophysical jets are typically
formed: X-ray binary systems, gamma ray bursts (GRBs), active galactic nuclei
(AGN), etc. Our method is based on the study of the exact solutions of the
Teukolsky master equation for electromagnetic perturbations of the Kerr metric.
By imposing original boundary conditions on the solutions so that they describe
a collimated electromagnetic outflow, we obtain the spectra of possible {\em
primary jets} of radiation, introduced here for the first time. The theoretical
spectra of primary electromagnetic jets are calculated numerically. Our main
result is a detailed description of the qualitative change of the behavior of
primary electromagnetic jet frequencies under the transition from the KBH to
the KNS, considered here as a bifurcation of the Kerr metric. We show that
quite surprisingly the novel spectra describe linearly stable primary
electromagnetic jets from both the KBH and the KNS. Numerical investigation of
the dependence of these primary jet spectra on the rotation of the Kerr metric
is presented and discussed.Comment: 18 pages, 35 figures, LaTeX file. Final version. Accepted for
publication in Astrophysics and Space Science. Amendments. Typos corrected.
Novel notion -"primary jet" is introduced. New references and comments adde
The Afterglow and Environment of the Short GRB111117A
We present multi-wavelength observations of the afterglow of the short
GRB111117A, and follow-up observations of its host galaxy. From rapid optical
and radio observations we place limits of r \gtrsim 25.5 mag at \deltat \approx
0.55 d and F_nu(5.8 GHz) < 18 \muJy at \deltat \approx 0.50 d, respectively.
However, using a Chandra observation at t~3.0 d we locate the absolute position
of the X-ray afterglow to an accuracy of 0.22" (1 sigma), a factor of about 6
times better than the Swift-XRT position. This allows us to robustly identify
the host galaxy and to locate the burst at a projected offset of 1.25 +/- 0.20"
from the host centroid. Using optical and near-IR observations of the host
galaxy we determine a photometric redshift of z=1.3 (+0.3,-0.2), one of the
highest for any short GRB, and leading to a projected physical offset for the
burst of 10.5 +/- 1.7 kpc, typical of previous short GRBs. At this redshift,
the isotropic gamma-ray energy is E_{gamma,iso} \approx 3\times10^51 erg
(rest-frame 23-2300 keV) with a peak energy of E_{pk} \approx 850-2300 keV
(rest-frame). In conjunction with the isotropic X-ray energy, GRB111117A
appears to follow our recently-reported E_x,iso-E_gamma,iso-E_pk universal
scaling. Using the X-ray data along with the optical and radio non-detections
we find that for a blastwave kinetic energy of E_{K,iso} \approx E_{gamma,iso},
the circumburst density is n_0 \sim 3x10^(-4)-1 cm^-3 (for a range of
epsilon_B=0.001-0.1). Similarly, from the non-detection of a break in the X-ray
light curve at t<3 d, we infer a minimum opening angle for the outflow of
theta_j> 3-10 degrees (depending on the circumburst density). We conclude that
Chandra observations of short GRBs are effective at determining precise
positions and robust host galaxy associations in the absence of optical and
radio detections.Comment: ApJ accepted versio
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