87 research outputs found
Gamma-Ray Burst afterglow scaling coefficients for general density profile
Gamma-ray burst (GRB) afterglows are well described by synchrotron emission
originating from the interaction between a relativistic blast wave and the
external medium surrounding the GRB progenitor. We introduce a code to
reconstruct spectra and light curves from arbitrary fluid configurations,
making it especially suited to study the effects of fluid flows beyond those
that can be described using analytical approximations. As a check and first
application of our code we use it to fit the scaling coefficients of
theoretical models of afterglow spectra. We extend earlier results of other
authors to general circumburst density profiles. We rederive the physical
parameters of GRB 970508 and compare with other authorsComment: 11 pages, 5 figures. Revised edition removes references to unphysical
chromatic break and adds appendix on hot region directly behind shoc
On the structure of the burst and afterglow of Gamma-Ray Bursts I: the radial approximation
We have proposed three paradigms for the theoretical interpretation of
gamma-ray bursts (GRBs). (1) The relative space-time transformation (RSTT)
paradigm emphasizes how the knowledge of the entire world-line of the source
from the moment of gravitational collapse is a necessary condition to interpret
GRB data. (2) The interpretation of the burst structure (IBS) paradigm
differentiates in all GRBs between an injector phase and a beam-target phase.
(3) The GRB-supernova time sequence (GSTS) paradigm introduces the concept of
induced supernova explosion in the supernovae-GRB association. These three
paradigms are illustrated using our theory based on the vacuum polarization
process occurring around an electromagnetic black hole (EMBH theory) and using
GRB 991216 as a prototype. We illustrate the five fundamental eras of the EMBH
theory: the self acceleration of the pair-electromagnetic plasma (PEM
pulse), its interaction with the baryonic remnant of the progenitor star (PEMB
pulse). We then study the approach of the PEMB pulse to transparency, the
emission of the proper GRB (P-GRB) and its relation to the ``short GRBs''.
Finally the three different regimes of the afterglow are described within the
fully radiative and radial approximations. The best fit of the theory leads to
an unequivocal identification of the ``long GRBs'' as extended emission
occurring at the afterglow peak (E-APE). The relative intensities, the time
separation and the hardness ratio of the P-GRB and the E-APE are used as
distinctive observational test of the EMBH theory and the excellent agreement
between our theoretical predictions and the observations are documented. The
afterglow power-law indexes in the EMBH theory are compared and contrasted with
the ones in the literature, and no beaming process is found for GRB 991216.Comment: 96 pages, 40 figures, to appear on Int. Journ. Mod. Phys.
Gamma-Ray Bursts via the Neutrino Emission from Heated Neutron Stars
A model is proposed for gamma-ray bursts based upon a neutrino burst of about
10^52 ergs lasting a few seconds above a heated collapsing neutron star. This
type of thermal neutrino burst is suggested by relativistic hydrodynamic
studies of the compression, heating, and collapse of close binary neutron stars
as they approach their last stable orbit, but may arise from other sources as
well. We present a hydrodynamic simulation of the formation and evolution of
the pair plasma associated with such a neutrino burst. This pair plasma leads
to the production of ~10^51 - 10^52 ergs in gamma-rays with spectral and
temporal properties consistent with observed gamma-ray bursts.Comment: Final version. 30 pages, 10 figures, 6 tables, accepted for
publication in The Astrophysical Journa
Jet Precession Driven by Neutrino-Cooled Disc for Gamma-Ray Bursts
A model of jet precession driven by a neutrino-cooled disc around a spinning
black hole is present in order to explain the temporal structure and spectral
evolution of gamma-ray bursts (GRBs). The differential rotation of the outer
part of a neutrino dominated accretion disc may result in precession of the
inner part of the disc and the central black hole, hence drives a precessed jet
via neutrino annihilation around the inner part of the disc. Both analytic and
numeric results for our model are present. Our calculations show that a black
hole-accretion disk system with black hole mass ,
accretion rate , spin parameter
and viscosity parameter may drive a precessed jet with period P=1
s and luminosity erg s, corresponding to the scenario for
long GRBs. A precessed jet with s and erg s may be
powered by a system with , , , and , possibly being responsible for the
short GRBs. Both the temporal and spectral evolution in GRB pulse may explained
with our model. GRB central engines likely power a precessed jet driven by a
neutrino-cooled disc. The global GRB lightcurves thus could be modulated by the
jet precession during the accretion timescale of the GRB central engine. Both
the temporal and spectral evolution in GRB pulse may be due to an viewing
effect due to the jet precession.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Structured frameworks to increase the transparency of the assessment of benefits and risks of medicines: current status and possible future directions
Structured frameworks for benefit-risk analysis in drug licensing decisions are being implemented across a number of regulatory agencies worldwide. The aim of these frameworks is to aid the analysis and communication of the benefit-risk assessment throughout the development, evaluation, and supervision of medicines. In this review, authors from regulatory agencies, pharmaceutical companies, and academia share their views on the different frameworks and discuss future directions
Sterile neutrinos and supernova nucleosynthesis
A light sterile neutrino species has been introduced to explain
simultaneously the solar and atmospheric neutrino puzzles and the results of
the LSND experiment, while providing for a hot component of dark matter.
Employing this scheme of neutrino masses and mixings, we show how
matter-enhanced active-sterile neutrino transformation followed by
active-active neutrino transformation can solve robustly the neutron deficit
problem encountered by models of r-process nucleosynthesis associated with
neutrino-heated supernova ejecta.Comment: 29 pages, 3 postscript figures, submitted to Phys. Rev.
Neutrino pair annihilation near accreting, stellar-mass black holes
We investigate the energy-momentum deposition due to neutrino-antineutrino
annihilation in the vicinity of axisymmetric, accreting black holes (BHs) by
numerically ray-tracing neutrino trajectories in a Kerr space-time.
Hyperaccreting stellar-mass BHs are widely considered as energy sources that
can drive ultrarelativistic outflows with the potential to produce gamma-ray
bursts. In contrast to earlier works, we provide an extensive and detailed
parameter study of the influence of general relativistic (GR) effects and of
different neutrinosphere geometries. These include idealized thin disks, tori,
and spheres, or are constructed as non-selfgravitating equilibrium matter
distributions for varied BH rotation. Considering isothermal neutrinospheres
with the same temperature and surface area, we confirm previous results that
compared to Newtonian calculations, GR effects increase the annihilation rate
measured by an observer at infinity by a factor of 2 when the neutrinosphere is
a disk. However, in case of a torus and a sphere the influence of GR effects is
globally only ~25%, although locally it can be significantly larger.
Independent of whether GR effects are included, disks yield the highest energy
deposition rates, followed by tori and, with the lowest rates, spheres. For
disks and tori, increasing the angular momentum of the BH from 0 to 1 enhances
the energy deposition rate measured by an observer at infinity by roughly a
factor of 2 due to the shrinking inner radius of the neutrinosphere. (abridged)Comment: 18 pages, 8 figures, accepted by A&
Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO
Gamma-ray bursts are believed to originate in core-collapse of massive stars.
This produces an active nucleus containing a rapidly rotating Kerr black hole
surrounded by a uniformly magnetized torus represented by two counter-oriented
current rings. We quantify black hole spin-interactions with the torus and
charged particles along open magnetic flux-tubes subtended by the event
horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of
frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with
GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii)
aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich
et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al.
2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating
LIGO/Virgo detectors enables searches for nearby events and their spectral
closure density 6e-9 around 250Hz in the stochastic background radiation in
gravitational waves. At current sensitivity, LIGO-Hanford may place an upper
bound around 150MSolar in GRB030329. Detection of Egw thus provides a method
for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49
Standardising Clinical Caremaps: Model, Method and Graphical Notation for Caremap Specification
Standardising care can improve patient safety and outcomes, and reduce the cost of providing healthcare services. Caremaps were developed to standardise care, but contemporary caremaps are not standardised. Confusion persists in terms of terminology, structure, content and development process. Unlike existing methods in the literature, the approach, model and notation presented in this chapter pays special attention to incorporation of clinical decision points as first-class citizens within the modelling process. The resulting caremap with decision points is evaluated through creation of a caremap for women with gestational diabetes mellitus. The proposed method was found to be an effective way for comprehensively specifying all features of caremaps in a standardised way that can be easily understood by clinicians. This chapter contributes a new standardised method, model and notation for caremap content, structure and development
LOW-Γ JETS from COMPACT STELLAR MERGERS: CANDIDATE ELECTROMAGNETIC COUNTERPARTS to GRAVITATIONAL WAVE SOURCES
The American Astronomical Society. All rights reserved.Short gamma-ray bursts (GRBs) are believed to be produced by relativistic jets from mergers of neutron stars (NSs) or NSs and black-holes (BHs). If the Lorentz-factors Γ of jets from compact stellar mergers follow a similar power-law distribution to those observed for other high-energy astrophysical phenomena (e.g., blazars, active galactic nuclei), the population of jets should be dominated by low-Γ outflows. These jets will not produce prompt gamma-rays, but jet energy will be released as X-ray/optical/radio transients when they collide with the ambient medium. Using Monte Carlo simulations, we study the properties of such transients. Approximately 78% of merger jets Mpc result in failed GRBs if the jet Γ follows a power-law distribution of index -1.75. X-ray/optical transients from failed GRBs will have broad distributions of their characteristics: light-curves peak tp ∼ 0.1-10 days after a merger; flux peaks for X-ray 10-6 mJy ≲ Fx ≲ 10-2 mJy; and optical flux peaks at 14 ≲ mg ≲ 22. X-ray transients are detectable by Swift XRT, and ∼85% of optical transients will be detectable by telescopes with limiting magnitude mg ≳ 21, for well localized sources on the sky. X-ray/optical transients are followed by radio transients with peak times narrowly clustered around tp ∼ 10 days, and peak flux of ∼10-100 mJy at 10 GHz and ∼0.1 mJy at 150 MHz. By considering the all-sky rate of short GRBs within the LIGO/Virgo range, the rate of on-axis orphan afterglows from failed GRBs should be 2.6(26) per year for NS-NS(NS-BH) mergers, respectively. Since merger jets from gravitational-wave (GW) trigger events tend to be directed to us, a significant fraction of GW events could be associated with the on-axis orphan afterglow
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