4,016 research outputs found
Time domain calculation of the electromagnetic self-force on eccentric geodesics in Schwarzschild spacetime
I calculate the self-force acting on a particle with electric charge q moving
on a generic geodesic around a Schwarzschild black hole. Using methods similar
to those developed for the scalar field case discussed in a previous paper, I
investigate the relative sizes of the conservative (half-advanced plus
half-retarded) and dissipative (half-advanced minus half-retarded) pieces of
the self-force. I also display the regularization parameters used in the
mode-sum regularization scheme.Comment: 24 pages; 21 figures; revtex
Extended Working Life Policies Country Experiences: Chapter 8 Austria
This chapter deals with the labour market situation of older (50+)workers and pension policies in Austria, a country where gender differences are strongly pronounced over the entire lifecourse. The target of recent policies is not primarily to tackle the negative effects of the system for women, but to decrease pension costs by discouraging early retirement and inducing employers to keep and/or employ older workers. However, this will have some gendered effects since recent policy changes will increase women's lower legal retirement age stepwise (60) to match that of men(65) in 2033. Although caring time already partly contributes topension payments, this does not substantially decrease the large gender pension gap
A magnetar engine for short GRBs and kilonovae
We investigate the influence of magnetic fields on the evolution of binary
neutron-star (BNS) merger remnants via three-dimensional (3D)
dynamical-spacetime general-relativistic (GR) magnetohydrodynamic (MHD)
simulations. We evolve a postmerger remnant with an initial poloidal magnetic
field, resolve the magnetoturbulence driven by shear flows, and include a
microphysical finite-temperature equation of state (EOS). A neutrino leakage
scheme that captures the overall energetics and lepton number exchange is also
included. We find that turbulence induced by the magnetorotational instability
(MRI) in the hypermassive neutron star (HMNS) amplifies magnetic field to
beyond magnetar-strength (). The ultra-strong toroidal
field is able to launch a relativistic jet from the HMNS. We also find a
magnetized wind that ejects neutron-rich material with a rate of
.
The total ejecta mass in our simulation is . This makes the ejecta from the HMNS an important component
in BNS mergers and a promising source of -process elements that can power a
kilonova. The jet from the HMNS reaches a terminal Lorentz factor of
in our highest-resolution simulation. The formation of this jet is aided by
neutrino-cooling preventing the accretion disk from protruding into the polar
region. As neutrino pair-annihilation and radiative processes in the jet (which
were not included in the simulations) will boost the Lorentz factor in the jet
further, our simulations demonstrate that magnetars formed in BNS mergers are a
viable engine for short gamma-ray bursts (sGRBs).Comment: Resubmitted versio
IllinoisGRMHD: An Open-Source, User-Friendly GRMHD Code for Dynamical Spacetimes
In the extreme violence of merger and mass accretion, compact objects like
black holes and neutron stars are thought to launch some of the most luminous
outbursts of electromagnetic and gravitational wave energy in the Universe.
Modeling these systems realistically is a central problem in theoretical
astrophysics, but has proven extremely challenging, requiring the development
of numerical relativity codes that solve Einstein's equations for the
spacetime, coupled to the equations of general relativistic (ideal)
magnetohydrodynamics (GRMHD) for the magnetized fluids. Over the past decade,
the Illinois Numerical Relativity (ILNR) Group's dynamical spacetime GRMHD code
has proven itself as a robust and reliable tool for theoretical modeling of
such GRMHD phenomena. However, the code was written "by experts and for
experts" of the code, with a steep learning curve that would severely hinder
community adoption if it were open-sourced. Here we present IllinoisGRMHD,
which is an open-source, highly-extensible rewrite of the original
closed-source GRMHD code of the ILNR Group. Reducing the learning curve was the
primary focus of this rewrite, with the goal of facilitating community
involvement in the code's use and development, as well as the minimization of
human effort in generating new science. IllinoisGRMHD also saves computer time,
generating roundoff-precision identical output to the original code on
adaptive-mesh grids, but nearly twice as fast at scales of hundreds to
thousands of cores.Comment: 37 pages, 6 figures, single column. Matches published versio
GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate Mass Black Hole
A highly unusual pair of a gamma-ray burst (GRB) GRB060218 and an associated
supernova SN2006aj has puzzled theorists for years. A supernova shock breakout
and a jet from a newborn stellar mass compact object were put forward to
explain its multiwavelength signature. We propose that the source is naturally
explained by another channel, a tidal disruption of a white dwarf (WD) by an
intermediate mass black hole (IMBH). The tidal disruption is accompanied by a
tidal pinching, which leads to the ignition of a WD and a supernova. Some
debris falls back onto the IMBH, forms a disk, which quickly amplifies the
magnetic field, and launches a jet. We successfully fit soft X-ray spectrum
with the Comptonized blackbody emission from a jet photosphere. The optical/UV
emission is consistent with self-absorbed synchrotron from the expanding jet
front. The accretion rate temporal dependence Mdot(t) in a tidal disruption
provides a good fit to soft X-ray lightcurve. The IMBH mass is found to be
about 10^4Msun in three independent estimates: (1) fitting tidal disruption
Mdot(t) to soft X-ray lightcurve; (2) computing the jet base radius in a jet
photospheric emission model; (3) inferring the central BH mass based on a host
dwarf galaxy stellar mass. The supernova position is consistent with the center
of the host galaxy, while low supernova ejecta mass is consistent with a WD
mass. High expected rate of tidal disruptions in dwarf galaxies is consistent
with one source observed by Swift satellite over several years at GRB060218
distance of 150Mpc. The encounters with the WDs provide a lot of fuel for IMBH
growth.Comment: 15 pages, 5 figures, accepted to ApJ, minor change
General Relativistic Three-Dimensional Multi-Group Neutrino Radiation-Hydrodynamics Simulations of Core-Collapse Supernovae
We report on a set of long-term general-relativistic three-dimensional (3D)
multi-group (energy-dependent) neutrino-radiation hydrodynamics simulations of
core-collapse supernovae. We employ a full 3D two-moment scheme with the local
M1 closure, three neutrino species, and 12 energy groups per species. With
this, we follow the post-core-bounce evolution of the core of a nonrotating
- progenitor in full unconstrained 3D and in octant symmetry for
. We find the development of an asymmetric runaway
explosion in our unconstrained simulation. We test the resolution dependence of
our results and, in agreement with previous work, find that low resolution
artificially aids explosion and leads to an earlier runaway expansion of the
shock. At low resolution, the octant and full 3D dynamics are qualitatively
very similar, but at high resolution, only the full 3D simulation exhibits the
onset of explosion.Comment: Accepted to Ap
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