3,989 research outputs found

    Time domain calculation of the electromagnetic self-force on eccentric geodesics in Schwarzschild spacetime

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    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

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    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

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    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 (1015G10^{15}\, \mathrm{G}). 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 M˙ej1×101Ms1\dot{M}_{\mathrm{ej}} \simeq 1 \times10^{-1}\, \mathrm{M_{\odot}\, s^{-1}}. The total ejecta mass in our simulation is 5×103M5\times 10^{-3}\, \mathrm{M_{\odot}}. This makes the ejecta from the HMNS an important component in BNS mergers and a promising source of rr-process elements that can power a kilonova. The jet from the HMNS reaches a terminal Lorentz factor of 5\sim 5 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

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    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

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    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

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    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 2727-MM_\odot progenitor in full unconstrained 3D and in octant symmetry for \gtrsim380ms 380\,\mathrm{ms}. 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