570 research outputs found
General Relativistic Simulations of Jet Formation in a Rapidly Rotating Black Hole Magnetosphere
To investigate the formation mechanism of relativistic jets in active
galactic nuclei and micro-quasars, we have developed a new general relativistic
magnetohydrodynamic code in Kerr geometry. Here we report on the first
numerical simulation of jet formation in a rapidly-rotating (a=0.95) Kerr black
hole magnetosphere. We study cases in which the Keplerian accretion disk is
both co-rotating and counter-rotating with respect to the black hole rotation.
In the co-rotating disk case, our results are almost the same as those in
Schwarzschild black hole cases: a gas pressure-driven jet is formed by a shock
in the disk, and a weaker magnetically-driven jet is also generated outside the
gas pressure-driven jet. On the other hand, in the counter-rotating disk case,
a new powerful magnetically-driven jet is formed inside the gas pressure-driven
jet. The newly found magnetically-driven jet in the latter case is accelerated
by a strong magnetic field created by frame dragging in the ergosphere. Through
this process, the magnetic field extracts the energy of the black hole
rotation.Comment: Co-rotating and counter-rotating disks; 8 pages; submitted to ApJ
letter
Developing Tools for Multimessenger Gravitational Wave Astronomy
We present work in progress to craft open-sourced numerical tools that will
enable the calculation of electromagnetic counterparts to gravitational
waveforms: the {\tt GiRaFFE} (General Relativistic Force-Free Electrodynamics)
code. {\tt GiRaFFE} numerically solves the general relativistic
magnetohydrodynamics system of equations in the force-free limit, to model the
magnetospheres surrounding compact binaries, in order (1) to characterize the
nonlinear interaction between the source and its surrounding magnetosphere, and
(2) to evaluate the electromagnetic counterparts of gravitational waves,
including the production of collimated jets. We apply this code to various
configurations of spinning black holes immersed in external magnetic field, in
order to both test our implementation, and to explore the effect of strong
gravitational field, high spins and of misalignment between the magnetic field
lines an black hole spin, on the electromagnetic output and the collimation of
Poynting jets.
We will extend our work to collisions of black holes immersed in external
magnetic field, which are prime candidates for coincident detection in both
gravitational and electromagnetic spectra.Comment: 6 pages, 6 figures, MG15 proceeding
Non-thermal Processes in Black-Hole-Jet Magnetospheres
The environs of supermassive black holes are among the universe's most
extreme phenomena. Understanding the physical processes occurring in the
vicinity of black holes may provide the key to answer a number of fundamental
astrophysical questions including the detectability of strong gravity effects,
the formation and propagation of relativistic jets, the origin of the highest
energy gamma-rays and cosmic-rays, and the nature and evolution of the central
engine in Active Galactic Nuclei (AGN). As a step towards this direction, this
paper reviews some of the progress achieved in the field based on observations
in the very high energy domain. It particularly focuses on non-thermal particle
acceleration and emission processes that may occur in the rotating
magnetospheres originating from accreting, supermassive black hole systems.
Topics covered include direct electric field acceleration in the black hole's
magnetosphere, ultra-high energy cosmic ray production, Blandford-Znajek
mechanism, centrifugal acceleration and magnetic reconnection, along with the
relevant efficiency constraints imposed by interactions with matter, radiation
and fields. By way of application, a detailed discussion of well-known sources
(Sgr A*; Cen A; M87; NGC1399) is presented.Comment: invited review for International Journal of Modern Physics D, 49
pages, 15 figures; minor typos corrected to match published versio
Scenarios for ultrafast gamma-ray variability in AGN
We analyze three scenarios to address the challenge of ultrafast gamma-ray
variability reported from active galactic nuclei. We focus on the energy
requirements imposed by these scenarios: (i) external cloud in the jet, (ii)
relativistic blob propagating through the jet material, and (iii) production of
high-energy gamma rays in the magnetosphere gaps. We show that while the first
two scenarios are not constrained by the flare luminosity, there is a robust
upper limit on the luminosity of flares generated in the black hole
magnetosphere. This limit depends weakly on the mass of the central black hole
and is determined by the accretion disk magnetization, viewing angle, and the
pair multiplicity. For the most favorable values of these parameters, the
luminosity for 5-minute flares is limited by ,
which excludes a black hole magnetosphere origin of the flare detected from
IC310. In the scopes of scenarios (i) and (ii), the jet power, which is
required to explain the IC310 flare, exceeds the jet power estimated based on
the radio data. To resolve this discrepancy in the framework of the scenario
(ii), it is sufficient to assume that the relativistic blobs are not
distributed isotropically in the jet reference frame. A realization of scenario
(i) demands that the jet power during the flare exceeds by a factor the
power of the radio jet relevant to a timescale of years.Comment: 15 pages, accepted by Ap
GiRaFFE: An Open-Source General Relativistic Force-Free Electrodynamics Code
We present GiRaFFE, the first open-source general relativistic force-free
electrodynamics (GRFFE) code for dynamical, numerical-relativity generated
spacetimes. GiRaFFE adopts the strategy pioneered by McKinney and modified by
Paschalidis and Shapiro to convert a GR magnetohydrodynamic (GRMHD) code into a
GRFFE code. In short, GiRaFFE exists as a modification of IllinoisGRMHD, a
user-friendly, open-source, dynamical-spacetime GRMHD code. Both GiRaFFE and
IllinoisGRMHD leverage the Einstein Toolkit's highly-scalable infrastructure to
make possible large-scale simulations of magnetized plasmas in strong,
dynamical spacetimes on adaptive-mesh refinement (AMR) grids. We demonstrate
that GiRaFFE passes a large suite of both flat and curved-spacetime code tests
passed by a number of other state-of-the-art GRFFE codes, and is thus ready for
production-scale simulations of GRFFE phenomena of key interest to relativistic
astrophysics.Comment: 23 pages, 4 figures. Consistent with published versio
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