scholarly journals Accelerating AGN jets to parsec scales using general relativistic MHD simulations

2019 ◽  
Vol 490 (2) ◽  
pp. 2200-2218 ◽  
Author(s):  
K Chatterjee ◽  
M Liska ◽  
A Tchekhovskoy ◽  
S B Markoff
Keyword(s):  
Ambient Medium ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Opening Angle ◽  
Long Baseline ◽  
General Relativistic ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations ◽  
Jet Collimation ◽  
Sheath Structure

ABSTRACT Accreting black holes produce collimated outflows, or jets, that traverse many orders of magnitude in distance, accelerate to relativistic velocities, and collimate into tight opening angles. Of these, perhaps the least understood is jet collimation due to the interaction with the ambient medium. In order to investigate this interaction, we carried out axisymmetric general relativistic magnetohydrodynamic simulations of jets produced by a large accretion disc, spanning over 5 orders of magnitude in time and distance, at an unprecedented resolution. Supported by such a disc, the jet attains a parabolic shape, similar to the M87 galaxy jet, and the product of the Lorentz factor and the jet half-opening angle, γθ ≪ 1, similar to values found from very long baseline interferometry (VLBI) observations of active galactic nuclei (AGNs) jets; this suggests extended discs in AGNs. We find that the interaction between the jet and the ambient medium leads to the development of pinch instabilities, which produce significant radial and lateral variability across the jet by converting magnetic and kinetic energy into heat. Thus pinched regions in the jet can be detectable as radiating hotspots and may provide an ideal site for particle acceleration. Pinching also causes gas from the ambient medium to become squeezed between magnetic field lines in the jet, leading to enhanced mass loading and deceleration of the jet to non-relativistic speeds, potentially contributing to the spine-sheath structure observed in AGN outflows.

scholarly journals 3D magnetized jet break-out from neutron-star binary merger ejecta: afterglow emission from the jet and the ejecta

2021 ◽  
Vol 502 (2) ◽  
pp. 1843-1855
Author(s):  
Antonios Nathanail ◽  
Ramandeep Gill ◽  
Oliver Porth ◽  
Christian M Fromm ◽  
Luciano Rezzolla
Keyword(s):  
Neutron Star ◽  
Thermal Emission ◽  
Opening Angle ◽  
Hollow Core ◽  
Binary Neutron Star ◽  
Vlbi Observations ◽  
Superluminal Motion ◽  
General Relativistic ◽  
Star Binary ◽  
Magnetohydrodynamic Simulations

ABSTRACT We perform 3D general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of θcore ≈ 4°, an opening angle of θjet ≳ 10°, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also compute the non-thermal afterglow emission of the relativistic outflow and fit it to the panchromatic afterglow from GRB170817A, together with the superluminal motion reported from VLBI observations. In this way, we deduce an observer angle of $\theta _{\rm obs}= 35.7^{\circ \, \, +1.8}_{\phantom{\circ \, \, }-2.2}$. We further compute the afterglow emission from the ejected matter and constrain the parameter space for a scenario in which the matter responsible for the thermal kilonova emission will also lead to a non-thermal emission yet to be observed.

scholarly journals Jet-torus connection in radio galaxies

2018 ◽  
Vol 609 ◽  
pp. A80 ◽  
Author(s):  
C. M. Fromm ◽  
M. Perucho ◽  
O. Porth ◽  
Z. Younsi ◽  
E. Ros ◽  
...  
Keyword(s):  
Thermal Emission ◽  
Ambient Medium ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Asymmetric Structures ◽  
Long Baseline ◽  
Volume Method ◽  
Index Maps ◽  
Thermal Absorption ◽  
Core Shift

Context. High resolution very long baseline interferometry observations of active galactic nuclei have revealed asymmetric structures in the jets of radio galaxies. These asymmetric structures may be due to internal asymmetries in the jets or they may be induced by the different conditions in the surrounding ambient medium, including the obscuring torus, or a combination of the two. Aims. In this paper we investigate the influence of the ambient medium, including the obscuring torus, on the observed properties of jets from radio galaxies. Methods. We performed special-relativistic hydrodynamic (SRHD) simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat, which is based on a second-order accurate finite-volume method and an approximate Riemann solver. Using a newly developed radiative transfer code to compute the electromagnetic radiation, we modelled several jets embedded in various ambient medium and torus configurations and subsequently computed the non-thermal emission produced by the jet and thermal absorption from the torus. To better compare the emission simulations with observations we produced synthetic radio maps, taking into account the properties of the observatory. Results. The detailed analysis of our simulations shows that the observed properties such as core shift could be used to distinguish between over-pressured and pressure matched jets. In addition to the properties of the jets, insights into the extent and density of the obscuring torus can be obtained from analyses of the single-dish spectrum and spectral index maps.

scholarly journals Disc Tearing and Bardeen-Petterson Alignment in GRMHD Simulations of Highly Tilted Thin Accretion Discs

2020 ◽  
Author(s):  
M Liska ◽  
C Hesp ◽  
A Tchekhovskoy ◽  
A Ingram ◽  
M van der Klis ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Nuclei ◽  
Accretion Discs ◽  
Emission Model ◽  
Sharp Drop ◽  
Frame Dragging ◽  
General Relativistic ◽  
Magnetohydrodynamic Simulations ◽  
Future Work ◽  
X Ray Binaries

Abstract Luminous active galactic nuclei (AGN) and X-Ray binaries (XRBs) often contain geometrically thin, radiatively cooled accretion discs. According to theory, these are – in many cases – initially highly misaligned with the black hole equator. In this work, we present the first general relativistic magnetohydrodynamic simulations of very thin (h/r∼0.015-0.05) accretion discs around rapidly spinning (a∼0.9) black holes and tilted by 45-65 degrees. We show that the inner regions of the discs with h/r≲0.03 align with the black hole equator, though out to smaller radii than predicted by analytic work. The inner aligned and outer misaligned disc regions are separated by a sharp break in tilt angle accompanied by a sharp drop in density. We find that frame-dragging by the spinning black hole overpowers the disc viscosity, which is self-consistently produced by magnetized turbulence, tearing the disc apart and forming a rapidly precessing inner sub-disc surrounded by a slowly precessing outer sub-disc. We find that the system produces a pair of relativistic jets for all initial tilt values. At small distances the black hole launched jets precess rapidly together with the inner sub-disc, whereas at large distances they partially align with the outer sub-disc and precess more slowly. If the tearing radius can be modeled accurately in future work, emission model independent measurements of black hole spin based on precession-driven quasi-periodic oscillations may become possible.

scholarly journals General Relativistic Simulation of Jet Formation from Magnetized Accretion Disk

1997 ◽  
Vol 163 ◽  
pp. 667-671
Author(s):  
Shinji Koide ◽  
Kazunari Shibata ◽  
Takahiro Kudoh
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Accretion Disk ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Numerical Code ◽  
Jet Formation ◽  
Relativistic Jet ◽  
Relativistic Regime ◽  
General Relativistic

AbstractRecently, superluminal motions are observed not only from active galactic nuclei but also in our Galaxy. These phenomena are explained as relativistic jets propagating almost toward us with Lorentz factor more than 2. For the formation of such a relativistic jet, magnetically driven mechanism around a black hole is most promising. We have extended the 2.5D Newtonian MHD jet model (Shibata & Uchida 1986) to general relativistic regime. For this purpose, we have developed a general relativistic magnetohydrodynamic (GRMHD) numerical code and applied it to the simulation of the magnetized accretion disk around a black hole. We have found the formation of magnetically driven jets with 86 percent of light velocity (i.e. Lorentz factor ~ 2.0).

scholarly journals BL LAC POPULATION STUDY AT HIGH ENERGIES

2014 ◽  
Vol 28 ◽  
pp. 1460177
Author(s):  
LUCIE GÉRARD ◽  
GILLES HENRI ◽  
SANTIAGO PITA ◽  
MICHAEL PUNCH
Keyword(s):  
Active Galactic Nuclei ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Opening Angle ◽  
Parent Population ◽  
High Energies ◽  
Relativistic Jet ◽  
Radiative Model ◽  
Doppler Factor ◽  
Bl Lacs

In the framework of Active Galactic Nuclei (AGN) unification, BL Lacs and their parent population would share the same intrinsic characteristics, the observational differences being due to the orientation of the relativistic jet compared to the line of sight. BL Lacs would be the objects whose jet is oriented towards us, their emission being amplified by the relativistic Doppler boosting. Constraints arising from fast variability and/or large optical depth to pair production commonly imply large Lorentz factors. The growing number of BL Lacs detected at HE (> 100 MeV) and VHE (> 100 GeV) is a challenge for this unification scheme. Indeed, the high values of Doppler factor needed in the simplest radiative model to explain the emission of these sources imply a large density for the parent population. A possible solution to this Doppler factor crisis lies in considering different geometries for the jet. In this study, we use the BL Lacs detected at HE and VHE to investigate the intrinsic properties of the associated parent population. Using the results presented in Fermi's second AGN catalog and performing MC simulations of the parent population, we constrain the jet parameters: its intrinsic luminosity, Lorentz factor and geometric opening angle. The simulated density of parent population and Doppler factors of the objects detectable at HE within this population are presented according to the jet parameters.

scholarly journals Centrifugal acceleration of protons by a supermassive black hole

2020 ◽  
Vol 492 (4) ◽  
pp. 4884-4891 ◽  
Author(s):  
Ya N Istomin ◽  
A A Gunya
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Galactic Nuclei ◽  
Rotation Frequency ◽  
Azimuthal Velocity ◽  
Lorentz Factor ◽  
Centrifugal Acceleration ◽  
Poloidal Magnetic Field ◽  
Field Lines ◽  
Sgr A

ABSTRACT Centrifugal acceleration is due to the rotating poloidal magnetic field in the magnetosphere that creates the electric field which is orthogonal to the magnetic field. Charged particles with finite cyclotron radii can move along the electric field and receive energy. Centrifugal acceleration pushes particles to the periphery, where their azimuthal velocity reaches the speed of light. We calculated particle trajectories by numerical and analytical methods. The maximum obtained energies depend on the parameter of the particle magnetization κ, which is the ratio of rotation frequency of magnetic field lines in the magnetosphere ΩF to non-relativistic cyclotron frequency of particles ωc, κ = ΩF/ωc <<1, and on the parameter α which is the ratio of toroidal magnetic field BT to the poloidal one BP, α = BT/BP. It is shown that for small toroidal fields, α < κ1/4, the maximum Lorentz factor γm is only the square root of magnetization, γm = κ−1/2, while for large toroidal fields, α > κ1/4, the energy increases significantly, γm = κ−2/3. However, the maximum possible acceleration, γm = κ−1, is not achieved in the magnetosphere. For a number of active galactic nuclei, such as M87, maximum values of Lorentz factor for accelerated protons are found. Also, for special case of Sgr. A*, estimations of the maximum proton energy and its energy flux are obtained. They are in agreement with experimental data obtained by HESS Cherenkov telescope.

Emission modelling of hydrodynamic AGN jet simulations

2018 ◽  
Vol 14 (S342) ◽  
pp. 209-213
Author(s):  
Izak P. van der Westhuizen ◽  
Brian van Soelen ◽  
Petrus J. Meintjes
Keyword(s):  
Supersonic Flow ◽  
Active Galactic Nuclei ◽  
Ambient Medium ◽  
Strong Shock ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Single Frequency ◽  
First Case ◽  
Emission Modelling ◽  
Collimated Beam

AbstractRadio-loud Active Galactic Nuclei (AGN) produce relativistic jets that can be modelled with relativistic hydrodynamic (RHD) simulations. In this study we present two such simulations of jets, used to investigate the parameters required to reproduce structures consistent with both FR I and FRII jets. In the first simulation a Lorentz factor of 10 and supersonic flow of Mach 30 were chosen, while for the second simulation a Lorentz factor of 1.0014 with a supersonic flow of Mach 4 was used. Over similar distances scales the first case shows a well collimated beam with a strong shock at the interface between the jet and ambient medium while the second case shows a less stable beam and a larger cocoon. To determine whether the simulated physical structures are consistent with the observed FR I/II jets, the synchrotron emission has been calculated to produce radio maps at a single frequency of 1.5 GHz.

scholarly journals Jet propagation in expanding medium for gamma-ray bursts

2020 ◽  
Vol 500 (1) ◽  
pp. 627-642
Author(s):  
Hamid Hamidani ◽  
Kunihito Ioka
Keyword(s):  
Numerical Simulations ◽  
Gamma Ray ◽  
Ambient Medium ◽  
Gamma Ray Bursts ◽  
Analytical Models ◽  
Opening Angle ◽  
Binary Neutron Star ◽  
Merger Event ◽  
Lateral Width ◽  
Jet Collimation

ABSTRACT The binary neutron star (BNS) merger event GW170817 clearly shows that a BNS merger launches a short gamma-ray burst (sGRB) jet. Unlike collapsars, where the ambient medium is static, in BNS mergers the jet propagates through the merger ejecta that is expanding outward at substantial velocities (∼0.2c). Here, we present semi-analytical and analytical models to solve the propagation of GRB jets through their surrounding media. These models improve our previous model by including the jet collimation by the cocoon self-consistently. We also perform a series of 2D numerical simulations of jet propagation in BNS mergers and in collapsars to test our models. Our models are consistent with numerical simulations in every aspect (the jet head radius, the cocoon’s lateral width, the jet opening angle including collimation, the cocoon pressure, and the jet–cocoon morphology). The energy composition of the cocoon is found to be different depending on whether the ambient medium is expanding or not; in the case of BNS merger jets, the cocoon energy is dominated by kinetic energy, while it is dominated by internal energy in collapsars. Our model will be useful for estimating electromagnetic counterparts to gravitational waves.

scholarly journals VLBA Imaging of a Large Sample of Blazars

1998 ◽  
Vol 164 ◽  
pp. 159-160
Author(s):  
J. M. Attridge ◽  
D. H. Roberts ◽  
J. F.C. Wardle
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Galactic Nuclei ◽  
Ambient Medium ◽  
Surrounding Medium ◽  
Galactic Nuclei ◽  
Large Sample ◽  
Field Lines ◽  
5 Ghz ◽  
The Magnetic Field

AbstractAs part of our continuing study of parsec-scale magnetic fields in active galactic nuclei we have obtained deep polarization-sensitive images of the blazar 1055+018 with the VLBA at 5 GHz. These dramatic images reveal a magnetized layer of material on the outer surfaces of the jet, distinct from the bulk of the jet. This morphology suggests interaction of the jet with the surrounding medium, the resulting shear stretching the magnetic field lines in the direction of the flow. Further multi-frequency polarization-sensitive observations of 1055+018 offer the opportunity to study radio jet-ambient medium interactions in detail.

scholarly journals Jet kinematics of the quasar 4C+21.35 from observations with the KaVA very long baseline interferometry array

2019 ◽  
Vol 486 (2) ◽  
pp. 2412-2421 ◽  
Author(s):  
Taeseok Lee ◽  
Sascha Trippe ◽  
Motoki Kino ◽  
Bong Won Sohn ◽  
Jongho Park ◽  
...  
Keyword(s):  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Time Resolved ◽  
The Core ◽  
Long Baseline ◽  
Boston University ◽  
Time Period ◽  
Spectrum Radio ◽  
Very Long Baseline Array

Abstract We present the jet kinematics of the flat spectrum radio quasar (FSRQ) 4C+21.35 using time-resolved KaVA very long baseline interferometry array radio maps obtained from 2014 September to 2016 July. During two out of three observing campaigns, observations were performed bi-weekly at 22 and 43 GHz quasi-simultaneously. At 22 GHz, we identified three jet components near the core with apparent speeds up to (14.4 ± 2.1)c. The timing of the ejection of a new component detected in 2016 is consistent with a γ-ray flare in 2014 November. At 43 GHz, we found four inner jet (<3 mas) components with speeds from (3.5 ± 1.4)c to (6.8 ± 1.5)c. Jet component speeds tend to be higher with increasing distances from the core. We compared our data with archival Very Long Baseline Array (VLBA) data from the Boston University (BU) 43 GHz and the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) 15.4 GHz monitoring programmes. Whereas MOJAVE data and our data are in good agreement, jet speeds obtained from the BU programme data in the same time period are about twice as high as the ones we obtain from the KaVA data. The discrepancy at 43 GHz indicates that radio arrays with different angular resolution identify and trace different jet features even when the data are obtained at the same frequency and at the same time. The flux densities of jet components decay exponentially, in agreement with a synchrotron cooling time-scale of ∼1 yr. Using known electron Lorentz factor values (∼9000), we estimate the magnetic field strength to be ∼1–3 $\mu$T. When adopting a jet viewing angle of 5°, the intrinsic jet speed is of order 0.99c.

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