scholarly journals GRMHD simulations of BH activation by small scale magnetic loops: Formation of striped jets and active coronae

2021 ◽  
Author(s):  
Anna Chashkina ◽  
Omer Bromberg ◽  
Amir Levinson
Keyword(s):  
Black Holes ◽  
Magnetic Fields ◽  
Current Sheet ◽  
Numerical Experiments ◽  
Small Scale ◽  
X Ray ◽  
Current Sheets ◽  
Cyclic Behaviour ◽  
General Relativistic ◽  
Equatorial Current

Abstract We have performed a series of numerical experiments aimed at studying the activation of Kerr black holes (BHs) by advection of small scale magnetic fields. Such configurations may potentially give rise to the formation of quasi-striped Blandford-Znajek jets. It can also lead to enhanced dissipation and generation of plasmoids in current sheets formed in the vicinity of the BH horizon, which may constitute a mechanism to power the hard X-ray emission seen in many accreting BH systems (a la lamppost models). Our analysis suggests that formation of quasi-striped jets with significant power may be possible provided loops with alternating polarity having sizes larger than ∼10rg or so can be maintained (either form sporadically or advected from outside) at a radius ≲ 102rg. This conclusion is consistent with recent results of general relativistic force-free simulations. We also find that the accretion dynamics exhibits cyclic behaviour in MAD states, alternating between high accretion phases and quenched accretion phases during which the magnetosphere becomes force-free out to radii ≳ 10rg. We suggest that such a behaviour should lead to notable variations of the observed luminosity and image of the inner disc (BH shadow image). Finally, we find that the transition between accreted loops on the BH gives rise to the formation of current sheets and energetic plasmoids on the jet boundary during intermittent periods when the jet becomes inactive, in addition to an equatorial current sheet that forms during peaks in the jet activity.

scholarly journals Small-Scale Structure Deduced from X- and γ-ray Timing Measurements

2001 ◽  
Vol 205 ◽  
pp. 244-251
Author(s):  
M. Coleman Miller
Keyword(s):  
Black Holes ◽  
Neutron Stars ◽  
Small Scale ◽  
Large Area ◽  
X Ray ◽  
Strong Gravity ◽  
Thermonuclear Burning ◽  
General Relativistic ◽  
Γ Ray ◽  
Area X

X-ray timing observations of neutron stars and black holes are among the few available probes of ultrastrong magnetic fields, strong gravity, high densities, and the propagation of thermonuclear burning. Here we review the evidence for these effects revealed with data from the Rossi Explorer in the last five years. We also discuss the exciting prospects for making the first quantitative tests of strong-gravity general relativistic predictions with a large-area X-ray timing mission.

scholarly journals The Lx–Luv–Lradio relation and corona–disc–jet connection in optically selected radio-loud quasars

2020 ◽  
Vol 496 (1) ◽  
pp. 245-268 ◽  
Author(s):  
S F Zhu (朱世甫) ◽  
W N Brandt ◽  
B Luo (罗斌) ◽  
Jianfeng Wu (武剑锋) ◽  
Y Q Xue (薛永泉) ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Small Scale ◽  
Spectral Slope ◽  
Physical Processes ◽  
X Ray ◽  
Accretion Flow ◽  
Radio Jets ◽  
Spectrum Radio ◽  
Uniform Sample

ABSTRACT Radio-loud quasars (RLQs) are more X-ray luminous than predicted by the X-ray–optical/UV relation (i.e. $L_\mathrm{x}\propto L_\mathrm{uv}^\gamma$) for radio-quiet quasars (RQQs). The excess X-ray emission depends on the radio-loudness parameter (R) and radio spectral slope (αr). We construct a uniform sample of 729 optically selected RLQs with high fractions of X-ray detections and αr measurements. We find that steep-spectrum radio quasars (SSRQs; αr ≤ −0.5) follow a quantitatively similar $L_\mathrm{x}\propto L_\mathrm{uv}^{\gamma }$ relation as that for RQQs, suggesting a common coronal origin for the X-ray emission of both SSRQs and RQQs. However, the corresponding intercept of SSRQs is larger than that for RQQs and increases with R, suggesting a connection between the radio jets and the configuration of the accretion flow. Flat-spectrum radio quasars (FSRQs; αr > −0.5) are generally more X-ray luminous than SSRQs at given Luv and R, likely involving more physical processes. The emergent picture is different from that commonly assumed where the excess X-ray emission of RLQs is attributed to the jets. We thus perform model selection to compare critically these different interpretations, which prefers the coronal scenario with a corona–jet connection. A distinct jet component is likely important for only a small portion of FSRQs. The corona–jet, disc–corona, and disc–jet connections of RLQs are likely driven by independent physical processes. Furthermore, the corona–jet connection implies that small-scale processes in the vicinity of supermassive black holes, probably associated with the magnetic flux/topology instead of black hole spin, are controlling the radio-loudness of quasars.

Time-Dependent Magneto-Convection with Hexagonal Planform

1982 ◽  
Vol 4 (4) ◽  
pp. 373-376 ◽  
Author(s):  
J.M. Lopez ◽  
J.O. Murphy
Keyword(s):  
High Resolution ◽  
Magnetic Fields ◽  
Time Dependent ◽  
Convection Cell ◽  
Small Scale ◽  
Solar Photosphere ◽  
X Ray ◽  
Bright Spots

High-resolution observations indicate that very strong, small scale magnetic fields in the solar photosphere are concentrated into ropes which emerge through it. The scale of these ropes is only a few hundred kilometres across (Stenflo 1976) and their strength is estimated to vary between 1,000 and 2,000 G (Harvey 1977). These features are closely related to photospheric granular convection. The flux is observed as X-ray bright spots and sheet-like crinkles in the dark intergranular lanes, and is buffeted and shifted about by the granules (Dunn and Zirker 1973). Further, the crinkles can be resolved into separate features which outline small micropores as though a flux sheet at the end of a convection cell has separated into several isolated tubes (Galloway and Weiss 1981).

scholarly journals Rossby wave instability and high-frequency quasi-periodic oscillations in accretion discs orbiting around black holes

2019 ◽  
Vol 625 ◽  
pp. A116 ◽  
Author(s):  
P. Varniere ◽  
F. Casse ◽  
F. H. Vincent
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Rossby Wave ◽  
High Frequency ◽  
Binary Systems ◽  
Wave Instability ◽  
Periodic Oscillations ◽  
X Ray ◽  
General Relativistic ◽  
Frequency Ratios

Context. The rather elusive high-frequency quasi-periodic oscillations (HFQPOs) observed in the X-ray light curve of black holes have been seen in a wide range of frequencies, even within one source. Also notable is the detection of “pairs” of HFQPOs with a close-to-integer ratio between the frequencies. Aims. The aim of this paper is to investigate some of the possible observables that we could obtain from the Rossby wave instability (RWI) active in the accretion disc surrounding the compact object. Methods. Using the newly developed GR-AMRVAC code able to follow the evolution of the RWI in a full general relativistic framework, we explore how RWI can reproduce observed HFQPO frequency ratios and whether or not it is compatible with observations. In order to model the emission coming from the disc we have linked our general relativistic simulations to the general relativistic ray-tracing GYOTO code and delivered synthetic observables that can be confronted with actual data from binary systems hosting HFQPOs. Results. We demonstrate that some changes in the physical conditions prevailing in the part of the disc where RWI can be triggered lead to various dominant RWI modes whose ratio recovers frequency ratios observed in various X-ray binary systems. In addition we also show that when RWI is triggered near to the last stable orbit of a spinning black hole, the amplitude of the X-ray modulation increases with the spin of the black hole. Revisiting published data on X-ray binary systems, we show that this type of relationship actually exists in five systems where an indirect measurement of the spin of the black hole is available.

scholarly journals Black Hole Flares: Ejection of Accreted Magnetic Flux through 3D Plasmoid-mediated Reconnection

2022 ◽  
Vol 924 (2) ◽  
pp. L32
Author(s):  
B. Ripperda ◽  
M. Liska ◽  
K. Chatterjee ◽  
G. Musoke ◽  
A. A. Philippov ◽  
...  
Keyword(s):  
Black Holes ◽  
Magnetic Flux ◽  
Current Sheet ◽  
High Energy ◽  
Magnetized Plasma ◽  
Low Density ◽  
Very High Energy ◽  
General Relativistic ◽  
Sgr A ◽  
Relativistic Magnetohydrodynamics

Abstract Magnetic reconnection can power bright, rapid flares originating from the inner magnetosphere of accreting black holes. We conduct extremely high-resolution (5376 × 2304 × 2304 cells) general-relativistic magnetohydrodynamics simulations, capturing plasmoid-mediated reconnection in a 3D magnetically arrested disk for the first time. We show that an equatorial, plasmoid-unstable current sheet forms in a transient, nonaxisymmetric, low-density magnetosphere within the inner few Schwarzschild radii. Magnetic flux bundles escape from the event horizon through reconnection at the universal plasmoid-mediated rate in this current sheet. The reconnection feeds on the highly magnetized plasma in the jets and heats the plasma that ends up trapped in flux bundles to temperatures proportional to the jet’s magnetization. The escaped flux bundles can complete a full orbit as low-density hot spots, consistent with Sgr A* observations by the GRAVITY interferometer. Reconnection near the horizon produces sufficiently energetic plasma to explain flares from accreting black holes, such as the TeV emission observed from M87. The drop in the mass accretion rate during the flare and the resulting low-density magnetosphere make it easier for very-high-energy photons produced by reconnection-accelerated particles to escape. The extreme-resolution results in a converged plasmoid-mediated reconnection rate that directly determines the timescales and properties of the flare.

scholarly journals Diffuse Josephson Radiation in Turbulence

2021 ◽  
Vol 9 ◽  
Author(s):  
R. A. Treumann ◽  
Wolfgang Baumjohann
Keyword(s):  
High Temperature ◽  
Magnetic Fields ◽  
Oscillation Frequency ◽  
Josephson Junctions ◽  
Diffuse Radiation ◽  
Plasma Turbulence ◽  
Small Scale ◽  
Current Sheets

The possibility of generating diffuse radiation in extended astronomical media by plasma turbulence is investigated under the assumption that the turbulence can be understood as an ensemble of small-scale magnetic filaments (narrow current sheets) forming a texture around a large number of magnetic depletions or voids. On astronomically microscopic scales, the dilute high temperature medium (plasma) is to be considered ideally conducting, forming a collection of Josephson junctions between two such adjacent quasi-superconductors. The oscillation frequency of those junctions depends on the part of the spectrum that contributes to the oscillation, causing weak radio backgrounds. Lowest Josephson frequencies/energies near zero may become sources of quasi-stationary magnetic fields.

scholarly journals Returning radiation in strong gravity around black holes: reverberation from the accretion disc

2020 ◽  
Vol 498 (3) ◽  
pp. 3302-3319
Author(s):  
D R Wilkins ◽  
J A García ◽  
T Dauser ◽  
A C Fabian
Keyword(s):  
Black Holes ◽  
Strong Field ◽  
Time Lag ◽  
Accretion Disc ◽  
X Rays ◽  
X Ray ◽  
Gravitational Fields ◽  
Strong Gravity ◽  
General Relativistic ◽  
Strong Gravitational Fields

ABSTRACT We study reflected X-ray emission that returns to the accretion disc in the strong gravitational fields around black holes using General Relativistic ray-tracing and radiative transfer calculations. Reflected X-rays that are produced when the inner regions of the disc are illuminated by the corona are subject to strong gravitational light bending, causing up to 47 per cent of the reflected emission to be returned to the disc around a rapidly spinning black hole, depending upon the scale height of the corona. The iron Kα line is enhanced relative to the continuum by 25 per cent, and the Compton hump by up to a factor of 3. Additional light traveltime between primary and secondary reflections increases the reverberation time lag measured in the iron K band by 49 per cent, while the soft X-ray lag is increased by 25 per cent and the Compton hump response time is increased by 60 per cent. Measured samples of X-ray reverberation lags are shown to be consistent with X-rays returning to the accretion disc in strong gravity. Understanding the effects of returning radiation is important in interpreting reverberation observations to probe black holes. Reflected X-rays returning to the disc can be uniquely identified by blueshifted returning iron K line photons that are Compton scattered from the inner disc, producing excess, delayed emission in the 3.5–4.5 keV energy range that will be detectable with forthcoming X-ray observatories, representing a unique test of General Relativity in the strong field limit.

scholarly journals 8.2. Magnetic fields and black holes in galactic nuclei

1998 ◽  
Vol 184 ◽  
pp. 341-348
Author(s):  
R. D. Blandford
Keyword(s):  
Black Holes ◽  
Conference Proceedings ◽  
Magnetic Fields ◽  
Binary Systems ◽  
Galactic Center ◽  
Galactic Nuclei ◽  
X Ray

Recent observations have strengthened the dynamical arguments for the presence of black holes in X-ray binary systems, the Galactic center and the nuclei of the majority of bright galaxies. They have also drawn attention to the fact that accretion does not always proceed in the simple, stationary manner envisaged in early theories. I wish to discuss four related topics that are relevant to understanding the behavior of accreting black holes. (In view of the length constraints imposed by conference proceedings I shall make no attempt to give adequate bibliographic references for what follows.)

A Discussion on the physics of the solar atmosphere - Current sheets

1976 ◽  
Vol 281 (1304) ◽  
pp. 497-505
Keyword(s):  
Magnetic Field ◽  
Simple Model ◽  
Magnetic Fields ◽  
Current Sheet ◽  
Solar Atmosphere ◽  
Thermal Instability ◽  
Critical Value ◽  
Two Dimensional ◽  
Current Sheets ◽  
Dipole Sources

Current sheets are believed to be of prime importance in the solar atmosphere. Low down they may form at supergranulation boundaries, whereas up in the corona they have been suggested as a prominence formation site. In addition, they may occur when rapidly emerging flux presses up against pre-existing magnetic fields: if rapid magnetic field annihilation and reconnection is then triggered, a surge or a flare may be produced. Comments are given about three aspects of general current sheet theory. The position and shape of the current sheet which forms between two-dimensional dipole sources is calculated. The thermal instability which occurs when the length of the sheet exceeds a critical value is described. Finally, a simple model of magnetic field annihilation is presented.

High-Resolution Three-Dimensional MHD Simulations of Plasmoid Formation in Solar Flares

2020 ◽  
Author(s):  
Joel Dahlin ◽  
Spiro Antiochos ◽  
C. Richard DeVore
Keyword(s):  
Current Sheet ◽  
Adaptive Mesh Refinement ◽  
Large Scale ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Dimensional Structure ◽  
Small Scale ◽  
Ample Evidence ◽  
Current Sheets

<p>In highly conducting plasmas, reconnecting current sheets are often unstable to the generation of plasmoids, small-scale magnetic structures that play an important role in facilitating the rapid release of magnetic energy and channeling that energy into accelerated particles. There is ample evidence for plasmoids throughout the heliosphere, from in situ observations of flux ropes in the solar wind and planetary magnetospheres to remote-sensing imaging of plasma ‘blobs’ associated with explosive solar activity such as eruptive flares and coronal jets. Accurate models for plasmoid formation and dynamics must capture the large-scale self-organization responsible for forming the reconnecting current sheet. However, due to the computational difficulty inherent in the vast separation between the global and current sheet scales, previous numerical studies have typically explored configurations with either reduced dimensionality or pre-formed current sheets. We present new three-dimensional MHD studies of an eruptive flare in which the formation of the current sheet and subsequent reconnection and plasmoid formation are captured within a single simulation. We employ Adaptive Mesh Refinement (AMR) to selectively resolve fine-scale current sheet dynamics. Reconnection in the flare current sheet generates many plasmoids that exhibit highly complex, three-dimensional structure. We show how plasmoid formation and dynamics evolve through the course of the flare, especially in response to the weakening of the reconnection “guide field” linked to the global reduction of magnetic shear. We discuss implications of our results for particle acceleration and transport in eruptive flares as well as for observations by Parker Solar Probe and the forthcoming Solar Orbiter.</p>

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