Observations show that at least some gamma-ray bursts (GRBs) happen simultaneously with core-collapse supernovae (SNe), thus linking by a common thread nature's two grandest explosions. We review here the growing evidence for and theoretical implications of this association, and conclude that most long-duration soft-spectrum GRBs are accompanied by massive stellar explosions (GRB-SNe). The kinetic energy and luminosity of well-studied GRB-SNe appear to be greater than those of ordinary SNe, but evidence exists, even in a limited sample, for considerable diversity. The existing sample also suggests that most of the energy in the explosion is contained in nonrelativistic ejecta (producing the supernova) rather than in the relativistic jets responsible for making the burst and its afterglow. Neither all SNe, nor even all SNe of Type Ibc produce GRBs. The degree of differential rotation in the collapsing iron core of massive stars when they die may be what makes the difference.

The Supernova Gamma-Ray Burst Connection

Black hole accretion flows can be divided into two broad classes: cold and hot. Whereas cold accretion flows consist of cool optically thick gas and are found at relatively high mass accretion rates, hot accretion flows, the topic of this review, are virially hot and optically thin, and occur at lower mass accretion rates. They are described by accretion solutions such as the advection-dominated accretion flow and luminous hot accretion flow. Because of energy advection, the radiative efficiency of these flows is in general lower than that of a standard thin accretion disk. Moreover, the efficiency decreases with decreasing mass accretion rate. Observations show that hot accretion flows are associated with jets. In addition, theoretical arguments suggest that hot flows should produce strong winds. Hot accretion flows are believed to be present in low-luminosity active galactic nuclei and in black hole X-ray binaries in the hard and quiescent states. The prototype is Sgr A*, the ultralow-luminosity supermassive black hole at our Galactic center. The jet, wind, and radiation from a supermassive black hole with a hot accretion flow can interact with the external interstellar medium and modify the evolution of the host galaxy.

Hot Accretion Flows Around Black Holes

We examine the disc-jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the X-ray and radio bands. We compile a sample of ∼100 active galactic nuclei with measured masses, 5-GHz core emission, and 2-10 keV luminosities, together with eight galactic black holes with a total of ∼50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L R ) and the X-ray (L X ) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and L X , at a highly significant level. In particular, we show that the sources define a 'Fundamental Plane' in the three-dimensional (log L R , log L X , log M) space, given by log L R = (0.60 + 0 . 1 1 -0.11) log L X + (0.78 + 0 . 1 1 -0.09) log M + 7.33 + 4 . 0 5 -4.07, with a substantial scatter of σ R = 0.88. We compare our results to the theoretical relations between radio flux, black hole mass, and accretion rate derived by Heinz & Sunyaev. Such relations depend only on the assumed accretion model and on the observed radio spectral index. Therefore, we are able to show that the X-ray emission from black holes accreting at less than a few per cent of the Eddington rate is unlikely to be produced by radiatively efficient accretion, and is marginally consistent with optically thin synchrotron emission from the jet. On the other hand, models for radiatively inefficient accretion flows seem to agree well with the data.

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A Fundamental plane of black hole activity

We present a unified semiquantitative model for the disc–jet coupling in black hole X-ray binary systems. In the process we have compiled observational aspects from the existing literature, as well as performing new analyses. We argue that during the rising phase of a black hole transient outburst the steady jet known to be associated with the canonical ‘low/hard’ state persists while the X-ray spectrum initially softens. Subsequently, the jet becomes unstable and an optically thin radio outburst is always associated with the soft X-ray peak at the end of this phase of softening. This peak corresponds to a ‘soft very high state’ or ‘steep power-law’ state. Softer X-ray states are not associated with ‘core’ radio emission. We further demonstrate quantitatively that the transient jets associated with these optically thin events are considerably more relativistic than those in the ‘low/hard’ X-ray state. This in turn implies that, as the disc makes its collapse inwards, the jet Lorentz factor rapidly increases, resulting in an internal shock in the outflow, which is the cause of the observed optically thin radio emission. We provide simple estimates for the efficiency of such a shock in the collision of a fast jet with a previously generated outflow that is only mildly relativistic. In addition, we estimate the jet power for a number of such transient events as a function of X-ray luminosity, and find them to be comparable to an extrapolation of the functions estimated for the ‘low/hard’ state jets. The normalization may be larger, however, which may suggest a contribution from some other power source such as black hole spin, for the transient jets. Finally, we attempt to fit these results together into a coherent semiquantitative model for the disc–jet coupling in all black hole X-ray binary systems.

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Towards a unified model for black hole X-ray binary jets

▪ Abstract Black holes of stellar mass and neutron stars in binary systems are first detected as hard X-ray sources using high-energy space telescopes. Relativistic jets in some of these compact sources are found by means of multiwavelength observations with ground-based telescopes. The X-ray emission probes the inner accretion disk and immediate surroundings of the compact object, whereas the synchrotron emission from the jets is observed in the radio and infrared bands, and in the future could be detected at even shorter wavelengths. Black-hole X-ray binaries with relativistic jets mimic, on a much smaller scale, many of the phenomena seen in quasars and are thus called microquasars. Because of their proximity, their study opens the way for a better understanding of the relativistic jets seen elsewhere in the Universe. From the observation of two-sided moving jets it is inferred that the ejecta in microquasars move with relativistic speeds similar to those believed to be present in quasars. The simultan...

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Sources of Relativistic Jets in the Galaxy

A number of astronomical systems have been discovered that generate collimated flows of plasma with velocities close to the speed of light. In all cases, the central object is probably a neutron star or black hole and is either accreting material from other stars or is in the initial violent stages of formation. Supercomputer simulations of the production of relativistic jets have been based on a magnetohydrodynamic model, in which differential rotation in the system creates a magnetic coil that simultaneously expels and pinches some of the infalling material. The model may explain the basic features of observed jets, including their speed and amount of collimation, and some of the details in the behavior and statistics of different jet-producing sources.

https://science.sciencemag.org/content/sci/291/5501/84.full.pdf

Magnetohydrodynamic Production of Relativistic Jets

Relativistic jets are observed in both active galactic nuclei (AGNs) and iimicroquasars ˇˇ in our Galaxy. It is believed that these relativistic jets are ejected from the vicinity of black holes. To investigate the formation mechanism of these jets, we have developed a new general relativistic magnetohydrodynamic (GRMHD) code. We report on the basic methods and test calculations to check whether the code repro- duces some analytical solutions, such as a standing shock and a Keplerian disk with a steady state infall- ing corona or with a corona in hydrostatic equilibrium. We then apply the code to the formation of relativistic MHD jets, investigating the dynamics of an accretion disk initially threaded by a uniform poloidal magnetic —eld in a nonrotating corona (either in a steady state infall or in hydrostatic equilibrium) around a nonrotating black hole. The numerical results show the following: as time goes on, the disk loses angular momentum as a result of magnetic braking and falls into the black hole. The infalling motion of the disk, which is faster than in the nonrelativistic case because of general relativistic eUects below is the Schwarzschild radius), is strongly decelerated around by centrifugal 3r S (r S r \ 2r S force to form a shock inside the disk. The magnetic —eld is tightly twisted by the diUerential rotation, and plasma in the shocked region of the disk is accelerated by the JB force to form bipolar rela- tivistic jets. In addition, and interior to, this magnetically driven jet, we also found a gas-pressuredriven jet ejected from the shocked region by the gas-pressure force. This two-layered jet structure is formed not only in the hydrostatic corona case but also in the steady state falling corona case. Subject headings: accretion, accretion disksblack hole physicsgalaxies: jetsMHDrelativity

https://iopscience.iop.org/article/10.1086/307667/pdf

Relativistic Jet Formation from Black Hole Magnetized Accretion Disks: Method, Tests, and Applications of a General RelativisticMagnetohydrodynamic Numerical Code

Using numerical simulations, we modeled the general relativistic magnetohydrodynamic behavior of a plasma flowing into a rapidly rotating black hole in a large-scale magnetic field. The results show that a torsional Alfven wave is generated by the rotational dragging of space near the black hole. The wave transports energy along the magnetic field lines outward, causing the total energy of the plasma near the hole to decrease to negative values. When this negative energy plasma enters the horizon, the rotational energy of the black hole decreases. Through this process, the energy of the spinning black hole is extracted magnetically

https://science.sciencemag.org/content/sci/295/5560/1688.full.pdf

Extraction of Black Hole Rotational Energy by a Magnetic Field and the Formation of Relativistic Jets

To investigate the formation mechanism of relativistic jets in active galactic nuclei and microquasars, we have developed a new general relativistic magnetohydrodynamic code in Kerr geometry. Here we report on the —rst numerical simulations 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 corotating and counter- rotating with respect to the black hole rotation, and investigate the —rst D50 light-crossing times. In the corotating disk case, our results are almost the same as those in Schwarzschild black hole cases: a gas pressuredriven jet is formed by a shock in the disk, and a weaker magnetically driven jet is also gener- ated outside the gas pressuredriven jet. On the other hand, in the counter-rotating disk case, a new powerful magnetically driven jet is formed inside the gas pressuredriven jet. The newly found magneti- cally driven jet in the latter case is accelerated by a strong magnetic —eld created by frame dragging in the ergosphere. Through this process, the magnetic —eld extracts the energy of the black hole rotation. Subject headings: accretion, accretion disksblack hole physicsgalaxies: jetsmagnetic —elds ¨ methods: numericalMHDrelativity

General relativistic simulations of early 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.

Shinji Koide

Papers

Magnetohydrodynamic Production of Relativistic Jets

Relativistic Jet Formation from Black Hole Magnetized Accretion Disks: Method, Tests, and Applications of a General RelativisticMagnetohydrodynamic Numerical Code

Extraction of Black Hole Rotational Energy by a Magnetic Field and the Formation of Relativistic Jets

General relativistic simulations of early jet formation in a rapidly rotating black hole magnetosphere

General Relativistic Simulations of Jet Formation in a Rapidly Rotating Black Hole Magnetosphere