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Abstract: A model of magnetic coupling (MC) of a rotating black hole (BH) with advection-dominated accretion flow (MCADAF) is proposed. It turns out that MCADAF provides a natural explanation for the transition radius between ADAF and SSD, and could be used to interpret the highest luminosity of GX 339-4 in hard-state. A very steep emissivity index can be produced in the innermost part of the MCADAF, which is consistent with the recent XMM-Newton observations of the nearby bright Seyfert 1 galaxy MCG-6-30-15 and with two X-ray binaries (XRBs): XTE J1655-500 and GX 339-4. In addition, we estimate the BH spins in Seyfert 1 galaxy MCG-6-30-15 and in the two XRBs based on this model. [Copyright &y& Elsevier]

A toy model for jet powers and radio loudness of active galactic nuclei (AGNs) is proposed based on the coexistence of the Blandford–Znajek and magnetic coupling processes in black hole (BH) accretion discs. It turns out that both the jet powers and radio loudness of AGNs are controlled by more than one physical parameter besides the BH spin. The observed dichotomy between radio-loud and radio-quiet AGNs is well interpreted by the two parameters, the BH spin and the power-law index of the variation of the magnetic field on the disc. Furthermore, we discuss the correlation of jet powers with radio loudness of AGNs in terms of the two parameters. It is found that the contours of radio loudness are approximately in accord with those of jet powers for several 3CR radio sources, implying roughly that the stronger jet powers correspond to stronger radio loudness. In addition we discuss the correlation of the jet powers and radio loudness of AGNs with the position of the inner edge of the accretion disc. These results imply that the‘spin paradigm’ for radio loudness of AGNs might be modified by a scenario containing more physical parameters. [ABSTRACT FROM AUTHOR]

A toy model for magnetic extraction of energy from black hole (BH) accretion disk is discussed by considering the restriction of the screw instability to the magnetic field configuration. Three mechanisms of extracting energy magnetically are involved. (1) The Blandford–Znajek (BZ) process is related to the open magnetic field lines connecting the BH with the astrophysical load; (2) the magnetic coupling (MC) process is related to the closed magnetic field lines connecting the BH with its surrounding disk; and (3) a new scenario (henceforth the DL process) for extracting rotational energy from the disk is related to the open field lines connecting the disk with the astrophysical load. The expressions for the electromagnetic powers and torques are derived by using the equivalent circuits corresponding to the above energy mechanisms. It turns out that the DL power is comparable with the BZ and MC powers as the BH spin approaches unity. The radiation from a quasi-steady thin disk is discussed in detail by applying the conservation laws of mass, energy and angular momentum to the regions corresponding to the MC and DL processes. In addition, the poloidal currents and the current densities in BH magnetosphere are calculated by using the equivalent circuits. [Copyright &y& Elsevier]

ABSTRACT The transfer of energy and angular momentum in the magnetic coupling (MC) of a rotating black hole (BH) with its surrounding accretion disc is discussed based on a mapping relation derived by considering the conservation of magnetic flux with two basic assumptions: (i) the magnetic field on the horizon is constant, (ii) the magnetic field on the disc surface varies as a power law with the radial coordinate of the disc. The following results are obtained: (i) the transfer direction of energy and angular momentum between the BH and the disc depends on the position of a co-rotation radius relative to the MC region on the disc, which is eventually determined by the BH spin; (ii) the evolution characteristics of a rotating BH in the MC process without disc accretion are depicted in a parameter space, and a series of values of the BH spin are given to indicate the evolution characteristics; (iii) the efficiency of converting accreted mass into radiation energy of a BH–disc system is discussed by considering the coexistence of disc accretion and the MC process; (iv) the MC effects on disc radiation and the emissivity index are discussed and it is concluded that they are consistent with the recent XMM–Newton observation of the nearby bright Seyfert 1 galaxy MCG–6-30-15 with reference to a variety of parameters of the BH–disc system. [ABSTRACT FROM AUTHOR]

Taking into account the energy and angular momentum transferred from a rotating black hole (BH) to the inner accretion disk by the magnetic connection (MC) process, we simulate the x-ray spectra from the disk-corona system with two different magnetic configurations using the Monte Carlo method. The results show that the MC process reduces the ratio of the power dissipated in the corona to the total and softens the spectrum. The influence of the MC process is stronger with a higher BH spin, a larger accretion rate, and a larger and more centralized magnetic flux threading the disk. The comparison of the model spectra with the observational data suggests that large-scale magnetic fields accumulating in the inner disk could be a candidate explanation for the hard-to-soft state evolutions in BH binaries. [ABSTRACT FROM AUTHOR]

The continued observations of Sw J1644+57 in X-ray and radio bands accumulated a rich data set to study the relativistic jet launched in this tidal disruption event. The X-ray light curve of Sw J1644+57 from 5-30 days presents two kinds of quasi-periodic variations: a 200 s quasi-periodic oscillation (QPO) and a 2.7 day quasi-periodic variation. The latter has been interpreted by a precessing jet launched near the Bardeen-Petterson radius of a warped disk. Here we suggest that the ∼200 s QPO could be associated with a second, narrower jet sweeping the observer line-of-sight periodically, which is launched from a spinning black hole in the misaligned direction with respect to the black hole's angular momentum. In addition, we show that this two-component jet model can interpret the radio light curve of the event, especially the re-brightening feature starting ∼100 days after the trigger. From the data we infer that inner jet may have a Lorentz factor of Γj ∼ 5.5 and a kinetic energy of Ek, iso ∼ 3.0 × 1052 erg, while the outer jet may have a Lorentz factor of Γj ∼ 2.5 and a kinetic energy of Ek, iso ∼ 3.0 × 1053 erg. [ABSTRACT FROM AUTHOR]

The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta (Γ0) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between Γ0 and isotropic γ-ray energy: Γ0∝E0.25γ, iso, 52. By including more GRBs with updated data and more methods to derive Γ0, we confirm this correlation and obtain Γ0 ≃ 91E0.29γ, iso, 52. Evaluating the mean isotropic γ-ray luminosities Lγ, iso of the GRBs in the same sample, we discover an even tighter correlation Γ0 ≃ 249L0.30γ, iso, 52. We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive Γ0∝L0.22γ, iso, which is consistent with the data. This suggests that the central engine of long GRBs is likely a stellar mass black hole surrounded by a hyper-accreting disk. [ABSTRACT FROM AUTHOR]