arXiv subjects

Wei-Hua Lei

Publications and source records attributed to Wei-Hua Lei.

77 records · Page 5Linked to original sources

arXiv2009

A Model of Magnetically Induced Disc-Corona for Black Hole Binaries

We propose a model of magnetic connection (MC) of a black hole with its surrounding accretion disc based on large-scale magnetic field. The MC gives rise to transport of energy and angular momentum between the black hole and the disc, and the closed field lines pipe the hot matter evaporated from the disc, and shape it in the corona above the disc to form a magnetically induced disc-corona system, in which the corona has the same configuration as the large-scale magnetic field. We numerically solve the dynamic equations in the context of the Kerr metric, in which the large-scale magnetic field is determined by dynamo process and equipartition between magnetic pressure and gas pressure. Thus we can obtain a global solution rather than assuming the distribution of large-scale magnetic field beforehand. The main MC effects lie in three aspects. (1) The rotational energy of a fast-spinning black hole can be extracted, enhancing the dissipation in the accretion disc, (2) the closed field lines provide a natural channel for corona matter escaping from disc and finally falling into black hole, and (3) the scope of the corona can be bounded by the conservation of magnetic flux. We simulate the high-energy spectra of this system by using Monte-Carlo method, and find that the relative hardness of the spectra decreases as accretion rate or black hole spin $a_*$ increases. We fit the typical X-ray spectra of three black-hole binaries (GRO J1655-40, XTE 1118+480 and GX 339-4) in the low/hard or very high state.

astro-ph.HE↗

arXiv2008

Hyperaccretion after the Blandford-Znajek Process: a New Model for GRBs with X-Ray Flares Observed in Early Afterglows

We propose a three-stage model with Blandford-Znajek (BZ) and hyperaccretion process to interpret the recent observations of early afterglows of Gamma-Ray Bursts (GRBs). In the first stage, the prompt GRB is powered by a rotating black hole (BH) invoking the BZ process. The second stage is a quiet stage, in which the BZ process is shut off, and the accretion onto the BH is depressed by the torque exerted by the magnetic coupling (MC) process. Part of the rotational energy transported by the MC process from the BH is stored in the disk as magnetic energy. In the third stage, the MC process is shut off when the magnetic energy in the disk accumulates and triggers the magnetic instability. At this moment, the hyperaccretion process may onset, and the jet launched in this restarted central engine generates the observed X-ray flares. This model can account for energies and timescales of GRBs with X-ray flares observed in early afterglows.

astro-ph↗

arXiv2007

Effects of Magnetic Fields on Neutrino-dominated Accretion Model for Gamma-ray Bursts

Many models of gamma-ray bursts suggest a common central engine: a black hole of several solar masses accreting matter from a disk at an accretion rate from 0.01 to 10 M_\sun / s. The inner region of the disk is cooled by neutrino emission and large amounts of its binding energy were liberated, which could trigger the fireball. We improve the neutrino-dominated accreting flows by considering the effects of the magnetic fields, and find that more than half of the liberating energy can be extracted directly by the large-scale magnetic fields on the disk. And it turns out that the temperature of the disk is a bit lower than the neutrino-dominated accreting flows without magnetic field. Therefore, The outflows are magneticallydominated rather than neutrino dominated. In our model, neutrino mechanism can fuel some GRBs (not the brightest ones), but cannot fuel X-ray flares. However, the magnetic processes (both BZ and electromagnetic luminosity from a disk) are viable mechanisms for most of GRBs and the following X-ray flares.

astro-ph↗

arXiv2006

Screw Instability of Magnetic Field and Gamma-Ray Bursts in Type Ib/C Supernovae

A toy model for gamma-ray burst supernovae (GRB-SNe) is discussed by considering the effects of screw instability of magnetic field in black hole (BH) magnetosphere. The screw instability in the Blandford-Znajek (BZ) process (henceforth SIBZ) can coexist with the screw instability in the magnetic coupling (MC) process (henceforth SIMC). It turns out that both SIBZ and SIMC occur inevitably, provided that the following parameters are greater than some critical values, i.e., (i) the BH spin, (ii) the power-law index describing the magnetic field at the disk, and (iii) the vertical height of the astrophysical load above the equatorial plane of the rotating BH. The features of several GRBs are well fitted. In our model the durations of the long GRBs depend on the evolve time of the half-opening angle. A small fraction of energy is extracted from the BH via the BZ process to power a GRB, while a large fraction of energy is extracted from the BH via the MC process to power an associated supernova. In addition, the variability time scales of tens of msec in the light curves of the GRBs are fitted by two successive flares due to SIBZ.

astro-ph↗

arXiv2002

An Analytic Model of Black Hole Evolution and Gamma Ray Bursts

An analytic model of the evolution of a rotating black hole (BH) is proposed by considering the coexistence of disk accretion with the Blandford-Znajek process. The evolutionary characteristics of the BH are described in terms of three parameters: the BH spin $a_*$, the ratio $k$ of the angular velocity of the magnetic field lines to that of the BH horizon and the parameter $λ$ indicating the position of the inner edge of the disk. It is shown that the ratio $k$ being a little greater than 0.5 affects the evolutionary characteristics of the BH significantly, and the BH spin increases rather than decreases in its evolutionary process provided that the initial value of the BH spin is located in an appropriate value range determined by ratio $k$. Our calculations show that the system of a BH accretion disk with $k=0.6$ might provide a much higher output energy in a shorter timescale for gamma-ray bursts than the same system with $k=0.5$.

astro-ph↗