In the fireball model, it is more physically realistic that ganuna-ray burst （GRB） ejecta have a range of bulk Lorentz factors （assuming M ∝ Г^-8）. The low Lorentz factor part of the ejecta will catch up with the high Lorentz factor part when the latter is decelerated by the surrounding medium to a comparable Lorentz factor. Such a process will develop a long-lasting weak reverse shock until the whole ejecta are shocked. Meanwhile, the forward shocked materials are gradually supplied with energy from the ejecta that are catching-up, and thus the temporal decay of the forward shock emission will be slower than that without an energy supply. However, the reverse shock may be strong. Here, we extend the standard reverse-forward shock model to the case of radially nonuniform ejecta. We show that this process can be classified into two cases： the thick shell case and the thin shell case. In the thin shell case, the reverse shock is weak and the temporal scaling law of the afterglow is the same as that in Sad ＆ Meszaros （2000）. However, in the thick shell case, the reverse shock is strong and thus its emission dominates the afterglow in the high energy band. Our results also show slower decaying behavior of the afterglow due to the energy supply by low Lorentz factor materials, which may help the understanding of the plateau observed in the early optical and X-ray afterglows.
In this paper,we present a simplified model for a magnetized neutrino-dominated accretion flow(NDAF) in which the effect of black hole(BH) spin is taken into account by adopting a set of relativistic correction factors,and the magnetic field is parameterized as β,the ratio of the magnetic pressure to the total pressure.It is found that the disc properties are sensitive to the values of the BH spin and β,and more energy can be extracted from NDAFs by using a faster spin and lower β.
LEI WeiHua,WANG DingXiong,ZHANG Lei,GAN ZhaoMing & ZOU YuanChuan School of Physics,Huazhong University of Science and Technology,Wuhan 430074,China
We propose a two-component jet model consistent with the observations of several gamma ray bursts （GRBs） and active galactic nuclei （AGNs）. The jet consists of inner and outer components, which are supposed to be driven by the Blandford- Znajek （BZ） and Blandford-Payne （BP） processes, respectively. The baryons in the BP jet are accelerated centrifugally via the magnetic field anchored in the accretion disk. The BZ jet is assumed to be entrained in a fraction of accreting matter leaving the inner edge of the accretion disk, and the baryons are accelerated in the conversion from electromagnetic energy to kinetic energy. By fitting the Lorentz factors of some GRBs （GRB 030329, GRB 051221A and GRB 080413B） and AGNs （Cen A, Mkn 501 and Mkn 421） with this model, we constrain the physical parameters related to the accretion and outflow of these two kinds of objects. We conclude that the spine/sheath structure of the jet from these sources can be interpreted naturally by the BZ and BP processes.
Wei XieWei-Hua LeiYuan-Chuan ZouDing-Xiong WangQingwen WuJiu-Zhou Wang
