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Tail Emission from a Ring-like Jet: Its Application to Shallow Decays of Early Afterglows and GRB 050709

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Chinese Journal of Astronomy and Astrophysics 2006年第5期6卷 551-554页

作者： yuan-chuan zou Zi-Gao Dai Department of Astronomy Nanjing University Nanjing 210093

Similar to the case of pulsars the magnetic axis and the spin axis of gamma-ray burst sources may not lie on the same line. This may cause the formation of a ring-like jet due to collimation of the precessing magnetic axis. We analyze the tail emission from such a jet, and find that it has a shallow decay phase with a temporal index of - 1/2 if the Lorentz factor of the ejecta is not very high, which is consistent with the shallow decay phase of some early X-ray afterglow detected by Swift. The ring-like jet has a tail cusp with sharp rising and very sharp decay. This effect can provide an explanation for the re-brightening and sharp decay of the X-ray afterglow＇of GRB 050709.

关键词： gamma rays bursts - X-rays general

Early afterglows from radially structured outflows and the application to X-ray shallow decays

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Research in Astronomy and Astrophysics 2009年第8期9卷 911-920页

作者： Xue-Wen Liu Xue-Feng Wu yuan-chuan zou Tan Lu Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Joint Center for Particle Nuclear Physics and Cosmology （J-CPNPC） Nanjing 210093 China Department of Astronomy ＆ Astrophysics Pennsylvania State University University Park PA 16802 USA Department of Physics Huazhong University of Science and Technology Wuhan 430074 China

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.

关键词： gamma-rays bursts -- hydrodynamics -- radiation mechanisms nonther- mal -- shock waves

Modeling the quasi-periodic oscillation of Swift J1644+57

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Research in Astronomy and Astrophysics 2020年第2期20卷 31-36页

作者： Meng-Meng Zheng Shuang-Xi Yi Fa-Yin Wang yuan-chuan zou School of Physics and Physical Engineering Qufu Normal UniversityQufu 273165China School of Astronomy and Space Science Nanjing UniversityNanjing 210093China School of Physics Huazhong University of Science and TechnologyWuhan 430074China

A 200-second X-ray quasi-periodicity in the 2-8 ke V band from Swift J1644+57 was found by Reis et *** the onset time of quasi-periodic oscillation(QPO),we show that Swift J1644+57 is a plunging *** QPO may be related to discrete clumps from the accretion disk falling into a supermassive black hole,then the outflow in the jet may be also *** estimate the lifetime of clumps to be about several hundreds seconds and the fraction of clumpy ejecta to be about 30% from the *** other possible model involves the interface between the inflow and jet magnetosphere in the magnetically choked accretion *** and numerical simulations indicate that a magnetic Rayleigh-Taylor and Kelvin-Helmholtz unstable magnetospheric interface can produce a jet-disk QPO *** event may be the first evidence of jet-disk *** observations,the two models are comparable.

关键词： accretion accretion discs gamma-ray burst:general radiation mechanism:non-thermal

The updated Bulk Lorentz Factors of Gamma-Ray Burst X-Ray Flares

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Research in Astronomy and Astrophysics 2017年第6期17卷 37-46页

作者： Shao-Qiang Xi Shuang-Xi Yi yuan-chuan zou Fa-Yin Wang College of Physics and Engineering Qufu Normal University Qufu 273165 China School of Physics Huazhong University of Science and Technology Wuhan 430074 China School of Astronomy and Space Science Nanjing University Nanjing 210093 China Key Laboratory of Modem Astronomy and Astrophysics (Nanjing University) Nanjing 210093 China

X-ray flares are the most common phenomena in the afterglow phase of gamma-ray bursts （GRBs） in the Swift era, and are known as a canonical component in X-ray afterglows. In this work, we constrain the Lorentz factor of X-ray flares with an updated sample. We extensively search for X-ray light curves showing flare and jet break simultaneously. A smooth broken power law function is used to fit the jet breaks in 11 GRBs. We also use a smooth broken power law function to fit the profile of X-ray flares, and the total number of the flares is 20. We obtain the lower and upper limits of Lorentz factor （Гx） with the timescale, half-opening angle and mean luminosity of the X-ray flares for interstellar medium （ISM） and wind cases. The lower limits on Px range from tens to a few hundred, and the upper limits are mainly about a few hundred. We also apply the limited Lorentz factor to test correlations of Г0 - γ,iso and Г0 - Lγ,iso for GRBs, and find X-ray flares in the ISM case are much more consistent with those of prompt emission than the wind case in a statistical sense for both correlations. X-ray flares are almost consistent with the trend in the correlations of Г0 - Eγ,iso（Lγ,iso） for prompt GRBs, indicating X-ray flares and prompt bursts may have the same physical origin.

关键词： gamma ray bursts -radiation mechanism: non-thermal

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

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Chinese Journal of Astronomy and Astrophysics 2008年第4期8卷 404-410页

作者： Wei-Hua Lei Ding-Xiong Wang yuan-chuan zou Lei Zhang Department of Physics Huazhong University of Science and Technology Wuhan 430074 China

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 magnetic instability. At this moment, the hyperaccretion process may set in, and the jet launched in this restarted central engine generates the observed X-ray flares. This model can account for the energies and timescales of GRBs with X-ray flares observed in early afterglows.

关键词： accretion, accretion disks - black hole physics - magnetic fields - gammarays bursts

Implication from GRB 221009A:Can TeV emission come from the GRB prompt phase?

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Science China(Physics,Mechanics & Astronomy) 2023年第8期66卷 139-149页

作者： Kai Wang Zhi-Peng Ma Ruo-Yu Liu yuan-chuan zou Zhuo Li Zi-Gao Dai Department of Astronomy School of PhysicsHuazhong University of Science and TechnologyWuhan 430074China School of Astronomy and Space Science Nanjing UniversityNanjing 210023China Key Laboratoryof Modern Astronomy and Astrophysics Ministry of EducationNanjing UniversityNanjing 20023China Department of Astronomy School of PhysicsPeking UniversityBeijing 100871China Kavli Institute for Astronomy and Astrophysics Peking UniversityBeijing 100871China Department of Astronomy University of Science and Technology of ChinaHefei 230026China

Recently,the B.O.A.T.(“brightest of all time”)gamma-ray burst,dubbed GRB 221009A,was detected by various ***,the GRB presented very-high-energy(VHE,energy above 0.1 Te V)gamma-ray emission with energy extending above 10 Te V,as reported by the Large High Altitude Air Shower Observatory(LHAASO).We here demonstrate that the VHE and especially>10 Te V emission may originate from the internal hadronic dissipation of the GRB,without the need of invoking any exotic processes as suggested by some previous *** possible prompt origin of LHAASO photons may imply the first detection of the GRB prompt phase in the VHE *** also discuss the constraints on the properties of the GRB ejecta from multiwavelength and multi-messenger observations,which favors a magnetically dominated GRB *** suggested Poynting-flux-dominated GRB ejecta in this work supports the Blandford&Znajek(BZ)mechanism as the possible central engine model of GRB,as well as the possible strong magnetic dissipation and acceleration.

关键词： cosmological neutrinos neutrino astronomy high energy astrophysics gamma-ray bursts cosmic rays

Revisiting gamma-ray burst afterglows with time-dependent parameters

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Research in Astronomy and Astrophysics 2018年第2期18卷 53-72页

作者： Chao Yang yuan-chuan zou Wei Chen Bin Liao Wei-Hua Lei Yu Liu School of Physics Huazhong University of Science and Technology

The relativistic external shock model of gamma-ray burst （GRB） afterglows has been estab- lished with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons ee and for the magnetic field eB, the number density of the environment n and the index of the power- law distribution of shocked electrons p. A lot of modified models have been constructed to consider the variety of GRB afterglows, such as： the wind medium environment by letting n change with radius, the energy injection model by letting kinetic energy change with time and so on. In this paper, by as- suming all four parameters （except p） change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling GRB afterglows. Some interesting results are obtained. For example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. As an application, through modeling the afterglow of GRB 060607A, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range.

关键词： (stars:) gamma.ray burst: general -- methods: analytical

A two-component jet model based on the Blandford-Znajek and Blandford-Payne processes

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Research in Astronomy and Astrophysics 2012年第7期12卷 817-828页

作者： Wei Xie Wei-Hua Lei yuan-chuan zou Ding-Xiong Wang Qingwen Wu Jiu-Zhou Wang School of Physics Huazhong University of Science and Technology Wuhan 430074 China Department of Physics and Astronomy University of Nevada Las Vegas 4505 MarylandParkway Box 454002 Las Vegas NV89154-4002 USA

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.

关键词： gamma rays: bursts -- galaxies: jets -- accretion accretion disks --magnetic fields -- jets and outflows

Extending the correlation of L_R-L_X to gamma-ray bursts

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Research in Astronomy and Astrophysics 2015年第5期15卷 617-622页

作者： Jing L Jing-Wen Xing yuan-chuan zou Wei-Hua Lei Qing-Wen Wu Ding-Xiong Wang GXU-NAOC Center for Astrophysics and Space Sciences Department of PhysicsGuangxi University Guangxi Key Laboratory for Relativistic Astrophysics School of Physics Huazhong University of Science and Technology

The well-known correlation between radio luminosity （LR） and X-ray luminosity （Lx）, LR/LX 10^-5, holds for a variety of objects, such as active galactic nuclei, Galactic black holes, solar flares and cool stars. Here we extend the relation to gamma-ray bursts （GRBs） and find that the GRBs also obey a similar LR - LX relation, with a slightly different slope of LR ∝ LX^1.1. This relation implies that the explosions that occur on different scales may have a common underlying origin.

关键词： gamma-ray bursts general -- quasars general -- stars black holes