arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1006.3073astro-ph.HE
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甚高洛伦兹因子火球和伽马射线暴谱

Very High Lorentz Factor Fireballs and Gamma-Ray Burst Spectra

Kunihito Ioka

摘要:

在伽马射线暴(GRB)火球框架中,周围物质的无碰撞卷吸引入了相对论性重子分量。我们发现,一半的火球能量可以从辐射转移到光球下的重子的共动热运动。然而,贫重子的火球可以通过光球层之外的相对论性无碰撞压力(所谓的无碰撞体加速)再膨胀到非常高的洛伦兹因子(VHLF)Γ~ 10^3-10^6,导致内部和外部冲击。VHLF内激波的简单同步辐射产生(i)在费米GeV爆发中观察到的具有可变性的额外幂律谱分量,直到未来切伦科夫望远镜阵列(CTA)的TeV范围,(ii)具有弱光度依赖性的GeV起始延迟t_{delay} ~ L^{-1/5},GRB 090926的光谱中断是由同步辐射冷却中断或由动力学时间限制的最大同步辐射截止引起的,而不是由e+-产生截止引起的。相对论性重子分量还可以通过pp、pγ(Bethe-Heitler和photomeson)和库仑热化过程将光球热光子加热到GRB主带谱。在这个热光球-内-外激波模型中,我们可以预言~TeV中微子和GeV γ射线的相互关系,这可能是用IceCube探测到的。光谱峰值和光度(米德)的关系也重现,如果祖星几乎是相同的。我们还讨论了早期X射线余辉和短伽玛暴的陡/浅衰减。

英文摘要:

Collisionless entrainment of the surrounding matter imports the relativistic baryon component in the Gamma-Ray Burst (GRB) fireball frame. We show that half the fireball energy can be transferred from radiation to the comoving hot motions of baryons under the photosphere. The yet baryon-poor fireball can reexpand to a very high Lorentz factor (VHLF) Γ~ 10^3-10^6 by its own relativistic collisionless pressure beyond the photosphere (so-called collisionless bulk acceleration), leading to internal and external shocks. A simple synchrotron emission from the VHLF internal shocks produces (i) the extra power-law spectral component with variability observed in the Fermi GeV bursts, up to the TeV range for the future Cherenkov Telescope Array (CTA), (ii) the GeV onset delay with a weak luminosity dependence t_{delay} ~ L^{-1/5}, and (iii) the spectral break of GRB 090926 by the synchrotron cooling break or the maximum synchrotron cutoff limited by the dynamical time, not by the e+- creation cutoff. The relativistic baryon component could also heat the photospheric thermal photons into the main GRB Band spectrum via pp, pγ(Bethe-Heitler and photomeson), and Coulomb thermalization processes. In this hot photosphere-internal-external shock model, we can predict the anticorrelation of ~TeV neutrinos and GeV gamma-rays, which may be detectable using IceCube. The spectral peak and luminosity (Yonetoku) relation is also reproduced if the progenitor stars are nearly identical. We also discuss the steep/shallow decay of early X-ray afterglows and short GRBs.

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