Trans-Relativistic Blast Waves in Supernovae as Gamma-Ray Burst Progenitors
Trans-Relativistic Blast Waves in Supernovae as Gamma-Ray Burst Progenitors
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超新星中的反相对论爆炸波作为伽马射线爆发的前身
DOI：
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
C. McKee
中科院分区：
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作者：
J. Tan;C. Matzner;C. McKee
我们研究了爆炸恒星外层中冲击波对相对论速度的加速作用。通过将爆炸的能量集中在最外层的抛射物中，这种跨相对论冲击波可以作为伽马射线暴(GRB)的先驱；特别是，困扰许多模型的伽马射线暴的“重子加载”问题被绕过了。震后加速有效地提高了相对论抛射的动能。我们给出了物理激励的解析表达式来描述超新星中的跨相对论冲击波，并用测试问题的数值模拟验证了这些表达式。研究了恒星结构对质量抛射的影响，我们发现，当光度接近爱丁顿极限时，相对论抛射在更中心的凝聚包络中得到增强，例如对于辐射包络。给出了估算给定子的相对论喷射物产生量的简便公式。我们将我们的解析和数值方法应用于SN1998bw的一个模型，发现与以前的研究相比，相对论抛射显著增强。我们推测伽马暴980425与SN1998bw有关，可能是由于一次近似球形的爆炸产生了约10-6M☉的中等相对论抛射物，平均洛伦兹因子为~2，然后与质量损失率约为10-4M☉yr-1的密集星周风相互作用。不需要高度不对称的爆炸。大质量恒星中“超新星”爆炸的极端模型能够解释许多观测到的宇宙学伽玛暴所需要的能量学和相对论抛射速度。然而，最高能量的爆发需要喷射物的不对称排出，这可能是由旋转扁平的祖细胞引起的。我们给出了白矮星吸积塌缩和中子星相变引起的爆炸的简化模型和模拟。虽然我们发现与之前的研究相比，相对论喷发的能量有所增加，但除非引用极端的爆炸能量和不对称性，否则不太可能在当前探测器的宇宙学距离内观察到这些爆炸。
We investigate the acceleration of shock waves to relativistic velocities in the outer layers of exploding stars. By concentrating the energy of the explosion in the outermost ejecta, such trans-relativistic blast waves can serve as the progenitors of gamma-ray bursts (GRBs); in particular, the "baryon-loading" problem that plagues many models of GRBs is circumvented. Postshock acceleration is effective in boosting the kinetic energy in relativistic ejecta. We present physically motivated analytic expressions to describe trans-relativistic blast waves in supernovae, and we validate these expressions against numerical simulations of test problems. Investigating the effect of stellar structure on mass ejection, we find that relativistic ejecta are enhanced in more centrally condensed envelopes, e.g., for radiative envelopes, when the luminosity approaches the Eddington limit. Convenient formulae are presented with which to estimate the production of relativistic ejecta from a given progenitor. We apply our analytic and numerical methods to a model of SN 1998bw, finding significantly enhanced relativistic ejecta compared to previous studies. We propose that GRB 980425 is associated with SN 1998bw and may have resulted from an approximately spherical explosion producing ~10-6 M☉ of mildly relativistic ejecta with mean Lorentz factor ~ 2, which then interacted with a dense circumstellar wind with a mass-loss rate of approximately a few times 10-4 M☉ yr-1. A highly asymmetric explosion is not required. An extreme model of "hypernova" explosions in massive stars is able to account for the energetics and relativistic ejecta velocities required by many of the observed cosmological GRBs. However, the most energetic bursts require asymmetric expulsion of ejecta, perhaps caused by rotationally flattened progenitors. We present simplified models and simulations of explosions resulting from accretion-induced collapse of white dwarfs and phase transitions of neutron stars. While we find increased energies in relativistic ejecta compared to previous studies, these explosions are unlikely to be observed at cosmological distances with current detectors, unless extreme explosion energies and asymmetries are invoked.