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arXiv 1007.2228astro-ph.HE
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伽马射线暴热发射和非热发射之间的联系:一般考虑和GRB090902B个例研究

The Connection Between Thermal and Non-Thermal Emission in Gamma-ray Bursts: General Considerations and GRB090902B as a Case Study

Asaf Pe'er, Bin-Bin Zhang, Felix Ryde, Sinéad McGlynn, Bing Zhang, Robert D. Preece, Chryssa Kouveliotou

摘要:

光球(热)辐射是伽马射线暴(GRB)“火球”模型所固有的。我们在这里表明,在伽玛射线暴的即时发射阶段的分析包括这个组件自然解释了费米卫星在其整个能带上看到的一些即时伽玛射线暴光谱。亚MeV的峰值被解释为多色黑体发射,和高能量的尾巴,延伸到GeV带,结果从大致相似的贡献同步辐射,同步自康普顿(SSC)和康普顿热光子的高能电子起源后耗散的动能以上的光球。我们展示了这种分析方法如何在一个完整的,自洽的图片的物理条件在两个发射站点的热辐射和非热辐射。我们研究了光谱的热和非热部分之间的联系,并展示了如何从数据推导出自由模型参数的值。我们对GRB 090902 B进行了分析,得到了洛伦兹因子在920 <= η<= 1070范围内,光球半径r_{ph}为7.2 - 8.4 * 10^{11} cm,耗散半径r_γ>= 3.5 - 4.1 * 10^{15} cm。通过与余辉数据的比较,我们推断出大部分的动能被耗散,并且大部分的能量由电子和磁场携带。如此高的δ_d值对“内震”作为伽玛暴主要能量耗散机制提出了质疑。

英文摘要:

Photospheric (thermal) emission is inherent to the gamma-ray burst (GRB) "fireball" model. We show here, that inclusion of this component in the analysis of the GRB prompt emission phase naturally explains some of the prompt GRB spectra seen by the Fermi satellite over its entire energy band. The sub-MeV peak is explained as multi-color black body emission, and the high energy tail, extending up to the GeV band, results from roughly similar contributions of synchrotron emission, synchrotron self Compton(SSC) and Comptonization of the thermal photons by energetic electrons originating after dissipation of the kinetic energy above the photosphere. We show how this analysis method results in a complete, self consistent picture of the physical conditions at both emission sites of the thermal and non-thermal radiation. We study the connection between the thermal and non-thermal parts of the spectrum, and show how the values of the free model parameters are deduced from the data. We demonstrate our analysis method on GRB090902B: We deduce a Lorentz factor in the range 920 <= η<= 1070, photospheric radius r_{ph} ~ 7.2 - 8.4 * 10^{11} cm and dissipation radius r_γ>= 3.5 - 4.1 * 10^{15} cm. By comparison to afterglow data, we deduce that a large fraction, epsilon_d ~85% - 95% of the kinetic energy is dissipated, and that large fraction, ~equipartition of this energy is carried by the electrons and the magnetic field. This high value of epsilon_d questions the "internal shock" scenario as the main energy dissipation mechanism for this GRB.

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