GRB 221009A 的尺寸演化与余辉模型的比较
Comparing the size evolution of GRB 221009A with afterglow models
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中文总结 AI 辅助
通过 VLBI 测量 GRB 221009A 的余辉尺寸演化，约束喷流参数，并发现现有标准余辉模型预测与观测不符，凸显尺寸测量的独立探针价值。
中文摘要 AI 辅助
我们展示了利用全球 VLBI 网络在爆发后 231 至 750 天之间于 5 GHz 频段对 GRB 221009A 进行的甚长基线干涉测量（VLBI）观测。观测数据的质量使我们能够测量源表面亮度分布的亚毫角秒半高全宽，在爆发后 231 天和 391 天时，其 1σ 等效误差分别为 13% 和 30%。通过将这些新的尺寸测量值的时间演化与文献中先前发表的 5 GHz 和 8 GHz 数据拟合成单一幂律 $\propto t^a$，我们得到斜率 $a = 0.52^{+0.14}_{-0.12}$。利用公开代码 VegasAfterglow，我们模拟了 5 GHz 尺寸演化，考虑了由喷流在均匀星际介质（ISM）或具有类风密度轮廓的周围介质中减速产生的前向激波的余辉辐射。该模型约束了准直校正的 Sedov 比，即喷流动能 $E_\mathrm{jet}$ 与周围介质密度（ISM 情形下为 $n$，风情形下为 $A_\star$）之比，在 ISM 情形下为 $\log[(E_\mathrm{jet}/n)\\,\mathrm{erg}^{-1}\\,\mathrm{cm}^{-3}] = 54.2^{+0.4}_{-0.5}$，在风情形下为 $\log[(E_\mathrm{jet}/A_\star)\\,\mathrm{erg}^{-1}] = 51.7^{+0.4}_{-0.2}$。在文献中基于标准余辉模型拟合 GRB 221009A 光变曲线和光谱、且可用 VegasAfterglow 重现的工作中，没有任何一组最佳拟合参数在 $2\sigma$ 范围内与这些约束兼容。此外，我们表明它们预测的尺寸演化与观测结果不兼容。我们的结果强调了 GRB 余辉尺寸测量作为其动力学、结构和辐射机制独立探针的重要性。
英文摘要
We present very long baseline interferometry (VLBI) observations of GRB221009A obtained with the global-VLBI network at 5 GHz between 231 and 750 days after the burst. The quality of our observations allowed us to measure the sub-milliarcsecond full-width at half maximum of the source surface brightness distribution with a one-sigma equivalent error of 13% and 30% at 231 and 391 days post-burst, respectively. By fitting the temporal evolution of these new size measurements alongside those previously published in the literature at 5 and 8 GHz with a single power law $\propto t^a$, we find a slope of $a = 0.52^{+0.14}_{-0.12}$. Using the public code VegasAfterglow, we model the 5 GHz size evolution considering the afterglow emission of the forward shock produced by a jet decelerating in either a homogeneous interstellar medium (ISM) or into a surrounding medium with a wind-like density profile. The model constrains the collimation-corrected Sedov ratio, that is, the ratio of the jet kinetic energy $E_\mathrm{jet}$ to the density of the surrounding medium ($n$ in the ISM scenario, or $A_\star$ in the wind scenario), in the range $\log[(E_\mathrm{jet}/n)\,\mathrm{erg}^{-1}\,\mathrm{cm}^{-3}] = 54.2^{+0.4}_{-0.5}$ for the ISM scenario and $\log[(E_\mathrm{jet}/A_\star)\,\mathrm{erg}^{-1}] = 51.7^{+0.4}_{-0.2}$ for the wind scenario. Among the works in the literature that fit the light curves and spectra of GRB221009A based on the standard afterglow model, and which can be reproduced with VegasAfterglow, none has best-fitting parameters that are compatible with these constraints within $2σ$. Moreover, we show that their predicted size evolution is not compatible with the observed one. Our results highlight the importance of size measurements of GRB afterglows as an independent probe of their dynamics, structure, and emission mechanisms.
发表机构
- INAF Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）
- INFN – sezione di Milano-Bicocca（意大利国家核物理研究院米兰比可卡分部）
- Joint Institute for VLBI ERIC (JIVE)（甚长基线干涉测量欧洲国际合作机构联合研究所）
- ASTRON, Netherlands Institute for Radio Astronomy（荷兰射电天文研究所）
- INAF Istituto di Radioastronomia（意大利国家天体物理研究所射电天文研究所）
- Department of Physics, George Washington University（乔治华盛顿大学物理系）
- David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto（多伦多大学戴维·A·邓普尔天文学与天体物理学系）
- Dunlap Institute for Astronomy and Astrophysics, University of Toronto（多伦多大学邓普尔天文学与天体物理研究所）
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