The polarization-Angle flip in GRB prompt emission
文献类型：期刊论文
| 作者 | Cheng, Kangfa4; Zhao XH(赵晓红)1,2,3 ; Mao JR(毛基荣)1,2,3; Chen, Zhifu4
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| 刊名 | Astronomy and Astrophysics
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| 出版日期 | 2024-07-01 |
| 卷号 | 687 |
| 关键词 | magnetic fields polarization radiation mechanisms: non thermal relativistic processes stars: jets gamma rays: stars |
| ISSN号 | 0004-6361 |
| DOI | 10.1051/0004-6361/202348050 |
| 产权排序 | 第2完成单位 |
| 文献子类 | Journal article (JA) |
| 英文摘要 | Context. In recent years, some polarization measurements of gamma-ray bursts (GRBs) have been reported, and the polarization-Angle (PA) rotation in the prompt emission phase has been found in several bursts. The physical mechanism of the PA evolution is still unclear. In this work, we studied the origin of the PA rotation in a toroidal magnetic field. Aims. We aim to provide an explanation for the PA rotation in GRBs and find the physical conditions that lead to the rotation by 90 degrees in the toroidal magnetic-field (MF) model. Moreover, we present some observable polarization properties in the MF model that can be tested in the future. Methods. We calculated the instantaneous polarization degree (PD) from a top-hat jet with different normalized viewing angles (q θv/θj), jet opening angles (θj), and jet Lorentz factors (I) in three wavebands. When the PD changes between positive and negative values, it means that the PA flips by 90 degrees. On these grounds, we can summarize the range of parameters required for these PA flips. Considering these parameter conditions, we can further estimate the observed rate of the GRBs exhibiting such PA rotations. Results. We find that the PA rotation in the toroidal MF is primarily related to three critical factors: The viewing angle, the jet opening angle, and the jet Lorentz factor. Additionally, the PA can experience flips of 90 degrees twice. The conditions for the flips are q 0.5 (except for q1) and yj (Iθj)2a 4. However, the two flips in the PA might not be concurrently observable due to the constraint of flux. Taking these conditions into account and assuming a random orientation between the jet axis and the line of sight (LOS), we obtain a theoretical upper limit (without any constraints) for the observed rate of GRBs in the X-ray or γ-ray band displaying the flips in PA as Rcha 80%. We further constrain the observed rate as Rcha 16% according to the maximal post-flip polarized flux level, where the observed rate of single and double flips each account for 8%. It should be noted that the observed rates are different in various wavebands. The observed rate of the second PA flip in the optical bands should be higher than that in the X-ray or γ-ray band since the flux in the optical band declines much slower than that in the X-ray or γ-ray band. Moreover, when the LOS is close to the jet edge (q→ 1), it is the easiest case in which to observe the 90-degree PA flip due to the relatively high post-flip polarized flux level. The first and second PA flips in a GRB pulse are most likely to occur at the observed times of tobsa [2a∼3]tpeak and ∼[3-4]tpeak, respectively, where tpeak is the peak time of the pulse. It is also noted that the PA flip would not happen before the peak time. © 2024 The Author(s). |
| 学科主题 | 天文学 ; 星系与宇宙学 |
| URL标识 | 查看原文 |
| 资助项目 | National Natural Science Foundation of China[12393811];National Natural Science Foundation of China[12393813];National Natural Science Foundation of China[U1831135] |
| 语种 | 英语 |
| 资助机构 | National Natural Science Foundation of China[12393811, 12393813, U1831135] |
| 源URL | [http://ir.ynao.ac.cn/handle/114a53/27462]  |
| 专题 | 星系类星体研究组 云南天文台_中国科学院天体结构与演化重点实验室 |
| 作者单位 | 1.Center for Astronomical Mega-Science, Chinese Academy of Science, 20A Datun Road, Chaoyang District, Beijing, 100012, China 2.Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Science, Kunming, 650011, China; 3.Yunnan Observatories, Chinese Academy of Sciences, Kunming, 650011, China; 4.School of Mathematics and Physics, Guangxi Minzu University, Nanning, 530006, China; |
| 推荐引用方式 GB/T 7714 | Cheng, Kangfa,Zhao XH,Mao JR,et al. The polarization-Angle flip in GRB prompt emission[J]. Astronomy and Astrophysics,2024,687. |
| APA | Cheng, Kangfa,赵晓红,毛基荣,&Chen, Zhifu.(2024).The polarization-Angle flip in GRB prompt emission.Astronomy and Astrophysics,687. |
| MLA | Cheng, Kangfa,et al."The polarization-Angle flip in GRB prompt emission".Astronomy and Astrophysics 687(2024). |
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来源：云南天文台
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