The Origin of the Prompt Emission for Short GRB 170817A: Photosphere Emission or Synchrotron Emission?
Meng,Yan-Zhi1,2; Geng,Jin-Jun3,4; Zhang,Bin-Bin3,4; Wei,Jun-Jie1; Xiao,Di3,4; Liu,Liang-Duan3,4; Gao,He5; Wu,Xue-Feng1; Liang,En-Wei6; Huang,Yong-Feng3,4; Dai,Zi-Gao3,4; Zhang,Bing7
Source PublicationThe Astrophysical Journal
AbstractAbstract The first gravitational-wave event from the merger of a binary neutron star system (GW170817) was detected recently. The associated short gamma-ray burst (GRB 170817A) has a low isotropic luminosity (~1047 erg s?1) and a peak energy Ep?~?145 keV during the initial main emission between ?0.3 and 0.4 s. The origin of this short GRB is still under debate, but a plausible interpretation is that it is due to the off-axis emission from a structured jet. We consider two possibilities. First, since the best-fit spectral model for the main pulse of GRB 170817A is a cutoff power law with a hard low-energy photon index ( ), we consider an off-axis photosphere model. We develop a theory of photosphere emission in a structured jet and find that such a model can reproduce a low-energy photon index that is softer than a blackbody through enhancing high-latitude emission. The model can naturally account for the observed spectrum. The best-fit Lorentz factor along the line of sight is ~20, which demands that there is a significant delay between the merger and jet launching. Alternatively, we consider that the emission is produced via synchrotron radiation in an optically thin region in an expanding jet with decreasing magnetic fields. This model does not require a delay of jet launching but demands a larger bulk Lorentz factor along the line of sight. We perform Markov Chain Monte Carlo fitting to the data within the framework of both models and obtain good fitting results in both cases.
Keywordgamma-ray burst: general gravitational waves radiation mechanisms: thermal
WOS IDIOP:0004-637X-860-1-aac2d9
PublisherThe American Astronomical Society
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Document Type期刊论文
Affiliation1.Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, People’s Republic of China;
2.University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
3.School of Astronomy and Space Science, Nanjing University, Nanjing 210093, People’s Republic of China;,
4.Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, People’s Republic of China
5.Department of Astronomy, Beijing Normal University, Beijing 100875, People’s Republic of China
6.Department of Physics and GXU-NAOC Center for Astrophysics and Space Sciences, Guangxi University, Nanning 530004, People’s Republic of China
7.Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154, USA
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GB/T 7714
Meng,Yan-Zhi,Geng,Jin-Jun,Zhang,Bin-Bin,et al. The Origin of the Prompt Emission for Short GRB 170817A: Photosphere Emission or Synchrotron Emission?[J]. The Astrophysical Journal,2018,860(1).
APA Meng,Yan-Zhi.,Geng,Jin-Jun.,Zhang,Bin-Bin.,Wei,Jun-Jie.,Xiao,Di.,...&Zhang,Bing.(2018).The Origin of the Prompt Emission for Short GRB 170817A: Photosphere Emission or Synchrotron Emission?.The Astrophysical Journal,860(1).
MLA Meng,Yan-Zhi,et al."The Origin of the Prompt Emission for Short GRB 170817A: Photosphere Emission or Synchrotron Emission?".The Astrophysical Journal 860.1(2018).
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