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标题：A new fitting function for GRB MeV spectra based on the internal shock synchrotron model
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作者：M. Yassine ; F. Piron ; F. Daigne 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2020
卷号：640
页码：1-18
DOI：10.1051/0004-6361/201937057
语种：English
出版社：EDP Sciences
摘要：Aims.The physical origin of the gamma-ray burst (GRB) prompt emission is still a subject of debate. Internal shock models have been widely explored, owing to their ability to explain most of the high-energy properties of this emission phase. While theBandfunction or other phenomenological functions are commonly used to fit GRB prompt emission spectra, we propose a new parametric function that is inspired by an internal shock physical model. We use this function as a proxy of the model to compare it easily to GRB observations.Methods.We built a parametric function that represents the spectral form of the synthetic bursts provided by our internal shock synchrotron model (ISSM). We simulated the response of theFermiinstruments to the synthetic bursts and fit the obtained count spectra to validate theISSMfunction. Then, we applied this function to a sample of 74 bright GRBs detected by theFermiGBM, and we computed the width of their spectral energy distributions around their peak energy. For comparison, we also fit the phenomenological functions that are commonly used in the literature. Finally, we performed a time-resolved analysis of the broadband spectrum of GRB 090926A, which was jointly detected by theFermiGBM and LAT. This spectrum has a complex shape and exhibits a power-law component with an exponential cutoff at high energy, which is compatible with inverse Compton emission attenuated by gamma-ray internal absorption.Results.This work proposes a new parametric function for spectral fitting that is based on a physical model. TheISSMfunction reproduces 81% of the spectra in the GBM bright GRB sample, versus 59% for theBandfunction, for the same number of parameters. It gives also relatively good fits to the GRB 090926A spectra. The width of the MeV spectral component that is obtained from the fits of theISSMfunction is slightly larger than the width from theBandfits, but it is smaller when observed over a wider energy range. Moreover, all of the 74 analyzed spectra are found to be significantly wider than the synthetic synchrotron spectra. We discuss possible solutions to reconcile the observations with the internal shock synchrotron model, such as an improved modeling of the shock microphysics or more accurate spectral measurements at MeV energies.
关键词：engamma-ray burst: generalradiation mechanisms: non-thermal