Gamma-ray Bursts (GRBs) are the most powerful transients in the Universe, over–shining for a few seconds all other γ-ray sky sources. Their emission is produced within narrowly collimated relativistic jets launched after the core–collapse of massive stars or the merger of compact binaries. THESEUS will open a new window for the use of GRBs as cosmological tools by securing a statistically significant sample of high-z GRBs, as well as by providing a large number of GRBs at low–intermediate redshifts extending the current samples to low luminosities. The wide energy band and unprecedented sensitivity of the Soft X-ray Imager (SXI) and X-Gamma rays Imaging Spectrometer (XGIS) instruments provide us a new route to unveil the nature of the prompt emission. For the first time, a full characterisation of the prompt emission spectrum from 0.3 keV to 10 MeV with unprecedented large count statistics will be possible revealing the signatures of synchrotron emission. SXI spectra, extending down to 0.3 keV, will constrain the local metal absorption and, for the brightest events, the progenitors’ ejecta composition. Investigation of the nature of the internal energy dissipation mechanisms will be obtained through the systematic study with XGIS of the sub-second variability unexplored so far over such a wide energy range. THESEUS will follow the spectral evolution of the prompt emission down to the soft X–ray band during the early steep decay and through the plateau phase with the unique ability of extending above 10 keV the spectral study of these early afterglow emission phases.

伽马射线暴 (GRB) 是宇宙中最强大的瞬变，它比所有其他γ射线天空源过度闪耀几秒钟。它们的发射是在大质量恒星的核心坍缩或致密双星合并后发射的狭隘准直的相对论喷流中产生的。THESEUS 将通过确保具有统计显着性的高z样本，为使用 GRB 作为宇宙学工具打开一个新窗口。GRBs，以及通过提供大量处于中低红移的 GRBs 将当前样本扩展到低光度。软 X 射线成像仪 (SXI) 和 X 伽玛射线成像光谱仪 (XGIS) 仪器的宽能带和前所未有的灵敏度为我们提供了一条揭示瞬发发射性质的新途径。首次对从 0.3 keV 到 10 MeV 的瞬发发射光谱进行全面表征，并具有前所未有的大量计数统计数据，这将有可能揭示同步加速器发射的特征。SXI 光谱，延伸至 0.3 keV，将限制局部金属吸收，对于最亮的事件，将限制前身的喷射物成分。对内部能量耗散机制的性质的研究将通过 XGIS 对迄今为止在如此宽的能量范围内尚未探索过的亚秒变化进行系统研究来获得。THESEUS 将跟踪快速发射在早期陡峭衰减期间向下到软 X 射线带的光谱演变，并通过平台阶段，具有将这些早期余辉发射阶段的光谱研究扩展到 10 keV 以上的独特能力。