The joint X and gamma-ray observations of GRB 090618 by a large number of satellites offer an unprecedented possibility of testing crucial aspects of theoretical models. In particular, it allows us to test (a) the formation of an optically thick e+e- baryon plasma self-accelerating to Lorentz factors in the range 200 < g < 3000; (b) its transparency condition with the emission of a component of 10^{53-54} baryons in the TeV region and (c) the collision of these baryons with the circumburst medium clouds, characterized by dimensions of 10^{15-16} cm. In addition, these observations offer the possibility of testing a new understanding of the thermal and power-law components in the early phase of this GRB. We test the fireshell model of GRBs in one of the closest (z = 0.54) and most energetic (Eiso = 2.90 x 10^{53} ergs) GRBs, namely GRB 090618. We analyze its emission using several spectral models, with special attention to the thermal and power-law components. We determine the fundamental parameters of a canonical GRB within the context of the fireshell model. We find evidences of the existence of two different episodes in GRB 090618. The first episode lasts 50 s and is characterized by a spectrum consisting of thermal component, which evolves between kT = 54 keV and kT = 12 keV. The second episode, which lasts for \sim 100s, behaves as a canonical long GRB with a Lorentz gamma factor at transparency of g = 495, a temperature at transparency of 29.22 keV and with characteristic masses of the surrounding clouds of \sim 10^{22-24} g. We support the recently proposed two-component nature of GRB 090618 by using specific theoretical analysis and illustrate that the episode 1 cannot be considered to be either a GRB or a part of a GRB event, but it appears to be related to the progenitor of the collapsing bare core leading to the formation of the black hole which we call a proto-black hole.
The Origin of the Photospheric Emission of GRB 220426A
GRB 220426 A是一个以光球辐射为主的明亮的伽马射线暴。我们进行了几次测试，以推测这种光球发射的起源。无量纲熵$η$很大，如果我们假设它是由中微子-反中微子湮灭机制发射的纯热火球，这是不寻常的。此外，流出具有较大的$η$，在最初的几秒内具有较低的光度$L$，使得时间分辨的$η-L$的趋势不能被描述为$η$和$L$之间的单调正相关。几乎完全热化坡印亭通量的混合流出可以解释准热谱以及大的$η$。更重要的是，磁场的存在可以影响质子密度和中子-质子耦合效应，从而可以解释观测到的时间分辨$η-L$的变化趋势。光球发射的其他来源，如非耗散混合流出或磁重联，不支持，因为它们的辐射效率低，这与GRB 220426 A的余辉未检测到不一致。因此，我们认为混合外流可能是最有可能的来源。
Relativistic jets from millisecond proto-magnetars
University of Greifswald（格赖夫斯瓦尔德大学）；Perimeter Institute for Theoretical Physics（基础物理研究所）；University of Guelph（圭尔夫大学）；Columbia University（哥伦比亚大学）；Flatiron Institute（平顿研究所）
