论文标题
辐射介导的电击伽马射线爆发发射中辐射介导的冲击的观察性特征
Observational characteristics of radiation-mediated shocks in photospheric gamma-ray burst emission
论文作者
论文摘要
来自伽马射线爆发（GRB）喷气机的光球发射可能会受到亚光层能量耗散的基本影响，这通常是由辐射介导的冲击（RMS）引起的。我们研究了这种发射的观察特征，特别是光谱特征。相关的冲击初始条件是使用简单的内部碰撞框架估算的，然后用作生成合成光谱光谱的RMS模型的输入。在此框架内，我们发现，如果自由火球加速始于$ r_0 \ sim 10^{10}〜$ cm，与流体动力学模拟一致，那么典型的光谱由一个宽阔的软幂段组成，由高能截止和X射线固化。合成光谱通常非常适合标准的截止功率（CPL）函数，因为X射线的硬化通常在当前检测器的可观察到的能量范围之内。 CPL-FITS的低能指数，$α$和峰值能量的值分别围绕$ \ sim -0.8 $和$ \ sim 220〜 $ kev，类似于典型的观察值。我们还确定了一个不可忽略的参数区域，用于我们所谓的``光学浅层冲击''：没有足够的散射以在解耦之前达到稳态光谱，从而产生更复杂的光谱。这些对于光学深度$τ\ sillsim 55 \，u_u^{ - 2} $，其中$ u_u =γ_Uβ_U$是在冲击休息框架中测得的上游的无尺度特定动量。
Emission from the photosphere in gamma-ray burst (GRB) jets can be substantially affected by subphotospheric energy dissipation, which is typically caused by radiation-mediated shocks (RMSs). We study the observational characteristics of such emission, in particular the spectral signatures. Relevant shock initial conditions are estimated using a simple internal collision framework, which then serve as inputs for an RMS model that generates synthetic photospheric spectra. Within this framework, we find that if the free fireball acceleration starts at $r_0 \sim 10^{10}~$cm, in agreement with hydrodynamical simulations, then the typical spectrum consists of a broad, soft power-law segment with a cutoff at high energies and a hardening in X-rays. The synthetic spectra are generally well fitted with a standard cutoff power-law (CPL) function, as the hardening in X-rays is commonly outside the observable energy range of current detectors. The CPL-fits yield values for the low-energy index, $α$, and the peak energy, $E_{\rm peak}$, that are centered around $\sim -0.8$ and $\sim 220~$keV, respectively, similar to typical observed values. We also identify a non-negligible parameter region for what we call ``optically shallow shocks'': shocks that do not accumulate enough scatterings to reach a steady-state spectrum before decoupling and thereby produce more complex spectra. These occur for optical depths $τ\lesssim 55 \, u_u^{-2}$, where $u_u = γ_uβ_u$ is the dimensionless specific momentum of the upstream as measured in the shock rest frame.
