Title: GRB 120422A: A Low-luminosity Gamma-ray Burst Driven by Central Engine Show Chinese title

Title: GRB 120422A：由中心引擎驱动的低亮度伽马射线暴

Abstract: GRB 120422A is a low-luminosity Gamma-ray burst (GRB) associated with a bright supernova, which distinguishes itself by its relatively short T90 ~ 5 s and an energetic X-ray tail. We analyze the Swift BAT and XRT data and discuss the physical implications. We show that the early steep decline in the X-ray light curve can be interpreted as the curvature tail of a late emission episode around 58-86 s, with a curved instantaneous spectrum at the end of the emission episode. Together with the main activity in the first ~ 20 s and the weak emission from 40 s to 60 s, the prompt emission is variable, which points towards a central engine origin, in contrast to the shock breakout origin as invoked to interpret some other nearby low-luminosity supernova GRBs. The curvature effect interpretation and interpreting the early shallow decay as the coasting external forward shock emission in a wind medium both give a constraint on the bulk Lorentz factor \Gamma to be around several. Comparing the properties of GRB 120422A and other supernova GRBs, we found that the main criterion to distinguish engine-driven GRBs from the shock breakout GRBs is the time-averaged luminosity, with a separation line of about ~ 10^48 erg s^-1. Show Chinese abstract

Abstract: GRB 120422A 是一个与明亮超新星相关的低光度伽马射线暴（GRB），其特征是相对较短的 T90 ~ 5 秒以及具有高能 X 射线尾部。 我们分析了 Swift BAT 和 XRT 数据，并讨论了其物理意义。 我们表明，X 射线光变曲线早期的急剧下降可以解释为大约 58-86 秒时一次晚些时候的发射事件的曲率尾部，且发射事件结束时存在一个弯曲的瞬时谱。 结合前约 20 秒的主要活动以及从 40 秒到 60 秒的弱发射，瞬发电磁辐射表现出变化性，这指向了一个中心引擎起源，而不是解释某些其他近邻低光度超新星 GRB 的冲击波突破起源。 曲率效应的解释以及将早期浅衰减解释为风介质中的外部向前冲击的无加速发射都对整体洛伦兹因子 \Gamma 给出了约束，约为几个。 通过比较 GRB 120422A 和其他超新星 GRB 的特性，我们发现区分引擎驱动 GRB 和冲击波突破 GRB 的主要标准是时间平均亮度，分离线约为 ~10^48 erg s^-1。