X-ray flares in gamma-ray bursts (GRBs) are believed to be generated by the late activities of central engine, and thus provide an useful tool to diagnose the properties of central objects. In this paper, we work on a GRB X-ray flare sample whose bulk Lorentz factors are constrained by two different methods and the jet opening angles are determined by the jet breaks in afterglow light curves. Considering a hyperaccreting stellar-mass black hole (BH) as the central engine of GRBs and the Blandford & Znajek process (BZ) as the jet production mechanism, we constrain the parameters of central engine by using the X-ray flare data. We find that the BZ mechanism is so powerful making it possible to interpret both GRB prompt emissions and bright X-ray flares. The wind parameter (p) and accreted mass (Md) fall into reasonable ranges. Our result is also applied to GRB 170817A. The late X-ray flare in GRB 170817A, if it is true, might not be a BH origin.

中文翻译：

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X射线耀斑对伽马射线暴中央发动机的约束特性

伽马射线暴 (GRB) 中的 X 射线耀斑被认为是由中央引擎的晚期活动产生的，因此为诊断中央物体的性质提供了有用的工具。在本文中，我们研究了 GRB X 射线耀斑样品，其体积洛伦兹因子受两种不同方法的约束，射流张角由余辉光曲线中的射流中断确定。考虑超吸积恒星质量黑洞（BH）作为伽马射线暴的中心引擎，Blandford & Znajek 过程（BZ）作为喷流的产生机制，我们利用 X 射线耀斑数据来约束中心引擎的参数。我们发现 BZ 机制非常强大，可以解释 GRB 瞬发发射和明亮的 X 射线耀斑。风参数（p）和吸积质量（Md）在合理范围内。我们的结果也适用于 GRB 170817A。GRB 170817A 中晚期的 X 射线耀斑，如果是真的，可能不是 BH 起源。