标题： 平均伽马射线暴X射线闪活动 显示英文标题

标题： On the average Gamma-Ray Burst X-ray flaring activity

摘要： 伽马射线暴X射线闪被认为是中心引擎的晚期活动标志。 我们计算了来自大型\emph{快速}五年数据库中的 44 个伽马暴（GRB）共同的静止能量带内的平均闪发亮度$< L >$的时间演化。 我们的工作强调了正确考虑闪发检测阈值相对于同时连续X射线发射的重要性。 在时间间隔$30 \rm{s}<t<1000\,\rm{s}$内，我们发现$< L >\propto t^{-2.7\pm 0.1}$；这意味着闪发各向同性能量比例是$E_{\rm{iso,flare}}\propto t^{-1.7}$。 闪发下连续辐射的衰减与平均闪发亮度演化紧密相关，典型的闪发到陡衰减亮度比是$L_{\rm{flare}}/L_{\rm{steep}}=4.7$：这表明闪发和连续辐射彼此之间密切相关。 我们通过不同的模型推断前身星的属性。 根据超吸积黑洞情景，当发生快速吸积（$t_{\rm{acc}}\ll t$）时，或者当原始星的最后 $\sim 0.5 M_{\sun}$ 质量的 $14 M_{\sun}$ 先祖恒星被吸积时，可以得到平均耀发光度标度。 或者，陡峭的 $\propto t^{-2.7}$ 行为可能是由供料盘状物的吸积激波的快速向外膨胀引发的。 如果相反我们假设引擎是一颗快速自转的磁星，那么它的旋转能量可以被提取来驱动喷流，其光度可能介于单极（$L\propto e^{-2t}$）和偶极（$L\propto t^{-2}$）情况之间。 在这两种情景下，我们都建议变化性——这是耀发活动的主要特征——作为不同种类不稳定性后果而形成。 显示英文摘要

摘要： Gamma-ray burst X-ray flares are believed to mark the late time activity of the central engine. We compute the temporal evolution of the average flare luminosity $< L >$ in the common rest frame energy band of 44 GRBs taken from the large \emph{Swift} 5-years data base. Our work highlights the importance of a proper consideration of the threshold of detection of flares against the contemporaneous continuous X-ray emission. In the time interval $30 \rm{s}<t<1000\,\rm{s}$ we find $< L >\propto t^{-2.7\pm 0.1}$; this implies that the flare isotropic energy scaling is $E_{\rm{iso,flare}}\propto t^{-1.7}$. The decay of the continuum underlying the flare emission closely tracks the average flare luminosity evolution, with a typical flare to steep-decay luminosity ratio which is $L_{\rm{flare}}/L_{\rm{steep}}=4.7$: this suggests that flares and continuum emission are deeply related to one another. We infer on the progenitor properties considering different models. According to the hyper-accreting black hole scenario, the average flare luminosity scaling can be obtained in the case of rapid accretion ($t_{\rm{acc}}\ll t$) or when the last $\sim 0.5 M_{\sun}$ of the original $14 M_{\sun}$ progenitor star are accreted. Alternatively, the steep $\propto t^{-2.7}$ behaviour could be triggered by a rapid outward expansion of an accretion shock in the material feeding a convective disk. If instead we assume the engine to be a rapidly spinning magnetar, then its rotational energy can be extracted to power a jet whose luminosity is likely to be between the monopole ($L\propto e^{-2t}$) and dipole ($L\propto t^{-2}$) cases. In both scenarios we suggest the variability, which is the main signature of the flaring activity, to be established as a consequence of different kinds of instabilities.